• 한국해양공학회지
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• 제19권6호통권67호
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.173-178
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• 2004

The estimation of springing responses for recent ships are carried out and application to a ship design are described. To this aim, springing effects on hull girder were re-evaluated including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder by the superposition method. The strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level and added asymptotic interpolation along the high frequency range. Several applications to the existing ships were carried out. They are Bishop and Price's container ship, S-175 container ship, large container, VLCC and ore carrier. One of them is compared with ship measurement result while another with that of model test. Comparison between analytical solution and numerical one for homogeneous beam type artificial ship shows good agreement. It is found that most springing energy came from high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega^{-3}\;instead\;of\;\omega^{-4}\;or\;\omega^{-5}$ for springing calculation.

• 대한조선학회논문집
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• 제32권2호
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• pp.103-107
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• 1995

선체거더의 종진동 현상은 60년대에 이미 조사된 바 있으나 기존 선박들에서는 종방향 기진력이 작았기 때문에 선체 종진동 현상이 거의 나타나지 않았다. 그러나 80년대 중반이후의 대형 저속디젤엔진 추진선에서는 추진축계 비틂 공진점에서 연성되어 작용하는 축계 종방향 기진력에 의하여 선체전체의 종진동이 유발될 수도 있다. 본 연구에서는 73,000톤 산적화물선에서 감지된 선체거더의 종진동 현상을 실선계측 및 해상기진기 실험 그리고 유한요소 해석방법으로 분석하였다. 분석결과 이러한 선체 종진동 현상은 Over-critical 축계 시스템을 갖춘 선박에서만 축계 종방향 기진력에 의해 나타날 수가 있으며 그 중에서도 주기관의 연속 사용금지구역(barred range)이 설정되지 않은 선박의 경우엔 하중조건에 따라 저속 입출항 운항시 선루를 포함한 선체에 심한 중진동이 발생될 수 있슴이 판명되었다.

• 대한조선학회논문집
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• 제42권6호
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• pp.631-636
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• 2005

One and three dimensional whipping response analyses of a naval surface combatant subjected to an underwater explosion bubble pulse were carried out to compare the efficiency and accuracy according to the modeling methods. In 1-D analysis, program UNDEXWHIP developed by KIMM was used, which is based on the thin-walled Timoshenko's beam theory and on the modal analysis method using wetted vibratory modes of the hull girder. In 3-D analysis, three finite element models were suggested using LS-DYNA/USA code, such as 3-D beam model considering geometric shape of wetted side shell, coarse and fine 3-D F.E. models. Through the comparison of results from the 1-D and 3-D analyses, it could be confirmed that 1-D analysis result is in good agreement with 3-D analysis ones, and that fine 3-D F.E. model, shock analysis one, is also used both in the shock response and whipping response analyses for the analyst effort and time savings.

• 대한조선학회지
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• 제21권4호
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• pp.40-48
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• 1984

The computer program DASH(Direct Analysis of Ship's Hull), based on the direct calculating procedure as proposed at the 4th ISSC(1970), was developed. The DASH program is designed by the following calculation procedure: 1) Derivation of the design wave loads through the ship motion analysis based on the strip theory. 2) Stress analysis of the hull girder based on the 7-degree of the freedom beam theory including the warping torsion effect. 3) Long-term prediction of the stresses based on the statistical approach using sea-spectrums and ocean wave data in the ship's route. An example calculation was performed for the purpose of a demonstration of the present approach on the 16,200 DWT Oil Tanker. The results are discussed and compared with the conventional method.

• 수산해양기술연구
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• 제21권1호
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• pp.67-74
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• 1985

본 논문에서 얻은 결과를 요약하면 다음과 같다. 1) slamming 충격력에 의한 선각의 굽힘 모우멘트와 전단력의 계산은 본 논문의 이론 전개방법에 의해 구하는 것이 Antonides의 적용 방법보다 더 타당하다고 생각된다. 2) 수치계산 예에서 보면 선체 중앙단면에서 가장 큰 sagging moment가 발생하며 Antonides의 결과치 보다 3~5%정도 더 크게 나타났다. 3) 기준진동형의 중첩항 수는 주어진 문제의 특성 및 요구되는 정도에 따라 결정되어야 하므로 고차 진동형에 대한 실측치와 이론치의 비교 분석이 선행되어야 한다고 생각된다.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.473-484
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• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• 대한조선학회논문집
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• 제43권3호
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• pp.340-350
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• 2006

This paper is concerned with a practical guide for the ultimate longitudinal strength assessments of ships' hull structure. Rigorous non-linear structural analysis for three tanker models has been carried out to examine the ultimate strength behavior. Formula of estimating the ultimate longitudinal strength has been proposed which is modified with the results of non-linear finite element analysis of hull girders. Computational reliability and accuracy of the large-scale non-linear finite element analysis and the proposed simplified formula are verified through comparing their results with that of 1/3 scale frigate model test and DNVs program. Additionally, the ultimate longitudinal strength for ten tanker models is compared with those by the method specified in the 2nd Draft of common structural rule for tankers, which is being developed by IACS.

• 대한조선학회 특별논문집
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• 대한조선학회 2009년도 특별논문집
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• pp.59-64
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• 2009

The propeller induced forces acting on a hull are surface forces and bearing forces. The bearing forces are the forces acting directly on the propeller which are transferred to the hull through the propeller bearings. The surface forces are those which act by fluid pressure directly on the various hull surfaces. Because the surface force is main source to oscillate stern constructions and deckhouse, the estimation of surface force is very important to predict response of forced vibration of that. The estimation methods were statistical analysis method, theoretical analysis method and method through model test.

• 한국해양공학회지
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• 제25권3호
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• pp.1-10
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• 2011

This paper estimates the residual longitudinal strength of a damaged double hull VLCC (Very Large Crude Carrier) under combined vertical and horizontal bending moments using Smith's method. The damage estimated in this study occurred due to collision or grounding accidents. The effects of the randomness of the yield stress, plate thickness, extent of damage, and the combination of these three parameters on the ultimate hull girder strength were investigated. Random variables were generated by a Monte Carlo simulation and applied to the double hull VLCC described by the ISSC (International Ship and Offshore Structures Congress) 2000 report.