Transient Wave Packets: New Application in CFD-Methods

2014 ◽  
Author(s):  
Günther F. Clauss ◽  
Sven Stuppe ◽  
Matthias Dudek
Keyword(s):  
Potential Theory ◽  
Wave Packets ◽  
Model Tests ◽  
Irregular Waves ◽  
Design Stage ◽  
Detailed Knowledge ◽  
Offshore Structure ◽  
Transient Wave ◽  
Space And Time ◽  
Hull Structure

Detailed knowledge of motion and seakeeping behaviour in an early design stage is indispensable in modern layout of marine offshore structures. Therefore, numerical methods are used to calculate the Response Amplitude Operators (RAO), which are generally based on potential theory or the Reynolds-Averaged-Navier-Stokes-Equation (RANSE). Calculations with potential-codes are commonly used, well established and time-saving. Main disadvantages are the neglect of viscous effects and the hull structure above the still water level. By using RANSE-methods, these nonlinear effects can be investigated in detail, but at the price of calculation time and extensive grid generation. To achieve sufficient RAOs in frequency domain, time-consuming and intensive calculations would be necessary with these CFD-methods, using seastate applications with regular or irregular waves only. Therefore, these methods are not convenient for standard motion analysis by now. Transient Wave Packets (TWP) represent an approved method at model tests, revealing the entire RAO for any offshore structure within one single, short test run. Main advantage of this technique is the accurate predictability and short superposition in space and time. Containing all elementary wavelengths of the generated initial wave spectra, the TWP-method could be used in RANSE-methods, implementing all necessary initial conditions to the CFD-solver. To reduce the calculation effort to a minimum in space and time, the superimposed wave train is generated near the investigated offshore structure by using modified, linear wave theory in spatial domain. To present this method by means of a practical example, the motion and sloshing behaviour of an offshore LNG-carrier (LNGC) are investigated in detail. For validation purpose, all results are compared to model tests, conducted in the seakeeping basin at Technische Universität Berlin (TUB), as well as numerical results of the potential theory solver WAMIT.

scholarly journals Theoretical and Experimental Study on Nonlinear Hydroelastic Responses and Slamming Loads of Ship Advancing in Regular Waves

2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
Jialong Jiao ◽  
Yulin Zhao ◽  
Yufei Ai ◽  
Chaohe Chen ◽  
Tianhui Fan
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Irregular Waves ◽  
Green Water ◽  
Design Stage ◽  
Regular Waves ◽  
Restoring Force ◽  
Wave Basin ◽  
Hull Structure ◽  
Hydrodynamic Wave

Wave loads estimation and structural strength evaluation are the fundamental work at the ship design stage. The hydroelastic responses and slamming strength issues are also concerned especially for large-scale high-speed ships sailing in harsh waves. To accurately predict the wave-induced motions and loads acting on the ship sailing in regular waves, a fully coupled 3D time-domain nonlinear hydroelasticity theory is developed in this paper. The vibration modal characteristics of the flexible hull structure derived by the 3D finite element method (FEM) and simplified 1D nonuniform Timoshenko beam theory are firstly described. The hydrostatic restoring force and hydrodynamic wave force are calculated on the real-time wetted surface of hull to address geometric nonlinearity due to the steep wave and large amplitude motions. The bow slamming and green water loads acting on the ship in severe regular waves are estimated by the momentum impact method and dam-breaking method, respectively. Moreover, a small-scaled segmented ship model is designed, constructed, and tested in a laboratory wave basin to validate the hydroelasticity algorithm. The results predicted by theoretical and experimental approaches are systemically compared and analyzed. Finally, future work for predictions of ship hydroelasticity and slamming loads in irregular waves is prospected.

scholarly journals SEAKEEPING OF A FAST DISPLACEMENT CATAMARAN

Transport ◽  
2005 ◽  
Vol 20 (1) ◽  
pp. 14-22 ◽  
Author(s):  
Vasilij Dyachkov ◽  
Jurij Makov
Keyword(s):  
Computer Program ◽  
Experimental Model ◽  
Calculation Method ◽  
Model Tests ◽  
Irregular Waves ◽  
Design Stage ◽  
Complex Method

