부유식 파랑에너지 변환시스템(Oscillating Water Column)에서 에너지 변환은 입력파와 챔버, 챔버내 공기의 상호작용으로 이루어진다. 이 논문은 파랑에너지를 기계적 운동으로 변환하는 기계적 특성을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하며, 이 상하운동은 챔버내의 압력 변화에 영향을 받는다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하여 오리피스를 통한 유량과 압력을 기준으로 에너지 변환요율을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 개구율 변화에 따른 운동응답을 비교하였다.

Petri nets(PN) have been introduced as a poweful analyzing and design tool for the discrete systems such as sequential control systems. However, one of the important problems in its applications is that the model can not be analyzed easily when we deal with large scale systems because of increase of the number of components of the systems. To overcome this problem, some methods for dividing or reducing of PN have been suggested. In this paper, an approach for hierarchical expression of PN based on Sequential Function Chart(SFC) and Bottom Up oriented Mehodology(BUM) is proposed. Especially, some definition and rules are defined in order to divide and compose sub PN. A measuring tank system will be described as a typical kind of discrete systems and modeled by some sub PN based on the SFC and BUM by the proposed method in this paper.

This paper describes a noble fault diagnosis method using inter node search technique in PN model. First, a complicated fault system is modeled as PN graphic expressions. Next, to find out sources for faults on which we focus, the PN model is analyzed using the backward chaining of T-invariance. In this step, the technique of inter node search is applied for reducing some range of sources in a fault. Also, colnposing method of incidence matrix in PN is proposed. Then, it makes the diagnosis system to very flelible system because new knowledges about the sources in a fault can be added easily to conventional systems. Finally, the proposed method is applied to the automobile trouble diagnosis system to confirm the validity of the method.

An engineering database system is presented for ship hull form and hasic design. Web i, nd clustering systems are adopted to develope the system. It is appeared that the system is efficient and useful for integrated ship design.

Price of Used Vessel is Key-point of Ship trading but it is very troublesome part. Because it is different from the Seller and the Buyer's caculated price, It is appropriated by The Sellers and The Buyers' mutual agreement. In case of the Buyers. it is difficult in calculating price of used ship without entrusting the ship broker, beca- use evaluation method of secondhanded vessel has not formulated and the ship broker has experientially computed Remain Value of used vessel. For this work, structure of ship trading market, trading flow, the factor of price composition and Affecting factor of price is reviewed, and it examined relationship with price. On these base, a computer software integrated database system and object-oriented technique is developed. The developed system is expected helpful to evaluation of remain value of the used vessel.

The more the population grow, the severer the shortage of a basic human needs such as food, clean water, energy resources and so on. We had proved the possibility of utilizing deep ocean water as a environmental friendly resource to solve comprehensively above-mentioned problems for mankind based on observation and analysis of water quality. This study aims to evaluate feasibility of deep ocean water application, and establish multipurpose development and cascade utilization system of deep ocean water in the coastal zone of East sea to promote ocean development and fisheries industries.

In this Paper, the resistance performances of twin hull forms, which are simplified as two-dimensional wedge shape, are experimentally investigated in low and middle speed ranges to find out the effect of distance between two hulls and fore-body shape for the future hull form development of catamaran type sweeping vessel. The model tests are performed for seven different cases for three models in the circulating water channel(CWC) of Inha Technical College. The free surface flows are observed together to investigate the relation between resistance performance and free surface characteristics. A conceptual design for the modification of bow hull form is presented and the efficiency is discussed.

This paper describes the development of catamaran type powerboat applicable to leisure and transportation in the sea. Recently, the increasing prosperity of the leisure population has resulted in an increased popularity and need for recreational equipment such as water leisure powerboat. To satisfy the popularity and the need, catamaran type powerboat is developed applicable to leisure and simultaneously, as a means of tranportation for a short distance in the sea through the design using 3-Dimensional modeling method and experiments in circulating wate channel.

