• Title/Summary/Keyword: 휘핑응답

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Comparison of UNDEX Whipping Response of Hull Girder according to Modeling Methods (해석모델링 방법에 따른 선체거더의 수중폭발 휘핑응답 비교)

  • Kwon, Jeong-Il;Chung, Jung-Hoon;Lee, Sang-Gab
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.6 s.144
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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.

A Study on the Whipping Phenomena Effect on the Structural Response of Large Container Ships (대형 컨테이너 선박의 구조 응답에 미치는 휘핑 영향도 분석)

  • Kim, Beom-Il;Kim, Min-Su;Seo, Sun-Kee;Park, Jae-Hong
    • Journal of the Society of Naval Architects of Korea
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    • v.55 no.4
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    • pp.341-349
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    • 2018
  • Recently, it has been reported that the whipping response, which is the elastic phenomenon of the ship, may be one of the causes of the ship accident. Unfortunately, the commonly used methodology for evaluating the whipping effect effectively has not been developed yet. In this study, we developed a procedure to estimate the whipping effect of hull in actual design stage. Fluid-structure interaction analysis was performed for a dominant short term sea state to obtain the time series data of vertical wave bending moment including the whipping response by slamming. In order to estimate the whipping effect by using the time series, some signal processing and statistical techniques such as low pass filtering, Weibull fitting and so on, were applied. the hydro-elasticity analysis was performed on container ships of various sizes to evaluate the whipping effect. The parameters that can affect the response of the hull vibration was selected and the effect of these parameters on whipping was analyzed.

A Study on Inelastic Whipping Responses in a Navy Ship by Underwater Explosion (수중 폭발에 의한 함체의 비탄성 휘핑 응답에 관한 연구)

  • Kim, Hyunwoo;Seo, Jae Hoon;Choung, Joonmo
    • Journal of the Society of Naval Architects of Korea
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    • v.58 no.6
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    • pp.400-406
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    • 2021
  • The primary effect of the far-field underwater explosion (UNDEX) is the whipping of the ship hull girder. This paper aims to verify why inelastic effects should be considered in the whipping response estimations from the UNDEX simulations. A navy ship was modeled using Timoshenko beam elements over the ship length uniformly keeping the constant midship section modulus. The transient UNDEX pressure was produced using two types of the Geers-Hunter doubly-asymptotic models: compressible and incompressible fluids. Because the UNDEX model based on incompressible fluid assumption provided more increased fluid volume acceleration in the bubble phase, the incompressible fluid-based UNDEX model was adopted for the inelastic whipping response analyses. The non-linear hull girder bending moment-curvature curve was used to embed inelastic effects in the UNDEX analyses where the Smith method was applied to derive the non-linear stiffness. We assumed two stand-off distances to see more apparent inelastic effects: 40.5 m and 35.5 m. In the case of the 35.5 m stand-off distance, there was a statistically significant inelastic effect in terms of the average of peak moments and the average exceeding proportional limit moments. For the conservative design of a naval ship under UNDEX, it is recommended to use incompressible fluid. In the viewpoint of cost-effective naval ship design, the inelastic effects should be taken into account.

Identification of Whipping Response using Wavelet Cross-Correlation (웨이블릿 교차상관관계를 이용한 변형체 선박의 휘핑 응답 식별)

  • Kim, Yooil;Kim, Jung-Hyun;Kim, Yonghwan
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.2
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    • pp.122-129
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    • 2014
  • Identification of the whipping response out of the combined wave-vibration response of a flexible sea going vessel is one of the most interesting research topic from ship designer's point of view. In order to achieve this goal, a novel methodology based on the wavelet cross-correlation technique was proposed in this paper. The cross-correlation of the wavelet power spectrum averaged across the frequency axis was introduced to check the similarity between the combined wave-vibration response and impulse response. The calculated cross-correlation of the wavelet power spectrum was normalized by the auto-correlation of the each spectrum with zero time lag, eventually providing the cross-correlation coefficient that stays between 0 and 1, precisely indicating the existence of the impulse response buried in the combined wave-vibration response. Additionally, the weight function was introduced while calculating the cross-correlation of the two spectrums in order to filter out the signal of lower frequency so that the accuracy of the similarity check becomes as high as possible. The validity of the proposed methodology was checked through the application to the artificially generated ideal combined wave-vibration signal, together with the more realistic signal obtained by running 3D hydroelasticity program WISH-Flex. The correspondence of the identified whipping instances between the results, one from the proposed method and the other from the calculated slamming modal force, was excellent.

