The Experts below are selected from a list of 16221 Experts worldwide ranked by ideXlab platform
Yong Zhao - One of the best experts on this subject based on the ideXlab platform.
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an Unstructured Mesh arbitrary lagrangian eulerian unsteady incompressible flow solver and its application to insect flight aerodynamics
Physics of Fluids, 2016Co-Authors: Xiaohui Su, Yong ZhaoAbstract:In this paper, an Unstructured Mesh Arbitrary Lagrangian-Eulerian (ALE) incompressible flow solver is developed to investigate the aerodynamics of insect hovering flight. The proposed finite-volume ALE Navier-Stokes solver is based on the artificial compressibility method (ACM) with a high-resolution method of characteristics-based scheme on Unstructured grids. The present ALE model is validated and assessed through flow passing over an oscillating cylinder. Good agreements with experimental results and other numerical solutions are obtained, which demonstrates the accuracy and the capability of the present model. The lift generation mechanisms of 2D wing in hovering motion, including wake capture, delayed stall, rapid pitch, as well as clap and fling are then studied and illustrated using the current ALE model. Moreover, the optimized angular amplitude in symmetry model, 45°, is firstly reported in details using averaged lift and the energy power method. Besides, the lift generation of complete cyclic cl...
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an Unstructured Mesh arbitrary lagrangian eulerian unsteady incompressible flow solver and its application to insect flight aerodynamics
Physics of Fluids, 2016Co-Authors: Yuanwei Cao, Yong ZhaoAbstract:In this paper, an Unstructured Mesh Arbitrary Lagrangian-Eulerian (ALE) incompressible flow solver is developed to investigate the aerodynamics of insect hovering flight. The proposed finite-volume ALE Navier-Stokes solver is based on the artificial compressibility method (ACM) with a high-resolution method of characteristics-based scheme on Unstructured grids. The present ALE model is validated and assessed through flow passing over an oscillating cylinder. Good agreements with experimental results and other numerical solutions are obtained, which demonstrates the accuracy and the capability of the present model. The lift generation mechanisms of 2D wing in hovering motion, including wake capture, delayed stall, rapid pitch, as well as clap and fling are then studied and illustrated using the current ALE model. Moreover, the optimized angular amplitude in symmetry model, 45°, is firstly reported in details using averaged lift and the energy power method. Besides, the lift generation of complete cyclic clap and fling motion, which is simulated by few researchers using the ALE method due to large deformation, is studied and clarified for the first time. The present ALE model is found to be a useful tool to investigate lift force generation mechanism for insect wing flight.
N A Adams - One of the best experts on this subject based on the ideXlab platform.
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a feature aware sph for isotropic Unstructured Mesh generation
Computer Methods in Applied Mechanics and Engineering, 2021Co-Authors: N A AdamsAbstract:Abstract In this paper, we present a feature-aware SPH method for the concurrent and automated isotropic Unstructured Mesh generation. Two additional objectives are achieved with the proposed method compared to the original SPH-based Mesh generator (Fu et al., 2019). First, a feature boundary correction term is introduced to address the issue of incomplete kernel support at the boundary vicinity. The Mesh generation of feature curves, feature surfaces and volumes can be handled concurrently without explicitly following a dimensional sequence. Second, a two-phase model is proposed to characterize the Mesh-generation procedure by a feature-size-adaptation phase and a Mesh-quality-optimization phase. By proposing a new error measurement criterion and an adaptive control system with two sets of simulation parameters, the objectives of faster feature-size adaptation and local Mesh-quality improvement are merged into a consistent framework. The proposed method is validated with a set of 2D and 3D numerical tests with different complexities and scales. The results demonstrate that high-quality Meshes are generated with a significant speedup of convergence.
