The dynamic model of a novel electric power steering (EPS) system integrated with active front steering function (the novel EPS system) is built.The concepts and quantitative expressions of the steering road feel,stee...The dynamic model of a novel electric power steering (EPS) system integrated with active front steering function (the novel EPS system) is built.The concepts and quantitative expressions of the steering road feel,steering sensibility,and steering operation stability are introduced.Based on quality engineering theory,the optimization algorithm is proposed by integrating the Monte Carlo descriptive sampling,elitist non-dominated sorting genetic algorithm (NSGA-Ⅱ) and 6-sigma design method.With the steering road feel and the steering portability as optimization targets,the system parameters are optimized by the proposed optimization algorithm.The simulation results show that the system optimized based on quality engineering theory can improve the steering road feel,guarantee steering stability and steering portability and thus provide a theoretical basis for the design and optimization of the novel electric power steering system.展开更多
To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire m...To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.展开更多
The connecting rod is one of the most important moving components in an internal combustion engine. The present work determined the possibility of using aluminium alloy 7075 material to design and manufacture a connec...The connecting rod is one of the most important moving components in an internal combustion engine. The present work determined the possibility of using aluminium alloy 7075 material to design and manufacture a connecting rod for weight optimisation without losing the strength of the connecting rod. It considered modal and thermal analyses to investigate the suitability of the material for connecting rod design. The parameters that were considered under the modal analysis were: total deformation, and natural frequency, while the thermal analysis looked at the temperature distribution, total heat flux and directional heat flux of the four connecting rods made with titanium alloy, grey cast iron, structural steel and aluminium 7075 alloy respectively. The connecting rod was modelled using Autodesk inventor2017 software using the calculated parameters. The steady-state thermal analysis was used to determine the induced heat flux and directional heat flux. The study found that Aluminium 7075 alloy deformed more than the remaining three other materials but has superior qualities in terms of vibrational natural frequency, total heat flux and lightweight compared to structural steel, grey cast iron and titanium alloy.展开更多
This paper presents a new computational method for forward uncertainty quantification(UQ)analyses on large-scale structural systems in the presence of arbitrary and dependent random inputs.The method consists of a gen...This paper presents a new computational method for forward uncertainty quantification(UQ)analyses on large-scale structural systems in the presence of arbitrary and dependent random inputs.The method consists of a generalized polynomial chaos expansion(GPCE)for statistical moment and reliability analyses associated with the stochastic output and a static reanalysis method to generate the input-output data set.In the reanalysis,we employ substructuring for a structure to isolate its local regions that vary due to random inputs.This allows for avoiding repeated computations of invariant substructures while generating the input-output data set.Combining substructuring with static condensation further improves the computational efficiency of the reanalysis without losing accuracy.Consequently,the GPCE with the static reanalysis method can achieve significant computational saving,thus mitigating the curse of dimensionality to some degree for UQ under high-dimensional inputs.The numerical results obtained from a simple structure indicate that the proposed method for UQ produces accurate solutions more efficiently than the GPCE using full finite element analyses(FEAs).We also demonstrate the efficiency and scalability of the proposed method by executing UQ for a large-scale wing-box structure under ten-dimensional(all-dependent)random inputs.展开更多
Elastography is a non-invasive medical imaging technique to map the spatial variation of elastic properties of soft tissues.The quality of reconstruction results in elastography is highly sensitive to the noise induce...Elastography is a non-invasive medical imaging technique to map the spatial variation of elastic properties of soft tissues.The quality of reconstruction results in elastography is highly sensitive to the noise induced by imaging measurements and processing.To address this issue,we propose a deep learning(DL)model based on conditional Generative Adversarial Networks(cGANs)to improve the quality of nonhomogeneous shear modulus reconstruction.To train this model,we generated a synthetic displacement field with finite element simulation under known nonhomogeneous shear modulus distribution.Both the simulated and experimental displacement fields are used to validate the proposed method.The reconstructed results demonstrate that the DL model with synthetic training data is able to improve the quality of the reconstruction compared with the well-established optimization method.Moreover,we emphasize that our DL model is only trained on synthetic data.This might provide a way to alleviate the challenge of obtaining clinical or experimental data in elastography.Overall,this work addresses several fatal issues in applying the DL technique into elastography,and the proposed method has shown great potential in improving the accuracy of the disease diagnosis in clinical medicine.展开更多
