• 대한조선학회논문집
• /
• 제49권1호
• /
• pp.52-59
• /
• 2012

Among many factors to be considered for higher safety level requirements, the hull stability in intact and damaged conditions in seaways is of utmost importance. Since the assessment of a damaged ship is complicated due to the highly non-linear behavior, it is widely acknowledged that computational fluid dynamics (CFD) methods are one of the most feasible approaches. Although many research activities are being reported on the damaged ship stability recently, most of them are not designed for validation of CFD studies. In this study, well-designed model tests were performed to build a CFD validation database, which is essential in developing better CFD methods for the damage stability assessment. The geometry of the damaged compartment and test conditions were determined based on preliminary CFD simulations. Free roll decay tests in calm water with both intact and damaged ships were performed and the roll motion characteristics were compared. The damaged ship showed a larger roll damping coefficient and more rapid decrease of roll amplitude than the intact ship. The primary reason of these efforts can be explained by the movement of the flooded water.

• 대한조선학회논문집
• /
• 제50권2호
• /
• pp.69-78
• /
• 2013

This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different methods are relatively in good agreement with the experiments, and these two results are similar in most wave frequency range. However, the discrepancies are apparent where the fluid motion is not governed by a single mode. But both of numerical methods over-predict the motion at the vicinity of the sloshing natural frequency. In order to correct the discrepancy, the modal damping needs to be investigated more precisely. Furthermore, another multi-modal approach, such as the Boussinesq-type method, seems to be required in the region of the intermediate liquid.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 추계학술대회 논문집
• /
• pp.169-173
• /
• 2001

This study presents the results of decoupling of free decay roll test data by discrete wavelet transform. Free roll decay test was performed to decide the coefficients of damping terms in equation of motion. During the experiment, a slight yaw motion was found while the model was in the free roll decay motion. Discrete wavelet transform was applied to the signal to extract the pure roll motion. The results were compared to those of the Fourier transform. DWT was able to decouple the two signals efficiently while the Fourier transform was not.

• Journal of Advanced Research in Ocean Engineering
• /
• 제2권2호
• /
• pp.81-85
• /
• 2016

Nonlinear wave loads can lead to resonant responses of offshore structures in sum or difference frequencies. In this study, the roll motion of an FPSO with a low natural frequency is simulated in the time domain. To generate the time signals of wave loads, the quadratic transfer functions of the second-order excitations are calculated in the frequency domain. The equations of motions based on the time memory functions are used to evaluate the roll responses in irregular waves. The roll damping in empirical form is accounted for in the simulation.

• 한국항공우주학회지
• /
• 제38권9호
• /
• pp.849-855
• /
• 2010

본 논문은 자유회전 테일핀을 갖는 커나드 유도 미사일에 대해 Falanga의 회전율 계산식을 자유회전 테일핀에 적용하여 자유회전 테일핀의 roll lock-in 현상을 예측하였다. 예측 결과의 정확도를 확인하기 위하여 Blair의 풍동시험 결과와 비교하여 검증하였다. 자유회전 테일핀의 회전율 계산 시에 필요한 테일핀의 롤링 모멘트는 풍동시험 결과를 이용하였고 롤 댐핑 모멘트는 missile DATCOM을 이용하여 계산하였다. 이를 자유회전 테일핀의 회전율 계산식에 대입하여 자유회전 테일핀의 회전율 및 Roll lock-in 현상을 예측하였으며 풍동시험 결과와 비교하였다. 검증결과, 자유회전 테일핀의 회전율 및 Roll lock-in 현상 예측 결과가 풍동시험 결과와 잘 일치하는 것을 확인 할 수 있었다.

