디지털 파랑 수조 내에서의 비선형 파랑 운동의 수치시뮬레이션

박종천,김경성 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.4

A digital wave tank (DWT) simulation technique has been developed by authors to investigate the interactions of fully nonlinear waves with 3D marine structures. A finite-difference/volume method and a modified marker-and-cell (MAC) algorithm have been used, which are based on the Navier-Stokes (NS) and continuity equations. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique or the Level-Set (LS) technique developed for one or two fluid layers. In this paper, some applications for various engineering problems with free-surface are introduced and discussed. It includes numerical simulation of marine environments by simulation equipments, fully nonlinear wave motions around offshore structures, nonlinear ship waves, ship motions in waves and marine flow simulation with free-surface. From the presented simulations, it seems that the developed DWT simulation technique can handle various engineering problems with free-surface and reliably predict hydrodynamic features due to the fully-nonlinear wave motions interacting with such marine structures.

Nonlinear dynamic response of cable-suspended systems under swinging and heaving motion

Guohua Cao,Naige Wang,Lei Wang,Zhencai Zhu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

In order to enhance the fidelity, convenient and flexibility of swinging motion, the structure of incompletely restrained cablesuspended system controlled by two drums was proposed, and the dynamic response of the system under swinging and heaving motion were investigated in this paper. The cables are spatially discretized using the assumed modes method and the system equations of motion are derived by Lagrange equations of the first kind. Based on geometric boundary conditions and linear complementary theory, the differential algebraic equations are transformed to a set of classical difference equations. Nonlinear dynamic behavior occurs under certain range of rotational velocity and frequency. The results show that asynchronous motion of suspension platform is easily caused imbalance for cable tension. Dynamic response of different swing frequencies were obtained via power frequency analysis, which could be used in the selection of the working frequency of the swing motion. The work will contribute to a better understanding of the swing frequency, cable tension and posture with dynamic characteristics of unilateral geometric and kinematic constraints in this system, and it is also useful to investigate the accuracy and reliability of instruments in future.

NUMERICAL SIMULATIONS OF FULLY NONLINEAR WAVE MOTIONS IN A DIGITAL WAVE TANK

J.C. Park(박종천),K.S. Kim(김경성) 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.4

A digital wave tank (DWT) simulation technique has been developed by authors to investigate the interactions of fully nonlinear waves with 3D marine structures. A finite-difference/volume method and a modified marker-and-cell (MAC) algorithm have been used, which are based on the Navier-Stokes (NS) and continuity equations. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique or the Level-Set (LS) technique developed for one or two fluid layers. In this paper, some applications for various engineering problems with free-surface are introduced and discussed. It includes numerical simulation of marine environments by simulation equipments, fully nonlinear wave motions around offshore structures, nonlinear ship waves, ship motions in waves and marine flow simulation with free-surface. From the presented simulations, it seems that the developed DWT simulation technique can handle various engineering problems with free-surface and reliably predict hydrodynamic features due to the fully-nonlinear wave motions interacting with such marine structures.

Boundary control of marine risers with bending couplings

T. L. Nguyen,K. D. Do,J. Pan 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

The aim of this paper is to design a boundary controller at the top end for global stabilization of twodimensional marine risers under environmental disturbances. Based on the energy approach, equations of motion of the risers including bending couplings are derived. Due to these couplings, the riser dynamics exhibit mutual effects between transverse motions. The Lyapunov direct method is used to design the boundary controller. Stability analysis of the closed-loop system is carried out using the Lyapunov stability theory. Numerical simulations illustrate the results.

