Resistance of full-scale beams against close-in explosions.Numerical modeling and field tests

This paper explores the performances of a finite element simulation including four concrete models applied to a full-scale reinforced concrete beam subjected to blast loading. Field test data has been used to compare model results for each case. The numerical modelling has been, carried out using the suitable code LS-DYNA. This code integrates blast load routine(CONWEP) for the explosive description and four different material models for the concrete including: Karagozian & Case Concrete, Winfrith, Continuous Surface Cap Model and Riedel-Hiermaier-Thoma models, with concrete meshing based on 10, 15, and 20 mm. Six full-scale beams were tested: four of them used for the initial calibration of the numerical model and two more tests at lower scaled distances. For calibration, field data obtained employing pressure and accelerometers transducers were compared with the results derived from the numerical simulation. Damage surfaces and the shape of rupture in the beams have been used as references for comparison. Influence of the meshing on accelerations has been put in evidence and for some models the shape and size of the damage in the beams produced maximum differences around 15%. In all cases, the variations between material and mesh models are shown and discussed.

Experimental investigations on small-and full-scale ship models with polyurea coatings subjected to underwater explosion

Nowadays, the mitigation of damage to a ship caused by the underwater explosion attracts more and more attention from the modern ship designers. In this study, two kinds of scale tests were conducted to investigate the effects of polyurea coatings on the blast resistance of hulls subjected to underwater explosion. Firstly, small-scale model tests with different polyurea coatings were carried out. Results indicate that polyurea has a better blast resistance performance when coated on the front face, which can effectively reduce the maximum deflection of the steel plate by more than 20% and reduce the deformation energy by 35.7%-45.4%. Next, a full-scale ship(approximately 50 m × 9 m) under loadings produced by the detonation of 33 kg of spherical TNT charges was tested, where a part of the ship was coated with polyurea on the front face(8 mm + 24 mm) and not on the contrast area. Damage characteristics on the bottom were statistically analyzed based on a 3D scanning technology, indicating that polyurea contributes to enhancing the blast protection of the ship. However, damage results of this test were different from those of the small-scale tests. Moreover, the deformation area of the bottom with polyurea was greatly increased by 40.1% to disperse explosion energy, a conclusion that cannot be drown from the small-scale tests.

A Non-geometrically Similar Model for Predicting the Wake Field of Full-scale Ships

The scale effect leads to large discrepancies between the wake fields of model-scale and actual ships, and causes differences in cavitation performance and exciting forces tests in predicting the performance of actual ships. Therefore, when test data from ship models are directly applied to predict the performance of actual ships, test results must be subjected to empirical corrections. This study proposes a method for the reverse design of the hull model. Compared to a geometrically similar hull model, the wake field generated by the modified model is closer to that of an actual ship. A non-geometrically similar model of a Korean Research Institute of Ship and Ocean Engineering （KRISO）’s container ship （KCS） was designed. Numerical simulations were performed using this model, and its results were compared with full-scale calculation results. The deformation method of getting the wake field of full-scale ships by the non-geometrically similar model is applied to the KCS successfully.

Stiffness Degradation Modeling for Composite Wind Turbine Blades Based on Full-Scale Fatigue Testing

In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testing of a blade.A novel non-linear fatigue damage accumulation model is proposed using the damage assessment theories of composite laminates for the first time.Then,a stiffness degradation model is established based on the correlation of fatigue damage and residual stiffness of the composite laminates.Finally,a stiffness degradation model for the blade is presented based on the full-scale fatigue testing.The scientific rationale of the proposed stiffness model of blade is verified by using full-scale fatigue test data of blade with a total length of 52.5 m.The results indicate that the proposed stiffness degradation model of the blade agrees well with the fatigue testing results of this blade.This work provides a basis for evaluating the fatigue damage and lifetime of blade under cyclic fatigue loading.

