In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a c...In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a crucial role in ensuring the stability of the electrical energy output and the efficiency of the overall system.A corresponding mathematical model for the hydraulic PTO system has been established,the factors that influence its performance have been studied,and an algorithm for solving the optimal working pressure has been derived in this paper.Moreover,a PID control method to enable the hydraulic PTO system to automatically achieve optimal performance under different wave conditions has been designed.The results indicate that,compared with single-chamber hydraulic cylinders,double-chamber hydraulic cylinders have a wider application range and greater performance;the accumulator can stabilize the output power of the hydraulic PTO system and slightly increase it;excessively large or small hydraulic motor displacement hinders system performance;and each wave condition corresponds to a unique optimal working pressure for the hydraulic PTO system.In addition,the relationship between the optimal working pressure P_(m)and the pressure P_(h)of the wave force acting on the piston satisfies P_(m)^(2)=∫_(t_(1))^(t_(2))P_(h)^(2)dt/(t_(2)-t_(1)).Furthermore,adjusting the hydraulic motor displacement automatically via a PID controller ensures that the actual working pressure of the hydraulic PTO system consistently reaches or approaches its theoretically optimal value under various wave conditions,which is a very effective control method for enhancing the performance of the hydraulic PTO system.展开更多
Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a...Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a specific bridge project as an example to introduce the technology of hydraulically sliding formwork for the construction of main piers of highway bridges.An in-depth analysis of the project’s construction process found that this technology can effectively improve construction efficiency,ensure the quality of concrete pouring,and significantly reduce the potential safety hazards of working at heights.It provides a reliable technical solution for constructing the main piers of highway bridges and has important reference significance for similar projects.展开更多
Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a...Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a key factor.The rock micro-cracking mechanism under gradient pore water pressure was analyzed on the scale of mineral particles and it was combined with macroscopic boundary conditions of rock hydraulic fracturing,obtaining the propagation criterion of HF in rock based on the rock micro-cracking mechanism which was verified by experiment.The results show that the disturbed skeleton stress induced by the disturbance of gradient pore water pressure in rock equals the pore water pressure difference.The overall range of the defined mechanical shape factor a/b is around 1,but greater than0.5.Under the combined influence of pore water pressure differences and macroscopic boundary stresses on the rock micro-cracking,micro-cracks form among rock mineral particles,micro-cracks connect to form micro-hydraulic fracture surfaces,and micro-hydraulic fracture surfaces open to form macrohydraulic fractures.HF begins to form at the micro-cracking initiation pressure(MCIP),which was tested by keeping the HF tip near the initiation point.The theoretical value of MCIP calculated by the proposed propagation criterion is close to MCIP tested.展开更多
The research of reliability design for impact vibration of hydraulic pressure pipeline systems is still in the primary stage,and the research of quantitative reliability of hydraulic components and system is still inc...The research of reliability design for impact vibration of hydraulic pressure pipeline systems is still in the primary stage,and the research of quantitative reliability of hydraulic components and system is still incomplete.On the condition of having obtained the numerical characteristics of basic random parameters,several techniques and methods including the probability statistical theory,hydraulic technique and stochastic perturbation method are employed to carry out the reliability design for impact vibration of the hydraulic pressure system.Considering the instantaneous pressure pulse of hydraulic impact in pipeline,the reliability analysis model of hydraulic pipeline system is established,and the reliability-based optimization design method is presented.The proposed method can reflect the inherent reliability of hydraulic pipe system exactly,and the desired result is obtained.The reliability design of hydraulic pipeline system is achieved by computer programs and the reliability design information of hydraulic pipeline system is obtained.This research proposes a reliability design method,which can solve the problem of the reliability-based optimization design for the hydraulic pressure system with impact vibration practically and effectively,and enhance the quantitative research on the reliability design of hydraulic pipeline system.The proposed method has generality for the reliability optimization design of hydraulic pipeline system.展开更多
Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key c...Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.展开更多
