This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less impor...This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time,before the damping forces can dissipate a significant portion of the energy input into the system.The development of two sine series solutions,relating to different types of impulsive loadings,one involving a single concentrated force and the other a distributed line load,are presented.This study revealed that when a simply supported Euler-Bernoulli beam,resting on a Winkler soil model,is subject to an impact load,the resulting vertical displacements,bending moments and shear forces produced along the span of the beam are considerably affected.In particular,the quantification of this effect is best observed,relative to the corresponding static solution,via an amplification factor.The computed impact amplification factors,for the sub-grade moduli used in this study,were in magnitude greater than 2,thus confirming the multiple-degree-of-freedom nature of the problem.展开更多
An analytical method for analyzing the thermal vibration of multi-directional functionally graded porous rectangular plates in fluid media with novel porosity patterns is developed in this study.Mechanical properties ...An analytical method for analyzing the thermal vibration of multi-directional functionally graded porous rectangular plates in fluid media with novel porosity patterns is developed in this study.Mechanical properties of MFG porous plates change according to the length,width,and thickness directions for various materials and the porosity distribution which can be widely applied in many fields of engineering and defence technology.Especially,new porous rules that depend on spatial coordinates and grading indexes are proposed in the present work.Applying Hamilton's principle and the refined higher-order shear deformation plate theory,the governing equation of motion of an MFG porous rectangular plate in a fluid medium(the fluid-plate system)is obtained.The fluid velocity potential is derived from the boundary conditions of the fluid-plate system and is used to compute the extra mass.The GalerkinVlasov solution is used to solve and give natural frequencies of MFG porous plates with various boundary conditions in a fluid medium.The validity and reliability of the suggested method are confirmed by comparing numerical results of the present work with those from available works in the literature.The effects of different parameters on the thermal vibration response of MFG porous rectangular plates are studied in detail.These findings demonstrate that the behavior of the structure within a liquid medium differs significantly from that within a vacuum medium.Thereby,they offer appropriate operational approaches for the structure when employed in various mediums.展开更多
This study explores the effects of dynamic and static loading on rock bolt performance a key factor in maintaining the structural safety of coal mine roadways susceptible to coal bursts.Employing a housemade load fram...This study explores the effects of dynamic and static loading on rock bolt performance a key factor in maintaining the structural safety of coal mine roadways susceptible to coal bursts.Employing a housemade load frame to simulate various failure scenarios,pretension-impact-pull tests on rock bolts were conducted to scrutinize their dynamic responses under varied static load conditions and their failure traits under combined loads.The experimental results denote that with increased impact energy,maximum and average impact loads on rock bolts escalate significantly under pretension,initiating plastic deformation beyond a certain threshold.Despite minor reductions in the yield load due to impactinduced damage,pretension aids in constraining post-impact deformation rate and fluctuation degree of rock bolts.Moreover,impact-induced plastic deformation causes internal microstructure dislocation,fortifying the stiffness of the rock bolt support system.The magnitude of this fortification is directly related to the plastic deformation induced by the impact.These findings provide crucial guidance for designing rock bolt support in coal mine roadway excavation,emphasizing the necessity to consider both static and dynamic loads for improved safety and efficiency.展开更多
The performance of geosynthetic-reinforced embankments under traffic moving loads is always a hotspot in the geotechnical engineering field.A three-dimensional(3D)model of a geosynthetic-reinforced embankment without ...The performance of geosynthetic-reinforced embankments under traffic moving loads is always a hotspot in the geotechnical engineering field.A three-dimensional(3D)model of a geosynthetic-reinforced embankment without drainage consolidation was established using the finite element software ABAQUS.In this model,the traffic loads were simulated by two moving loads of rectangular pattern,and their amplitude,range,and moving speed were realized by a Fortran subroutine.The embankment fill was simulated by an equivalent linear viscoelastic model,which can reflect its viscoelasticity.The geogrid was simulated by the truss element,and the geocell was simulated by the membrane element.Infinite elements were utilized to weaken the boundary effect caused by the model geometry at the boundaries.Validation of the established numerical model was conducted by comparing the predicted deformations in the cross-section of the geosynthetic-reinforced embankment with those from the existing literature.On this basis,the dynamic stress and strain distribution in the pavement structure layer of the geosynthetic-reinforced embankment under a moving load was also analyzed.Finally,a parametric study was conducted to examine the influences of the different types of reinforcement,overload,and the moving load velocity on the geosynthetic-reinforced embankment.展开更多
The stability control of fissured rock is difficult,especially under static and dynamic loads in deep coal mines.In this paper,the dynamic mechanical properties,strain rate evolution and energy dissipation of fissured...The stability control of fissured rock is difficult,especially under static and dynamic loads in deep coal mines.In this paper,the dynamic mechanical properties,strain rate evolution and energy dissipation of fissured and anchored rocks were respectively obtained by SHPB tests.It was found that bolt can provide supporting efficiency-improving effect for fissured rock against dynamic disturbance,and this effect increased quadratically with decrease in anchoring angles.Then,the energy dissipation mechanism of anchored rock was obtained by slipping model.Furthermore,bolt energy-absorbing mechanism by instantaneous tensile-shear deformation was expressed based on material mechanics,which was the larger the anchoring angle,the smaller the energy absorption,and the less the contribution to supporting efficiency improvement.On this basis,the functional relationship between energy dissipation of anchored rock and energy absorption of bolt was established.Taking the coal-gangue separation system of Longgu coal mine as an example,the optimal anchoring angle can be determined as 57.5°–67.5°.Field monitoring showed fissured rock with the optimal anchoring angle,can not only effectively control the deformation,but also fully exert the energy-absorbing and efficiency-improving effect of bolt itself.This study provides guidance to the stability control and supporting design for deep engineering under the same or similar conditions.展开更多
Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant ...Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile,and thus aerodynamic load changes significantly with operational height.This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations,such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces.Specifically,computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting,such as that of the recessed cavity on a Class 800 train.From an aerodynamic perspective,this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing,although the difference between the two is found to reduce with increasing pantograph extension.Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour.The results obtained show how considering aerodynamic forces enhance the realism of the models,leading to behaviour of the pantograph-catenary contact forces closely matching that seen in experimental tests.展开更多
Dynamic wheel-rail contact forces induced by a severe form of wheel tread damage have been measured by a wheel impact load detector during full-scale field tests at different vehicle speeds.Based on laser scanning,the...Dynamic wheel-rail contact forces induced by a severe form of wheel tread damage have been measured by a wheel impact load detector during full-scale field tests at different vehicle speeds.Based on laser scanning,the measured three-dimensional damage geometry is employed in simulations of dynamic vehicle-track interaction to calibrate and verify a simulation model.The relation between the magnitude of the impact load and various operational parameters,such as vehicle speed,lateral position of wheel-rail contact,track stiffness and position of impact within a sleeper bay,is investigated.The calibrated model is later employed in simulations featuring other forms of tread damage;their effects on impact load and subsequent fatigue impact on bearings,wheel webs and subsurface initiated rolling contact fatigue of the wheel tread are assessed.The results quantify the effects of wheel tread defects and are valuable in a shift towards condition-based maintenance of running gear,and for general assessment of the severity of different types of railway wheel tread damage.展开更多
To address the issues of limited demand response data,low generalization of demand response potential evaluation,and poor demand response effect,the article proposes a demand response potential feature extraction and ...To address the issues of limited demand response data,low generalization of demand response potential evaluation,and poor demand response effect,the article proposes a demand response potential feature extraction and prediction model based on data mining and a demand response potential assessment model for adjustable loads in demand response scenarios based on subjective and objective weight analysis.Firstly,based on the demand response process and demand response behavior,obtain demand response characteristics that characterize the process and behavior.Secondly,establish a feature extraction and prediction model based on data mining,including similar day clustering,time series decomposition,redundancy processing,and data prediction.The predicted values of each demand response feature on the response day are obtained.Thirdly,the predicted data of various characteristics on the response day are used as demand response potential evaluation indicators to represent different demand response scenarios and adjustable loads,and a demand response potential evaluation model based on subjective and objective weight allocation is established to calculate the demand response potential of different adjustable loads in different demand response scenarios.Finally,the effectiveness of the method proposed in the article is verified through examples,providing a reference for load aggregators to formulate demand response schemes.展开更多
Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on a...Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.展开更多
In this article,the seismic performance of box-shaped steel piers embedded with energy-dissipating shells under a multi-directional seismic load is investigated.A finite element(FE)model was accurately established and...In this article,the seismic performance of box-shaped steel piers embedded with energy-dissipating shells under a multi-directional seismic load is investigated.A finite element(FE)model was accurately established and verified by the quasi-static test results.A parametric analysis of the hysteretic behaviour of a novel box-shaped steel pier under eccentric pressure was carried out on this basis.We discussed the influence of the eccentricity,axial compression ratio,thickness of embedded shell,ratio of slenderness,spacing of transverse stiffening ribs on the embedded shell,and width-to-thickness ratio of wallboard on the anti-seismic performance of a novel box-shaped steel bridge pier.The results revealed that the load carrying capacity and ductility coefficient of the specimen are substantially influenced by the eccentricity,variation in the axial compression ratio,and slenderness ratio.The specimen′s plastic energy dissipation capacity can be effectively improved by increasing the thickness of the embedded shell.The spacing of the transverse stiffening ribs only marginally affects seismic performance.In addition,the width-to-thickness ratio of the wallboard exerts a more considerable influence on the deformability of the square-section specimen.Finally,a formula for calculating the bearing capacity of the novel box-shaped steel piers under cyclic loading is proposed.展开更多