To analyze the influence of surface texture on friction properties of Cr12 Mo V', ordinary grinder and spinning technology were adopted to obtain the grooved surface morphology of samples, and then the impact of s...To analyze the influence of surface texture on friction properties of Cr12 Mo V', ordinary grinder and spinning technology were adopted to obtain the grooved surface morphology of samples, and then the impact of spindle speed and feed in z-direction on surface morphology in the process of spinning was studied. In addition, the corresponding friction coefficient of sample was obtained through friction and wear tests. The results show that the peak clipping and the valley filling were conducted on the grinding surface, which could improve the surface roughness effectively and make the grinding trench-type wear scar more uniform. Both the area ratio of groove and groove spacing increased initially and then decreased with the increase of the spindle speed or the feed in z-direction. As a kind of micro-process, the groove could influence the friction coefficient of sample surface, whose distribution was beneficial to the reduction of friction coefficient. Compared with the surface obtained through ordinary grinding, grooved surface morphology through spinning technology was more conductive to reduce the friction coefficient, which could be reduced by 25%. When the friction coefficient of sample was reduced to the minimum, the texture of groove corresponded had an optimal area ratio and an optimal groove spacing, 37.5% and 27.5 μm, respectively.展开更多
Next-generation vehicle control and future autonomous driving require further advances in vehicle dynamic state estimation. This article provides a concise review, along with the perspectives, of the recent developmen...Next-generation vehicle control and future autonomous driving require further advances in vehicle dynamic state estimation. This article provides a concise review, along with the perspectives, of the recent developments in the estimation of vehicle dynamic states. The definitions used in vehicle dynamic state estimation are first introduced, and alternative estimation structures are presented. Then, the sensor configuration schemes used to estimate vehicle velocity, sideslip angle, yaw rate and roll angle are presented. The vehicle models used for vehicle dynamic state estimation are further summarized, and representative estimation approaches are discussed. Future concerns and perspectives for vehicle dynamic state estimation are also discussed.展开更多
Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an...Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel(diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation(EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24% and 31%,respectively,The NOx emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.展开更多
Three kinds of cast iron coatings were prepared by atmospheric plasma spraying. During the spraying, the mild steel substrate temperature was controlled to be averagely 50, 180, and 240°C, respectively. Abrasive ...Three kinds of cast iron coatings were prepared by atmospheric plasma spraying. During the spraying, the mild steel substrate temperature was controlled to be averagely 50, 180, and 240°C, respectively. Abrasive wear tests were conducted on the coatings under a dry friction condition. It is found that the abrasive wear resistance is enhanced with the substrate temperature increasing. SEM observations show that the wear losses of the coatings during the wear tests mainly result from the spalling of the splats. Furthermore, the improved wear resistance of the coatings mainly owes to the formation of oxides and the enhancement in the mechanical properties with the substrate temperature increasing.展开更多
Speech signals in frequency domain were separated based on discrete wavelet transform (DWT) and independent component analysis (ICA). First, mixed speech signals were decomposed into different frequency domains by DWT...Speech signals in frequency domain were separated based on discrete wavelet transform (DWT) and independent component analysis (ICA). First, mixed speech signals were decomposed into different frequency domains by DWT and the subbands of speech signals were separated using ICA in each wavelet domain; then, the permutation and scaling problems of frequency domain blind source separation (BSS) were solved by utilizing the correlation between adjacent bins in speech signals; at last, source signals were reconstructed from single branches. Experiments were carried out with 2 sources and 6 microphones using speech signals at sampling rate of 40 kHz. The microphones were aligned with 2 sources in front of them, on the left and right. The separation of one male and one female speeches lasted 2.5 s. It is proved that the new method is better than single ICA method and the signal to noise ratio is improved by 1 dB approximately.展开更多
With the worsening of energy crisis and environmental pollution,electric vehicles with four in?wheel motors have been paid more and more attention. The main research subject is how to reasonably distribute the driving...With the worsening of energy crisis and environmental pollution,electric vehicles with four in?wheel motors have been paid more and more attention. The main research subject is how to reasonably distribute the driving torque of each wheel. Considering the longitudinal motion,lateral motion,yaw movement and rotation of the four wheels,the tire model and the seven DOF dynamic model of the vehicle are established in this paper. Then,the torque distribution method is proposed based on road adhesion margin,which can be divided into anti ? slip control layer and torque distribution layer. The anti?slip control layer is built based on sliding mode variable structure control,whose main function is to avoid the excessive slip of wheels caused by road conditions. The torque distribution layer is responsible for selecting the torque distribution method based on road adhesion margin. The simulation results show that the proposed torque distribution method can ensure the vehicle quickly adapt to current road adhesion conditions,and improve the handling stability and dynamic performance of the vehicle in the driving process.展开更多
