• Structural Engineering and Mechanics
• /
• v.50 no.6
• /
• pp.797-816
• /
• 2014

Cooling tower is analyzed as an assembly of layered nonlinear shell elements. Geometric representation of the shell is enabled through layered nonlinear shell elements to define the different layers of reinforcements and concrete by considering the material nonlinearity of each layer for the cooling tower shell. Modal analysis using Ritz vector analysis and nonlinear time history analysis by direct integration method have been carried out to study the effects of the inclination of the supporting columns of the cooling tower shell on its dynamic characteristics. The cooling tower is supported by I-type columns and ${\Lambda}$-type columns supports having the different inclination angles. Relevant comparisons of the dynamic response of the structural system at the base level (at the junction of the column and shell), throat level and at the top of the tower have been made. Dynamic response of the cooling tower is found to be significantly sensitive to the change of the inclination of the supporting columns. It is also found that the stiffness of the structure system increases with increase in inclination angle of the supporting columns, resulting in decrease of the period of the structural system. The participation of the stiffness of the tower in structural response of the cooling tower is fund to be dependent of the change in the inclination angle and even in the types of the supporting columns.

• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.3
• /
• pp.407-417
• /
• 2015

Recently, piezo-aeroelastic energy harvesting has received greater attention. In the present study, a piezo-aeroelastic energy harvester using a nonlinear trailing-edge flap is proposed, and its nonlinear aeroelastic behaviors are investigated. The energy harvester is modeled using a piezo-aeroelastic model of a two-dimensional typical section airfoil with a trailing-edge flap (TEF). A piezo-aeroelastic analysis is carried out using RL and time-integration methods, and the results are verified with the experimental data. The linearizing method using a describing function is used for the frequency domain analysis of the nonlinear piezo-aeroelastic system. From the linear and nonlinear piezo-aeroelastic analysis, the limit cycle oscillation (LCO) characteristics of the proposed energy harvester with the nonlinear TEF are investigated in both the frequency and time domains. Finally, the authors discuss the air speed range for effective piezo-aeroelastic energy harvesting.

• Proceedings of the KIEE Conference
• /
• 1987.11a
• /
• pp.82-85
• /
• 1987

The objective of this paper is to develop computer programs to aid in the design and analysis of control systems in which nonlinear characteristics exist. Control systems are dynamic systems, which can be described using various mathematical models. A convenient model for digital computer simulation is the state model in which described using a set of linear and non linear first order differential equations. The digital simulation was performed on a IBM PC/XT personal computer, and the computer language was BASIC. There are four possible configurations from which a user may choose. When running a program, the user is asked to enter the system parameters according to a specified control system configurations are; 1. A control system with a nonlinear element followed by a plant in a feedback configurations(NLSVF1). 2. A control system with a nonlinear device situated between two plants in a feedback configurations(NLSVF2). 3. A control system with a nonlinear element followed by a plant, followed by a the dealy in feedback configurations(TLAG). 4. A motor and load with a backlash nonlinearity between dynamic portions of the motor/load configurations (BACKLASH). The matrix from state equations are integrated using combination the trapezoidal method and fixed point iteration. Several cases which have nonlinearity were implemented on the computer and the results were discussed.

• Proceedings of the KIEE Conference
• /
• 2006.07a
• /
• pp.8-9
• /
• 2006

This paper presents a new methodology to calculate an optimal solution of equilibrium to power system differential algebraic equations. It employs a nonlinear interior point method for solving the optimization formulation, which includes dynamic equations representing two-axis synchronous generator models with AVR and speed governing control, algebraic equations, and steady-state nonlinear loads. Equilibrium optimization (EOPT) is useful for diverse purposes in power system analysis and control with consideration of the system frequency constraint.

• Journal of Mechanical Science and Technology
• /
• v.20 no.7
• /
• pp.941-949
• /
• 2006

Nonlinear behavior analysis was used to verify whether a one-way clutch is effective for reducing the torsional vibration of a paired spur gear system under periodic excitation. The dynamic responses were studied over a wide frequency range by speed sweeping to check the nonlinear behavior using numerical integration. The gear system with a one-way clutch showed typical nonlinear behavior. The oscillating component of the dynamic transmission error was reduced over the entire frequency range compared to a system without a one-way clutch. The one-way clutch also eliminated unsteady continuous jump phenomena over multiple solution bands, and prevented double-side contact, even with very small backlash. Installing a one-way clutch on both sides of the gear system was more effective at mitigating the negative effects of external periodic excitation and various parameter changes than a conventional gear system without a one-way clutch.

