• Structural Engineering and Mechanics
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• 제43권6호
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• pp.795-821
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• 2012

The size and topology of geometrically nonlinear dome structures are optimized thereby minimizing both its entire weight & joint (node) displacements and maximizing load-carrying capacity. Design constraints are implemented from provisions of American Petroleum Institute specification (API RP2A-LRFD). In accordance with the proposed design constraints, the member responses computed by use of arc-length technique as a nonlinear structural analysis method are checked at each load increment. Thus, a penalization process utilized for inclusion of unfeasible designations to genetic search is correspondingly neglected. In order to solve this complex design optimization problem with multiple objective functions, Non-dominated Sorting Genetic Algorithm II (NSGA II) approach is employed as a multi-objective optimization tool. Furthermore, the flexibility of proposed optimization is enhanced thereby integrating an automatic dome generating tool. Thus, it is possible to generate three distinct sphere-shaped dome configurations with varying topologies. It is demonstrated that the inclusion of brace (diagonal) members into the geometrical configuration of dome structure provides a weight-saving dome designation with higher load-carrying capacity. The proposed optimization approach is recommended for the design optimization of geometrically nonlinear dome structures.

• 한국철도학회논문집
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• 제9권6호
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• pp.778-783
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• 2006

This study investigates the ultimate behavior of reinforced concrete beams by means of practical nonlinear finite element (FE) analyses. Uniaxial constitutive models for the concrete and steel material are selected in this study. The adopted material model is integrated into the ABAQUS fiber beam elements through a user-defined material subroutine (UMAT). Within a developed nonlinear finite element framework, the FE results have been compared to experimental results reported by other researchers. It has been found that the proposed finite element model is capable of predicting the initial cracking load level, the yield load, the ultimate load, and the crack distribution with acceptable accuracy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.840-841
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• 2008

Power capacitors are widely used to compensate the low power factor of the linear load and/or nonlinear load. Especially, nonlinear loads generates the harmonic current and it gives an undesirable effect on the power capacitors. In this paper, harmonic current from nonlinear load to the power capacitors is calculated by the computer simulation and it is compared with the experimental results.

• 대한기계학회논문집A
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• 제33권8호
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• pp.779-785
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• 2009

This paper is concerned with a computational approach for topology optimization of geometrically nonlinear structures following specific load-displacement trajectories. In our previous works, attention was paid to stabilize topology optimization involving large displacement and a method called the element connectivity parameterization was developed. Here, we aimed to extend the element connectivity parameterization method to find an optimal geometrically nonlinear structure yielding a specific load-displacement trajectory. In contrast to designing a stiffest structure, the trajectory design problem requires special consideration in topology optimization formulation and solution procedure. Some numerical problems were considered to test the developed element connectivity parameterization based formulation.

• Journal of Power Electronics
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• 제13권3호
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• pp.409-418
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• 2013

This paper presents an enhanced control strategy which consists of a proportional-integral controller and a repetitive controller (RC) for improving the voltage performance of distributed generation (DG) under nonlinear load conditions. The proposed voltage controller is able to maintain a sinusoidal voltage at the point of common coupling (PCC) of the DG regardless of the harmonic voltage drop in the system impedance due to nonlinear load currents. In addition, by employing the delay time of the RC at one-sixth of the fundamental period, the proposed RC can overcome the slow response drawback of the traditional PI-RC. The proposed control strategy is analyzed and the design of the RC is presented in detail. The feasibility of the proposed control strategy is verified through simulation and experimental results.

• 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.

• Steel and Composite Structures
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• 제42권1호
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• pp.23-32
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• 2022

In this paper, a nonlinear numerical method to solve the large deflection problem is introduced. And the non-dimensional load-deflection behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates is parametrically investigated. The large deflection problem is formulated according to the von Kármán nonlinear theory and the (1,1,0)^* hierarchical model, and it is approximated by 2-D natural element method (NEM). The shear locking phenomenon is suppressed by the selectively reduced integration method. The nonlinear matrix equations are solved by combining the incremental loading scheme and the Newton-Raphson iteration method. The proposed method is validated from the benchmark experiments, where the propose method shows an excellent agreement with the reference methods. The nonlinear behavior of FG-CNTRC plates is evaluated in terms of the non-dimensional load-deflection curve, and it is parametrically investigated with respect to the existence/non-existence and gradient pattern of CNTs, the width-to-thickness and aspect ratios of plates and the type of boundary conditions. The non-dimensional central deflection is significantly reduced when CNTs and added, and it decreases with the volume fraction of CNTs. But, it shows a uniform increase in proportion to the width-to-thickness and aspect ratios. Both the gradient pattern of CNTs and the type of boundary conditions do also show the remarkable effects.

• Journal of Power Electronics
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• 제4권3호
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• pp.188-196
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• 2004

The dielectric barrier discharge is recognized as one of the efficient methods of ultraviolet light generation and ozone production. As well, it is widely utilized for gaseous wastes neutralization and other technological processes in industry. This electrochemical reaction is electrically equivalent to a nonlinear capacitive load that represents some difficulties for designing the power supply. Therefore, a conventional power supply is designed for a drastically simplified model of the load and generally is not optimal. This paper presents a fast simulation approach for the nonlinear capacitive model representation of the dielectric barrier discharge load lamp. The main idea of the proposed method is to use analytical solutions of the differential state equations for the load and find the unknown initial conditions for the steady state by an optimization method. The derived expressions for the analytical solutions are rather complicated, however they greatly reduce the calculation time, which make sense when a deeper analysis is performed. This paper introduces the proposed simulation method and gives some examples of its application such as estimation of the load equivalent parameters and load matching conditions.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제16권3호
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• pp.163-172
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• 2016

Electric load forecasting is essential for effective power system planning and operation. Complex and nonlinear relationships exist between the electric loads and their exogenous factors. In addition, time-series load data has non-stationary characteristics, such as trend, seasonality and anomalous day effects, making it difficult to predict the future loads. This paper proposes a locally-weighted polynomial neural network (LWPNN), which is a combination of a polynomial neural network (PNN) and locally-weighted regression (LWR) for daily shortterm peak load forecasting. Model over-fitting problems can be prevented effectively because PNN has an automatic structure identification mechanism for nonlinear system modeling. LWR applied to optimize the regression coefficients of LWPNN only uses the locally-weighted learning data points located in the neighborhood of the current query point instead of using all data points. LWPNN is very effective and suitable for predicting an electric load series with nonlinear and non-stationary characteristics. To confirm the effectiveness, the proposed LWPNN, standard PNN, support vector regression and artificial neural network are applied to a real world daily peak load dataset in Korea. The proposed LWPNN shows significantly good prediction accuracy compared to the other methods.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.209-218
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• 2003

The analytical studies included nonlinear finite element analysis of split-tee connection details subjected to axial load and lateral load. A three-dimensional model of the connections between CFT columns and H-beams has been developed. Both initial geometrical imperfections and residual stresses are taken into consideration. A geometrically nonlinear load-displacement analysis of the structure containing the imperfection is then performed, using the Riks method. Analytical results are compared with existing experimental results. Extensive parametric analyses are carried out to investigate the relation of the connections between CFT columns and H-beam to various parameters such as the axial load, column width-thickness ratio, and split-tee thickness.