To explore the safety of highway traffic operations,the vehicle state and guardrail deformation during highway guardrail collisions are simulated and analyzed.The vehicle-guardrail collision is simulated by finite ele...To explore the safety of highway traffic operations,the vehicle state and guardrail deformation during highway guardrail collisions are simulated and analyzed.The vehicle-guardrail collision is simulated by finite element software such as LS-DYNA and HyperMesh.The vehicle speed settings are 60,80,100 and 120 km/h,and the collision angles are 5°,10°,15°and 20°.The guardrail deformation,vehicle acceleration and energy changes under different collision speeds and angles are studied.The research results show that at the same collision speed,an increase in the collision angle causes more serious damage to the vehicle,a greater transverse displacement of the guardrail,and a greater range of car acceleration fluctuations.When the collision angle is the same,an increase in the collision speed causes greater lateral displacement of the guardrail,a greater vehicle acceleration fluctuation range,and more serious vehicle damage.The results of the study can provide a reference for demonstrating highway guardrail safety.展开更多
A global planning algorithm for intelligent vehicles is designed based on the A* algorithm, which provides intelligent vehicles with a global path towards their destinations. A distributed real-time multiple vehicle c...A global planning algorithm for intelligent vehicles is designed based on the A* algorithm, which provides intelligent vehicles with a global path towards their destinations. A distributed real-time multiple vehicle collision avoidance(MVCA)algorithm is proposed by extending the reciprocal n-body collision avoidance method. MVCA enables the intelligent vehicles to choose their destinations and control inputs independently,without needing to negotiate with each other or with the coordinator. Compared to the centralized trajectory-planning algorithm, MVCA reduces computation costs and greatly improves the robustness of the system. Because the destination of each intelligent vehicle can be regarded as private, which can be protected by MVCA, at the same time MVCA can provide a real-time trajectory planning for intelligent vehicles. Therefore,MVCA can better improve the safety of intelligent vehicles. The simulation was conducted in MATLAB, including crossroads scene simulation and circular exchange position simulation. The results show that MVCA behaves safely and reliably. The effects of latency and packet loss on MVCA are also statistically investigated through theoretically formulating broadcasting process based on one-dimensional Markov chain. The results uncover that the tolerant delay should not exceed the half of deciding cycle of trajectory planning, and shortening the sending interval could alleviate the negative effects caused by the packet loss to an extent. The cases of short delay(< 100100 ms) and low packet loss(< 5%) can bring little influence to those trajectory planning algorithms that only depend on V2 V to sense the context, but the unpredictable collision may occur if the delay and packet loss are further worsened. The MVCA was also tested by a real intelligent vehicle, the test results prove the operability of MVCA.展开更多
Based on the basic principle of vehicle crash analysis using the finite element method, a car finite element model was built by using Hypermesh software. To simulate the front collision test of the car, the LS-DYNA so...Based on the basic principle of vehicle crash analysis using the finite element method, a car finite element model was built by using Hypermesh software. To simulate the front collision test of the car, the LS-DYNA software is adopted to calculate the deformation of the car and the acceleration time history curves during the crashing process;the anti-impact capability of the car is evaluated from this simulation. The results demonstrate that the improvement of local structure can promote the crashworthiness of the car, but the further improvement needs a major change of the car structure.展开更多
The max collision force of ship-bridge collision is one of the most importantreferences for bridge design. By mean linear digital simulation method, the collision forces ofthe collisions between rigid bridge pier and ...The max collision force of ship-bridge collision is one of the most importantreferences for bridge design. By mean linear digital simulation method, the collision forces ofthe collisions between rigid bridge pier and ship bow were calculated out for four different ships,whose tonnages are 5 000,10 000,50 000 and 60 000 DWT respectively. Curves of collisionforce-penetration and absorbed energy-penetration are obtained, and the data of the max loads arethen summarized. On the basis of these curves and data, a set of curves describing therelationships between max collision forces and tonnages of the ships are successfully presented, bywhich the max collision forces of the ships-bridge with different tonnages and in differentvelocities can be estimated easily and reliably.展开更多