• The KSFM Journal of Fluid Machinery
• /
• v.20 no.1
• /
• pp.15-20
• /
• 2017

The small turbocharger for the automotive application is designed to operate up to 200,000 rpm to increase system efficiency. Because of high rotation speed of turbocharger, floating ring bearing are widely adopted due to its low friction loss and high rotordynamic stability. This paper presents a linear and nonlinear analysis model for a turbocharger rotor supported by a semi-floating ring bearing. The rotordynamic model for the turbocharger rotor was constructed based on the finite element method and fluid film forces were calculated based on the infinitely short bearing assumption. In linear analysis, we considered fluid film force as stiffness and damping element and in nonlinear analysis, the fluid film force was calculated by solving the time dependent Reynolds equation. We verified the developed theoretical model by comparing to modal test results of test rotors. The analysis results show that there are two unstable modes, which are conical and cylindrical modes. These unstable modes appear as sub-synchronous vibrations in nonlinear analysis. In nonlinear analysis, frequency jump phenomenon demonstrated when vibration mode is changed from conical mode to cylindrical one. This jump phenomenon was also demonstrated in the test. However, the natural frequency measured in the test differs from those obtained using nonlinear analysis.

• The Journal of the Acoustical Society of Korea
• /
• v.27 no.3E
• /
• pp.95-103
• /
• 2008

In this paper, the new hybrid adaptive Volterra filter was proposed to be applied for compensating the nonlinear distortion of memoryless nonlinear systems with saturation characteristics. Through computer simulations as well as the analytical analysis, it could be shown that it is possible for both conventional Volterra filter and proposed hybrid Volterra filter, to be applied for linearizing the memoryless nonlinear system with nonlinear distortion. Also, the simulations results demonstrated that the proposed hybrid filter may have faster convergence speed and better capability of compensating the nonlinear distortion than the conventional Volterra filter.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.639-644
• /
• 2007

The accurate peak response estimation of a seismically excited structure with frictional damping system(FDS) is very difficult since the structure with FDS shows nonlinear behavior dependent on the structural period, loading characteristics, and relative magnitude between the frictional force and the excitation load. Previous studies have estimated that by replacing a nonlinear system with an equivalent linear one or by employing the response spectrum obtained based on nonlinear time history and statistical analysis. In the case that on earthquake load is defined with probabilistic characteristics, the corresponding response of the structure with FDS has probabilistic distribution. In this study, nonlinear time history analyses were performed for the structure with FDS subjected to artificial earthquake loads generated using Kanai-Tajimi filter. An equation for the probability density function (PDF) of the displacement response is proposed by adapting the PDF of the normal distribution. Finally, coefficients of the proposed PDF is obtained by regression analysis of the statistical distribution of the time history responses. Finally, the correlation between PDFs and statistical response distribution is presented.

• Journal of Korean Association for Spatial Structures
• /
• v.17 no.3
• /
• pp.45-55
• /
• 2017

The objective of this study is to estimate the mechanical characteristics and nonlinear behaviors on the geometric nonlinear analysis of curved cable-membrane roof systems for long span lightweight roof structures. The weight of a cable-membrane roof dramatically can reduce, but the single layer cable-membrane roof systems are too flexible and difficult to achieve the required structural stiffness. A curved cable roof system with reverse curvature works more effectively as a load bearing system, the pretension of cables can easily increase the structural stiffness. The curved cable roof system can transmit vertical loads in up and downward direction, and work effectively as a load bearing structure to resists self-weights, snow and wind loads. The nonlinear behavior and mechanical characteristics of a cable roof system has greatly an affect by the sag and pretension. This paper is carried out analyzing and comparing the tensile forces and deflection of curved roof systems by vertical loads. The elements for analysis uses a tension only cable element and a triangular membrane element with 3 degree of freedom in each node. The authors will show that the curved cable-membrane roof system with reverse curvature is a very lightweight and small deformation roof for external loads.

• Journal of applied mathematics & informatics
• /
• v.27 no.1_2
• /
• pp.335-341
• /
• 2009

In this paper, a system of nonsmooth equations reformulated from a nonlinear complementarity problem with nonsmooth data is studied. The formulas of some subdifferentials for related functions in this system of nonsmooth equations are developed. The present work can be applied to Newton methods for solving this kind of nonlinear complementarity problem.