In this paper, consider the three cases of decide for appling point a general Simple Genetic Algorithm about heuristic method(Bottom and Left Sliding) at the piece auto-nesting on the row plate. The 1st case, about only using the Simple Genetic Algorithm. The 2nd case, applied the heuristic method to the genetic operating of the Simple Genetic Algorithm. The 3rd case, applied the heuristic method to the final result of the Simple Genetic Algorirhm. The estimation of final result were proceed to developed simulation program in this research.

Intensive experimental investigations were carried out to provide information of the effects of inflow on the rolling characteristics and stability of ships, which becomes great concern in relation to ship's capsizing. A series of systematic experiments have been performed considering the effects cf combined motion of roll-heave-sway and relevant parameters, such as roll angle and period, tank water height etc. To accommodate this type of experiments with 3-degree of freedom of motion, a bench tester has been developed and verified using existing data. Also, theoretical application of anti-roll tank has been incorporated to support the process of investigation. A model of Ro-Ro ships is used in the present study as this type of vessels, as well as fishing vessels, with large open decks, can loose stability rapidly when there is inflow on the decks.

The ASME B3l.4〔1〕and B3l.8 〔2〕codes use the thin wall formula to predict hoop stress in a pipe. To account for the external pressure, the above codes simply subtract the external pressure from the internal pressure. The thin wall formula using this differential pressure does not give the same hoop stress as the thick wall formula. This paper proposes an improved equation to predict pipe hoop stress subjected to both internal and external pressure. Compared to the conventional thin wall formula, the improved formula has additional terms, which improve the agreement with the thick wall formula and account for external pressure. The improved formula is less conservative than the conventional thin wall formula, but slightly more conservative than the thick wall formula. The formula is simpler and easier to use than the thick wall formula and will save pipe material cost as well as installation cost compared to using the conventional thin wall formula. The savings will increase as the water depth increases.

This paper aims to make a feasibility study and to propose a master plan for the development of "integrated ocean energy utilization system", which utilizes various renewable ocean energies. Fossils energy, as the most important energy resources which are inevitable for the living and industrial development, becomes exhausted and its consumption creates serious environmental problem. It is important to utilize renewable ocean energy for a sustainable and environmentally friendly development. We survey the integrated utilization of ocean energy based on surveyed energy density distribution and propose concepts of integrated ocean energy utilization plant for both onshore and offshore system. The results of this study can support national effort for renewable energy development utilizing integrated ocean energy and refer as a guideline for the technical development of sustainable integrated ocean energy.

This technical note is intended to introduce a state-of-the-art offshore construction vessel. This unique vessel is for multi-purpose Field Development Ship (FDS) for deepwater to ultra-deepwater. The FDS is a construction vessel with dynamic positioning (DP) system intended to develop offshore oil and gas field in water depth up to 3000 m. The design criteria and main capacities of the vessel are discussed.

개발 목표로서, 최대 속도가 60knots인 초고속 단동 선형을 탄생시키기 위해서는 이 선형을 포함한 7척의 유사 선형들의 유체역학적인 성능에 대해 CWC에서의 모형선 시험과 computer simulation을 통해 계측값과 수치 계산값을 구하여 비교, 검토를 수행하였다. 그 결과, 60B2형이 모든 성능면에서 가장 우수하다는 평가를 얻었다. 그래서 본 논문에서는 이 선형의 설계 특성에 관해 기술하고자 한다.

When ship claps against the ocean structure sited at shallow water, the time simulation of motion responses of dolphin-moored ocean structure is presented. The equatien of motion based on Cummin's theory of impulse responses are employed, and solved in time domain by using the Newmark $\beta$ method. The added mass and damping coefficients involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The impact forces due to ship collision are modeled as two method, and those are elastic and non-elastic collisions. The mooring forces for dolphin systems of scean structure are considered as linear spring system.

In this paper, the real-time prediction of high temperature creep strength and creep strength and creep life for nickel-based superalloy Udimet 720 (high-temperature and high-pressure gas turbine engine materials) was performed on round-bar type specimens under pure load at the temperatures of 538, 649 and 704$^{\circ}C$. The predictive equation of ISM creep has better reliability than that of LMP and LMP-ISM, and its reliability is getting better for long time creep prediction(10$^3$~10sup/5/ｈ).

