Experiments with potatoes were carried out in order to analyze the variation of the temperature and the mean dry basis moisture content over time,the effect of the drying conditions on the drying rate,and the relation...Experiments with potatoes were carried out in order to analyze the variation of the temperature and the mean dry basis moisture content over time,the effect of the drying conditions on the drying rate,and the relationship between deformation and dry basis moisture content.A two-way sequentially coupled thermo-hydro-mechanical math model was developed on the basis of Fickian diffusion theory,Fourier’s law of heat conduction and thermoelasticity mechanics in order to analyze the spatio-temporal distributions of moisture,temperature and drying stresses in the potatoes.The transient mathematical model,composed of a system of partial differential equations,was solved by finite difference methods.The numerical results obtained by using the mathematical model were in good agreement with the experimental data.The variations in temperature and moisture distributions,drying curves and stresses within potatoes over time were simulated,and the ways in which these are affected by the drying conditions were discussed.This work could help in developing an understanding of the relationship between mass and heat transfer,shrinkage,stress,and physical degradation of biological materials.展开更多
Surgical simulators need to simulate deformation and cutting of deformable objects. Adaptive octree mesh based cutting methods embed the deformable objects into octree meshes that are recursively refined near the cutt...Surgical simulators need to simulate deformation and cutting of deformable objects. Adaptive octree mesh based cutting methods embed the deformable objects into octree meshes that are recursively refined near the cutting tool trajectory. Deformation is only applied to the octree meshes; thus the deformation instability problem caused by degenerated elements is avoided. Biological tissues and organs usually contain complex internal structures that are ignored by previous work. In this paper the deformable objects are modeled as voxels connected by links and embedded inside adaptive octree meshes. Links swept by the cutting tool are disconnected and object surface meshes are reconstructed from disconnected links. Two novel methods for embedding triangular meshes as internal structures are proposed. The surface mesh embedding method is applicable to arbitrary triangular meshes, but these meshes have no physical properties. The material sub-region embedding method associates the interiors enclosed by the triangular meshes with physical properties, but requires that these meshes are watertight, and have no self-intersections, and their smallest features are larger than a voxel. Some local features are constructed in a pre-calculation stage to increase simulation performance. Simulation tests show that our methods can cut embedded structures in a way consistent with the cutting of the deformable objects. Cut fragments can also deform correctly along with the deformable objects.展开更多
As 3D digital photographic and scanning devices produce higher resolution images, acquired geometric data sets grow more complex in terms of the modeled objects＇ size, geometry, and topology. As a consequence, point-...As 3D digital photographic and scanning devices produce higher resolution images, acquired geometric data sets grow more complex in terms of the modeled objects＇ size, geometry, and topology. As a consequence, point-sampled geometry is becoming ubiquitous in graphics and geometric information processing, and poses new challenges which have not been fully resolved by the state-of-art graphical techniques. In this paper, we address the challenges by proposing a meshless computational framework for dynamic modeling and simulation of solids and thin-shells represented as point sam- ples. Our meshless framework can directly compute the elastic deformation and fracture propagation for any scanned point geometry, without the need of converting them to polygonal meshes or higher order spline representations. We address the necessary computational techniques, such as Moving Least Squares, Hierarchical Discretization, and Modal Warping, to effectively and efficiently compute the physical simulation in real-time. This meahless computational framework aims to bridge the gap between the point-sampled geometry with physics-based modeling and simulation governed by partial differential equations.展开更多
Laparoscopic surgery has many advantages, but it is difficult for a surgeon to achieve the necessary surgical skills. Recently, virtual training simulations have been gaining interest because they can provide a safe a...Laparoscopic surgery has many advantages, but it is difficult for a surgeon to achieve the necessary surgical skills. Recently, virtual training simulations have been gaining interest because they can provide a safe and efficient learning environment for medical students and novice surgeons. In this paper, we present a hybrid modeling method for simulating gallbladder removal that uses both the boundary element method （BEM） and the finite element method （FEM）. Each modeling method is applied according to the deformable properties of human organs： BEM for the liver and FEM for the gallbladder. Connective tissues between the liver and the gallbladder are also included in the surgical simulation. Deformations in the liver and the gallbladder models are transferred via connective tissue springs using a mass-spring method. Special effects and techniques are developed to achieve realistic simulations, and the software is integrated into a custom-designed haptic interface device. Various computer graphical techniques are also applied in the virtual gallbladder removal laparoscopic surgery training. The detailed techniques and the results of the simulations are described in this paper.展开更多
基金the Program for New Century Excellent Talents in Universities(No.NCET-13-0651)。
文摘Experiments with potatoes were carried out in order to analyze the variation of the temperature and the mean dry basis moisture content over time,the effect of the drying conditions on the drying rate,and the relationship between deformation and dry basis moisture content.A two-way sequentially coupled thermo-hydro-mechanical math model was developed on the basis of Fickian diffusion theory,Fourier’s law of heat conduction and thermoelasticity mechanics in order to analyze the spatio-temporal distributions of moisture,temperature and drying stresses in the potatoes.The transient mathematical model,composed of a system of partial differential equations,was solved by finite difference methods.The numerical results obtained by using the mathematical model were in good agreement with the experimental data.The variations in temperature and moisture distributions,drying curves and stresses within potatoes over time were simulated,and the ways in which these are affected by the drying conditions were discussed.This work could help in developing an understanding of the relationship between mass and heat transfer,shrinkage,stress,and physical degradation of biological materials.
