• Structural Engineering and Mechanics
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• 제52권3호
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• pp.485-505
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• 2014

This study aimed to develop an approach to accurately predict the wind models and wind effects of large wind turbines. The wind-induced vibration characteristics of a 5 MW tower-blade coupled wind turbine system have been investigated in this paper. First, the blade-tower integration model was established, which included blades, nacelle, tower and the base of the wind turbine system. The harmonic superposition method and modified blade element momentum theory were then applied to simulate the fluctuating wind field for the rotor blades and tower. Finally, wind-induced responses and equivalent static wind loads (ESWL) of the system were studied based on the modified consistent coupling method, which took into account coupling effects of resonant modes, cross terms of resonant and background responses. Furthermore, useful suggestions were proposed to instruct the wind resistance design of large wind turbines. Based on obtained results, it is shown from the obtained results that wind-induced responses and ESWL were characterized with complicated modal responses, multi-mode coupling effects, and multiple equivalent objectives. Compared with the background component, the resonant component made more contribution to wind-induced responses and equivalent static wind loads at the middle-upper part of the tower and blades, and cross terms between background and resonant components affected the total fluctuation responses, while the background responses were similar with the resonant responses at the bottom of tower.

• 대한기계학회논문집A
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• 제31권11호
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• pp.1059-1068
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• 2007

Nonlinear response structural optimization is performed using equivalent loads (NROEL). Nonlinear response optimization is extremely cost because many nonlinear analyses are required. In NROEL, the external loads are transformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response field of linear analysis as that of nonlinear analysis. The primitive from of theory has been published. In this research, the theory is investigated with large scale example problems. Four examples are solved by using NROEL. Conventional optimization with sensitivity analysis using the finite difference method (FDM) is also applied to the same examples. Moreover, response surface optimization method is applied to the last two examples. The results of the optimizations are compared. In nonlinear response optimization of large scale problems, hundreds (or even thousands) of nonlinear analyses are expected to satisfy the convergence criteria. However, in nonlinear response optimization using equivalent loads, only tens of nonlinear analyses are required. The results are discussed and the usefulness of NROEL is presented.

• 국제초고층학회논문집
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• 제8권4호
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• pp.265-273
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• 2019

The purpose of this review paper is to briefly describe main the features of novel procedures developed by the National of Standards and Technology (NIST) for the design of tall buildings. Topics considered in the paper include: the division of tasks between wind and structural engineers; the determination of wind effects with specified mean recurrence intervals by accounting for wind directionality; the risk-consistent design of structures subjected to multiple wind hazards; iterative dynamic analyses and member sizing, including the use of modern optimization approaches; and commonalities of and differences between Database-assisted Design (DAD) and Equivalent Static Wind Loads procedures. An example of the application of the DAD procedure is presented for a reinforced concrete structure. Also included in the paper is an introduction to ongoing research on the estimation of wind load factors or of augmented design mean recurrence intervals commensurate with the uncertainties in the factors that determine the wind effects.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.383-392
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• 2009

The static and dynamic analyses of simply supported beams are studied by using the U-transformation method and the finite difference method. When the beam is divided into the mesh of equal elements, the mesh may be treated as a periodic structure. After an equivalent cyclic periodic system is established, the difference governing equation for such an equivalent system can be uncoupled by applying the U-transformation. Therefore, a set of single-degree-of-freedom equations is formed. These equations can be used to obtain exact analytical solutions of the deflections, bending moments, buckling loads, natural frequencies and dynamic responses of the beam subjected to particular loads or excitations. When the number of elements approaches to infinity, the exact error expression and the exact convergence rates of the difference solutions are obtained. These exact results cannot be easily derived if other methods are used instead.

• 대한기계학회논문집A
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• 제31권12호
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• pp.1165-1172
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• 2007

The spacer grid set is a part of a nuclear fuel assembly. The set has a spring and the spring supports the fuel rods safely. Although material nonlinearity is involved in the deformation of the spring, nonlinearity has not been considered in design of the spring. Recently a nonlinear response structural optimization method has been developed using equivalent loads. It is called nonlinear response optimization equivalent loads (NROEL). In NROEL, the external loads are transformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response field of linear analysis as that of nonlinear analysis. Shape optimization of the spring is carried out based on EL. The objective function is defined by minimizing the maximum stress in the spring while mass is limited and the support force of the spring is larger than a certain value. The results are verified by nonlinear response analysis. ABAQUS is used for nonlinear response analysis and GENESIS is employed for linear response optimization.