Full-scale Water Modeling on Flow Field of Continuous Casting Mold

In the continuous casting process of aluminum killed steel grades,nozzle clogging is a common problem.Argon is usually injected into the casting channel through stoppers or nozzles to minimize clogs;however,complex two-phase flow regimes appear,and the flow in the mold might deteriorate.This could result in a higher defect rate in the cast product and should be avoided as much as possible.Therefore,it is important to understand the interaction between process conditions and the refractory products used and their impact on the flow pattern in the mold.In this study,a full-scale water model was established to simulate the slab casting process.Three nozzle shapes and three immersion depths were applied to investigate the flow behavior and liquid level fluctuations by the full-scale water model.The relationship between the flow behavior and continuous casting parameters was evaluated.The results provide guidance for the design and production of the refractory nozzle and the operation of the continuous casting plant.

Full-scale model tests and nonlinear analysis of prestressed concrete simply supported box girders

Full-scale model tests were carried out on a 30 m span prestressed concrete box girder and a 20 m span prestressed concrete hollow slab. Failure models were prestressed reinforcement tensile failure and crashing of roof concrete, respectively. The ductility indexes of the box girder and hollow slab were 1.99 and 1.23, respectively, according to the energy viewpoint. Based on the horizontal section hypothesis, the nonlinear computation procedure was established using the limited banding law, and it could carry out the entire performance analysis including the unloading, mainly focusing on the ways to achieve the unloading curves computation through stress-strain, moment-curvature and load-displacement curves. Through the procedure, parameters that influence on the bearing capacity, deformation performance and ductility of the structures were analyzed. Those parameters were quantity of prestressed reinforcement and tension coefficients of prestressed reinforcement. From the analysis, some useful conclusions can be obtained.

Experimental and analytical study on design performance of full-scale viscoelastic dampers

Viscoelastic（VE） dampers, with their stiffness and energy dissipation capabilities, have been widely used in civil engineering for mitigating wind-induced vibration and seismic responses of structures, thus enhancing the comfort of residents and serviceability of equipment inside. In past relevant research, most analytical models for characterizing the mechanical behavior of VE dampers were verified by comparing their predictions with performance test results from small-scale specimens, which might not adequately or conservatively represent the actual behavior of full-scale dampers, especially with regard to the ambient temperature, temperature rise, and heat convection effects. Thus, in this study, by using a high-performance testing facility with a temperature control system, full-scale VE dampers were dynamically tested with different displacement amplitudes, excitation frequencies, and ambient temperatures. By comparing the analytical predictions with the experimental results, it is demonstrated that adopting the fractional derivative method together with considering the effects of excitation frequencies, ambient temperatures, temperature rises, softening, and hardening, can reproduce the design performance of full-scale VE dampers very well.

Full-scale modeling of chemical experiments

Computational chemistry methods are playing an increasingly pivotal role in chemical experiments.From quantum chemistry simulations to finite element simulations,researchers can always find an appropriate simulation method to elucidate the specific mechanisms at a certain resolution scale.However,in organic or inorganic synthesis,the synthesis mechanisms span multiple spatial and temporal scales of chemical experiments.Furthermore,the intricate nature of these mechanisms renders it impossible for any single simulation method to provide a comprehensive depiction of the entire process.In this perspective,using zeolite and polymer synthesis simulations as examples,we stress the significance of fullscale modeling techniques for chemical experiments and urge the corresponding sophisticated simulation platform.

A deep neural network based surrogate model for damage identification in full-scale structures with incomplete noisy measurements

The paper introduces a novel approach for detecting structural damage in full-scale structures using surrogate models generated from incomplete modal data and deep neural networks(DNNs).A significant challenge in this field is the limited availability of measurement data for full-scale structures,which is addressed in this paper by generating data sets using a reduced finite element(FE)model constructed by SAP2000 software and the MATLAB programming loop.The surrogate models are trained using response data obtained from the monitored structure through a limited number of measurement devices.The proposed approach involves training a single surrogate model that can quickly predict the location and severity of damage for all potential scenarios.To achieve the most generalized surrogate model,the study explores different types of layers and hyperparameters of the training algorithm and employs state-of-the-art techniques to avoid overfitting and to accelerate the training process.The approach’s effectiveness,efficiency,and applicability are demonstrated by two numerical examples.The study also verifies the robustness of the proposed approach on data sets with sparse and noisy measured data.Overall,the proposed approach is a promising alternative to traditional approaches that rely on FE model updating and optimization algorithms,which can be computationally intensive.This approach also shows potential for broader applications in structural damage detection.