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a consistent parallel isotropic Unstructured Mesh generation method based on multi phase sph
Computer Methods in Applied Mechanics and Engineering, 2020Co-Authors: N A AdamsAbstract:Abstract In this paper, we propose a consistent parallel Unstructured Mesh generator based on a multi-phase SPH method. A set of physics-motivated modeling equations are developed to achieve the targets of domain decomposition, communication volume optimization and high-quality Unstructured Mesh generation simultaneously. A unified density field is defined as the target function for both partitioning the geometry and distributing the Mesh-vertexes. A multi-phase Smoothing Particle Hydrodynamics (SPH) method is employed to solve the governing equations. All the optimization targets are achieved implicitly and consistently by the particle relaxation procedure without constructing triangulation/tetrahedralization explicitly. The target of communication reduction is achieved by introducing a surface tension model between distinct partitioning sub-domains, which are characterized by colored SPH particles. The resulting partitioning diagram features physically localized sub-domains and optimized interface communication. The target of optimizing the Mesh quality is achieved by introducing a tailored equation-of-state (EOS) and a smooth isotropic kernel function. The Mesh quality near the interface of neighboring sub-domains is improved by gradually removing the surface-tension force once a steady state is achieved. The proposed method is developed basing on a new parallel environment for multi-resolution SPH to exploit both coarse- and fine-grained parallelism. A set of benchmarks are conducted to verify that all the optimization targets are achieved consistently within the current framework.
Matthew D Piggott - One of the best experts on this subject based on the ideXlab platform.
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efficient Unstructured Mesh generation for marine renewable energy applications
Renewable Energy, 2018Co-Authors: Alexandros Avdis, Adam S Candy, Jon Hill, Stephan C Kramer, Matthew D PiggottAbstract:Renewable energy is the cornerstone of preventing dangerous climate change whilst maintaining a robust energy supply. Tidal energy will arguably play a critical role in the renewable energy portfolio as it is both predictable and reliable, and can be put in place across the globe. However, installation may impact the local and regional ecology via changes in tidal dynamics, sediment transport pathways or bathymetric changes. In order to mitigate these effects, tidal energy devices need to be modelled, to predict hydrodynamic changes. Robust Mesh generation is a fundamental component required for developing simulations with high accuracy. However, Mesh generation for coastal domains can be an elaborate procedure. Here, we describe an approach combining Mesh generators with Geographical Information Systems. We demonstrate robustness and efficiency by constructing a Mesh with which to examine the potential environmental impact of a tidal turbine farm installation in the Orkney Islands. The Mesh is then used with two well-validated ocean models, to compare their flow predictions with and without a turbine array. The results demonstrate that it is possible to create an easy-to-use tool to generate high-quality Meshes for combined coastal engineering, here tidal turbines, and coastal ocean simulations.
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three dimensional tsunami propagation simulations using an Unstructured Mesh finite element model
Journal of Geophysical Research, 2013Co-Authors: Yusuke Oishi, Stephan C Kramer, Matthew D Piggott, Takuto Maeda, G S Collins, Hiroaki Tsushima, Takashi FurumuraAbstract:[1] Large-scale tsunami propagation simulations from the fault region to the coast are conducted using a three-dimensional (3-D) parallel Unstructured Mesh finite element code (Fluidity-ICOM). Unlike conventional 2-D approximation models, our tsunami model solves the full 3-D incompressible Navier-Stokes (NS) equations. The model is tested against analytical solutions to simple dispersive wave propagation problems. Comparisons of our 3-D NS model results with those from linear shallow water and linear dispersive wave models demonstrate that the 3-D NS model simulates the dispersion of very short wavelength components more accurately than the 2-D models. This improved accuracy is achieved using only a small number (three to five) of vertical layers in the Mesh. The numerical error in the wave velocity compared with the linear wave theory is less than 3% up to kH = 40, where k is the wave number and H is the sea depth. The same 2-D and 3-D models are also used to simulate two earthquake-generated tsunamis off the coast of Japan: the 2004 off Kii peninsula and the 2011 off Tohoku tsunamis. The linear dispersive and NS models showed good agreement in the leading waves but differed especially in their near-source, short wavelength dispersive wave components. This is consistent with the results from earlier tests, suggesting that the 3-D NS simulations are more accurate. The computational performance on a parallel computer showed good scalability up to 512 cores. By using a combination of Unstructured Meshes and high-performance computers, highly accurate 3-D tsunami simulations can be conducted in a practical timescale.
