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In this paper, the dynamic implosion responses of ring-stiffened cylindrical tubes under external hydrostatic pressure are reported. The ring-stiffened cylinder models were fabricated from commercial seamless aluminium-alloy 6061-T6 tubes. Six external stiffened models were constructed: three models with three stiffeners, and the other three with five stiffeners. To quantify the effects of stiffening on the structural behaviour, implosion tests were also performed on another three unstiffened tube models. In this study, a total of nine tube models were tested until their failure. Implosion was initiated by increasing the hydrostatic pressure in the chamber until the tubes collapsed, and the effects of different types of pressurising media were investigated: (i) water only and (ii) water and nitrogen gas combined. The implosion pressure pulse near the collapsing tube was recorded during the event. The models with five stiffeners increased the implosion pressure pulse by approximately 3.5 times compared with the unstiffened model.

Accurate estimation of shear flows in thin-walled beam section is the key issue to evaluate shear stress distribution of ship hull transverse section under the shear forces acting on hull girder. It is regarded that the method using the warping functions obtained by finite element formulation is the state of the art of this field. Recently, however, IACS took effect the new version of CSR in which direct calculation process of shear flow was suggested. In the direct calculation process, shear flow of ship hull section can be obtained by the addition of determinate and indeterminate shear flows calculated respectively. So, in this paper, the shear flow evaluation codes based on the process proposed by IACS CSR and warping function based method were developed respectively. The calculated results of shear flows for the several examples of ship sections were compared with each other and considered in detail.

2 The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

컨테이너선의 전손 사고 (MAIB, 2008; NK, 2014)로 인하여, 최종 종강도 능력(capacity)에 대한 검증 필요성이 증대되고 있 다. 또한, 선체 크기가 점점 대형화 됨에 따라 휘핑에 의한 종굽 힘 하중이 추가되는 상황 임에도 컨네이너선의 최종 종강도 요건 에 강제 규정이 현재까지 선급규칙에 반영되지 못하고 있는 실정 이다. 이에 따라, 현재 국제선급연합회(IACS)는 산적화물선과 탱 커선에 적용하던 공통구조규칙 (IACS, 2014)의 최종 종강도 요 건을 컨테이너선에도 적용하기 위하여 통일규칙 (IACS, 2010)을 개정 중에 있다. 본 연구는 CSR의 최종 종강도 계산에 사용되는 간이해석법을 사용하여 두 척의 크기가 다른 컨테이너선의 최종 종강도를 계산하고 이를 비선형 유한요소해석 결과와 비교하여 CSR의 간이해석법의 적용 가능성을 검증하고, 화물하중 및 수압 과 같은 면외 하중(out of plane load)에 따른 이중저 굽힘으로 인한 최종 종강도 감소량을 계산하여 이에 대한 안전계수를 제시 하고자 하였다. 먼저, IACS의 CSR의 간이계산법을 사용하여 컨테이너선의 최 종 종강도를 계산한 결과를 Table 1에 나타내었다. 계산된 최종 종강도는 호깅(hogging) 조건에서 M (M = Ms + 1.2*Mw, 여기 서 Ms: 정수 중 굽힘 모멘트, Mw: 파랑 중 수직 굽힘 모멘트, 1.2: 신뢰성 해석을 통하여 결정된 Mw에 대한 부분 안전계수, CSR Part 1, Chap 5, Sec. 2.2 참조)의 150% 정도로 설계 종 강도와 비교하여 충분한 최종 종강도를 보유하고 있음을 알 수 있다. 그러나, CSR의 간이계산법은 화물 하중 및 수압 등의 면 외 하중에 의한 이중저 구조의 굽힘을 반영하지 못하고 있다. 따 라서, 이러한 면외 하중이 포함된 실제 운항조건을 고려할 경우 최종 종강도는 감소될 것이다. CSR의 간이계산법은 Smith 법(Smith’s method)로 알려진 방 법으로 선체횡단면을 구성하는 모든 구조부재를 보강판(one-bay pISSN:1225-1143, Vol. 52, No. 4, pp. 349-355, August 2015

According to SOLAS Regulation XII/6.5.3 and IMO GBS functional requirement(IMO, 2010), the structural redundancy of multi-bay stiffened panel in cargo area of bulk carrier should be provided enough in order to endure the initial design load though one bay of the stiffened panel is damaged due to plastic deformation or fatigue crack. To satisfy structural redundancy, Harmonized Common Structural Rules (hereinafter CSR-H, IACS, 2014) proposed to use 1.15 instead of 1.0 for buckling usage factor of stiffened panel in cargo area. This paper shows that buckling usage factor in CSR-H for structural redundancy is somewhat conservative considering the ultimate strength calculated by using nonlinear FEA for the damaged condition which is only one bay's plastic deformation due to colliding by weigh object like a bucket. Also, this paper presents that increasing of plate thickness only is more effective to get enough structural redundancy.