Despite the frequent use of ring-stiffened cylinders as a submarine pressure hull or members of various types of offshore sutructures, their ultimate strength analysis methods have not been well established because of their complex structural characteristics. This paper has established the method how to use commercial softwares based on the finite element method to implement the ultimate strength analysis of ring-stiffened cylinders covering both types of initial imperfections, I. e. initial deformation and initial stress by combining two separately offered functions of common commercial finite element softwares, linear elastic buckling analysis and nonlinear stress analysis. Developed method was applied to one of the world-widely used commercial softwares, ABAQUS for the analysis of ring-stiffened cylinders. This paper ends with some useful information about the imperfection sensitivity of ultimate strength of ring-stiffened cylinders.

The potential pollution problems resulting from tanker collision necessitate the requirement for an effective structural design and the development of relevant safety regulation. During a few decades, the great effort has been made by International Maritime Organization and the Administration, etc, to reduce oil spillage from collision accidents. However there is still a need for investigation in the light of structural evaluation method for the experiments and rational analysis, and design development for an operational purpose of ships. This study is aimed at investigating a complicated structural response of bow structures of oil carriers for assessing the energy dissipation and crushing mechanics of striking vessel through a methodology of the numerical analysts for the various models and its design changes. Through this study an optimal bow construction absorbing great portion of kinetic energy in the least penetration depth prior to reach to the cargo area and an effective location of collision bulkhead are investigated. In order to obtain a rational results in this study, three stages of response analysis procedures are performed as follows; 1). 16 simplified ship models are used to investigate the structural response against bow collision with variation of primary and secondary members. Mass and speed are also varied in two conditions. 2). 21 models conisted of 5 size of full scaled oil carriers are used to perform the collision simulation with the various sizes and deadweight delivered in a recent which are complied with SOLAS and MARPOL. 3). 36 models of 100k oil carrier are used to investigate the structural response and its influence to the collision bulkhead against bow collision in variation with location of collision bulkhead, primary mombers, framing system and colliding conditions, etc.

자기유변유체감쇠기를 이용한 반능동 제어 시스템은 최근에 개발되어 승용차의 승차감 향상을 위한 진동제어에 사용되고 있다. 본 연구에서는 바람, 지진, 파랑 등에 대한 대형구조물의 진동제어를 위한 MR 감쇠기의 적용성을 분석하기 위하여, 미국 토목학회에서 제안한 76층 건물의 풍하중에 대한 진동제어에 관한 Benchmark Problem에 대하여 수치모의 해석을 수행하였다. 연구결과로부터, 풍하중에 대한 고층 건물의 진동제어를 위하여 MR 감쇠기를 이용한 반능동 제어의 성능은 능동형 동조질량 감쇠기의 성능과 유사함을 확인할 수 있었다.

Formal safety assessment (FSA) is defined as a structured and systematic methodology aimed at enhancing maritime safety including protection of life, health, and the marine environment and property, by using risk and cost/benefit assessment or, more specifically, it is a process of identifying hazard, evaluating risk and deciding on course of action to control those risks. Emphasis is placed on the structural aspect of the failure of cargo hold. This study is expected to illustrate how a new methodology, i.e. the Formal Safety Assessment, can be applied to specific ship safety problems.

Ring-stiffened cylinders are widely used as the pressure hull of submarines and underwater vehicles. For large ring-stiffened cylinders cylindrical shells are fbricated by cold rolling of flat plates and then welding of curved shells. After forming cylinders ring-stiffeners are welded on th the cylinders. Due to these cold roiling and welding initial shape imperfections and residual stresses exists in fabricated ring-stiffened cylinders. It is well known that the initial shape and material imperfections affect the ultimate strength of ring-stiffened cylinders significantly. In this paper previous researches on the effects of initial shape imperfections and residual stresses are briefly reviewed Recently a numerical analysis computer program was developed to predict the ultimate strength of ring-stiffened cylinders subjected to hydrostatic pressure, which is based on the Dynamic Relaxation technique. This program was employed to numerically investigate those effects. The numerical predictions were substantiated with relevant experimental results.

