8,254 research outputs found

    Modelling mitral valvular dynamics–current trend and future directions

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    Dysfunction of mitral valve causes morbidity and premature mortality and remains a leading medical problem worldwide. Computational modelling aims to understand the biomechanics of human mitral valve and could lead to the development of new treatment, prevention and diagnosis of mitral valve diseases. Compared with the aortic valve, the mitral valve has been much less studied owing to its highly complex structure and strong interaction with the blood flow and the ventricles. However, the interest in mitral valve modelling is growing, and the sophistication level is increasing with the advanced development of computational technology and imaging tools. This review summarises the state-of-the-art modelling of the mitral valve, including static and dynamics models, models with fluid-structure interaction, and models with the left ventricle interaction. Challenges and future directions are also discussed

    Real Time Animation of Virtual Humans: A Trade-off Between Naturalness and Control

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    Virtual humans are employed in many interactive applications using 3D virtual environments, including (serious) games. The motion of such virtual humans should look realistic (or ‘natural’) and allow interaction with the surroundings and other (virtual) humans. Current animation techniques differ in the trade-off they offer between motion naturalness and the control that can be exerted over the motion. We show mechanisms to parametrize, combine (on different body parts) and concatenate motions generated by different animation techniques. We discuss several aspects of motion naturalness and show how it can be evaluated. We conclude by showing the promise of combinations of different animation paradigms to enhance both naturalness and control

    Thermal comfort models for indoor spaces and vehicles—Current capabilities and future perspectives

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    International audienceThroughout this paper, we reviewed the most popular thermal comfort models and methods of assessing thermal comfort in buildings and vehicular spaces. Most of them are limited to specific steady state, thermally homogenous environments and only a few of them address human responses to both non-uniform and transient conditions with a detailed thermo-regulation model. Some of them are defined by a series of international standards which stayed unchanged for more than a decade. The article proposes a global approach, starting from the physiological reaction of the body in thermal stress conditions and ending with the model implementation. The physiological bases of thermal comfort are presented, followed by the main thermal comfort models and standards and finishing with the current methods of assessing thermal comfort in practice. Within the last part we will focus mainly on thermal manikin experimental studies, and on CFD (computational fluid dynamics) numerical approach, as in our opinion these methods will be mostly considered for future development in this field of researc

    An Algorithm for Structural Topology Optimization of Multibody Systems

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    Topology Optimization (TO) of static structures with fixed loading is a very interesting topic in structural mechanics that has found many applications in industrial design tasks. The extension of the theory to dynamic loading for designing a Multibody System (MBS) with bodies which are lighter and stronger can be of high interest. The objective of this thesis work is to investigate one of the possible ways of extending the theory of the static structural Topology Optimization to Topology Optimization of dynamical bodies embedded in a Multibody System (TOMBS) with large rotational and transitional motion. The TOMBS is performed for all flexible bodies simultaneously based on the overall system dynamical response. Simulation of the MBS behavior is done using the finite element formalism and modal reduction. A modified formulation of Solid Isometric Material with Penalization (SIMP) method is suggested to avoid numerical instabilities and non-convergence of the optimization algorithm implemented for TOMBS. The nonlinear differential algebraic equation of motion is solved numerically using Backward Differential Formula (BDF) with variable step size in SundialsTB and Assimulo integrators implemented in Matlab and Python. The approach can find many applications in designing vehicle systems, high speed robotic manipulators, airplanes and space structures. Also, to show the current capability of the tools in the industry to design a body under dynamic loading using the multiple static load cases, the lower A-arm of double wishbone suspension system is designed in Abaqus/TOSCA, where, the loads are collected from rigid multibody simulation in Dymola.In everyday life, people deal with different kinds of mechanical machines and mechanisms. These mechanisms are a set of mechanical and electrical parts designed to perform a specific task. Among the others, the task of a mechanical part is to carry a load or transfer it. The key question a designer should ask is how to design the part in terms of the shape, material, weight, etc. in order for the part to be optimal. This is a question that can be answered using structural optimization. Particularly in this thesis work it is tried to suggest an algorithm for optimizing the shape or material distribution of the parts within a multibody system. The method is called topology optimization of multibody system. The behavior of the system as a whole is considered to design each individual mechanical part

