A Method for Designing the Backbone for the Segmented Model of an Ultra-Large Container Carrier

2019 ◽  
Author(s):  
Hui Li ◽  
Jian Zou ◽  
Weijia Sheng ◽  
Xuecong Hu ◽  
Wenjia Hu
Keyword(s):  
Experimental Studies ◽  
Complex Form ◽  
Bending Moment ◽  
Torsional Stiffness ◽  
Mode Shapes ◽  
Wave Loads ◽  
Torsional Moment ◽  
Wave Load ◽  
Segmented Model ◽  
Vertical Bending Moment

Abstract The segmented model test is often used to study the wave load characteristics of large ships as it can account for the hydroealstic effect. The vertical bending moment (VBM) is of crucial importance in ensuring the safety of ocean-going vessels in rough seas, and there exists in the literature a large number of experimental studies of the VBM. For ships with large openings in the deck, for instance, container ships, the lateral wave loads, such as horizontal bending moment (HBM) and torsional moment (TM) in quartering seas, are as important as VBM. There are, however, few studies on the measurement of the coupled horizontal-torsional vibrations of such ships in model tests. In the paper, a method is proposed for designing flexible backbone models that satisfy the similarities of vertical and horizontal bending stiffness as well as the torsional stiffness, and the measurement of the wave load components is also described. In order to meet the similarity of the hull girder stiffness, the backbone cross-section of a complex form is designed. Finite element method (FEM) is used to calculate the natural frequencies and mode shapes of the segmented model. Measurement of the vertical bending moment, horizontal bending moment and torsional moment are calibrated by applying various combinations of loads.

scholarly journals Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran

2015 ◽  
Vol 59 (02) ◽  
pp. 69-84
Author(s):  
Jason John McVicar ◽  
Jason Lavroff ◽  
Michael Richard Davis ◽  
Giles Thomas
Keyword(s):  
High Speed ◽  
Bending Strength ◽  
Experimental Studies ◽  
Bending Moment ◽  
Higher Order ◽  
Acute Angle ◽  
Beam Model ◽  
Higher Order Modes ◽  
Hull Structure ◽  
Vertical Bending Moment

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.

Improvement of Wave Loads Estimation From Spatial Pressure Distribution on Ship Hull

2019 ◽  
Author(s):  
Kurniawan T. Waskito ◽  
Masashi Kashiwagi
Keyword(s):  
Pressure Distribution ◽  
Pressure Sensors ◽  
Estimation Method ◽  
Bending Moment ◽  
Ship Hull ◽  
Accurate Estimation ◽  
Wave Loads ◽  
Local Pressure ◽  
Shipbuilding Industry ◽  
Vertical Bending Moment

Abstract In modern shipbuilding industry, merchant ships tend to increase in size. Accurate prediction of the vertical bending moment in large-maplitude waves has become important for structural design. For establishment of an accurate estimation method, more detailed local hydrodynamic quantities such as the spatial pressure distribution on the whole ship hull surface should be checked. For that purpose, the experiment has been conducted by means of Fiber Bragg Grating (FBG) sensing technology. Using the measured local pressure distribution by only sticking the FBG pressure sensors onto the hull surface, we can evaluate the wave loads; which may lead to establishment of a new evaluation method for the wave loads without using a segmented model. We confirm favorable agreement of the pressure distribution between measurement and computation by Rankine Panel Method (RPM). Furthermore, the vertical bending moment computed at some transverse sections shows favorable agreement between measured and computed results.