Dynamic behavior of new cutting subgrade structure of expensive soil under train loads coupling with service environment

Expansive soil is sensitive to dry and wet environment change. And the volume deformation and inflation pressure of expansive soil may induce to cause the deformation failure of roadbed or many other adverse effects. Aimed at a high-speed railway engineering practice in the newly built Yun-Gui high-speed railway expansive soil section in China, indoor vibration test on a full-scaled new cutting subgrade model is carried out. Based on the established track-subgrade-foundation of expansive soil system dynamic model test platform, dynamic behavior of new cutting subgrade structure under train loads coupling with extreme service environment(dry, raining, and groundwater level rising) is analyzed comparatively. The results show that the subgrade dynamic response is significantly influenced by service conditions and the dynamic response of subgrade gradually becomes stable with the increasing vibration times under various service environment conditions. The vertical dynamic soil stress is related with the depth in an approximate exponential function, and the curves of vertical dynamic soil stress present a "Z" shape distribution along transverse distance. The peak value of dynamic soil stress appears below the rail, and it increases more obviously near the roadbed surface. However, the peak value of dynamic soil stress is little affected outside 5.0 m of center line. The vibration velocity and acceleration are in a quadratic curve with an increase in depth, and the raining and groundwater level rising increase both the vibration velocity and the acceleration. The vertical deformations at different depths are differently affected by service environment in roadbed. The deformation of roadbed increases sharply when the water gets in the foundation of expansive soil, and more than 60% of the total deformation of roadbed occurs in expansive soil foundation. The laid waterproofing and drainage structure layer, which weakens the dynamic stress and improves the track regularity, presents a positive effect on the control deformation of roadbed surface. An improved empirical formula is then proposed to predict the dynamic stress of ballasted tracks subgrade of expansive soil.

Object-level change detection based on full-scale image segmentation and its application to Wenchuan Earthquake

Aiming at object fragmentation and poor detection results caused by discontinuous segmentation scale in object-level change detection,a new object-level change detection method based on the full-scale object tree is presented in this paper.The core idea of this new algorithm is to establish the full-scale object tree based on convexity model theory and integrate full-scale image segmentation techniques and change detection into the whole process.Some Wenchuan Earthquake images are taken as an example to discuss the new method for earthquake damage detection and evaluation in urban area,landslide detection,and extraction of barrier lake boundary.The application shows that the new method is robust and it provides an advanced tool for the quantitative detection and evaluation of earthquake damage.

High-frequency interference waves in low strain dynamic testing of X-section concrete piles

Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.

Finite Element Simulations of Dynamic Fracture of Full-Scale Gas Transmission Pipelines

The dynamic crack growth in a full-scale gas pipeline of API X80 steel is analyzed using the finite element method with the cohesive zone model. Based on the simulation, it is revealed that for the moderate steady-state crack growth, the crack-tip-opening angle strongly depends on the crack growth speed. In addition, the threshold initial crack sizes under different internal pressures are analyzed, which show a significant three-dimensional effect due to the wall thickness of the pipeline. The presented model offers a feasible way to study some details of the dynamic fracture of full-scale pipelines when tests are difficult or expensive.

