Full Stochastic Fatigue Analysis of Stiffened Panels Subjected to Wave Slamming

2008 ◽  
Author(s):  
Dilnei Schmidt ◽  
Carlos A. Bardanachvili ◽  
Paulo M. Videiro
Keyword(s):  
Structural Analysis ◽  
Time Domain ◽  
Ocean Basin ◽  
Sea Surface ◽  
Stiffened Panel ◽  
Random Wave ◽  
Offshore Structure ◽  
Stiffened Panels ◽  
Wave Slamming ◽  
Supporting Structures

The aim of the present work is the evaluation of the fatigue lifespan of a horizontal stiffened panel of an offshore structure subjected to random wave slamming. In order to achieve this objective, a methodology for time-domain slamming prediction was developed. Time series for the relative distance and velocity between the bottom panel and sea surface and the angle between the panel and the sea surface are simulated to provide a way to evaluate when the slamming occurs and the loads associated with slamming, using factor calibrated after a model test on ocean basin. With the loads obtained from these simulations, the structural analysis is then performed, considering all the shell plating, main stiffeners as well as other main supporting structures, by using a finite element structural analysis. The fatigue lifespan is estimated in a complete stochastic analysis, considering all possible sea states during the lifetime of the offshore structure as well as each probability of occurrence associated. All phases of the methodology used for the evaluation of the slamming loads and the fatigue analyses are presented.

Response Based Time Domain Structural Analysis on Floating Offshore Platform

2019 ◽  
Author(s):  
Johyun Kyoung ◽  
Sagar Samaria ◽  
Jang Whan Kim ◽  
Brian Duffy
Keyword(s):  
Structural Analysis ◽  
Time Domain ◽  
Phase Relationship ◽  
Time History ◽  
Offshore Platform ◽  
Time Interval ◽  
Floating Platform ◽  
Offshore Structure ◽  
Offshore Industry ◽  
External Loads

Abstract Performing the structural analysis and its integrity evaluation is the ultimate goal of design. However, design value estimation based on load-based analysis is still used as a conventional procedure in the offshore industry. The conventional method can be overly conservative and unrealistic with inconsistent load conditions since external loads such as mooring/riser and higher order hull response is inconsistently considered based on simplified linear assumptions. To assess the reliable integrity of a floating offshore platform, the response-based analysis has been successfully applied. This paper presents a response-based time domain structural analysis of a floating offshore platform. Direct time domain structural analysis is applied by mapping of external environment loads on the floating platform at every instantaneous time interval. Accordingly, correct phase relationship between the various external loads and hull motion including nonlinear effects can be considered. For computational efficiency, present study uses a set of load components based on an efficiently selected basis function for hull motion and environment loadings. The stress time history is obtained directly by synthesizing the load components, and hence an actual time-domain structural response can be captured effectively. Thus, same structural analysis results can be used to evaluate both strength and fatigue criterion for a floating offshore structure. Present analysis method is successfully applied to the evaluation of extreme global strength for a conventional semisubmersible platform. Present time domain analysis result on the structure response is compared with conventional load-based analysis result.

Extreme Response Prediction for Fixed Offshore Structures by Monte Carlo Time Simulation Technique

2016 ◽  
Author(s):  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
M. B. Johari ◽  
G. Najafian
Keyword(s):  
Monte Carlo ◽  
Statistical Properties ◽  
Simulation Technique ◽  
Random Wave ◽  
Wave Loading ◽  
Offshore Structure ◽  
Sampling Variability ◽  
Time Simulation ◽  
Wide Range ◽  
Extreme Response

For an offshore structure, wind, wave, current, tide, ice and gravitational forces are all important sources of loading which exhibit a high degree of statistical uncertainty. The capability to predict the probability distribution of the response extreme values during the service life of the structure is essential for safe and economical design of these structures. Many different techniques have been introduced for evaluation of statistical properties of response. In each case, sea-states are characterised by an appropriate water surface elevation spectrum, covering a wide range of frequencies. In reality, the most versatile and reliable technique for predicting the statistical properties of the response of an offshore structure to random wave loading is the time domain simulation technique. To this end, conventional time simulation (CTS) procedure or commonly called Monte Carlo time simulation method is the best known technique for predicting the short-term and long-term statistical properties of the response of an offshore structure to random wave loading due to its capability of accounting for various nonlinearities. However, this technique requires very long simulations in order to reduce the sampling variability to acceptable levels. In this paper, the effect of sampling variability of a Monte Carlo technique is investigated.

