• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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• pp.182-189
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• 2012

This study suggests a dynamic design process for deciding properly design parameters of a mass-spring type Wave Energy Converter (WEC) to achieve sufficient energy conversion from wave to power generator. The WEC mechanism, in this research, consists of a rigid sprung body, a platform, suspension springs and dampers. The rigid sprung body is supported on the platform via springs and dampers and vibrates translationally in the heave direction under wave excitation. At last the resulting heave motion of the sprung body is transmitted to rotating motion of the electric generator by rack and pinion, and transmission gears. For the purpose of vibration analysis, the WEC mechanism has been simply modelled as a mass-spring-damper system under harmonic base excitation. Its maximum displacement transmissibility and steady state response can be determined by using elementary vibration theory if the harmonic ocean wave data were provided. With the vibration analysis results, the suggested dynamic design process of WEC can determine all the design parameters of the WEC mechanism, such as sprung body mass, suspension spring constant, and damping coefficient that can give sufficient relative displacement transmissibility and the associated inertia moment to drive the electric generator and transmission gears.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.546-554
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• 2021

In the signal processing of synthetic aperture sonar, it is subject that the platform in which the sensor array is installed moves along the straight line path. In practical operation in underwater, however, the sensor platform will have trajectory disturbances, diverting from the line path. It causes phase errors in measured signals and then produces deteriorated SAS images. In this study, in order to develop towed SAS, as tools to remove the phase errors associated with the trajectory disturbances of the towfish, motion compensation technique using Redundant Phase Center (RPC) and also Phase Gradient Autofocus (PGA) method is investigated. The performances of these two approaches are examined by means of a simulation for SAS system having a sway disturbance.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.116-123
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• 2004

The demand for the stable and comfortable cabin of a high speed passenger ship is increasing. The study on shipboard comfort has been mainly concentrated on the motion control of a whole hull body. In this study, however, a new control system operated by two parallel robots (3RPS, 3SPR) such as the active suspension system of motor vehicle is proposed. The goal of this control is keeping zero velocity of the upper robot (cabin) although the lower robot (ship) is moving by the waves. Jacobian matrix was used to design the controller, From the simulation results, the remarkable reduction of motion of the cabin (upper platform) was observed. The 3SPR parallel robot shows better performance compared to the 3RPS robot.

• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.161-172
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• 1995

A numerical procedure is described fro predicting the motion and structural responses of tension leg platforms(TLPs) in waves. The developed numerical approach is based on a combination of a three dimensional source distribution method and the dynamic response analysis method, in which the superstructure of TLPs is assumed flexible instead of the rigid body assumption used in tow-step analysis method. Both the hydrodynamic interactions among TLP members, such as columns and pontoons, and the structural whole structure are formulated using element-fixed coordinate systems which have the origin at the node of the each hull element and move parallel to a space-fixed coordinate system. Numerical results are compared with the experimental and numerical ones, which are obtained in the literature, concerning the motion and structural responses of a TLP in waves. The results of comparison confirmed the validity of the proposed approach.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.4
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• pp.361-367
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• 2010

This paper reports the development of a mobile robot for patrol using a single laser range finder. A Laser range finder is useful for outdoor environment regardless of illumination change or various weather conditions. In this paper we combined the motion control of the mobile robot and the algorithm for detecting the outdoor environment. For obstacle avoidance, we adopted the Vector Field Histogram algorithm. A laser range finder is mounted on the mobile robot and looking down the road with a small tilt angle. We propose an algorithm for detecting the surface of the road. The outdoor patrol robot platform is equipped with a DGPS system, a gyro-compass sensor, and a laser range finder. The proposed obstacle avoidance and road detection algorithms were experimentally tested in success.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.585-592
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• 2008

The aging society comes, the number of the old people expended. Technical aids allow elderly and handicapped people to live independently in their private homes as long as they wish. As a contribution to these required technological solutions, a demonstrator platform for a walking assistance robot. robot which has the capability to perform fetch and carry and various other supporting tasks. In this study, we addresses the development of a walking assistance robot system. We execute static analysis, vibration analysis and flexible dynamics to reserve stability at the design. Each motion of the robot uses a linear actuator and gears. Motion can be distinguished into 3 parts depending on the up & down, rotation, and cushion trans. In each motion, we compare the displacement of the case to be rigid with the case to be flexible. As a result, manufactured and feasibility of the walking assistance robot is validated through preliminary experiments.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.19-28
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• 1999

In this study, a real-time simulation system and a washout algorithm for an excavator have been developed for a driving simulator with six degrees of freedom. The excavator model consisting of a boom. bucket, upper frame, lower frame and four wheels, has total 11 degrees of freedom. The suggested washout algorithm consists of high and low pass filters with second order. The high pass filters cut off low frequency of the motion cues limited by platform motion. The cut off frequency for the tilt coordination are suggested for a realistic regeneration of excavator motion.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.3
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• pp.229-237
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• 2008

For predicting the motion and structural responses of tension leg platforms(TLPs) in regular waves, a numerical scheme is introduced. The numerical approach in this paper is based on a combination of the three dimensional source distribution method and the finite element method. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural response analysis. The drag forces on the submerged slender members, which are proportional to the square of relative velocity, are newly included in order to estimate the responses of members with better accuracy. Comparisons with other's results verifies the works in this paper.

• Journal of Ocean Engineering and Technology
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• v.35 no.2
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• pp.99-112
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• 2021

The prediction of maneuverability is very important in the design process of an underwater vehicle. In this study, we predicted the steady turning ability of a symmetrical underwater vehicle while considering interactions between the yaw rate and drift/rudder angle through a simulation-based methodology. First, the hydrodynamic force and moment, including coupled derivatives, were obtained by computational fluid dynamics (CFD) simulations. The feasibility of CFD results were verified by comparing static drift/rudder simulations to vertical planar motion mechanism (VPMM) tests. Turning motion simulations were then performed by solving 2-degree-of-freedom (DOF) equations with CFD data. The turning radius, drift angle, advance, and tactical diameter were calculated. The results show good agreement with sea trial data and the effects on the turning characteristics of coupled interaction terms, especially between the yaw rate and drift angle.

• Geomechanics and Engineering
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• v.7 no.6
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• pp.613-631
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• 2014

To complement the method of field-scale seismic ground motion simulations by buried blast techniques, the application and evaluation of the capability of a numerical modeling platform to simulate buried explosion-induced ground motion at a real soil site is presented in this paper. Upon a layout of the experimental setup at a level site wherein multiple charges that were buried over a large-diameter circle and detonated in a planned sequence, the formulation of a numerical model of the soil and the explosives using the finite element code LS-DYNA is developed for the evaluation of the resulting ground motion and surface subsidence. With a compact elastoplastic cap model calibrated for the loess soils on the basis of the site and laboratory test program, numerical solutions are obtained by explicit time integration for various dynamic aspects and their relation with the field blast experiment. Quantitative comparison of the computed ground acceleration time histories at different locations and induced spatial subsidence on the surface afterwards is given for further engineering insights in regard to the capabilities and limitations of both the numerical and experimental approaches.