Mass-Spring Model for Simulation of Heart Valve Tissue Mechanical Behavior

Heart valves are functionally complex, making surgical repair difficult. Simulation-based surgical planning could facilitate repair, but current finite element (FE) studies are prohibitively slow for rapid, clinically oriented simulations. Mass-spring (M-S) models are fast but can be inaccurate. We quantify speed and accuracy differences between an anisotropic, nonlinear M-S and an efficient FE membrane model for simulating both biaxial and pressure loading of aortic valve (AV) leaflets. The FE model incurs approximately 10 times the computational cost of the M-S model. For simulated biaxial loading, mean error in normal strains is <1% for both FE and M-S models for equibiaxial loading but increases for non-equibiaxial states for the M-S model (7%). The M-S model was less able to simulate shear behavior, with mean strain error of approximately 80%. For pressurized AV leaflets, the M-S model predicts similar leaflet dimensions to the FE model (within 2.6%), and the coaptation zone is similar between models. The M-S model simulates in-plane behavior of AV leaflets considerably faster than the FE model and with only minor differences in the deformed mesh. While the M-S model does not allow explicit control of shear response, shear does not strongly influence shape of the simulated AV under pressure.Engineering and Applied Science

Real-time Knowledge-based Fuzzy Logic Model for Soft Tissue Deformation

In this research, the improved mass spring model is presented to simulate the human liver deformation. The underlying MSM is redesigned where fuzzy knowledge-based approaches are implemented to determine the stiffness values. Results show that fuzzy approaches are in very good agreement to the benchmark model. The novelty of this research is that for liver deformation in particular, no specific contributions in the literature exist reporting on real-time knowledge-based fuzzy MSM for liver deformation

Improvements to physically based cloth simulation

Physically based cloth simulation in computer graphics has come a long way since the 1980s. Although extensive methods have been developed, physically based cloth animation remains challenging in a number of aspects, including the efficient simulation of complex internal dynamics, better performance and the generation of more effects of friction in collisions, to name but a few. These opportunities motivate the work presented in this thesis to improve on current state of the art in cloth simulation by proposing methods for cloth bending deformation simulation, collision detection and friction in collision response. The structure of the thesis is as follows. A literature review of work related to physically based cloth simulation including aspects of internal dynamics, collision handling and GPU computing for cloth simulation is given in Chapter 2. In order to provide a basis for understanding of the work of the subsequent chapters of the thesis, Chapter 3 describes and discusses main components of our physically based cloth simulation framework which can be seen as the basis of our developments, as methods presented in the following chapters use this framework. Chapter 4 presents an approach that effectively models cloth non-linear features in bending behaviour, such as energy dissipation, plasticity and fatigue weakening. This is achieved by a simple mathematical approximation to an ideal hysteresis loop at a high level, while in textile research bending non-linearity is computed using complex internal friction models at the geometric structure level. Due to cloth flexibility and the large quantity of triangles, in a robust cloth system collision detection is the most time consuming task. The approach proposed in Chapter 5 improves performance of collision detection using a GPU-based approach employing spatial subdivision. It addresses a common issue, uneven triangle sizes, which can easily impair the spatial subdivision efficiency. To achieve this, a virtual subdivision scheme with a uniform grid is used to virtually subdivide large triangles, resulting in a more appropriate cell size and thus a more efficient subdivision. The other common issue that limits the subdivision efficiency is uneven triangle spatial distributions, and is difficult to tackle via uniform grids because areas with different triangle densities may require different cell sizes. In order to address this problem, Chapter 6 shows how to build an octree grid to adaptively partition space according to triangle spatial distribution on a GPU, which delivers further improvements in the performance of collision detection. Friction is an important component in collision response. Frictional effects include phenomena that are velocity dependent, such as stiction, Stribeck friction, viscous friction and the stick-slip phenomenon, which are not modelled by the classic Coulomb friction model adopted by existing cloth systems. Chapter 7 reports a more comprehensive friction model to capture these additional effects. Chapter 8 concludes this thesis and briefly discusses potential avenues for future work

Large Steps in GPU-based Deformable Bodies Simulation ⋆

The interactive deformation and visualization of volumetric objects is still a challenging problem for many application areas. We present a novel integrated system which implements physically-based deformation and volume visualization of tetrahedral meshes on modern graphics hardware by exploiting the last features of vertex and fragment shaders. We achieve fast and stable deformation of tetrahedral meshes by means of a GPU-based implicit solver and present a hardware-based single-pass raycaster for deformed tetrahedral meshes. Thus, direct visualization of the inner structures of the deformed mesh is possible, while keeping the data on the graphics hardware throughout the entire simulation. Key words: GPU computing, deformable bodies, implicit integration, physical simulation, volume rendering. PACS: 83.20.jpg, 07.05.Tp, 02.70.Bf