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Adapted simple algorithm for Incompressible SPH Fluids With a Broad Range Viscosity

IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS 2022年第9期28卷 3168-3179页

作者： Liu, Shusen He, Xiaowei Wang, Wencheng Wu, Enhua Chinese Acad Sci Inst Software State Key Lab Comp Sci Beijing 100864 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China Chinese Acad Sci Inst Software Key Lab Human Comp Interact Beijing 100864 Peoples R China Univ Macau Taipa 999078 Macau Peoples R China

In simulating viscous incompressible SPH fluids, incompressibility and viscosity are typically solved in two separate stages. However, the interference between pressure and shear forces could cause the missing of behaviors that include preservation of sharp surface details and remarkable viscous behaviors such as buckling and rope coiling. To alleviate this problem, we introduce for the first time the semi-implicit method for pressure linked equations (simple) into SPH to solve incompressible fluids with a broad range viscosity. We propose to link incompressibility and viscosity solvers, and impose incompressibility and viscosity constraints iteratively to gradually remove the interference between pressure and shear forces. We will also discuss how to solve the particle deficiency problem for both incompressibility and viscosity solvers. Our method is stable at simulating incompressible fluids whose viscosity can range from zero to an extremely high value. Compared to state-of-the-art methods, our method not only produces realistic viscous behaviors, but is also better at preserving sharp surface details.

关键词： Viscosity Mathematical model Couplings Interference Computational modeling Software Force Smoothed particle hydrodynamics (SPH) simple algorithm fluid simulation incompressibility viscosity

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A simple algorithm and min-max formula for the inverse arborescence problem

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DISCRETE APPLIED MATHEMATICS 2021年 295卷 85-93页

作者： Frank, Andras Hajdu, Gergely Eotvos Lorand Univ Dept Operat Res MTA ELTE Egervary Res Grp Pazmany P S 1-C H-1117 Budapest Hungary

In 1998, Hu and Liu developed a strongly polynomial algorithm for solving the inverse arborescence problem that aims at minimally modifying a given cost-function on the edge-set of a digraph D so that an input spanning arborescence of D becomes a cheapest one. In this note, we develop a conceptually simpler algorithm along with a new min-max formula for the minimum modification of the cost-function. The approach is based on a link to a min-max theorem and a simple (two-phase greedy) algorithm by the first author from 1979 concerning the primal optimization problem of finding a cheapest subgraph of a digraph that covers an intersecting family along with the corresponding dual optimization problem, as well. (C) 2021 The Author(s). Published by Elsevier B.V.

关键词： Inverse combinatorial optimization Arborescence Min-max theorem simple algorithm

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Introducing compressibility with simple algorithm

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MATHEMATICS AND COMPUTERS IN SIMULATION 2021年 180卷 328-353页

作者： Qin, Jian Pan, Huachen Rahman, M. M. Tian, Xiaoqing Zhu, Zefei Hangzhou Dianzi Univ Sch Mech Engn Hangzhou 310018 Peoples R China

A comparative assessment between simple and its variant simple-C is conducted based on two-dimensional (2-D) incompressible flows, using a cell-centered finite-volume Li-formulation on a collocated grid. The simple-C (simple Compressibility) scheme additionally combines the concept of artificial compressibility (AC) with the pressure Poisson equation, provoking the diagonal dominance of influence coefficients. An improved nonlinear momentum interpolation scheme is employed at the cell face in discretizing the continuity equation to suppress pressure oscillations. The pseudo-time step Delta t(i) remains the same in both schemes to conserve an analogous scaling with momentum and scalar nodal influence coefficients. Numerical experiments in reference to buoyancy-driven cavity flow dictate that both contrivances execute a residual smoothing enhancement, facilitating an avoidance of the velocity/pressure under-relaxation (UR). However, compared with the simple approach, included benefits of the simple-C method are the use of larger Courant numbers, enhanced robustness and convergence. Excellent consistency is obtained between results available in the literature and numerical solutions obtained by both simple and simple-C solvers. The segregated simple algorithm is finally reformulated in conjunction with a new slope/flux limiter function to predict fluid flow at all speeds. Numerical results show that the compressible variant of simple replicates correct shock speed, well-resolved shock front, contact discontinuity and rarefaction waves when compared with analytical solutions. Compressible laminar flows are computed to further support the accuracy and robustness of proposed algorithm. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of International Association for Mathematics and Computers in Simulation (IMACS).