A study for the structural strength analysis on the doubler plate subjected to the axial, biaxial in-plane compression and shear load has been performed through the systematic evaluation process. In order to estimate the proper static strength of doubler plate, non-linear elasto-plastic analysis is introduced. Gap element modeling for contact effect between main plate and doubler is prepared and nonlinear analysis procedures are illustrated based on MSC/N4W . In addition, some design guides are suggested through the consideration of several important effects such as corrosion of main plate, doubler width, doubler length and doubler thickness. Finally theses results are compared with developed design formula based on the buckling strength and general trends and design guides according to the variation of design parameters are discussed.

In this paper, the tensile test of three kinds of the specimens was performed. Type I specimen is without notch and type II, III specimens have a radius of semi-circular edge crack of 2.5mm, 4.0mm. The tensile load(20kN and 30kN) was applied to the specimen by Universal Testing Machine. 3D-ESPI system and strain gauge measured simultaneously the strain in the center of the specimen and near the edge crack. The test results were compared with each other. Moreover, the stress concentration factor based on geometric information was calculated to confirm the accuracy of the strain measured by 3D-ESPI system. The calculated strain was compared with the measured one by 3D-ESPI system. As a result, it was confirmed that 3D-ESPI system measured the right strain near the semi-circular edge crack of the specimens.

Nakdong estuary is located at south-eastern coast of the Korea. A lot of sediment from upper river was deposited at this area. It has caused many problems such as changes in topography and tidal current. In this paper, field observation data on tidal currents and sediments were investigated as well as historical topographic changes by dredging and reclamation of the foreshore. Then, the numerical model considered the settling velocity of the suspended solids according to the particle size was applied to examine the characteristic of deposition. The results are as follows : 1. Changes of characteristics of deposition were caused by topographic changes of Nakdong estuary 2. Characteristics of deposition were influenced by river plume and tidal currents. 3. Numerical model which considers settling velocity reappeared distribution of deposition by particle-size. 4. Used model is only resonable for discussion in the quality, so, it is strongly suggested that the new model development is needed including the quatitative deposition processes.

In this study, the effects on hydraulic characteristics are discussed as the permeable underlayer width of the rubble mound structure changes. A series of hydraulic experiments were performed and wave run-up, reflection and set-up were investigated. Results indicated that wave run-down was affected by the water out from the permeable underlayer during down-rush. As the width increased, relative wave run-up decreased.

A digital seismic data acquisition and processing system using a PC has been developed in order to replace the analog data acquisition system of shallow marine seismic survey. An A/D converter that has 12bits of resolution and 225KHz of conversion rate was ued to acquire data, and a data acquisition software was developed as a Windows program which provides convenience of use. Raw data acquired at field has been saved to the hard-disk simultaneously. The signal to noise ratio, vertical and horizontal resolution could be improved by a digital data processing of the raw data. The digital processing of the raw data includss gain recovery, filtering, deconvolution, and muting. With the prediction deconvolution algorithm multiple reflections appearing on the shallow marine seismic section could be removed successfully.

A numelical model has been developed for the permeable coastal structures to simulate hydraulic characteristics on the permeable slopes, which interact with internal flow field of the structures. The model includes hydraulics in the porous medium. Numerical model was calibrated using hydraulic model experiments performed in 2-D wave flume in the Institute of Orean Hydraulics in PKNU. Good agreement were obtained with the model which employed inertia resistance term than with the conventional model, PBREAK.

