fluid-structure interaction models for drill-string vibrations are often of reduced order. However, both the structure and the surrounding fluid are non-linear, which can lead to complex coupled dynamic. In this paper...
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fluid-structure interaction models for drill-string vibrations are often of reduced order. However, both the structure and the surrounding fluid are non-linear, which can lead to complex coupled dynamic. In this paper, a coupled fluid-structure model is developed, where the flow is reduced to multiple cross-sections and solved with the lattice-Boltzmann method, while the finite element method is employed to discretize a region of the drill-string. In sequence, the whirling dynamics and the fluid forces are analysed for different configurations. The process is repeated disregarding the fluid-interaction with the aim of evaluating the fluid forces. The fluid forces estimated through the solution of the Navier-Stokes equation shows that the fluid acts in both dissipation and excitation of the vibrations. The dissipation is seen when high frequency dynamics is expected, whereas the lower frequencies are excited.
Computational modelling of whole-heart function is a useful tool to study heart mechanics and haemodynamics. Many existing heart models focus on electromechanical aspect without considering physiological valves and us...
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Computational modelling of whole-heart function is a useful tool to study heart mechanics and haemodynamics. Many existing heart models focus on electromechanical aspect without considering physiological valves and use simplified fluid models instead. In this study we develop a four-chamber heart model featuring realistic chamber geometry, detailed valve modelling, hyperelasticity with fibre architecture and fluid-structure interaction analysis. Our model is used to investigate heart behaviours with different modelling assumptions including restricted/free valve annular dynamics, and with/without heart-pericardium interactions. Our simulation results capture the interactions between valve leaflet and surrounding flow, typical left ventricular flow vortices, typical venous and transvalvular flow waveform, and physiological heart deformations such as atrioventricular plane movement. The improvement of ventricular filling and atrial emptying at early diastole is evident with free annulus. In addition, we find that the added pericardial forces on the heart have a predominant effect on atrial wall deformation especially during atrial contraction, and further help with the atrial filling process. Most importantly, the current study provides a framework for comprehensive multi-physics whole-heart modelling considering all heart valves and fluid-structure interactions.
In the nuclear power plant, the spent fuel pool (SFP) is an important nuclear security structure, it uses as temporary storage for spent fuel assemblies and removes the decaying heat with pool water from spent fuel as...
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In the nuclear power plant, the spent fuel pool (SFP) is an important nuclear security structure, it uses as temporary storage for spent fuel assemblies and removes the decaying heat with pool water from spent fuel assemblies. The issue of seismic safety concerning nuclear facilities has always been a primary concern for the country located in an earthquake-prone zone. When an earthquake strikes the spent fuel pool, it could lead water to sloshing behavior. It may produce additional forces on the pool and cause water overflow. It is therefore critical to investigate the sloshing phenomenon in a seismic assessment of the SFP. The objective of the paper is concerned with the problem of modeling the fluid-structure interaction (FSI) analysis with a SFP under Beyond-Design-Basis Earthquake (BDBE). The study focuses on the sloshing phenomena with the finite element analysis (FEA) code LS-DYNA. To be concerned about the structural integrity of the spent fuel pool, this paper also applied ACI-349 and ASME code to evaluate the seismic performance of the structure and the safety margin. The results show that the Taiwan BWR Mark-I Nuclear Power Plant spent fuel pool can maintain its structural integrity under the beyond-design basis earthquakes.
Bypass surgery is a commonly employed method for treating coronary artery diseases, involving the use of grafts to bypass occluded arteries. However, graft occlusion remains a concern due to mechanical disparities bet...
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Bypass surgery is a commonly employed method for treating coronary artery diseases, involving the use of grafts to bypass occluded arteries. However, graft occlusion remains a concern due to mechanical disparities between the grafts and native arteries. This study aims to compare the mechanical properties of three frequently used grafts in coronary bypass surgeries: human saphenous veins, mammary arteries, and radial arteries. Stressrelaxation tests were conducted on samples obtained from these vessels, and their mechanical properties were characterized. The stress-strain curves of each sample were fitted using the quasi-linear viscoelastic (QLV) model, with MATLAB software used to extract the model's constants. Additionally, fluid-structure simulations were performed employing the extracted viscoelastic mechanical properties of the vessels. The analysis revealed that the saphenous vein exhibited the highest elastic coefficient (0.5247) and non-linearity coefficient (0.8135) among the studied grafts. The mammary artery demonstrated nearly seven times greater viscoelasticity compared to the other graft options. Furthermore, the examination of shear stress distribution indicated lower shear stress regions in the radial and mammary artery specimens compared to the saphenous specimens. Notably, the lower wall of the host artery exhibited the greatest oscillatory shear index (OSI), with the radial specimen displaying the highest oscillation in this region compared to the other two specimens. The mechanical characterization results presented in this study hold potential applications in pathogenic and clinical investigations of heart diseases, aiding in the development of appropriate treatment approaches.
We address a system of equations modeling an incompressible fluid interacting with an elastic body. We prove the local existence when the initial velocity belongs to the space H1.5+& varepsilon;\documentclass[12pt...
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We address a system of equations modeling an incompressible fluid interacting with an elastic body. We prove the local existence when the initial velocity belongs to the space H1.5+& varepsilon;\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$H<^>{1.5+\epsilon }$$\end{document} and the initial structure velocity is in H1+& varepsilon;\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$H<^>{1+\epsilon }$$\end{document}, where & varepsilon;is an element of(0,1/20)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\epsilon \in (0, 1/20)$$\end{document}.