关键词： simple algorithm Artificial compressibility Under-relaxation factor Convergence and robustness Limiter function

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Exploring simple algorithm for all speeds

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AIN SHAMS ENGINEERING JOURNAL 2023年第2期14卷

作者： Rahman, M. M. Liu, Wenchang Lv, Ming Pan, Huachen Hangzhou Dianzi Univ Sch Mech Engn Hangzhou 310018 Peoples R China

The segregated simple algorithm is developed on a curvilinear collocated grid using a cell-centered finite-volume D-formulation to speculate all-speed fluid flows. The occurrence of velocity-pressure decoupling is unraveled by invoking a consistently formulated dual-dissipation scheme. A modified flux-difference scheme calculates viscous fluxes at all speeds. A local Mach number based indicator is ini-tiated to impose a constraint on the actual state of compressibility, related to the density-updating in the corrector step of simple algorithm. The positivity in influence coefficients' diagonal-dominance with the corrector step is guaranteed by the current contrivance, preventing the need for an under-relaxation (UR) factor. For a selected low Mach number flow, comparisons reveal the relevance of incompressible approach, sprung from the unique compressible solver. (c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams Uni-versity. This is an open access article under the CC BY license (http://***/licenses/by/4.0/).

关键词： simple algorithm Under-relaxation Compressibility Diagonal dominance Convergence and robustness

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An Efficient Parallel Implementation of the simple algorithm Based on a Multigrid Method

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NUMERICAL ANALYSIS AND APPLICATIONS 2020年第1期13卷 1-16页

作者： Kozelkov, A. S. Lashkin, S. V. Kurkin, A. A. Kornev, A. V. Vyalykh, A. M. Russian Fed Nucl Ctr All Russian Res Inst Expt Phys Pr Mira 37 Sarov 607188 Nizhegorodskaya Russia Alekseev Nizhny Novgorod State Syst Univ Ul Minina 24 Nizhnii Novgorod 603950 Russia Natl Res Univ Moscow Avit Inst Volokolamskoe Sh 4 Moscow 125993 Russia

This paper deals with a parallel implementation of the simple (Semi-Implicit Method for Pressure-Linked Equations) algorithm to numerically solve the Navier-Stokes system of equations for viscous incompressible flows. A mechanism of interprocess communication using a mesh decomposition with virtual cells and an algebraic multigrid method is proposed. A method of distributed matrix storage and an algorithm for matrix-vector operations reducing the number of interprocess communications are presented. The results of a series of numerical experiments on structured and unstructured grids (including a problem of external aerodynamics) are presented. Based on the results obtained, an analysis of the influence of multigrid solver settings on the overall efficiency of the algorithm is made. It is shown that the parallel algorithm based on an algebraic multigrid technique proposed for the simple method makes it possible to efficiently calculate problems on hundreds of processors.

关键词： Computational fluid dynamics (CFD) simple algorithm Multigrid solver Modeling

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simple algorithm for current and voltage control of LCL DSTATCOM for power quality improvement

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IET GENERATION TRANSMISSION & DISTRIBUTION 2019年第3期13卷 423-434页

作者： Myneni, Hareesh Kumar, Ganjikunta Siva Natl Inst Technol Dept Elect Engn Warangal Andhra Pradesh India