An easy calibration method was presented for in-situ measurement of displacement in the order of nanometer during micro-tensile test for thin films by using CCD camera as a sensing device. The calibration of the sensi...An easy calibration method was presented for in-situ measurement of displacement in the order of nanometer during micro-tensile test for thin films by using CCD camera as a sensing device. The calibration of the sensing camera in the system is a central element part to measure displacement in the order of nanometer using images taken with the camera. This was accomplished by modeling the optical projection through the camera lens and relative locations between the object and camera in 3D space. A set of known 3D points on a plane where the film is located on is projected to an image plane as input data. These points, known as a calibration points, are then used to estimate the projection parameters of the camera. In the measurement system of the micro-scale by CCD camera, the calibration data acquisition and one-to-one matching steps between the image and 3D planes need precise data extraction procedures and repetitive user's operation to calibrate the measuring devices. The lack of the robust image feature extraction and easy matching prevent the practical use of these methods. A data selection method was proposed to overcome these limitations and offer an easy and convenient calibration of a vision system that has the CCD camera and the 3D reference plane with calibration marks of circular type on the surface of the plane. The method minimizes the user's intervention such as the fine tuning of illumination system and provides an efficient calibration method of the vision system for in-situ axial displacement measurement of the micro-tensile materials.展开更多
Machining and installation errors are unavoidable in mechanical structures. However, the effect of errors on radial stiffness of the mechanical elastic wheel(ME-Wheel) is not considered in previous studies. To this en...Machining and installation errors are unavoidable in mechanical structures. However, the effect of errors on radial stiffness of the mechanical elastic wheel(ME-Wheel) is not considered in previous studies. To this end, the interval mathematical model and interval finite element model of the ME-Wheel were both established and compared with bench test results. The intercomparison of the influence of the machining and installation errors on the ME-Wheel radial stiffness revealed good consistency among the interval mathematical analysis, interval finite element simulation,and bench test results. Within the interval range of the ME-Wheel machining and installation errors, parametric analysis of the combined elastic rings was performed at different initial radial rigidity values. The results showed that the initial radial stiffness of the flexible tire body significantly influenced the ME-Wheel radial stiffness, and the inverse relationship between the hinge unit length or suspension hub and the radial stiffness was nonlinear. The radial stiffness of the ME-Wheel is predicted by using the interval algorithm for the first time, and the regularity of the radial stiffness between the error and the load on the ME-Wheel is studied, which will lay the foundation for the exact study of the ME-Wheel dynamic characteristics in the future.展开更多
A numerical study of the crushing of thin-walled circular aluminum tubes has been carried out to investigate the crashworthiness behaviors under axial impact loading. These kinds of tubes are usually used in automobil...A numerical study of the crushing of thin-walled circular aluminum tubes has been carried out to investigate the crashworthiness behaviors under axial impact loading. These kinds of tubes are usually used in automobile and train structures to absorb the impact energy. Previous researches show that thin-walled circular tube has the highest energy absorption under axial impact amongst different structures. In this work, the crushing between two rigid flat plates and the tube rupture by 4 and 6 blades cutting tools is modeled with the help of ductile failure criterion using the numerical method. The tube material is aluminum EN AW-7108 T6 and its length and diameter are 300 mm and 50 mm, respectively. Using the artificial neural network(ANN), the most important surfaces of energy absorption parameters, including the maximum displacement of the striker, the maximum axial force, the specific energy absorption and the crushing force efficiency in terms of impact velocity and tube thickness are obtained and compared to each other. The analyses show that the tube rupture by the 6 blades cutting tool has more energy absorption in comparison with others. Furthermore, the results demonstrate that tube cutting with the help of multi-blades cutting tools is more stable, controllable and predictable than tube folding.展开更多
Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount...Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount of fuel injected between two injection pulses and the injection interval is varied keeping the injected fuel quantity constant. Results show that under the 70D90-10 injection pattern, the engine achieves the lower NOx-smoke emissions and BSFC compared with the single injection pattern. The heat release rate and the temperature show that the split injections increase the initial premixed burn and retards the diffusion burn. With the balance of these two effects, the maximum in-cylinder temperature decreases while the 50% heat release point is held at almost the same crank angle. Therefore, both NOx emission and BSFC are improved while keeping the smoke emission at the same level.展开更多