A force control high-order single-step-β method (HSM) for substructure pseudo-dynamic testing

This paper proposes a new technique which introduces the high-order single-step-β method(HSM)into the experimental study on the substructure pseudo-dynamic testing(SPDT).The technique is based on the proposed concept of equivalent shear stiffness which can meet the requirement of the HSM algorithm.A study is done to theoretically validate the technique by the numerical analysis of two-storey shear building structure,in comparison of the proposed substructure pseudo-dynamic testing algorithm with the central difference method(CDM).Then,a full-scale SPDT model,the three-storey frame-supported reinforced concrete short-limb masonry shear wall structure,is designed and tested to simulate the seismic response of the corresponding six-storey structure and verify the proposed force control HSM technique.Meanwhile,the techniques of both stiffness correction and force control are suggested to control algorithmic error,control error and measurement error.The results indicate that the force control HSM can be used in the full-scale multi-degree-of-freedom(MDOF)substructure pseudo-dynamic testing before descent segment of structure restoring force properties.

Lifetime Prediction of Wind Turbine Blade Based on Full-Scale Fatigue Testing

In order to predict the lifetime of products appropriately with long lifetime and high reliability,the accelerated degradation testing(ADT)has been proposed.Composite wind turbine blade is one of the most important components in wind turbine system.Its fatigue cycle is very long in practice.A full-scale fatigue testing is usually used to verify the design of a new blade.In general,the full-scale fatigue testing of blade is accelerated on the basis of the damage equivalent principle.During the full-scale fatigue test ing,blade is subjected to higher testing load than normal operat ing conditions;consequently,the performance degradation of the blade is hastened over time.The full-scale fatigue testing of blade is regarded as a special ADT.According to the fatigue failure criterion,we choose blade stiffness as the characteristic quantity of the blade performance,and propose an accelerated model(AM)for blade on the basis of the theories of ADT.Then,degradation path of the blade stiffness is modeled by using Gamma process.Finally,the lifet ime prediction of full-scale megawatt(MW)blade is conducted by combining the proposed AM and blade stiffness degradation model.The prediction results prove the reasonability and validity of this study.This can supply a new approach to predict the lifetime of the full-scale MW blade.

Image-Aided Analysis of Ballast Particle Movement Along a High-Speed Railway

As a core infrastructure of high-speed railways,ballast layers constituted by graded crushed stones feature noteworthy particle movement compared with normal railways,which may cause excessive settlement and have detrimental effects on train operation.However,the movement behavior remains ambiguous due to a lack of effective measurement approaches and analytical methods.In this study,an image-aided technique was developed in a full-scale model test using digital cameras and a colorbased identification approach.A total of 1274 surface ballast particles were manually dyed by discernible colors to serve as tracers in the test.The movements of the surface ballast particles were tracked using the varied pixels displaying tracers in the photos that were intermittently taken during the test in the perpendicular direction.The movement behavior of ballast particles under different combinations of train speeds and axle loads was quantitatively evaluated.The obtained results indicated that the surface ballast particle movements were slight,mainly concentrated near sleepers under low-speed train loads and greatly amplified and extended to the whole surface when the train speed reached 360 km.h-1.Additionally,the development of ballast particle displacement statistically resembled its rotation.Track vibration contributed to the movements of ballast particles,which specifically were driven by vertical acceleration near the track center and horizontal acceleration at the track edge.Furthermore,the development trends of ballast particle movements and track settlement under long-term train loading were similar,and both stabilized at nearly the same time.The track performance,including the vibration characteristics,accumulated settlement,and sleeper support stiffness,was determined to be closely related to the direction and distribution of ballast particle flow,which partly deteriorated under high-speed train loads.