scholarly journals Effects of plies orientations and initial geometric imperfections on buckling strength of a composite stiffened panel

2018 ◽  
Vol 191 ◽  
pp. 00008
Author(s):  
Ikram Feddal ◽  
Abdellatif Khamlichi ◽  
Koutaiba Ameziane
Keyword(s):  
Stiffened Panel ◽  
Buckling Mode ◽  
Element Analysis ◽  
Geometric Imperfections ◽  
Stiffened Panels ◽  
Specific Strength ◽  
Euler Buckling ◽  
Buckling Behavior ◽  
Composite Stiffened Panel ◽  
Strength And Stiffness

The use of composite stiffened panels is common in several activities such as aerospace, marine and civil engineering. The biggest advantage of the composite materials is their high specific strength and stiffness ratios, coupled with weight reduction compared to conventional materials. However, any structural system may reach its limit and buckle under extreme circumstances by a progressive local failure of components. Moreover, stiffened panels are usually assembled from elementary parts. This affects the geometric as well as the material properties resulting in a considerable sensitivity to buckling phenomenon. In this work, the buckling behavior of a composite stiffened panel made from carbon Epoxy Prepregs is studied by using the finite element analysis under Abaqus software package. Different plies orientations sets were considered. The initial distributed geometric imperfections were modeled by means of the first Euler buckling mode. The nonlinear Riks method of analysis provided by Abaqus was applied. This method enables to predict more consistently unstable geometrically nonlinear induced collapse of a structure by detecting potential limit points during the loading history. It was found that plies orientations of the composite and the presence of geometric imperfections have huge influence on the strength resistance.

scholarly journals The Prediction of Buckling Load of Laminated Composite Hat-Stiffened Panels Under Compressive Loading by Using of Neural Networks

2018 ◽  
Vol 12 (1) ◽  
pp. 468-480 ◽  
Author(s):  
Shashi Kumar ◽  
Rajesh Kumar ◽  
Sasankasekhar Mandal ◽  
Atul K. Rahul
Keyword(s):  
Neural Network ◽  
Finite Element ◽  
Network Architecture ◽  
Laminated Composite ◽  
Buckling Load ◽  
Stiffened Panel ◽  
Stiffness Ratio ◽  
Data Set ◽  
Stiffened Panels ◽  
Structural Problems

Background:Stiffened panels are being used as a lightweight structure in aerospace, marine engineering and retrofitting of building and bridge structure. In this paper, two efficient analytical computational tools, namely, Finite Element Analysis (FEA) and Artificial Neural Network (ANN) are used to analyze and compare the results of the laminated composite 750-hat-stiffened panels.Objective:Finite Element (FE) is an efficient and versatile method for the analysis of a complex problem. FE models have been used to generate data set of four different parameters. The four parameters are extensional stiffness ratio of skin in the longitudinal direction to the transverse direction, orthotropy ratio of the panel, the ratio of twisting stiffness to transverse flexural stiffness and smeared extensional stiffness ratio of stiffeners to that of the plate.Results and Conclusion:For training of ANN, multilayer feedforward back-propagation has been used as a network function with two-hidden layers in the neural network. The good network architecture is achieved after several iterations to predict the buckling load of the stiffened panel. ANN prediction for unknown new data set is in good agreement with FEA results of different cases, which show that ANN tool can be used for the design of complex structural problems in civil engineering and optimization of the laminated composite stiffened panel.

