• Smart Structures and Systems
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• 제20권3호
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• pp.263-272
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• 2017

This paper presents the time response of a mixed vibration system with the viscous damping and the hysteretic damping. There are two ways to derive the time response of such a vibration system. One is an analytical method, using the contour integral of complex functions to compute the inverse Fourier transforms. The other is an approximate method in which the analytic functions derived by Hilbert transform are expressed in the state space representation, and only the effective eigenvalues are used to efficiently compute the transient response. The unit impulse responses of the two methods are compared and the change in the damping properties which depend on the viscous and hysteretic damping values is investigated. The results showed that the damping properties of a mixed damping vibration system do not present themselves as a linear combination of damping properties.

• Journal of applied mathematics & informatics
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• 제39권5_6호
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• pp.601-616
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• 2021

Retrial queueing models have been studied extensively in the literature. These have many practical applications, especially in service sectors. However, retrial queueing models have their own limitations. Typically, analyzing such models involve level-dependent quasi-birth-and-death processes, and hence some form of a truncation or an approximate method or simulation approach is needed to study in steady-state. Secondly, in general, the customers are not served on a first-come-first-served basis. The latter is the case when a new arrival may find a free server while prior arrivals are waiting in the retrial orbit due to the servers being busy during their arrivals. In this paper, we take a different approach to the study of multi-server retrial queues in which the signals are generated in such a way to provide a reasonably fair treatment to all the customers seeking service. Further, this approach makes the study to be level-independent quasi-birth-and-death process. This approach is different from any considered in the literature. Using matrix-analytic methods we analyze MAP/M/c-type retrial queueing models along with Poisson signals in steady-state. Illustrative numerical examples including a comparison with previously published retrial queues are presented and they show marked improvements in providing a quality of service to the customers.

• 대한기계학회논문집
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• 제15권1호
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• pp.169-178
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• 1991

본 연구에서는 평면 변형률 강소성 유한요소법을 이용하여 유한요소 수식화를 유도하고 금형이 해석저인 함수로 묘사되는 드로잉 공정을 해석하고, 금형이 해석적인 함수로 묘사되지 않는 실제적인 자동차 성형품의 드로잉 공정을 해석하여 기존의 결과 와 비교하여 본 방법의 타당성을 검토하였다.

• Structural Engineering and Mechanics
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• 제50권4호
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• pp.487-500
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• 2014

An analytical solution for the nonlinear in-plane free oscillations of the suspended cable which contains the quadratic and cubic nonlinearities is investigated via the homotopy analysis method (HAM). Different from the existing analytical technique, the HAM is indeed independent of the small parameter assumption in the nonlinear vibration equation. The nonlinear equation is established by using the extended Hamilton's principle, which takes into account the effects of the geometric nonlinearity and quasi-static stretching. A non-zero equilibrium position term is introduced due to the quadratic nonlinearity in order to guarantee the rule of the solution expression. Therefore, the mth-order analytic solutions of the corresponding equation are explicitly obtained via the HAM. Numerical results show that the approximate solutions obtained by using the HAM are in good agreement with the numerical integrations (i.e., Runge-Kutta method). Moreover, the HAM provides a simple way to adjust and control the convergent regions of the series solutions by means of an auxiliary parameter. Finally, the effects of initial conditions on the linear and nonlinear frequency ratio are investigated.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1464-1470
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• 2009

RBDO approach based on a sampling method with the Kriging metamodel and Constraint Boundary Sampling (CBS), which is sequential sampling method to generate metamodels is proposed. The major advantage of the proposed RBDO approach is that it does not require Most Probable failure Point (MPP) which is essential for First-Order Reliability Method (FORM)-based RBDO approach. The Monte Carlo Sampling (MCS), most well-known method of the sampling methods for the reliability analysis is used to assess the reliability of constraints. In addition, a Cumulative Distribution Function (CDF) of the constraints is approximated using Moving Least Square (MLS) method from empirical distribution function. It is possible to acquire a probability of failure and its analytic sensitivities by using an approximate function of the CDF for the constraints. Moreover, a concept of inactive design is adapted to improve a numerical efficiency of the proposed approach. Computational accuracy and efficiency of the proposed RBDO approach are demonstrated by numerical and engineering problems.

