Effect of Dynamic Pressure Feedback Orifice on Stability of Cartridge-Type Hydraulic Pilot-Operated Relief Valve

Current research on pilot-operated relief valve stability is primarily conducted from the perspective of system dynamics or stability criteria,and most of the existing conclusions focus on the spool shape,damping hole size,and pulsation frequency of the pump.However,the essential factors pertaining to the unstable vibration of relief valves remain ambiguous.In this study,the dynamic behavior of a pilot-operated relief valve is investigated using the frequency-domain method.The result suggests that the dynamic pressure feedback orifice is vital to the dynamic characteristics of the valve.A large orifice has a low flow resistance.In this case,the fluid in the main spring chamber flows freely,which is not conducive to the stability of the relief valve.However,a small orifice may create significant flow resistance,thus restricting fluid flow.In this case,the oil inside the main valve spring chamber is equivalent to a high-stiffness liquid spring.The main mass-spring vibration system has a natural frequency that differs significantly from the operating frequency of the relief valve,which is conducive to the stability of the relief valve.Good agreement is obtained between the theoretical analysis and experiments.The results indicate that designing a dynamic pressure feedback orifice of an appropriate size is beneficial to improving the stability of hydraulic pilot-operated relief valves.In addition,the dynamic pressure feedback orifice reduces the response speed of the relief valve.This study comprehensively considers the stability,rapidity,and immunity of relief valves and expands current investigations into the dynamic characteristics of relief valves from the perspective of classical control theory,thus revealing the importance of different parameters.

Influence of dynamic pressure on deep underground soft rock roadway support and its application

Due to high ground stress and mining disturbance, the deformation and failure of deep soft rock roadway is serious, and invalidation of the anchor net-anchor cable supporting structure occurs. The failure characteristics of roadways revealed with the help of the ground pressure monitoring. Theoretical analysis was adopted to analyze the influence of mining disturbance on stress distribution in surrounding rock,and the change of stress was also calculated. Considering the change of stress in surrounding rock of bottom extraction roadway, the displacement, plastic zone and distribution law of principal stress difference under different support schemes were studied by means of FLAC3D. The supporting scheme of U-shaped steel was proposed for bottom extraction roadway that underwent mining disturbance. We carried out a similarity model test to verify the effect of support in dynamic pressure. Monitoring results demonstrated the change rules of deformation and stress of surrounding rock in different supporting schemes. The supporting scheme of U-shaped steel had an effective control on deformation of surrounding rock. The scheme was successfully applied in underground engineering practice, and achieved good technical and economic benefits.

Dynamic biomechanical effect of lower body positive pressure treadmill training for hemiplegic gait rehabilitation after stroke: A case report

BACKGROUND Lower body positive pressure(LBPP)treadmill has potential applications for improving the gait of patients after stroke,but the related mechanism remains unclear.CASE SUMMARY A 62-year-old male patient suffered from ischemic stroke with hemiplegic gait.He was referred to our hospital because of a complaint of left limb weakness for 2 years.The LBPP training was performed one session per day and six times per week for 2 wk.The dynamic plantar pressure analysis was taken every 2 d.Meanwhile,three-digital gait analysis and synchronous electromyography as well as clinical assessments were taken before and after LBPP intervention and at the 4-wk follow-up.During LBPP training,our patient not only improved his lower limb muscle strength and walking speed,but more importantly,the symmetry index of various biomechanical indicators improved.Moreover,the patient’s planter pressure transferring from the heel area to toe area among the LBPP training process and the symmetry of lower body biomechanical parameters improved.CONCLUSION In this study,we documented a dynamic improvement of gait performance in a stroke patient under LBPP training,which included lower limb muscle strength,walking speed,and symmetry of lower limb biomechanics.Our study provides some crucial clues about the potential dynamic mechanism for LBPP training on gait and balance improvement,which is related to rebuilding foot pressure distribution and remodeling symmetry of biomechanics of the lower limb.