The paper presents a complex method for the calculation of pitch and heave of a fast displacement catamaran. It incorporates speed factors, interference of catamaran hulls, stabilization factors and possibility to apply different stabilization cases including a stabilizer activation possibility. In the method the possibility to evaluate catamaran motions in irregular waves is also included. On the base of the presented method the computer program is developed and applied to calculate seakeeping characteristics of a catamaran stabilized with a fore passive wing. The results of calculation are in good compatibility with the experimental model tests of this catamaran in irregular waves. The calculation method could be effectively applied in the design stage of fast displacement catamarans or of fin stabilizers determining their effectiveness.

Extreme Wave Generation, Breaking, and Impact Simulations Using Wave Packets in REEF3D

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Hans Bihs ◽  
Arun Kamath ◽  
Mayilvahanan Alagan Chella ◽  
Øivind A. Arntsen
Keyword(s):  
Wave Packets ◽  
Wave Generation ◽  
Wave Forces ◽  
Breaking Wave ◽  
Extreme Wave ◽  
Offshore Structure ◽  
Transient Wave ◽  
Individual Wave ◽  
The Individual ◽  
Impact Simulations

On several occasions, freak waves have been observed in the past, some causing severe damage. In order to model such extreme wave conditions, one possibility is to use focused waves of first- or second-order based on irregular sea-state wave spectra. The wave phase is chosen such that the waves focus at a predetermined location and time, but the individual wave components become steep and start breaking before the focus location for large amplitudes. In this study, transient wave packets are used for extreme wave generation. Extreme waves are generated that are higher and only break at the concentration point using the transient wave packets method implemented in the open-source CFD model REEF3D. Model validation is performed by comparison to experimental results. The generation of wave packets with an 8.3 times shorter focus distance is investigated and the wave is replicated in a shorter domain with a 9% higher crest. The method is further used to generate a steepness induced-breaking wave and calculation of extreme wave forces on an offshore structure is demonstrated.

Seakeeping Tests With Gaussian Wave Packets

2005 ◽  
Author(s):  
Vini´cius Matos ◽  
Joel Sena Sales ◽  
S. H. Sphaier
Keyword(s):  
Transfer Function ◽  
The Body ◽  
Irregular Waves ◽  
Design Stage ◽  
Body Movements ◽  
Transient Waves ◽  
Hydrodynamic Behavior ◽  
Transient Wave ◽  
Accurate Evaluation ◽  
Floating Systems

An important property used in the design stage of floating systems is the RAO (Response Amplitude Operator), the transfer function, for motions, forces and so on. This importance has motivated the development of several analytical, numerical and experimental tools to obtain the hydrodynamic behavior of platforms and ships. Experimental model tests in wave tanks are advisable for the accurate evaluation of the body movements. Three known techniques are used to obtain the RAO curves: tests with regular, irregular and transient waves. In the present work, special attention is given to the technique used to perform model testing with one type of transient wave: the Gaussian Wave Packet. The advantages of using such technique are discussed and results are also presented for a semi-submersible model during tests carried out at Laborato´rio de Tecnologia Oceaˆnica - LabOceano/COPPE/UFRJ, Brazil. Numerical calculations and tests with regular and irregular waves are used for validation and comparison.

Model Tests for the Validation of Extreme Roll Motion Predictions

2002 ◽  
Author(s):  
Walter L. Kuehnlein ◽  
K.-E. Brink
Keyword(s):  
Practical Knowledge ◽  
Rapid Development ◽  
Model Tests ◽  
Design Stage ◽  
Roll Motion ◽  
Ministry Of Education ◽  
Following Seas ◽  
Early Design Stage ◽  
Shaped Container ◽  
Motion Characteristics

