Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force...Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.展开更多
A method is presented for estimating fatigue reliability under variable loading, which isbased on load cycles-fatigue life interference theory as well as cumulative fatigue damageanalysis. The basic opinion is that fo...A method is presented for estimating fatigue reliability under variable loading, which isbased on load cycles-fatigue life interference theory as well as cumulative fatigue damageanalysis. The basic opinion is that for variable loading the increment of failure probability pro-duced by each load cycle is determined by the stress level as well as the damage state at whichthis load cycle applies Contrast to 'conditional reliability-equivalent life methodology'. this meth-od calculates the equivalent cycle numbers between different stress levels according to cumulativefatigue damage rule but not equivalent failure probability.展开更多
This paper presents a novel transient lubrication model for the analysis of the variable load failure mechanism of high-speed pump used in Load Sensing Electro-Hydrostatic Actuator（LS-EHA）. Focusing on the slipper/s...This paper presents a novel transient lubrication model for the analysis of the variable load failure mechanism of high-speed pump used in Load Sensing Electro-Hydrostatic Actuator（LS-EHA）. Focusing on the slipper/swashplate pair partial abrasion, which is considered as the dominant failure mode in the high-speed condition, slipper dynamic models are established. A forth sliding motion of the slipper on the swashplate surface is presented under the fact that the slipper center of mass will rotate around the center of piston ball when the swashplate angle is dynamically adjusted. Besides, extra inertial tilting moments will be produced for the slipper based on the theorem on translation of force, which will increase rapidly when LS-EHA pump operates under highspeed condition. Then, a dynamic lubricating model coupling with fluid film thickness field, temperature field and pressure field is proposed. The deformation effects caused by thermal deflection and hydrostatic pressure are considered. A numerical simulation model is established to validate the effectiveness and accuracy of the proposed model. Finally, based on the load spectrum of aircraft flight profile, the variable load conditions and the oil film characteristics are analyzed, and series of variable load rules of oil film thickness with variable speed/variable pressure/variable displacement are concluded.展开更多
For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the...For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.展开更多
In view of the large energy loss problem in the traditional full hydraulic steering system,a scheme of replacing the ordinary pump with the priority valve with the load sensitive variable pump is proposed to make the ...In view of the large energy loss problem in the traditional full hydraulic steering system,a scheme of replacing the ordinary pump with the priority valve with the load sensitive variable pump is proposed to make the variable pump provide the corresponding flow rate according to the needs of the steering system to achieve the purpose of energy saving.Through the establishment of the system AMESim simulation model,the data comparison shows that the energy loss of the load sensitive variable steering system is significantly reduced relative to the traditional full hydraulic steering system.展开更多
A hybrid system proposed by three different specifications for the equipment of a tourist lodge in the headland of south-west Morocco was sized by analysing the limits of load profile constraints,such as hour-to-hour ...A hybrid system proposed by three different specifications for the equipment of a tourist lodge in the headland of south-west Morocco was sized by analysing the limits of load profile constraints,such as hour-to-hour variability(HHR),day-to-day variability(DDR)and the operating reserve rate(ROR).Based on the three-factor Doehlert matrix recommendations,the simulations employed an energy-sizing tool for hybrid renewable-energy systems.Testing was conducted with DDR at 5-30%,HHR at 10-30%and ROR at 0-20%.Under these conditions,a second-order polynomial relationship with a correlation rate of~90%was found between the net present cost(NPC)of the system,the levelized cost of electricity and the various constraint factors.The first specification,SPC(1),composed of generators and batteries,was introduced to control and validate the simulation independently of renewable energy,which showed a positive manifestation with the imposed constraints.The analysis expanded by introducing solar and wind energy resources.The SPC(2)configuration added PV modules to the SPC(1)and the SPC(3)configuration added wind turbines to SPC(2).The effect of DDR,HHR and ROR in the trials was significant by linear regression.At the same time,only DDR had a significant quadratic regression.The others,with their pairwise interactions,were insignificant.The desirability procedure made it possible to calculate the maximum limits of load profile constraint variables leading to targets of LCOE=0.41 US$/kWh and NPC=US$320080.1 of the load profile constraints:the DDR=15.47%and the HHR=26.55%at an ROR rate of 17.77%.展开更多
Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fa...Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.展开更多