We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms.Our numerical algorithm consistently deals wi...We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms.Our numerical algorithm consistently deals with both long-range(classical forces in the Vlasov term)and short-range(quantum processes in the collision term)interactions.Providing the relevant particle masses,charges and types(classical,fermionic or bosonic),as well as the external forces and the matrix elements(in the collisional integral),the algorithm consistently solves the coupled multi-particle kinetic equations.Currently,the framework is being tested and applied in the field of relativistic heavy-ion collisions;extensions to other plasma systems are straightforward.Our framework is a potential and competitive numerical platform for consistent plasma simulations.展开更多
Using CAE tools based on nonlinear finite element methods, full-frontalcollision dynamic simulation and analysis of a sedan car body with 3D tubular load bearing frame aretentatively carried out. Time histories of the...Using CAE tools based on nonlinear finite element methods, full-frontalcollision dynamic simulation and analysis of a sedan car body with 3D tubular load bearing frame aretentatively carried out. Time histories of the main collisional parameters are presented,improvements of the frame are partially made according to simulation results. Collisional simulationof the tubular frame alone indicates that, such new type of bodywork for sedan car is of goodpotentialities to meet the collision safety regulations.展开更多
The electron swarm parameters of SF6/N2 are calculated in the present study using an improved Monte Carlo collision simulation method (MCS). And some improved sampling techniques are also adopted. The simulation res...The electron swarm parameters of SF6/N2 are calculated in the present study using an improved Monte Carlo collision simulation method (MCS). And some improved sampling techniques are also adopted. The simulation results show that the improved simulation method can provide more accurate results.展开更多
The main ion-atomic collision treatment methods based on Monte-Carlo simulation are considered and discussed. We have proposed an efficient scheme for simulation of time between collisions taking into account cross-se...The main ion-atomic collision treatment methods based on Monte-Carlo simulation are considered and discussed. We have proposed an efficient scheme for simulation of time between collisions taking into account cross-section dependence on ion velocity and random generation of ion velocities and scattering angles after collisions. The developed algorithm of simulation of interval between collisions takes into account the change of relative velocity of ion-atom pair as well as the change of cross-section of collision and atomic concentration. At the same time, unlike the widely used “null-collision” method, both the probability of collision and change of particles’ state which determines this probability are taken into consideration for each particle independently in time. The simulation results according to the techniques proposed are found to be close to the theoretical values of ion drift velocities. It is revealed that the “null-collision” method results in exceeding of drift velocity in strong and intermediate fields. At the same time the proposed method of accumulation of probability under the same conditions gives values close to theoretical ones. In weak fields calculated values of drift velocity in both methods exceed theoretical values to some small extent.展开更多
In this review we discuss the recent progress in the simulation of soft active matter systems and in particular the hydrodynamics of microswimmers using the method of multiparticle collision dynamics,which solves the ...In this review we discuss the recent progress in the simulation of soft active matter systems and in particular the hydrodynamics of microswimmers using the method of multiparticle collision dynamics,which solves the hydrodynamic flows around active objects on a coarse-grained level.We first present a brief overview of the basic simulation method and the coupling between microswimmers and fluid.We then review the current achievements in simulating flexible and rigid microswimmers using multiparticle collision dynamics,and briefly conclude and discuss possible future directions.展开更多
Deep simulations have gained widespread attention owing to their excellent acceleration performances.However,these methods cannot provide effective collision detection and response strategies.We propose a deep interac...Deep simulations have gained widespread attention owing to their excellent acceleration performances.However,these methods cannot provide effective collision detection and response strategies.We propose a deep interac-tive physical simulation framework that can effectively address tool-object collisions.The framework can predict the dynamic information by considering the collision state.In particular,the graph neural network is chosen as the base model,and a collision-aware recursive regression module is introduced to update the network parameters recursively using interpenetration distances calculated from the vertex-face and edge-edge tests.Additionally,a novel self-supervised collision term is introduced to provide a more compact collision response.This study extensively evaluates the proposed method and shows that it effectively reduces interpenetration artifacts while ensuring high simulation efficiency.展开更多
