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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Ocean Engineering and Technology
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Journal DOI :
Korean Society of Ocean Engineers
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Volume & Issues
Volume 2, Issue 2 - Dec 1988
Volume 2, Issue 1 - Jun 1988
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A Study on the Motion Responses and the Drift Forces of Semi-Submersible Drilling Rigs in the Damaged Condition
Park, Rho-Sik ; Kim, Seong-Keun ; Kim, Jong-Hyeon ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 27~36
For the purposes of drilling oil field and extracting oil deep water in more rough weather, the size of drilling rigs must be estimated. In this paper, the three dimensional source distribution method is used and we assume 10 deg. heeling and trimming condition of the drilling rig(SR-192). Also, the effects of the hydrodynamic forces which include the drift forces for field method, and the motion responses are studied with changing the incident wave direction in the assumed inclining condition. The theory and numerical codes used in this thesis appeared to be very useful for the preliminary design of drilling rigs.
Optimal Control of Dynamic Positioned Vessel Using Kalman Filtering Techniques
Lee, Pan-Muk ; Lee, Sang-Mu ; Hong, Sa-Yeong ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 37~45
A dynamically positioned vessel must be capable of maintaining a specified position and direction by controlling the thruster devices. The motions of a vessel are often assuned to tne sum of low frequency(LF)motions and high frequency(HF)motions. The former is mainly due to wind, current and second order wave forces, while the latter is mainly due to first order wave forces. In order to avoid the high frequency thruser modulation, the control system must include filters to estimate the low frequency motions from the measured motion signals, This paper presents a control system based on Kalman filtering technique and optimal control tyeory. Using the combined kalmam filter, LF motion estimates and HF ones are achieved from the motion measurement of the vessel. The estimated low frequency motions are used as inputs to the dynamic positioning system. The thruster modulation is minimized using the optimal control theory; Linear Quadratic Gaussian(LQG)controller. The performances of the Kalman filter and the dynamic positioned vessel are investigated by computer simulation.
A Note on the Asymptotic Structure of the
Suh, Yong-Kweon ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 46~50
Automatic Interpretation of the Borehole Normal Resistivity Data by Using a Personal Computer
Kim, Jin-Hu ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 51~60
A data transform is performed by using a point-electrode focusing method in order to obtain accurate and objective interpretation of the borehole normal resistivity data. Two new synthetic curves can be generated through the data transform. The one is an approximate apparent resistivity curve, which would be used to predict the true resistivity of the formation. The other one is a bed boundary coefficient curve, which would be used to distinguish bed boundaries. The accuracy of the normal data interpretation can be improved and this method takes much less computational time than a linear inversion technique. Moreover, this method does not require an initial guess model and limitation of number of unknown parameters. Since this algorithm can be run on a personal computer, an immediate interpretation would be possible at the field work site. If an additional set of electrodes(a=125cm)is attached to a normal resistivity tool which is being used (a=25cm, 50cm, 100cm), the apparent resistivity for the point-electrode focusing device can be calculated, and it would maximize the use of short and long normal resistivity data and promote the accuracy of the interpretation.
A Prediction of Initial Fatigue Crack Propagation Life in a notched Component Taking Elasto-Plastic Behavior
Cho, Sang-Myung ; Kohsuke Horikawa ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 61~70
In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.
A Theoretical Investigation on Shakedown Analysis of Framed Structures
Lee, Jong-Seok ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 71~77
For the collapse of structures due to the variable repeated load, two types of collapse mechanisms, i.e., incremental collapse and alternating plasticity, exist. Under the similar variable repeated loading conditions there exists shakedown state in the structures. In shakedown state, the number of plastic hinges are not increased and all further loading will be resulted in the elastic moment changes. Namely, under the shakedown state, structures do not collapse. In this investigation, shakedown analysis are performed by composing new computer programs. Basic theories employed to compose the programs are as follows. 1. Newton-Raphson methods are added to the existing matrix method for the plastic analysis. 2. An effort to construct the stiffness of axial and bending springs attached at both ends of the member has been made. By using the programs developed, it is possible to anticipate the collapse mechanisms (Incremental collapse, alternating plasticity). Lastly for the verification of performance of the program, demonstration examples have been solved and the results are compared with other sources.