At present common stability criteria are based on practical knowledge gained from the operation of ships. Therewith the assessment of ship safety against capsizing is partly determined by long-term statistics of accidents. Regulations like the IMO-Resolution A 167 do not rate the typical seakeeping characteristics of different hull form geometries. Therefore strictly speaking, these criteria are just applicable for ships of similar types as included in statistics. Rapid development in ship design calls for the determination of ship and cargo safety in regard of extreme roll motions or capsizing during early design stage. Within the ROLL-S project, which was founded by the German Federal Ministry of Education and Research, dynamic stability tests with a box shaped Container Ship and a RO-RO vessel have been performed. The performance of model tests, which are intended to serve for the validation of numerical simulation methods, put high demands on test and data acquisition techniques. The data of the waves encountered, course and position, as well as the response of the model had to be determined by model tests in order to use these data for the validation of numerical ship motion simulations. During the tests extreme roll motions of the two considered vessels could be observed in head seas and in following seas. Besides critical motion characteristics in following seas, like broaching, parametric induced roll motion effects were investigated in head sea condition. Remark: This paper should be read in conjunction with paper OMAE 2002-28297 which describes generation and transformation of the used waves.

Springing Responses Analysis and Segmented Model Testing on a 550,000 DWT Ore Carrier

2016 ◽  
Author(s):  
Hui Li ◽  
Di Wang ◽  
Cheng Ming Zhou ◽  
Kaihong Zhang ◽  
Huilong Ren
Keyword(s):  
Natural Frequency ◽  
Design Stage ◽  
Resonant Vibration ◽  
Bending Moments ◽  
Wave Loads ◽  
Regular Waves ◽  
Segmented Model ◽  
Ship Model ◽  
Hull Structure ◽  
Stiffness Distribution

For ultra large ore carriers, springing response should be analyzed in the design stage since springing is the steady-state resonant vibration and has an important effect on the fatigue strength of hull structure. The springing response of a 550,000 DWT ultra large ore carrier has been studied by using experimental and numerical methods. A flexible ship model composed of nine segments was used in the experiment. The model segments were connected by a backbone with varying section, which can satisfy the request of natural frequency and stiffness distribution. The experiments in regular waves were performed and the motions and wave loads of the ship were measured. The experimental results showed that springing could be excited when the wave encounter frequency coincides with half or one-third the flexural natural frequency of the ship. In this paper, the analysis of the hydroelastic responses of the ultra large ore carrier was also carried out using a 3-D hydroelastic method. Comparisons between experimental and numerical results showed that the 3-D hydroelastic method could predict the motions and the vertical bending moments quite well. Based on this numerical method, the fatigue damage was estimated and the contribution of springing was analyzed.

scholarly journals OPTIMIZATION OF THE WAVECAT WAVE ENERGY CONVERTER

2012 ◽  
Vol 1 (33) ◽  
pp. 5 ◽  
Author(s):  
Hernan Fernandez ◽  
Gregorio Iglesias ◽  
Rodrigo Carballo ◽  
Alberte Castro ◽  
Marcos Sánchez ◽  
...  
Keyword(s):  
Physical Model ◽  
Wave Energy ◽  
Model Tests ◽  
Irregular Waves ◽  
Intermediate Water ◽  
Plan View ◽  
Santiago De Compostela ◽  
Wave Energy Converters ◽  
Physical Model Tests ◽  
The Difference

The development of efficient, reliable Wave Energy Converters (WECs) is a prerequisite for wave energy to become a commercially viable energy source. Intensive research is currently under way on a number of WECs, among which WaveCat©—a new WEC recently patented by the University of Santiago de Compostela. In this sense, this paper describes the WaveCat concept and its ongoing development and optimization. WaveCat is a floating WEC intended for operation in intermediate water depths (50–100 m). Like a catamaran, it consists of two hulls—from which it derives its name. The difference with a conventional catamaran is that the hulls are not parallel but convergent; they are joined at the stern, forming a wedge in plan view. Physical model tests of a 1:30 model were conducted in a wave tank using both regular and irregular waves. In addition to the waves and overtopping rates, the model displacements were monitored using a non-intrusive system. The results of the physical model tests will be used to validate the 3D numerical model, which in turn will be used to optimize the design of WaveCat for best performance under a given set of wave conditions.