The limitations in existing measures for absorbing pressure impact in hydraulic systems were summarized in this paper. Based on the forming principle of the oil in a hydrostatic closed pressure chamber, the underlying...The limitations in existing measures for absorbing pressure impact in hydraulic systems were summarized in this paper. Based on the forming principle of the oil in a hydrostatic closed pressure chamber, the underlying reasons of the pressure impact were analyzed theoretically, the intrinsic laws that the extent of the pressure impact in hydraulic oil lines are affected by some factors, such as oil elastic modulus, oil line's geometrical volume, and changing rate of oil volume versus time etc, were discussed. Experimental investigations into pressure impact in all pressure chambers because of shifting were conducted under different working conditions by employing a special experimental system. The effects of shifting time on pressure impact were studied. A new concept with universal meaning, i.e. optimal shifting time, and its characterizing parameter and the methods of shifting at optimal shifting time were also proposed. The results show that shifting time lag △t is of rationality and maneuverablility. The higher the working pressure, the shorter the shifting time.展开更多
The possibility to enhance the stability and robustness of electrohydraulic brake(EHB)systems is considered a subject of great importance in the automotive field.In such a context,the present study focuses on an actua...The possibility to enhance the stability and robustness of electrohydraulic brake(EHB)systems is considered a subject of great importance in the automotive field.In such a context,the present study focuses on an actuator with a four-way sliding valve and a hydraulic cylinder.A 4-order nonlinear mathematical model is introduced accordingly.Through the linearization of the feedback law of the high order EHB model,a sliding mode control method is proposed for the hydraulic pressure.The hydraulic pressure tracking controls are simulated and analyzed by MATLAB/Simulink soft considering separately different conditions,i.e.,a sine wave,a square wave and a square wave with superimposed sine disturbance.The results show that the proposed strategy can track the target within 0.25 s,and the mean observed error is less than 1.2 bar.Moreover,with such a strategy,faster response and less overshoot are possible,which should be regarded as significant advantages.展开更多
In the pump-controlled motor hydraulic transmission system,when the pressure pulsation frequencies seperately generated by the pump and the motor are close to each other,the hydraulic system will generate a strong pre...In the pump-controlled motor hydraulic transmission system,when the pressure pulsation frequencies seperately generated by the pump and the motor are close to each other,the hydraulic system will generate a strong pressure beat vibration phenomenon,which will seriously affect the smooth running of the hydraulic system.However,the modulated pressure signal also carries information related to the operating state of the hydraulic system,and a accurate extraction of pressure vibration characteristics is the key to obtain the operating state information of the hydraulic system.In order to extract the pressure beat vibration signal component effectively from the multi-component time-varying aliasing pressure signal and reconstruct the time domain characteristics,an extraction method of the pressure beat vibration characteristics of the hydraulic transmission system based on variational mode decomposition(VMD)is proposed.The experimental results show that the VMD method can accurately extract the pressure beat vibration characteristics from the high-pressure oil pressure signal of the hydraulic system,and the extraction effect is preferable to that of the traditional signal processing methods such as empirical mode decomposition(EMD).展开更多
Based on the analysis of the-state-of-the-art of pressure compensation of underwater hydraulic systems （UHSs）, a new method of pressure compensation of UHSs, whose hydraulic power unit is in the atmospheric circumst...Based on the analysis of the-state-of-the-art of pressure compensation of underwater hydraulic systems （UHSs）, a new method of pressure compensation of UHSs, whose hydraulic power unit is in the atmospheric circumstance, is proposed. And a pilot-operated relief valve with pressure compensation is realized. The pressure compensation precision is guaranteed by direct detection. Its dynamic performance and stability are improved by a dynamic feedback. Theoretical study, simulation and experiment show that the pilot-operated relief valve with pressure compensation has a fine property of tracking underwater ambient pressure and meet the requirement of underwater ambient pressure compensation.展开更多
In order to enhance the sealing quality and assemble efficiency of hydraulic supports, the evaluation system for the sealability of the hydraulic support and jack＇s seals was established through the testing and exper...In order to enhance the sealing quality and assemble efficiency of hydraulic supports, the evaluation system for the sealability of the hydraulic support and jack＇s seals was established through the testing and experimenting technology in respects, such as seals＇ dimensions, reasonable amounts of compression, sealability, life, resistance to pressure, etc. Through life detecting test of the seal, found the longest life seal ring under the same conditions, and through the reciprocating test of the hydraulic support, found the most appropriate amount of interference between the groove and the seal ring, thus, to decrease the leakage and extend the life span of the hydraulic support.展开更多
