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Effect of transformations of numerical parameters in automatic algorithm configuration

OPTIMIZATION LETTERS 2018年第8期12卷 1741-1753页

作者： Franzin, Alberto Caceres, Leslie Perez Stutzle, Thomas ULB IRIDIA 50 Av F Roosevelt B-1050 Brussels Belgium

We study the impact of altering the sampling space of parameters in automatic algorithm configurators. We show that a proper transformation can strongly improve the convergence towards better configurations;at the same time, biases about good parameter values, possibly based on misleading prior knowledge, may lead to wrong choices in the transformations and be detrimental for the configuration process. To emphasize the impact of the transformations, we initially study their effect on configuration tasks with a single parameter in different experimental settings. We also propose a mechanism for how to adapt towards an appropriate transformation and give exemplary experimental results of that scheme.

关键词： Automatic algorithm configuration numerical parameters Parameter tuning Parameter transformation

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numerical parameters for deep drawing simulation of a double bowl sink

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MATERIALS TESTING 2017年第5期59卷 480-484页

作者： Sener, Bora Yurci, Mehmet Emin Yildiz Tech Univ Dept Mech Engn TR-34349 Istanbul Turkey Yildiz Tech Univ Dept Mech Engn Mat Sci & Mfg Technol Div Istanbul Turkey

numerical parameters have significant impact on the results of finite element simulations. Wrong selection of these parameters causes erroneous results and too long computation time in the analyses. Therefore, numerical parameters should be selected properly in order to obtain accurate results in the finite element simulations. In this study, the effects of the numerical parameters used in finite element simulations are investigated. Deep drawing of a double bowl sink is modeled and simulations are done with different parameters. Influences of element size and refinement level on the blank, the effect of the number of elements on the die radius and dynamic effects are investigated and optimum parameters are determined. The results obtained are compared with experimental data, and a good agreement is observed.

关键词： numerical parameters finite element simulation deep drawing double bowl sink

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Effect of numerical parameters on plastic CTOD

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FRATTURA ED INTEGRITA STRUTTURALE 2017年第41期11卷 149-156页

作者： Antunes, F. V. Simoes, R. Branco, R. Prates, P. Univ Coimbra Coimbra Portugal

Fatigue crack growth (FCG) is associated with irreversible and non-linear processes happening at the crack tip. This explains different problems observed in the use of da/dN-Delta K curves, namely the inability to explain stress ratio and load history effects. The replacement of Delta K by nonlinear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. However, the determination of CTOD, using the finite element method, depends on different numerical parameters, not sufficiently studied so far. The objective here is to study the effect of these parameters on plastic CTOD, and therefore on da/dN-Delta CTODp curves. A transient behaviour was found at the beginning of numerical crack propagation which is linked to the formation of residual plastic wake. Therefore, a minimum number of crack increments is required to obtain stabilized values. On the other hand, the predicted Delta CTODp decreases with the distance to crack tip. Close to the crack tip, sensitivity to the measured values is much higher, but it also exists at remote positions. In addition, the mesh has a relatively low influence on Delta CTODp. Finally, the effect of the number of load cycles between crack increments greatly depends on material properties.

关键词： Crack tip opening displacement (CTOD) Plastic CTOD Finite element method numerical parameters

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Cup drawing predictions for a 6016-T4 aluminum alloy

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MATERIALS TESTING 2025年第6期67卷 1079-1087页

作者： Esener, Emre Aksen, Toros Arda Firat, Mehmet Bilecik Seyh Edebali Univ Mech Engn Bilecik Turkiye Sakarya Univ Mech Engn Sakarya Turkiye

This study investigates the interplay between process and computation parameters affecting the accuracy of finite element analysis (FEA) results for cup manufacturing. By revisiting the Esaform-2021 benchmark, this research aims to elucidate the impact of process parameters on FEA accuracy and recommend strategies for enhancing cup drawing fidelity. By conducting a parametric study focusing on the force-displacement behavior of a 6016-T4 alloy cup drawing process, an "optimized" force-displacement curve was obtained, demonstrating improved agreement with reference results. Die clearance, friction coefficient, time step size, and termination time are used in parametric finite element study. Key findings from the parametric study can be concluded that die clearance significantly affects punch force;a die clearance of 1.4 mm yielded the best match with experimental results, attributed to reduced blank-stuck phenomenon compared to smaller clearances. The friction coefficient showed a direct impact;a friction coefficient of mu = 0.1 accurately replicated the experimental peak force, highlighting the sensitivity of force predictions to friction parameters. Time step size and termination time demonstrated minimal influence on FEA results, suggesting prioritization of parameters accelerating solution time. Finally, the relationships between process and FEA computation parameters and predictions were revealed for more realistic cup drawing process prediction accuracy.