The recent trend of vehicle design aims at crash safety and environmentally-friendly aspect. For the crash safety aspect, the energy absorbing members should absorb collision energy sufficiently but for the environmen...The recent trend of vehicle design aims at crash safety and environmentally-friendly aspect. For the crash safety aspect, the energy absorbing members should absorb collision energy sufficiently but for the environmentally-friendly aspect, the vehicle structure must be light weight in order to improve the fuel efficiency and reduce the tail gas emission. Therefore, the light weight of vehicle must be achieved in a securing safety status of crash. An aluminum or carbon fiber reinforced plastics (CFRP) is representative one of the light-weight materials. Based on the respective collapse behavior of aluminum and CFRP member, the collapse behavior of hybrid thin-walled member was evaluated. The hybrid members were manufactured by wrapping CFRP prepreg sheets outside the aluminum hollow members in the autoclave. Because the CFRP is an anisotropic material whose mechanical properties, such as strength and elasticity, change with its stacking condition, the effects of the stacking condition on the collapse behavior evaluation of the hybrid thin-walled member were tested. The collapse mode and energy absorption capability of the hybrid thin-walled member were analyzed with the change of the fiber orientation angle and interface number.展开更多
Biodiesel is one of the most popular prospective alternative fuels and can be obtained from a variety of sources. Waste frying oil is one such source along with the various raw vegetable oils. However, some specific t...Biodiesel is one of the most popular prospective alternative fuels and can be obtained from a variety of sources. Waste frying oil is one such source along with the various raw vegetable oils. However, some specific technical treatments are required to improve certain fuel properties such as viscosity and calorific value of the biodiesel being obtained from waste cooking oil methyl ester(WCOME). Various treatments are applied depending on the source and therefore the composition of the cooking oil. This research investigated the performance of WCOME as an alternative biofuel in a four-stroke direct injection diesel engine. An 8-mode test was undertaken with diesel fuel and five WCOME blends. The best compromise blend in terms of performance and emissions was identified. Results showed that energy utilization factors of the blends were similar within the range of the operational parameters(speed, load and WCOME content). Increasing biodiesel content produced slightly more smoke and NOx for a great majority of test points, while the CO and THC emissions were lower.展开更多
Motion analyses are performed with the help of stability and simulation analysis, which can provide theoretical bases for applications of an electric vehicle with two independent drive motors. Compared with one-motor ...Motion analyses are performed with the help of stability and simulation analysis, which can provide theoretical bases for applications of an electric vehicle with two independent drive motors. Compared with one-motor drive electric vehicle, the two-motor drive electric vehicle has the advantage of easy layout, simple power train and good drivability and handling characteristics. Analysis shows the method connecting armatures of two DC motors in parallel can function as mechanical differential without a steering sensor, which can simplify structure and increase reliability of the controller. Computer simulations and experiment are carried out to verify conclusions.展开更多
Volumetric efficiency and air charge estimation is one of the most demanding tasks in control of today's internal combustion engines.Specifically,using three-way catalytic converter involves strict control of the ...Volumetric efficiency and air charge estimation is one of the most demanding tasks in control of today's internal combustion engines.Specifically,using three-way catalytic converter involves strict control of the air/fuel ratio around the stoichiometric point and hence requires an accurate model for air charge estimation.However,high degrees of complexity and nonlinearity of the gas flow in the internal combustion engine make air charge estimation a challenging task.This is more obvious in engines with variable valve timing systems in which gas flow is more complex and depends on more functional variables.This results in models that are either quite empirical(such as look-up tables),not having interpretability and extrapolation capability,or physically based models which are not appropriate for onboard applications.Solving these problems,a novel semi-empirical model was proposed in this work which only needed engine speed,load,and valves timings for volumetric efficiency prediction.The accuracy and generalizability of the model is shown by its test on numerical and experimental data from three distinct engines.Normalized test errors are 0.0316,0.0152 and 0.24 for the three engines,respectively.Also the performance and complexity of the model were compared with neural networks as typical black box models.While the complexity of the model is less than half of the complexity of neural networks,and its computational cost is approximately 0.12 of that of neural networks and its prediction capability in the considered case studies is usually more.These results show the superiority of the proposed model over conventional black box models such as neural networks in terms of accuracy,generalizability and computational cost.展开更多
The concept of shape factors of the fusion-solidification zone is proposed to describe the weld cross section geometry. According to these shape factors,the electron beam weld fusion-solidification zone is divided int...The concept of shape factors of the fusion-solidification zone is proposed to describe the weld cross section geometry. According to these shape factors,the electron beam weld fusion-solidification zone is divided into four typical shapes and the classification criterion for these typical shapes is suggested. An integrated parameter n1 combining the line power density of electron beam and material thermal properties is proposed to describe the relative power input,and another integrated parameter n2 combing the accelerating voltage and focusing current is proposed to reflect the power distribution in the keyhole. A series of new expressions,which can reflect the influence of focusing current,accelerating voltage,beam current,and material thermal properties,are developed to predict the fusion-solidification zone shape based on experimental results nonlinear fitting of n1 and n2.展开更多
