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COROTATIONAL TOTAL LAGRANGIAN FORMULATION FOR 3-DIMENSIONAL BEAM ELEMENT

AIAA JOURNAL 1992年第3期30卷 797-804页

作者： HSIAO, KM National Chiao Tung University Hsinchu Taiwan Republic of China

A corotational total Lagrangian formulation of beam element is presented for the nonlinear analysis of three-dimensional beam structures with large rotations but small strains. The nonlinear coupling among the bending, twisting, and stretching deformations is considered. All of the element deformations and equations are defined in body-attached element coordinates. Three rotation parameters are proposed to determine the orientation of the element cross section. Two sets of element nodal parameters termed explicit nodal parameters and implicit nodal parameters are introduced. The explicit nodal parameters are used in the assembly of the system equations from the element equations and chosen to be three components of the incremental translation vector and three components of the incremental rotation vector. The implicit nodal parameters are used to determine the deformations of the beam element and chosen to be three components of the total displacement vector and nodal values of the three rotation parameters. The element internal nodal forces corresponding to the implicit nodal parameters are obtained from the virtual work principle. numerical examples are presented and compared with the numerical and experimental results reported in the literature to demonstrate the accuracy and efficiency of the proposed method.

关键词： Beam (Structures) Stiffness Matrices Direct Stiffness Method Newton Raphson Method Young's Modulus Material Properties Aspect Ratio Six Degree of Freedom numerical algorithms Transverse Shear

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A data assimilation model for turbulent flows using continuous adjoint formulation

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PHYSICS OF FLUIDS 2018年第10期30卷 105108-105108页

作者： He, Chuangxin Liu, Yingzheng Gan, Lian Shanghai Jiao Tong Univ Sch Mech Engn Key Lab Educ Minist Power Machinery & Engn 800 Dongchuan Rd Shanghai 200240 Peoples R China Shanghai Jiao Tong Univ Gas Turbine Res Inst 800 Dongchuan Rd Shanghai 200240 Peoples R China Univ Durham Dept Engn Stockton Rd Durham DH1 3LE England

A generalized data assimilation model for turbulent flows using the continuous adjoint formulation is proposed. Within this formulation, the Spalart-Allmaras turbulence model is modified by adding a correction function beta as a spatially varying coefficient to the turbulence production term. The model-form error is thus corrected by optimizing the beta distribution, using the adjoint equations and the corresponding boundary conditions, to minimize the discrepancy between the predictions and observations. In addition, a constraint is applied to drive beta toward a large value to avoid the flow unsteadiness owing to the low eddy viscosity. The present adjoint-based data assimilation (ABDA) model is expected to be applicable to various flow conditions unsolvable by the simple optimization of the model constant. This model is fully equation-driven and is thus computationally cheaper than the discretized adjoint method, as well as convenient to be implemented in the existing computational fluid dynamics codes. The flow over a cylinder with synthetic observations, the free round jet, the flow over a hump, and the three-dimensional flow over a wall-mounted cube, all of which are challenging for original Reynolds-averaged Navier-Stokes simulations, are employed to successfully demonstrate the reliability and capacity of the present ABDA model. The first-order scheme applied to the adjoint equations exhibits little effects on the final assimilation results, but improves the robustness significantly, and drives beta to another solution that can also minimize the cost function. The present ABDA model is efficient in the heavy assimilation work of different types of shear and separated flows. Published by AIP Publishing.