Seismic Analysis of a Double-Hinged Articulated Offshore Tower

2008 ◽  
Author(s):  
Syed Danish Hasan ◽  
Nazrul Islam ◽  
Khalid Moin
Keyword(s):  
Seismic Analysis ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Forces ◽  
Offshore Structure ◽  
Concentrated Mass ◽  
Energy Principle ◽  
Rotational Angle ◽  
Sea Bed ◽  
Time Histories

The response of offshore structures under seismic excitation in deep water conditions is an extremely complex phenomenon. Under such harsh environmental conditions, special offshore structures called articulated structures are feasible owing to reduced structural weight. Whereas, conventional offshore structure requires huge physical dimensions to meet the desired strength and stability criteria, therefore, are uneconomical. Articulated offshore towers are among the compliant offshore structures. These structures consist of a ballast chamber near the bottom hinge and a buoyancy chamber just below the mean sea level, imparting controlled movement against the environmental loads (wave, currents, and wind/earthquake). The present study deals with the seismic compliance of a double-hinged articulated offshore tower to three real earthquakes by solving the governing equations of motion in time domain using Newmark’s-β technique. For this purpose Elcentro 1940, Taft 1952 and Northridge 1994 earthquake time histories are considered. The tower is modeled as an upright flexible pendulum supported to the sea-bed by a mass-less rotational spring of zero stiffness while the top of it rigidly supports a deck in the air (a concentrated mass above water level). The computation of seismic and hydrodynamic loads are performed by dividing the tower into finite elements with masses lumped at the nodes. The earthquake response is carried out by random vibration analysis, in which, seismic excitations are assumed to be a broadband stationary process. Effects of horizontal ground motions are considered in the present study. Monte Carlo simulation technique is used to model long crested random wave forces. Effect of sea-bed shaking on hydrodynamic modeling is considered. The dynamic equation of motion is formulated using Lagrangian approach, which is based on energy principle. Nonlinearities due to variable submergence and buoyancy, added mass associated with the geometrical non-linearities of the system are considered. The results are expressed in the form of time-histories and PSDFs of deck displacement, rotational angle, base and hinge shear, and the bending moment. The outcome of the response establishes that seismic sea environment is an important design consideration for successful performance of hinges, particularly, if these structures are situated in seismically active zones of the world’s ocean.

Finite Element Analysis of Top-Hat–Stiffened Panels of Fiber-Reinforced–Plastic Boat Structures

2007 ◽  
Vol 44 (01) ◽  
pp. 16-26
Author(s):  
Ömer Eksik ◽  
R. Ajit Shenoi ◽  
Stuart S. J. Moy ◽  
Han Koo Jeong
Keyword(s):  
Finite Element ◽  
Lateral Pressure ◽  
Three Dimensional ◽  
Element Model ◽  
Stiffened Panel ◽  
Element Analysis ◽  
Stiffened Panels ◽  
Fiber Reinforced Plastic ◽  
Reinforced Plastic ◽  
Experimental Findings

This paper describes the development of a finite element model in order to assess the static response of a top-hat-stiffened panel under uniform lateral pressure. Systematic calculations were performed for deflection, strain, and stress using the developed model based on the ANSYS three-dimensional solid element (SOLID45). The numerical modeling results were compared to the experimental findings for validation and to further understand an internal stress pattern within the different constituents of the panel for explaining the likely causes of the panel failure. Good correlation between experimental and numerical strains and displacements was achieved.

The Effect of Ply Orientation and Damage Detection in Composite Stiffened Panel Using Lamb Waves

2019 ◽  
Vol 298 ◽  
pp. 161-166
Author(s):  
Ouadia Mouhat ◽  
Abdelmajid Bybi ◽  
Ahmed El Bouhmidi ◽  
Hasnae Boubel ◽  
Omaima Elmrabet ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Composite Structures ◽  
Laminate Composite ◽  
Lamb Waves ◽  
Stiffened Panel ◽  
Signal Acquisition ◽  
Frequency Increase ◽  
Stiffened Panels ◽  
Composite Stiffened Panel ◽  
Ply Orientation

The present work proposes a vibration study with different surface and layers orientations at 0°, 15°, 30°, 45°, 60°, 75° and 90°using the Abaqus finite element code, the frequencies Stratified laminate composite panels were studied and the comparison between damaged structures and perfect structures we used stiffened panels based on T-shaped reinforced fibers. Lamb waves (LW) were widely proposed for the long-range inspection of Structural Structural Health Monitoring (SHM) oriented composite structures, the obtained results show the angle effects on the natural frequency increase at a peak then decrease in the form of a sinusoidal half-curve and the numerical results found in this work can be compared to those of other authors in the same area of ​​research, A piezoelectric actuator is used to design acoustic waves and a sensor is used for signal acquisition.

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