• Steel and Composite Structures
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• 제43권3호
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• pp.375-388
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• 2022

Nibellen structural system is a novel resilient bracing system based on the application of Bellville disks and Nitinol rods. The cyclic behavior of Nibellen assembly was obtained, and the design equations were developed based on the available literature. Seismic performance of the system was then studied analytically. Two groups of buildings with different lateral force resisting systems were designed and studied: one group with the Nibellen system, and the other with the special concentrically braced frame system. Each building group consisted of 5-, 10-, and 15-story buildings. The Design-Base-Event (DBE) and Maximum Considered Event (MCE) were considered as the seismic hazard, and a suite of seven ground motions were scaled accordingly for response history analyses. Finally, the resiliency of the buildings was studied by obtaining the functionality curve of the buildings before and after the seismic event. The construction cost of the 5-story building with Nibellen bracing system increased but the post-earthquake cost decreased significantly. The application of Nibellen system in the 10- and 15-story buildings reduced both the construction and repair costs, considerably. Resiliency of all the buildings was improved when Nibellen system was used as the lateral force resisting system.

• 한국정밀공학회지
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• 제9권3호
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• pp.73-82
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• 1992

An industrial robot, installed real manufacturing processes an element of the system autmation, can be considered as an uncertain system due to dynamic uncertainties in inertial parameters and varying payloads. Most difficuties in controlling a robot manipulator are caused by the fact that the dynamic equations describing the motions of the manipulator are inherently nonlinear and heavily coupled effects between joints and associated links. Existing robot conrol systems have constant predefined gains and do not cover the complex dynamic interactions between manipulator joints. As a result, the manipulator is severly limited in range of application, speed of operation and variation of payload. The proposed controller is operated by adjusting its gains based on the response of the manipulator in such a way that the manipulator closely matches the reference model trajectories defined by the desinger. The proposed manipulator studied has two loops, an inner loop of model reference adaptive controller and an outer loop of state feedback controller with integral action to guarantee the stability of the adaptive scheme. This adaptation algorithm is based on the hyperstailiy approach with an improved Lyapunov function. The coupling among joints and the nonlinearity in the dynamic equation are explicitly considered. The designed manipulator controller shows good tracking performance in practical working environment, various load variations and parameter uncertainties.

• 한국산림과학회지
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• 제82권1호
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• pp.34-43
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• 1993

이 논문에서는 고정식 가선집재기를 중심으로 집재작업의 구조적 특성을 역학적 원리를 이용하여 해석하였다. 그리고 집재지의 지형여건, 시스템의 기하학적 형태 및 작업조건과의 함수관계에서 최대허용반송용량을 추정하기 위한 함수관계식을 힘과 모멘트의 평형조건으로부터 유도하는 과정을 제시하였다. 이러한 관계식 중에는 벌도목의 들어올려진 정도와 단선구조 cable 철선의 역학적 해석을 위한 기본 관계식들이 포함되었고, 단선구조 역학해석은 현수선원리를 기초로 하여 단선의 처짐이 고려되었다. 역학관계식들은 복잡한 비선형함수식들로 구성되어 이를 풀기 위한 과정을 제시하기 위하여 전산모델을 개발하였다, 이 모델에서는 계산목적상 Secant기법을 이용하였다. 또한 가상적인 데이타를 이용하여 전산모델의 적용예를 제시하였다.

• Coupled systems mechanics
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• 제7권4호
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• pp.373-393
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• 2018

This paper is concerned with the wave propagation behavior of rotating functionally graded temperature-dependent nanoscale beams subjected to thermal loading based on nonlocal strain gradient stress field. Uniform, linear and nonlinear temperature distributions across the thickness are investigated. Thermo-elastic properties of FG beam change gradually according to the Mori-Tanaka distribution model in the spatial coordinate. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The governing equations are derived by Hamilton's principle as a function of axial force due to centrifugal stiffening and displacement. By applying an analytical solution and solving an eigenvalue problem, the dispersion relations of rotating FG nanobeam are obtained. Numerical results illustrate that various parameters including temperature change, angular velocity, nonlocality parameter, wave number and gradient index have significant effect on the wave dispersion characteristics of the understudy nanobeam. The outcome of this study can provide beneficial information for the next generation researches and exact design of nano-machines including nanoscale molecular bearings and nanogears, etc.

• Ocean Systems Engineering
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• 제9권1호
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• pp.21-42
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• 2019

In this paper, the Finite-Analytic Navier-Stokes (FANS) code is coupled with an in-house finite-element code to study the dynamic interaction between a floating buoy and its mooring system. Hydrodynamic loads on the buoy are predicted with the FANS module, in which Large Eddy Simulation (LES) is used as the turbulence model. The mooring lines are modeled based on a slender body theory. Their dynamic responses are simulated with a nonlinear finite element module, MOORING3D. The two modules are coupled by transferring the forces and displacements of the buoy and its mooring system at their connections through an interface module. A free-decay model test was used to calibrate the coupled method. In addition, to investigate the capability of the present coupled method, numerical simulations of two degree-of-freedom vortex-induced motion of a CALM buoy in uniform currents were performed. With the study it can be verified that accurate predictions of the motion responses and tension responses of the CALM buoy system can be made with the coupling CFD-FEM method.