A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-ex...A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-exciter. The working principle of the hydraulic exciting system and wave exciter has been analyzed, and its excitation process has been illustrated. The law of every pipe＇s pressure fluctuation of the system is obtained by experiment. The theo- retical analysis and experimental data prove that the pipeline pressure periodically changes and the pipeline pressure fluctuation frequency is independently controlled by the excitation frequency of the wave-exciter. Every pipelinc＇s pressure wave is produced by system flow fluctuation and water hammer coupling. The pressure fluctuation rules of the system provide a theoretical basis for the study of the associated liberation system.展开更多
Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure an...Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure and pressure rise rate, obtain corresponding oil pressure value when the pressure rise rate of different gas content is maximum, and verify the accuracy of this conclusion by the FLUENT simulation software. On this basis, a rapid pressure building device of the hydraulic system is developed and designed. The above oil pressure value is used as the working cut-off pressure of the rapid pressure building device, and then the hydraulic oil pump continues to pressurize to the highest working pressure required by the system. The research content can replace the hydraulic system from the initial low pressure to the rapid pressure build-up of the oil, thus increasing the construction pressure of the hydraulic system. The research results show that the rapid pressure building device effectively reduces the time for the hydraulic system to establish pressure. Through the analysis of theoretical derivation and the collected experimental data, the error is about 5.9%, which verifies the correctness of the theoretical formula.展开更多
Fluid and solid interaction analysis of hydraulic support under the coming pressure of roof rocks was presented. The mathematical model of the system was proposed and numerical studies by the character line method wer...Fluid and solid interaction analysis of hydraulic support under the coming pressure of roof rocks was presented. The mathematical model of the system was proposed and numerical studies by the character line method were carried out.展开更多
Fault diagnosis expert system for hydraulic support is studied.The system is achieved by Turbo prolong Language, it summaries the experience of the domain expert and sets up a fault tree, knowledge base is developed b...Fault diagnosis expert system for hydraulic support is studied.The system is achieved by Turbo prolong Language, it summaries the experience of the domain expert and sets up a fault tree, knowledge base is developed by a productive rule.According to the feature of diagnosis, the system selects forward non determination inferring and limited depth first search strategy.It can accomplish expert diagnosis of more than 50 kinds faults in hydraulic support.展开更多
In order to study the effect of splitter blades on the internal and external sound field of the hydraulic turbine,the paper chose a centrifugal pump with a specific speed ns=33 reversed as a hydraulic turbine as the r...In order to study the effect of splitter blades on the internal and external sound field of the hydraulic turbine,the paper chose a centrifugal pump with a specific speed ns=33 reversed as a hydraulic turbine as the research object,and added the short blades on the original impeller to form a new splitter impeller.Based on the Re-Normalization Group(RNG)k-εturbulence model to conduct numerical simulation for the hydraulic turbine,this thesis calculated the internal and external acoustic field by means of the acoustic boundary element(BEM)and finite element(FEM)and analyzed the noise radiation characteristics of the two models under different working conditions.The results show that the blade frequency is the main factor affecting the inlet and outlet sound pressure,and the optimized model decreases the inlet and outlet sound pressure levels by 6.84 and 7.24 dB in optimal working conditions.Rotor-stator interaction is the main reason for the flow-induced noise of hydraulic turbine volute appearing,the optimized model can effectively reduce the impeller and volute rotor-stator interaction and the flow-induced noise of volute.Outfield maximum sound pressure appears at the inlet and the volute tongue,which decreased by 1.84,6.07,and 5.24 dB at each operating condition.To sum up,splitter blades can improve hydraulic characteristics and flow field noise in the hydraulic turbine.展开更多