Lateral Pressure of RC Silos with Static and Dynamic Granular Materials

This paper aims at analyzing material-induced lateral pressure of RC cylinder silo in both static and dynamic condition using the finite element method( FEM). In the finite element software ABAQUS,concrete material is modeled by concrete damaged plasticity model,and stored materials in silo is modeled by the hypoplastic theory.In terms of numerical model,shell elements( S4R) and solid elements( C3D8) are applied for model silo wall and stored materials respectively. The interaction between silo wall and stored materials is simulated by Coulomb friction model and penalty contact constrain provided by ABAQUS.The numerical results are verified with the existing experimental data that are designed to ensure the validation of such numerical model using FEM and it obtains good agreements between numerical results and experimental data. Then the material parameters are analyzed in both static and dynamic condition.According to the analysis,it is clear that critical friction angle,initial void ratio and minimum void ratio have an obvious effect on static lateral pressure while all the material parameters affect dynamic lateral pressure at different levels. In addition,differences of silo wall between elastic and plastic state are analyzed in dynamic condition. The numerical results show that it contributes to increasing dynamic pressure when silo wall enters into the plastic state. Finally,this paper discusses the time-history lateral pressure at different heights along silo wall,and analytical results indicate that larger acceleration values play main roles in producing the maximum lateral pressure at higher part of the silo wall.

Mechanical behavior analysis of high power commercial lithium-ion batteries

In application,lithium-ion cells undergo expansion during cycling.The mechanical behavior and the impact of external stress on lithium-ion battery are important in vehicle application.In this work,18 Ah high power commercial cell with Li Ni_(0.5)Co_(0.2)Mn_(0.3)O_(2)/graphite electrode were adopted.A commercial compress machine was applied to monitor the mechanical characteristics under different stage of charge(SOC),lifetime and initial external force.The dynamic and steady force was obtained and the results show that the dynamic force increases as the SOC increasing,obviously.During the lifetime with high power driving mode,different external force is shown to have a great impact on the long-term cell performance,with higher stresses result in higher capacity decay rates and faster impedance increases.A proper initial external force(900 N)provides lower impedance increasing.Postmortem analysis of the cells with2000 N initial force suggests a close correlation between electrochemistry and mechanics in which higher initial force leads to higher direct current internal resistance(DCIR)increase rate.In addition,for the cell with higher external force,deformation of the cathode and thicker solid electrolyte interface(SEI)film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.In addition,for the cell with higher external force,deformation of the cathode and thicker SEI film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.

Study on Energy Conversion Characteristics in Volute of Pump as Turbine

A volute is a curved funnel with cross-sectional area increasing towards the discharge port.The volute of a centrifugal pump is the casing hosting the fluid being pumped by the impeller.In Pump-as-turbine devices(PAT),vice versa the volute plays the role of energy conversion element.In the present analysis,this process is analyzed using CFD.The results show that in the contraction section of volute the conversion between dynamic pressure energy and static pressure energy essentially depends on the reduction of flow area,while in the spiral section,frictional losses also play a significant role.From the throat to the end of the volute,the flow decreases in a wave-like manner.

Shaking table test for reinforcement of soil slope with multiple sliding surfaces by reinforced double-row anti-slide piles

Despite the continuous advancements of engineering construction in high-intensity areas,many engineering landslides are still manufactured with huge thrust force,and double-row piles are effective to control such large landslides.In this study,large shaking table test were performed to test and obtain multi-attribute seismic data such as feature image,acceleration,and dynamic soil pressure.Through the feature image processing analysis,the deformation characteristics for the slope reinforced by double-row piles were revealed.By analyzing the acceleration and the dynamic soil pressure time domain,the spatial dynamic response characteristics were revealed.Using Fast Fourier Transform and half-power bandwidth,the damping ratio of acceleration and dynamic soil pressure was obtained.Following that,the Seism Signal was used to calculate the spectral displacement of the accelerations to obtain the regional differences of spectral displacement.The results showed that the overall deformation mechanism of the slope originates from tension failure in the soil mass.The platform at the back of the slope was caused by seismic subsidence,and the peak acceleration ratio was positively correlated with the relative pile heights.The dynamic soil pressure of the front row piles showed an inverted"K"-shaped distribution,but that of the back row piles showed an"S"-shaped distribution.The predominant frequency of acceleration was 2.16 Hz,and the main frequency band was 0.7-6.87 Hz;for dynamic soil pressure,the two parameters became 1.15 Hz and 0.5-6.59 Hz,respectively.In conclusion,dynamic soil pressure was more sensitive to dampening effects than acceleration.Besides,compared to acceleration,dynamic soil pressure exhibited larger loss factors and lower resonance peaks.Finally,back row pile heads were highly sensitive to spectral displacement compared to front row pile heads.These findings may be of reference value for future seismic designs of double-row piles.

