• 한국해양공학회지
• /
• 제31권6호
• /
• pp.405-412
• /
• 2017

Because of the rapid development of computer technology in recent years, wave models can utilize parallel calculations for the high-resolution prediction of open sea and coastal areas with high accuracy. Parallel calculations also allow national agencies in the relevant sectors to produce marine forecasting data through massive parallel calculations. Meanwhile, the eastern coast of the Korean Peninsula has been increasingly damaged by swell-like high waves, and many researchers and scientists are continuing their efforts to anticipate and reduce the damage. In general, the short-term transformation of swell-like high waves can be reproduced relatively well in the third generation wave models, but the transformation of relatively long period waves needs to be simulated with higher accuracy in terms of the nonlinear wave interactions to gain a better understanding of the low-frequency wave generation and development mechanisms. In this study, we developed a calculation module to improve the calculation of the nonlinear energy transfer in the 3rd generation wave model and integrated it into the wave model to effectively consider the nonlinear wave interaction. First, the nonlinear energy transfer calculation module and third generation model were combined. Then, the combined model was used to reproduce the wave transformation due to the nonlinear interaction, and the performance of the developed operation module was verified.

• 한국해안해양공학회지
• /
• 제11권1호
• /
• pp.7-19
• /
• 1999

비선형 상호작용에 의한 풍파 성분간 에너지 전달은 스펙트럼의 발달에서 중요한 역할을 한다. 비선형 전달을 표현하는 Boltzmann적분을 계산하는 데에는 방대한 계산시간이 필요하기 때문에 파랑모형에서 비선형 상호작용을 고려하는 것을 불가능하다. 본 연구에서는 산란계수의 특성과 상호작용의 상세균형의 원리를 이용하여 비선형 전달을 효율적으로 계산하는 방법에 대하여 고찰하였다. Webb의 방법(IWm)은 특이점을 퇴화시켜 매우 안정한 계산 결과를 주지만 상세균형의 원리를 적용할 수 없기 때문에 계산의 효율성에는 한계가 있는 것으로 나타났다. 한편, Masuda의 방법(IMM)에서는 특이점을 해석적으로 처리하며 계산시간은 Pentinum 300MHz Processor에서 1.3초가 소요되었다. 따라서 IMM은 1차원 파랑모형에 실용적으로 사용할 수 있으며 취송시간과 취송거리에 의한 풍파 스펙트럼의 성장 과정 연구등에 매우 유용하다.

• Journal of Electrical Engineering and Technology
• /
• 제9권6호
• /
• pp.1935-1943
• /
• 2014

In recent years, the induction machines are increasingly being used as self-excited induction generators (SEIG). This generator is especially widely employed for small-scale power plants driven by renewable energy sources. The application of power electronic components in the induction generator control (IGC) and the loading of SEIG using nonlinear loads will generate harmonic currents. This paper analyzes the propogation of harmonic currents on the SEIG with nonlinear loads. Transfer function method in the frequency domain is used to calculate the gain and phase angle of each harmonic current component which are generated by a nonlinear loads. Through the superposition approach, this method has also been used to analyze the propagation of harmonic currents from nonlinear load to the stator windings. The simulation for the propagation of harmonic currents for a 4 pole, 1.5 kW, 50Hz, 3.5A, Y-connected, rotor-cage SEIG with energy-saving lamps, have provided results almost the same with the experiment. It can prove that the validity of the proposed models and methods. The study results showed that the propagation of harmonic currents on the stator windings rejects high order harmonics and attenuates low order harmonics, consequently THDI diminish significantly on the stator windings.

• 한국해안해양공학회지
• /
• 제7권1호
• /
• pp.116-125
• /
• 1995

파하중과 해류하중을 받는 단일 자유도계를 동적 해석하여 비선형 거동을 나타냄을 보이고 고차의 비선형 전이함수를 포함한 모델을 적용하여 그 비선형 차수를 알아낸다. 먼저 구조물에 단일 정현파, 두 파의 합성파 그리고 불규칙파 하중을 차례로 가하면서 각 하중조건마다 세가지 비선형 요인의 효과를 조사한다. 이로부터 단일 자유도계의 공진주파수에서 파의 에너지는 존재하지 않지만 비선형 요인에 의해 응답 성분이 나타남을 보인다. 다음으로 Volterra 급수에 근거한 고차 전이함수(higher order transfer function)모델을 적용하여 유연한 단일 자유도계의 비선형 거동이 성공적으로 모델화됨을 보이며 또한 비선형성이 2차나 3차로 명백히 나타남을 보인다.