基金Projects(51005115,51205191)supported by the National Natural Science Foundation of ChinaProject(QC201101)supported by the Visiting Scholar Foundation of the Automobile Engineering Key Laboratory of Jiangsu Province,China+1 种基金Project(SKLMT-KFKT-201105)supported by the Visiting Scholar Foundation of the State Key Laboratory of Mechanical Transmission in Chongqing University,ChinaProjects(NS2013015,NS2012086)supported by the Funds from the Postgraduate Creative Base in Nanjing University of Areonautics and Astronautics,and NUAA Research Funding,China
文摘The dynamic model of a novel electric power steering (EPS) system integrated with active front steering function (the novel EPS system) is built.The concepts and quantitative expressions of the steering road feel,steering sensibility,and steering operation stability are introduced.Based on quality engineering theory,the optimization algorithm is proposed by integrating the Monte Carlo descriptive sampling,elitist non-dominated sorting genetic algorithm (NSGA-Ⅱ) and 6-sigma design method.With the steering road feel and the steering portability as optimization targets,the system parameters are optimized by the proposed optimization algorithm.The simulation results show that the system optimized based on quality engineering theory can improve the steering road feel,guarantee steering stability and steering portability and thus provide a theoretical basis for the design and optimization of the novel electric power steering system.
基金supported by the National Natural Science Foundation of China(grant number 51805086)the Natural Science Foundation of Fujian Province,China(grant number 2018J01763)。
文摘To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.
文摘The connecting rod is one of the most important moving components in an internal combustion engine. The present work determined the possibility of using aluminium alloy 7075 material to design and manufacture a connecting rod for weight optimisation without losing the strength of the connecting rod. It considered modal and thermal analyses to investigate the suitability of the material for connecting rod design. The parameters that were considered under the modal analysis were: total deformation, and natural frequency, while the thermal analysis looked at the temperature distribution, total heat flux and directional heat flux of the four connecting rods made with titanium alloy, grey cast iron, structural steel and aluminium 7075 alloy respectively. The connecting rod was modelled using Autodesk inventor2017 software using the calculated parameters. The steady-state thermal analysis was used to determine the induced heat flux and directional heat flux. The study found that Aluminium 7075 alloy deformed more than the remaining three other materials but has superior qualities in terms of vibrational natural frequency, total heat flux and lightweight compared to structural steel, grey cast iron and titanium alloy.
基金Project supported by the National Research Foundation of Korea(Nos.NRF-2020R1C1C1011970 and NRF-2018R1A5A7023490)。
文摘This paper presents a new computational method for forward uncertainty quantification(UQ)analyses on large-scale structural systems in the presence of arbitrary and dependent random inputs.The method consists of a generalized polynomial chaos expansion(GPCE)for statistical moment and reliability analyses associated with the stochastic output and a static reanalysis method to generate the input-output data set.In the reanalysis,we employ substructuring for a structure to isolate its local regions that vary due to random inputs.This allows for avoiding repeated computations of invariant substructures while generating the input-output data set.Combining substructuring with static condensation further improves the computational efficiency of the reanalysis without losing accuracy.Consequently,the GPCE with the static reanalysis method can achieve significant computational saving,thus mitigating the curse of dimensionality to some degree for UQ under high-dimensional inputs.The numerical results obtained from a simple structure indicate that the proposed method for UQ produces accurate solutions more efficiently than the GPCE using full finite element analyses(FEAs).We also demonstrate the efficiency and scalability of the proposed method by executing UQ for a large-scale wing-box structure under ten-dimensional(all-dependent)random inputs.
基金National Natural Science Foundation of China (12002075)National Key Research and Development Project (2021YFB3300601)Natural Science Foundation of Liaoning Province in China (2021-MS-128).
文摘Elastography is a non-invasive medical imaging technique to map the spatial variation of elastic properties of soft tissues.The quality of reconstruction results in elastography is highly sensitive to the noise induced by imaging measurements and processing.To address this issue,we propose a deep learning(DL)model based on conditional Generative Adversarial Networks(cGANs)to improve the quality of nonhomogeneous shear modulus reconstruction.To train this model,we generated a synthetic displacement field with finite element simulation under known nonhomogeneous shear modulus distribution.Both the simulated and experimental displacement fields are used to validate the proposed method.The reconstructed results demonstrate that the DL model with synthetic training data is able to improve the quality of the reconstruction compared with the well-established optimization method.Moreover,we emphasize that our DL model is only trained on synthetic data.This might provide a way to alleviate the challenge of obtaining clinical or experimental data in elastography.Overall,this work addresses several fatal issues in applying the DL technique into elastography,and the proposed method has shown great potential in improving the accuracy of the disease diagnosis in clinical medicine.