In order to regulate the physical characteristics of an ocean dumping material in the south-eastern East Sea, the diffusion characteristics with the observation, hydraulic experiment and numerical experiment data are investigated. The main results are as follows; (1) Spying CTD observation result of the area of Jung in the East Sea, the ocean dumping area had influenced the Tsushima warm current of high temperature and salinity. Horizontal turbulent diffusivity is 1.913${\times}$10$^{7}$ $\textrm{cm}^2$/sec by drogue tracking. (2) From the experiment of settling, the initial settling velocity of each material is 1.0∼2.7 cm/sec according to the specific gravity and initial concentration. In the pycnocline, particles didn't settle under the pycnocline any more and accumulated. It is signified that calculation of the sedimentation rate of the ocean dumping material including of vertical diffustion must be regard the pycnocline in the ocean area have well-developed pycnocline. (3) Vertical turbulent diffusivity were 2.219${\times}$10$^{-8}$∼8,874${\times}$10$^{-4}$ $\textrm{cm}^2$/sec from the experiment of settling. And, the pycnocline influenced the vertical turbulent diffusivity. (4) From the result of diffusion simulation in the East Sea, the co-concentration line of 0.05 ppm and 0.1 ppm are limited at dumping area after 200 days. The constant concentration line of 0.01 ppm is distributed to the vicinity of Ulleungdo and Tokdo, but isn't distributed to the coastal area of East Sea and southern area of Jung in the East Sea.

The purpose of this study is to develop the time-dependent, one-dimensional numerical model on the interaction between irregular waves and two-layer permeable coastal structures, by extending and modifying the numerical model PBREAK(Wurjanto and Kobayashi, 1992) which is applicable only to one-layer permeable coastal structures. The two-layer permeable coastal structure consists of two permeable underlayers with different permeable media resting on an impermeable slope and an armor layer covering the permeable underlayer. The numerical model of this study simulates the wave over rough permeable underlayer of arbitrary geometry as well as the waves inside two-permeable underlayers of arbitrary thickness for specified normally-incident irregular waves. The utility of the numerical model is founded from comparing with PBREAK and the four hydraulic model tests under irregular waves. The sensitivities of computed results according to typical parameters(porosity, stone diameter, horizontal width of the permeable underlayer) and major factors(friction factor of primary armor layer etc.) discussed.

Electro-Rheological(ER) fluids change their apparent viscosity according to the electric field strength. Therefore, there are many practical applications using the ER fluids. ER effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of starch based ER fluid were reported. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply, The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to 200s$^{-1}$ in 2 minutes. This thesis presents Bingham properties of ER fluids subjected to temperature variations. The temperature dependence of the viscosity was determined for ER fluids consisting of 35 weight % starch particles in automatic transmission oil.

The added resistance of a ship advancing in waves can be split into the resistance due to the radiation wave and the resistance due to the diffraction wave. In this study, the former has been calculated by a method based on Maruo's formula. The latter must be calculated by other methods. Ship motion is calculated by the usual strip method. The amplitude of two dimensional far-field waves is calculated using the improved Green integral equation. The present numerical method can be used for the estimation of the added resistance due to the radiation wave since the present numerical result is much smaller than other existing numerical results considered to be overestimated.

An experimental method to investigate the dynamic charasteristics of buoys in extreme environmental condition is established. Because the buoy model requires a resonable size for accurate experiment, the test condition in model basin that satisfies the similarity law is hardly met with capability of test facilities. It is suggested that the linear wave component that is unable to satisy similarity is separated with others. The model experiment can be carried out with mitigated condition for the linear wave components while others including wave drift, current and wind are keeping the similarities. Then the result is extrapolated to give the dynamic behavior of buoys in extreme condition because linear wave component is soley responsible to oscillatory buoy motion and other environmental components are applied as a initial tension. the similarity for current and wind conditions is viewed as equivalence of restoring forces. the validity of proposed method is examined with different types of standard ocean buoys and it indicates that the linearity of measured characteristics is assured with a limitation of resonable distance between test and estimated wave conditions.

In this paper, statistical properties of waves in the sea area of Pohang, Korea are examined absed on 1998-1999's wave data from directional wave buoy which is located Pohang(Janggigog). Wave data aquisition rate, monthly maximium, minimum and mean wave heights, frequency of wave direction are summarized. Wave height and period scatter diagrams and n-year return period wave heights are estimated. Wave periods of maximum wave heights are also estimated.