关键词： Computational fluid dynamics Turbulent flows Turbulence theory and modelling numerical algorithms Data visualization Vortex dynamics Turbulence simulations

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Long-Term Analytical Boundedness Conditions for Relative Orbits Under Third-Body Perturbations

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2019年第10期42卷 2331-2341页

作者： Nie, Tao Gurfil, Pini Zhang, Shijie Harbin Inst Technol Res Ctr Satellite Technol Harbin 150001 Heilongjiang Peoples R China Technion Israel Inst Technol Fac Aerosp Engn IL-32000 Haifa Israel

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Enhancement of the finite-element method for the analysis of vertical train-track interactions

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART F-JOURNAL OF RAIL AND RAPID TRANSIT 2009年第6期223卷 609-620页

作者： Yang, S. C. Korea Railroad Res Inst Vehicle & Track Res Dept Uiwang Si 437757 Gyeonggi Do South Korea

The accuracy of the simulation of train-track interaction can be improved by adding a node at the point of loading, when a contact force exists within the beam element that models the rail. This causes difficulties in the formulation and entails large computational times since the node moves along with the point of contact. In this study, a more simplified method that can represent the discontinuities of slope deflection at the location of both the sleeper and of the moving contact force, while employing the customary finite-element method, has been presented. The simulation of the existence of such an added node without explicitly including it is realized by modifying the Hertzian spring coefficient and adding the additional mass matrix to the existing mass matrix. Also, to enhance the convergence and to overcome the computational burden of load vector calculations at all iterations, a modified Newmark-beta integral scheme is proposed. The suggested model was validated by comparing the results with field-test data and other numerical models reported in the literature by other researchers.

关键词： train-track interaction finite-element Timoshenko beam discontinuity in slope deflection numerical algorithms wheel flat

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Machine learning-based multi-objective optimization for efficient identification of crystal plasticity model parameters

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COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2023年第PartB期403卷

作者： Veasna, Khem Feng, Zhangxi Zhang, Qi Knezevic, Marko Univ New Hampshire Dept Math & Stat Durham NH 03824 USA Univ New Hampshire Dept Mech Engn Durham NH 03824 USA

A set of constitutive model parameters along with crystallography governs the activation of deformation mechanisms in crystal plasticity. The constitutive parameters are typically established by fitting of mechanical data, while microstructural data is used for verification. This paper develops a Pareto-based multi-objective machine learning methodology for efficient identification of crystal plasticity constitutive parameters. Specifically, the methodology relays on a Gaussian processes-based surrogate model to limit the number of calls to a given crystal plasticity model, and, consequently, to increase the computational efficiency. The constitutive parameters pertaining to an Elasto-Plastic Self-Consistent (EPSC) crystal plasticity model including a dislocation density-based hardening law, a backstress law, and a phase transformations law are identified for two materials, a dual phase (DP) steel, DP780, subjected to load reversals and a stainless steel (SS), 316L, subjected to strain rate and temperature sensitive deformation. The latter material undergoes plasticity-induced martensitic phase transformations. The optimization objectives were the quasi static flow stress data for the DP steel case study, while a set of strain-rate and temperature sensitive flow stress and phase volume fraction data for the SS case study. The procedure and results for the two case studies are presented and discussed illustrating advantages and versatility of the developed methodology. In particular, the efficiency of the developed methodology over an existing genetic algorithm methodology is discussed. Additionally, the parameters identified for the SS case study were utilized to simulate three biaxial tensile loading paths using a finite element implementation of EPSC for further verification. (c) 2022 Elsevier B.V. All rights reserved.

关键词： Crystal plasticity Machine learning numerical algorithms Parameter identification

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Constitutive-damage modeling and computational implementation for simulation of elasto-viscoplastic-damage behavior of polymeric foams over a wide range of strain rates and temperatures

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INTERNATIONAL JOURNAL OF PLASTICITY 2020年 130卷 102712-102712页

作者： Lee, Jeong-Ho Ryu, Dong-Man Lee, Chi-Seung Boston Univ Dept Mech Engn Boston MA 02215 USA Michigan State Univ Dept Mech Engn E Lansing MI 48824 USA Pusan Natl Univ Hosp Biomed Res Inst Busan 49241 South Korea Pusan Natl Univ Sch Med Dept Convergence Med Busan 49241 South Korea Pusan Natl Univ Sch Med Dept Biomed Engn Busan 49241 South Korea

