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.

scholarly journals Method for Prediction of Extreme Wave Loads Based on Ship Operability Analysis Using Hindcast Wave Database

2021 ◽  
Vol 9 (9) ◽  
pp. 1002
Author(s):  
Tamara Petranović ◽  
Antonio Mikulić ◽  
Marko Katalinić ◽  
Maro Ćorak ◽  
Joško Parunov
Keyword(s):  
Transfer Functions ◽  
Extreme Values ◽  
Bending Moment ◽  
Ship Motions ◽  
Bending Moments ◽  
Wave Loads ◽  
Extreme Wave ◽  
Short Term ◽  
Passenger Ship ◽  
Limiting Values

The method for the prediction of extreme vertical wave bending moments on a passenger ship based on the hindcast database along the shipping route is presented. Operability analysis is performed to identify sea states when the ship is not able to normally operate and which are likely to be avoided. Closed-form expressions are used for the calculation of transfer functions of ship motions and loads. Multiple operability criteria are used and compared to the corresponding limiting values. The most probable extreme wave bending moments for the short-term sea states at discrete locations along the shipping route are calculated, and annual maximum extreme values are determined. Gumbel probability distribution is then fitted to the annual extreme values, and wave bending moments corresponding to a return period of 20 years are determined for discrete locations. The system reliability approach is used to calculate combined extreme vertical wave bending moment along the shipping route. The method is employed on the example of a passenger ship sailing across the Adriatic Sea (Split, Croatia, to Ancona, Italy). The contribution of the study is the method for the extreme values of wave loads using the hindcast wave database and accounting for ship operational restrictions.

Hydroelastic Motion of Aircushion Type Large Floating Structures With Several Aircushions Using a Three-Dimensional Theory

2009 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda ◽  
Mayumi Togane
Keyword(s):  
Theoretical Calculations ◽  
Three Dimensional ◽  
Prediction Method ◽  
Free Water ◽  
Bending Moment ◽  
Linear Potential ◽  
Floating Structures ◽  
Wide Wavelength Range ◽  
Linear Potential Theory ◽  
Vertical Bending Moment

This paper describes hydroelastic motion and effect of motion reduction of aircushion supported large floating structures. Motion reduction effects due to presence of aircushions have been confirmed from theoretical calculations with the zero-draft assumption. A three-dimensional prediction method has been developed for considering draft influence of division walls of aircushions. It is investigated that hydroelastic motion reduction is possible or not by using the three-dimensional theoretical calculations. In addition, the aircushion types are supported by many aircushions which are small related to wavelengths. The Green’s function method is applied to the prediction method with the linear potential theory in which effect of free water surfaces within aircushions are considered. Hydroelastic responses are estimated as not only elastic motion but also a vertical bending moment. From the results, the response reduction is confirmed, in particular, to the vertical bending moment in wide wavelength range and in whole structure area.

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.

Influence of Whipping on Long-term Vertical Bending Moment

2004 ◽  
Vol 48 (04) ◽  
pp. 261-272
Author(s):  
Gro Sagli Baarholm ◽  
Jørgen Juncher Jensen
Keyword(s):  
Nonlinear Response ◽  
Extreme Values ◽  
Bending Moment ◽  
Sea Waves ◽  
Short Term ◽  
Strip Theory ◽  
Long Time ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper is concerned with estimating the response value corresponding to a long return period, say 20 years. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. It is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is applied. Long-term extreme values are estimated using a set of sea states that have a certain probability of occurrence, known as the contour line approach. Effect of whipping is included by assuming that the whipping and wave-induced responses are independent, but the effect of correlation of the long-term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by Xia et al (1998). Results are presented for the S-175 containership (ITTC 1983) in head sea waves. The analysis shows that whipping increases the vertical bending moment and that the correlation is significant.

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.

Longitudinal Forces and Bending Moments of a FPSO

2007 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Andre´ Kauffeldt ◽  
Katja Jacobsen
Keyword(s):  
Time Domain ◽  
Bending Moment ◽  
Time Domain Analysis ◽  
Rogue Waves ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Neutral Axis ◽  
Water Line ◽  
Line Level ◽  
Vertical Bending Moment

For the design of FPSOs the vertical bending moment is a key parameter to ensure safe operation. If analyzed at water line level, however, the unknown influence of longitudinal forces may distort the results. Hence, a segmented FPSO model with midship force transducers at two levels is investigated in various deterministic wave sequences to identify the vertical bending moment and its associated neutral axis as well as the superimposing longitudinal forces. It is shown that the neutral axis is far below the water line level, with the consequence, that extreme cyclic loads at deck level would be expected. However, as the associated longitudinal forces — even if significant — generate a counteracting moment, this effect is largely compensated. Both, frequency- and time-domain results are presented. With frequency-domain analysis the profound data for the standard assessment of structures, concerning seakeeping behaviour, operational limitations and fatigue are obtained. In addition, time-domain analysis in real rogue waves gives indispensable data on extremes, i.e. motions and structural forces.

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.

Short Term Distribution of Loads Acting on a Cruise Vessel in Extreme Seas Using a Body Nonlinear Time Domain With Second Order Froude-Krylov Pressure

2015 ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Surface Condition ◽  
Bending Moment ◽  
The Body ◽  
Short Term ◽  
Weakly Nonlinear ◽  
Strip Theory ◽  
Vertical Bending Moment ◽  
Nonlinear Time Domain

Short term probability distribution of the vertical bending moment acting on a cruise vessel in extreme seas is calculated using a body nonlinear time domain method based on strip theory. The hydrodynamic forces are calculated for the exact wetted surface area under the incident wave profile. The incident potential satisfies the weakly nonlinear free surface condition based on the Stokes expansion. The disturbance potential satisfies the linear free surface and body boundary conditions. Certain practical engineering techniques are employed for the calculation of the body nonlinear forces. The statistics and the probability of distribution of the numerical vertical bending moment are compared with the experimental results measured in the wave tank.

Non Linearity of Extreme Vertical Bending Moment: Comparison of Design Wave Approaches and Short Term Approaches

2013 ◽  
Author(s):  
Guillaume de Hauteclocque ◽  
Quentin Derbanne ◽  
Therard Mienahou
Keyword(s):  
Linear Time ◽  
Bending Moment ◽  
Short Term ◽  
Bulk Carriers ◽  
Non Linear ◽  
Hydrodynamic Calculations ◽  
The Difference ◽  
Vertical Bending Moment ◽  
Term Analysis

The evaluation of extreme bending moment corresponding to a 25 years return period requires very long simulations on a large number of sea states. This long term analysis is easy to do with a linear model of the ship response, but is impractical when using a time consuming model including non linear loads (Froude-Krylov and hydrostatic non linear forces). In that case some simplified methods need to be applied. These methods are often based on equivalent Design Sea States (DSS) or Equivalent Design Waves (EDW). The different methods are applied to large database of ships, containing 19 tankers, 29 bulk carriers, and 9 container-ships, in full load or ballast condition. Linear hydrodynamic calculations are carried out to define the extreme linear vertical bending moment, and to define the DSS and the EDW. Then non linear time domain sea-keeping computations are performed, taking into account Froude-Krylov hydrostatic pressure correction and large motions. The difference between linear and non linear hogging and sagging extremes are computed for each type of DSS and EDW.

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