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accurate representation of geostrophic and hydrostatic balance in Unstructured Mesh finite element ocean modelling
Ocean Modelling, 2011Co-Authors: James R Maddison, David P Marshall, Matthew D PiggottAbstract:Abstract Accurate representation of geostrophic and hydrostatic balance is an essential requirement for numerical modelling of geophysical flows. Potentially, Unstructured Mesh numerical methods offer significant benefits over conventional structured Meshes, including the ability to conform to arbitrary bounding topography in a natural manner and the ability to apply dynamic Mesh adaptivity. However, there is a need to develop robust schemes with accurate representation of physical balance on arbitrary Unstructured Meshes. We discuss the origin of physical balance errors in a finite element discretisation of the Navier–Stokes equations using the fractional timestep pressure projection method. By considering the Helmholtz decomposition of forcing terms in the momentum equation, it is shown that the components of the buoyancy and Coriolis accelerations that project onto the non-divergent velocity tendency are the small residuals between two terms of comparable magnitude. Hence there is a potential for significant injection of imbalance by a numerical method that does not compute these residuals accurately. This observation is used to motivate a balanced pressure decomposition method whereby an additional “balanced pressure” field, associated with buoyancy and Coriolis accelerations, is solved for at increased accuracy and used to precondition the solution for the dynamical pressure. The utility of this approach is quantified in a fully non-linear system in exact geostrophic balance. The approach is further tested via quantitative comparison of Unstructured Mesh simulations of the thermally driven rotating annulus against laboratory data. Using a piecewise linear discretisation for velocity and pressure (a stabilised P1P1 discretisation), it is demonstrated that the balanced pressure decomposition method is required for a physically realistic representation of the system.
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anisotropic Mesh adaptivity for multi scale ocean modelling
Philosophical Transactions of the Royal Society A, 2009Co-Authors: Matthew D Piggott, Patrick E Farrell, C R Wilson, Gerard J Gorman, Christopher C PainAbstract:Research into the use of Unstructured Mesh methods in oceanography has been growing steadily over the past decade. The advantages of this approach for domain representation and non-uniform resolution are clear. However, a number of issues remain, in particular those related to the computational cost of models produced using Unstructured Mesh methods compared with their structured Mesh counterparts. Mesh adaptivity represents an important means to improve the competitiveness of Unstructured Mesh models, where high resolution is only used when and where necessary. In this paper, an optimization-based approach to Mesh adaptivity is described where emphasis is placed on capturing anisotropic solution characteristics. Comparisons are made between the results obtained with uniform isotropic resolution, isotropic adaptive resolution and fully anisotropic adaptive resolution.
Xiaohui Su - One of the best experts on this subject based on the ideXlab platform.
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an Unstructured Mesh arbitrary lagrangian eulerian unsteady incompressible flow solver and its application to insect flight aerodynamics
Physics of Fluids, 2016Co-Authors: Xiaohui Su, Yong ZhaoAbstract:In this paper, an Unstructured Mesh Arbitrary Lagrangian-Eulerian (ALE) incompressible flow solver is developed to investigate the aerodynamics of insect hovering flight. The proposed finite-volume ALE Navier-Stokes solver is based on the artificial compressibility method (ACM) with a high-resolution method of characteristics-based scheme on Unstructured grids. The present ALE model is validated and assessed through flow passing over an oscillating cylinder. Good agreements with experimental results and other numerical solutions are obtained, which demonstrates the accuracy and the capability of the present model. The lift generation mechanisms of 2D wing in hovering motion, including wake capture, delayed stall, rapid pitch, as well as clap and fling are then studied and illustrated using the current ALE model. Moreover, the optimized angular amplitude in symmetry model, 45°, is firstly reported in details using averaged lift and the energy power method. Besides, the lift generation of complete cyclic cl...