The material behavior and damage of polymeric foams (e.g., polyurethane foam and polystyrene foam) are extremely complex under compression, depending on strain rates and temperatures. In the present study, the elasto-viscoplastic-damage behavior of polymeric foams over a wide range of strain rates and temperature is evaluated and predicted using the modified Gurson-TvergaardNeedleman-Lemaitre (GTNL) model and the modified Khan-Huang-Liang (KHL) model. A modified GTNL model is introduced to describe phenomena of decreasing void volume fraction and elastic modulus for polymeric foams under uniaxial compression. The modified KHL model is proposed to evaluate the nonlinear strain rate- and temperature-dependent material behavior of polymeric foams. The full derivation of the implicit integration algorithm of the proposed modified GTNL-KHL model is introduced, and a user-defined material (UMAT) subroutine for commercial finite element analysis code (i.e., ABAQUS) is established. Using the UMAT, the damage characteristics (e.g., void volume fraction and elastic modulus changes) and the nonlinear material behavior (e.g., linear elastic, softening/plateau and densification) of polymeric foams under uniaxial compression with various strain rates and temperatures are successfully simulated.

关键词： Polymeric foams Constitutive behavior Elastic-viscoplastic material Finite elements numerical algorithms

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Computationally efficient identification of continuous-time Lur'e-type systems with stability guarantees

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AUTOMATICA 2022年 136卷 110012-110012页

作者： Shakib, Mohammad Fahim Pogromsky, Alexander Yu Pavlov, Alexey van de Wouw, Nathan Eindhoven Univ Technol Dept Mech Engn Eindhoven Netherlands NTNU Dept Geosci & Petr Trondheim Norway Univ Minnesota Dept Civil Environm & Geoengn Minneapolis MN USA

In this paper, we propose a parametric system identification approach for a class of continuous-time Lur'e-type systems. Using the Mixed-Time-Frequency (MTF) algorithm, we show that the steady-state model response and the gradient of the model response with respect to its parameters can be computed in a numerically fast and efficient way, allowing efficient use of global and local optimization methods to solve the identification problem. Furthermore, by enforcing the identified model to be inside the set of convergent models, we certify a stability property of the identified model, which allows for reliable generalized usage of the model also for other excitation signals than those used to identify the model. The effectiveness and benefits of the proposed approach are demonstrated in a simulation case study. Furthermore, we have experimentally shown that the proposed approach provides fast identification of both medical equipment and patient parameters in mechanical ventilation and, thereby, enables improved patient treatment. (C) 2021 The Author(s). Published by Elsevier Ltd.

关键词： System identification Parameter identification Nonlinear systems numerical algorithms Global stability Steady-state errors Wiener Hammerstein Nonlinear feedback

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On discontinuities when computing the stress-field from the strain: A finite volume discretization

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INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2022年 254卷

作者： Cameron, Benjamin C. Tasan, C. Cem MIT Dept Civil & Environm Engn Cambridge MA USA Univ Southampton Dept Mech Engn Southampton England MIT Dept Mat Sci & Engn Cambridge MA 02142 USA

This article focuses on developing a finite volume discretization for a recently-developed and widely-applicable system of PDEs, enabling computation of the full-field stress from a measured strain field and traction boundary conditions. This is applicable to datasets obtained via DIC, and applies when the material properties are unknown. Interestingly, the strain or strain-rate discontinuities at the interfaces between finite volumes cause reflection and transmission of the principal stresses. Hence, we analytically analyze the solution structure in this case, enabling the development of the discretization. In addition, analysis is conducted translating knowledge of the traction at the boundary into boundary conditions, so that the numerical method can be applied to a variety of loading conditions. The finite volume discretization is validated using strain fields obtained from finite element simulations. The developed discretization enables the system of equations to be applied to irregular geometries, finite deformation, general boundary conditions, and avoids instabilities that arise due to the Courant-Friedrichs-Lewy condition, significantly increasing the range of applications for which these PDEs can be applied.

