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Multibody dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to knee joint degeneration and restoration. Current three-dimensional multibody knee models are either quasi-static with deformable contact or dynamic with rigid contact. This study proposes a computationally efficient methodology for combining multibody dynamic simulation methods with a deformable contact knee model. The methodology requires preparation of the articular surface geometry, development of efficient methods to calculate distances between contact surfaces, implementation of an efficient contact solver that accounts for the unique characteristics of human joints, and specification of an application programming interface for integration with any multibody dynamic simulation environment. The current implementation accommodates natural or artificial tibiofemoral joint models, small or large strain contact models, and linear or nonlinear material models. Applications are presented for static analysis (via dynamic simulation) of a natural knee model created from MRI and CT data and dynamic simulation of an artificial knee model produced from manufacturer's CAD data. Small and large strain natural knee static analyses required 1 min of CPU time and predicted similar contact conditions except for peak pressure, which was higher for the large strain model. Linear and nonlinear artificial knee dynamic simulations required 10 min of CPU time and predicted similar contact force and torque but different contact pressures, which were lower for the nonlinear model due to increased contact area. This methodology provides an important step toward the realization of dynamic musculoskeletal models that can predict in vivo knee joint motion and loading simultaneously.
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PMID:Multibody dynamic simulation of knee contact mechanics. 1556 15

Transparency is an important graphics effect that can be used to significantly increase the realism of the rendered scene or to enable more effective visual inspection in engineering visualization. In this paper, we propose achieving interactive transparency rendering of a static scene by sorting the triangles in back-to-front order on CPU and supplying the sorted triangles to the graphics pipeline for rendering on GPU hardware. Our sorting method sorts the triangles in object space and is built upon the Binary Space Partition (BSP) and depth-sort methods with its behavior readily tunable to exploit the strengths of both methods. We propose novel techniques to optimize the BSP construction process with respect to multiple factors including tree construction time, tree size, and expected sorting cost. We also propose an improved depth-sort algorithm that can produce correct depth order without triangle split when no cyclic occlusion exists. We demonstrate that the proposed system results in a penalty factor of 4-6 for various types of parts, among which the largest one has nearly 1.2 million triangles. In addition, the penalty factor may be further improved if sorting in CPU and rendering in GPU are executed in parallel. Two approximation strategies are also studied to test the practicality of our system against large CAD assemblies. Experimental results on an assembly containing over 16 million triangles distributed in about 10,000 transparent parts show that the proposed system still results in a penalty factor of 4-6 while producing few artifacts.
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PMID:Interactive transparency rendering for large CAD models. 1614 55

We propose several interactive global illumination techniques for a diverse set of massive models. We integrate these techniques within a progressive rendering framework that aims to achieve both a high rendering throughput and an interactive responsiveness. To achieve a high rendering throughput, we utilize heterogeneous computing resources consisting of CPU and GPU. To reduce expensive data transmission costs between CPU and GPU, we propose to use separate, decoupled data representations dedicated for each CPU and GPU. Our representations consist of geometric and volumetric parts, provide different levels of resolutions, and support progressive global illumination for massive models. We also propose a novel, augmented volumetric representation that provides additional geometric resolutions within our volumetric representation. In addition, we employ tile-based rendering and propose a tile ordering technique considering visual perception. We have tested our approach with a diverse set of large-scale models including CAD, scanned, simulation models that consist of more than 300 million triangles. By using our methods, we are able to achieve ray processing performances of 3 M~20 M rays per second, while limiting response time to users within 15~67 ms. We also allow dynamic modifications of light, and interactive setting of materials, while efficiently supporting novel view rendering.
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PMID:T-ReX: interactive global illumination of massive models on heterogeneous computing resources. 2443 27

Simbiotics is a spatially explicit multiscale modeling platform for the design, simulation and analysis of bacterial populations. Systems ranging from planktonic cells and colonies, to biofilm formation and development may be modeled. Representation of biological systems in Simbiotics is flexible, and user-defined processes may be in a variety of forms depending on desired model abstraction. Simbiotics provides a library of modules such as cell geometries, physical force dynamics, genetic circuits, metabolic pathways, chemical diffusion and cell interactions. Model defined processes are integrated and scheduled for parallel multithread and multi-CPU execution. A virtual lab provides the modeler with analysis modules and some simulated lab equipment, enabling automation of sample interaction and data collection. An extendable and modular framework allows for the platform to be updated as novel models of bacteria are developed, coupled with an intuitive user interface to allow for model definitions with minimal programming experience. Simbiotics can integrate existing standards such as SBML, and process microscopy images to initialize the 3D spatial configuration of bacteria consortia. Two case studies, used to illustrate the platform flexibility, focus on the physical properties of the biosystems modeled. These pilot case studies demonstrate Simbiotics versatility in modeling and analysis of natural systems and as a CAD tool for synthetic biology.
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PMID:Simbiotics: A Multiscale Integrative Platform for 3D Modeling of Bacterial Populations. 2949 30