Ian Turner - One of the best experts on this subject based on the ideXlab platform.
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an Unstructured Mesh finite element method for solving the multi term time fractional and riesz space distributed order wave equation on an irregular convex domain
Applied Mathematical Modelling, 2019Co-Authors: Y M Zhao, F.l. Wang, Ian TurnerAbstract:Abstract In this paper, the numerical analysis for a multi-term time fracstional and Riesz space distributed-order wave equation is discussed on an irregular convex domain. Firstly, the equation is transformed into a multi-term time-space fractional wave equation using the mid-point quadrature rule to approximate the distributed-order Riesz space derivative. Next, the equation is solved by discretising in time using a Crank–Nicolson scheme and in space using the finite element method (FEM) with an Unstructured Mesh, respectively. Furthermore, stability and convergence are investigated by introducing some important lemmas on irregular convex domain. Finally, some examples are provided to show the effectiveness and correctness of the proposed numerical method.
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Unstructured Mesh finite difference finite element method for the 2d time space riesz fractional diffusion equation on irregular convex domains
Applied Mathematical Modelling, 2018Co-Authors: Libo Feng, Ian Turner, Qianqian Yang, Pinghui ZhuangAbstract:Fractional differential equations are powerful tools to model the non-locality and spatial heterogeneity evident in many real-world problems. Although numerous numerical methods have been proposed, most of them are limited to regular domains and uniform Meshes. For irregular convex domains, the treatment of the space fractional derivative becomes more challenging and the general methods are no longer feasible. In this work, we propose a novel numerical technique based on the Galerkin finite element method (FEM) with an Unstructured Mesh to deal with the space fractional derivative on arbitrarily shaped convex and non-convex domains, which is the most original and significant contribution of this paper. Moreover, we present a second order finite difference scheme for the temporal fractional derivative. In addition, the stability and convergence of the method are discussed and numerical examples on different irregular convex domains and non-convex domains illustrate the reliability of the method. We also extend the theory and develop a computational model for the case of a multiply-connected domain. Finally, to demonstrate the versatility and applicability of our method, we solve the coupled two-dimensional fractional Bloch-Torrey equation on a human brain-like domain and exhibit the effects of the time and space fractional indices on the behaviour of the transverse magnetization.
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a novel Unstructured Mesh finite element method for solving the time space fractional wave equation on a two dimensional irregular convex domain
Fractional Calculus and Applied Analysis, 2017Co-Authors: Xiaoyun Jiang, Ian TurnerAbstract:Most existing research on applying the finite element method to discretize space fractional operators is studied on regular domains using either uniform structured triangular Meshes, or quadrilateral Meshes. Since many practical problems involve irregular convex domains, such as the human brain or heart, which are difficult to partition well with a structured Mesh, the existing finite element method using the structured Mesh is less efficient. Research on the finite element method using a completely Unstructured Mesh on an irregular domain is of great significance. In this paper, a novel Unstructured Mesh finite element method is developed for solving the time-space fractional wave equation on a two-dimensional irregular convex domain. The novel Unstructured Mesh Galerkin finite element method is used to discretize in space and the Crank-Nicolson scheme is used to discretize the Caputo time fractional derivative. The implementation of the Unstructured Mesh Crank-Nicolson Galerkin method (CNGM) is detailed and the stability and convergence of the numerical scheme are analysed. Numerical examples are presented to verify the theoretical analysis. To highlight the ability of the proposed Unstructured Mesh Galerkin finite element method, a comparison of the Unstructured Mesh with the structured Mesh in the implementation of the numerical scheme is conducted. The proposed numerical method using an Unstructured Mesh is shown to be more effective and feasible for practical applications involving irregular convex domains.