Using stochastic dynamic simulation for railway vehicle collision still faces many challenges,such as high modelling complexity and time-consuming.To address the challenges,we introduce a novel data-driven stochastic ...Using stochastic dynamic simulation for railway vehicle collision still faces many challenges,such as high modelling complexity and time-consuming.To address the challenges,we introduce a novel data-driven stochastic process modelling(DSPM)approach into dynamic simulation of the railway vehicle collision.This DSPM approach consists of two steps:(i)process description,four kinds of kernels are used to describe the uncertainty inherent in collision processes;(ii)solving,stochastic variational inferences and mini-batch algorithms can then be used to accelerate computations of stochastic processes.By applying DSPM,Gaussian process regression(GPR)and finite element(FE)methods to two collision scenarios(i.e.lead car colliding with a rigid wall,and the lead car colliding with another lead car),we are able to achieve a comprehensive analysis.The comparison between the DSPM approach and the FE method revealed that the DSPM approach is capable of calculating the corresponding confidence interval,simultaneously improving the overall computational efficiency.Comparing the DSPM approach with the GPR method indicates that the DSPM approach has the ability to accurately describe the dynamic response under unknown conditions.Overall,this research demonstrates the feasibility and usability of the proposed DSPM approach for stochastic dynamics simulation of the railway vehicle collision.展开更多
Collision properties of minibus when traveling at high speed are studied. Based on the display dynamics and basic theoretical of contact collision analysis, the front crash finite element model of minibus is built by ...Collision properties of minibus when traveling at high speed are studied. Based on the display dynamics and basic theoretical of contact collision analysis, the front crash finite element model of minibus is built by Hypermesh. The model is simulated under the 50 km/h by ANSYS/Ls-Dyna solver. Finally, the deformation of the front rail, B pillar acceleration curve and the steering column intrusion are got. It is important to improve safety design for minibus.展开更多
This paper describes an algorithm of collision detection between moving objects in machin-ing process simulation. Graphical simulation of machining has been recognized to be useful for NCprogram verification , since t...This paper describes an algorithm of collision detection between moving objects in machin-ing process simulation. Graphical simulation of machining has been recognized to be useful for NCprogram verification , since the programmer of the machining operator can easily find some faults inthe NC program visually. But it is difficult to visually detect collisions arnong moving objects such ascutting tools , workpieces and fixtures, a data structure to represent moving objects and an algorithmof collision detection between moving objects are proposed. A moving object can be represented by ahierarchical sphere octree and its motion can be described by a quadratic function of time. A collisionoccurs in the case that the distance between any two sphere centers in the respective two moving ob-jects is equal to the sum of the radii of these two spheres, and the radii of these two spheres are lessthan a given precision. By solving the equations that satisfy the conditions of collision between thespheres recursively , we obtain the time and the position of the collision between these two moving ob-Jects.展开更多
At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines (OWT) is of g...At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines (OWT) is of great practical signifieance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic proeess of the collision between a typical 3MW offshore wind turbine model with monopile fi)undation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and aluminum foam and adaptive mesh tectmique for large structure deformation have been taken into considera- tion. Proposed is a crashworthy device for OWF of new conceptual steel sphere shell-cireular ring aluminum foam pad, and the good pe.rfurmanee of the device under the conditions of ship-OWT front impact and side impact has been verified from the views of theoretical analysis and numerical results. The new crashworthy device can effectively smooth the contact force and reduce the top structure dynamic response, using its own structure plastic deformation to absorb most of the ship collision enerty. As a result, the main structure of the OWF and the inside key electric control equipments can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. What is more, the sphere configuratiun design of the crashworthy device can effectively guide the ship to run away from the main OWT structure and reduce the damage of the ship and OWT to some degree during side impact.展开更多