基金Project(51275543)supported by the National Natural Science Foundation,ChinaProject(KJ1603804)supported by the Research Projects of Chongqing Commission of Science and Technology,China
文摘To analyze the influence of surface texture on friction properties of Cr12 Mo V', ordinary grinder and spinning technology were adopted to obtain the grooved surface morphology of samples, and then the impact of spindle speed and feed in z-direction on surface morphology in the process of spinning was studied. In addition, the corresponding friction coefficient of sample was obtained through friction and wear tests. The results show that the peak clipping and the valley filling were conducted on the grinding surface, which could improve the surface roughness effectively and make the grinding trench-type wear scar more uniform. Both the area ratio of groove and groove spacing increased initially and then decreased with the increase of the spindle speed or the feed in z-direction. As a kind of micro-process, the groove could influence the friction coefficient of sample surface, whose distribution was beneficial to the reduction of friction coefficient. Compared with the surface obtained through ordinary grinding, grooved surface morphology through spinning technology was more conductive to reduce the friction coefficient, which could be reduced by 25%. When the friction coefficient of sample was reduced to the minimum, the texture of groove corresponded had an optimal area ratio and an optimal groove spacing, 37.5% and 27.5 μm, respectively.
基金supported by the National Natural Science Foundation of China(61403158,61520106008)the Project of the Education Department of Jilin Province(2016-429)
文摘Next-generation vehicle control and future autonomous driving require further advances in vehicle dynamic state estimation. This article provides a concise review, along with the perspectives, of the recent developments in the estimation of vehicle dynamic states. The definitions used in vehicle dynamic state estimation are first introduced, and alternative estimation structures are presented. Then, the sensor configuration schemes used to estimate vehicle velocity, sideslip angle, yaw rate and roll angle are presented. The vehicle models used for vehicle dynamic state estimation are further summarized, and representative estimation approaches are discussed. Future concerns and perspectives for vehicle dynamic state estimation are also discussed.
文摘Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel(diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation(EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24% and 31%,respectively,The NOx emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.
基金supported by the Special Fund for Basic Scientific Research of Central Colleges, Chang'an University (No.CHD2009JC131)
文摘Three kinds of cast iron coatings were prepared by atmospheric plasma spraying. During the spraying, the mild steel substrate temperature was controlled to be averagely 50, 180, and 240°C, respectively. Abrasive wear tests were conducted on the coatings under a dry friction condition. It is found that the abrasive wear resistance is enhanced with the substrate temperature increasing. SEM observations show that the wear losses of the coatings during the wear tests mainly result from the spalling of the splats. Furthermore, the improved wear resistance of the coatings mainly owes to the formation of oxides and the enhancement in the mechanical properties with the substrate temperature increasing.
基金Supported by Tianjin Municipal Science and Technology Commission (No.09JCYBJC02200)
文摘Speech signals in frequency domain were separated based on discrete wavelet transform (DWT) and independent component analysis (ICA). First, mixed speech signals were decomposed into different frequency domains by DWT and the subbands of speech signals were separated using ICA in each wavelet domain; then, the permutation and scaling problems of frequency domain blind source separation (BSS) were solved by utilizing the correlation between adjacent bins in speech signals; at last, source signals were reconstructed from single branches. Experiments were carried out with 2 sources and 6 microphones using speech signals at sampling rate of 40 kHz. The microphones were aligned with 2 sources in front of them, on the left and right. The separation of one male and one female speeches lasted 2.5 s. It is proved that the new method is better than single ICA method and the signal to noise ratio is improved by 1 dB approximately.
基金supported by the Natural Science Foundation of Jiangsu Province(No. BK20151472)the Research Project of Key Laboratory of Advanced Manufacture Technology for Automobile Parts(Chongqing University of Technology) , Ministry of Education (No. 2015KLMT04)
文摘With the worsening of energy crisis and environmental pollution,electric vehicles with four in?wheel motors have been paid more and more attention. The main research subject is how to reasonably distribute the driving torque of each wheel. Considering the longitudinal motion,lateral motion,yaw movement and rotation of the four wheels,the tire model and the seven DOF dynamic model of the vehicle are established in this paper. Then,the torque distribution method is proposed based on road adhesion margin,which can be divided into anti ? slip control layer and torque distribution layer. The anti?slip control layer is built based on sliding mode variable structure control,whose main function is to avoid the excessive slip of wheels caused by road conditions. The torque distribution layer is responsible for selecting the torque distribution method based on road adhesion margin. The simulation results show that the proposed torque distribution method can ensure the vehicle quickly adapt to current road adhesion conditions,and improve the handling stability and dynamic performance of the vehicle in the driving process.
