1,721,371 research outputs found
A mixed particle-mode function method for nonlinear marine fluid-structure interaction problems with free surface
No full textIn this study, a computational model which couples particle method for fluid part and modal superposition for structure part is developed to investigate the Fluid Structure Interaction problems with free surface.As a Lagrangian mesh-free method, the MPS (Moving Particle Semi-implicit) method is very suitable for simulating violent flows such as breaking waves on free surface. However, despite its wide range of applicability, the original MPS algorithm suffers from some inherent difficulties in obtaining an accurate fluid pressure in both spatial and time domain. Different modifications to improve the method have been proposed in the literature. In this study, the following modifications are proposed to improve the accuracy of pressure calculations and the stability of the method: i) A density error compensation source term in the pressure Poisson equation with no artificial term in the formulation, ii) New solid and free surface boundary handling methods, iii) Particle position shifting and collision handling, and iv) A new version of “cell-link” neighbour particle searching strategy, which reduces about 6.5/9 ( 72%) of the searching area compared with traditional “cell-link” algorithm. For problems where violent free surface deformation only occur in a constrained area, the efficiency of MPS is further improved by weakly coupling with BEM (Boundary Element Method).For the structure that undergoes very large rigid motions and relatively small elastic deformation, an efficient computational model that couples the rigid-body and flexible modes in the same set of formulation. Unlike the traditional modal analysis, this model takes into account the mutual effect between rigid-body motion and flexible deformation. It is more efficient compared with FE(Finite Element) method, regardless of the size of the structure. For 2D cases,if only the first three modes are chosen to represent the flexible deformation of the structure, it only results in a 6 x 6 equation system to be solved.For the fluid structure interaction coupling, the Gauss-Seidel iteration with Aitken relaxation scheme is used.The effectiveness of the proposed modifications for MPS method is validated by a 2D Dam-break flow. Furthermore, various typical impact flow problems in marine engineering are simulated to test the applicability of the modified MPS method. It includes 2D/3D Dam-break with different boundary conditions (such as obstacle in the middle of the tank, spring supported rigidwall and flexible cantilever beam), liquid sloshing, wedge-shape and ship-section-shape dropping problems. The weak coupling scheme between MPS and BEM are also tested by the 2D breaking solitary wave impacting a flexible wall problem. The coupling of fluid and structure solver is also tested by various problems including 2D flexible wedge dropping and 2D/3D floating beam/ship slamming problems. The numerical results obtained are found to be in good agreement with the available numerical or experimental results. With the proposed modifications, the stability and accuracy of the pressure field are improved in spatial and time domains. The proposed structure model also proves to be effective
Research on the distribution characteristics of a novel oil displacement system for conformance control in microporous media
No full textThis study aims to investigate the distribution characteristics of a novel hydrogel system (HDS) for in-depth conformance control. Through a combination of static gelation experiments and core flow experiments, the thickening performance and seepage characteristics in porous media of the novel HDS system was studied. Considering the viscosity changes and dynamic chain extension reactions of the HDS system, the Darcy-Brinkman-Stokes (DBS) micro-continuum approach was applied to develop a multi-physical mathematical model for the migration of HDS system in a pore-throat network. Therefore, a 4-meter core experiment and multi-scale numerical modeling were conducted to analyze the dynamic chain extension efficiency and spatial distribution characteristics of the HDS system. Additionally, machine learning techniques were used to define the dynamic chain extension reaction index (RI) and identify its critical threshold, exploring the effects of varying injection parameters, solution concentrations, and permeabilities on the chain extension behavior. Results show that HDS molecular chains form aggregated structures that evolve into a unique spatial network. As the network structure becomes denser, the viscosity of HDS system increases rapidly. As the core permeability increases, the core throat size enlarges, and the compatibility between the HDS system molecular aggregates and the pore throat improves. HDS system shows good transmission performance during migration in the long core. Numerical simulations and machine learning techniques were employed to define the dynamic chain extension RI, examining how RI changes under varying injection parameters, solution concentrations, and permeabilities. As permeability, HDS system concentration, and injection rate increase, the RI also increases. The results are presented in the RI graph, offering theoretical insights for deep profile adjustment and the development of reagent systems
Mixed FE-SP method for nonlinear structure-water interactions with freak waves
