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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Society of Naval Architects of Korea
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Journal DOI :
The Society of Naval Architects of Korea
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Volume & Issues
Volume 52, Issue 6 - Dec 2015
Volume 52, Issue 5 - Oct 2015
Volume 52, Issue 4 - Aug 2015
Volume 52, Issue 3 - Jun 2015
Volume 52, Issue 2 - Apr 2015
Volume 52, Issue 1 - Feb 2015
Selecting the target year
A Study on the Optimal Shape Design of a Floating Offshore Wind Turbine
Park, Jeong-Hoon ; Shin, Hyunkyoung ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 171~179
DOI : 10.3744/SNAK.2015.52.3.171
Usually, in case of wind turbines on land, there are a lot of constraints for installation such as the insufficient installation space and noise pollution. On March 11, 2011, a nuclear leakage accident occurred due to the tsunami caused by the earthquake in Japan and then there have been a rapidly growing interest in floating offshore wind turbines. In this study, an optimization of the substructure of a semi-submersible type floating offshore wind turbine was made. Design variables were set and design alternatives were fixed. UOU-FAST was used for motion analysis in combined environmental conditions of waves and wind. Response Amplitude Operators(RAOs) were compared between the design alternatives.
An Experimental Study on Preparation Method of Granular EG/AD Model Ice
Cho, Seong-Rak ; Ha, Jung-Seok ; Jeong, Seong-Yeob ; Kang, Kuk-Jin ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 180~186
DOI : 10.3744/SNAK.2015.52.3.180
This study proposed a new method of preparing granular ethylene glycol/aliphatic detergent (EG/AD) model ice that has both strength and uniform thickness. Various sheets of granular model ice prepared in ice tanks are surveyed and their preparation procedures are analyzed. We not only made a new granular model ice using the EG/AD solution but also measured its thickness, strength, and density. In addition, we found that the strength of the model ice could be controlled by varying the time and air temperature in the consolidation phase. Based on the results of this study, we verified that granular EG/AD model ice can be prepared more uniformly and effectively than columnar EG/AD model ice. This study is intended to contribute to reducing the time required for the ice model test and the operation of the ice model basin.
A Semi-Analytic Approach for Analysis of Parametric Roll
Lee, Jae-Hoon ; Kim, Yonghwan ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 187~197
DOI : 10.3744/SNAK.2015.52.3.187
This study aims the development of a semi-analytic method for the parametric roll of large containerships advancing in longitudinal waves. A 1.5 Degree-of-Freedom(DOF) model is proposed to account the change of transverse stability induced by wave elevations and vertical motions (heave and pitch). By approximating the nonlinearity of restoring moment at large heel angles, the magnitude of roll amplitude is predicted as well as susceptibility check for parametric roll occurrence. In order to increase the accuracy of the prediction, the relationship between righting arm(GZ) and metacentric height(GM) is examined in the presence of incident waves, and then a new formula is proposed. Based on the linear approximation of the mean and first harmonic component of GM, the equation of parametric roll in irregular wave excitations is introduced, and the computational results of the proposed model are validated by comparing those of weakly nonlinear simulation based on an impulse-response-function method combined with strip theory. The present semi-analytic doesn’ t require heavy computational effort, so that it is very efficient particularly when numerous sea conditions for the analysis of parametric roll should be considered.
Numerical Computations of Impact Forces Acting on Breakwater Plate of Bow Deck of Container Carrier
Lee, Seohyun ; Lew, Jaemoon ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 198~205
DOI : 10.3744/SNAK.2015.52.3.198
In this study, numerical studies using a Computational Fluid Dynamics(CFD) method were carried out to estimate the green water load acting on the breakwater plate of bow deck of container carrier, KCS. For the green load water load analysis, a full load condition was considered. The relative motions at bow deck were calculated from the seakeepig analysis. Statistical analysis were carried out to estimate the long term response of the relative motions with the North Atlantic wave scatter diagram. The equivalent design wave was determined from the RAO of the relative motions at bow and the long term responses. CFD geometry modeling with three different locations and simulations for the green water loads were carried out in the equivalent design waves. A commercial CFD program, STAR-CCM+ Ver. 8.04, was used and the green water pressures on the breakwater plate were calculated successfully. The CFD analysis for green water loads can be used as a useful design tool for the evaluation of the breakwater plate of the container vessel.
