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Dynamics Analysis (dynamics + analysis)
Selected AbstractsSingularity-Free Brownian Dynamics Analyses of Rotational Dynamics: Non-Spherical Nanoparticles in SolutionMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2005Stine Nalum Naess Abstract Summary: From kinetic theory we have rigorously derived singularity-free Brownian dynamics analyses of nanoparticle rotational dynamics. The rigid non-spherical nanoparticles incorporate all three rotational degrees of freedom. This was achieved by using the components of Cartesian rotation vectors as the generalized coordinates describing angular orientation. The new results constitute an important advance compared to the situation when Eulerian angles specify angular orientation. Our finding eliminates one of the main longstanding obstacles to detailed studies of nanoparticle rotational dynamics in the diffusion time domain. The described formalism is applicable to a wide range of nanoparticle systems including liquid crystals, biopolymers, and colloids. [source] Design Considerations for Plate and Frame Ultrafiltration Modules by Computational Fluid Dynamics Analysis,THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2006Mauro M. Dal-Cin Abstract Pressure and flow maldistributions were studied in a full-scale industrial plate and frame ultrafiltration module, operating in a Z flow pattern, for the recovery of used motor oils. Solutions were obtained using (1) a three-dimensional solution of the Navier-Stokes equation using computational fluid dynamics and (2) Bernoulli's equation and a momentum balance in one dimension. Fluid decelerations and accelerations generated pressure increases and decreases in the distributor and collector, respectively, biasing the flow distribution to the last channel. Several modifications to the original design were evaluated; the most effective was larger distributor and collector diameters, which greatly improved the uniformity of the flow distribution and transmembrane pressure, and reduced the overall pressure drop in a bank. A variable diameter distributor and collector module was designed using the 1-D model. Flow distribution was significantly improved but also yielded an undesirable overall higher pressure drop and a pressure maldistribution in the bank. The maldistribution of the main inlet manifold to the distributors in the first bank was strongly dependent on the module design. The flow distribution across the width of a channel became uniform within a short distance, essentially eliminating the need to consider this design aspect any further. Flows at the bank outlets, and hence inlets of the following bank, showed uniform lateral distribution in all cases, suggesting that future modelling work can be limited to a fraction of the module width, based on symmetry, in order to gain computational efficiency. On a étudié les mauvaises distributions de pression et d'écoulement dans un module d'ultrafiltration à plateaux et à cadres à l'échelle industrielle, fonctionnant dans un schéma d'écoulement en Z, pour la récupération des huiles de moteurs usées. Des solutions ont été obtenues avec (1) une solution tridimensionnelle de l'équation de Navier-Stokes utilisant la mécanique des fluides par ordinateur, et (2) l'équation de Bernoulli et un bilan de quantité de mouvement unidimensionnel. Les décélérations et accélérations de fluide entraînent des augmentations et diminutions de pression dans le distributeur et le collecteur, respectivement, ce qui fausse la distribution d'écoulement dans le dernier canal. On a évalué plusieurs modifications du concept original; la plus efficace sont des diamètres de distributeur et de collecteur plus larges, qui permettent d'améliorer grandement l'uniformité de la distribution d'écoulement et la pression transmembranaire, et qui réduisent la perte de charge globale dans une batterie. Un module de distributeur et de collecteur de diamètres variables a été conçu au moyen du modèle 1D. La distribution d'écoulement est significativement améliorée mais cause une perte de charge globale plus grande indésirable et une mauvaise distribution de pression dans la batterie. La mauvaise distribution du manifold d'entrée principal vers les distributeurs dans la première batterie est fortement dépendante de la conception du module. La distribution d'écoulement dans toute la largeur d'un canal devient uniforme sur une courte distance, éliminant essentiellement le besoin d'approfondir cet aspect de la conception. L'écoulement en sortie de batteries et donc à l'entrée des batteries suivantes montre une distribution latérale uniforme dans tous les cas, ce qui suggère que le travail de modélisation futur peut se limiter à une fraction de la largeur du module, pour des raisons de symétrie, pour gagner de l'efficacité numérique. [source] Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 5 2010Jingchun Wu Abstract An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 µm. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 µm. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 µm compared to 50 µm and 200 µm. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized. [source] An Estimation Method of Hemolysis within an Axial Flow Blood Pump by Computational Fluid Dynamics AnalysisARTIFICIAL ORGANS, Issue 10 2003Tetsuya Yano Abstract: Evaluation of hemolysis within a blood pump on a computer is useful for developing rotary blood pumps. The flow fields in the axial flow blood pump were analyzed using computational fluid dynamics (CFD). A blood damage index was calculated based on the changes in shear stress with time along 937 streamlines. Hemolysis of the pumps was measured using bovine blood. A good correlation between the computed and measured hemolysis results was observed. CFD analysis is useful for estimating hemolysis of rotary blood pumps on a computer. [source] Singularity-Free Brownian Dynamics Analyses of Rotational Dynamics: Non-Spherical Nanoparticles in SolutionMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2005Stine Nalum Naess Abstract Summary: From kinetic theory we have rigorously derived singularity-free Brownian dynamics analyses of nanoparticle rotational dynamics. The rigid non-spherical nanoparticles incorporate all three rotational degrees of freedom. This was achieved by using the components of Cartesian rotation vectors as the generalized coordinates describing angular orientation. The new results constitute an important advance compared to the situation when Eulerian angles specify angular orientation. Our finding eliminates one of the main longstanding obstacles to detailed studies of nanoparticle rotational dynamics in the diffusion time domain. The described formalism is applicable to a wide range of nanoparticle systems including liquid crystals, biopolymers, and colloids. [source] Intravascular Mechanical Cavopulmonary Assistance for Patients With Failing Fontan PhysiologyARTIFICIAL ORGANS, Issue 11 2009Sonya S. Bhavsar Abstract To provide a viable bridge-to-transplant, bridge-to-recovery, or bridge-to-surgical reconstruction for patients with failing Fontan physiology, we are developing a collapsible, percutaneously inserted, magnetically levitated axial flow blood pump to support the cavopulmonary circulation in adolescent and adult patients. This unique blood pump will augment pressure and thus flow in the inferior vena cava through the lungs and ameliorate the poor hemodynamics associated with the univentricular circulation. Computational fluid dynamics analyses were performed to create the design of the impeller, the protective cage of filaments, and the set of diffuser blades for our axial flow blood pump. These analyses included the generation of pressure,flow characteristics, scalar stress estimations, and blood damage indexes. A quasi-steady analysis of the diffuser rotation was also completed and indicated an optimal diffuser rotational orientation of approximately 12°. The numerical predictions of the pump performance demonstrated a pressure generation of 2,25 mm Hg for 1,7 L/min over 3000,8000 rpm. Scalar stress values were less than 200 Pa, and fluid residence times were found to be within acceptable ranges being less than 0.25 s. The maximum blood damage index was calculated to be 0.068%. These results support the continued design and development of this cavopulmonary assist device, building upon previous numerical work and experimental prototype testing. [source] Single crystal structure and molecular dynamics analysis of a myo -inositol derivativeACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2000Jan Dillen The crystal structure of 5- O - tert -butyldimethylsilyl-3,4- O -carbonyl-1,2- O -cyclohexylidene-2-oxo-3-oxa-4-bornanylcarbonyl- d - myo -inositol has been studied by single-crystal X-ray diffraction at both room temperature and 173,K. At room temperature, the tert -butyldimethylsilyl group exhibits dynamical disorder. A molecular dynamics simulation was used to model the disorder and this indicates that the group librates between two stable conformations in the crystal. Approximate relative energies of the different forms and energy barriers for the transition were obtained by empirical force field methods. Calculations of the thermal motion of the atoms are in good qualitative, but fair to poor quantitative agreement with the X-ray data. [source] Design of cellular porous biomaterials for wall shear stress criterionBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Yuhang Chen Abstract The microfluidic environment provided by implanted prostheses has a decisive influence on the viability, proliferation and differentiation of cells. In bone tissue engineering, for instance, experiments have confirmed that a certain level of wall shear stress (WSS) is more advantageous to osteoblastic differentiation. This paper proposes a level-set-based topology optimization method to regulate fluidic WSS distribution for design of cellular biomaterials. The topological boundary of fluid phase is represented by a level-set model embedded in a higher-dimensional scalar function. WSS is determined by the computational fluid dynamics analysis in the scale of cellular base cells. To achieve a uniform WSS distribution at the solid,fluid interface, the difference between local and target WSS is taken as the design criterion, which determines the speed of the boundary evolution in the level-set model. The examples demonstrate the effectiveness of the presented method and exhibit a considerable potential in the design optimization and fabrication of new prosthetic cellular materials for bioengineering applications. Biotechnol. Bioeng. 2010;107:737,746. © 2010 Wiley Periodicals, Inc. [source] Stability and Dynamics of Domain-Swapped Bovine-Seminal RibonucleaseCHEMISTRY & BIODIVERSITY, Issue 5 2004Kalyan The proteins of the ribonuclease-A (RNase-A) family are monomeric, with the exception of bovine-seminal ribonuclease (BS-RNase). BS-RNase is formed by swapping the N-terminal helices across the two monomeric units. A molecular-dynamics (MD) study has been performed on the protein for a simulation time of 5.5,ns to understand the factors responsible for the stability of the dimer. Essential dynamics analysis and motional correlation of the protein atoms yielded the picture of a stabilising, yet flexible, interface. We have investigated the role of intermolecular H-bonding, protein/water interaction, and protein/water networks in stabilising the dimer. The networks of interchain H-bonds involving side-chain/side-chain or side-chain/main-chain (ScHB) interactions between the two chains have also been studied. The ability of protein atoms in retaining particular H2O molecules was investigated as a function of the accessible surface area (ASA), depth, and hydration parameters, as well as their participation in protein/water networks. [source] | ||||||||||