Macro-microscopic dynamic characteristics of the ballast bed induced by the variation of moisture content

Due to the excellent drainage performance of the ballast,existing studies mainly focus on the dynamic response of ballast under field capacity or saturation.Attention has rarely been paid to dynamic changes in moisture content and potential influences.In this article,we firstly conduct a model test to determine the variation of ballast moisture content under artificial rainfall.After that,a full-scale model test with cyclic loading is carried out to study the effect of moisture content variation on the macro-microscopic response of the ballast bed,where several wireless particle sensors are installed to obtain ballast motion characteristics at strategic locations.The results show that the moisture content increases gradually and stabilizes at a flat peak under rainfall,despite the excellent drainage performance of ballast bed.After halting rainfall,the moisture content drops back to field capacity,which indicates dynamic flowing surface water on ballast particles under rainfall.Such flowing surface water brings changes to the original dynamic equilibrium of ballast bed:macroscopically,the deformation rate of stabilized ballast bed increases significantly,reaching a local peak under field capacity;microscopically,the x-and z-angular accelerations of the ballast show positive correlation with rainfall intensity.The multiscale responses indicate that field capacity is a critical moisture content.

Safety analysis of temporary anchorage system for immersed tube in Shenzhen-Zhongshan Link

In the construction of the Shenzhen-Zhongshan Link,a temporary anchorage system,distributed uniformly along the pipe wall,has been employed.To assess the safety and reliability of this system,a combined method utilizing numerical analysis and model experiments was applied to study the safety of the temporary anchorage system and the reliability of the tension rods.Firstly,an overall model of the caisson segment based on GINA rebound force was established to analyze the stress state of the entire system.Secondly,a comprehensive numerical analysis and model experiment verification were conducted for the single tensioning system,revealing its failure mode and safety margin.The results indicate that the tension rod systems are uniformly stressed at an average of 444 k N during underwater jointing,with a safety factor of 1.94.At this point,the maximum von Mises stresses appearing at the front plate corners and the lower edge of the U-groove,with stress values of 181.8 MPa and 172.4 MPa,and safety factors of 1.54 and 1.71,respectively.When the tension rod force reaches 940 k N,the tensioning system reaches its bearing limit,with initial yielding occurring at the front plate corners.Model experiments were conducted to verify the theoretical analysis results,under a test load of 444 k N,the stresses at the front plate corners and the lower edge of the U-groove were 159.6 and 195.9 MPa,respectively.As the test load increased to 940 k N,these stresses reached 390 and 389 MPa,exhibiting good agreement with the numerical analysis.Considering the uncertainty of loads and materials,a reliability analysis of the tension rods was conducted,yielding a reliability index of 4.34,meeting the secondary safety standard.Based on the comprehensive analysis,it can be concluded that the temporary anchorage system in the caisson segments of the Shenzhen-Zhongshan Link exhibits excellent safety margins.

Si/Si C-based DD hetero-structure IMPATTs as MM-wave power-source:a generalized large-signal analysis

A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation （~ 2%, i.e. small-signal conditions） results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode＇s negative conductance （5 × 106 S/m2）, susceptance （10.4 × 107 S/m2）, average breakdown voltage （207.6 V）, and power generating efficiency （15%, RF power： 25.0 W at 94 GHz） are obtained as a function of oscillation amplitude （50% of DC breakdown voltage） for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal （〉 50%） voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.

Helicopter blades running elevation measurement using omnidirectional vision

Omnidirectional dynamic space parameters of high-speed rotating helicopter blades are precise 3 D vector description of the blades. In particular, the elevation difference is directly related to the aerodynamic performance and maneuverability of the helicopter. The state of the art detection techniques based on optics and common vision have several drawbacks, such as high demands on devices but poor extensibility, limited measurement range and fixed measurement position. In this paper, a novel approach of helicopter blades running elevation measurement is proposed based on omnidirectional vision. With the advantages of panoramic visual imaging integration, 360° field of view and rotation in-variance, high-resolution images of all rotating blades positions are obtained at one time. By studying the non-linear calibration and calculation model of omnidirectional vision system, aiming at solving the problem of inaccurate visual space mapping model,the omnidirectional and full-scale measurement of the elevation difference are finalized. Experiments are carried out on our multifunctional simulation blades test system and the practical blades test tower, respectively. The experimental results demonstrate the effectiveness of the proposed method and show that the proposed method can considerably reduce the complexity of measurement.