Studies on Ventilation Control for a Ventilated Supercavitating Vehicle
Kim, Seonhong ; Kim, Nakwan ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 206~221
DOI : 10.3744/SNAK.2015.52.3.206
Supercavitation is a modern technique which can be used to surround an underwater vehicle with a bubble in order to reduce the resistance of the vehicle. When the vehicle is at low speed in the deep sea, the cavitation number is relatively big and it is difficult to generate a cavity large enough to envelope the vehicle. In this condition, the artificial cavity, called ventilated cavity, can be used to solve this problem by supplying gas into the cavity and can maintain supercavitating condition. In this paper, a relationship between the ventilation gas supply rate and the cavity shape is determined. Based on the relationship a ventilation rate control is developed to maintain the supercavitating state. The performance of the ventilation control is verified with a depth change control. In addition, dynamics modeling for the supercavitating vehicle is performed by defining forces and moments acting on the vehicle body in contact with water. Simulation results show that the ventilation control can maintain the supercavity of an underwater vehicle at low speed in the deep sea.
Comparative Study on Wave Induced Fatigue Analysis Methods for Steel Catenary Riser
Lee, Jeong-Dae ; Lee, Sung-Je ; Jang, Chang-Hwan ; Jun, Seock-Hee ; Oh, Yeong-Tae ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 222~235
DOI : 10.3744/SNAK.2015.52.3.222
The purpose of this study is to suggest guidelines for riser fatigue analysis in terms of selection of reasonable analysis method. Three analysis methods (spectral, regular wave, rain-flow counting) are introduced and compared. As the riser systems give non-linear response, the time-domain analysis method is more preferred than frequency-domain analysis method. The spectral fatigue analysis method, however, is still useful for identifying fatigue prone areas. Once stress RAO is established, fatigue damage can be calculated very quickly. The regular wave method and the rain-flow counting method are more time consuming but give more exact results compare to spectral method. In case of regular wave method, a set of regular waves which represent random sea states is considered for dynamic analysis. The rain-flow counting method is the most intuitive and exact method because it refers time history stresses containing most of non-linear effects of the riser system. However, it is not common for early design stage to use rain-flow counting method because of its high cost. In this study, it was confirmed that the regular wave method is the most cost effective way in specific cases. However, if the system is highly non-linear, it seems that the regular wave method gives less accurate results than rain-flow counting method. Therefore, it is imperative that the engineers select appropriate analysis method based on design stage and given engineering period. This paper also discusses the theoretical background of each calculation method and hydrodynamic aspects of marine riser systems. A steel catenary riser (SCR) line on FPSO was considered and marine dynamic program (OrcaFlex) was used for static and dynamic analysis.
An Experimental Study on Ventilated Supercavitation of the Disk Cavitator
Kim, Byeung-Jin ; Choi, Jung-Kyu ; Kim, Hyoung-Tae ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 236~247
DOI : 10.3744/SNAK.2015.52.3.236
In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.
Fatigue Life Prediction of CFRP using Fatigue Progressive Damage Model
Jang, Jae-Wook ; Cho, Je-Hyoung ; Oh, Dong-Jin ; Kim, Myung-Hyun ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 248~254
DOI : 10.3744/SNAK.2015.52.3.248
The strength and fatigue life of Satin and Twill-woven CF/epoxy composite(CFRP) have been investigated. Damage mechanism fatigue method has been used to assess fatigue damage accumulation. It is based on measured residual stiffness and residual strength of carbon-fiber reinforced plastic(CFRP) laminates under cyclic loading. Fatigue damage evolution in composite laminates and predict fatigue life of the laminates were simulated by finite element analysis(FEA) method. The stress analysis was carried out in MSC patran/Nastran. A modified Hashin's failure criterion di rmfjapplied to predict the failure of the experimental data of fatigue life but a Ye-delamination criterion was ignored because of 2D modeling. Almost linear stiffness and strength degradation were observed during most of the fatigue process. These stress distribution data were adopted in the simulation to simulate fatigue behavior and estimate life of the laminates. From the results, the predicted fatigue life is more conservatively estimated than the experimental results.