No full textThis paper develops a mixed finite element – smoothing particle method for violent water-structure interactions involving freak waves and separation between structure and water. The structure undergoes a large rigid motion of 6 DOF with a small elastic deformation, so that its elastic displacement relative to the rigid motion can be represented in a mode summation based on FE analysis. The water is assumed inviscid - incompressible and its motion governed by nonlinear N-S equation. On the coupling interface where no FS separation happens, the equilibrium and consistence conditions are required. The numerical iteration process is suggested to solve the nonlinear FSI equations, and validation examples are shown a good agreement with available experiment results
Coupled MPS-modal superposition method for 2D nonlinear fluid-structure interaction problems with free surface
No full textIn this paper, a coupled MPS-modal superposition method is developed for 2D nonlinear fluid-structure interaction problems. In this method, the rigid-body and relatively small elastic deformation are coupled together, which considers the mutual effect between them. The elastic deformation of the structure is represented by a mode superposition formulation, which is more efficient compared with FEM, regardless of the size of the structure. For 2D cases, if the first three modes are chosen to represent the flexible deformation of the structure, it only results in a 6×6 matrix equation to be solved. For the fluid motion, the modified Moving Particle Semi-implicit (MPS) method, which significantly reduces the fluctuation of pressure calculation of the original MPS method, is used.Two nonlinear problems, i.e. breaking-water-dam impacting a floating beam and flexible wedge slamming into the water are simulated to demonstrate the performance of the developed method. The numerical simulations show that this coupling model is capable of providing stable results that are generally in good agreement with the available experimental data. For the highly nonlinear case with very large rigid motions, the mutual effect between elastic deformation and rigid motions could accumulate to a relatively remarkable level shown by the curves of trajectories or acceleration history of the body mass centre. This also indicates the importance of mutual effect to analyse highly nonlinear FSI problems with large rigid-body motions and relatively small flexible deformation.KeywordsMoving particle semi-implicit (MPS) method; Fluid structure interaction (FSI); Modal superposition; Free surface flow; Floating beam; Flexible wedge droppin
Combined force decomposition approach and CFD simulation methods for 2D water entry and exit problem
No full textThe force decomposition approach is extended to solve the two-dimensional (2D) water entry and exit problems. Two typical scenarios, direct water exit and continuous water entry and exit, are examined. It reveals that the total force is irrelevant to the body velocity but to the acceleration. More specifically, the force can be expressed as the multiplication of constant values, body acceleration and a non-dimensional coefficient, and the coefficient is related only to the displacement and immersion condition of the body while independent of its motion condition. Two typical body shapes, a widely used wedge model and a practical ship section model, are examined here. CFD simulation is employed here to directly extract the non-dimensional coefficients, which avoids complex calculations for the wetted length of body by analytical models. The force decomposition approach with the obtained coefficients provides a means to quickly and accurately predict the hydrodynamic force acting on body for water exit scenarios. The proposed method is verified by comparing its results with CFD simulations in the complicated motion cases with varying acceleration. Furthermore, this work provides a potential tool to calculate the total force acting on any entire 3D hull that is divided into several independent 2D slice
Dynamic interactions of an integrated vehicle–electromagnetic energy harvester–tire system subject to uneven road excitations
No full textAn investigation is undertaken of an integratedmechanical-electromagnetic coupling system consisting of arigid vehiclewith heave, roll, and pitchmotions, four electromagneticenergy harvesters and four tires subject to unevenroad excitations in order to improve the passengers’ ridingcomfort and harvest the lost engine energy due to unevenroads. Following the derived mathematical formulations andthe proposed solution approaches, the numerical simulationsof this interaction system subject to a continuous sinusoidalroad excitation and a single ramp impact are completed. Thesimulation results are presented as the dynamic responsecurves in the forms of the frequency spectrum and the timehistory, which reveals the complex interaction characteristicsof the system for vibration reductions and energy harvestingperformance. It has addressed the coupling effects on thedynamic characteristics of the integrated system caused by:(1) the natural modes and frequencies of the vehicle; (2) thevehicle rolling and pitching motions; (3) different road excitationson four wheels; (4) the time delay of a road ramp toimpact both the front and rear wheels, etc., which cannot betackled by an often used quarter vehicle model. The guidelinesfor engineering applications are given. The developedcoupling model and the revealed concept provide a meanswith analysis idea to investigate the details of four energyharvester motions for electromagnetic suspension designsin order to replace the current passive vehicle isolators andto harvest the lost engine energy. Potential further researchdirections are suggested for readers to consider in the future