• Ocean Systems Engineering
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• 제11권1호
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• pp.1-16
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• 2021

Experimental and numerical investigations were conducted to study the performance of a surface-fixed horizontal porous wave barrier in regular waves. The characteristics of the reflection and transmission coefficients, energy dissipation, and vertical wave force were examined versus different porosities of the barrier. Numerical simulations based on 3D Reynolds Averaged Navier-Stokes equations with standard low-Re k-ε turbulent closure and volume of fluid approach were accomplished and compared with the experimental results conducted in a 2D wave tank. Experimental measurements and numerical simulations were shown to be in satisfactory agreement. The qualitative wave behavior propagating over a horizontal porous barrier such as wave run-up, wave breaking, air entrapment, jet flow, and vortex generation was reproduced by CFD computation. Through the discrete harmonic decomposition of the vertical wave force on a wave barrier, the nonlinear characteristics were revealed quantitatively. It was concluded that the surface-fixed horizontal barrier is more effective in dissipating wave energy in the short wave period region and more energy conversion was observed from the first harmonic to higher harmonics with the increase of porosity. The present numerical approach will provide a predictive tool for an accurate and efficient design of the surface-fixed horizontal porous wave barrier.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1998년도 제13차 학술회의논문집
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• pp.301-307
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• 1998

The goal of this paper is to describe an advanced method of the fault diagnois using Control Theory with reference to a crack detection, a new way to localize the crack position under infulence of the plant disturbance and white measurement noise on a rotating shaft. As a first step, the shaft is physically modelled with a finite element method as usual and the dynamic mathematical model is derived from it using the Hamilton - principle and in this way the system is modelled by various subsystems. The equations of motion with crack is established by adaption of the local stiffness change through breathing and gaping from the crack to the equation of motion with un-damaged shaft. This is supposed to be regarded as reference for the given system. Based on the fictitious model of the time behaviour induced from vibration phenomena measured at the bearings, a nonlinear State Observer is designed in order to detect the crack on the shaft. This is elementary NL- observer(EOB). Using the elementary observer, an Estimator(Observer) Bank is established and arranged at the certain position on the shaft. In case a crack is found and its position is known, the procedure for the estimation of the depth is going to begin.

• 한국생산제조학회지
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• 제22권1호
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• pp.1-7
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• 2013

Pneumatic cylinders are widely used to actuators in automatic equipments because they are relatively inexpensive, simple to install and maintain, offer robust design and operation, are available in a wide range of standard sizes and design alternatives. This paper presents a comparative study among the dynamic characteristics of meter-out and meter-in speed control of pneumatic cushion cylinders with a relief valve type cushion mechanism. Because of the nonlinear differential equations and a requirement for simultaneous iterative solution in a mathematical model of a double acting pneumatic cushion cylinder, a computer simulation is carried out to investigate pressure, temperature, mass flow rate in cushion chamber and displacement and velocity time histories of piston under various operating conditions. It is found that the piston velocity and pressure response in meter-in speed control are more oscillatory than with meter-out those when pneumatic cushion cylinders are driven at a high-speed. In meter-out speed control, the effective area of the flow control valve is larger than that of meter-in, and the supply pressure has to be much higher than the pressure required to move the load because it has also to overcome the back pressure in cushion chamber.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.893-897
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• 2006

Structures with additional frictional damping system have strong nonlinearity that the dynamic behavior is highly affected. by the relative magnitude between frictional force and excitation load. In this study, normalized response spectra of the structures with non-dimensional friction force are obtained through nonlinear time history analyses of the mass-normalized single degree of freedom systems using 20 ground motion data recorded on rock site. The variation of the control performance of frictional damping system is investigated in terms of the dynamic load and the structural natural period, of which effects were not considered in the previous studies. Least square curve fitting equations are presented for describing those normalized response spectrum and optimal non-dimensional friction forces are obtained for controlling the peak displacement and absolute acceleration of the structure based on the derivative of the curve fitted design spectrum.

• 한국정밀공학회지
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• 제25권9호
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• pp.86-94
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• 2008

A total stroke of an opening or closing motion of a hinge mechanism in a folder-type mobile phone is composed of two portions. In the first portion, human fingers act a force to open or close the folder. In this portion, the rotating folder compresses the coil spring installed in the mechanism. In the last portion, this compressed coil spring generates a torque to rotate the folder. The main merit of this study is that we have designed a hinge mechanism to be operated by a uniform torque in the first portion of the total stroke. The uniform torque means that it is constant along the folder's swing angle. This mechanism will give softer feeling to human fingers. A pair of contours in the mechanism plays an important role. It transforms rotation into translation in the first portion; on the other hand, it transforms translation into rotation in the last portion. In this study, we have developed an algorithm to obtain the pair of contour curves. We divided the total contour curves into finite sub-intervals. Assuming that the curves in every sub-interval are parabolas, we have obtained the coefficients of them by solving systems of nonlinear equations recursively.