The blades of flexible propellers are formed by overlaying and adhering many layers of thin glass-fiber fabric sheets, are compressed and dried in the rigid mold. The current manufacturing process can not avoid the rather irregular deformation of the blades composed of non-isotropic non-uniform fabric structures, and inevitably introduces the different shape-forming errors between blades. In this paper, several flexible model propellers are precisely measured with three-dimensional optical instrument and compared with the original design geometry. The model propellers with the as-measured geometry are evaluated with the lifting-surface-theory-based propeller analysis code. The open-water performance are presented and discussed. The importance of the manufacturing accuracy is addressed to be able to apply the flexible propellers for propulsion of marine vehicles.

The high-skewed and/or composite propellers of current interests to reduce the ship vibration and to increase the acoustic performance are likely to be exposed to the unexpected structural problems. One typical example is that the added mass effect on the propellers working in the non-uniform wake field reduces the natural frequency of the propeller leading to the resonance with the low-frequency excitation of the external forces. To avoid this resonance problem during the design stage, the technique of fluid-structure interaction has been developed, but the higher-order effect of the blade geometry deformation is not yet considered in evaluating the added mass effects. In this paper the fluid boundary-value problem is formulated by the potential-based panel method in the inviscid fluid region with the velocity inflow due to the body deformation, and the structural response of the solid body under the hydrodynamic loading is solved by applying the finite element method which implements the 20-node iso-parametric element model. The fluid-structure problem is solved iteratively. A basic fluid-sturcture interaction study is performed with the simple rectangular plates of thin thickness with various planform submerged in the water of infinite extent. The computations show good correlation with the experimental results of Linholm, et al. (1965).

necessary to be able to evaluate the structural response of the blades to the hydrodynamic loadings, and then the influence of the blade deformation upon the hydrodynamic loadings. We use the lifting-surface-theory-based propeller analysis and design codes in solving the hydrodynamic problem, and the finite-element-method program formulated with 20-node iso-parametric solid elements for the analysis of the structural response. The two different hydrodynamic and structural programs are arranged to communicate through the carefully-designed interface scheme which leads to the derivation of the geometric parameters such as the pitch, the rake and the skew distributions common to both programs. The design of flexible propellers, suitable for manufacturing, is shown to perform the required thrust performance when deformed in operation. Sample design shows the fast iteration scheme and the robustness of the design procedure of the flexible propellers.

Recently, to reduce the noise and vibration levels of ships, hi gh skewed marine propellers with thinner thickness are adopted widely,however, such propeller design trend causes to reduce the stren gth of blades. Propeller blades are rotating continuously in ir regular wake field of ships. So, it is necessary to examine the strengt h of them precisely including from a viewpoint of fatigue stren gth. In present paper, the fatigue strength of propeller blades was inv estigated. Firstly, fatigue tests for Al Bronze, the representa tive propellermaterial, were carried out. The S-N curve was obtained for the assessment of the fatigue crack initiation life. And the material properties C, m for the fatigue crack propagation analysis base d on the Paris' equation were derived. For the 2nd stage, the s tructural responses of propeller blades in irregular ship wake field was carried out using the finite element analysis code. And the fat igue strength of propeller blades were considered based on the calcu lated stress levels and material characteristics for fatigue st rength.Keywords :Propeller blade(추진기 날개), Finite element structural analysis(유한 요소 구조해석), Fatigue strength analysis(피로강도해석), Fatigue test(피로실험), S-N approach(S-N 법), Crack propagation(균열진전)

In this study, we are focusing our attention on lift characteristics of the low aspect wings for Wing-In Ground effect crafts (WIG). Experimental measurements at an open-type wind tunnel are carried out and results are comparatively presented. In order to simulate the realistic ground condition in where the WIG craft is flying, moving ground is implemented by a conveyor belt rotating with the same velocity of the inflow. We consider two different wings (NACA0012 and DHMTU section) which have four different aspect ratios (0.5, 1.0, 1.5 and 2.0). Forces acting on the wings are measured and lift characteristics are elaborately investigated for various different conditions. In addition, end-plate effects are estimated. Results are validated by comparing with theoretic solutions of the symmetric airfoil. Present results show that ground effects are differently generated in moving or fixed ground conditions, and hence left characteristics are affected by the ground condition. Consequen tly, accurate aerodynamic forces acting on the WIG craft are guaranteed in a realistic moving ground condition.