    Design and validation of decision and control systems in automated driving

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    xxvi, 148 p.En la última década ha surgido una tendencia creciente hacia la automatización de los vehículos, generando un cambio significativo en la movilidad, que afectará profundamente el modo de vida de las personas, la logística de mercancías y otros sectores dependientes del transporte. En el desarrollo de la conducción automatizada en entornos estructurados, la seguridad y el confort, como parte de las nuevas funcionalidades de la conducción, aún no se describen de forma estandarizada. Dado que los métodos de prueba utilizan cada vez más las técnicas de simulación, los desarrollos existentes deben adaptarse a este proceso. Por ejemplo, dado que las tecnologías de seguimiento de trayectorias son habilitadores esenciales, se deben aplicar verificaciones exhaustivas en aplicaciones relacionadas como el control de movimiento del vehículo y la estimación de parámetros. Además, las tecnologías en el vehículo deben ser lo suficientemente robustas para cumplir con los requisitos de seguridad, mejorando la redundancia y respaldar una operación a prueba de fallos. Considerando las premisas mencionadas, esta Tesis Doctoral tiene como objetivo el diseño y la implementación de un marco para lograr Sistemas de Conducción Automatizados (ADS) considerando aspectos cruciales, como la ejecución en tiempo real, la robustez, el rango operativo y el ajuste sencillo de parámetros. Para desarrollar las aportaciones relacionadas con este trabajo, se lleva a cabo un estudio del estado del arte actual en tecnologías de alta automatización de conducción. Luego, se propone un método de dos pasos que aborda la validación de ambos modelos de vehículos de simulación y ADS. Se introducen nuevas formulaciones predictivas basadas en modelos para mejorar la seguridad y el confort en el proceso de seguimiento de trayectorias. Por último, se evalúan escenarios de mal funcionamiento para mejorar la seguridad en entornos urbanos, proponiendo una estrategia alternativa de estimación de posicionamiento para minimizar las condiciones de riesgo

    NASA SBIR abstracts of 1990 phase 1 projects

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    The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number

    A numerical tool for predicting the spatial decay of freestream turbulence.

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    The present numerical work is an attempt towards modelling of freely decaying homogeneous isotropic turbulence with its application in experimental modelling of the effect of incident turbulence on flow around 2D and 3D bluff-bodies. Both steady, Reynolds Averaged Navier Stokes (RANS) and unsteady, Large Eddy Simulation (LES), 3-D numerical computational fluid dynamics (CFD) techniques have been employed to characterise the inviscid decay of large-scale turbulence in terms of the characteristic r.m.s turbulent velocity fluctuations ( ) and the local integral length scale (Lu). The large-scale turbulent properties extracted from the current numerical simulations are inter-related and are shown to behave predominantly as Saffman turbulence, which states Lu3 ≈ constant. The other focus from the current study was on modelling inlet conditions for bluff-bodies in a freestream flow. A set of three-correlation equations are formulated based on the large-scale turbulent properties that are effective in estimating the initial and local freestream turbulence conditions. The set of prediction equations can be deemed useful for researchers developing wind-tunnel models in the presence of freestream turbulence. Additionally, the set of equations is also reliable in determining appropriate near-constant turbulent conditions based on the upstream inlet conditions. The current study aims at designing the region of constant turbulent properties of a desired magnitude that can be helpful for boundary layer and heat transfer studies over a bluff-body

    A Novel Framework to Model the Short and Medium Term Mechanical Response of the Medial Gastrocnemius

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    Musculoskeletal disorders (MSDs) are the second largest cause of disability worldwide and cost the UK National Health Service (NHS) over £4.7 billion yearly. One holistic approach to alleviate this burden is to create in silico models that provide insight into MSDs which will improve diagnostic and therapeutic procedures. This thesis presents a modelling framework that analyses the mechanical behaviour of anatomical skeletal muscles. The anatomical geometry and fibre paths of the medial gastrocnemius muscle were acquired from the Living Human Data Library (LHDL). The medial gastrocnemius model was further sophisticated by incorporating morphological representations of the aponeurosis and myotendon transition region. Having carried out a finite element analysis on the medial gastrocnemius, it was found that the morphology and size of the transition region significantly affected the mechanical response of the muscle. Three illustrative simulations were subsequently carried out on the model, to better understand the muscle’s mechanical response in differing mechanical environments: (1) the effects of high extensions on the muscle’s mechanical response, (2) lengthening of the aponeurosis - a phenomenon often observed following aponeurosis regression - and (3) the stress-strain regime of the muscle when the tendon experiences a laceration and heals over 21 days. These models show the regions that experienced the highest strains were the muscle-tendon transition regions. As MSDs tend to be of a degenerative nature and progress over time, the temporal changes of the mechanical response of skeletal muscle tissue is of great interest. In the penultimate chapter, the medial gastrocnemius was assessed across various remodelling regimes. It was found that the muscle returned to homeostasis only when both the muscle and tendon remodelled – albeit, at different remodelling rates. Whilst this observation seems intuitive, most other growth and remodelling models of skeletal muscles have only remodelled either the muscle or tendon constituent. The model developed in this thesis therefore has the potential to inform multi-scale musculo-skeletal muscle models thus providing a significant contribution to understanding MSDs
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