Influence of Salt Solution Concentration on Corrosion Pit Growth Characteristic of Dual Phase Steel
Oh, Sae-Wook ; Kang, Ho-Min ; Kim, Tae-Man ; Do, Yeong-Min ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 78~86
In order to investigate the corrosion pit occurrence and growth characteristic of M.E.F.(martensite encapsulated islands of ferrite) dual phase steel was made with a suitable heat treatment of raw material(SS41), a corrosion fatigue test was performed under rotary bending in the salt solution having a concentration from 0.01 wt percent to 3.5 wt percent. The fatigue strength of dual phase steel was remarkably decreased with an increase in concentration of salt solution; approximately from 63% to 80% in case of dual phase steel and from 40% to 71% in case of raw material. Corrosion pit occurred in the martensite phase and fatigue cracks from corrosion pits were selectively propagated in martensite phases. In the observation of corrosion pits at the origin of fatigue cracks, it had been found that corrosion pits were grown into hemispherical pits and a/c(the surface diameter, 2c and the depth, a of corrosion pit)was about 1.0-1.5regardless of the variation of salt solution concentration. The difference of corrosion pit depth growth rate was increased with an increase in concentration of salt solution according to an increase in stress level.
A Study on the Wear Characteristics of Austempered Ductile Cast Iron in Corrosive Environments
Kang, Myug-Soon ; Jun, Tae-Ok ; Park, Heung-Sik ; Jin, Dong-Gyu ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 87~95
This paper is studied to know corrowive wear characteristics of austempered ductile cast ironin corrosive environments against mating SM45C hardened two test pieces in distilled water and NaCl aqueous solution. The corrosive wear mechanism was investigated by scanning electron microscopy and retained austenite volume fraction was investigated by X-ray diffractometer. The experimental result show that the corrosive wear characteristics depend largely on the
which is influenced by the critical sliding distance
shorted with increasing NaCl concentration. It was found that the carbides in matrix have a significant effect on their corrosive wear resisance and the fine acicular bainite showed corrosive wear resistance stronger than that of the coarse acicular and platelet bainite. From above results the model of corrosive wear mechanism in corrosive environments is proposed.
A Photoelastic Study on the Stress Intensity Factor of Circular Disk with an Are-crack
Lee, Chi-Woo ; Kim, Tae-Gyu ; Yang, Jang-Hong ; O, Se-Uk ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 96~103
The stress distribution in the vicinity of the crack tip in the fracture mechanics is ordenarily indicated by the stress intensity factor. In the analysis of stress intensity factors, there are many theoretical and experimental methods. The stress analysis in photoelastic technique is usually made by using the difference of the principal stress of isochromatic fringe patterns. In this paper, the teflon molding technique is adopted to make a test specimen with a circular arc-crack, and that upgraded the accuracy of experiment. As the result, the experimental values of the stress intensity factors for the circular disk with a straight crack are coincided with the theoretical values. But, there is quite a difference between this expermental results on the finite plate for circular arc-crack and its theoretical values on the infinite one. Therefore, a boundary condition with regard to the loading condition on finite disk must be considered.
Micro-Surface-Cracks Behavior of 304 Stainless Steel Under Creep-Fatigue Interaction at Elevated Temperature
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 104~111
This paper deals with the micro-surface-cracks behavior on the unnotched smooth specimens of Type 304 stainless steel at
in air under creep and creep-fatigue conditions that have 10 mim and 1 min load holding times respectively. The behaviors of the micro-surface-cracks have been visualized by means of surface replica method and optical micro-photography. The quantitative characteristics of initiation, growth and coalescence of micro-surface-cracks have been investigated by observing and measuring the crack growth behaviors. some of the important results are as follows: Main crack initiates at grain boundary in the early stage(10 to 20%)of its life time and grows through coalescence and finally leads to fracture. The distribution of micro-surface-crack length, 2a, can be plotted against the composite Weibull distribution. The growth rate of the main crack can be plotted against the stress intensity factor, crack tip opering displacement and J integral.