In consideration of the special environmental conditions of coal equipment in mining, the seamless steel tube of hy-draulic prop made of 20^# carbon steel was taken as the substrate, and 316L stainless steel powder wa...In consideration of the special environmental conditions of coal equipment in mining, the seamless steel tube of hy-draulic prop made of 20^# carbon steel was taken as the substrate, and 316L stainless steel powder was used to clad the sub-strate by a fiber-coupled semiconductor laser. The microstructure of the cladding layer was determined by metalloscope. The hardness, wear resistance and corrosion resistance of the cladding layer were measured. The results show that metallurgy bind-ing interface between the cladding layer and the substrate is obtained without defects such as cracks and pores. The hardness of the cladding layer is much higher than that of the matrix, and the wear resistance and corrosion resistance are simultaneously better. According to the analysis, it is summarized that the improvement in performance of the cladding layer is closely related to the change of microstructure and the thermal effect in the cladding process. The maximum hardness occurs in the equiaxed zone, and with the grain coarsening, the hardness reduces simultaneously. In addition, the precipitated phase, hard particles and trace elements also have a great influence on the properties of the cladding layer, and they will prevent the surface from ab-rasion and reduce the plastic deformation of the matrix. It is verified that the 316L stainless steel is suitable for the 20^# steel in laser cladding repairing process. Since this study focused on coal machine equipment parts, it has certain practical significance for the repair of hydraulic equipment.展开更多
Perforation is a pivotal technique employed to establish main flow channels within the reservoir formation at the outset of hydraulic fracturing operations.Optimizing perforation designs is critical for augmenting the...Perforation is a pivotal technique employed to establish main flow channels within the reservoir formation at the outset of hydraulic fracturing operations.Optimizing perforation designs is critical for augmenting the efficacy of hydraulic fracturing and boosting oil or gas production.In this study,we employ a hybrid finite-discrete element method,known as the continuous–discontinuous element method(CDEM),to simulate the initiation of post-perforation hydraulic fractures and to derive enhanced design parameters.The model incorporates the four most prevalent perforation geometries,as delineated in an engineering technical report.Real-world perforations deviate from the ideal cylindrical shape,exhibiting variable cross-sectional profiles that typically manifest as an initial constriction followed by an expansion,a feature consistent across all four perforation types.Our simulations take into account variations in perforation hole geometries,cross-sectional diameters,and perforation lengths.The findings show that perforations generated by the 39g DP3 HMX perforating bullet yield the lowest breakdown pressure,which inversely correlates with increases in sectional diameter and perforation length.Moreover,this study reveals the relationship between breakdown pressure and fracture degree,providing valuable insights for engineers and designers to refine perforation strategies.展开更多
Understanding the mechanical response of Q2 loess subjected to dry-wet cycles(DWCs)is the premise for the rational design of a hydraulic tunnel.Taking the Hanjiang-to-Weihe south line project in China as the research ...Understanding the mechanical response of Q2 loess subjected to dry-wet cycles(DWCs)is the premise for the rational design of a hydraulic tunnel.Taking the Hanjiang-to-Weihe south line project in China as the research background,the microstructure evolution,strength degradation and compression characteristics of Q2 loess under different DWCs were investigated,and the fluid-solid coupling analysis of the hydraulic tunnel was carried out using the FLAC3D software.The amplification effect of tunnel surrounding soil pressure(SSP)and its influence on the long-term stability of the tunnel under different DWCs were obtained.The results showed that the pore microstructure parameters of the undisturbed and remolded loess basically tend to be stable after the number of DWCs exceeds 3.The porosity of Q2 loess is increased by 26%.The internal friction angle and cohesion of Q2 loess are decreased by 35%and 31%,respectively.The vertical strain of Q2 loess is increased by 55%after considering the DWCs.After the DWCs stabilized,the SSP ratio is increased between 10%and 25%.With the increase in buried depth of the tunnel,the SSP ratio is increased by 8%e10%.The SSP is reduced from 8%to 16%by the rise in groundwater level.As the number of DWCs increases and the burial depth of the tunnel decreases,the distribution of SSP becomes progressively more non-uniform.Based on the amplification factor and the modified compressive arch theory,the SSP distribution model of loess tunnel was proposed,which can be preliminarily applied to the design of supporting structures considering DWCs.展开更多
While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf...While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.展开更多
In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To in...In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part＇s strain status on the forming limit diagram （FLD） were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52071094 and 51979065).