Collision avoidance decision-making models of multiple agents in virtual driving environment are studied. Based on the behavioral characteristics and hierarchical structure of the collision avoidance decision-making i...Collision avoidance decision-making models of multiple agents in virtual driving environment are studied. Based on the behavioral characteristics and hierarchical structure of the collision avoidance decision-making in real life driving, delphi approach and mathematical statistics method are introduced to construct pair-wise comparison judgment matrix of collision avoidance decision choices to each collision situation. Analytic hierarchy process (AHP) is adopted to establish the agents' collision avoidance decision-making model. To simulate drivers' characteristics, driver factors are added to categorize driving modes into impatient mode, normal mode, and the cautious mode. The results show that this model can simulate human's thinking process, and the agents in the virtual environment can deal with collision situations and make decisions to avoid collisions without intervention. The model can also reflect diversity and uncertainly of real life driving behaviors, and solves the multi-objective, multi-choice ranking priority problem in multi-vehicle collision scenarios. This collision avoidance model of multi-agents model is feasible and effective, and can provide richer and closer-to-life virtual scene for driving simulator, reflecting real-life traffic environment more truly, this model can also promote the practicality of driving simulator.展开更多
For a screening process, the collision and penetration phenomena between particles and screen plate is standard behavior and with collision the mechanical energy of the vibrating screen can be transmitted to the feed....For a screening process, the collision and penetration phenomena between particles and screen plate is standard behavior and with collision the mechanical energy of the vibrating screen can be transmitted to the feed. In order to recognize further the collision process and the law of penetrating motion, with the spring-dashpot-slider contact model of the distinct element method (DEM), a mathematical model which can describe the collision process has been established and a program for simulating the motion of a single particle on the screen plate developed by VC++. NET. To evaluate the handling capacity of the screen that deals with difficult screening material, an instantaneous penetrating coefficient is defined. The moving period of the screen plate is divided into four stages. By analyzing the state of contact collision at each stage, it is pointed out that the collision ranging from 3π/2 to 2π period is the most favorable aperture for penetration of particles, while the collision ranging from π/2 to n period is the most unfavorable. The numerical simulation result further indicates that increasing the amplitude of the screen plate has a much greater effect on the augmentation of instantaneous penetration coefficient than increasing the vibration frequency.展开更多
Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical ...Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical Weber number(We) was used to evaluate the coalescence or separation of droplets. The relationship between the collision parameter and the critical We indicated whether slow coalescence or bouncing of droplets occurred. The critical We was 5.5, which means that the droplets gradually coalesce when We ≤ 5.5, whereas they bounce when We > 5.5. For the carbonate wire feeding into liquid steel, a mathematical model implementing a combined computational fluid dynamics(CFD)–discrete element method(DEM) approach was developed to simulate the movement and coalescence of variably sized droplets in a bottom-argon-blowing ladle. In the CFD model, the flow field was solved on the premise that the fluid was a continuous medium. Meanwhile, the droplets were dispersed in the DEM model, and the coalescence criterion of the particles was added to simulate the collision-coalescence process of the particles. The numerical simulation results and observations of inclusion coalescence in steel samples are consistent.展开更多
基金supported by the Key Lab of Road Structure&Material in Chang’an University,Ministry of Transport(grant number 300102212504)by the National Natural Science Foundation of China(grant number 71771047).
文摘To explore the safety of highway traffic operations,the vehicle state and guardrail deformation during highway guardrail collisions are simulated and analyzed.The vehicle-guardrail collision is simulated by finite element software such as LS-DYNA and HyperMesh.The vehicle speed settings are 60,80,100 and 120 km/h,and the collision angles are 5°,10°,15°and 20°.The guardrail deformation,vehicle acceleration and energy changes under different collision speeds and angles are studied.The research results show that at the same collision speed,an increase in the collision angle causes more serious damage to the vehicle,a greater transverse displacement of the guardrail,and a greater range of car acceleration fluctuations.When the collision angle is the same,an increase in the collision speed causes greater lateral displacement of the guardrail,a greater vehicle acceleration fluctuation range,and more serious vehicle damage.The results of the study can provide a reference for demonstrating highway guardrail safety.