A Study on Friction Welding of SM45C to SCM4 Steel Bars and the Fatigue Properties
O, Se-Gyu ; Kim, Bu-An ; Kim, Seon-Jin ; Nam, Sang-Hun ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 112~121
A study on friction welding of carbon steel bar (SM45C) to chrome molybedenum steel bar(SCM4) is examined experimentally through tensile test, hardness test, microstructure test and fatigue test. so, this paper deals with optimizing the welding concitions and analyzing various mechanical properties about friction welds of SM45C to SCM4 steel bars. The results obtained are summarized as follows; 1) For friction welded joints of SM45C to SCM4 steel bars, the total upset(U)increases linearly with an increase of heating time (
) till 6s. 2) The determined optimum welding conditions are heating time (
)2s, upsetting time(
), 3s, heating pressure(
(39.2MPa), upsetting pressure(
(78.4MPa) and rotating speed(N), 2, 000rpm when the total upset(U) is 3.4mm, resulting in a computed relationship between the joint tensile strength .sigma.
and the total upset U(mm); .sigma.
+17.03U + 66.00 3) As the elongation is increased more and more, the fracture position becomes away from weld interface and the fractures are similar to those of SM45C. Fracture is taken place on SM45C side. 4) The weld interface of two dissimilar materials is mixed strongly, and the heat affected zone is about 2.0mm at SM45C while about 2.7 mm at SCM4 side. Therefore, the welded zone and heat affected zone are very narrow, comparing with those of the joints welded by the other welding methods. 5) The fatigue strengths at N=10
cycles of SM45C, SCM4 and friction welded joints are 23kgf/
(220.5 MPa), and 22.5kgf/
(220.5MPa) respectively, and fracture at friction welded joint takes place at the side of SM45C. 6) The hardness of the friction weld interface is 3 times higher than that of base metal. 7) Fatigue strength of friction welded joint is higher than that of base metal. 8) Notch sensitivity factor of friction welded joint is lower than that of base metal.
Study on the Retardation Effect of Overload on the Corrosion Fatigue Crack Propagation Al-Alloy used for the Shipbuilding
Lim, Uh-Joh ; Lee, Jong-Rark ; Lee, Jin-Yeol ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 122~129
Recently with the rapid development in marine and shipbuliding industries such as marine structures, ship and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics which was closed up an important role in mechanical design. In this study, the 5086 Al-alloy was tested by use of rotary bending fatigue tester. The retardation effect of overload on the corrosion fatigue crack propagation in sea environment was quantitatively studied. 1) Retardation effect of corrosion fatigue crack propagation is most eminent when overload ratio is 1.52, overload magnitude corresponds to about 77% and 55% of yield strength and tensile strength respectively. 2) After overload ratio 1.52 was used, retardation of corrosion fatigue crack growth rate is largely retarded and quasi-threshold stress intensity factor range(
) appears. 3) According to m of experimental constant, retardation effect of corrosion fatigue crack propagation corresponds to about 25% of constant stress amplitude when overload ratio is 1.52. 4) When overload ratio 1.52 was used, retardation parameter (RP) decreases to about 0.43 and corrosion sensitivity (S)decreses to about 2.1.
Mass Transfer and Hydraulic Kinematic Character Using Lattices Packings by Countercurrent Flow of Gas-Liquid Phase in Packing Column
Kim, Jang-Ho ; Ha, Sang-An ;
Journal of Ocean Engineering and Technology, volume 2, issue 2, 1988, Pages 130~137
This thesis introduced that character of a treatment technique for a mading synthetic resin Hifiow-Ring. The material system of packings make an experiment air
under general conditions. Lattices packing compared with conventional packings was proved low pressure loss and high separation efficiency for high loading per trans unit. And an inflow materal tested for absorption and rectification, it made an experiment under a range regular temperature, low energy and small amount of money. That made possible in simple equation, volume material tranfer coefficient
. a by absorption or
.a calculated in all range loading. The peculiarity pressure loss
for Hiflow-ring contributed to a fall cost of energy, a grade number of a vacuum rectification and absorption calculation.