文摘In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a crucial role in ensuring the stability of the electrical energy output and the efficiency of the overall system.A corresponding mathematical model for the hydraulic PTO system has been established,the factors that influence its performance have been studied,and an algorithm for solving the optimal working pressure has been derived in this paper.Moreover,a PID control method to enable the hydraulic PTO system to automatically achieve optimal performance under different wave conditions has been designed.The results indicate that,compared with single-chamber hydraulic cylinders,double-chamber hydraulic cylinders have a wider application range and greater performance;the accumulator can stabilize the output power of the hydraulic PTO system and slightly increase it;excessively large or small hydraulic motor displacement hinders system performance;and each wave condition corresponds to a unique optimal working pressure for the hydraulic PTO system.In addition,the relationship between the optimal working pressure P_(m)and the pressure P_(h)of the wave force acting on the piston satisfies P_(m)^(2)=∫_(t_(1))^(t_(2))P_(h)^(2)dt/(t_(2)-t_(1)).Furthermore,adjusting the hydraulic motor displacement automatically via a PID controller ensures that the actual working pressure of the hydraulic PTO system consistently reaches or approaches its theoretically optimal value under various wave conditions,which is a very effective control method for enhancing the performance of the hydraulic PTO system.
文摘Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a specific bridge project as an example to introduce the technology of hydraulically sliding formwork for the construction of main piers of highway bridges.An in-depth analysis of the project’s construction process found that this technology can effectively improve construction efficiency,ensure the quality of concrete pouring,and significantly reduce the potential safety hazards of working at heights.It provides a reliable technical solution for constructing the main piers of highway bridges and has important reference significance for similar projects.
基金supported by the National Key Research and Development Program of China (No.2021YFC2902102)the National Natural Science Foundation of China (Nos.52374103 and 52274013)。
文摘Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a key factor.The rock micro-cracking mechanism under gradient pore water pressure was analyzed on the scale of mineral particles and it was combined with macroscopic boundary conditions of rock hydraulic fracturing,obtaining the propagation criterion of HF in rock based on the rock micro-cracking mechanism which was verified by experiment.The results show that the disturbed skeleton stress induced by the disturbance of gradient pore water pressure in rock equals the pore water pressure difference.The overall range of the defined mechanical shape factor a/b is around 1,but greater than0.5.Under the combined influence of pore water pressure differences and macroscopic boundary stresses on the rock micro-cracking,micro-cracks form among rock mineral particles,micro-cracks connect to form micro-hydraulic fracture surfaces,and micro-hydraulic fracture surfaces open to form macrohydraulic fractures.HF begins to form at the micro-cracking initiation pressure(MCIP),which was tested by keeping the HF tip near the initiation point.The theoretical value of MCIP calculated by the proposed propagation criterion is close to MCIP tested.
基金supported by National Natural Science Foundation of China(Grant Nos.5113500310972088)
文摘The research of reliability design for impact vibration of hydraulic pressure pipeline systems is still in the primary stage,and the research of quantitative reliability of hydraulic components and system is still incomplete.On the condition of having obtained the numerical characteristics of basic random parameters,several techniques and methods including the probability statistical theory,hydraulic technique and stochastic perturbation method are employed to carry out the reliability design for impact vibration of the hydraulic pressure system.Considering the instantaneous pressure pulse of hydraulic impact in pipeline,the reliability analysis model of hydraulic pipeline system is established,and the reliability-based optimization design method is presented.The proposed method can reflect the inherent reliability of hydraulic pipe system exactly,and the desired result is obtained.The reliability design of hydraulic pipeline system is achieved by computer programs and the reliability design information of hydraulic pipeline system is obtained.This research proposes a reliability design method,which can solve the problem of the reliability-based optimization design for the hydraulic pressure system with impact vibration practically and effectively,and enhance the quantitative research on the reliability design of hydraulic pipeline system.The proposed method has generality for the reliability optimization design of hydraulic pipeline system.
基金Supported by National Key R&D Program of China(Grant No.2018YFB1702503)National Program on Key Basic Research Project of China(973 Program,Grant No.2013CB035403)Startup Fund for Youngman Research at SJTU(SFYR at SJTU)
文摘Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.