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.

This paper deals with the structural assessment of metallic and non-metallic stiffened/monocoque plated marine structures unde r a lateral pressure load to identify appropriate combination of ma terial and section configuration, especially at the preliminary marine structural design stage. A generic rectangular plated structure is exemplified from the metallic superstructure of a marine ve ssel and itsstructural topology is varied for the structural assessment. In total 13 different structural t opologies are proposed and assessed using appropriate elastic solutions in conjunction with a set of stre ss and deflection limits obtained from practice. The geometry dimensions and weights of the structural topologies are calculated, and su bsequently, the costs of the materials used in the structural topologies are reviewed to discuss the cost-effectiveness of the materials . Finally, conclusions are made with the aim of suggesting suitable structural topology for the marine structural member considered in this paper.Keywords :Metallic stiffener section shape(금속재료 보강재 단면 형상), FRP stiffene r section shape(복합재료 보강재 단면 형상), Optimal sectionshape(최적 단면 형상), Structural assessment(구조적 평가), Weight effectiveness(중량 효율성), Cost effectiveness(비용 효율성)

A WIG(Wing-In-Ground effect) craft flies close to the water surface by utilizing a cushion of relatively high pressurized air between its wing and water surface. This implies that when one designs such craft it is important to have lightweight structures with adequate strength to resist external loads with some margins. To investigate this requirement, this paper dealswith the structural analysis of the bottom plate of small WIG craft having a design landing weight of 1.2-ton. As building materials for the WIG craft, pre-preg carbon/epoxy composites are considered. The strength information of the bottom plate isobtained using the first-ply-failure analysis in conjunction with a mid-plane symmetric laminated plate theory. As a result, thefirst-ply-failure location, load and deflection of the bottom plate are obtained. The calculated strength information is comparedwith the water reaction load for the bottom plate of seaplanes considered when they land on the water surface –the same fluid-structure interaction mechanism as that of WIG craft. In the calculation of seaplane water reaction load information, therules shown in FAR(Federal Aviation Regulations) Part 25 are used. Through the comparison, the structural integrity of the bottom plate for the WIG craft is checked.Keywords : WIG craft(위그선), Composites(복합재료), Bottom plate(선저판), Lamination scheme(적층계획), The first-ply-failure(적층판의 초기파괴), Structural integrity(구조 건전성)

The reliability analysis tool provided with the commercial structure-analysis package, ANSYS 9.0, is relatively easy to use and allows solutions to be rapidly obtained. However, the tool cannot guarantee the results of the reliability analysis since it can only provide an outline tendency of the probability of failure without giving an accurate numerical value of the probability of failure at the regions that a designer requires. The independent commercial reliability analysis code, NESSUSS 7.0, also has problems in that it may not necessarily converge and can waste computation time from having to undertake unnecessary repetitive structure analyses for design variables that have little significance to the structural integrity of the object being designed. A design methodology and a software module, which can make up for the current deficiencies in these commercial packages, have been developed by the authors and are presented in this paper. This paper describes how the methodology and the software module ...

A strength problem of propeller blades for large container ship s at astern condition has been occasionally reported due to the application of a highly skewed propeller which can reduce the hull surface fluctuation forces. A finite element analysis code for propeller blade was developed and utilized since 1985. Recently, however, furth er fine mesh modeling for finite element analysis is required to yield higher accuracy in the analysis. The present study shows an application of FE analysis code to the highly sk ewed propeller for large container ships. Results of FE analysis show that the number of FE mesh affects largely on strength, and also the calculated strength with fine mesh gives good agreements to those of other FEM codes. A method to enlarge strength near the trailing edge was introduced considering the strength criterion on the blade. ※Keywords: FE strength analysis(유한요소 강도해석), Highly skewed propeller(고스큐 프로펠러), Strength decrease(강성저하), Fine mesh(정밀 격자), Astern condition(역회전 상태)

A hybrid Cartesian/immersed boundary code is expanded to simulate flow field around a three-dimensional body which undergoes large dynamic deformation. Immersed boundary nodes are automatically distributed based on the edges crossing triangles on body boundary. Velocity vectors are reconstructed at those immersed boundary nodes along local normal lines to the boundary. The reconstruction of pressure is avoided using the hybrid staggered/non-staggered grid method. The developed code is validated through comparisons with other results on laminar flow over a sphere. The code is applied to simulate flow around a foil which is attached to a body of revolution and rotates under periodic deformation. The periodic variation of the tip vortex is observed and the effects of the deformation on hydrodynamic force acting on the body are investigated.