Wind Load and Flow Field Change with Respect to Various Configurations of a Drillship
Jung, Youngin ; Kwon, Kijung ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 255~264
DOI : 10.3744/SNAK.2015.52.3.255
Wind load and flow field of a drillship with respect to various super structures were experimentally investigated in KARI 1m-wide wind tunnel with an atmospheric boundary layer simulation. Six-component external balance and Particle image velocimetry technique were used to measure wind load and velocity vectors in the flow-field around the model respectively. The experimental model was an imaginary shaped drillship with an approximated model which has 1/640 scale compared with recent typical drillships. The test Reynolds number based on the overall length was about 1.5×10
. It was found that dominant factors influencing on ship wind load are cabin shape and cabin height. Round cabin has smaller axial wind load and narrow boundary layer around the ship than rectangular one, but its yawing moment at certain angles becomes higher. Low cabin height also show positive effects on axial wind load too. Hull shape and forecastle shape show relatively small influences on wind loads except for slight changes around ±45° wind directions.
Comparison Analysis on Requirements of Structural Members by Application of the Harmonized Common Structural Rules
Sung, Chi Hyun ; Lee, Seung-Keon ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 265~274
DOI : 10.3744/SNAK.2015.52.3.265
International organizations and classification societies established rules and regulations to which shipbuilders and ship operators should comply during design, construction, even operation keeping from hazard to life of crews and ocean environment. Hence, rules and regulations could be guidelines for design and construction of ship sometimes. In practical wise, ship structure designers be predisposed to design lightest and easy-to-product structures which satisfy rules and regulations. Therefore, changes of rules and regulations are remarkably important issue to related industries. In 2006, IACS established and released Common Structural Rules for Bulk Carrier and Common Structural Rules for Double Hull Oil Tanker. These CSRs are consolidated and unified rules of class society's rules. But these two rules are different from each other. IACS has plan to release unified rule of two ship type called Harmonized Common Structural Rule for Bulk Carriers and Oil Tankers. This new rule will be effective from July 2015. Hence, bulk carrier and double hull oil tanker whose contract date is on and thereafter July 2015 should be complied with CSR-H. Therefore, it is highly important to be aware of consequences and cause of consequences with respect to CSR-H. The object of this research is to compare requirements of structure scantling in way of midship area for selected target ship according to CSRs and CSR-H and to analysis cause of deviation between two rules.
Experimental Evaluation of the Performance of Large-Capacity Mounts for Naval Shipboard Equipments
Moon, Seok-Jun ; Kim, Heung-Sub ; Park, Jin-Woo ; Park, Jin-Ho ; Oh, Kwang-Suk ; Jeong, Jong-Ahn ;
Journal of the Society of Naval Architects of Korea, volume 52, issue 3, 2015, Pages 275~281
DOI : 10.3744/SNAK.2015.52.3.275
Mounts for shipboard equipment in naval ships play an important role for vibration and shock suppression. New large-capacity resilient mounts, SDR-D30 and SDR-D45, have been developed. This paper involves performance tests for the mount which have maximum load of 30 kN and 45 kN, respectively. The performance tests have been carried out for several mounts based on military standards, such as MIL-M-19863D(SH), MIL-M-21693C(SH), MIL-M-17508F(SH), and MIL-S-901D(NAVY). The test items consist of deflection at upper rate load test, dynamic stiffness, uniformity, static load-deflection(axial, transverse and longitudinal), drift test, fatigue test, and shock test. From these performance tests, it is confirmed that the two mounts have good performances based on military standards.