Whipping analysis of hull girders considering slamming impact loads (슬래밍 충격하중을 고려한 선체 휘핑 해석)

  • Seong-Whan Park;Keun-Bae Lee;Chae-Whan Rim
    • Journal of the Society of Naval Architects of Korea
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    • v.37 no.3
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    • pp.99-109
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    • 2000
  • Elastic dynamic responses analysis program for ship hulls considering slamming impact loads due to the voyage in large amplitude waves is developed. Ship hull structures are modeled by a thin-walled beam model in order to consider effects of shear deformation. The momentum slamming theory is used to derive nonlinear hydrodynamic forces considering intersection between wave particles and ship section. For the validation of the developed computer program, motions of a V-shaped simple section model and S-175 standard container model are calculated and analyzed. In each numerical example, time histories of relative displacement, velocity and vertical bending moment of a ship section are derived, considering the effect of slamming impacts in various wave conditions.ures near the free surface as well as the wake of the hydrofoil.

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Structural Assessment of Container ships Considering Hydroelastic Responses (컨테이너선의 유탄성 응답을 고려한 구조강도 평가 기술)

  • Park, Jun Seok;Choi, Byung Ki;Choi, Ju Hyuck;Jung, Byoung Hoon
    • Special Issue of the Society of Naval Architects of Korea
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    • 2017.10a
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    • pp.80-87
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    • 2017
  • This paper is related to structural assessment considering the hydroelastic response of ultra large container ships, especially from whipping (bow or stern impacts) and from springing (resonance). In general, whipping contributes both to increased fatigue and extreme loading, while springing does mainly contribute to increased fatigue loading. To evaluate the hydroelastic response quantitatively with high accuracy, numerical code considering hydro-structure coupling was applied and fatigue strength of a 13,100 TEU class containership was verified. The segmented model test and full scale measurement were also needed to assess the effect of whipping and springing on the fatigue and extreme capacity in more realistic way and for verification of the numerical tools. With reference to class rule, fatigue assessment considering springing effect and extreme assessment considering whipping effect were introduced.

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Study of the Prediction of Fatigue Damage Considering the Hydro-elastic Response of a Very Large Ore Carrier (VLOC) (유탄성 응답을 고려한 초대형 광탄 운반선(VLOC)의 피로 손상 예측 기법에 관한 연구)

  • Kim, Beom-Il;Song, Kang-Hyun
    • Journal of Ocean Engineering and Technology
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    • v.33 no.1
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    • pp.33-41
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    • 2019
  • Estimating fatigue damage is a very important issue in the design of ships. The springing and whipping response, which is the hydro-elastic response of the ship, can increase the fatigue damage of the ship. So, these phenomena should be considered in the design stage. However, the current studies on the the application of springing and whipping responses at the design stage are not sufficient. So, in this study, a prediction method was developed using fluid-structural interaction analysis to assess of the fatigue damage induced by springing and whipping. The stress transfer function (Stress RAO) was obtained by using the 3D FE model in the frequency domain, and the fatigue damage, including linear springing, was estimated by using the wide band damage model. We also used the 1D beam model to develop a method to estimate the fatigue damage, including nonlinear springing and whipping by the vertical bending moment in the short-term sea state. This method can be applied to structural members where fatigue strength is weak to vertical bending moments, such as longitudinal stiffeners. The methodology we developed was applied to 325K VLOC, and we analyzed the effect of the springing and whipping phenomena on the existing design.