文摘The limitations in existing measures for absorbing pressure impact in hydraulic systems were summarized in this paper. Based on the forming principle of the oil in a hydrostatic closed pressure chamber, the underlying reasons of the pressure impact were analyzed theoretically, the intrinsic laws that the extent of the pressure impact in hydraulic oil lines are affected by some factors, such as oil elastic modulus, oil line's geometrical volume, and changing rate of oil volume versus time etc, were discussed. Experimental investigations into pressure impact in all pressure chambers because of shifting were conducted under different working conditions by employing a special experimental system. The effects of shifting time on pressure impact were studied. A new concept with universal meaning, i.e. optimal shifting time, and its characterizing parameter and the methods of shifting at optimal shifting time were also proposed. The results show that shifting time lag △t is of rationality and maneuverablility. The higher the working pressure, the shorter the shifting time.
基金supported by the National Natural Science Foundation of China[grant number 51565011]the Foundation of Educational Department of Jiangxi Province[grant number GJJ180302].
文摘The possibility to enhance the stability and robustness of electrohydraulic brake(EHB)systems is considered a subject of great importance in the automotive field.In such a context,the present study focuses on an actuator with a four-way sliding valve and a hydraulic cylinder.A 4-order nonlinear mathematical model is introduced accordingly.Through the linearization of the feedback law of the high order EHB model,a sliding mode control method is proposed for the hydraulic pressure.The hydraulic pressure tracking controls are simulated and analyzed by MATLAB/Simulink soft considering separately different conditions,i.e.,a sine wave,a square wave and a square wave with superimposed sine disturbance.The results show that the proposed strategy can track the target within 0.25 s,and the mean observed error is less than 1.2 bar.Moreover,with such a strategy,faster response and less overshoot are possible,which should be regarded as significant advantages.
基金National Natural Science Foundation of China(No.51675399)。
文摘In the pump-controlled motor hydraulic transmission system,when the pressure pulsation frequencies seperately generated by the pump and the motor are close to each other,the hydraulic system will generate a strong pressure beat vibration phenomenon,which will seriously affect the smooth running of the hydraulic system.However,the modulated pressure signal also carries information related to the operating state of the hydraulic system,and a accurate extraction of pressure vibration characteristics is the key to obtain the operating state information of the hydraulic system.In order to extract the pressure beat vibration signal component effectively from the multi-component time-varying aliasing pressure signal and reconstruct the time domain characteristics,an extraction method of the pressure beat vibration characteristics of the hydraulic transmission system based on variational mode decomposition(VMD)is proposed.The experimental results show that the VMD method can accurately extract the pressure beat vibration characteristics from the high-pressure oil pressure signal of the hydraulic system,and the extraction effect is preferable to that of the traditional signal processing methods such as empirical mode decomposition(EMD).
基金This project is supported by National Natural Science Foundation of China(No.50475105).
文摘Based on the analysis of the-state-of-the-art of pressure compensation of underwater hydraulic systems （UHSs）, a new method of pressure compensation of UHSs, whose hydraulic power unit is in the atmospheric circumstance, is proposed. And a pilot-operated relief valve with pressure compensation is realized. The pressure compensation precision is guaranteed by direct detection. Its dynamic performance and stability are improved by a dynamic feedback. Theoretical study, simulation and experiment show that the pilot-operated relief valve with pressure compensation has a fine property of tracking underwater ambient pressure and meet the requirement of underwater ambient pressure compensation.
文摘In order to enhance the sealing quality and assemble efficiency of hydraulic supports, the evaluation system for the sealability of the hydraulic support and jack＇s seals was established through the testing and experimenting technology in respects, such as seals＇ dimensions, reasonable amounts of compression, sealability, life, resistance to pressure, etc. Through life detecting test of the seal, found the longest life seal ring under the same conditions, and through the reciprocating test of the hydraulic support, found the most appropriate amount of interference between the groove and the seal ring, thus, to decrease the leakage and extend the life span of the hydraulic support.