Numerical study on the resonance response of spar-type floating platform in 2-D surface wave

최응영,조진래,정의봉 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.1

This paper is concerned with the numerical study on the resonance response of a rigid spar-type floating platform in coupled heave and pitch motion. Spar-type floating platforms, widely used for supporting the offshore structures, offer an economic advantage but those exhibit the dynamically high sensitivity to external excitations due to their shape at the same time. Hence, the investigation of their dynamic responses, particularly at resonance, is prerequisite for the design of spar-type floating platforms which secure the dynamic stability. Spar-type floating platform in 2-D surface wave is assumed to be a rigid body having 2-DOFs, and its coupled dynamic equations are analytically derived using the geometric and kinematic relations. The motion-variance of the metacentric height and the moment of inertia of floating platform are taken into consideration, and the hydrodynamic interaction between the wave and platform motions is reflected into the hydrodynamic force and moment and the frequency-dependent added masses. The coupled nonlinear equations governing the heave and pitch motions are solved by the RK4 method, and the frequency responses are obtained by the digital Fourier transform. Through the numerical experiments to the wave frequency, the resonance responses and the coupling in resonance between heave and pitch motions are investigated in time and frequency domains.

안티롤링 진자를 이용한 부유체의 횡동요 저감

박석주(Sok-Chu Park),이금주(Geum-Joo Yi),박경일(Kyung-Il Park) 한국항해항만학회 2016 한국항해항만학회지 Vol.40 No.6

부유체의 횡동요는 승조원의 피로를 누적시키고, 심지어 구조물 전체를 전복시키기 까지 하고, 또 선체에 반복적인 외력을 가하는등 부유체의 안정성과 구조물의 안전에 심대한 영향을 끼친다. 그래서 거의 모든 선박의 경우에는 빌지킬을 설치하여 횡동요를 감소시키고 있고, 특수한 경우에는 안티롤링 탱크나 핀 스태빌라이저나 자이로스코프 등을 설치하여 횡동요를 줄이고 있다. 그러나 안티롤링 탱크는 설치하는데 용적을 많이 차지하고, 핀 스태빌라이저나 자이로스코프는 설치비와 유지 관리비가 많이 든다. 본 연구에서는 안티롤링 진자를 이용하여 부유체의 횡동요를 줄이고자 한다. 보통 단진자라고 하면 질량체를 끈으로 어디엔가 고정시켜 놓고 자유롭게 흔들리는 구조를 말한다. 여기에서는 통상의 진자 대신에 진자를 원궤도에 올려놓아서 단진동 운동을 하도록 하는 원리를 이용한다. 제안한 장치를 실험선에 적용하여 그 효능을 입증하였다. 안티롤링 탱크의 약 1/8의 중량과 약 1/6의 용적을 가진 안티롤링 진자를 이용하여 이것보다 더 좋은 효과를 낼 수 있음을 확인 하였다. 여기에 더하여 선체에 안티롤링 진자를 부가한 모델의 선형운동방정식과 비선형 운동방정식을 제시하였다. A ship’s rolling motion can make crew and passengers sick and/or apply forces to the structure that cause damage.. Therefore bilge keels are equipped in most ships for anti-rolling. In special cases, anti-rolling tanks (ARTs), fin stabilizers, or gyroscopes can be installed. However, ARTs require a large area to install, and fin stabilizers and gyroscopes are costly to install and expensive to operate. This paper suggests a Anti-rolling pendulum (ARP) to reduce roll motion. ARPs acts like ARTs. However, the ARP has a circular shaped guidance arc instead of the string or wire of a simple pendulum. The device suggested has about 1/8 the weight and 1/6 the volume of a ART and is more effective. This study derives the nonlinear and linear differential equations of system motion.