Mechanical characteristic variation of ballastless track in highspeed railway:effect of train–track interaction and environment loads

Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train–track dynamic interaction loads,but also suffer from complex environmental loads,the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks.This work aims to reveal the effect of train–track interaction and environment loads on the mechanical characteristic variation of ballastless tracks in high-speed railways,particularly focusing on the typical interface damage evolution between track layers.To this end,a finite element model of a double-block ballastless track involving the cohesive zone model for the track interface is first established to analyze the mechanical properties of the track interface under the loading–unloading processes of the negative temperature gradient load(TGL)followed by the same cycle of the positive TGL.Subsequently,the effect of wheel–rail longitudinal interactions on the nonlinear dynamic characteristics of the track interface is investigated by using a vehicle-slab track vertical-longitudinal coupled dynamics model.Finally,the influence of dynamic water pressure induced by vehicle dynamic load on the mechanical characteristics and damage evolution of the track interface is elucidated using a fluid–solid coupling method.Results show that the loading history of the positive and negative TGLs has a great impact on the nonlinear development and distribution of the track interface stress and damage;the interface damage could be induced by the wheel–rail longitudinal vibrations at a high vehicle running speed owing to the dynamic amplification effect caused by short wave irregularities;the vehicle dynamic load could produce considerable water pressure that presents nonlinear spatial–temporal characteristics at the track interface,which would lead to the interface failure under a certain condition due to the coupled dynamic effect of vehicle load and water pressure.

Research on combustion characteristics of scramjet combustor with different flight dynamic pressure conditions

Combustion characteristics in a scramjet combustor equipped with a thin strut were observed and discussed in this paper.A series of numerical simulations were carried out under different flight dynamic pressure conditions.The parameters of cold flow field and combustion field were used to analyze the combustion characteristics.Based on the basic data,the mixing efficiency,characteristics of flame establishment and propagation as well as combustion field characteristics were discussed in this paper.The influence laws of lower dynamic pressure conditions were further revealed to optimize combustor performance.Results indicated that properly reducing the flight dynamic pressure can enhance the mixing of kerosene.The diffusion of kerosene determined the distribution of combustion zone and heat release.Then,the influencing factor that affected the chemical reaction rate was revealed to shorten chemical reaction time.And the higher flight Mach number made the flame propagation velocity faster and the combustion stability stronger.The fuel mixing became the main factor and low dynamic pressure had little effect on laminar flame propagation velocity under high Mach number conditions.The investigations in this paper are helpful for understanding the combustion characteristics under low dynamic pressure conditions.

Investigation of Changes in Flow Parameters along the Transport Line in Installations for Pneumatic Transport of Cotton

The article presents the results of a study of changes in the parameters of the flow, velocity and pressure of air along the cotton transportation line in pneumatic transport installations and their dependence on the parameters of the pipeline. The purpose of the research is to theoretically substantiate the choice of the pipeline diameter depending on the properties of the material (cotton), the required processing capacity and pipeline throughput. In the research, an analytical method was used to study changes in the pressure of the air flow along the transportation line at different pipeline diameters. It is established that, according to the existing calculation method, the flow pressure along the transportation line is reduced to zero. At the same time, various scientists have proposed various analytical and empirical dependencies, which, in turn, give different ideas about the resistance of the inner surface of the pipes to the movement of air and material flow and do not describe the real situation, especially when transporting material from a long distance. This requires in-depth theoretical and applied research to establish real patterns of changes in flow parameters along the material (cotton) transportation line.

Geomechanics model test research on large deformation control mechanism of roadway disturbed by strong dynamic pressure

