Influence of the Bow Shape on Loads in High and Steep Waves

2010 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Marco Klein ◽  
Matthias Dudek
Keyword(s):  
Bending Moment ◽  
Model Tests ◽  
Experimental Program ◽  
Wave Steepness ◽  
Regular Waves ◽  
Bulk Carrier ◽  
Wave Heights ◽  
Wave Profiles ◽  
Steep Waves ◽  
Vertical Bending Moment

To ensure survival of floating structures in rough seas, a precise knowledge of global and local loads is an inevitable integral part for safe design. One of the key parameters is the vertical bending moment. Not only vertical forces but — as previous investigations revealed — also longitudinal forces significantly contribute to the vertical wave bending moment. Three segmented ships, equipped with force transducers, are investigated systematically in high and steep regular waves and in harsh wave environments at several cruising speeds to identify the structural loads. The model tests are carried out in the seakeeping basin of the Technical University Berlin at a scale of 1:70. To cover possible influences of the bow geometry, three different types of vessels are chosen, a bulk carrier with a full bow, a Ro/Ro vessel and a container vessel with a V-shaped frame design. For identifying the influence of the wave height and steepness on the vertical bending moment, model tests in regular waves with different crest/trough asymmetries are performed with the Ro/Ro vessel and the bulk carrier. The program can be subdivided into three parts, each characterized by the same wave lengths with varying wave steepness. The first test series includes regular waves with small amplitudes, thus linear wave theory can be applied. In the second part the same (regular) wave lengths have been generated with increased wave heights, i.e. increasing crest/trough asymmetries and wave profiles within Stokes II domain. During the last part of the experimental program the wave heights are further increased to reach wave profiles within Stokes III domain. For the evaluation of the test results in regular waves — in particular in high steep waves — the results are compared to the respective Response Amplitude Operator determined by the transient wave package technique. Here the focus lies on the asymmetry of the hogging and sagging loads with respect to the wave steepness and the bow geometry of the investigated ship models. Furthermore, the influence of the freeboard height on the vertical bending moment is analysed. For this purpose a container vessel is investigated with two different freeboard configurations in a harsh wave environment.

Ship Operational and Safety Aspects of Ballast Water Exchange at Sea

1994 ◽  
Vol 31 (04) ◽  
pp. 315-326
Author(s):  
John B. Woodward ◽  
Michael G. Parsons ◽  
Armin W. Troesch
Keyword(s):  
Bending Moment ◽  
Bending Moments ◽  
University Of Michigan ◽  
Bulk Carrier ◽  
Rough Water ◽  
Design Values ◽  
Wave Heights ◽  
Ballast Tanks ◽  
The University ◽  
Wave Induced

A dry bulk carrier, a tanker, and a containership—taken as typical of ships trading to U.S. ports—are analyzed for possible hazards caused by emptying and refilling ballast tanks at sea. Using hydrostatic data furnished by the shipowners, hull bending moments and stabilities are investigated to find the tank-emptying operations that produce the greatest changes in those parameters. As should be expected, bending moment changes do not exceed allowable stillwater values. Changes in GM are insignificant. The worst hydrostatic cases serve as a guide to conditions that should be analyzed in rough water. The University of Michigan SHIPMO program shows that in waves of 10-ft significant height wave-induced bending moments and shears are far below the design values published by the American Bureau of Shipping. On the other hand, in waves of 20-ft significant height, the maximum wave heights that occur occasionally can cause moments or shears that exceed design values. For the 20-ft case, both linear and nonlinear versions of SHIPMO are used.

Steep Wave Effects on Wave Induced Vertical Bending Moment Using a 3D Numerical Wave Tank

2017 ◽  
Author(s):  
Shivaji Ganesan Thirunaavukarasu ◽  
Debabrata Sen ◽  
Yogendra Parihar
Keyword(s):  
Comparative Study ◽  
Incident Wave ◽  
Bending Moment ◽  
Wave Steepness ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Strip Theory ◽  
Numerical Wave ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper presents a detail comparative study on wave induced vertical bending moment (VBM) between linear and approximate nonlinear calculations using a 3D numerical wave tank (NWT) method. The developed numerical approach is in time domain where the ambient incident waves can be defined by any suitable wave theory. Certain justifying approximations employed in the solution of the interaction hydrodynamics (diffraction and radiation) enabling the NWT to generate stable long duration time histories of all parameters of interest. This is an extension of our earlier works towards the development of a practical NWT based solution for wave-structure interactions [1]. After a brief outline of the implemented numerical details, a comprehensive validation and verification of vertical shear force (VSF) and bending moment RAOs computed using the linearized version of the NWT against the usual linear results of strip theory and 3D panel codes are presented. Next we undertake the comparative study between the fully linear and approximate nonlinear versions of the present code for different incident wave steepness. In the approximate nonlinear formulation, the ambient incident wave is defined by the full nonlinear numerical wave model based on Fourier approximation method which can generate very steep steady periodic nonlinear waves up to the near wave breaking limit. The nonlinearities associated with the incident Froude Krylov and hydrostatic restoring forces/moments are exact up to the instantaneous wetted surface at the displaced location, but the hydrodynamic diffraction and radiation effects are linearized around the mean wetted surface. The standard S175 container hull is considered for the comparative studies because of its geometric nonlinearities. Numerical simulations are performed for four different wave lengths with increasing wave steepness. It is observed that the computed wave induced VBM amidships from the approximate nonlinear results can be almost 30% higher compared to the results from a purely linear solution, which can be a critical issue from the safety point. Significant higher harmonics are also observed in the approximate nonlinear results which at some times may be responsible for exciting the undesirable whipping/springing responses.

