• Structural Engineering and Mechanics
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• 제64권2호
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• pp.259-270
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• 2017

The stochastic vibration response of the sandwich beam with the nonlinear adjustable visco-elastomer core and supported mass under stochastic support motion excitations is studied. The nonlinear dynamic properties of the visco-elastomer core are considered. The nonlinear partial differential equations for the horizontal and vertical coupling motions of the sandwich beam are derived. An analytical solution method for the stochastic vibration response of the nonlinear sandwich beam is developed. The nonlinear partial differential equations are converted into the nonlinear ordinary differential equations representing the nonlinear stochastic multi-degree-of-freedom system by using the Galerkin method. The nonlinear stochastic system is converted further into the equivalent quasi-linear system by using the statistic linearization method. The frequency-response function, response spectral density and mean square response expressions of the nonlinear sandwich beam are obtained. Numerical results are given to illustrate new stochastic vibration response characteristics and response reduction capability of the sandwich beam with the nonlinear visco-elastomer core and supported mass under stochastic support motion excitations. The influences of geometric and physical parameters on the stochastic response of the nonlinear sandwich beam are discussed, and the numerical results of the nonlinear sandwich beam are compared with those of the sandwich beam with linear visco-elastomer core.

• 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.

• Ocean Systems Engineering
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• 제9권3호
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• pp.219-240
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• 2019

This paper presents the comparison between SFT response with linear and nonlinear cables. The dynamic response analysis of submerged floating tunnel (SFT) is presented computationally with linear and nonlinear tension legs cables. The analysis is performed computationally for two wave directions one at 90 degrees (perpendicular) to tunnel and other at 45 degrees to the tunnel. The tension legs or cables are assumed as linear and non- linear and the analysis is also performed by assuming one tension leg or cable is failed. The Response Amplitude Operators (RAO's) are computed for first order waves, second order waves for both failure and non-failure case of cables. For first order waves- the SFT response is higher for sway and heave degree of freedom with nonlinear cables as compared with linear cables. For second order waves the SFT response in sway degree of freedom is bit higher response with linear cables as compared with nonlinear cables and the SFT in heave degree of freedom has higher response at low time periods with nonlinear cables as compared with linear cables. For irregular waves the power spectral densities (PSD's) has been computed for sway and heave degrees of freedom, at $45^0$ wave direction PSD's are higher with linear cables as compared with nonlinear cables and at $90^0$ wave direction the PSD's are higher with non-linear cables. The mooring force responses are also computed in y and z directions for linear and nonlinear cables.

• 대한전기학회논문지:시스템및제어부문D
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• 제52권5호
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• pp.259-267
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• 2003

In this paper, we propose a nonlinear variable PID controller using a cell-mediated immune response. An immune feedback response is based on the functioning of biological T-cells. An immune feedback response and P-controller of conventional PID controllers resemble each other in role and mechanism. Therefore, we extend immune feedback mechanism to nonlinear PE controller. And in order to choose the optimal nonlinear PID controller games, we also propose the on-line tuning algorithm of nonlinear functions parameters in immune feedback mechanism. The trained parameters of nonlinear functions are adapted to the variations of the system parameters and any command velocity. And the adapted parameters obtained outputs of nonlinear functions with an optimal control performance. To verify performances of the proposed control systems, the speed control of nonlinear BC motor is performed. The simulation results show that the proposed control systems are effective in tracking a command velocity under system variations.

• Geomechanics and Engineering
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• 제6권6호
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• pp.531-544
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• 2014

Studies of earthquakes over the last 50 years and the examination of dynamic soil behavior reveal that soil behavior is highly nonlinear and hysteretic even at small strains. Nonlinear behavior of soils during a seismic event has a predominant role in current site response analysis approaches. Common approaches to ground response analysis include linear, equivalent linear and nonlinear methods. These methods of ground response analysis may also be categorized into time domain and frequency domain concepts. Simplicity in developing analytical relations and accuracy in considering soils' dynamic properties dependency to loading frequency are benefits of frequency domain analysis. On the other hand, nonlinear methods are complicated and time consuming mainly because of their step by step integrations in time intervals. In part Ι of this paper, governing equations for seismic response analysis of surcharged and layered soils were developed using fundamental of wave propagation theory based on transfer function and boundary conditions. In this part, nonlinear seismic ground response is analyzed using extended HFTD method. The extended HFTD method benefits Newton-Raphson procedure which applies regular iterations and follows soils' fundamental stress-strain curve until convergence is achieved. The nonlinear HFTD approach developed here are applied to some examples presented in this part of the paper. Case studies are carried in which effects of some influencing parameters on the response are investigated. Results show that the current approach is sufficiently accurate, efficient, and fast converging. Discussions on the results obtained are presented throughout this part of the paper.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.251-262
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• 2007

This paper examines the application of artificial neural networks (ANN) to the response prediction of geometrically nonlinear truss structures. Two types of analysis (deterministic and probabilistic analyses) are considered. A three-layer feed-forward backpropagation network with three input nodes, five hidden layer nodes and two output nodes is firstly developed for the deterministic response analysis. Then a back propagation training algorithm with Bayesian regularization is used to train the network. The trained network is then successfully combined with a direct Monte Carlo Simulation (MCS) to perform a probabilistic response analysis of geometrically nonlinear truss structures. Finally, the proposed ANN is applied to predict the response of a geometrically nonlinear truss structure. It is found that the proposed ANN is very efficient and reasonable in predicting the response of geometrically nonlinear truss structures.

• 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.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.71-78
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• 2005

In performance-based design methods, it is clear that the evaluation of the nonlinear response is required. The methods available to the design engineer today are nonlinear tim history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. The nonlinear time analysis is the most accurate method in computing the nonlinear response of structures, but it is time-consuming and necessitate more efforts. Some codes proposed the capacity spectrum method based on the nonlinear static analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. The nonlinear direct spectrum method is proposed and studied to evaluate nonlinear response of structures, without iterative computations, given by the structural linear vibration period and yield strength from the pushover analysis. The purpose of this paper is to compare the accuracy and the reliability of approximate nonlinear methods with respect to RC dual system and various earthquakes.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.631-638
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• 2006

This paper considers the nonlinear direct spectrum method to estimate seismic performance of mixed building structures without iterative computations, given dynamic property $T_1$ from stiffness skeleton curve and nonlinear pseudo acceleration $A_{1y}$ and/or ductility ratio $\mu$ from response spectrum. Nonlinear response history analysis has been performed and analysed with various earthquakes for evaluation of correctness and confidence of nonlinear direct spectrum method.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1107-1110
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• 2003

Valuable insight into the nonlinear dynamics of a system can be gleaned from its response to a single intense short pulse. We derive expressions for the corresponding nonlinear response functions and show that the fluctuation-dissipation theorem may be extended beyond the linear response limit to an arbitrary pulse intensity. As an illustrative example, we calculate response functions up to 11th order for the regular Lorentz gas in two dimensions.