Industrial production of chemical cement leads to extreme emissions of greenhouse gases.Biological or bioinspired sustainable materials for soil treatment projects can be employed instead of chemical cement to heal th...Industrial production of chemical cement leads to extreme emissions of greenhouse gases.Biological or bioinspired sustainable materials for soil treatment projects can be employed instead of chemical cement to heal the carbon cycle in the ecosystem.The enzyme-induced calcite precipitation(EICP)method is one of the novel bio-inspired technologies that can be employed in soil treatment projects to increase desired properties of soils.While the monotonic and cyclic behavior of the enzymatically treated sands has been investigated comprehensively,the strain accumulation pattern in these improved soils under cyclic traffic loads has not been evaluated yet.In this paper,confined and unconfined cyclic compression tests are applied to the enzymatically lightly cemented sands,and the effects of the different parameters on their strain accumulation pattern are investigated for the first time in the literature.This study uses two types of specimens with unconfined compression strengths(UCS)equal to 42 kPa and 266 kPa.It is shown that the treated specimens have a rate-dependent behavior where cyclic loads with low frequencies lead to more resilient and plastic strains in the specimens.The results show that by approaching the maximum applied stresses to the UCS of the specimens(by breaking more calcite bonds between sand particles),the rate dependency behavior of specimens will reduce.Investigation of the effects of the cementation level demonstrated that by increasing the amount of the precipitated calcite from 0.38%to 0.83%,accumulated plastic strains are reduced almost 95%under the same loading condition.Effects of the initial static loads,confining pressures,the number of cycles,and amplitudes of the cyclic loads are also evaluated.展开更多
Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB ...Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures,a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens(rock on outside,backfill on inside)with different volume fractions of rock(VF=0.48,0.61,0.73,and 0.84),confining pressures(0,6,9,and 12 MPa),and cyclic loading rates(200,300,400,and 500 N/s).The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops,acoustic emission events,and post-failure X-ray 3D fracture morphology.The results showed significant differences between cyclic and monotonic loadings of RB specimens,particularly with regard to the generation of shear microcracks,the development of stress memory and strain hardening,and the contact forces and associated friction that develops along the rock-backfill interface.One important finding is that as a function of the number of cycles,the elastic strain increases linearly and the dissipated energy increases exponentially.Also,compared with monotonic loading,the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage.Another finding is that compared with monotonic loading,more shear microcracks are generated during every reloading stage,but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation.The transition from elastic to plastic behavior varies depending on the parameters of each test(confinement,volume fraction,and cyclic rate),and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction,400 N/s cyclic loading rate,and 9 MPa confinement.All the findings have important practical implications on the ability of backfill to support underground excavations.展开更多
Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and respons...Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.展开更多
Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fa...Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.展开更多
Failure of irregular rock samples may provide implications in the rapid estimation of rock strength,which is imperative in rock engineering practice.In this work,analytical,experimental and numerical investigations we...Failure of irregular rock samples may provide implications in the rapid estimation of rock strength,which is imperative in rock engineering practice.In this work,analytical,experimental and numerical investigations were carried out to study the mechanical properties and failure characteristics of rock spheres under paired point loads.Analytical solutions indicted that with the increase in sample size(contact angle)and decrease in Poisson’s ratio,the uneven tensile stress in theta direction decreased.Then laboratory experiments were carried out to investigate the load characteristics and failure mode of spherical marble samples with different sizes subjected to a pair of diametral point loads.The discrete element method(DEM)was adopted to study the failure process of rock spheres.The effect of the sphere diameter on the point load contact angle was examined in terms of peak load,crushed zone distribution and energy dissipation.Experimental and numerical results showed that the samples primarily fail in tension,with crushed zones formed at both loading points.With increase in the sample size,the contact angle,crushed area and total work increase.As the specimen diameter increases from 30 mm to 50 mm,the peak load on the specimen increases from 3.6 kN to 8.8 kN,and the percentage of crushed zone(ratio of crushing zone to sample radius,d/r)increased from 0.191 to 0.262.The results of the study have implications for understanding the failure of irregular rock specimens under point loading conditions and their size effects.展开更多
Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,t...Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.展开更多
The safety of civilian and military infrastructure is a concern due to an increase in explosive risks,which has led to a demand for high-strength civil infrastructure with improved energy absorption capacity.In this s...The safety of civilian and military infrastructure is a concern due to an increase in explosive risks,which has led to a demand for high-strength civil infrastructure with improved energy absorption capacity.In this study,a Finite Element(FE)numerical model was developed to determine the effect of hybrid Fibre Reinforced Polymer(FRP)as a strengthening material on full-scale Reinforced Concrete(RC)slabs.The reinforcing materials under consideration were Carbon(CFRP)and Glass(GFRP)fibres,which were subjected to blast loads to determine the structural response.A laminated composite fabric material model was utilized to model the failure of composite,which facilitates the consideration of strain rate effects.The damaged area of the laminate is determined in the FE model,and it is in good agreement with the corresponding experimental results in the literature.Models containing different stacking sequences were built to demonstrate their efficiency in resisting blast loads.In general,the damaged area was reduced when a hybrid reinforcement with CFRP as the top layer was used.展开更多