Influence of Wave Group Characteristics on Loads in Severe Seas

2011 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Matthias Dudek ◽  
Marco Klein
Keyword(s):  
Critical Loads ◽  
Target Position ◽  
Bending Moment ◽  
Ship Design ◽  
Main Question ◽  
Wave Group ◽  
Regular Waves ◽  
Worst Case ◽  
Bow Flare ◽  
Vertical Bending Moment

The precise knowledge of loads and motions in extreme sea states is indispensable to ensure reliability and survival of ships and floating offshore structures. In the last decades, several accidents in severe weather with disastrous consequences have shown the need for further investigations. Besides the sea state behavior and the local structural loads, one key parameter for safe ship design is the vertical bending moment. Previous investigations revealed that different ship design criteria, such as bow geometry and wave board height, affect the global loads significantly. Investigations in regular waves as well as in single high waves of vessels with different bow flares and freeboard heights show that the vertical bending moment increases significantly with increasing bow flare and freeboard height. Furthermore it became apparent that critical loads and motions do not have to come along with the highest wave which results in the main question of this paper: What is the worst case scenario — the highest rogue wave or a wave group with certain frequency characteristics? Which sea states have to be taken into account for the experimental evaluation of limiting criteria? This paper presents investigations in different critical wave sequences, i.e. two real-sea registrations accompanied by results in regular waves to evaluate the influence of the encountering wave characteristics on the vertical bending moment. For the model tests in the seakeeping basin of the Technical University Berlin a segmented RoRo vessel with large bow flare has been built at a scale of 1:70 and equipped with force transducers. The paper proves that critical loads and motions depend most notably on combinations of wave height, wave group sequences, crest steepness, encountering speed and the ships target position: Even small wave heights with unfavorable wave lengths can cause a critical situation.

Calculation of Vertical Bending Moment Acting on an Ultra Large Containership in Large Amplitude Waves

2015 ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Large Amplitude ◽  
Bending Moment ◽  
Regular Waves ◽  
Structural Dynamic ◽  
Strip Theory ◽  
Structural Dynamic Characteristics ◽  
Wetted Surface Area ◽  
The Time Domain ◽  
Hydroelastic Response ◽  
Vertical Bending Moment

The time domain method is further extended here in order to calculate the hydroelastic response of an ultra large containership in regular waves. Based on strip theory, the hydrodynamic and the hydrostatic forces are calculated for the instantaneous wetted surface area. Slamming forces are calculated using a Von Karman approach in which the water pile up during slamming is neglected. Timoshenko beam which takes into account the shear deformation and rotary inertia is used to model the structural dynamic characteristics of the hull. The beam is discretized using the finite element method and the ship vibration is solved using the modal analysis. The method is used to calculate the vertical bending moment acting on an ultra large containership in large amplitude regular waves. The results are compared with the experimental results measured in wave tank.

Systematic Investigation of Loads and Motions of a Bulk Carrier in Extreme Seas

2009 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Andre´ Kauffeldt ◽  
Marco Klein
Keyword(s):  
Time Domain ◽  
Bending Moment ◽  
Rogue Waves ◽  
Frequency Domain Analysis ◽  
Systematic Investigation ◽  
The European Union ◽  
Bulk Carrier ◽  
Precise Knowledge ◽  
Response Amplitude Operators ◽  
Vertical Bending Moment

