Hydroelastic Response of a Ship Structural Detail to Seakeeping Loads Using a Top-Down Scheme

2012 ◽  
Author(s):  
François-Xavier Sireta ◽  
Quentin Derbanne ◽  
Fabien Bigot ◽  
Šime Malenica ◽  
Eric Baudin
Keyword(s):  
Fatigue Life ◽  
Life Assessment ◽  
Mode Shapes ◽  
Fe Model ◽  
Structural Detail ◽  
Top Down ◽  
Local Pressure ◽  
Ship Structure ◽  
Fine Mesh ◽  
Structural Details

In order to investigate the local response of a ship structure, it is necessary to transfer the seakeeping loading to a 3DFEM model of the structure. A common approach is to transfer the seakeeping loads calculated by a BEM method to the FEM model. Following the need to take into account the dynamic response of the ship to the wave excitation, some methods based on a modal approach have been recently developed that include the dry structural modes in the hydro-structure coupling procedure and allow to compute the springing and whipping response of the ship structure to the seakeeping loads. In the context of the fatigue life assessment of a structural detail, a very fine FE model is required. A very large number of seakeeping loading cases also need to be considered to account for all the conditions encountered by the ship through its life. It becomes then clear that because of the CPU time issue, the whole FE model can not be very fine. This is why a hierarchical top-down analysis procedure is commonly used, in which the global ship structure is modelled in a coarse manner using one finite element between web frames. The structural details are modelled separately using a fine meshing. Such top-down methods are commonly used for the estimation of the quasi-static response of structural details to the seakeeping loads. This paper presents a methodology in which a top-down method is used to estimate the springing response of a ship structural detail loaded with wave pressure, and its fatigue life. The global dry structural modes are transferred to the detail fine model using the shape functions of the finite elements of the global model. The hydrodynamic pressures are computed directly on the fine mesh model, avoiding any interpolation error. The imposed displacements at the fine mesh boundary are computed using the same method that is used to transfer the structural mode shapes, and the local pressure induced loads and inertia loads are applied on the fine mesh nodes. This method is applied for the calculation of the elongation of a strain gauge which is installed in the passage way of an ultra large container ship.

scholarly journals FATIGUE LIFE ASSESSMENT OF REACTOR COOLANT SYSTEM COMPONENTS BY USING TRANSFER FUNCTIONS OF INTEGRATED FE MODEL

2010 ◽  
Vol 42 (5) ◽  
pp. 590-599 ◽  
Author(s):  
Shin-Beom Choi ◽  
Yoon-Suk Chang ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
Myung-Jo Jhung ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Transfer Functions ◽  
Life Assessment ◽  
Fe Model ◽  
Reactor Coolant ◽  
Fatigue Life Assessment ◽  
System Components ◽  
Coolant System

The Application of S-N Curves Considering Mismatch of Stress Concentration Between Test Specimen and Structure

1998 ◽  
Vol 42 (01) ◽  
pp. 68-78
Author(s):  
Sergei V. Petinov ◽  
Anil K. Thayamballi
Keyword(s):  
Test Specimen ◽  
Local Strain ◽  
Statistical Correlation ◽  
Life Assessment ◽  
Structural Detail ◽  
Numerical Examples ◽  
Fatigue Life Assessment ◽  
Allowable Stresses ◽  
Structural Details ◽  
Conventional Manner

This paper presents a procedure for the adjustment of S-N diagrams for noncontinuous welded joints in the fatigue analysis of structural details. The adjustment takes into account the effects of differences in geometry between the test specimen underlying the S-N curve and the hull structural detail it is applied to, considering the inelastic response of material at the anticipated crack origin, multiple modes of loading, and their statistical correlation. The basis of the approach is a comparison of relative fatigue lives for the structural detail of interest and the corresponding baseline specimen, using the local strain approach to fatigue, with extensions to the high-cycle regime. An S-N diagram so corrected is used in the conventional manner to predict fatigue damage or to establish related allowable stresses. The procedure developed is thus entirely compatible with present fatigue life assessment methods. The developed procedure is illustrated through numerical examples.