关键词： parametric modeling cup drawing aluminum alloy process parameters numerical parameters

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Cross-section distortion and springback characteristics of double-cavity aluminum profile in force controlled stretch-bending

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Transactions of Nonferrous Metals Society of China 2024年第8期34卷 2476-2490页

作者： Zhi-wen LIU Zi-xuan DONG Cong-chang XU Jie YI Luo-xing LI School of Mechanical Engineering University of South ChinaHengyang 421001China State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan UniversityChangsha 410082China

3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent *** the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were *** formation mechanisms of cross-section distortion and springback were *** effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were *** results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential *** stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of *** aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to *** unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after *** pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains *** increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback ***-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.

关键词： hollow aluminum profile force controlled stretch-bending numerical parameters springback analysis approach cross-section distortion springback process parameters

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CHARACTERISTICS OF SNOW SCATTERING WITH BICONTINUOUS MEDIA DISCRETE DIPOLE APPROXIMATION AND MEMLS

CHARACTERISTICS OF SNOW SCATTERING WITH BICONTINUOUS MEDIA D...

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IEEE International Geoscience and Remote Sensing Symposium (IGARSS)

作者： Luo, Chunzeng Tan, Shurun Pan, Jinmei Zhejiang Univ Zhejiang Univ Univ Illinois Urbana Champaign Inst Haining 314400 Zhejiang Peoples R China Zhejiang Univ Coll Informat Sci & Elect Engn State Key Lab Modern Opt Instrumentat Hangzhou 310027 Peoples R China Univ Illinois Dept Elect & Comp Engn Urbana IL 61801 USA Chinese Acad Sci Aerosp Informat Res Inst State Key Lab Remote Sensing Sci Beijing 100101 Peoples R China

ISBN: (数字)9781665427920

ISBN: (纸本)9781665427920

Microwave remote sensing is effective in monitoring snow distribution over large areas. The dense media radiative transfer model provides theoretical basis for deriving snow information through its scattering to electromagnetic waves. The microwave emission model of layered snowpacks (MEMLS) and the dense media radiative transfer model with bicontinuous media approximation of snow (DMRT-Bicontinuous media) are two widely adopted models. Both models assume a random media representation of snow. In this paper, the scattering properties of both models are compared and analyzed to provide guidance in model selection. Sensitivity of the bicontinuous media discrete dipole approximation (DDA) to its numerical parameters is also discussed to improve usability of the model.

关键词： snow microwave radiative transfer model MEMLS DMRT Bicontinuous media scattering theory numerical parameters

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numerical Investigation of Hydrogen Jet Dispersion Below and Around a Car in a Tunnel

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ENERGIES 2023年第18期16卷 6483页

作者： Koutsourakis, Nektarios Tolias, Ilias C. Giannissi, Stella G. Venetsanos, Alexandros G. Natl Ctr Sci Res Demokritos Environm Res Lab INRASTES Patriarchou Grigoriou E & 27 Neapoleos Str Aghia Paraskevi 15341 Greece