关键词： Constitutive behavior Characteristics Mechanical testing numerical algorithms Inverse problem

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DEVELOPMENT OF A 3-DIMENSIONAL MODEL FOR THE DARRIEUS ROTOR AND ITS WAKE

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JOURNAL OF PROPULSION AND POWER 1995年第2期11卷 185-195页

作者： RAJAGOPALAN, RG BERG, DE KLIMAS, PC SANDIA NATL LABS TECH STAFFALBUQUERQUENM 87185

A computational procedure suitable for simulating the flowfield, performance, and interference of a curved-bladed, three-dimensional Darrieus wind turbine is presented. The rotor blades are modeled as time-averaged sources in the steady, laminar momentum equations solved on a Cartesian grid. As an illustration of the potential of the method, terrain and generator box influence on the behavior of the turbine are simulated in a uniform freestream wind. The generator box of the turbine is modeled as a solid cube and viscous no-slip boundary conditions are prescribed on the generator box and the ground plane, The influence of the terrain on the flowfield of the turbine is considered for two hypothetical, two-dimensional ridge-lines. Computed turbine performance, such as the power coefficient and the normal force coefficient, are compared with results from Sandia field tests and a theoretical method based on stream-tube momentum balance for a stand-alone turbine. Quantitative differences in the performance of the Sandia 17-m turbine with and without the hypothetical terrains are discussed. Qualitative behavior of the flowfield under the influence of the ground plane is also presented with the help of velocity vector plots acid path lines.

关键词： Vertical Axis Wind Turbines Aerodynamic Characteristics Angle of Attack Turbine Blades Flow Conditions Conservation Equations Velocity Profiles Navier Stokes Equations Computational Fluid Dynamics numerical algorithms

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An improved discrete velocity method (DVM) for efficient simulation of flows in all flow regimes

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PHYSICS OF FLUIDS 2018年第6期30卷 062005-062005页

作者： Yang, L. M. Shu, C. Yang, W. M. Chen, Z. Dong, H. Natl Univ Singapore Dept Mech Engn 10 Kent Ridge Crescent Singapore 119260 Singapore Nanjing Univ Aeronaut & Astronaut Dept Aerodynam Coll Aerosp Engn Yudao St Nanjing 210016 Jiangsu Peoples R China

In this paper, an improved discrete velocity method (DVM) is developed for efficient simulation of fluid problems in all flow regimes. Compared with the conventional explicit DVM, the present scheme could effectively remove its drawbacks of low accuracy and efficiency in continuum flow regime with no deterioration of its performance in rarefied flow regime. One of the novel strategies adopted in the new method is to introduce a prediction step for solving the macroscopic governing equation. By using the prediction step, the equilibrium state is first estimated before solving the discrete velocity Boltzmann equation (DVBE). As a result, the collision term in the DVBE can be discretized implicitly to improve the stability and efficiency of the conventional explicit DVM. Another contribution of the new method is to physically reconstruct numerical flux at the cell interface by incorporating the collision effect into the process. To maintain simplicity and efficiency of the conventional DVM, in the present scheme, the collision effect in the flux reconstruction at the cell interface is considered through the solution of the macroscopic governing equation. This can effectively control the effect of numerical dissipation in the process of updating the macroscopic flow variables in the continuum flow regime. Analyses indicate that the prediction step does not contribute to the evolution of distribution functions in the highly rarefied flow regime while dominating the solutions in the continuum flow regime. Accordingly, the improved scheme automatically converges toward the conventional explicit DVM in the free molecular flow regime and approaches the Navier-Stokes solver in the continuum flow regime. Published by AIP Publishing.

关键词： Kinetic theory Nonequilibrium statistical mechanics Fluid flows Navier Stokes equations Microfluidics Finite volume methods Equilibrium thermodynamics Rarefied gas dynamics Hypersonic flows numerical algorithms

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