BACKGROUND Lactose intolerance(LI)is commonly seen in East Asian countries.Several studies showed that lactose or milk loading has been used as a treatment for lactose malabsorption(LM)in Western countries,but there h...BACKGROUND Lactose intolerance(LI)is commonly seen in East Asian countries.Several studies showed that lactose or milk loading has been used as a treatment for lactose malabsorption(LM)in Western countries,but there have been no reports regarding this type of treatment in Japan.As lactose or milk loading requires ingestion of large amounts of lactose within a short period,this is considered to be too harsh for Japanese people because of their less habitual milk consumption(175 mL per day in average)than Western people.In this study,we demonstrated lactose tolerance acquisition in a suitable way for Japanese.AIM To examine the efficacy of lactose(cow’s milk)loading treatment in patients with LM.METHODS Individuals with abdominal symptoms induced by milk or dairy products(LI symptoms)were identified with a questionnaire.A 20 g lactose hydrogen breath test(LHBT)was carried out to confirm LM diagnosis and to evaluate co-existence of small intestinal bacterial overgrowth(SIBO).Respondents diagnosed with LM were selected as study subjects and were treated with incremental loads of cow’s milk,starting from 30 mL and increasing up to 200 mL at 4-7 d intervals.After the treatment,changes in symptoms and LM diagnostic value of 20 g LHBT were investigated.Stool samples pre-and post-treatment were examined for changes in intestinal microbiota using 16S rRNA sequencing.Informed consent was obtained prior to each stage of the study.RESULTS In 46 subjects with LI symptoms(10-68 years old,mean age 34 years old)identified with the questionnaire,35(76.1%)were diagnosed with LM by 20 g LHBT,and 6 had co-existing SIBO.The treatment with incremental cow’s milk was carried out in 32 subjects diagnosed with LM(14-68 years old,median age 38.5 years old).The mean period of the treatment was 41±8.6 d.Improvement of symptoms was observed in 29(90.6%;95%confidence interval:75.0%-98.0%)subjects.Although 20 g LHBT indicated that 10(34.5%)subjects had improved diagnostic value of LM,no change was observed in 16(55.2%)subjects.Analysis of the fecal intestinal microbiota showed a significant increase in Blautia in 7 subjects who became symptom-free after the treatment(P=0.0313).CONCLUSION LM was diagnosed in approximately 75%of the subjects who had LI.Incremental loads of cow’s milk is regarded as a useful treatment for LM without affecting everyday life.展开更多
In the presentmanuscript,a Layer-Wise(LW)generalizedmodel is proposed for the linear static analysis of doublycurved shells constrained with general boundary conditions under the influence of concentrated and surface ...In the presentmanuscript,a Layer-Wise(LW)generalizedmodel is proposed for the linear static analysis of doublycurved shells constrained with general boundary conditions under the influence of concentrated and surface loads.The unknown field variable is modelled employing polynomials of various orders,each of them defined within each layer of the structure.As a particular case of the LW model,an Equivalent Single Layer(ESL)formulation is derived too.Different approaches are outlined for the assessment of external forces,as well as for non-conventional constraints.The doubly-curved shell is composed by superimposed generally anisotropic laminae,each of them characterized by an arbitrary orientation.The fundamental governing equations are derived starting from an orthogonal set of principal coordinates.Furthermore,generalized blending functions account for the distortion of the physical domain.The implementation of the fundamental governing equations is performed bymeans of the Generalized Differential Quadrature(GDQ)method,whereas the numerical integrations are computed employing theGeneralized IntegralQuadrature(GIQ)method.In the post-processing phase,an effective procedure is adopted for the reconstruction of stress and strain through-the-thickness distributions based on the exact fulfillment of three-dimensional equilibrium equations.A series of systematic investigations are performed in which the static response of structures with various curvatures and lamination schemes,calculated by the present methodology,have been successfully compared to those ones obtained fromrefined finite element three-dimensional simulations.Even though the present LW approach accounts for a two-dimensional assessment of the structural problem,it is capable of well predicting the three-dimensional response of structures with different characteristics,taking into account a reduced computational cost and pretending to be a valid alternative to widespread numerical implementations.展开更多
In order to ensure the safe operation of the compressors used in water chillers,in the present study some interlock protections have been added to the related design.These include a low pressure protection,a high pres...In order to ensure the safe operation of the compressors used in water chillers,in the present study some interlock protections have been added to the related design.These include a low pressure protection,a high pressure protection,an exhaust temperature protection and a differential pressure protection.Some tests have been conducted by tuning the saturation suction and exhaust temperatures of the compressor through adjustment of the cold source outlet temperature and the ambient temperature.The results show that the ambient temperature increases with decreasing device load and increasing fan speed under the same saturated suction temperature;the device refrigerating capacity steps up with augmenting load and dropping saturation exhaust temperature,while it is not greatly affected by the fan speed.Moreover,the Energy efficiency ratio(COP)decreases with the rise of the saturation exhaust temperature.This parameter is not affected much by the device load and fan speed at high saturation exhaust temperature,while it improves on increasing the device load and decreasing the fan speed at low saturation exhaust temperature.展开更多
基金l’UniversitéLaval for the financial support of his sabbatical year at Dipartimento di Bioscienze e Territorio,Universitàdegli Studi del Molise in Campobasso,Italy。
文摘This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time,before the damping forces can dissipate a significant portion of the energy input into the system.The development of two sine series solutions,relating to different types of impulsive loadings,one involving a single concentrated force and the other a distributed line load,are presented.This study revealed that when a simply supported Euler-Bernoulli beam,resting on a Winkler soil model,is subject to an impact load,the resulting vertical displacements,bending moments and shear forces produced along the span of the beam are considerably affected.In particular,the quantification of this effect is best observed,relative to the corresponding static solution,via an amplification factor.The computed impact amplification factors,for the sub-grade moduli used in this study,were in magnitude greater than 2,thus confirming the multiple-degree-of-freedom nature of the problem.