Determination of global design loads for large high-speed catamarans

2002 ◽  
Vol 216 (1) ◽  
pp. 79-94
Author(s):  
S E Heggelund ◽  
T Moan ◽  
S Oma
Keyword(s):  
High Speed ◽  
Bending Moment ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear ◽  
Design Loads ◽  
Linear Effects ◽  
Operational Criteria ◽  
Vertical Bending Moment

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

scholarly journals Effects of wave loads on the strength of semisubmersible drilling platform

2021 ◽  
Vol 9 (4B) ◽  
Author(s):  
Fei Wang ◽  
◽  
Xiong Deng ◽  
Keyword(s):  
Numerical Model ◽  
Service Life ◽  
Response Spectra ◽  
Ocean Wave ◽  
Wave Loads ◽  
Torsional Moment ◽  
Shearing Force ◽  
Wave Load ◽  
Failure Risk ◽  
High Level

In order to reduce the failure risk of the structures of semisubmersible drilling platform during its service life, this research studies the effects of ocean wave loads on the strength of the platform’s structures. The response spectra of the platform obtained from model test in wave tank were used to verify the accuracy of the numerical model employed in this research. Eight wave load cases, which may affect the strength of the platform but not involved in the classification societies such as ABS and DNV, were newly considered in this research. The results of the research indicate that a) four of the eight newly added wave load cases are found to be greatly affecting the strength of the platform and need to be considered in designing the structures; b) torsional moment and shearing force caused by the ocean wave would cause the stress of the structures of platform at a high level and need to be carefully evaluated.

Probabilistic Analysis of Nonlinear Wave Loads on Ships Using Weibull, Generalized Gamma, and Pareto Distributions

2004 ◽  
Vol 48 (03) ◽  
pp. 202-217
Author(s):  
Lihua Wang ◽  
Torgeir Moan
Keyword(s):  
Nonlinear Wave ◽  
Probabilistic Analysis ◽  
Goodness Of Fit ◽  
Bending Moment ◽  
Wave Loads ◽  
Wave Load ◽  
Threshold Method ◽  
Generalized Gamma ◽  
Time Histories ◽  
Load Peak

The statistics of nonlinear wave- induced bending moment in ship hull girders in a short-term period is studied. Systematic probabilistic analysis is performed directly on wave load time histories for different ship types under various sea state and ship speed conditions. The order statistics concept and peak-over-threshold method are used for estimation of the extreme wave loads. The generalized gamma, generalized Pareto, and Weibull distributions are utilized for describing wave load peak values. The three distributions are evaluated and compared with respect to the shape parameters, goodness of fit of the models to the wave load data, and statistical uncertainty in the extreme estimates. Important features of the wave load statistics are also revealed.

Design and Make of a Segmented Ship Model for Vertical Bending Moment Measurement

2018 ◽  
Author(s):  
Jingxia Yue ◽  
Yulong Guo ◽  
Lihua Peng
Keyword(s):  
Model Test ◽  
Large Scale ◽  
Bending Moment ◽  
Structural Safety ◽  
Scale Model ◽  
Wave Load ◽  
Scaled Model ◽  
Ship Model ◽  
Section Modulus ◽  
Vertical Bending Moment

With the development of the large-scale ship, the hull becomes more and more “soft” and “elastic”. Accurate simulation of ship’s hydro-elastic performance through scaled model test plays an important role in structural safety assessment. This paper presents the detail preparation of a segmented model which is used to investigate the vertical bending moment (VBM) for a 260m TEU container ship. Some innovative concepts were involved in the scaled model design. Firstly, the segmentation of the ship model was based on the hull’s vertical vibration mode for better simulation of the hull’s rigidity distribution. Secondly, the section of the backbone beam was varied by polishing along ship length in order to simulate the varied section modulus of ship hull. Thirdly, new backbone fixed type was carried out by two flange plates for a better wave load transmission. Besides, some useful techniques were provided, including the model making technique, calibration technique, and backbone system technique. It increases the feasibility of test, at a certain extent. Finally, an overview of the ongoing large scale model test plan and its future development directions is prospected.