By using the modified iteration method of large deflection theory of plates with variable thichness[1], we solve the problem of circular plates with variable thickness subjected to combined loads under the boundary co...By using the modified iteration method of large deflection theory of plates with variable thichness[1], we solve the problem of circular plates with variable thickness subjected to combined loads under the boundary conditions of the clamped edges and get comparatively more accurate second-order approximate analytical solution. If the results of this paper are degraded into the special cases, the results coinciding with those of papers [1,2] can be obtained. In this paper, the characteristic curves are plotted and some comparisons are made. The results of this paper are satisfactory.展开更多
A research concerning the coupling conditions of gas leakage through suction valves and capacity regulation is performed in an industrial reciprocating compressor.Both internal flow and thermodynamic characteristic ar...A research concerning the coupling conditions of gas leakage through suction valves and capacity regulation is performed in an industrial reciprocating compressor.Both internal flow and thermodynamic characteristic are discussed in detail.The results show that the capacity of compressor can be regulated steplessly by controlling suction valve closure moment.And then the quantitative relationship between the capacity load and the closing angle of suction valve is revealed.The capacity load and valve leakage rate show obvious different features in P-V diagrams,which makes it easier to define appropriate features for detecting cracked or broken reciprocating compressor valves under varying load conditions.A set of curves of compression work and discharge gas mass are obtained and a method for rating thermal performance of a compressor is presented using these curves.展开更多
A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions o...A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.展开更多
Ignoring the influence of flow velocity and flow temperature on muffling performance,performance tests were conducted without airflow in the development phase of the muffler which accounts to the difficulty of obtaini...Ignoring the influence of flow velocity and flow temperature on muffling performance,performance tests were conducted without airflow in the development phase of the muffler which accounts to the difficulty of obtaining a perfect match between the actual noise reduction effect and the design goal.Based on the two-load test theory,a set of high-temperature and high-speed airflow simulation measurement devices for the muffler has been built.In order to avoid the impact of high-temperature and high-speed airflow on the sensor,a high temperature resistant sensor holder has been designed for the test rig.The sound pressure has been measured in the pipe by using the lead-out measurement.In addition,a variable impedance load is placed at the end of the test tube to realize the switch between two different impedance loads by the wave handle of the variable impedance load.A sound source correction method is proposed to decrease the random fluctuation of the spectral characteristics of the output noise signal,which is caused by the acoustic impedance variation at the connection between the transition pipeline and the combined sound source system.Finally,an acoustic software has been used to calculate the transmission loss of the muffler in the presence of high temperature airflow.In comparing the experimental measurements and the simulation results,the small difference shows that:the bench not only can effectively simulate high-temperature and flow velocity environment of the engine but also accurately test the transmission loss of the muffler.展开更多
We used an analytical high-level battery model to estimate the battery lifetime for a given load.The experimental results show that this model to predict battery lifetime under variable loads is more appropriate than ...We used an analytical high-level battery model to estimate the battery lifetime for a given load.The experimental results show that this model to predict battery lifetime under variable loads is more appropriate than that under constant loads.展开更多
Hydraulic equipment in engineering, in different working stages, different speed, load, variable load and variable speed is one of the most frequently encountered problems, to solve this problem is usually used to con...Hydraulic equipment in engineering, in different working stages, different speed, load, variable load and variable speed is one of the most frequently encountered problems, to solve this problem is usually used to continuously adjustable pressure, adjustable flow control to achieve. In this paper, the structure design of a combination of oil tanks, combined with oil circuit examples in the case of no need to adjust the pressure, adjust the flow rate, to achieve the high speed, light load of the typical operating requirements and hydraulic servo feedback.展开更多
Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation ar...Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation are proposed from the viewpoint of both damagemechanics and fracture mechanics. Then the individual isodamage D-S_a-S_m-N surface under constantamplitude loading is constructed and the two-dimensional individual Miner's rule is derived.Consequently, the two-dimensional probabilistic Miner's rule (TPMiner) is established and proved fora population subjected to variable amplitude loading. Finally, with successfully experimentverification, TPMiner proves be to very useful and feasible in fatigue reliability theory.展开更多