文摘An analytical method for analyzing the thermal vibration of multi-directional functionally graded porous rectangular plates in fluid media with novel porosity patterns is developed in this study.Mechanical properties of MFG porous plates change according to the length,width,and thickness directions for various materials and the porosity distribution which can be widely applied in many fields of engineering and defence technology.Especially,new porous rules that depend on spatial coordinates and grading indexes are proposed in the present work.Applying Hamilton's principle and the refined higher-order shear deformation plate theory,the governing equation of motion of an MFG porous rectangular plate in a fluid medium(the fluid-plate system)is obtained.The fluid velocity potential is derived from the boundary conditions of the fluid-plate system and is used to compute the extra mass.The GalerkinVlasov solution is used to solve and give natural frequencies of MFG porous plates with various boundary conditions in a fluid medium.The validity and reliability of the suggested method are confirmed by comparing numerical results of the present work with those from available works in the literature.The effects of different parameters on the thermal vibration response of MFG porous rectangular plates are studied in detail.These findings demonstrate that the behavior of the structure within a liquid medium differs significantly from that within a vacuum medium.Thereby,they offer appropriate operational approaches for the structure when employed in various mediums.
基金supported by the National Natural Science Foundation of China(Nos.52074151,51927807,and 52274123)Tiandi Science and Technology Co.,Ltd.(No.2022-2-TDMS012)。
文摘This study explores the effects of dynamic and static loading on rock bolt performance a key factor in maintaining the structural safety of coal mine roadways susceptible to coal bursts.Employing a housemade load frame to simulate various failure scenarios,pretension-impact-pull tests on rock bolts were conducted to scrutinize their dynamic responses under varied static load conditions and their failure traits under combined loads.The experimental results denote that with increased impact energy,maximum and average impact loads on rock bolts escalate significantly under pretension,initiating plastic deformation beyond a certain threshold.Despite minor reductions in the yield load due to impactinduced damage,pretension aids in constraining post-impact deformation rate and fluctuation degree of rock bolts.Moreover,impact-induced plastic deformation causes internal microstructure dislocation,fortifying the stiffness of the rock bolt support system.The magnitude of this fortification is directly related to the plastic deformation induced by the impact.These findings provide crucial guidance for designing rock bolt support in coal mine roadway excavation,emphasizing the necessity to consider both static and dynamic loads for improved safety and efficiency.
基金This research was funded through the National Natural Science Foundation of China(Grant Nos.52108299 and 52178312)the China Postdoctoral Science Foundation(Grant No.2021M693740)the Basal Research Fund Support by Chongqing University.
文摘The performance of geosynthetic-reinforced embankments under traffic moving loads is always a hotspot in the geotechnical engineering field.A three-dimensional(3D)model of a geosynthetic-reinforced embankment without drainage consolidation was established using the finite element software ABAQUS.In this model,the traffic loads were simulated by two moving loads of rectangular pattern,and their amplitude,range,and moving speed were realized by a Fortran subroutine.The embankment fill was simulated by an equivalent linear viscoelastic model,which can reflect its viscoelasticity.The geogrid was simulated by the truss element,and the geocell was simulated by the membrane element.Infinite elements were utilized to weaken the boundary effect caused by the model geometry at the boundaries.Validation of the established numerical model was conducted by comparing the predicted deformations in the cross-section of the geosynthetic-reinforced embankment with those from the existing literature.On this basis,the dynamic stress and strain distribution in the pavement structure layer of the geosynthetic-reinforced embankment under a moving load was also analyzed.Finally,a parametric study was conducted to examine the influences of the different types of reinforcement,overload,and the moving load velocity on the geosynthetic-reinforced embankment.
基金the financial support from the National Natural Science Foundation of China(Nos.52374094,52174122 and 52374218)Excellent Youth Fund of Shandong Natural Science Foundation(No.ZR2022YQ49)Taishan Scholar Project in Shandong Province(Nos.tspd20210313 and tsqn202211150)。
文摘The stability control of fissured rock is difficult,especially under static and dynamic loads in deep coal mines.In this paper,the dynamic mechanical properties,strain rate evolution and energy dissipation of fissured and anchored rocks were respectively obtained by SHPB tests.It was found that bolt can provide supporting efficiency-improving effect for fissured rock against dynamic disturbance,and this effect increased quadratically with decrease in anchoring angles.Then,the energy dissipation mechanism of anchored rock was obtained by slipping model.Furthermore,bolt energy-absorbing mechanism by instantaneous tensile-shear deformation was expressed based on material mechanics,which was the larger the anchoring angle,the smaller the energy absorption,and the less the contribution to supporting efficiency improvement.On this basis,the functional relationship between energy dissipation of anchored rock and energy absorption of bolt was established.Taking the coal-gangue separation system of Longgu coal mine as an example,the optimal anchoring angle can be determined as 57.5°–67.5°.Field monitoring showed fissured rock with the optimal anchoring angle,can not only effectively control the deformation,but also fully exert the energy-absorbing and efficiency-improving effect of bolt itself.This study provides guidance to the stability control and supporting design for deep engineering under the same or similar conditions.