Experimental Assessment of the Performance of CECO Wave Energy Converter in Irregular Waves

2018 ◽  
Author(s):  
Claudio A. Rodríguez ◽  
F. Taveira-Pinto ◽  
P. Rosa-Santos
Keyword(s):  
Wave Energy ◽  
Transfer Functions ◽  
Nonlinear Effects ◽  
Model Tests ◽  
Experimental Results ◽  
Irregular Waves ◽  
Scale Model ◽  
Experimental Assessment ◽  
Simplified Approach ◽  
Wave Basin

A new concept of wave energy device (CECO) has been proposed and developed at the Hydraulics, Water Resources and Environment Division of the Faculty of Engineering of the University of Porto (FEUP). In a first stage, the proof of concept was performed through physical model tests at the wave basin (Rosa-Santos et al., 2015). These experimental results demonstrated the feasibility of the concept to harness wave energy and provided a preliminary assessment of its performance. Later, an extensive experimental campaign was conducted with an enhanced 1:20 scale model of CECO under regular and irregular long and short-crested waves (Marinheiro et al., 2015). An electric PTO system with adjustable damping levels was also installed on CECO as a mechanism of quantification of the WEC power. The results of regular waves tests have been used to validate a numerical model to gain insight into different potential configurations of CECO and its performance (López et al., 2017a,b). This paper presents the results and analyses of the model tests in irregular waves. A simplified approach based on spectral analyses of the WEC motions is presented as a means of experimental assessment of the damping level of the PTO mechanism and its effect on the WEC power absorption. Transfer functions are also computed to identify nonlinear effects associated to higher waves and to characterize the range of periods where wave absorption is maximized. Furthermore, based on the comparison of the present experimental results with those corresponding to a linear numerical potential model, some discussions are addressed regarding viscous and other nonlinear effects on CECO performance.

Evaluation of a Small and Fast Planing Boat’s Seakeeping Performance at the Design Stage

2015 ◽  
Author(s):  
Dong Jin Kim ◽  
Sun Young Kim
Keyword(s):  
Model Tests ◽  
Full Scale ◽  
Scale Model ◽  
Design Stage ◽  
Small Scale ◽  
Irregular Wave ◽  
Seakeeping Performance ◽  
Head Waves ◽  
Scale Ratio ◽  
Free Running

Seakeeping performance of a planing boat should be sufficiently considered and evaluated at the design stage for its safe running in rough seas. Model tests in seakeeping model basins are often performed to predict the performance of full-scale planing boats. But, there are many limitations of tank size and wave maker capacity, in particular, for fast small planing boats due to small scale ratio and high Froude numbers of their scale models. In this research, scale model tests are tried in various test conditions, and results are summarized and analyzed to predict a 3 ton-class fast small planing boats designed. In a long and narrow tank, towing tests for a bare hull model are performed with regular head waves and long crested irregular head waves. Motion RAOs are derived from irregular wave tests, and they are in good agreements with RAOs in regular waves. Next, model ships with one water-jet propulsion system are built, and free running model tests are performed in ocean basins. Wave conditions such as significant heights, modal periods, and directions are varied for the free running tests. Motion RMS values, and RAOs are obtained through statistical approaches. They are compared with the results in captive tests for the bare hull model, and are used to predict the full-scale boat performances.

Experimental Determination of Water Motions Inside a Moonpool

2017 ◽  
Author(s):  
Bastien Abeil
Keyword(s):  
Experimental Determination ◽  
Transfer Functions ◽  
Side Wall ◽  
Model Tests ◽  
Irregular Waves ◽  
Video Recordings ◽  
Non Linear ◽  
Relative Water ◽  
Water Elevation

Model tests of a drillship with a rectangular moonpool opening were conducted in regular and irregular waves from the bow and bow-quarter. Most tests were conducted at zero speed, the rest was performed with the model towed to a speed of 10 kn. From the video-recordings and transfer functions of the measured relative water elevation inside the moonpool, the typical piston and first sloshing modes are well captured, for wave frequencies that agree relatively well with relevant formulations. A few tests conducted at varying wave amplitudes show that the water elevation is non-linear by nature, while repeat tests conducted with the moonpool fitted with two layers of side wall flanges shows that these can reduce the water motions by nearly 40 %.

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