• Structural Engineering and Mechanics
• /
• 제83권1호
• /
• pp.31-43
• /
• 2022

A nonlinear gas-spring tuned mass damper is proposed to mitigate the seismic responses of the multi-degree-of-freedom (MDOF) structure, in which the nine-story benchmark model is selected as the controlled object. The nonlinear mechanical properties of the gas-spring are investigated through theoretical analysis and experiments, and the damper's control parameters are designed. The control performance and damping mechanism of the proposed damper attached to the MDOF structure are systematically studied, and its reliability is also explored by parameter sensitivity analysis. The results illustrate that the nonlinear gas-spring TMD can transfer the primary structure's vibration energy from the lower to the higher modes, and consume energy through its own relative movement. The proposed damper has excellent "Reconciling Control Performance", which not only has a comparable control effect as the linear TMD, but also has certain advantages in working stroke. Furthermore, the control parameters of the gas-spring TMD can be determined according to the external excitation amplitude and the gas-spring's initial volume.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
• /
• pp.12-15
• /
• 1994

To establish the sea surface temperature estimation scheme for the upcoming advanced remote sensor, the quasi-analytical solution of the approximated radiative transfer equation which express the radiative transfer process of the radiant energy radiated from the sea surface to the satellite is approximated into the non-linear equation. To solve the simultaneous approximated radiative transfer equation which express the radiative transfer process of the radiant energy radiated from the sea surface to the satellite is approximated into the nonlinear equation. To solve the simultaneous approximated radiative transfer equation at each channel, the constrained non-linear optimization technique is adopted. To define the coefficients of the approximated radiative transfer equation and the constraints, the satellite detected radiance and the total transmittance are computed from the 1350 kinds of simulated atmosphere / surface models via radiative transfer code. The verification from the simulated data show the sufficient result.

• 동력기계공학회지
• /
• 제2권1호
• /
• pp.31-38
• /
• 1998

A diffuser, an important equipment to change kinetic energy into pressure energy, has been studied for a long time. Though experimental and theoretical researches have been done, the understanding of energy transfer and detailed mechanism of energy dissipation is unclear. As far as numerical prediction of diffuser flows are concerned, various numerical studies have also been done. On the contrary, many turbulence models have constraint to the applicability of diffuser-like complex flows, because of anisotropy of turbulence near the wall and of local nonequilibrium induced by an adverse pressure gradient. The existing $k-{\epsilon}$ turbulence models have some problems in the case of being applied to complex turbulent flows. The purpose of this paper is to test the applicability of the nonlinear $k-{\epsilon}$ model concerning diffuser-like flows with expansion and streamline curvature. The results show that the nonlinear $k-{\epsilon}$ turbulence model predicted well the coefficient of pressure, velocity profiles and turbulent kinetic energy distributions, however the shear stress prediction was failed.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권4호
• /
• pp.729-739
• /
• 2017

The objective of this study was to optimize minimum-energy impulsive spacecraft intercept using genetic algorithms. A mathematical model was established on two-body system based on f and g solution and universal variable to address spacecraft intercept problem for non-coplanar elliptical orbits. This nonlinear problem includes many local optima due to discontinuity and strong nonlinearity. In addition, since it does not provide a closed-form solution, it must be solved using a numerical method. Therefore, the initial guess is that a very sensitive factor is needed to obtain globally optimal values. Genetic algorithms are effective for solving these kinds of optimization problems due to inherent properties of random search algorithms. The main goal of this paper was to find minimum energy solution for orbit transfer problem. The numerical solution using initial values evaluated by the genetic algorithm matched with results of Hohmann transfer. Such optimal solution for unrestricted arbitrary elliptic orbits using universal variables provides flexibility to solve orbit transfer problems.

• 한국해안해양공학회지
• /
• 제11권1호
• /
• pp.20-33
• /
• 1999

심해에서 풍파의 성장은 바람에 의한 에너지 입력, 비선형 상호작용에 의한 에너지 전달 및 백파에 의한 에너지 소산에 의하여 결정된다. 본 연구에서는 두가지의 비선형 계산법(IMM 모형과 WAM 모형)을 사용하여 풍파 스펙트럼의 시간발전 특성을 상호비교하였다. 비선형 에너지 전달은 첨두주파수의 저주파 천이, 스펙트럼의 과대평가 현상, 스펙트럼의 자기상사적 발달 등에서 중심적인 역할을 하는 것으로 나타났다. 특히, 고주파 성분의 방향 분포가 쌍봉형으로 발전되는 경향이 있는데 이러한 현상도 비선형 상호작용의 역할로 설명되었다. 주파수 스펙트럼에서 고주파측의 꼬리는 주파수의 -4승에 비례하는 형상으로 발전되는 것이 확인되었다. 외부의 원인으로 스펙트럼에 도입되는 섭동은 자기상사 기구에 의하여 빠르게 제거되는데 이는 파랑수치 모형에서 비선형 상호작용이 모형의 안정화에 크게 기여함을 의미한다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권12호
• /
• pp.5614-5633
• /
• 2018

Mobile Edge Computing (MEC) and Wireless Power Transfer (WPT) are both recognized as promising techniques, one is for solving the resource insufficient of mobile devices and the other is for powering the mobile device. Naturally, by integrating the two techniques, task will be capable of being executed by the harvested energy which makes it possible that less intrinsic energy consumption for task execution. However, this innovative integration is facing several challenges inevitably. In this paper, we aim at prolonging the battery life of mobile device for which we need to maximize the harvested energy and minimize the consumed energy simultaneously, which is formulated as residual energy maximization (REM) problem where the offloading ratio, energy harvesting time, CPU frequency and transmission power of mobile device are all considered as key factors. To this end, we jointly optimize the offloading ratio, energy harvesting time, CPU frequency and transmission power of mobile device to solve the REM problem. Furthermore, we propose an efficient convex optimization and sequential unconstrained minimization technique based combining method to solve the formulated multi-constrained nonlinear optimization problem. The result shows that our joint optimization outperforms the single optimization on REM problem. Besides, the proposed algorithm is more efficiency.