Experimental and Numerical Study of Wave-Induced Load Effects of Open Ships in Oblique Seas

2011 ◽  
Vol 55 (02) ◽  
pp. 100-123 ◽  
Author(s):  
Suji Zhu ◽  
Mingkang Wu ◽  
Torgeir Moan
Keyword(s):  
Shear Force ◽  
Numerical Study ◽  
Bending Moment ◽  
Vertical Shear ◽  
Torsional Moment ◽  
Numerical Predictions ◽  
Load Effects ◽  
Computer Codes ◽  
Wave Induced ◽  
Vertical Bending Moment

Open ships inherently possess low torsional rigidity because of their open deck structural configuration. Some of the structural failures for open ships are caused by wave-induced torsional moment in combination with other load components in oblique seas. Relatively few experimental results about horizontal bending and torsional moments in oblique seas have been published, however. Further, test data for vertical shear force and vertical bending moment in oblique seas are quite scarce. A backbone model has been recently tested by the Center for Ships and Ocean Structures (CeSOS) in the towing tank and ocean basin at the Marine Technology Center. The model consists of 15 box-shaped segments, in addition to bow and stern segments, which are interconnected by an aluminum beam on the top. Model tests in oblique seas without forward speed were first carried out to provide basic comparisons. Tests in head and oblique seas with speeds were then conducted in regular waves. Irregular wave tests were also carried out to assess the spectral responses and peak distributions of cross-sectional load effects. Load effects at 7 longitudinal positions were measured through strain gauges, including vertical shear force (VSF), vertical bending moment (VBM), horizontal bending moment (HBM), and torsional moment (TM). The motivation of this paper is to perform a benchmark study by comparing numerical predictions of different computer codes with these test results. The uncertainties in the experiments and the computer codes are discussed, and conclusions are presented at the end of this paper.

A Segmented Model Test of a Container Ship in Head Seas

2017 ◽  
Author(s):  
Brandon M. Taravella ◽  
Kyle E. Marlantes
Keyword(s):  
Computer Program ◽  
Experimental Studies ◽  
Bending Moment ◽  
Order Effect ◽  
Linear Quadratic ◽  
Segmented Model ◽  
Hull Girder ◽  
Strip Theory ◽  
Significant Length ◽  
The University

Dynamic global hull girder response is an important part of the structural design of a ship, especially one with significant length and bow flare. Experimental studies were conducted at the University of New Orleans’ towing tank where a segmented model of a containership was tested in head seas and zero speed. Bending strain at 3 locations along the model’s hull was measured. The results showed peak sagging bending moment that is approximately 25% larger than the peak hogging bending moment at midship. Minor differences were found between positive heave amplitude and negative heave peaks. The results of the experiment were also compared to an “in-house” non-linear quadratic strip theory computer program. The experimental results compared quite well with the numerical results. The results of the experiments and computer program indicate that the dynamic bending moment response is predominantly a second-order effect and linear predictions are not sufficient.

Analysis of Design Wave Loads on an FPSO Accounting for Abnormal Waves

2005 ◽  
Vol 128 (3) ◽  
pp. 241-247 ◽  
Author(s):  
C. Guedes Soares ◽  
Nuno Fonseca ◽  
Ricardo Pascoal ◽  
Guenther F. Clauss ◽  
Christian E. Schmittner ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Prediction Method ◽  
Bending Moment ◽  
Rogue Waves ◽  
Wave Loads ◽  
Short Term ◽  
Operational Lifetime ◽  
Standard Linear ◽  
Long Term Prediction ◽  
Vertical Bending Moment

The paper presents an analysis of structural design wave loads on an FPSO. The vertical bending moment at midship induced by rogue waves are compared with rule values. The loads induced by deterministic rogue waves were both measured in a seakeeping tank and calculated by an advanced time domain method. Two procedures are used to calculate the expected extreme vertical bending moment during the operational lifetime of the ship. The first one relies on a standard linear long term prediction method, which results from the summation of short term distribution of maxima weighted by their probability of occurrence. The short term stationary seastates are represented by energy spectra and the ship responses by linear transfer functions. The second one is a generalization of the former and it accounts for the nonlinearity of the vertical bending moment, by using nonlinear transfer functions of the bending moment sagging peaks which depend of the wave height.

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