MOERI-KORDI (Maritime and Ocean Engineering Research Institute—Korea Ocean Research and Development Institute) has conducted the development of an unmanned underwater vehicle (UUV) for 6000 m deep-sea exploration, which was completed in 2006. Several pressure vessels were mounted on the UUV frame for loading electric and electronic equipment. The pressure vessels were constructed with titanium alloy Ti–6Al–4V for two main cylindrical canisters and with aluminium alloy Al6061–T6 for several hemispherical housings of electric motor drivers, respectively. This article presents the design process of the pressure vessels and experimental results acquired by high-pressure tests, which were conducted with the cooperation between MOERI-KRISO and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The pressure vessels were designed on the basis of the buckling analysis as well as structural yielding analysis, and checked the safety by the finite-element analysis (FEA) and analytical (empirical) formula...

To calculate the fluid-structure interaction(FSI) problem rationally, it should be the basic technology to analyse each domain of fluid and structure accurately. In this paper, a new FSI analysis algorithm was introduced using the 3D solid finite element for structural analysis and CFD code based on the HCIB method for viscous flow analysis. The fluid and structural domain were analysed successively and alternatively in time domain. The structural domain was analysed by the Newmark-b direct time integration sc heme using the pressure field calculated by the CFD code. The results for example calcu lation were compared with other research and it was shown that those coincided each other. So we can conclude that the developed algorithm can be applied to the general FSI probl ems. ※Keywords: FSI(Fluid-Structure Interaction), 3D FEM, CFD, HCIB method(Hybrid Cartesian/ Immersed Boundary 법), Newmark-β method 1. 서언 수중 혹은 공기 중에서 운동하는 구조체 또는 슬로싱, 슬래밍과 같은 유제 충격에 의한 선체의 동적 거동을 정확히 평가하여 설계에 반영하기 위한 노력은 오래 전부터 지속되어 왔다. 이러한 구조와 유체의 상호작용에 관한 문제는 초기에는 구

This paper presents an experimental study on deformations and force characteristics of flexible plates both in air and water. The focus is on the complicated interaction problem between the fluid and flexible structures. The displacements and forces of free oscillating plates are measured and compared with each others. The effects of several plate coefficients are investigated i.e. plate thickness, aspect ratio, plate area, plate width ratio, bending angle. For the verification of the experimental results, some of them are compared with numerical simulation and show reasonable agreements.

An experiment method has been developed to analyse the vibration characteristics of marine propeller blades, and vibration tests have been carried out on the model scale propeller in air and in water. The driving point transfer function(acceleration/excitation force) has been measured and modified by compensating the attachment effect of the impedance head. The measured natural frequencies in air have been compared with the theoretical results by an in-house FEM code PROSTEC. The added masses have been derived by comparing the measured natural frequencies in air and in water, and the results have been compared to the results using existing formula based on experience.

Several types of steel structures which are employed in offshore petroleum activities are constructed with tubular members. These structures are usually subjected to various types of loads such as normal functional loads and environmental loads. Furthermore, accidental loads may also act on the leg or bracing members due to supply boat collisions and objects droppings from platform decks. The extent of damage caused by these loads ranges from total collapse of the structure to small damage which may not have serious consequence at the time of accident. To make optimal design decisions regarding structural safety and economical efficiency, it is very important to be able to assess the influence of damages on the performance of damaged structural members. In the End report, a series of calculations is performed to study the effects of different parameters on the load carrying capacity of such damaged members under pure bending. And the results of analysis are compared with experiment results.

Loads on offshore structures are largely transferred to the bracing members in the form of axial forces. The detrimental effects of imperfections on compressive strength are well recognized. Damage in the members of offshore structures would significantly affect the compressive behavior of the members. As a result, such damages may also affect the ability of the structure to withstand the functional and environmental loads. It is important to be able to assess the residual strength of damaged members quickly and accurately. This will help operators to make the decision whether the member has to be repaired or not. In this study, a series of calculation is performed to study the effects of different parameters on the behavior of such damaged members under axial load. And the results of analysis are compared with those of experiment.

