• 제목/요약/키워드: rational function approximation

검색결과 35건 처리시간 0.018초

NURBS-based isogeometric analysis for thin plate problems

  • Shojaee, S.;Valizadeh, N.
    • Structural Engineering and Mechanics
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    • 제41권5호
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    • pp.617-632
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    • 2012
  • An isogeometric approach is presented for static analysis of thin plate problems of various geometries. Non-Uniform Rational B-Splines (NURBS) basis function is applied for approximation of the thin plate deflection, as for description of the geometry. The governing equation based on Kirchhoff plate theory, is discretized using the standard Galerkin method. The essential boundary conditions are enforced by the Lagrange multiplier method. Several typical examples of thin plate and thin plate on elastic foundation are solved and compared with the theoretical solutions and other numerical methods. The numerical results show the robustness and efficiency of the proposed approach.

분포정수계 유압관로 모델의 동특성 해석 (Analysis of Dynamic Characteristics of Hydraulic Transmission Lines with Distributed Parameter Model)

  • 김도태
    • 드라이브 ㆍ 컨트롤
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    • 제15권4호
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    • pp.67-73
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    • 2018
  • The paper deals with an approach to time domain simulation for closed end at the downstream of pipe, hydraulic lines terminating into a tank and series lines with change of cross sectional area. Time domain simulation of a fluid power systems containing hydraulic lines is very complex and difficult if the transfer functions consist of hyperbolic Bessel functions which is the case for the distributed parameter dissipative model. In this paper, the magnitudes and phases of the complex transfer functions of hydraulic lines are calculated, and the MATLAB Toolbox is used to formulate a rational polynomial approximation for these transfer functions in the frequency domain. The approximated transfer functions are accurate over a designated frequency range, and used to analyze the time domain response. This approach is usefully to simulate fluid power systems with hydraulic lines without to approximate the frequency dependent viscous friction.

Design, Analysis, and Equivalent Circuit Modeling of Dual Band PIFA Using a Stub for Performance Enhancement

  • Yousaf, Jawad;Jung, Hojin;Kim, Kwangho;Nah, Wansoo
    • Journal of electromagnetic engineering and science
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    • 제16권3호
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    • pp.169-181
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    • 2016
  • This work presents a new method for enhancing the performance of a dual band Planer Inverted-F Antenna (PIFA) and its lumped equivalent circuit formulation. The performance of a PIFA in terms of return loss, bandwidth, gain, and efficiency is improved with the addition of the proposed open stub in the radiating element of the PIFA without disturbing the operating resonance frequencies of the antenna. In specific cases, various simulated and fabricated PIFA models illustrate that the return loss, bandwidth, gain, and efficiency values of antennas with longer optimum open stub lengths can be enhanced up to 4.6 dB, 17%, 1.8 dBi, and 12.4% respectively, when compared with models that do not have open stubs. The proposed open stub is small and does not interfere with the surrounding active modules; therefore, this method is extremely attractive from a practical implementation point of view. The second presented work is a simple procedure for the development of a lumped equivalent circuit model of a dual band PIFA using the rational approximation of its frequency domain response. In this method, the PIFA's measured frequency response is approximated to a rational function using a vector fitting technique and then electrical circuit parameters are extracted from it. The measured results show good agreement with the electrical circuit results. A correlation study between circuit elements and physical open stub lengths in various antenna models is also discussed in detail; this information could be useful for the enhancement of the performance of a PIFA as well as for its systematic design. The computed radiated power obtained using the electrical model is in agreement with the radiated power results obtained through the full wave electromagnetic simulations of the antenna models. The presented approach offers the advantage of saving computation time for full wave EM simulations. In addition, the electrical circuit depicting almost perfect characteristics for return loss and radiated power can be shared with antenna users without sharing the actual antenna structure in cases involving confidentiality limitations.

A topology optimization method of multiple load cases and constraints based on element independent nodal density

  • Yi, Jijun;Rong, Jianhua;Zeng, Tao;Huang, X.
    • Structural Engineering and Mechanics
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    • 제45권6호
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    • pp.759-777
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    • 2013
  • In this paper, a topology optimization method based on the element independent nodal density (EIND) is developed for continuum solids with multiple load cases and multiple constraints. The optimization problem is formulated ad minimizing the volume subject to displacement constraints. Nodal densities of the finite element mesh are used a the design variable. The nodal densities are interpolated into any point in the design domain by the Shepard interpolation scheme and the Heaviside function. Without using additional constraints (such ad the filtering technique), mesh-independent, checkerboard-free, distinct optimal topology can be obtained. Adopting the rational approximation for material properties (RAMP), the topology optimization procedure is implemented using a solid isotropic material with penalization (SIMP) method and a dual programming optimization algorithm. The computational efficiency is greatly improved by multithread parallel computing with OpenMP to run parallel programs for the shared-memory model of parallel computation. Finally, several examples are presented to demonstrate the effectiveness of the developed techniques.

Spline 함수(函數)와 선형방정식(線型方程式)을 이용한 수간(樹幹) 및 임분간곡선(林分幹曲線)모델 (Stem and Stand Taper Model Using Spline Function and Linear Equation)

  • 이우균
    • 한국산림과학회지
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    • 제83권1호
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    • pp.63-74
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    • 1994
  • 단목(單木) 또는 임분(林分)의 생장파악 및 예측을 위해서는 수간형태(樹幹形態)의 파악이 선행되어야 한다. 또한 임분의 생장을 동적(動的)으로 파악하기 위해서는 수간형태(樹幹形態)를 수식화(數式化)할 필요가 있다. 그러나 수간(樹幹)은 전체적으로는 원추형(圓錐型)에 가깝지만 그 가늘어지는 정도가 부분적으로 다르기 때문에 하나의 식(式)으로 표현하기엔 어려움이 있으므로, 부분적으로 상이한 계수를 갖는 구간추정식(區間推定式)으로 표현하는 것이 이상적이다. 본 논문에서는 spline함수로부터 유도된 단목간곡선의 집합으로부터, 선형관계식을 이용하여 임분간곡선(林分幹曲線)을 수식화하는 방법을 소개하였다. 이와 같이 수간형태(樹幹形態)를 수식화(數式化) 한 단목 및 임분의 간곡선식(幹曲線式)은 임분(林分)의 발달과정을 동적(動的)으로 파악할 수 있게 하여 임분생장연구의 다양성 및 합리적 산림계획모델의 기초를 제공한다.

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