• International Journal of Automotive Technology
• /
• 제6권2호
• /
• pp.141-148
• /
• 2005

In order to reduce the time and costs of improving the performance of vehicle suspensions, the techniques for optimizing damping and air spring characteristic were proposed. A full vehicle model for a bus is constructed with a car body, front and rear suspension linkages, air springs, dampers, tires, and a steering system. An air spring and a damper are modeled with nonlinear characteristics using experimental data and a curve fitting technique. The objective function for ride quality is WRMS (Weighted RMS) of the power spectral density of the vertical acceleration at the driver's seat, middle seat and rear seat. The objective function for handling performance is the RMS (Root Mean Squares) of the roll angle, roll rate, yaw rate, and lateral acceleration at the center of gravity of a body during a lane change. The design variables are determined by damping coefficients, damping exponents and curve fitting parameters of air spring characteristic curves. The Taguchi method is used in order to investigate sensitivity of design variables. Since ride and handling performances are mutually conflicting characteristics, the validity of the developed optimum design procedure is demonstrated by comparing the trends of ride and handling performance indices with respect to the ratio of weighting factors. The global criterion method is proposed to obtain the solution of multi-objective optimization problem.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1132-1137
• /
• 2007

This paper describes a Unified Chassis Control (UCC) strategy to prevent vehicle rollover by integrating individual modular chassis control systems such as Electronic Stability Control (ESC) and Continuous Damping Control (CDC). The UCC threshold is determined from a rollover index computed by estimated roll angle, roll rate and measured lateral acceleration. A direct yaw moment control method is used to design the ESC based on a 2-D bicycle model. Similarly, the CDC is designed based on a 2-D roll model using a direct roll moment control method. The performance of the proposed UCC scheme is investigated and compared to that of modular chassis controllers through computer simulations using a validated vehicle simulator. It is shown that the proposed the UCC can lead to improvements in vehicle stability and efficient actuation of chassis control systems.

• 한국해양공학회지
• /
• 제13권1호통권31호
• /
• pp.130-137
• /
• 1999

The wing-flap stabilizing system attached under the hull bottom of a small fishing vessel to prevent the capsize by controlling the roll motions has been developed. This paper describes the background of the system design together with the experimental results. The effectiveness of the system is proven by the towing tank tests with a 1/4 scale model, showing that the roll motions of the model are much reduced by the active flap control in multidirectional irregular waves forward speeds.

• International Journal of Aeronautical and Space Sciences
• /
• 제13권4호
• /
• pp.468-473
• /
• 2012

Cost is an important aspect in designing a target drone, however the poor performance of low cost IMU, GPS, and microcontrollers prevents the use of complex algorithms, such as ARS, or INS/GPS to estimate attitude angles. We propose an autopilot which uses rate gyro and GPS only for a target drone to follow a prescribed path for anti-aircraft training. The autopilot consists of an altitude hold, roll hold, and path following controller. The altitude hold controller uses vertical speed output from a GPS to improve phugoid damping. The roll hold controller feeds back yaw rate after filtering the dutch roll oscillation to estimate the roll angle. The path following controller operates as an outer loop of the altitude and roll hold controllers. A 6-DOF simulation showed that the proposed autopilot guides the target drone to follow a prescribed path well from the view point of anti-aircraft gun training.

• 해양환경안전학회지
• /
• 제29권6호
• /
• pp.688-696
• /
• 2023

본 연구에서는 어선의 운동성능을 향상하기 위해 부착되는 부가물의 조합과 파라미터 변경에 따른 어선의 자유 횡 동요 감쇠와 저항 성능을 평가하였다. 성능 평가를 위해 전산유체역학(Computational Fluid Dynamics)을 이용한 수치해석을 수행하였으며, 주요 부가물인 빌지킬과 선저킬의 조합과 치수 변경에 따른 횡 동요 주기와 감쇠 계수의 변화를 확인하였다. 선저킬의 경우 길이가 변화함에 따른 횡 동요 감쇠 계수의 변화가 상대적으로 크지 않음을 확인하였다. 반면 빌지킬의 경우 길이와 각도의 증가에 따라서 횡 동요 감쇠 계수가 증가함을 확인하였다. 4가지 부가물 조합 조건과 나선의 저항 성능을 비교하였으며, 부가물에 의한 어선의 자세와 압력분포의 변화로 인해 저항이 증가함을 확인하였다. 본 연구 결과를 통해 부가물 크기와 배치가 어선의 운동 및 저항 성능에 미치는 영향을 확인할 수 있었으며, 어선 적용 시에 도움이 될 수 있을 것으로 기대한다.