In Sik Nho

A finite element approach to anisotropic damage of ductile materials in large deformations Part I: an anisotropic ductile elastic-plastic-damage model

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.

A Study on Simplified Sloshing Impact Response Analysis for Membrane-Type LNG Cargo Containment System

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.

Non-linear Large Deformation Analysis of Elastic Rubber Mount

AbstractA lot of equipments installed in ships must be isolated for rel axing the shock, vibration and noise using the elastic mounts. Most of the elastic mounts are made of the rubber, however it is not easy to design the effective rubber mount. Because, in general, the rubber has a non-linear constitutive characteristics especially for a large deformation. So, there are many difficulties to estimate the accurate structural response of rubber which is the basis of the shape design of the mounts. In this study, the detailed non-linear viscoelastic large deformation finite element analysis method w as dealt with. And to verify validity of the present analysis scheme, the results were compa red with experiments. ※Keywords: Viscoelastic(점탄성), Elastic mount(탄성마운트), Large deformation(대변형), Hyper-elastic(초탄성) 1. 서 론 선박의 탑재 장비는 진동/소음/충격의 완화를 위하여 선체로부터 시스템을 절연해야 할 필요가있다. 특히 함정에 탑재되는 장비는 수중충격 뿐 접수일: 2007년 12월 28일 승인일: 2008년 4월 8일✝교신저자, isnho@cnu.ac.kr, 016-403-6622 만 아니라 수중방사소음에 대한 까다로운 제한 조건 때문에 주로 고무재질로 이루어진 탄성 지지 마운트가 개발/사용되고 있다(Choi et al. 2002). 그러나 고무 재질 자체가 시간의존적인 점탄성 거동을 포함하는 고도의 비선형적인 응력-변형률 특성을 지니고 있어 이론적으로는 정확한 성능 예측이 어려운 실정이다. 또한 정확한 해석 기법의 부재로 인하여 탄성 마운트를 설계/제작하는 과정에

A finite element approach to anisotropic damage of ductile materials in large deformations Part II: finite element formulation and applications

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.

Design Algorithm of Flexible Propeller by Fluid-Structure Interactive Analysis

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.

A Fundamental Study for Time History Modeling of Fluid Impact Pressure

AbstractTo consider effects of essential parameters of water impact pressure on dynamic structural responses of bow bottom structures, a parametric study for a ship bottom panel is carried out. The idealized pressure time history models were assumed by triangular and rectangular shapes in time domain. The main loading parameters are duration time and peak pressure value maintaining the same impulse value. The str uctural models for local bottom stiffened panels of a container ship are analysed. The n atural frequency analysis and transient dynamic response analysis are performed using MSC /NASTRAN. Added mass effects of contacting water are considered and the pressure dis tributions are assumed to be uniform in the whole water contacting surface. The effects of loading parameters on the structural responses, especially maximum displacements, are con sidered. Besides the peak pressure value, effects of duration time correlated with natural frequencies are thought to be the important parameters.

Design of Highly Skewed Propeller considering the Blade Strength

AbstractA 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)

MarkIII LNG 방열 시스템의 강도평가를 위한 삼각형 충격 하중에 대한 구조응답에 대한 연구

It has been well known the sloshing pressure has complex shape and various patterns. The pattern of sloshing pressure is variously characterized by the pressure amplitude, duration time and skewness. The structural response induced by the sloshing pressure is also affected by the pattern of sloshing pressure and the type of structural members. In order to understand the structural response by the perspective view of categorized pattern, it is more efficient to make simple sloshing pressure pattern than to reflect the complex pressure history. In this study, the sloshing pressures obtained by the small scale model test are simplified with respect to their duration and skewness. Dynamic analyses of Mark-III LNG CCS are then parametrically performed with the consideration of various types of sloshing impact. Meanwhile, the failure pressures given the duration and skewness are investigated after parametric calculations are conducted to investigate the effect of pressure parameters on the structural response.

Structural Safety Assessment of Mark III Membrane Type Liquid Natural Gas Cargo Containment System under Ice Collision

In this study, a method for analyzing the collision and interaction between ice bergy bits and a Mark III type liquid natural gas (LNG) carrier was considered, and the structural safety of a ships hull and cargo containment system (CCS) was evaluated. In the analysis, a constitutive model implementing the strain rate dependant mechanical propert y was used to consider the typical material characteristics of ice rationally. A relatively simple and easy ice structure interaction analysis p rocedure, compared with the accurate but complicated FSI analys is scheme, was suggested. When the ice bergy bits collided with ships side hull under the four assumed scenarios, the structural behaviors of the ship structure and LNG CCS were simulated by applying the suggested ice collision analysis procedure using the commercial hydro-code LS-DYNA. In addition, the effects of the shapes and colliding speed of the ice bergy bits on the ice-str ucture interaction and safety of the CCS were examined in detail.

Structural Assessment of the Optimal Section Shape of FRP Based Stiffeners

Abstract 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)