• 대한기계학회논문집A
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• 제28권4호
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• pp.467-474
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• 2004

A numerical method and algorithms is proposed to perform optimization of non-linear response structures. An analytical and numerical method based finite element method is also proposed for the transformation of non-linear response into linear response. Loads transformed from this method are defined as the equivalent linear loads. With the loads and the transformed response, linear static optimization is performed for nonlinear response structure with geometric and/or material non-linearity. The results of the optimization are compared with them of typical non-linear response optimization using finite difference method. The proposed method is very efficient and derives good solution.

• 대한기계학회논문집A
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• 제29권3호
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• pp.369-386
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• 2005

Various aspects of structural optimization techniques under transient loads are extensively reviewed. The main themes of the paper are treatment of time dependent constraints, calculation of design sensitivity, and approximation. Each subject is reviewed with the corresponding papers that have been published since 1970s. The treatment of time dependent constraints in both the direct method and the transformation method is discussed. Two ways of calculating design sensitivity of a structure under transient loads are discussed - direct differentiation method and adjoint variable method. The approximation concept mainly focuses on re- sponse surface method in crashworthiness and local approximation with the intermediate variable Especially, as an approximated optimization technique, Equivalent Static Load method which takes advantage of the well-established static response optimization technique is introduced. And as an application area of dynamic response optimization technique, the structural optimization in flexible multibody dynamic systems is re- viewed in the viewpoint of the above three themes

• 대한기계학회논문집A
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• 제35권1호
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• pp.1-10
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• 2011

본 논문은 등가정하중을 이용하여 단조공정의 예비성형체 및 빌렛의 형상설계를 위한 최적화 방법을 제안한다. 단조공정에서 예비성형체의 형상은 최종 성형품의 품질을 결정하는데 중요한 역할을 한다. 본 연구는 빌렛 및 예비성형체의 형상을 설계하기 위하여 등가정하중법을 사용하였다. 등가정하중법은 비선형 동적하중을 등가정하중으로 변환하고 여기서 구한 등가정하중을 이용하여 선형 응답 최적화를 수행하는 방법이다. 설계변수의 갱신은 선형 응답 최적화와 비선형 해석을 통하여 이루어진다. 본 논문에 포함된 예제는 원하는 단조품의 생산을 위한 최적의 예비성형체와 빌렛의 형상을 도출하여 제안한 방법의 유용성을 검증한다. 비선형 해석과 선형 응답 최적화는 각각 LS-DYNA와 NASTRAN을 사용하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.694-699
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• 2007

The spacer grid set is a part of a nuclear fuel assembly. The set has a spring and the spring supports the fuel rods safely. Although material nonlinearity is involved in the deformation of the spring,nonlinearity has not been considered in design of the spring. Recently a nonlinear response structural optimization method has been developed using equivalent loads. It is called nonlinear response optimization equivalent loads (NROEL). In NROEL, the external loads are teansformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response no EL. The objective function is defined by minimizing the maximum stress in the spring while is limited and the support force of the spring is larger than a certain value. The results are verified by nonlinear. ABAQUS is used for nonlinear response analysis and GENESIS is employed for linear response optimization.

• 대한기계학회논문집A
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• 제39권3호
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• pp.259-268
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• 2015

본 논문은 등가정하중을 이용하여 튜브 하이드로포밍 공정을 위한 최적설계를 제안한다. 튜브 하이드로포밍 공정의 최적설계는 유체의 압력과 축 방향 압입량에 대한 적절한 하중경로를 결정하고, 이를 통하여 성형해석 후 결함이 없는 원하는 형상의 제품을 얻는 것을 목적으로 한다. 그러나 기존의 등가정하중법은 하중을 설계변수로 고려하지 못한다. 또한 튜브 하이드로포밍 공정의 최적설계에서 고려하는 비선형 두께 응답을 고려하기 위한 최적화가 필요하다. 따라서 본 연구에서는 튜브 하이드로포밍 공정의 최적설계에 적합한 새로운 등가정하중을 제시한다. 또한 새로운 등가정하중을 이용한 최적설계 프로세스를 제시한다. 제시한 최적설계방법의 사용 가능성은 예제를 통하여 확인한다.