• Computers and Concrete
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• 제9권5호
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• pp.327-340
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• 2012

The search for a design that meets both performance and safety, with minimal cost and lesser environmental impact was always the goal of structural engineers. In general, the design of conventional reinforced concrete structures is an iterative process based on rules of thumb established from the personal experience and intuition of the designer. However, such procedure makes the design process exhaustive and only occasionally leads to the best solution. In such context, this work presents the development and implementation of a mathematical formulation for obtaining optimal sections of reinforced concrete columns subjected to uniaxial flexural compression, based on the verification of strength proposed by the Brazilian standard NBR 6118 (ABNT 2007). To minimize the cost of the reinforced concrete columns, the Simulated Annealing optimization method was used, in which the amount and diameters of the reinforcement bars and the dimensions of the columns cross sections were considered as discrete variables. The results obtained were compared to those obtained from the conventional design procedure and other optimization methods, in an attempt to verify the influence of resistance class, variations in the magnitudes of bending moment and axial force, and material costs on the optimal design of reinforced concrete columns subjected to uniaxial flexural compression.

• Structural Engineering and Mechanics
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• 제45권1호
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• pp.95-110
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• 2013

In the recent decade, practical of wavelet technique is being utilized in various domain of science. Particularly, engineers are interested to the wavelet solution method in the time series analysis. Fundamentally, seismic responses of structures against time history loading such as an earthquake, illustrates optimum capability of systems. In this paper, a procedure using particularly discrete Haar wavelet basis functions is introduced, to solve dynamic equation of motion. In the proposed approach, a straightforward formulation in a fluent manner is derived from the approximation of the displacements. For this purpose, Haar operational matrix is derived and applied in the dynamic analysis. It's free-scaled matrix converts differential equation of motion to the algebraic equations. It is shown that accuracy of dynamic responses relies on, access of load in the first step, before piecewise analysis added to the technique of equation solver in the last step for large scale of wavelet. To demonstrate the effectiveness of this scheme, improved formulations are extended to the linear and nonlinear structural dynamic analysis. The validity and effectiveness of the developed method is verified with three examples. The results were compared with those from the numerical methods such as Duhamel integration, Runge-Kutta and Wilson-${\theta}$ method.

• 한국항공우주학회지
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• 제38권7호
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• pp.684-692
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• 2010

본 논문에서는 지구-달 천이를 위한 최적 궤도 설계에 관한 연구를 수행하였다. 지구와 달의 인력을 동시에 고려한 평면상 제한 3체 궤도 운동 모델을 바탕으로 지구 출발시에는 순간 추력을, 지구-달 천이 과정 및 달 임무궤도 투입시에는 연속 추력을 사용하는 혼합형 궤도전이 방법을 제시하였다. 최적화 풀이 방법으로서 Direct Transcription 및 Collocation을 이용한 비선형 프로그래밍 기법을 적용하였으며, 지구 출발 및 달 임무궤도 투입 궤적의 형상은 순간 추력의 연속 추력에 대한 상대 가중치 및 비행시간에 의하여 매우 달라질 수 있음을 파악하였다.

• 한국방재학회 논문집
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• 제7권5호
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• pp.27-35
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• 2007

본 연구는 지진운동의 영향 하에서 강제 모멘트 골조로 이루어진 post-Northridge 연결부를 갖는 보의 탄성 및 비탄성 거동을 모델하기 위한 부등단면 보 요소를 제시한다. 단면감소 연결부를 갖는 부등단면 보의 탄성강성 행렬은 수치적분이 필요치 많은 수식으로 표현된다. 소성모델은 분포형이며 강체링크로 연결된 일련의 비선형 힌지로 구성 되어있고 경화법칙은 단조 및 임의 주기 하중에 대한 비탄성 거동과 국부좌굴의 효과를 고려할 수 있다. 모델의 대조와 검증은 동반논문에 제시되어있다.

• 한국경영과학회지
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• 제41권3호
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• pp.23-36
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• 2016

We consider a model that minimizes the total cost incurred by assigning available weapons to existing targets in order to reduce enemy threats, which is called the weapon target assignment problem (WTAP). This study addresses the stochastic versions of WTAP, in which data, such as the probability of destroying a target, are given randomly (i.e., data are identified with certain probability distributions). For each type of random data or parameter, we provide a stochastic optimization model on the basis of the expected value or scenario enumeration. In particular, when the probabilities of destroying targets depending on weapons are stochastic, we present a stochastic programming formulation with a simple recourse. We show that the stochastic model can be transformed into a deterministic equivalent mixed integer programming model under a certain discrete probability distribution of randomness. We solve the stochastic model to obtain an optimal solution via the mixed integer programming model and compare this solution with that of the deterministic model.