This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48...This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48%)to clarify the effect of load change on the furnace processes.A computational fluids dynamics model was established;the flow field,temperature profile,species concentration and NOx emissions were predicted numerically;and the influence of burner tilt angles was evaluated.Simulation results indicate that a decrease in boiler load decreases the gas velocity,attenuates the airflow rotations,and increases the tangent circle size.The high-temperature zone and flame moved toward the side walls.Such behaviors impair air-fuel mixing,heat transfer and steady combustion in the furnace.In terms of species concentrations,a decrease in boiler load increased the O2 content,decreased the CO content,and decreased the char burnout rates only slightly.A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m^(3),respectively.Burner tilt angles are important in coal combustion and NOx emissions.A burner angle of-15°favors heat transfer and low NOx emissions(<185 mg/m^(3))for the current tangentially fired boiler.展开更多
A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-p...A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter a which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental aluminium alloy, and multi-level loading of 45 steel. Fatigue lives data for two-level loading, multi-level loading of LY12CZ predicted are within a factor of 2 scatter band.展开更多
Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the pa...Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the paper.One method is to simplify the original multi-level load spectra to spectral load with fewer level and was verified by the experimental data of five levels and seven levels load spectra.The equivalent damage here is not equivalent fatigue life,but equivalent number of spectral blocks.Moreover,it was proved that a section of low stress load cannot be converted into the highest stress load considering equivalent damage.The other is to convert the life distribution under multi-level load spectra into that of constant amplitude spectrum according to a certain principle,that is,equivalent damage is achieved through equivalent fatigue life,and two groups of three levels spectral data were used for experimental verification.The results show that equivalent damage simplification approach of multi-level load spectra is feasible,and it achieve that the damage of one loading block before and after the simplification is equal in probability statistics.The life distribution of load simplified as constant amplitude spectrum is consistent with test data.The simplification method presented in this paper can be generalized and is a predictive engineering method which does not depend on experimental data.展开更多
基金Supported by National Key Basic Research Program of China(973 Program,Grant No.2014CB046405)State Key Laboratory of Fluid Power and Mechatronic Systems(Zhejiang University)Open Fund Project(Grant No.GZKF-201502)Hebei Military and Civilian Industry Development Funds Projects of China(Grant No.2015B060)
文摘Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.
文摘A method is presented for estimating fatigue reliability under variable loading, which isbased on load cycles-fatigue life interference theory as well as cumulative fatigue damageanalysis. The basic opinion is that for variable loading the increment of failure probability pro-duced by each load cycle is determined by the stress level as well as the damage state at whichthis load cycle applies Contrast to 'conditional reliability-equivalent life methodology'. this meth-od calculates the equivalent cycle numbers between different stress levels according to cumulativefatigue damage rule but not equivalent failure probability.
基金supported by the National Natural Science Foundation of China(Nos.51620105010,51675019 and 51575019)the National Basic Research Program of China(No.2014CB046402)+1 种基金the ‘‘111" Projectthe Excellence Foundation of BUAA for PhD Students
文摘This paper presents a novel transient lubrication model for the analysis of the variable load failure mechanism of high-speed pump used in Load Sensing Electro-Hydrostatic Actuator（LS-EHA）. Focusing on the slipper/swashplate pair partial abrasion, which is considered as the dominant failure mode in the high-speed condition, slipper dynamic models are established. A forth sliding motion of the slipper on the swashplate surface is presented under the fact that the slipper center of mass will rotate around the center of piston ball when the swashplate angle is dynamically adjusted. Besides, extra inertial tilting moments will be produced for the slipper based on the theorem on translation of force, which will increase rapidly when LS-EHA pump operates under highspeed condition. Then, a dynamic lubricating model coupling with fluid film thickness field, temperature field and pressure field is proposed. The deformation effects caused by thermal deflection and hydrostatic pressure are considered. A numerical simulation model is established to validate the effectiveness and accuracy of the proposed model. Finally, based on the load spectrum of aircraft flight profile, the variable load conditions and the oil film characteristics are analyzed, and series of variable load rules of oil film thickness with variable speed/variable pressure/variable displacement are concluded.
文摘For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.