During their lifetime ships often operate in severe weather and rough sea states. To ensure survival, a precise knowledge of global and local loads is an inevitable integral part for a safe design. One of the key parameters for ship design is the vertical bending moment. Not only vertical forces but also longitudinal forces can contribute to this bending moment. As the overall effect of longitudinal forces is still not fully understood, all structural loads are investigated in detail, especially in extreme seas. Within the project “Handling Waves”, funded by the European Union, three segmented ships, equipped with force transducers, are investigated systematically at several cruising speeds and in various deterministic wave sequences to identify structural loads, i.e. the vertical bending moment as well as the superimposing longitudinal forces. Within this paper a detailed overview of the results for the bulk carrier is given and both, frequency- and time-domain results are presented. With Response Amplitude Operators (RAOs), delivered by 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 analyses in rogue waves such as the so called “New Year Wave” provide essential data for extreme motions and structural loads. Former investigations on a FPSO revealed that, due to the location of the neutral axis, the longitudinal forces are significant and generate a counteracting moment compared to the vertical bending moment [1]. The new results show to what extent the above mentioned conclusions are applicable for various hull designs.

Application of Breather Solutions for the Investigation of Wave/Structure Interaction in High Steep Waves

2012 ◽  
Author(s):  
Günther F. Clauss ◽  
Marco Klein ◽  
Matthias Dudek ◽  
Miguel Onorato
Keyword(s):  
Real World ◽  
Wave Structure ◽  
Model Tests ◽  
Design Stage ◽  
Regular Waves ◽  
Freak Waves ◽  
Structure Interaction ◽  
Steep Waves ◽  
The Impact ◽  
Wave Structure Interaction

During the design process of floating structures, different specifications have to be aligned such as the range of application, the warranty of economical efficiency as well as the reliability and are an inevitable integral part of the evaluation process during the design stage. The validation of the performance by means of model tests in terms of sea state behavior and the associated local and global structural loads are an important milestone within this process. Therefore it is necessary to determine an adequate test procedure which covers all essential areas of interest. Thereby one field of interest are limiting criteria of the design such as maximum local and global loads as well as maximum accelerations due to the impact of extraordinarily high waves, at which the floating structure has to survive. Different alternatives are available to conduct model tests in high, steep waves — transient wave packages, regular waves, irregular waves with random phases or more sophisticated deterministic tailored irregular wave sequences such as reproductions from numerical simulations and real-world measurements. This paper introduces a new approach for the systematic investigation of wave/structure interaction in high, steep waves. Exact solutions of the nonlinear Schrodinger equation — the so called breather solutions — are implemented for the generation of extraordinarily high waves. Three types of breather solutions are investigated in the seakeeping basin and to cover the full range of interest, each solution has been used to generate freak waves at certain frequencies. To evaluate the applicability of breather solutions for model tests two types of ships — a LNG Carrier and a Chemical Tanker — are investigated in the seakeeping basin. The ships are segmented and connected with strain gauges to detect the vertical wave bending moment. Furthermore, green water probes are installed on deck to evaluate the local impact on the bow of the freak waves. The obtained results are compared to investigations in regular waves with certain frequency and steepness as well as in real-world freak wave reproductions.

Study on vertical motion reduction of a trimaran based on collaborative controlled appendages

2020 ◽  
Vol 17 (6) ◽  
pp. 172988142097677
Author(s):  
Zhilin Liu ◽  
Linhe Zheng ◽  
Guosheng Li ◽  
Shouzheng Yuan ◽  
Songbai Yang
Keyword(s):  
Experimental Study ◽  
Vertical Motion ◽  
Model Tests ◽  
Wave Period ◽  
Regular Waves ◽  
Towing Tank ◽  
Vertical Stability ◽  
Stabilization Control ◽  
Stability Performance

In recent years, the trimaran as a novel ship has been greatly developed. The subsequent large vertical motion needs to be studied and resolved. In this article, an experimental study for a trimaran vertical stabilization control is carried out. Three modes including the bare trimaran (the trimaran without appendages, the trimaran with fixed appendages, and the trimaran with controlled appendages) are performed through model tests in a towing tank. The model tests are performed in regular waves. The range of wave period is 2.0–4.0 s, and the speed of the carriage is 2.93 and 6.51 m/s. The results of the three modes show the fixed appendages and the actively controlled appendages are all effective for the vertical motion reduction of the trimaran. Moreover, the controlled appendages are more effective for the vertical stability performance of the trimaran.

Load Combination for Fatigue Analysis of Ship Structures

2004 ◽  
Author(s):  
Yung S. Shin ◽  
Booki Kim ◽  
Alexander J. Fyfe
Keyword(s):  
Bending Moment ◽  
Linear Summation ◽  
Load Combination ◽  
Longitudinal Stiffeners ◽  
Stress Components ◽  
Tank Pressure ◽  
Wave Induced ◽  
Vertical Bending Moment ◽  
Oil Tanker

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The methodology is based on a theory of a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-tem sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in cargo and ballast tanks of a crude oil tanker at midship section. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.

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