基金support of RSSB to this work via the project RSSB/COF-UOH-49 is greatly appreciated.The authors also acknowledge the support by FCT,through IDMEC,under LAETA,project UIDB/50022/2020.
文摘Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile,and thus aerodynamic load changes significantly with operational height.This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations,such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces.Specifically,computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting,such as that of the recessed cavity on a Class 800 train.From an aerodynamic perspective,this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing,although the difference between the two is found to reduce with increasing pantograph extension.Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour.The results obtained show how considering aerodynamic forces enhance the realism of the models,leading to behaviour of the pantograph-catenary contact forces closely matching that seen in experimental tests.
基金funded from the European Union's Horizon 2020 research and innovation programme in the project In2Track3 under grant agreement No.101012456.
文摘Dynamic wheel-rail contact forces induced by a severe form of wheel tread damage have been measured by a wheel impact load detector during full-scale field tests at different vehicle speeds.Based on laser scanning,the measured three-dimensional damage geometry is employed in simulations of dynamic vehicle-track interaction to calibrate and verify a simulation model.The relation between the magnitude of the impact load and various operational parameters,such as vehicle speed,lateral position of wheel-rail contact,track stiffness and position of impact within a sleeper bay,is investigated.The calibrated model is later employed in simulations featuring other forms of tread damage;their effects on impact load and subsequent fatigue impact on bearings,wheel webs and subsurface initiated rolling contact fatigue of the wheel tread are assessed.The results quantify the effects of wheel tread defects and are valuable in a shift towards condition-based maintenance of running gear,and for general assessment of the severity of different types of railway wheel tread damage.
基金the National Natural Science Foundation of China Youth Fund,Research on Security Low Carbon Collaborative Situation Awareness of Comprehensive Energy System from the Perspective of Dynamic Security Domain(52307130).
文摘To address the issues of limited demand response data,low generalization of demand response potential evaluation,and poor demand response effect,the article proposes a demand response potential feature extraction and prediction model based on data mining and a demand response potential assessment model for adjustable loads in demand response scenarios based on subjective and objective weight analysis.Firstly,based on the demand response process and demand response behavior,obtain demand response characteristics that characterize the process and behavior.Secondly,establish a feature extraction and prediction model based on data mining,including similar day clustering,time series decomposition,redundancy processing,and data prediction.The predicted values of each demand response feature on the response day are obtained.Thirdly,the predicted data of various characteristics on the response day are used as demand response potential evaluation indicators to represent different demand response scenarios and adjustable loads,and a demand response potential evaluation model based on subjective and objective weight allocation is established to calculate the demand response potential of different adjustable loads in different demand response scenarios.Finally,the effectiveness of the method proposed in the article is verified through examples,providing a reference for load aggregators to formulate demand response schemes.
文摘Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.
基金National Science Foundation of China under Grant No.51778248Natural Science Foundation of Fujian Province under Grant No.2018J01075+2 种基金Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University under Grant No.ZQN-PY312Research Trained Fund for Outstanding Young Researcher in Higher Education Institutions of Fujian ProvinceSubsidized Project for Postgraduates′Innovative Fund in Scientific Research of Huaqiao University under Grant No.18013086021。
文摘In this article,the seismic performance of box-shaped steel piers embedded with energy-dissipating shells under a multi-directional seismic load is investigated.A finite element(FE)model was accurately established and verified by the quasi-static test results.A parametric analysis of the hysteretic behaviour of a novel box-shaped steel pier under eccentric pressure was carried out on this basis.We discussed the influence of the eccentricity,axial compression ratio,thickness of embedded shell,ratio of slenderness,spacing of transverse stiffening ribs on the embedded shell,and width-to-thickness ratio of wallboard on the anti-seismic performance of a novel box-shaped steel bridge pier.The results revealed that the load carrying capacity and ductility coefficient of the specimen are substantially influenced by the eccentricity,variation in the axial compression ratio,and slenderness ratio.The specimen′s plastic energy dissipation capacity can be effectively improved by increasing the thickness of the embedded shell.The spacing of the transverse stiffening ribs only marginally affects seismic performance.In addition,the width-to-thickness ratio of the wallboard exerts a more considerable influence on the deformability of the square-section specimen.Finally,a formula for calculating the bearing capacity of the novel box-shaped steel piers under cyclic loading is proposed.