基金supported by a grant (08-K1401-00610) from the Center of Nanoscale Mechatronics and Manufacturingone of the 21st Century Frontier Research Programs which are supported by the Ministry of Education,Science and Technology in Korea,Industry-University Partnership Laboratory Supporting Business"New Professor Support Program from Seoul National University of Technology"
文摘An easy calibration method was presented for in-situ measurement of displacement in the order of nanometer during micro-tensile test for thin films by using CCD camera as a sensing device. The calibration of the sensing camera in the system is a central element part to measure displacement in the order of nanometer using images taken with the camera. This was accomplished by modeling the optical projection through the camera lens and relative locations between the object and camera in 3D space. A set of known 3D points on a plane where the film is located on is projected to an image plane as input data. These points, known as a calibration points, are then used to estimate the projection parameters of the camera. In the measurement system of the micro-scale by CCD camera, the calibration data acquisition and one-to-one matching steps between the image and 3D planes need precise data extraction procedures and repetitive user's operation to calibrate the measuring devices. The lack of the robust image feature extraction and easy matching prevent the practical use of these methods. A data selection method was proposed to overcome these limitations and offer an easy and convenient calibration of a vision system that has the CCD camera and the 3D reference plane with calibration marks of circular type on the surface of the plane. The method minimizes the user's intervention such as the fine tuning of illumination system and provides an efficient calibration method of the vision system for in-situ axial displacement measurement of the micro-tensile materials.
基金Supported by National Natural Science Foundation of China(Grant No.11672127)Major Exploration Project of the General Armaments Department of China(Grant No.NHA13002)+1 种基金Fundamental Research Funds for the Central Universities of China(Grant No.NP2016412,NP2018403,NT2018002)Jiangsu Provincial Innovation Program for Graduate Education and the Fundamental Research Funds for the Central Universities of China(Grant No.KYLX16_0330)
文摘Machining and installation errors are unavoidable in mechanical structures. However, the effect of errors on radial stiffness of the mechanical elastic wheel(ME-Wheel) is not considered in previous studies. To this end, the interval mathematical model and interval finite element model of the ME-Wheel were both established and compared with bench test results. The intercomparison of the influence of the machining and installation errors on the ME-Wheel radial stiffness revealed good consistency among the interval mathematical analysis, interval finite element simulation,and bench test results. Within the interval range of the ME-Wheel machining and installation errors, parametric analysis of the combined elastic rings was performed at different initial radial rigidity values. The results showed that the initial radial stiffness of the flexible tire body significantly influenced the ME-Wheel radial stiffness, and the inverse relationship between the hinge unit length or suspension hub and the radial stiffness was nonlinear. The radial stiffness of the ME-Wheel is predicted by using the interval algorithm for the first time, and the regularity of the radial stiffness between the error and the load on the ME-Wheel is studied, which will lay the foundation for the exact study of the ME-Wheel dynamic characteristics in the future.
文摘A numerical study of the crushing of thin-walled circular aluminum tubes has been carried out to investigate the crashworthiness behaviors under axial impact loading. These kinds of tubes are usually used in automobile and train structures to absorb the impact energy. Previous researches show that thin-walled circular tube has the highest energy absorption under axial impact amongst different structures. In this work, the crushing between two rigid flat plates and the tube rupture by 4 and 6 blades cutting tools is modeled with the help of ductile failure criterion using the numerical method. The tube material is aluminum EN AW-7108 T6 and its length and diameter are 300 mm and 50 mm, respectively. Using the artificial neural network(ANN), the most important surfaces of energy absorption parameters, including the maximum displacement of the striker, the maximum axial force, the specific energy absorption and the crushing force efficiency in terms of impact velocity and tube thickness are obtained and compared to each other. The analyses show that the tube rupture by the 6 blades cutting tool has more energy absorption in comparison with others. Furthermore, the results demonstrate that tube cutting with the help of multi-blades cutting tools is more stable, controllable and predictable than tube folding.
基金This project is supported by National Natural Science Foundation of China(No. 50676107)State Key Laboratory of Automotive Safety and Energyof China (No. KF2006-07).