Some modifications of MPS method for incompressible free surface flow
No full textAs a Lagrangian mesh-free method, the Moving Particle Semi-implicit (MPS)[1] method is very suitable for simulating violent flows, such as breaking waves on free surface. However, despite its wide range of applicability, the original MPS algorithm suffers from some inherent difficulties in obtaining an accurate fluid pressure in both spatial and time domain. Different modifications to improve the method have been proposed [2-5] in the literature. In this paper, the authors developed a particle position shifting and collision handling technique which could effectively suppress the pressure fluctuation. In addition, a new version of “cell-link” neighbour particle searching strategy, which reduces about 7/9 (~78%) of the searching area compared with traditional “cell-link” algorithm, is proposed.The developed MPS method with the proposed modifications has been tested on two free surface flow problems: 2D dam break and liquid sloshing. The numerical results obtained are found to be in good agreement with the available numerical and experimental results. With the proposed modifications, the stability and accuracy of the pressure field are improved in spatial and time domains
Modified MPS method for the 2D Fluid structure interaction problem with free surface
Full text linkAs a Lagrangian mesh-free method, the Moving Particle Semi-implicit (MPS) method is very suitable for simulating violent flows, such as breaking waves on free surface. However, despite its wide range of applicability, the original MPS algorithm suffers from some inherent difficulties in obtaining an accurate fluid pressure in both spatial and time domain. Different modifications to improve the method have been proposed in the literature. In this paper, we propose the following modifications to improve the accuracy of pressure calculations and the stability of the method: i) A mixed source term in the pressure Poisson equation with no artificial term in the formulation, ii) New solid and free surface boundary handling methods, iii) Particle position shifting and collision handling, and iv) A new version of “cell-link” neighbour particle searching strategy, which reduces about 6.5/9 (?72%) of the searching area compared with traditional “cell-linked” algorithm.The proposed modifications are verified and validated by some model free-surface flow problems, such as a two-dimensional dam break (with rigid and flexible structures on the impacting end - FSI model), liquid sloshing and ship cross section dropping problems. The numerical results obtained are found to be in good agreement with the available numerical or experimental results. With the proposed modifications, the stability and accuracy of the pressure field are improved in spatial and time domains
Reduced Order Modeling (ROM) based method for the two-dimensional water exit problem using snapshot Proper Orthogonal Decomposition (POD) and CFD simulations
No full textIn this paper, the concepts of snapshot Proper Orthogonal Decomposition (POD) and Reduced Order Modeling (ROM) are combined (referred to the POD-ROM method) to solve the two-dimensional (2D) water exit problem. Attention is paid to the pressure distribution along the wetted surface of the body. Computational Fluid Dynamics (CFD) simulations are employed to obtain high-fidelity data on pressure distribution. After applying snapshot POD, it is found that two POD basis modes for the wedge model and three modes for the ship section model are adequate to capture dynamic features of the pressure distribution without losing too much detail. It can also be observed that neither the body motion state nor the initial immersion condition influences all POD functions of the wedge model, but the temporal POD functions of the ship section model are significantly dependent on the initial immersion height. A group of empirical formulae is provided to deal with this issue. The validity and reliability of our POD-ROM method are assessed by investigating water exit cases with both constant and time-varying body accelerations. In this context, after deriving POD functions of any given 2D body from a single CFD simulation, predictions of the pressure distribution along the body can be facilitated for further water exit cases
The weak coupling between MPS and BEM for wave structure interaction simulation
No full textAs a Lagrangian type meshless method, the MPS is suitable for violent free surface problems. In this paper, for problems where violent free surface deformation only occur in a constrained area, the efficiency of MPS is further improved by weak coupling with BEM. More specifically, the whole computational domain is modeled by BEM whereas the MPS model only covers the violent flow area. Since the computational time of BEM is negligible compared with the time required by MPS, the overall computational efficiency could be improved by this coupling scheme (depends on how much of the MPS domain is replaced by BEM). The MPS model is advanced by the information from BEM result at each time step up to the time when the free surface is about to break. The MPS solver will continue the simulation with the “old” BEM information just before breaking, based on the assumption that the flow change at the MPS–BEM interface area is small enough. The proposed scheme is validated by two problems and a relatively good accuracy is obtained by comparing with published results in the literature
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