The cutting simulation of soft tissue is important in virtual surgery.It includes three major challenges in computation:Soft tissue simulation,collision detection,and handling,as well as soft tissue models.In order to...The cutting simulation of soft tissue is important in virtual surgery.It includes three major challenges in computation:Soft tissue simulation,collision detection,and handling,as well as soft tissue models.In order to address the earlier challenges,we propose a virtual cutting system based on the mass-spring model.In this system,MSM is utilized to simulate the soft tissue model.Residual stress is introduced to the model for simulating the shrinking effect of soft tissue in cutting.Second,a cylinder-based collision detection method is used to supervise the collision between surgical tools and soft tissue.Third,we simulate the cutting operation with a three-stage cutting method with swept volume,B´ezier curve,and an algorithm named shortest distance nodes matching method.In order to verify the system performance,we carry out three validation experiments on the proposed system:Cutting accuracy experiment,collision detection validation,and practical cutting evaluation.Experiments indicate that our system can well perform the shrinking effect of soft tissue in cutting.The system has fast and accurate collision detection.Moreover,the system can reconstruct smooth incisions vividly.展开更多
Fuel spray is the pivotal process of direct injection engine combustion.The accuracy of spray simula- tion determines the reliability of combustion calculation.However,the traditional techniques of spray simulation in...Fuel spray is the pivotal process of direct injection engine combustion.The accuracy of spray simula- tion determines the reliability of combustion calculation.However,the traditional techniques of spray simulation in KIVA and commercial CFD codes are very susceptible to grid resolution.As a conse- quence,predicted engine performance and emission can depend on the computational mesh.The two main causes of this problem are the droplet collision algorithm and coupling between gas and liquid phases.In order to improve the accuracy of spray simulation,the original KIVA code is modified using the cross mesh droplet collision(CMC)algorithm and gas phase velocity interpolation algorithm.In the constant volume apparatus and D.I.diesel engine,the improvements of the modified KIVA code in spray simulation accuracy are checked from spray structure,predicted average drop size and spray tip penetration,respectively.The results show a dramatic decrease in grid dependency.With these changes,the distorted phenomenon of spray structure is vanished.The uncertainty in predicted aver- age drop size is reduced from 30 to 5μm in constant volume apparatus calculation,and the uncertainty is further reduced to 2μm in an engine simulation.The predicted spray tip penetrations in engine simulation also have better consistency in medium and fine meshes.展开更多
The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the re...The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.展开更多
基金This work was supported,in part,by the National Nature Science Foundation of China under Grant Nos.61502240,61502096,61304205,61773219in part,by the Natural Science Foundation of Jiangsu Province under Grant Nos.BK20191401 and BK20201136+2 种基金in part,by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)fundin part,by the Collaborative Innovation Center of Atmospheric Environment and Equipment Technology(CICAEET)fundNUIST Students’Platform for Innovation and Entrepreneurship Training Program.
文摘The cutting simulation of soft tissue is important in virtual surgery.It includes three major challenges in computation:Soft tissue simulation,collision detection,and handling,as well as soft tissue models.In order to address the earlier challenges,we propose a virtual cutting system based on the mass-spring model.In this system,MSM is utilized to simulate the soft tissue model.Residual stress is introduced to the model for simulating the shrinking effect of soft tissue in cutting.Second,a cylinder-based collision detection method is used to supervise the collision between surgical tools and soft tissue.Third,we simulate the cutting operation with a three-stage cutting method with swept volume,B´ezier curve,and an algorithm named shortest distance nodes matching method.In order to verify the system performance,we carry out three validation experiments on the proposed system:Cutting accuracy experiment,collision detection validation,and practical cutting evaluation.Experiments indicate that our system can well perform the shrinking effect of soft tissue in cutting.The system has fast and accurate collision detection.Moreover,the system can reconstruct smooth incisions vividly.
基金Supported by the National Basic Research Program of China(Grant No.2001CB209207)and the National Natural Science Foundation of China(Grant No.50676036)
文摘Fuel spray is the pivotal process of direct injection engine combustion.The accuracy of spray simula- tion determines the reliability of combustion calculation.However,the traditional techniques of spray simulation in KIVA and commercial CFD codes are very susceptible to grid resolution.As a conse- quence,predicted engine performance and emission can depend on the computational mesh.The two main causes of this problem are the droplet collision algorithm and coupling between gas and liquid phases.In order to improve the accuracy of spray simulation,the original KIVA code is modified using the cross mesh droplet collision(CMC)algorithm and gas phase velocity interpolation algorithm.In the constant volume apparatus and D.I.diesel engine,the improvements of the modified KIVA code in spray simulation accuracy are checked from spray structure,predicted average drop size and spray tip penetration,respectively.The results show a dramatic decrease in grid dependency.With these changes,the distorted phenomenon of spray structure is vanished.The uncertainty in predicted aver- age drop size is reduced from 30 to 5μm in constant volume apparatus calculation,and the uncertainty is further reduced to 2μm in an engine simulation.The predicted spray tip penetrations in engine simulation also have better consistency in medium and fine meshes.
基金supported by the National Natural Science Foundation of China(Grants No.11361002 and 91230111)the Natural Science Foundation of Ningxia,China(Grant No.NZ13086)+1 种基金the Project of Beifang University of Nationalities,China(Grant No.2012XZK05)the Foreign Expert Project of Beifang University of Nationalities,China,and the Visiting Scholar Foundation of State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,China(Grant No.2013A011)
文摘The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.