基金supported by National Natural Science Foundation of China under Grant No.50775154Shanxi Province Science Foundation of China under Grant No.2011011026-2
文摘A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-exciter. The working principle of the hydraulic exciting system and wave exciter has been analyzed, and its excitation process has been illustrated. The law of every pipe＇s pressure fluctuation of the system is obtained by experiment. The theo- retical analysis and experimental data prove that the pipeline pressure periodically changes and the pipeline pressure fluctuation frequency is independently controlled by the excitation frequency of the wave-exciter. Every pipelinc＇s pressure wave is produced by system flow fluctuation and water hammer coupling. The pressure fluctuation rules of the system provide a theoretical basis for the study of the associated liberation system.
基金Support by the National Natural Science Foundation of China(No.51505315)the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi+1 种基金the Collaborative Innovation Center of Taiyuan Heavy Machinery Equipment Fundedthe Fund for Shanxi“1331 Project”Key Subjects Construction
文摘Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure and pressure rise rate, obtain corresponding oil pressure value when the pressure rise rate of different gas content is maximum, and verify the accuracy of this conclusion by the FLUENT simulation software. On this basis, a rapid pressure building device of the hydraulic system is developed and designed. The above oil pressure value is used as the working cut-off pressure of the rapid pressure building device, and then the hydraulic oil pump continues to pressurize to the highest working pressure required by the system. The research content can replace the hydraulic system from the initial low pressure to the rapid pressure build-up of the oil, thus increasing the construction pressure of the hydraulic system. The research results show that the rapid pressure building device effectively reduces the time for the hydraulic system to establish pressure. Through the analysis of theoretical derivation and the collected experimental data, the error is about 5.9%, which verifies the correctness of the theoretical formula.
文摘Fluid and solid interaction analysis of hydraulic support under the coming pressure of roof rocks was presented. The mathematical model of the system was proposed and numerical studies by the character line method were carried out.
文摘Fault diagnosis expert system for hydraulic support is studied.The system is achieved by Turbo prolong Language, it summaries the experience of the domain expert and sets up a fault tree, knowledge base is developed by a productive rule.According to the feature of diagnosis, the system selects forward non determination inferring and limited depth first search strategy.It can accomplish expert diagnosis of more than 50 kinds faults in hydraulic support.
基金the support of the Science and Technology Plan Project of Gansu Province,China(Grant Nos.20JR5RA447,20JR10RA174,20JR10RA203)Colleges and Universities Industrial Support Program Projects of Gansu Province(Grant No.2020C-20)Key Laboratory of Fluid and Power Machinery,Ministry of Education,Xihua University(Grant No.szjj2019-016,LTDL2020-007).
文摘In order to study the effect of splitter blades on the internal and external sound field of the hydraulic turbine,the paper chose a centrifugal pump with a specific speed ns=33 reversed as a hydraulic turbine as the research object,and added the short blades on the original impeller to form a new splitter impeller.Based on the Re-Normalization Group(RNG)k-εturbulence model to conduct numerical simulation for the hydraulic turbine,this thesis calculated the internal and external acoustic field by means of the acoustic boundary element(BEM)and finite element(FEM)and analyzed the noise radiation characteristics of the two models under different working conditions.The results show that the blade frequency is the main factor affecting the inlet and outlet sound pressure,and the optimized model decreases the inlet and outlet sound pressure levels by 6.84 and 7.24 dB in optimal working conditions.Rotor-stator interaction is the main reason for the flow-induced noise of hydraulic turbine volute appearing,the optimized model can effectively reduce the impeller and volute rotor-stator interaction and the flow-induced noise of volute.Outfield maximum sound pressure appears at the inlet and the volute tongue,which decreased by 1.84,6.07,and 5.24 dB at each operating condition.To sum up,splitter blades can improve hydraulic characteristics and flow field noise in the hydraulic turbine.