This study proposes a simple control algorithm for LCL-filter-based distribution static compensator (DSTATCOM) for power quality improvement. The proposed algorithm is able to operate DSTATCOM in both current control mode (CCM) and voltage control mode (VCM) by controlling point of common coupling (PCC) voltage. However, in the conventional method, controlling both filter current and PCC voltage is required to operate DSTATCOM in CCM and VCM, respectively. The achieving of CCM and VCM operations with only PCC voltage controlling method reduces the computational burden on the controller since it eliminates the necessity of filter current sensors. For smooth reference tracking, the interfacing LCL-filter parameters are designed based on the switching dynamics of hysteresis controller (HC) and harmonic order to be compensated by DSTATCOM. The total interfacing inductance value required in LCL DSTATCOM is low when compared with conventional DSTATCOM (L-filter-based DSTATCOM);therefore, the required dc-link voltage is reduced. An adaptive dc-link voltage control has been implemented to improve LCL-DSTATCOM performance in terms of switching voltage stress and efficiency. To show the efficacy of the proposed algorithm, simulation and experimental studies have been performed.

关键词： power grids static VAr compensators power filters PI control power supply quality compensation electric current control power distribution control power system harmonics voltage control LCL-DSTATCOM performance voltage stress efficiency simulation experimental studies simple algorithm current voltage control LCL DSTATCOM power quality improvement simple control algorithm LCL-filter-based distribution static compensator CCM voltage control mode VCM common coupling voltage PCC voltage controlling method filter current sensors interfacing LCL-filter parameters hysteresis controller conventional DSTATCOM filter-based DSTATCOM required dc-link voltage dc-link voltage control

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simple electrocardiography algorithm for localizing accessory pathway in patients with Wolff-Parkinson-White syndrome

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ACTA CARDIOLOGICA 2022年第8期77卷 729-733页

作者： Raharjo, Sunu Budhi Putro, Ardhestiro Hanindyo Santoso, Anwar Hanafy, Dicky Armein Hermanto, Dony Yugo Humaira, Sarah Yuniadi, Yoga Univ Indonesia Fac Med Natl Cardiovasc Ctr Harapan Kita Dept Cardiol & Vasc Med Jakarta Indonesia Ridwan Meuraksa Hosp Jakarta Indonesia Univ Indonesia Fac Med Jakarta Indonesia

Background Existing algorithms to predict the location of an accessory pathway (AP) in Wolff-Parkinson-White Syndrome (WPW) have good sensitivity and specificity but complex with various accuracy and inter-observer agreement rates. A simple algorithm with high accuracy and inter-observer agreement rates is needed. Methods This was a cross-sectional and retrospective diagnostic study. The data were collected by total population sampling from January 2015 to January 2017. Forty-seven patients were included in the study. Data collected were pre-ablation 12-lead ECGs and ablation reports. These ECGs were evaluated by two independent observers using the simplified algorithm and compared with ablation results. Results The algorithm had a sensitivity of 45% on the left free wall, 80% on septal, 92% on the right free wall, and the specificity of 96% on the left free wall, 69% on the septal, 85% on the right free wall for AP prediction. The positive predictive value was 90% on the left free wall, 55% on the septal, and 67% on the right free wall APs. The negative predictive value was 70% on the left free wall, 88% on the septal, and 97% on right free wall AP. The positive likelihood ratio was 11.23 on the left free wall, 2.23 on septal and 6.57 on right free wall APs, and the negative likelihood ratio was 0.57 on left free wall APs, 0.28 on septal, and 0.09 on the right free wall APs. algorithm accuracy varied from 73-87%. Inter-observer agreement calculation was kappa 0.93 for left free wall AP, 0.78 for septal AP, and 0.74 for right free wall AP. Conclusion This simple algorithm has a remarkable accuracy and inter-observer agreement;therefore, it may prove to be helpful even to non-electrophysiologists and has the potential to be integrated into clinical practice

关键词： simple algorithm Wolff-Parkinson-White syndrome ablation

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A simple-based algorithm with enhanced velocity corrections: The COMPLEX method

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COMPUTERS & FLUIDS 2020年第0期198卷 104396-000页