文摘Industrial production of chemical cement leads to extreme emissions of greenhouse gases.Biological or bioinspired sustainable materials for soil treatment projects can be employed instead of chemical cement to heal the carbon cycle in the ecosystem.The enzyme-induced calcite precipitation(EICP)method is one of the novel bio-inspired technologies that can be employed in soil treatment projects to increase desired properties of soils.While the monotonic and cyclic behavior of the enzymatically treated sands has been investigated comprehensively,the strain accumulation pattern in these improved soils under cyclic traffic loads has not been evaluated yet.In this paper,confined and unconfined cyclic compression tests are applied to the enzymatically lightly cemented sands,and the effects of the different parameters on their strain accumulation pattern are investigated for the first time in the literature.This study uses two types of specimens with unconfined compression strengths(UCS)equal to 42 kPa and 266 kPa.It is shown that the treated specimens have a rate-dependent behavior where cyclic loads with low frequencies lead to more resilient and plastic strains in the specimens.The results show that by approaching the maximum applied stresses to the UCS of the specimens(by breaking more calcite bonds between sand particles),the rate dependency behavior of specimens will reduce.Investigation of the effects of the cementation level demonstrated that by increasing the amount of the precipitated calcite from 0.38%to 0.83%,accumulated plastic strains are reduced almost 95%under the same loading condition.Effects of the initial static loads,confining pressures,the number of cycles,and amplitudes of the cyclic loads are also evaluated.
基金We acknowledge the funding support from the National Natural Science Foundation of China Youth Fund(Grant No.52004019)the National Natural Science Foundation of China(Grant No.41825018)China Postdoctoral Science Foundation(Grant No.2023M733481).
文摘Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures,a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens(rock on outside,backfill on inside)with different volume fractions of rock(VF=0.48,0.61,0.73,and 0.84),confining pressures(0,6,9,and 12 MPa),and cyclic loading rates(200,300,400,and 500 N/s).The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops,acoustic emission events,and post-failure X-ray 3D fracture morphology.The results showed significant differences between cyclic and monotonic loadings of RB specimens,particularly with regard to the generation of shear microcracks,the development of stress memory and strain hardening,and the contact forces and associated friction that develops along the rock-backfill interface.One important finding is that as a function of the number of cycles,the elastic strain increases linearly and the dissipated energy increases exponentially.Also,compared with monotonic loading,the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage.Another finding is that compared with monotonic loading,more shear microcracks are generated during every reloading stage,but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation.The transition from elastic to plastic behavior varies depending on the parameters of each test(confinement,volume fraction,and cyclic rate),and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction,400 N/s cyclic loading rate,and 9 MPa confinement.All the findings have important practical implications on the ability of backfill to support underground excavations.
基金National Natural Science Foundation of China under Grant No.52278503。
文摘Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.
文摘Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.
文摘Failure of irregular rock samples may provide implications in the rapid estimation of rock strength,which is imperative in rock engineering practice.In this work,analytical,experimental and numerical investigations were carried out to study the mechanical properties and failure characteristics of rock spheres under paired point loads.Analytical solutions indicted that with the increase in sample size(contact angle)and decrease in Poisson’s ratio,the uneven tensile stress in theta direction decreased.Then laboratory experiments were carried out to investigate the load characteristics and failure mode of spherical marble samples with different sizes subjected to a pair of diametral point loads.The discrete element method(DEM)was adopted to study the failure process of rock spheres.The effect of the sphere diameter on the point load contact angle was examined in terms of peak load,crushed zone distribution and energy dissipation.Experimental and numerical results showed that the samples primarily fail in tension,with crushed zones formed at both loading points.With increase in the sample size,the contact angle,crushed area and total work increase.As the specimen diameter increases from 30 mm to 50 mm,the peak load on the specimen increases from 3.6 kN to 8.8 kN,and the percentage of crushed zone(ratio of crushing zone to sample radius,d/r)increased from 0.191 to 0.262.The results of the study have implications for understanding the failure of irregular rock specimens under point loading conditions and their size effects.
基金funding support from National Natural Science Foundation of China(Grant No.52179109)Jiangsu Provincial Natural Science Foundation(Grant No.BK20230967)Open Research Fund of State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures,Shijiazhuang Tiedao University(Grant No.KF2022-02).
文摘Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.
基金supported by the Foreign Young Talents Project China(No.QN2021014006L)National Natural Science Foundation of China(Nos.51878354&51308301)+1 种基金the Natural Science Foundation of Jiangsu Province(Nos.BK20181402&BK20130978)333 Talent High-Level Projects of Jiangsu Province and Qinglan Project of Jiangsu Higher Education Institutions.Any research results expressed in this paper are those of the writers and do not necessarily reflect the views of the foundations.
文摘The safety of civilian and military infrastructure is a concern due to an increase in explosive risks,which has led to a demand for high-strength civil infrastructure with improved energy absorption capacity.In this study,a Finite Element(FE)numerical model was developed to determine the effect of hybrid Fibre Reinforced Polymer(FRP)as a strengthening material on full-scale Reinforced Concrete(RC)slabs.The reinforcing materials under consideration were Carbon(CFRP)and Glass(GFRP)fibres,which were subjected to blast loads to determine the structural response.A laminated composite fabric material model was utilized to model the failure of composite,which facilitates the consideration of strain rate effects.The damaged area of the laminate is determined in the FE model,and it is in good agreement with the corresponding experimental results in the literature.Models containing different stacking sequences were built to demonstrate their efficiency in resisting blast loads.In general,the damaged area was reduced when a hybrid reinforcement with CFRP as the top layer was used.