基金supported by the National Natural Science Foundation of China(61572229,6171101066)the Key Scientific and Technological Projects for Jilin Province Development Plan(20170204074GX,20180201068GX)Jilin Provincial International Cooperation Foundation(20180414015GH)。
文摘A global planning algorithm for intelligent vehicles is designed based on the A* algorithm, which provides intelligent vehicles with a global path towards their destinations. A distributed real-time multiple vehicle collision avoidance(MVCA)algorithm is proposed by extending the reciprocal n-body collision avoidance method. MVCA enables the intelligent vehicles to choose their destinations and control inputs independently,without needing to negotiate with each other or with the coordinator. Compared to the centralized trajectory-planning algorithm, MVCA reduces computation costs and greatly improves the robustness of the system. Because the destination of each intelligent vehicle can be regarded as private, which can be protected by MVCA, at the same time MVCA can provide a real-time trajectory planning for intelligent vehicles. Therefore,MVCA can better improve the safety of intelligent vehicles. The simulation was conducted in MATLAB, including crossroads scene simulation and circular exchange position simulation. The results show that MVCA behaves safely and reliably. The effects of latency and packet loss on MVCA are also statistically investigated through theoretically formulating broadcasting process based on one-dimensional Markov chain. The results uncover that the tolerant delay should not exceed the half of deciding cycle of trajectory planning, and shortening the sending interval could alleviate the negative effects caused by the packet loss to an extent. The cases of short delay(< 100100 ms) and low packet loss(< 5%) can bring little influence to those trajectory planning algorithms that only depend on V2 V to sense the context, but the unpredictable collision may occur if the delay and packet loss are further worsened. The MVCA was also tested by a real intelligent vehicle, the test results prove the operability of MVCA.
文摘Based on the basic principle of vehicle crash analysis using the finite element method, a car finite element model was built by using Hypermesh software. To simulate the front collision test of the car, the LS-DYNA software is adopted to calculate the deformation of the car and the acceleration time history curves during the crashing process;the anti-impact capability of the car is evaluated from this simulation. The results demonstrate that the improvement of local structure can promote the crashworthiness of the car, but the further improvement needs a major change of the car structure.
文摘The max collision force of ship-bridge collision is one of the most importantreferences for bridge design. By mean linear digital simulation method, the collision forces ofthe collisions between rigid bridge pier and ship bow were calculated out for four different ships,whose tonnages are 5 000,10 000,50 000 and 60 000 DWT respectively. Curves of collisionforce-penetration and absorbed energy-penetration are obtained, and the data of the max loads arethen summarized. On the basis of these curves and data, a set of curves describing therelationships between max collision forces and tonnages of the ships are successfully presented, bywhich the max collision forces of the ships-bridge with different tonnages and in differentvelocities can be estimated easily and reliably.
基金supported by National Natural Science Foundation of China(No.12105227)。
文摘We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms.Our numerical algorithm consistently deals with both long-range(classical forces in the Vlasov term)and short-range(quantum processes in the collision term)interactions.Providing the relevant particle masses,charges and types(classical,fermionic or bosonic),as well as the external forces and the matrix elements(in the collisional integral),the algorithm consistently solves the coupled multi-particle kinetic equations.Currently,the framework is being tested and applied in the field of relativistic heavy-ion collisions;extensions to other plasma systems are straightforward.Our framework is a potential and competitive numerical platform for consistent plasma simulations.
基金This project is supported by Provincial Science Foundation of Guangdong, China (No.990574).
文摘Using CAE tools based on nonlinear finite element methods, full-frontalcollision dynamic simulation and analysis of a sedan car body with 3D tubular load bearing frame aretentatively carried out. Time histories of the main collisional parameters are presented,improvements of the frame are partially made according to simulation results. Collisional simulationof the tubular frame alone indicates that, such new type of bodywork for sedan car is of goodpotentialities to meet the collision safety regulations.
基金National Natural Science Foundation of China(Nos.50607004,90715029)the Science Foundation of Hunan University,China
文摘The electron swarm parameters of SF6/N2 are calculated in the present study using an improved Monte Carlo collision simulation method (MCS). And some improved sampling techniques are also adopted. The simulation results show that the improved simulation method can provide more accurate results.
文摘The main ion-atomic collision treatment methods based on Monte-Carlo simulation are considered and discussed. We have proposed an efficient scheme for simulation of time between collisions taking into account cross-section dependence on ion velocity and random generation of ion velocities and scattering angles after collisions. The developed algorithm of simulation of interval between collisions takes into account the change of relative velocity of ion-atom pair as well as the change of cross-section of collision and atomic concentration. At the same time, unlike the widely used “null-collision” method, both the probability of collision and change of particles’ state which determines this probability are taken into consideration for each particle independently in time. The simulation results according to the techniques proposed are found to be close to the theoretical values of ion drift velocities. It is revealed that the “null-collision” method results in exceeding of drift velocity in strong and intermediate fields. At the same time the proposed method of accumulation of probability under the same conditions gives values close to theoretical ones. In weak fields calculated values of drift velocity in both methods exceed theoretical values to some small extent.