基金Key Research and Development Project of Shanxi Province(No.201603D121002-2)
文摘In consideration of the special environmental conditions of coal equipment in mining, the seamless steel tube of hy-draulic prop made of 20^# carbon steel was taken as the substrate, and 316L stainless steel powder was used to clad the sub-strate by a fiber-coupled semiconductor laser. The microstructure of the cladding layer was determined by metalloscope. The hardness, wear resistance and corrosion resistance of the cladding layer were measured. The results show that metallurgy bind-ing interface between the cladding layer and the substrate is obtained without defects such as cracks and pores. The hardness of the cladding layer is much higher than that of the matrix, and the wear resistance and corrosion resistance are simultaneously better. According to the analysis, it is summarized that the improvement in performance of the cladding layer is closely related to the change of microstructure and the thermal effect in the cladding process. The maximum hardness occurs in the equiaxed zone, and with the grain coarsening, the hardness reduces simultaneously. In addition, the precipitated phase, hard particles and trace elements also have a great influence on the properties of the cladding layer, and they will prevent the surface from ab-rasion and reduce the plastic deformation of the matrix. It is verified that the 316L stainless steel is suitable for the 20^# steel in laser cladding repairing process. Since this study focused on coal machine equipment parts, it has certain practical significance for the repair of hydraulic equipment.
基金support from the National Natural Science Foundation of China(Grant Nos.52178324,12102059)the China Postdoctoral Science Foundation(Grant No.2023M743604)+1 种基金the Beijing Natural Science Foundation(Grant No.3212027),the National Key R&D Program of China(Grant No.2023YFC3007203)the 2019 Foreign Experts Plan of Hebei Province.
文摘Perforation is a pivotal technique employed to establish main flow channels within the reservoir formation at the outset of hydraulic fracturing operations.Optimizing perforation designs is critical for augmenting the efficacy of hydraulic fracturing and boosting oil or gas production.In this study,we employ a hybrid finite-discrete element method,known as the continuous–discontinuous element method(CDEM),to simulate the initiation of post-perforation hydraulic fractures and to derive enhanced design parameters.The model incorporates the four most prevalent perforation geometries,as delineated in an engineering technical report.Real-world perforations deviate from the ideal cylindrical shape,exhibiting variable cross-sectional profiles that typically manifest as an initial constriction followed by an expansion,a feature consistent across all four perforation types.Our simulations take into account variations in perforation hole geometries,cross-sectional diameters,and perforation lengths.The findings show that perforations generated by the 39g DP3 HMX perforating bullet yield the lowest breakdown pressure,which inversely correlates with increases in sectional diameter and perforation length.Moreover,this study reveals the relationship between breakdown pressure and fracture degree,providing valuable insights for engineers and designers to refine perforation strategies.
基金the National Natural Science Foundation of China(Grant Nos.52279110,52178355 and 52108339).
文摘Understanding the mechanical response of Q2 loess subjected to dry-wet cycles(DWCs)is the premise for the rational design of a hydraulic tunnel.Taking the Hanjiang-to-Weihe south line project in China as the research background,the microstructure evolution,strength degradation and compression characteristics of Q2 loess under different DWCs were investigated,and the fluid-solid coupling analysis of the hydraulic tunnel was carried out using the FLAC3D software.The amplification effect of tunnel surrounding soil pressure(SSP)and its influence on the long-term stability of the tunnel under different DWCs were obtained.The results showed that the pore microstructure parameters of the undisturbed and remolded loess basically tend to be stable after the number of DWCs exceeds 3.The porosity of Q2 loess is increased by 26%.The internal friction angle and cohesion of Q2 loess are decreased by 35%and 31%,respectively.The vertical strain of Q2 loess is increased by 55%after considering the DWCs.After the DWCs stabilized,the SSP ratio is increased between 10%and 25%.With the increase in buried depth of the tunnel,the SSP ratio is increased by 8%e10%.The SSP is reduced from 8%to 16%by the rise in groundwater level.As the number of DWCs increases and the burial depth of the tunnel decreases,the distribution of SSP becomes progressively more non-uniform.Based on the amplification factor and the modified compressive arch theory,the SSP distribution model of loess tunnel was proposed,which can be preliminarily applied to the design of supporting structures considering DWCs.
基金financially supported by the Fundamental Research Funds for the Central Universities of China(NO.2015XKMS002)the Priority Academic Program Development of Jiangsu Higher Education Institutions of Chinagratefully acknowledge financial support of the above-mentioned agencies
文摘While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.
文摘In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part＇s strain status on the forming limit diagram （FLD） were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.