Accidental release from a hydrogen car tank in a confined space like a tunnel poses safety concerns. This Computational Fluid Dynamics (CFD) study focuses on the first seconds of such a release, which are the most critical. Hydrogen leaks through a Thermal Pressure Relief Device (TPRD), forms a high-speed jet that impinges on the street, spreads horizontally, recirculates under the chassis and fills the area below it in about one second. The "fresh-air entrainment effect" at the back of the car changes the concentrations under the chassis and results in the creation of two "tongues" of hydrogen at the rear corners of the car. Two other tongues are formed near the front sides of the vehicle. In general, after a few seconds, hydrogen starts moving upwards around the car mainly in the form of buoyant blister-like structures. The average hydrogen volume concentrations below the car have a maximum of 71%, which occurs at 2 s. The largest "equivalent stoichiometric flammable gas cloud size Q9" is 20.2 m3 at 2.7 s. Smaller TPRDs result in smaller hydrogen flow rates and smaller buoyant structures that are closer to the car. The investigation of the hydrogen dispersion during the initial stages of the leak and the identification of the physical phenomena that occur can be useful for the design of experiments, for the determination of the TPRD characteristics, for potential safety measures and for understanding the further distribution of the hydrogen cloud in the tunnel.

关键词： hydrogen CFD dispersion safety tunnel car fuel-cell vehicle TPRD impinging jet ADREA-HF physical parameters numerical parameters parametric studies sensitivity tests best-practice guidelines

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A new method for optimizing a set of nonlinear parameters: application in total Hartree-Fock atomic energy calculations

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THEORETICAL CHEMISTRY ACCOUNTS 2020年第4期139卷 1-6页

作者： Jorge, Francisco E. Neto, Antonio Canal Univ Fed Espirito Santo Dept Fis Ave Fernando Ferrari 514 BR-29075910 Vitoria ES Brazil

A new method for optimizing a set of numerical parameters is presented. This method does not depend on prior knowledge of the goal function and of its derivatives. Besides, it is robust and does not require any other method to achieve result near the global extreme (maximum/minimum) of the goal function. However, as the computational time spent by our method increases with the number of numerical parameters and with the size of each parameter to be optimized, in this work, it is applied together with the IGCHF method to construct accurate uncontracted basis sets to describe the ground states of some atoms. In these cases, the parameters to be optimized are the exponents of the Gaussian functions and the minimum total HF energy criterion is guaranteed by the variational principle. It is verified that the results calculated with the proposed new method are better than those obtained with the Monte Carlo and particle swarm methods, although the computational times spent in some cases by it are larger than those of the other two methods.

关键词： A new method for optimization numerical parameters Composite algorithm Decimal search Total atomic HF energy

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Determination of the numerical parameters of a Continuous Damage Model for the Structural Analysis of Clay Brick Masonry

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MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS 2012年第6期15卷 1013-1021页

作者： Mangueira, Felipe Barbosa Neto, Luttgardes de Oliveira Azambuja, Maximiliano dos Anjos Univ Estadual Paulista UNESP Dept Civil Engn Bauru SP Brazil

Models based on the continuous damage theory present good responses in representing the nonlinear behavior of reinforced concrete structures with loss of strength and stiffness of the material. However, damage theory is rarely employed in the analysis of masonry structures and numerical simulations are currently performed mostly by Finite Element Method formulations. A computational program was designed to determine the numerical parameters of a damage model of the physical properties of masonry components, solid clay brick and mortar. The model was formulated based on the composition of tensile and compressive surface strengths in the plane stress state. The numerical parameters, the corresponding curves of the activation surfaces and the evolution of the surfaces are presented. The results were fed into the computational program based on the Boundary Element Method (BEM) for the simulation of masonry walls, and two types of masonry were simulated. The results confirm the good performance of the model and the program based on the BEM.

关键词： damage model numerical parameters clay brick masonry BEM

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A System of Models for Constructing a Progressive Income Tax Scale

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IFAC-PapersOnLine 2018年第32期51卷 474-478页

作者： Chistyakov, S.V. Uspasskaya, I.S. Kvitko, A.N. Kichinsky, D.B. Saint Petersburg State University St Petersburg199034 Russia Lanit-Tercom St Petersburg198504 Russia

This paper considers a system of two mathematical models for constructing an average tax rates scale. The first model with six specified numerical parameters is intended for constructing the average tax rates scale and represents a certain variational game-theoretic model. The second — approximating one — is meant for constructing a marginal tax rates schedule based on the optimal average tax rates scale. It is a problem of the best approximation to the optimal average tax rates schedule by average tax rates scales, and it can be presented in a tabular form traditional for economy. © 2018

关键词： Taxation Game theory Best approximations Game theoretical models Game theoretic model Income tax Model approximations numerical parameters Tax rates

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