基金Key R&D Plan of Shandong Province(2015GGX105005)。
文摘In view of the large energy loss problem in the traditional full hydraulic steering system,a scheme of replacing the ordinary pump with the priority valve with the load sensitive variable pump is proposed to make the variable pump provide the corresponding flow rate according to the needs of the steering system to achieve the purpose of energy saving.Through the establishment of the system AMESim simulation model,the data comparison shows that the energy loss of the load sensitive variable steering system is significantly reduced relative to the traditional full hydraulic steering system.
文摘A hybrid system proposed by three different specifications for the equipment of a tourist lodge in the headland of south-west Morocco was sized by analysing the limits of load profile constraints,such as hour-to-hour variability(HHR),day-to-day variability(DDR)and the operating reserve rate(ROR).Based on the three-factor Doehlert matrix recommendations,the simulations employed an energy-sizing tool for hybrid renewable-energy systems.Testing was conducted with DDR at 5-30%,HHR at 10-30%and ROR at 0-20%.Under these conditions,a second-order polynomial relationship with a correlation rate of~90%was found between the net present cost(NPC)of the system,the levelized cost of electricity and the various constraint factors.The first specification,SPC(1),composed of generators and batteries,was introduced to control and validate the simulation independently of renewable energy,which showed a positive manifestation with the imposed constraints.The analysis expanded by introducing solar and wind energy resources.The SPC(2)configuration added PV modules to the SPC(1)and the SPC(3)configuration added wind turbines to SPC(2).The effect of DDR,HHR and ROR in the trials was significant by linear regression.At the same time,only DDR had a significant quadratic regression.The others,with their pairwise interactions,were insignificant.The desirability procedure made it possible to calculate the maximum limits of load profile constraint variables leading to targets of LCOE=0.41 US$/kWh and NPC=US$320080.1 of the load profile constraints:the DDR=15.47%and the HHR=26.55%at an ROR rate of 17.77%.
文摘Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.
文摘By using the modified iteration method of large deflection theory of plates with variable thichness[1], we solve the problem of circular plates with variable thickness subjected to combined loads under the boundary conditions of the clamped edges and get comparatively more accurate second-order approximate analytical solution. If the results of this paper are degraded into the special cases, the results coinciding with those of papers [1,2] can be obtained. In this paper, the characteristic curves are plotted and some comparisons are made. The results of this paper are satisfactory.
基金the National Natural Science Foundation of China(No.52101343)State Key Laboratory of Compressor Technology(An Hui Laboratory of Compressor Technology)(No.SKL-YSJ201808/SKL-YSJ201911)。
文摘A research concerning the coupling conditions of gas leakage through suction valves and capacity regulation is performed in an industrial reciprocating compressor.Both internal flow and thermodynamic characteristic are discussed in detail.The results show that the capacity of compressor can be regulated steplessly by controlling suction valve closure moment.And then the quantitative relationship between the capacity load and the closing angle of suction valve is revealed.The capacity load and valve leakage rate show obvious different features in P-V diagrams,which makes it easier to define appropriate features for detecting cracked or broken reciprocating compressor valves under varying load conditions.A set of curves of compression work and discharge gas mass are obtained and a method for rating thermal performance of a compressor is presented using these curves.
基金supported by the Gas Turbine Establishment of China (Grant No. GTE022006084)
文摘A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.
基金Supported by National Key Research and Development Program(2016YFD0700704B)。
文摘Ignoring the influence of flow velocity and flow temperature on muffling performance,performance tests were conducted without airflow in the development phase of the muffler which accounts to the difficulty of obtaining a perfect match between the actual noise reduction effect and the design goal.Based on the two-load test theory,a set of high-temperature and high-speed airflow simulation measurement devices for the muffler has been built.In order to avoid the impact of high-temperature and high-speed airflow on the sensor,a high temperature resistant sensor holder has been designed for the test rig.The sound pressure has been measured in the pipe by using the lead-out measurement.In addition,a variable impedance load is placed at the end of the test tube to realize the switch between two different impedance loads by the wave handle of the variable impedance load.A sound source correction method is proposed to decrease the random fluctuation of the spectral characteristics of the output noise signal,which is caused by the acoustic impedance variation at the connection between the transition pipeline and the combined sound source system.Finally,an acoustic software has been used to calculate the transmission loss of the muffler in the presence of high temperature airflow.In comparing the experimental measurements and the simulation results,the small difference shows that:the bench not only can effectively simulate high-temperature and flow velocity environment of the engine but also accurately test the transmission loss of the muffler.
