Cheon-Hong Min

Damage Detection Using Finite Element Model Updating

In this study, a damage detection method that uses sensitivity-based finite (FE) element model updating with the natural frequency and zero frequency was proposed. The stiffness matrix for a structure was modified using the sensitivity-based FE model updating method. A sensitivity analysis was used to update the FE model, and the natural frequencies and zero frequencies were considered as target parameters to supplement the information on the vibration characteristics. The locations and values of the damages were estimated from the modified stiffness matrix. Several numerical examples were considered to verify the performance of the proposed method.

Study on Damage Detection Method using Meta Model

This paper presents an effective damage detection method using a meta model. A meta model is an approximation model that uses the relations between the design and response variables. It eliminates the need for repetitive analyses of computationally expensive models during the optimization process. In this study, a response surface model was employed as the meta model. The surface model was estimated using the correlation of the stiffness and natural frequencies of the structures. The locations and values of the damages were identified using a meta model-based damage detection method. Two numerical examples (a cantilever beam and jacket structure) were considered to verify the performance of the proposed method. As a result, the damages to the structures were accurately detected.

A Study on the Simulation-based Design for Optimum Arrangement of Buoyancy Modules in Marine Riser System

*** 한국해양과학기술원 부설 선박해양플랜트연구소 해양플랜트산업기술센터 ABSTRACT: This paper reports a simulation-based design method for the optimized arrangement design of buoyancy modules in a marine riser system. A buoyancy module is used for the safe operation and structural stability of the riser. Engineers design buoyancy modules based on experience and experimental data. However, they are difficult to design because of the difficulty of conducting real sea experiments and quantifying the data. Therefore, a simulation-based design method is needed to tackle this problem. In this study, we developed a simulation-based design algorithm using a multi-body dynamic simulation and genetic algorithm to perform optimization arrangement design of a buoyancy module. The design results are discussed in this paper.

Hydraulic Cylinder Design of Lifting Pump Mounting and Structural Safety Estimation of Mounting using Multi-body Dynamics

When a deep-seabed lifting pump is kept this device has bending and deformation in the axis due to its long length(8m). These influences can be caused a breakdown. Therefore, a mounting mus t be developed to keep the lifting pump safe. This paper discusses the hydraulic cylinder design of the lifting pump and structural safety estimation of the mounting using SBD(simulation-based design). The multi-body dynamic simulation method is used, which has been used in the automotive, structural, ship building, and robotics industries. In this study, the position and diameter of the hydraulic cylinder were determined based on the results of the strokes and buckling loads for the design positions of the hydraulic cylinder. A structural dynamic model of the mounting system was constructed using the determined design values, and the structural safety was evaluated using this dynamic model. According to these results, this system has a sufficient safety factor to manufacture.

A Study on the Steering Performance and Turning Radius of Four-Rows Tracked Vehicle on Hard Ground

This study proposes a method to determine the effective angular velocity of each motor of a specific four-rows tracked vehicle (FRTV) in order to follow a given turning radius. The configuration of the four-rows tracked vehicle is introduced, and its dynamics analysis model is built using the DAFUL commercial software. The soil has been assumed to be hard ground, and the friction force between the ground and the tracked links is calculated using the Coulomb friction model. This paper uses a simulation to show that the error in the position increased with respect to the angle of the curvatures, so a method is proposed to compensate for the error in the motion of the motors. Various simulations are then carried out to verify the proposed formulation. The effects of the soil characteristics and the driving velocity will be further investigated in future studies.

Steering performance test of underwater mining robot

A pilot-scale mining robot for manganese nodule has been developed by KRISO (Korea Research Institute of Ships and Ocean Engineering) in 2012. The robot consists of two unit-modules having an identical mechanical and hydraulic configuration. Each unit module has two tracks, two pick-up devices with attitude control devices, two crushers, one discharging pump, and hydraulic system. In 2013, Sea-trial has been performed at 130m depth in the east sea of South Korea. To strictly keep and follow the pre-defined complex path with a constant forward speed, steering characteristics of the mining robot are required. To know the characteristics of the robot, steering performance test was executed with appointed steering ratios. Also, for the reliable driving of the robot, the velocity pattern of four-columns tracks is determined by numerical simulation. To actuate track motor as a commanded velocity, PI controller is designed from system identification method and gain tuning rule.