• Composites Research
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• 제17권2호
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• pp.9-14
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• 2004

본 연구는 FRP 보강 콘크리트 슬래브의 휨거동에 관한 이론적 연구로서 FRP 보강 콘크리트 슬래브를 구조적 직교이방성판으로 간주하고 고전적 직교이방성판이론에 따른 휨해석 및 유한요소해석을 수행하였다. FRP 보강 콘크리트 슬래브를 직교이방성판으로 모델링하기 위해서는 각 하중한대별로 실제 구조물의 거동에 부합하는 직교이방성판의 휨강성을 결정하는 것이 중요하다. 본 연구에서는 탄성등가법을 적용하여 FRP 보강 콘크리트 슬래브와 등가인 직교이방성판의 휨강성을 결정하였으며, 탄성등가법에 의해 결정된 휨강성을 사용하여 유한요소해석 수행을 위한 강성행렬의 결정방법을 제안하였다. 또한, 이론식에 의한 해석결과와 제안된 강성행렬을 사용하여 해석한 유한요소해석 결과를 실험결과와 비교하였다.

• Nuclear Engineering and Technology
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• 제4권2호
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• pp.102-108
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• 1972

등방성이고 단면적이 상수인 경우의 지발 중성자를 가진 시간 종속 중성자 수송 방정식이 해석적으로 풀어지고 있다. 두 개로 구분된 시간 영역에 있어서의 방정식이 점근적 방법에 의하여 원래의 수송 방정식으로부터 얻어 지고 있다. 각 시간 영역에 있어서의 근사해는 중성자 속도의 역수 정도로 시간에 있어서 균일하게 유용하다는 것이 보여 지고 있다.

• 한국통신학회논문지
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• 제24권7B호
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• pp.1268-1278
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• 1999

본 논문에서는 ATM 망에서 VBR MPEG 비디오 트래픽에 대한 리키버킷 기반의 UPC 제어 시 적절한 트래픽 기술자 조합을 선정할 수 있는 해석적 방법을 제안한다. 장면기반 비디오 트래픽 모델링을 통해 UPC에서의 셀 위반확률을 해석적으로 유도하고, 이를 이용하여 원하는 UPC 제어 위반확률을 갖는 트래픽 기술자의 조합을 선정할 수 있음을 보인다. 실험 대상 MPEG 비디오 시퀀스에 대해 본 논문에서 제안한 해석적 트래픽 기술자 dimensioning 결과가 실제 시뮬레이션에 의한 선정결과를 잘 근사화 함을 모의실험을 통해 보인다. 마지막으로 망에서 호 수락제어로 ON/OFF 소스의 등가대역폭을 이용할 경우, 가능한 트래픽 기술자 조합에 대해 할당되는 등가대역폭을 분석하여 효율적인 트래픽 기술자 선정방안을 제안한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1993년도 추계학술대회논문집; 반도아카데미, 26 Nov. 1993
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• pp.77-83
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• 1993

In this paper, the dynamics of a 2-DOF not 1:1 resonant Hamiltonian system are studied. In the first part of the work, the behaviors of special periodic orbits called normal modes are examined by means of the harmonic balance method and their approximate stability ar analyzed by using the Synge's concept named stability in the kinematico-statical sense. Secondly, the global dynamics of the system for low and high energy are studied in terms of a perturbation analysis and Poincare' maps. In this part, one can see that the unstable normal mode generates chaotic motions resulting from the transverse intersections of the stable and unstable manifolds. Although there exist analytic methods for proving the existence of infinitely many periodic orbits, chaos, they cannot be applied in our case and thus, the Poincare' maps constructed by direct numerical integrations are utilized fot detecting chaotic motions. In the last part of the work, the existence of arbitrarily many periodic orbits of the system are proved by using a subharmonic Melnikov's method. We also study the possibility of the breakdown of invariant KAM tori only when h>h$_{0}$ (h$_{0}$:bifurcating energy) and investigate the generality of the destruction phenomena of the rational tori in the systems perturbed by stiffness and inertial coupling.

• 대한산업공학회지
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• 제23권1호
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• pp.147-162
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• 1997

When designing workplaces or arranging controls on panel, devices and controls should be placed within the reach of operator's arm or foot to guarantee effective performances. Most of the existing research on the reach volume were based on measurements of a few subject's arm reach, and limited to Caucasian and Chinese populations. Furthermore, reach volume considering foot or trunk motion have not been investigated. Range of human joint motion and that of two degrees of freedom motion are needed to generate reach volume analytically using the sweeping algorithm. However, range of two degrees of freedom motion has not been measured up to now. Therefore, range of two degrees of freedom motion was measured in this research, where 47 college students were participated voluntarily as subjects. The results showed that the motion of one joint can be limited by the motion of another motion, that is to say, the shoulder flexion was decreased significantly when the shoulder was adducted or abducted. Second, new approximate algorithms generating reach volumes were suggested, in which range of two degrees of freedom motion was used as input data. Depending upon the body segment included such as trunk, arm and leg, three types of reach volume were provided, in which the human body was modeled as a multilink system based on the robot kinematics and the sweeping method was employed. Reach volume generated analytically in this study showed statistically reasonable results when compared with that obtained from direct measurement.