Comprehensive mechanized top-coal caving mining is one of the efficient mining methods in coal mines.However,the goaf formed by comprehensive mechanized top-coal caving mining is high,and the goaf roof collapse will cause strong dynamic pressure disturbance,especially the collapse of thick hard roof.Strong dynamic pressure disturbance has an influence on the stability of the roadway,which can lead to large deformation.In order to solve the above problem,a comprehensive pressure releasing and constant resistance energy absorbing control method is proposed.Comprehensive pressure releasing can change the roadway roof structure and cut off the stress transfer between goaf and roadway,which can improve the stress environment of the roadway.The constant resistance energy absorbing(CREA)anchor cable can absorb the energy of surrounding rock deformation and resist the impact load of gangue collapse,so as to ensure the stability of roadway disturbed by strong dynamic pressure.A three-dimensional geomechanics model test is carried out,based on the roadway disturbed by strong dynamic pressure of the extra-large coal mine in western China,to verify the control effect of the new control method.The stress and displacement evolution laws of the roadway with traditional control method and new control method are analyzed.The pressure releasing and energy absorbing control mechanism of the new control method is clarified.The geomechanics model test results show that the new control method can increase the range of low stress zone by 150%and reduce the average stress and the displacement by 34.7%and 67.8%respectively,compared with the traditional control method.The filed application results show that the new control method can reduce the roadway surrounding rock displacement by 67.4%compared with the traditional control method.It shows that the new control method can effectively control the displacement of the roadway disturbed by strong dynamic pressure and ensure that the roadway meets the safety requirements.On this basis,the engineering suggestions for large deformation control of this kind of roadway are put forward.The new control method can provide a control idea for the roadway disturbed by strong dynamic pressure.

Effects of dynamic ultra-high pressure homogenization on the structure and functional properties of casein

Dynamic ultra-high pressure homogenization(UHPH)is a novel high-pressure processing technique.In this study,the effects of dynamic UHPH on the structure and functional properties of casein were systematically investigated.It was found that the functional properties of casein changed with dynamic UHPH treatment,and the treatment at 150 MPa could significantly improve casein aqueous solubility,foaming and emulsifying properties.These functional improvements could be attributed to its structural changes,since the dynamic UHPH treatment could change the secondary structure,promote the interchange reaction between the disulfide bond and the sulfhydryl group,and increase the surface hydrophobicity.The obtained results could broaden the application of casein and provide ideas for the non-thermal processing of proteins.

Dynamic pressure change in a rotating, laterally oscillating cylindrical container

We examined wave phenomena pertinent to water in a rotating,laterally oscillating cylindrical container.In particular,we measured the time-dependent dynamic water pressure and pressure change by fast Fourier transform analysis.The swirling of water in the container had three frequency components;the frequency responses of each frequency component are reported herein.When swirling occurs in a rotating cylindrical container,it was found that the wave rotating in the same direction as the rotation of the cylindrical container and the wave rotating in the opposite direction to the cylindrical container exist at the same time.The swirling direction was determined by the relationship of these magnitude.

A Systematic Review of Forensic Approaches to Disasters: Gaps and Challenges

Disaster forensic approaches aim to identify the causes of disasters to support disaster risk management.However,few studies have conducted a systematic literature review of scientific articles that labeled themselves as a forensic approach to disasters.This article provides a qualitative analysis of these forensic studies,focusing on five main issues:(1)the methodologies applied;(2)the forensic approaches used in the disaster risk management phases;(3)the hazards addressed;(4)if the methodologies involve social participation,and using what types of participation;and(5)if there are references to urban planning in the scientific studies analyzed.Our results showed a predominance of the Forensic Investigations of Disasters(FORIN)and Post-Event Review Capability(PERC)methodologies used in isolation or combination.There is a need for methodologies that engage people in participatory FORIN,fostering the co-production of knowledge and action research approaches.

Graphene aerogel-based vibration sensor with high sensitivity and wide frequency response range

Compared with piezoresistive sensors,pressure sensors based on the contact resistance effect are proven to have higher sensitivity and the ability to detect ultra-low pressure,thus attracting extensive research interest in wearable devices and artificial intelligence systems.However,most studies focus on static or low-frequency pressure detection,and there are few reports on high-frequency dynamic pressure detection.Limited by the viscoelasticity of polymers(necessary materials for traditional vibration sensors),the development of vibration sensors with high frequency response remains a great challenge.Here,we report a graphene aerogel-based vibration sensor with higher sensitivity and wider frequency response range(2 Hz–10 kHz)than both conventional piezoresistive and similar sensors.By modulating the microscopic morphology and mechanical properties,the super-elastic graphene aerogels suitable for vibration sensing have been prepared successfully.Meanwhile,the mechanism of the effect of density on the vibration sensor’s sensitivity is studied in detail.On this basis,the sensitivity,signal fidelity and signal-to-noise ratio of the sensor are further improved by optimizing the structure configuration.The developed sensor exhibits remarkable repeatability,excellent stability,high resolution(0.0039 g)and good linearity(non-linearity error<0.8%)without hysteresis.As demos,the sensor can not only monitor low-frequency physiological signals and motion of the human body,but also respond to the high-frequency vibrations of rotating machines.In addition,the sensor can also detect static pressure.We expect the vibration sensor to meet a wider range of functional needs in wearable devices,smart robots,and industrial equipment.