The flaring system of FPSO burns out the byproduct natural gas. The thermal loading due to radiative heat of flaring gas leads to undesirable thermal-stresses on itself. Nowadays it needs to understand the amount of thermal loading of flaring system since the requirement for the safety of the flaring system. However, few studies have been performed on the thermal environment and radiative heat flux on the FPSO flaring system. Present study suggests a procedure to model the thermal environment and a FEA process to analyze the temperature distribution and thermal stresses of FPSO flaring system. In order to get the temperature distribution, the radiative heat conditions and convective heat conditions are included in the heat transfer analysis. By making the use of temperature obtained through heat transfer analysis, the thermal stress analyses are performed. The results of the present study can be used to design the flaring system and determine the heat shield in the flaring system

The interaction between a ship and sea ice is a complex process depending on the ice properties, the ice geometry and the relative velocity between the ship and the ice. The effect of important parameters such as ship speed and ice thickness on the impact force are studied by means of finite element model. Idealized ice element types are applied to finite element model in order to survey the impact force and the structural response of icebreaker ARAON subjected to sea ices. Interaction behaviors obtained by finite element model considering the varying parameters are also discussed to compare the numerical results with the design data of ARAON.Copyright © 2014 by ASME

A finite element analysis model for material and geometrical non-linearities due to large plastic deformations of ductile materials is presented using the continuum damage mechanics approach. To overcome limitations of the conventional plastic analysis, a fourth-order tensor damage, defined in Part I of this paper to represent the stiffness degradation in the finite strain regime, is incorporated. General forms of an updated Lagrangian (U.L.) finite element procedure are formulated to solve the governing equations of the coupled elastic–plastic-damage analysis, and a computer program is developed for two-dimensional plane stress/strain problems. A numerical algorithm to treat the anisotropic damage is proposed in addition to the non-linear incremental solution algorithm of the U.L. formulation. Selected examples, compared with published results, show the validity of the presented finite element approach. Finally, the necking phenomenon of a plate with a hole is studied to explore plastic damage in large strain deformations.

During past decades, many material models using the continuum damage mechanics (CDM) approach have been proposed successfully in the small deformation regime to describe inelastic behaviors and fracturing phenomena of a material. For ductile materials, large deformation takes place at the level of damage appearance. Damage is anisotropic in nature. In this paper, the ductile damage at finite deformations is modeled as an anisotropic tensor quantity. Then, a fourth-order symmetric stress correction tensor is proposed for computationally efficient and easy implementation in the finite element formulations. Consequently, an explicit form of the fourth-order constitutive equations of the proposed elastic-plastic-damage model is derived. Both isotropic and kinematic hardening effects are included in the formulation. The new constitutive model can predict not only the elastic-plastic behaviors, but also the sequential variations of ductile materials. An evaluation of the constitutive and damage evolution equations is presented.

Sloshing assessment of LNG cargo tanks is expected to satisfy the required structural strength of insulation components. It is difficult to estimate the sloshing pressure and structural response of cargo containment in real size because of the uncertainty of intensive computation time as well as the complexity of sloshing motion. In this study, several procedural components are suggested to meet the endurable strength of LNG CCS during the design of LNG cargo containment. The measured sloshing impacts from small scale model test are treated by individual impacts. Thereafter, static and transient structural response of LNG CCS is sequentially performed in order to evaluate the structural strength. The structural response is also calculated in time series through convolution method considering the history of pressure. It is used to investigate the structural response induced by the history of impacts. Finally, an idealized fluid structure interaction on the localized insulation panel is investigated in order to evaluate the structural strength in actual scale.

WIG(Wing-In-Ground effect) craft flies close to the water surface by utilizing a cushion of relatively high pressurized air between its wing and the water surface. This implies that such a craft needs to have lightweight structures with adequate strength to resist external hydrodynamic loads. As a part of ongoing efforts at designing, this paper performs the strength assessment of the stiffened FRP panels of small WIG craft. WIG craft considered in this paper has a design landing weight of 1.5-ton and carbon/epoxy composite materials are used extensively to satisfy the design weight of the structural members. The strength assessment of the stiffened FRP panels is done in accordance with the procedures developed within the first-ply-failure regime in conjunction with the selection of a laminated composite plate theory and failure criteria for anisotropic materials. Structural configurations of the panel are varied under the constraint of equal panel weight. They are laminated composite plates having different ply stacking sequences and sandwich plates having different core materials. As a result, the loads and deflections that produce failures, in terms of the first-ply-failure, are calculated and useful findings are derived for the structural design of WIG craft.