SINGULAR PERIODIC SOLUTIONS OF A CLASS OF ELASTODYNAMICS EQUATIONS

Yuan, Xuegang,Zhang, Yabo The Korean Society for Computational and Applied M 2009 Journal of applied mathematics & informatics Vol.27 No.3

A second order nonlinear ordinary differential equation is obtained by solving the initial-boundary value problem of a class of elas-todynamics equations, which models the radially symmetric motion of a incompressible hyper-elastic solid sphere under a suddenly applied surface tensile load. Some new conclusions are presented. All existence conditions of nonzero solutions of the ordinary differential equation, which describes cavity formation and motion in the interior of the sphere, are presented. It is proved that the differential equation has singular periodic solutions only when the surface tensile load exceeds a critical value, in this case, a cavity would form in the interior of the sphere and the motion of the cavity with time would present a class of singular periodic oscillations, otherwise, the sphere remains a solid one. To better understand the results obtained in this paper, the modified Varga material is considered simultaneously as an example, and numerical simulations are given.

Singular periodic solutions of a class of elastodynamics equations

Xuegang Yuan,Yabo Zhang 한국전산응용수학회 2009 Journal of applied mathematics & informatics Vol.27 No.3

A second order nonlinear ordinary differential equation is obtained by solving the initial-boundary value problem of a class of elastodynamics equations, which models the radially symmetric motion of a incompressible hyper-elastic solid sphere under a suddenly applied surface tensile load. Some new conclusions are presented. All existence conditions of nonzero solutions of the ordinary differential equation, which describes cavity formation and motion in the interior of the sphere, are presented. It is proved that the differential equation has singular periodic solutions only when the surface tensile load exceeds a critical value, in this case, a cavity would form in the interior of the sphere and the motion of the cavity with time would present a class of singular periodic oscillations, otherwise, the sphere remains a solid one. To better understand the results obtained in this paper, the modified Varga material is considered simultaneously as an example, and numerical simulations are given. A second order nonlinear ordinary differential equation is obtained by solving the initial-boundary value problem of a class of elastodynamics equations, which models the radially symmetric motion of a incompressible hyper-elastic solid sphere under a suddenly applied surface tensile load. Some new conclusions are presented. All existence conditions of nonzero solutions of the ordinary differential equation, which describes cavity formation and motion in the interior of the sphere, are presented. It is proved that the differential equation has singular periodic solutions only when the surface tensile load exceeds a critical value, in this case, a cavity would form in the interior of the sphere and the motion of the cavity with time would present a class of singular periodic oscillations, otherwise, the sphere remains a solid one. To better understand the results obtained in this paper, the modified Varga material is considered simultaneously as an example, and numerical simulations are given.

수중운동체 기동 모사를 위한 선형·비선형 운동방정식 비교 분석

이호진(Hojin Lee),현철(Chul Hyun),김현승(Hyunseung Kim),김창환(Changhwan Kim) 한국해군과학기술학회 2023 Journal of the KNST Vol.6 No.4

In this paper, we derived nonlinear and linear 6-DOF motion equations that can represent the maneuvers of underwater vehicles with symmetric shapes and high-speed running. Each motion equation was integrated with a control model of the same form using a commercial program, and numerical simulations were performed for various maneuver conditions. The simulation results showed that the results of the nonlinear and linear motion equations were almost identical in most cases. We confirmed that a simplified linear model can be used for rough characteristic analysis or control performance verification under conditions where there are not many sharp maneuvers.

국내⋅외 계기지진 정보를 활용한 중⋅약진 지역의 스펙트럴 가속도 응답 예측식

신동현,김형준 한국지진공학회 2018 한국지진공학회논문집 Vol.22 No.2

This study develops an empirical prediction equation of spectral acceleration responses of earthquakes which can induce structural damages. Ground motion records representing hazards of low-to-moderate seismic regions were selected and organized with several influential factors affecting the response spectra. The empirical equation and estimator coefficients for acceleration response spectra were then proposed using a robust nonlinear optimization coupled with a regression analysis. For analytical verification of the prediction equation, response spectra used for low-to-moderate seismic regions were estimated and the predicted results were comparatively evaluated with measured response spectra. As a result, the predicted shapes of response spectra can simulate the graphical shapes of measured data with high accuracy and most of predicted results are distributed inside range of correlation of variation (COV) of 30% from perfectly correlated lines.