基金This project acknowledges funding from the Austrian Science Fund(FWF)through a Lise-Meitner Fellowship(Grant No.M 2458-N36)。
文摘In this review we discuss the recent progress in the simulation of soft active matter systems and in particular the hydrodynamics of microswimmers using the method of multiparticle collision dynamics,which solves the hydrodynamic flows around active objects on a coarse-grained level.We first present a brief overview of the basic simulation method and the coupling between microswimmers and fluid.We then review the current achievements in simulating flexible and rigid microswimmers using multiparticle collision dynamics,and briefly conclude and discuss possible future directions.
基金This project was funded by Natural Science Foundation of Guangdong Province,No.2020B010165004。
文摘Deep simulations have gained widespread attention owing to their excellent acceleration performances.However,these methods cannot provide effective collision detection and response strategies.We propose a deep interac-tive physical simulation framework that can effectively address tool-object collisions.The framework can predict the dynamic information by considering the collision state.In particular,the graph neural network is chosen as the base model,and a collision-aware recursive regression module is introduced to update the network parameters recursively using interpenetration distances calculated from the vertex-face and edge-edge tests.Additionally,a novel self-supervised collision term is introduced to provide a more compact collision response.This study extensively evaluates the proposed method and shows that it effectively reduces interpenetration artifacts while ensuring high simulation efficiency.
基金supported by the National Key Research and Development Project(No.2019YFB1405401)the National Natural Science Foundation of China(No.5217120056)。
文摘Using stochastic dynamic simulation for railway vehicle collision still faces many challenges,such as high modelling complexity and time-consuming.To address the challenges,we introduce a novel data-driven stochastic process modelling(DSPM)approach into dynamic simulation of the railway vehicle collision.This DSPM approach consists of two steps:(i)process description,four kinds of kernels are used to describe the uncertainty inherent in collision processes;(ii)solving,stochastic variational inferences and mini-batch algorithms can then be used to accelerate computations of stochastic processes.By applying DSPM,Gaussian process regression(GPR)and finite element(FE)methods to two collision scenarios(i.e.lead car colliding with a rigid wall,and the lead car colliding with another lead car),we are able to achieve a comprehensive analysis.The comparison between the DSPM approach and the FE method revealed that the DSPM approach is capable of calculating the corresponding confidence interval,simultaneously improving the overall computational efficiency.Comparing the DSPM approach with the GPR method indicates that the DSPM approach has the ability to accurately describe the dynamic response under unknown conditions.Overall,this research demonstrates the feasibility and usability of the proposed DSPM approach for stochastic dynamics simulation of the railway vehicle collision.
基金This research was financially supported by the Fund Project: Chongqing Jiaotong University graduate education innovation fund project (Grant NO. 20130138) and Natural Science Foundation of science and technology commission of Chongqing (Grant NO. cstc2013jjB 60001).
文摘Collision properties of minibus when traveling at high speed are studied. Based on the display dynamics and basic theoretical of contact collision analysis, the front crash finite element model of minibus is built by Hypermesh. The model is simulated under the 50 km/h by ANSYS/Ls-Dyna solver. Finally, the deformation of the front rail, B pillar acceleration curve and the steering column intrusion are got. It is important to improve safety design for minibus.
文摘This paper describes an algorithm of collision detection between moving objects in machin-ing process simulation. Graphical simulation of machining has been recognized to be useful for NCprogram verification , since the programmer of the machining operator can easily find some faults inthe NC program visually. But it is difficult to visually detect collisions arnong moving objects such ascutting tools , workpieces and fixtures, a data structure to represent moving objects and an algorithmof collision detection between moving objects are proposed. A moving object can be represented by ahierarchical sphere octree and its motion can be described by a quadratic function of time. A collisionoccurs in the case that the distance between any two sphere centers in the respective two moving ob-jects is equal to the sum of the radii of these two spheres, and the radii of these two spheres are lessthan a given precision. By solving the equations that satisfy the conditions of collision between thespheres recursively , we obtain the time and the position of the collision between these two moving ob-Jects.