The time simulation of slow drift motions of moored FPSO in waves is presented. The equation of motion based on Cummin's theory of impulse responses are employed, and are consisted of horizonal plane -surge, sway and yaw. The added mass coefficients, wave damping coefficients, first order wave exciting forces and the second order wave drift forces involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The mooring lines are modeled quasistatically as catenary for chains and touchdown. As for numerical example, time domain analyses are carried out for a box-type FPSO in long crest irregular wave condition.

In this case study, under conideration of field situations, such as increase of water level, height increment of the marine structure, dredging and backfill, the stability analysis of sliding and lateral flow of the marine structure in OOOharbor was carried out, and foundation reinforcement methods was presented. based on the results of site investigation, the stability analysis of slope sliding and lateral flow was performed as following. In section BH-1, 2, the analysis was performed in two cases that the marine structure was heightened and filled, and not heightened and filled. In section BH-1, 4, heightened and filled. The analysis results showed that the stabilities of slope sliding and lateral flow in section BH-1, 2, 3, 4 were unstable. After additional reinforcements with Deep Mortar Pile, the stabilities in section BH-1, 2, 3, 4 were evaluated as efficiently large.

The subsidence characteristics of artificial reef in the unsteady flow such as tidal flow were investigated. The scour and subsidence characteristics were confirmed in the steady flow field, wave field and steady flow-wave field. In a main study, the interaction of Flow-Sediment Movement-Structure Behavior and scour.subsidence mechanism were discussed in the unsteady flow field and the unsteady flow-wave field. Most of all, the continuous artificial reef subsidence from the scour was occurred by periodic behavior of artificial reef. This behavior is result from the asymmetric ground, and is influenced by maximum velocity, duration time and direction of flow.

괘도차량에 부착된 물분사추진기의 유동해석을 실험과 포텐셜해석 그리고 점성해석을 사용하여 그 결과를 비교하였다. 예인수조에서 여러 차량 전진속도에 대해서 임펠러 회전수를 조정하여 제트속도를 변화시키면서 덕트표면에서의 정압을 계측하였다. 이는 제트시스템의 효율을 추정하기 위함이고 관로를 통한 에너지분포를 알 수 있다. 점성유동해석을 위해 지배방정식은 비압축성 Navier-Stokes 방정식을 유한체적법을 사용하여 이산화하고 해석하였으며 난류영향은 표준 ĸ-$\varepsilon$난류모형을 사용하여 유동을 해석하고 실험결과 및 포텐셜 해석결과와 비교하였다.

WLV LPSRUWDQW WR UHDOL］ H GLUHFWLRQDO VSHFWUXP ZDYP VHDNHHSLQJ SHU IRUPDQFH Rl PDULQH YHKLF OHV WK SUDF LWHUDWLRQ PHWK RG LQ WKH YLHZ S H DQG FRPSDUH WKH SU.

This paper describes the effect of step bilge on motion characteristics of FPSO. The purpose of the present study is to investigate motion responses of FPSO with two types of step bilge. Model test result shows that the performance of the bottom type step bilge, that is designed to avoid collision, is as good as that of the side type step bilge.

There are advantages in the installation of dual subsea pipelines over two separate single lines. In many case it can reduce the cost for trench, back-filling and installation. However the installation of dual pipelines often requires technical challenges. Dual Pipelines should be placed to be stable to external loading not only during the installation but also in the design life. Dual pipelines in trench can reduce the influence of external forces. To investigate applied forces as slope changes, number of experiments are conducted with PIV (Particle Image Velocimetry) in a circulating water channel. Numerical approaches are also made to compare with experimental results. The velocity fields around dual pipelines in trench are investigated and analysed. Comparison of both results show similar pattern of flow around dual pipelines. it is proved that the trench slope affects the pipeline stability significantly. The results can be applied in the stability design of dual pipelines in trench section. The complex flow patterns can be referenced effectively linked in the understanding of fluid around circular bodies in trench.