In this paper, we study the non -linear dynamic response generated as a result of a fluid-structure interaction between a flexible structure and a flowing fluid, when the structure is subjected to non -linear excitati...
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In this paper, we study the non -linear dynamic response generated as a result of a fluid-structure interaction between a flexible structure and a flowing fluid, when the structure is subjected to non -linear excitations. In first place, the use of semi-discrete approximations allowed us to show that the motion of a flexible structure coupled with a surrounding fluid flowing could be modelled and analysed via a coupled Complex Cubic Ginzburg-Landau equations (CCGLEs). Through the obtained CCGLEs, we were able to show that modulational instability (MI) is the main mechanism responsible for the generation of vortex shedding. Moreover, we showed that the stability of continuous wave depends on the coupling parameters between the fluid and the structure. Secondly, using a mathematical method, namely the G'/G expansion method, we found that vortex wave trains could be generated as cylindrical waves. These results are highly significant from a theoretical point of view and could be a plus to explain the process of generation of K & aacute;rm & aacute;n Vortex as a consequence of unstable coupling between two continuous wave in the fluid-structure system. Moreover, considering the industrial interest, such as floating wind turbines, this work aims to provide an additional understanding of the interactions between a flexible body and a surrounding flow.
Oil shale is characterized by a dense structure, low proportion of pores and fissures, and low permeability. Pore-fracture systems serve as crucial channels for shale oil migration, directly influencing the production...
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Oil shale is characterized by a dense structure, low proportion of pores and fissures, and low permeability. Pore-fracture systems serve as crucial channels for shale oil migration, directly influencing the production efficiency of shale oil resources. Effectively stimulating oil shale reservoirs remains a challenging and active research topic. This investigation employed shale specimens obtained from the Longmaxi Formation. Scanning electron microscopy, fluid injection experiments, and fluid-structure interaction simulations were used to comprehensively analyze structural changes and fluid flow behavior under high temperatures from microscopic to macroscopic scales. Experimental results indicate that the temperature has little effect on the structure and permeability of shale before 300 degrees C. However, there are two threshold temperatures within the range of 300 to 600 degrees C that have significant effects on the structure and permeability of oil shale. The first threshold temperature is between 300 and 400 degrees C, which causes the oil shale porosity, pore-fracture ratio, and permeability begin to increase. This is manifested by the decrease in micropores and mesopores, the increase in macropores, and the formation of a large number of isolated pores and fissures within the shale. The permeability increases but not significantly. The second threshold temperature is between 500 and 600 degrees C, which increases the permeability of oil shale significantly. During this stage, micropores and mesopores are further reduced, and macropores are significantly enlarged. A large number of connected and penetrated pores and fissures are formed. More numerous and thicker streamlines appear inside the oil shale. The experimental results demonstrate that high temperatures significantly alter the microstructure and permeability of oil shale. At the same time, the experimental results can provide a reference for the research of in-situ heating techniques in oil shale rese
Optimization tools have been increasingly gaining ground in the design of turbomachinery components. However, there is a noticeable lack of studies applying topology optimization to design these types of equipment. En...
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Optimization tools have been increasingly gaining ground in the design of turbomachinery components. However, there is a noticeable lack of studies applying topology optimization to design these types of equipment. Enhancing the design of these components is crucial to reducing vibration levels and extending their useful life. This study focuses on topology optimization of rotating structures considering turbulent swirl flow and natural frequency constraints. The proposed optimization problem aims to minimize compliance while adhering to volume and natural frequency constraints, specifically targeting the three lowest natural frequencies. The governing equations are solved using separate domains: the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations with the k-omega\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$k-\upomega$$\end{document} turbulence model for the fluid and linear elasticity with 2D axisymmetry for the solid. The optimization is carried out using the Topology Optimization of Binary structures with Geometry Trimming (TOBS-GT) method, which employs discrete (binary) design variables. Two numerical examples are explored: the rotating wall and the multiple rotating structures. The rotating wall example investigates the penalization factor, rotational speed, and natural frequency constraint influence in the optimized designs. In addition, the multiple rotating structures example explores the effects of rotational speed, natural frequency constraint, and positive internal pressure within the channel.
Most studies, standards, and codes on wind pressure distributions commonly disregard the influence of the flexibility of structures. Nevertheless, in the case of tensile-membrane structures, their flexibility cannot b...
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Most studies, standards, and codes on wind pressure distributions commonly disregard the influence of the flexibility of structures. Nevertheless, in the case of tensile-membrane structures, their flexibility cannot be ignored, so this study presents the results of numerical simulations evaluating wind pressure coefficient distributions on tensile-membrane structures, accounting for fluid-structure interaction (FSI) choosing the most common geometry: the hyperbolic paraboloid. Various curvature configurations, wind incidence directions, and structural models (both open and enclosed) were analyzed. The FSI solution involves a twoway partitioned simulation between Computational fluid Dynamics, Computational Structural Dynamics and through a coupling system that culminates in the derivation of final pressure coefficient distributions. Results indicate that pressure coefficients obtained for rigid models underestimate those obtained by the FSI methodology, which accounts for deformations altering the interaction between the fluid and membrane.
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