基金supported by the National Natural Science Foundation of China(Grant No.50538020)the National Science and Technology Planning(Grant No.2006BAJ03B00)
文摘At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines (OWT) is of great practical signifieance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic proeess of the collision between a typical 3MW offshore wind turbine model with monopile fi)undation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and aluminum foam and adaptive mesh tectmique for large structure deformation have been taken into considera- tion. Proposed is a crashworthy device for OWF of new conceptual steel sphere shell-cireular ring aluminum foam pad, and the good pe.rfurmanee of the device under the conditions of ship-OWT front impact and side impact has been verified from the views of theoretical analysis and numerical results. The new crashworthy device can effectively smooth the contact force and reduce the top structure dynamic response, using its own structure plastic deformation to absorb most of the ship collision enerty. As a result, the main structure of the OWF and the inside key electric control equipments can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. What is more, the sphere configuratiun design of the crashworthy device can effectively guide the ship to run away from the main OWT structure and reduce the damage of the ship and OWT to some degree during side impact.
基金supported by National Basic Research Program (973 Program,No.2004CB719402)National Natural Science Foundation of China (No.60736019)Natural Science Foundation of Zhejiang Province, China(No.Y105430).
文摘Collision avoidance decision-making models of multiple agents in virtual driving environment are studied. Based on the behavioral characteristics and hierarchical structure of the collision avoidance decision-making in real life driving, delphi approach and mathematical statistics method are introduced to construct pair-wise comparison judgment matrix of collision avoidance decision choices to each collision situation. Analytic hierarchy process (AHP) is adopted to establish the agents' collision avoidance decision-making model. To simulate drivers' characteristics, driver factors are added to categorize driving modes into impatient mode, normal mode, and the cautious mode. The results show that this model can simulate human's thinking process, and the agents in the virtual environment can deal with collision situations and make decisions to avoid collisions without intervention. The model can also reflect diversity and uncertainly of real life driving behaviors, and solves the multi-objective, multi-choice ranking priority problem in multi-vehicle collision scenarios. This collision avoidance model of multi-agents model is feasible and effective, and can provide richer and closer-to-life virtual scene for driving simulator, reflecting real-life traffic environment more truly, this model can also promote the practicality of driving simulator.
基金Projects 50025411 supported by the China National Science Foundation for Distinguished Young Scholars 92010035 by National Natural Science Foun-dation of China 20030290015 by the Specific Research Foundation for Doctor Discipline of Colleges and Universities
文摘For a screening process, the collision and penetration phenomena between particles and screen plate is standard behavior and with collision the mechanical energy of the vibrating screen can be transmitted to the feed. In order to recognize further the collision process and the law of penetrating motion, with the spring-dashpot-slider contact model of the distinct element method (DEM), a mathematical model which can describe the collision process has been established and a program for simulating the motion of a single particle on the screen plate developed by VC++. NET. To evaluate the handling capacity of the screen that deals with difficult screening material, an instantaneous penetrating coefficient is defined. The moving period of the screen plate is divided into four stages. By analyzing the state of contact collision at each stage, it is pointed out that the collision ranging from 3π/2 to 2π period is the most favorable aperture for penetration of particles, while the collision ranging from π/2 to n period is the most unfavorable. The numerical simulation result further indicates that increasing the amplitude of the screen plate has a much greater effect on the augmentation of instantaneous penetration coefficient than increasing the vibration frequency.
基金financially supported by the National Natural Science Foundation of China (No. 51374081)
文摘Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical Weber number(We) was used to evaluate the coalescence or separation of droplets. The relationship between the collision parameter and the critical We indicated whether slow coalescence or bouncing of droplets occurred. The critical We was 5.5, which means that the droplets gradually coalesce when We ≤ 5.5, whereas they bounce when We > 5.5. For the carbonate wire feeding into liquid steel, a mathematical model implementing a combined computational fluid dynamics(CFD)–discrete element method(DEM) approach was developed to simulate the movement and coalescence of variably sized droplets in a bottom-argon-blowing ladle. In the CFD model, the flow field was solved on the premise that the fluid was a continuous medium. Meanwhile, the droplets were dispersed in the DEM model, and the coalescence criterion of the particles was added to simulate the collision-coalescence process of the particles. The numerical simulation results and observations of inclusion coalescence in steel samples are consistent.