본 연구에서는 연속 웨이블렛 변환을 이용하여 Ringing 현상을 연구하였다. 사용되어진 웨이블렛은 Morlet 웨이블렛이었고, 실험은 파수조에서 수행되었다. 또한 Ringing 현상을 다루고자 쇄파를 발생시켰다. 실험에 쓰인 모델은 수면을 통과하여 수직으로 고정된 원주 실린더였고, 이 실린더에 작용된 힘과 파고가 측정되어졌다. 이들은 연속 웨이블렛 변환으로 분석되어졌고, 이러한 분석으로 얻어진 scalogram 들은 고주파 성분이 쇄파 충격시 만들어진다는 사실을 시간영역상에서 보여주었다. 이는 기존의 스펙트럼 분석에서는 찾기 힘든 것이다. Coherence 분석도 위의 결론을 뒷받침해 주었다.

This paper describes the effect of hull form on motion characteristics of FPSO. The purpose of the present study is to investigate seakeeping performance of ship type FPSO in comparison with those of barge type FPSO. Model test result shows that the barge type FPSO is better in heave and pitch motion, while the ship type FPSO is superior in roll motion.

The characteristics of flow in dividing regions are precise, therefore their classification is very important not only in industry but also in hydrodynamics. By now, many studies of flow in dividing regions have been peformed, but flow characteristics that use visualization In dividing regions have not been studied. The present study of the PIV and the CFD exhibit average velocity distributions, kinetic energy distributions and total pressure distributions etc of the total flow field due to the development of the accurate visualization optical laser and of optical equipment. Also, PIV is accurate with the flows characteristics of the dividing region as continuous analysis is done using input equipment. The study analyzes velocity vector field, turbulence kinetic energy, turbulence viscosity of dividing regions with flow for visualization of the PIV and the CFD measurement in a dividing rectangular ducts.

Wet Underwater arc welding process is inverstigated by using experimentally developed flux coated underwater arc welding electrode and SS400 steel plate of 12mm thickness as base metal. Two kinds of different flux covered wet arc welding electrode of 3.2mm diameter (UW-1, UW-2) are individually developed and one of the improved underwater welding electrode (UW-2) may be put to practical use for underwater arc welding process.

This paper deals with determining the proper friction welding condition and analyzing various mechanical properties of friction welded joints of the bladepart heat resisting steel(STD11) for cold die punch to the shank part alloy steel(SCM440). And the in-process real-time weld quality evaluation technique by acoustic emission during friction welding of STD11 to SCM440 steels with higher confidence and reliability has been much required even though it might be the first trial approach for developing it. Also, the high temperature properties of STD11-SCM440 weld were considered in this paper.

This study reveals the thin sheet metal Process with multi-forming die that the name is progressive die, also high precision production part is made. They require analysis of many kinds of important factors, i.e. theory and practice of metal press working and its phenomena, die structure, machining condition for die making, die material, heat treatment of die components, know-how and so on. In this study, we designed and constructed a multi-forming progressive die as a bending working of multi-stage and peformed through the try out. Out of the characteristics of this paper that nothing might be ever seen before such as this type of research method on the all of processes of thin and high precision production part.

The progressive die performs a series of fundamental sheet metal working, particularly this study regards to develop the center carrier feeding type die for thick sheet metal(SS41, 2.5mm) production that is a specific division. In order to prevent defect on the production, the analysis of production part, optimum design of strip process layout, die design and die making and tryout etc. are necessary. In this study, we designed and predicted a progressive die of multi stages by wide collected data base and computer aided method.

In this paper, friction welding optimization for 1Cr0.5Mo to STS304 and AE applications for the weld quality evaluation were investigated The important results of this study are as follows : 1. The techiques for dissimilar friction welding optimization if the elevated temperature materials 1Cr0.5Mo and STS304 and its real-time weld quality evaluation by AE were developed, considering on both strength and toughness. 2. Quantitative relationship was identified among welding condition, weld quality and cumulative AE counts.