Fatigue Life Assessment of Fillet Welded Joint Considering the Relaxation and Redistribution of Residual Stresses

2004 ◽  
Author(s):  
Chang Doo Jang ◽  
Ha Cheol Song ◽  
Young Chun Jo
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Stress Relaxation ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Welded Joint ◽  
Life Assessment ◽  
Ship Structure ◽  
Fatigue Life Assessment ◽  
Plastic Analysis

This paper presents the fatigue life assessment procedure for the welded joint of ship structure. Test model is a boxing fillet specimen, the idealized welded joint model of longitudinal and transverse members in ship structure. Fatigue test was executed according to the 14-points S-N method of JSME, and experimental data were presented in the S-N curve based on HSS (Hot Spot Stress) approach. To define the fatigue life of crack initiation and crack propagation, S-N data for each length of crack were appraised. In this study, the new FE analysis algorithms for the estimation of residual stress relaxation due to external load and residual stress redistribution due to crack propagation were proposed to assess the effect of residual stresses on crack growth precisely. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis. In the analysis of crack propagation, the SIF (Stress Intensity Factor) range was evaluated by 1/4-point displacement extrapolation method, and the effect of welding residual stresses on fatigue behaviors was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data from the analysis.

Parameter Adaptation With Automatically Selected Co-Ordinates From Measured Eigenvectors As a Way to a Validated FE Model

1997 ◽  
Author(s):  
Manfred W. Zehn ◽  
Gerald Schmidt ◽  
Oliver Martin
Keyword(s):  
Mode Shape ◽  
Degrees Of Freedom ◽  
Natural Frequencies ◽  
High Sensitivity ◽  
Mode Shapes ◽  
Problem Solver ◽  
Fe Model ◽  
Parameter Adaptation ◽  
Fine Mesh ◽  
Reduction Techniques

Abstract This paper considers an algorithm on the basis of parameter adaptation for mass and stiffness embedded in the eigenvalue problem solver. The algorithm is intended for large finite element (FE) models. The errors, which can be reduced by the procedure described in this paper, occur due to detailed features, which would require an unduly fine mesh to be included in the model, or in uncertainties in the description of mechanical behaviour, material properties, etc. Another source for errors are model reduction techniques (superelement technique) necessary for the application of the model structure in an automatic control circuit (smart structures). It is a well-known fact that the natural frequencies can be measured much more accurately than mode shapes, for mode shapes can only be measured for accessible regions and normally for translational degrees of freedom (DOF). Therefore the algorithm uses only measured natural frequencies (frequency differences) and the calculated mode shape vectors to determine the parameter changes. In a new approach it is also possible to select automatically, or by experience, those co-ordinates from the measured mode shape vectors that correspond to points with high sensitivity or other very reliable points. An interface system designed to exchange data between the experimental modal analysis system (EMA) and the FE program ensures, that the measured and calculated mode shape vectors are orthonormalised in the same way and the points of the FE mesh correspond to the pick up points for the measurement. Examples of industrial parts at the end of the paper illustrate how the procedure works and what influence we can obtain by inclusion of some co-ordinates of measured mode shape vectors.

Modal Analysis of the Setar: A Numerical–Experimental Comparison

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hossein Mansour
Keyword(s):  
Modal Analysis ◽  
Laser Doppler Vibrometer ◽  
Mode Shapes ◽  
Experimental Comparison ◽  
Fe Model ◽  
Fe Method ◽  
Wide Range ◽  
Structural Details ◽  
Orthotropic Properties ◽  
Structural Mode

The setar, a Persian long-necked lute, is analyzed by means of experimental modal analysis and finite element (FE) method. The experimental analysis is performed using a combination of impulse hammer and laser Doppler vibrometer (LDV), which has led to the extraction of structural mode shapes, natural frequencies, and modal dampings. The FE model is developed taking into account structural details, such as orthotropic properties of the wood, direction of the grains, nonideal joints, and the effect of strings preload. Numerical results are shown to be in a very good agreement with the experimental data over a wide range of frequencies.

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