An experimental study on the hydro-elastic analysis of a circular cylindrical shell

Abstract Ocean structures and vehicles are exposed to severe ocean environment conditions such as waves, winds and currents. When such ocean structures and vehicles are designed, an accurate structure analysis is required to keep the system safely. Hydro-elastic analysis is one of key issues to design such structures and vehicles. In many pre-vious investigations, numerical analyses for hydro-elastic problem have been used. In this study, an experimental analysis is carried out and the circular cylindrical shell is considered. Dynamical characteristics for a circular cy-lindrical shell are identified by experimental vibration analysis in air and water. The natural frequencies and mode shapes are compared in air and water to obtain hydro-elastic effects. Some interesting results are found in the var-iation of natural frequencies and damping ratios of the circular cylindrical shell for different water contact depths. Keywords: Circular cylindrical shell; Modal identification; Experimental modal analysis; Hydro-elastic analysis; Natural fre-quency and mode

Identification of a Nonproportional Damping Matrix Using the Finite Element Model Updating

*Ocean System Engineering Research Division, Maritime and Ocean Engineering Research Institute, Korea Institute of Ocean Science and Technology, Daejeon, KoreaKEY WORDS: Nonproportional damping matrix 비비례 감쇠행렬, Identification of damping matrices 감쇠행렬 추정, FE model updating 유한요소 모델 개선, Zero frequency 제로주파수ABSTRACT: A new identification method for a nonproportional damping matri x using the finite element (FE) model updating technique is proposed. Mass and stiffness matrices of the undamped system ar e identified by FE model updating method. Sensitivity analysis is used to update the FE model, and zero frequencies are considered as design par ameters to supplement the information of vibration characterist ics. The nonproportional damping matrix is identified through the propos ed method. A numerical example is considered to verify the performance of the proposed method. As a result, the damping matrix of the nonprop ortional system is estimated accurately.교신저자 민천홍: 대전광역시 유성구 신성동 신성남로 65-12, 042-866-3886, min80123@kiost.ac 본 연구는 20012년 6월 개최된 한국해양과학기술협의회 공동학술대회에 발표된 논문을 근간으로 하고 있음을 밝힙니다 .

Study of the Measurement of Young's Modulus and Loss Factor for a Viscoelastic Damping Material Using a Multi Degree of Freedom Curve Fitting Method and RKU Equation

Offshore structures, such as a platform, a buoy, or a floating vessel, are exposed to several dynamic loads, and viscoelastic damping material is used to reduce the vibration of offshore structures. It is important to know the properties of viscoelastic materials because loss factor and Youngs modulus of the viscoelastic damping material are dependent on frequency and temperature. In this study, an advanced technique for obtaining accurate loss factor and Youngs modulus of the viscoelastic damping material is introduced based on a multi degree of freedom curve-fitting method and the RKU (Ross-Kerwin-Ungar) equations. The technique is based on a modified experimental procedure from ASTM E 756-04. Loss factor and Youngs modulus of the viscoelastic damping material are measured for different temperatures by perfor ming the test in a temperature-controlled vibration measurement room where temperature varies from 5 to 45 degrees Celsius.

Experimental Study on High Frequency Vibration Transfer Characteristic of Underwater Cylindrical Shell

*Agency for Defence Development, Jinhae, Korea**Graduate School of Korea Maritime University, Busan, Korea***Department of Ocean Engineering, Korea Maritime University, Busan, KoreaKEY WORDS: Cylindrical shell 원통형 구조물, High frequency vibration 고주파 진동, Excitation 가진, Noise 소음, Underwater vehicle 수중운동체ABSTRACT: Underwater vehicles such as UUVs (Unmanned Underwater Vehicles) and ROVs (Remotely Operated Vehicles) use sonar to detect their underwater environment or other underwater vehicles. The underwater vehicles designed recently have an electrical power system with high rotational speed. This system can generate high frequency vibra tions above 10 kHz, and these vibrations can cause bad (negativ e) effects on the performance of the sonar. In many previous investigations, nume rical analyses have been used for high frequency vibration prob lems. In this study, an experimental analysis was carried out, and a circular cylind rical shell was considered as the hull structure of an underwat er vehicle. Frequency transfer functions for the circular cylindrical shell were iden tified using an experimental vibration analysis in the air and in a fully-submerged condition. We compare the frequency transfer functions in the a ir and water to obtain hydro-elastic effects. It is found that the dynamic characteristics of the circular cylindrical shell are changed b y varying the response position.교신저자 박한일: 부산광역시 영도구 동삼 2동, 051-410-4326, hipark@hhu.ac.kr본 연구는 20011년 6월 개최된 한국해양과학기술협의회 공동학술대회에 발표된 논문을 근간으로 하고 있음을 밝힙니다 .