基金The MKE(the Ministry of Knowledge Economy),Korea,under the ITRC(Information Technology Research Center)support program supervised by the NIPA(National IT Industry Promotion Agency) (NIPA-2011-C1090-1021-0010)Seoul Metropolitan Government,under the Seoul R & BD Program supervised by Seoul Business Agency(No.ST110039)
文摘We used an analytical high-level battery model to estimate the battery lifetime for a given load.The experimental results show that this model to predict battery lifetime under variable loads is more appropriate than that under constant loads.
文摘Hydraulic equipment in engineering, in different working stages, different speed, load, variable load and variable speed is one of the most frequently encountered problems, to solve this problem is usually used to continuously adjustable pressure, adjustable flow control to achieve. In this paper, the structure design of a combination of oil tanks, combined with oil circuit examples in the case of no need to adjust the pressure, adjust the flow rate, to achieve the high speed, light load of the typical operating requirements and hydraulic servo feedback.
基金This project is supported by National Natural Science Foundation of China(No.59605010,No.59979015)Selected from Proceedings of 2000 the First International Conference on Mechanical Engineering
文摘Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation are proposed from the viewpoint of both damagemechanics and fracture mechanics. Then the individual isodamage D-S_a-S_m-N surface under constantamplitude loading is constructed and the two-dimensional individual Miner's rule is derived.Consequently, the two-dimensional probabilistic Miner's rule (TPMiner) is established and proved fora population subjected to variable amplitude loading. Finally, with successfully experimentverification, TPMiner proves be to very useful and feasible in fatigue reliability theory.
基金The authors acknowledge the support from the National Nature Science Foundation of China(No.51476058)and SINOPEC project(No.318015-6).
文摘This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48%)to clarify the effect of load change on the furnace processes.A computational fluids dynamics model was established;the flow field,temperature profile,species concentration and NOx emissions were predicted numerically;and the influence of burner tilt angles was evaluated.Simulation results indicate that a decrease in boiler load decreases the gas velocity,attenuates the airflow rotations,and increases the tangent circle size.The high-temperature zone and flame moved toward the side walls.Such behaviors impair air-fuel mixing,heat transfer and steady combustion in the furnace.In terms of species concentrations,a decrease in boiler load increased the O2 content,decreased the CO content,and decreased the char burnout rates only slightly.A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m^(3),respectively.Burner tilt angles are important in coal combustion and NOx emissions.A burner angle of-15°favors heat transfer and low NOx emissions(<185 mg/m^(3))for the current tangentially fired boiler.
基金supported by the National Natural Science Foundation of China(Grant No.10702027)Aviation Science Funds of China(Grant No.2011ZA52016)Program for Changjiang Scholars and Innovative Research Team in University(Grant No.Irt0906)
文摘A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter a which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental aluminium alloy, and multi-level loading of 45 steel. Fatigue lives data for two-level loading, multi-level loading of LY12CZ predicted are within a factor of 2 scatter band.
文摘Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the paper.One method is to simplify the original multi-level load spectra to spectral load with fewer level and was verified by the experimental data of five levels and seven levels load spectra.The equivalent damage here is not equivalent fatigue life,but equivalent number of spectral blocks.Moreover,it was proved that a section of low stress load cannot be converted into the highest stress load considering equivalent damage.The other is to convert the life distribution under multi-level load spectra into that of constant amplitude spectrum according to a certain principle,that is,equivalent damage is achieved through equivalent fatigue life,and two groups of three levels spectral data were used for experimental verification.The results show that equivalent damage simplification approach of multi-level load spectra is feasible,and it achieve that the damage of one loading block before and after the simplification is equal in probability statistics.The life distribution of load simplified as constant amplitude spectrum is consistent with test data.The simplification method presented in this paper can be generalized and is a predictive engineering method which does not depend on experimental data.