Experimental Investigation of the Transonic Shock Oscillation Characteristics in a Heavy-Duty Gas Turbine Compressor Cascade

This paper presents an experimental study of the self-sustained transonic shock oscillating behaviors in a heavy-duty gas turbine compressor cascade under the inlet Mach number of 0.85,0.90 and 0.95.The transonic shock patterns and the surface flow structures are captured by schlieren imaging and oil flow visualization.The time-averaged and instantaneous transonic shock oscillating behaviors at the near choke point and the near stall point are investigated by the Anodized Aluminum Pressure-Sensitive Paint(AA-PSP)surface pressure measurement.The normal passage shock dominant pattern and the detached bow shock dominant pattern at the near choke point and the near stall point are experimental characterized,respectively.The passage shock oscillation behaviors at the near choke point have been observed to undergo periodic pressure perturbations of the shock shift between the upstreamλshock feet mode and the downstreamλshock feet mode.The detached bow shock oscillation behaviors at the near stall point have been observed to undergo the pressure perturbations of the shock cycle movement between the upstream detached bow shock mode and the downstream detached bow shock mode.The differences between the shock shift mode and the shock cycle movement mode lead to the different streamwise oscillation travel ranges and different shock intensity variations under the same inlet Mach number.

Dynamic analysis of a flameless combustion model combustor

Flameless combustion is a new technology with the following advantages:1)Ultra-low emissions of both NOX and CO;2)fuel flexibility,from liquid fuels,natural gas to hydrogen-rich syngas;3)lower possibility of flashback and thermoacoustic oscillations.In this paper,we focus on the dynamic characteristics of a flameless model combustor.Experimental results show that flameless combustion can lower emissions while maintaining combustion stability.However,combining a pilot flame with flameless combustion may excite thermoacoustic instability.

Shaking table tests on a cantilever retaining wall with reinforced and unreinforced backfill

Physical modelling of cantilever retaining walls with and without backfill reinforcement was conducted on a 1g shaking table to evaluate the mitigation effect of reinforcement on system dynamics(g denotes the acceleration of gravity).The model wall has a height of 1.5 m with a scale ratio of 1/4 and retains dry sand throughout.The input motions are amplified to three levels of input peak base acceleration,0.11g,0.24g,and 0.39g,corresponding to minor,moderate,and major earthquakes,respectively.Investigation of the seismic response of the retaining walls focuses on acceleration and lateral displacement of the wall and backfill,dynamic earth pressures,and tensile load in the reinforcements(modeled by phosphor-bronze strips welded into a mesh).The inclusion of reinforcement has been observed to improve the integrity of the wall-soil system,mitigate vibration-related damage,and reduce the fundamental frequency of a reinforced system.Propagation of acceleration from the base to the upper portion is accompanied by time delay and nonlinear amplification.A reinforced system with a lower acceleration amplification factor than the unreinforced one indicates that reinforcement can reduce the amplification effect of input motion.Under minor and moderate earthquake loadings,reinforcement allows the inertia force and seismic earth pressure to be asynchronous and decreases the seismic earth pressure when inertia forces peak.During major earthquake loading,the wall is displaced horizontally less than the backfill,with soil pushing the wall substantially;the effect of backfill reinforcement has not been fully mobilized.The dynamic earth pressure is large at the top and diminishes toward the bottom.

Study on characteristics of well-test type curves for composite reservoir with sealing faults

The pressure response for the composite reservoirs with a sealing fault locating in inner and outer region is different,which neglected by previous researchers,would cause significant errors during well-test interpretations.Based on seepage theory,a well-test model of two-region radial composite reservoir with infinite outer boundary has been built in this study considering wellbore storage and skin effects.The solutions for this model and characteristics of the type curves have been analyzed by applying the method of mirror image,Laplace transformation and superposition principle,including a straight fault,a perpendicular fault and parallel faults cases.The study shows that the dimensionless pressure derivative curves would be obviously different in two cases:the well to fault distance is larger,and smaller than the half length of the inner-region radius.Therefore,type curves are presented with reasonable parameters to analyze the distance effect on the dynamic pressure response.The results in this study are of great significance。