文摘Surgical simulators need to simulate deformation and cutting of deformable objects. Adaptive octree mesh based cutting methods embed the deformable objects into octree meshes that are recursively refined near the cutting tool trajectory. Deformation is only applied to the octree meshes; thus the deformation instability problem caused by degenerated elements is avoided. Biological tissues and organs usually contain complex internal structures that are ignored by previous work. In this paper the deformable objects are modeled as voxels connected by links and embedded inside adaptive octree meshes. Links swept by the cutting tool are disconnected and object surface meshes are reconstructed from disconnected links. Two novel methods for embedding triangular meshes as internal structures are proposed. The surface mesh embedding method is applicable to arbitrary triangular meshes, but these meshes have no physical properties. The material sub-region embedding method associates the interiors enclosed by the triangular meshes with physical properties, but requires that these meshes are watertight, and have no self-intersections, and their smallest features are larger than a voxel. Some local features are constructed in a pre-calculation stage to increase simulation performance. Simulation tests show that our methods can cut embedded structures in a way consistent with the cutting of the deformable objects. Cut fragments can also deform correctly along with the deformable objects.
基金Supported by the National Science Foundation (Grant Nos. CCF-0727098, IIS-0710819)
文摘As 3D digital photographic and scanning devices produce higher resolution images, acquired geometric data sets grow more complex in terms of the modeled objects＇ size, geometry, and topology. As a consequence, point-sampled geometry is becoming ubiquitous in graphics and geometric information processing, and poses new challenges which have not been fully resolved by the state-of-art graphical techniques. In this paper, we address the challenges by proposing a meshless computational framework for dynamic modeling and simulation of solids and thin-shells represented as point sam- ples. Our meshless framework can directly compute the elastic deformation and fracture propagation for any scanned point geometry, without the need of converting them to polygonal meshes or higher order spline representations. We address the necessary computational techniques, such as Moving Least Squares, Hierarchical Discretization, and Modal Warping, to effectively and efficiently compute the physical simulation in real-time. This meahless computational framework aims to bridge the gap between the point-sampled geometry with physics-based modeling and simulation governed by partial differential equations.
基金supported by the Ministry of Culture, Sports and Tourism and the Korea Creative Content Agency in the Culture Technology Research & Development Program 2009supported in part by the Korea Institute of Science and Technology Institutional Program under Grant No. 2E23780
文摘Laparoscopic surgery has many advantages, but it is difficult for a surgeon to achieve the necessary surgical skills. Recently, virtual training simulations have been gaining interest because they can provide a safe and efficient learning environment for medical students and novice surgeons. In this paper, we present a hybrid modeling method for simulating gallbladder removal that uses both the boundary element method （BEM） and the finite element method （FEM）. Each modeling method is applied according to the deformable properties of human organs： BEM for the liver and FEM for the gallbladder. Connective tissues between the liver and the gallbladder are also included in the surgical simulation. Deformations in the liver and the gallbladder models are transferred via connective tissue springs using a mass-spring method. Special effects and techniques are developed to achieve realistic simulations, and the software is integrated into a custom-designed haptic interface device. Various computer graphical techniques are also applied in the virtual gallbladder removal laparoscopic surgery training. The detailed techniques and the results of the simulations are described in this paper.