• Computers and Concrete
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• 제8권1호
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• pp.71-96
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• 2011

Existing reinforced concrete (RC) beams can be strengthened with externally bolted steel plates to the sides of beams. The effectiveness of this type of bolted side-plate (BSP) beam can however be affected by partial interaction between the steel plates and RC beams due to the mechanical slip of bolts. To avoid over-estimation of the flexural strength and ensure accurate prediction of the load-deformation response of the beams, the effect of partial interaction has to be properly considered. In this paper, a special non-linear macro-finite-element model that takes into account the effects of partial interaction is proposed. The RC beam and the steel plates are modelled as two different elements, interacting through discrete groups of bolts. A layered method is adopted for the formulation of the RC beam and steel plate elements, while a special non-linear model based on a kinematic hardening assumption for the bolts is used to simulate the bolt group effect. The computer program SiBAN was developed based on the proposed approach. Comparison with the available experimental results shows that SiBAN can accurately predict the partial interaction behaviour of the BSP beams. Further numerical simulations show that the interaction between the RC beam and the steel plates is greatly reduced by the formation of plastic hinges and should be considered in analyses of the strengthened beams.

• Transactions on Control, Automation and Systems Engineering
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• 제1권2호
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• pp.134-140
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• 1999

The robust generalized H2 filtering problem for a class of discrete time uncertain linear systems satisfying the sum quadratic constraints(SQCs) is considered. The objective of this paper is to develop robust stability condition using SQCs and design a robust generalized Ha filter to take place of the existing robust Kalman filter. The robust generalized H2 filter is designed based on newly derived robust stability condition. The robust generalized Ha filter bounds the energy to peak gain from the energy bounded exogenous disturbances to the estimation errors under the given positive scalar ${\gamma}$. Unlike the robust Lalman filter, it does not require any spectral assumptions about the exogenous disturbances . Therefore the robust generalized H2 filter can be considered as a deterministic formulation of the robust Kalman filter. Moreover, the variance of the estimation error obtained by the proposed filter is lower than that by the existing robust Kalman filter. The robustness of the robust generalized H2 filter against the uncertainty and the exogenous signal is illustrated by a simple numerical example.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권11호
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• pp.551-558
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• 2002

A time-domain combined field integral equation (CFIE) is presented to obtain the transient scattering response from arbitrarily shaped three-dimensional conducting bodies. This formulation is based on a linear combination of the time-domain electric field integral equation (EFIE) with the magnetic field integral equation (MFIE). The time derivative of the magnetic vector potential in EFIE is approximated using a central finite difference approximation and the scalar potential is averaged over time. The time-domain CFIE approach produces results that are accurate and stable when solving for transient scattering responses from conducting objects. The incident spectrum of the field may contain frequency components, which correspond to the internal resonance of the structure. For the numerical solution, we consider both the explicit and implicit scheme and use two different kinds of Gaussian pulses, which may contain frequencies corresponding to the internal resonance. Numerical results for the EFIE, MFIE, and CFIE are presented and compared with those obtained from the inverse discrete Fourier transform (IDFT) of the frequency-domain CFIE solution.

• 대한기계학회논문집A
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• 제28권7호
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• pp.1038-1046
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• 2004

In order to acquire high-speed and high-precision performances in servomechanisms, an integrated design method have been proposed. Based on strict mathematical modeling and analysis of system performance according to design and operating parameters, a nonlinear constrained optimization problem including the relevant subsystem parameters of the servomechanism is formulated. Optimum design results of mechanical and electrical parameters are obtained according to the design parameters specified by designers through the integrated design processes. Motors are optimally selected from the servo motor database. Both the geometric errors referring to Abbe offset and the contour errors are minimized while required constraints such as stability conditions and saturated conditions are satisfied. This design methodology both offers the improved possibility to evaluate and optimize the dynamic motion performance of the servomechanism and improves the quality of the design process to achieve the required performance for high-speed/precision servomechanisms.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.1-18
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• 2020

Present research is aimed to investigate the free vibration behavior of functionally graded (FG) nanocomposite conical panel reinforced by graphene platelets (GPLs) on the elastic foundation. Winkler-Pasternak elastic foundation surrounds the mentioned shell. For each ply, graphaene platelets are randomly oriented and uniformly dispersed in an isotropic matrix. It is assumed that the Volume fraction of GPLs reainforcement could be different from layer to layer according to a functionally graded pattern. The effective elastic modulus of the conical panel is estimated according to the modified Halpin-Tsai rule in this manuscript. Cone is modeled based on the first order shear deformation theory (FSDT). Hamilton's principle and generalized differential quadrature (GDQ) approach are also used to derive and discrete the equations of motion. Some evaluations are provided to compare the natural frequencies between current study and some experimental and theoretical investigations. After validation of the accuracy of the present formulation and method, natural frequencies and the corresponding mode shapes of FG-GPLRC conical panel are developed for different parameters such as boundary conditions, GPLs volume fraction, types of functionally graded and elastic foundation coefficients.