作者： Aguerre, Horacio J. Venier, Cesar M. Pairetti, Cesar, I Marquez Damian, Santiago Nigro, Norberto M. UNL CONICET Ctr Invest Metodos Computacionales Santa Fe Argentina Univ Nacl Rosario Fac Ciencias Exactas Ingn & Agrimensura Escuela Ingn Mecan Rosario Argentina Univ Tecnol Nacl Fac Reg Santa Fe Santa Fe Argentina Univ Nacl Litoral Fac Ingn & Ciencias Hidr Santa Fe Argentina

This paper introduces a new pressure-velocity coupling algorithm based on the simpleC method. The new approach considers the neighbour velocity corrections of simpleC as a Taylor series expansion, introducing a first-order term to increase the accuracy of the approximation. The new term includes a velocity correction gradient which is assumed to be a scalar matrix constrained by means of a mass conservation equation. The stability of the method is analyzed via a Fourier decomposition of the error showing a better convergence rate than simple and simpleC for high relaxation factors. The new method is tested in two incompressible laminar flow problems. Then, the analysis is extended to a turbulent flow case. In all cases, the conclusions of the stability analysis are verified. The current proposal sets a theoretical baseline for further improvements of simple-based algorithms. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： simple algorithm Segregated methods Collocated grids OpenFOAM(R) Finite volume method

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Outflow velocity for simple algorithm for unsteady forced convection flows with variable density

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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER 2018年 92卷 73-77页

作者： Asako, Yutaka Faghri, Mohammad Tan, Lit Ken Sidik, Nor Azwadi bin Che Univ Technol Malaysia Dept Mech Precis Engn Malaysia Japan Int Inst Technol Jalan Sultan Yahya Petra Kuala Lumpur 54100 Malaysia Univ Rhode Isl Dept Mech Ind & Syst Engn Kingston RI 02881 USA

The simple algorithm for the pressure-velocity coupling has been adopted by many commercial and non-commercial CFD codes. The simple algorithm requires all normal velocities at the boundaries before solving the pressure correction equation. These velocities must imply an overall mass balance. In this paper, a new procedure to recalculate the outflow velocity for the Neumann type outflow boundary for forced convection with variable density is proposed. As an example of the utilization of this procedure, the outflow normal velocity of a circular duct was computed and the results were compared with the results using the new modified procedure.

关键词： simple algorithm Outlet flow velocity Variable density Forced convection

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Efficiency Analysis of the Parallel Implementation of the simple algorithm on Multiprocessor Computers

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JOURNAL OF APPLIED MECHANICS AND TECHNICAL PHYSICS 2017年第7期58卷 1242-1259页

作者： Lashkin, S. V. Kozelkov, A. S. Yalozo, A. V. Gerasimov, V. Yu. Zelensky, D. K. State Atom Energy Corp Rosatom Russian Fed Nucl Ctr All Russia Res Inst Expt Phys Sarov Nizhny Novgorod Russia Alekseev State Tech Univ Nizhnii Novgorod Russia

This paper describes the details of the parallel implementation of the simple algorithm for numerical solution of the Navier-Stokes system of equations on arbitrary unstructured grids. The iteration schemes for the serial and parallel versions of the simple algorithm are implemented. In the description of the parallel implementation, special attention is paid to computational data exchange among processors under the condition of the grid model decomposition using fictitious cells. We discuss the specific features for the storage of distributed matrices and implementation of vector-matrix operations in parallel mode. It is shown that the proposed way of matrix storage reduces the number of interprocessor exchanges. A series of numerical experiments illustrates the effect of the multigrid SLAE solver tuning on the general efficiency of the algorithm;the tuning involves the types of the cycles used (V, W, and F), the number of iterations of a smoothing operator, and the number of cells for coarsening. Two ways (direct and indirect) of efficiency evaluation for parallelization of the numerical algorithm are demonstrated. The paper presents the results of solving some internal and external flow problems with the evaluation of parallelization efficiency by two algorithms. It is shown that the proposed parallel implementation enables efficient computations for the problems on a thousand processors. Based on the results obtained, some general recommendations are made for the optimal tuning of the multigrid solver, as well as for selecting the optimal number of cells per processor.

关键词： computational fluid dynamics simple algorithm multigrid solver modeling

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