In this Paper, friction welding optimization for 1Cr0.5Mo-STS304($\Phi$14mm), AE applications for the weld quality evaluation and the applications of various life prediction methods such as LMP(Larson-Miller Parameter) and ISM(initial strain method) were investigated : the creep behaviors of those steels and the friction welded joints under static load were examined by ISM combined with LMP at 400, 500, 550 and $600^{\circ}C$, and the relationship between these two kinds of phenomena was studied. The real-time predicting equations of elevated-temperature creep life(fracture time) under any creep stress at any elevated- temperature could be developed by LMP and LMP-ISM, It was confirmed that the life prediction equations by LMP and LMP-ISM are effective only up to 10$^2$hrs and can not be used for long times of 10$^3$-10$^{6}$ hrs, but by ISM it can be used for long times creep prediction of more than 10$^4$hrs with most reliability.

Most parts of facilities in domestic petroleum plants and power plants are needed to be abandoned, repaired or replaced, because in Korea they were built in the 1960s and, they have been used under severe conditions and exposed corrosive environments. 2.25Cr- lMo steels have excellent high-temperature mechanical properties. Therefore, the material have been widely used as heat exchanger tubes, boiler headers and its tubes in such industries. But, those microstructural evolutions in high temperature such as precipitation and carbide coarsening give a reason to degrade the material. Especially, in case of this material, carbides induced embrittlement(CIE) is the primary reason for degrading mechanical properties at over 50$0^{\circ}C$. In this paper, we introduce a electrochemical polarization method for detecting CIE quantitatively.

In this study, CT specimen were prepared from Pressure Vessel Steel which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ and in the range of stress ratio of 0.05 and 0.3 by means of opening mode displacement. At the constant street ratio, the threshold stress intensity factor range ΔK$_{th}$ in the early stage of fatigue crack growth(Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth(Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm do/dN -ΔK in RegionII, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate do/dN is rapid in proportion to descending temperature in Region IIand the cryogenic-brittleness greatly affect a material with decreasing temperature.e.greatly affect a material with decreasing temperature.

In this study. CT specimens were prepared from ASME SA5l6 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ in the range of stress ratio of 0.1 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔKsub/th/ in the early stage of fatigue crack growth ( Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da.dN -ΔK in RegionII, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc., In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, two kinds of spring steel(SAE 9254, DIN 50CrV4) are made. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) on low stress condition, the single stage shot peening is not affected by nonmetallic inclusion under metal. (2) it is possible that the two-stage shot peening increases the fatigue life and the high stress, but, that is affected by nonmetallic inclusion under metal. (3) so far, beeasily 50CrV4 have made high stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

This paper was to investigate of a adhesiveness for the plasma sprayed coating materials did salt spray by acoustic emission method in tensile loadings. The powders used for the coating were nickel aluminum composite powder Ni-4,5wt.%Al and titanium dioxide powder Ti02. These powders were coated on a carbon steel S45C by plasma spray method. The salt solution was a 5% NaCl and the salt spray times were 2, 5 and 10 hours respectively. The salt solution penetrated into the surface of the substrate through pore of the coating layer built in the process of plasma spay. Corrosion productions formed on the surface of substrate. The adhesiveness between the substrate and the coating layer is weaken by corrosion and the exfoliation initiated chiefly at the corrosion surface of the substrate. The AE events and energy of the corroded coating specimens decreased as the salt spray times increased.

SG-50 steel is an important material and used for manufacturing a pressure vessel which the gas piping. In this investigation, the elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the elastic plastic fracture toughness. The side grooved specimen is very useful in estimation of the J$_{IC}$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides, it improves the accuracy of toughness values, decreases the scattering of them and tunneling and shear lip by the side groove.e.

The purpose of this study is to investigate the effect of nitriding on the fatigue strength and fatigue life of turbine rotor steel (ICr-lMo-0.25V), and acquire data on the fatigue strength of nitrided turbine rotor steel at high temperature (538$^{\circ}C$). Specimens were nitrided with various layer thicknesses (160$\mu$m, 270$\mu$m and 290$\mu$m) using the nitemper method. A microstructure analysis, microhardness test, surface roughness test, and fracture surface analysis were also carried out at room temperature in order to investigate the mechanical properties of the nitrided specimens.