文摘Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount of fuel injected between two injection pulses and the injection interval is varied keeping the injected fuel quantity constant. Results show that under the 70D90-10 injection pattern, the engine achieves the lower NOx-smoke emissions and BSFC compared with the single injection pattern. The heat release rate and the temperature show that the split injections increase the initial premixed burn and retards the diffusion burn. With the balance of these two effects, the maximum in-cylinder temperature decreases while the 50% heat release point is held at almost the same crank angle. Therefore, both NOx emission and BSFC are improved while keeping the smoke emission at the same level.
文摘The recent trend of vehicle design aims at crash safety and environmentally-friendly aspect. For the crash safety aspect, the energy absorbing members should absorb collision energy sufficiently but for the environmentally-friendly aspect, the vehicle structure must be light weight in order to improve the fuel efficiency and reduce the tail gas emission. Therefore, the light weight of vehicle must be achieved in a securing safety status of crash. An aluminum or carbon fiber reinforced plastics (CFRP) is representative one of the light-weight materials. Based on the respective collapse behavior of aluminum and CFRP member, the collapse behavior of hybrid thin-walled member was evaluated. The hybrid members were manufactured by wrapping CFRP prepreg sheets outside the aluminum hollow members in the autoclave. Because the CFRP is an anisotropic material whose mechanical properties, such as strength and elasticity, change with its stacking condition, the effects of the stacking condition on the collapse behavior evaluation of the hybrid thin-walled member were tested. The collapse mode and energy absorption capability of the hybrid thin-walled member were analyzed with the change of the fiber orientation angle and interface number.
文摘Biodiesel is one of the most popular prospective alternative fuels and can be obtained from a variety of sources. Waste frying oil is one such source along with the various raw vegetable oils. However, some specific technical treatments are required to improve certain fuel properties such as viscosity and calorific value of the biodiesel being obtained from waste cooking oil methyl ester(WCOME). Various treatments are applied depending on the source and therefore the composition of the cooking oil. This research investigated the performance of WCOME as an alternative biofuel in a four-stroke direct injection diesel engine. An 8-mode test was undertaken with diesel fuel and five WCOME blends. The best compromise blend in terms of performance and emissions was identified. Results showed that energy utilization factors of the blends were similar within the range of the operational parameters(speed, load and WCOME content). Increasing biodiesel content produced slightly more smoke and NOx for a great majority of test points, while the CO and THC emissions were lower.
文摘Motion analyses are performed with the help of stability and simulation analysis, which can provide theoretical bases for applications of an electric vehicle with two independent drive motors. Compared with one-motor drive electric vehicle, the two-motor drive electric vehicle has the advantage of easy layout, simple power train and good drivability and handling characteristics. Analysis shows the method connecting armatures of two DC motors in parallel can function as mechanical differential without a steering sensor, which can simplify structure and increase reliability of the controller. Computer simulations and experiment are carried out to verify conclusions.
文摘Volumetric efficiency and air charge estimation is one of the most demanding tasks in control of today's internal combustion engines.Specifically,using three-way catalytic converter involves strict control of the air/fuel ratio around the stoichiometric point and hence requires an accurate model for air charge estimation.However,high degrees of complexity and nonlinearity of the gas flow in the internal combustion engine make air charge estimation a challenging task.This is more obvious in engines with variable valve timing systems in which gas flow is more complex and depends on more functional variables.This results in models that are either quite empirical(such as look-up tables),not having interpretability and extrapolation capability,or physically based models which are not appropriate for onboard applications.Solving these problems,a novel semi-empirical model was proposed in this work which only needed engine speed,load,and valves timings for volumetric efficiency prediction.The accuracy and generalizability of the model is shown by its test on numerical and experimental data from three distinct engines.Normalized test errors are 0.0316,0.0152 and 0.24 for the three engines,respectively.Also the performance and complexity of the model were compared with neural networks as typical black box models.While the complexity of the model is less than half of the complexity of neural networks,and its computational cost is approximately 0.12 of that of neural networks and its prediction capability in the considered case studies is usually more.These results show the superiority of the proposed model over conventional black box models such as neural networks in terms of accuracy,generalizability and computational cost.
文摘The concept of shape factors of the fusion-solidification zone is proposed to describe the weld cross section geometry. According to these shape factors,the electron beam weld fusion-solidification zone is divided into four typical shapes and the classification criterion for these typical shapes is suggested. An integrated parameter n1 combining the line power density of electron beam and material thermal properties is proposed to describe the relative power input,and another integrated parameter n2 combing the accelerating voltage and focusing current is proposed to reflect the power distribution in the keyhole. A series of new expressions,which can reflect the influence of focusing current,accelerating voltage,beam current,and material thermal properties,are developed to predict the fusion-solidification zone shape based on experimental results nonlinear fitting of n1 and n2.