基金Supported by Grants of J-milk(Japan Dairy Association)。
文摘BACKGROUND Lactose intolerance(LI)is commonly seen in East Asian countries.Several studies showed that lactose or milk loading has been used as a treatment for lactose malabsorption(LM)in Western countries,but there have been no reports regarding this type of treatment in Japan.As lactose or milk loading requires ingestion of large amounts of lactose within a short period,this is considered to be too harsh for Japanese people because of their less habitual milk consumption(175 mL per day in average)than Western people.In this study,we demonstrated lactose tolerance acquisition in a suitable way for Japanese.AIM To examine the efficacy of lactose(cow’s milk)loading treatment in patients with LM.METHODS Individuals with abdominal symptoms induced by milk or dairy products(LI symptoms)were identified with a questionnaire.A 20 g lactose hydrogen breath test(LHBT)was carried out to confirm LM diagnosis and to evaluate co-existence of small intestinal bacterial overgrowth(SIBO).Respondents diagnosed with LM were selected as study subjects and were treated with incremental loads of cow’s milk,starting from 30 mL and increasing up to 200 mL at 4-7 d intervals.After the treatment,changes in symptoms and LM diagnostic value of 20 g LHBT were investigated.Stool samples pre-and post-treatment were examined for changes in intestinal microbiota using 16S rRNA sequencing.Informed consent was obtained prior to each stage of the study.RESULTS In 46 subjects with LI symptoms(10-68 years old,mean age 34 years old)identified with the questionnaire,35(76.1%)were diagnosed with LM by 20 g LHBT,and 6 had co-existing SIBO.The treatment with incremental cow’s milk was carried out in 32 subjects diagnosed with LM(14-68 years old,median age 38.5 years old).The mean period of the treatment was 41±8.6 d.Improvement of symptoms was observed in 29(90.6%;95%confidence interval:75.0%-98.0%)subjects.Although 20 g LHBT indicated that 10(34.5%)subjects had improved diagnostic value of LM,no change was observed in 16(55.2%)subjects.Analysis of the fecal intestinal microbiota showed a significant increase in Blautia in 7 subjects who became symptom-free after the treatment(P=0.0313).CONCLUSION LM was diagnosed in approximately 75%of the subjects who had LI.Incremental loads of cow’s milk is regarded as a useful treatment for LM without affecting everyday life.
文摘In the presentmanuscript,a Layer-Wise(LW)generalizedmodel is proposed for the linear static analysis of doublycurved shells constrained with general boundary conditions under the influence of concentrated and surface loads.The unknown field variable is modelled employing polynomials of various orders,each of them defined within each layer of the structure.As a particular case of the LW model,an Equivalent Single Layer(ESL)formulation is derived too.Different approaches are outlined for the assessment of external forces,as well as for non-conventional constraints.The doubly-curved shell is composed by superimposed generally anisotropic laminae,each of them characterized by an arbitrary orientation.The fundamental governing equations are derived starting from an orthogonal set of principal coordinates.Furthermore,generalized blending functions account for the distortion of the physical domain.The implementation of the fundamental governing equations is performed bymeans of the Generalized Differential Quadrature(GDQ)method,whereas the numerical integrations are computed employing theGeneralized IntegralQuadrature(GIQ)method.In the post-processing phase,an effective procedure is adopted for the reconstruction of stress and strain through-the-thickness distributions based on the exact fulfillment of three-dimensional equilibrium equations.A series of systematic investigations are performed in which the static response of structures with various curvatures and lamination schemes,calculated by the present methodology,have been successfully compared to those ones obtained fromrefined finite element three-dimensional simulations.Even though the present LW approach accounts for a two-dimensional assessment of the structural problem,it is capable of well predicting the three-dimensional response of structures with different characteristics,taking into account a reduced computational cost and pretending to be a valid alternative to widespread numerical implementations.
基金This work was supported by the National Natural Science Foundation of China(No.41877251)Major Science and Technology Projects of Xinxiang City(No.21ZD012).
文摘In order to ensure the safe operation of the compressors used in water chillers,in the present study some interlock protections have been added to the related design.These include a low pressure protection,a high pressure protection,an exhaust temperature protection and a differential pressure protection.Some tests have been conducted by tuning the saturation suction and exhaust temperatures of the compressor through adjustment of the cold source outlet temperature and the ambient temperature.The results show that the ambient temperature increases with decreasing device load and increasing fan speed under the same saturated suction temperature;the device refrigerating capacity steps up with augmenting load and dropping saturation exhaust temperature,while it is not greatly affected by the fan speed.Moreover,the Energy efficiency ratio(COP)decreases with the rise of the saturation exhaust temperature.This parameter is not affected much by the device load and fan speed at high saturation exhaust temperature,while it improves on increasing the device load and decreasing the fan speed at low saturation exhaust temperature.