CFD Reproduction of Model Test Generated Extreme Irregular Wave Events and Nonlinear Loads on a Vertical Column

2016 ◽  
Author(s):  
Csaba Pakozdi ◽  
Anders Östman ◽  
Erin E. Bachynski ◽  
Carl Trygve Stansberg
Keyword(s):  
Model Test ◽  
Vertical Cylinder ◽  
Control Signal ◽  
Test Case ◽  
Wave Loads ◽  
Reconstruction Procedure ◽  
Vertical Column ◽  
Irregular Wave ◽  
Wave Maker ◽  
The Waves

Recently, a method for numerical reproduction of measured irregular wave events has been developed. The measured motion of the wave maker flaps defines the wave kinematics at the boundary of the numerical simulation in order to generate the waves as described in (Pakozdi, Kendon, & Stansberg, 2011) and (Ostman, Pakozdi, Stansberg, Fagertun, & Vestbostad, 2015). When such data are not available, the control signal of the wave maker can, instead, be generated from a given free surface elevation following the same procedure as in model tests. Following this procedure automatically gives the possibility to subsequently reproduce the numerical wave experimentally using the obtained control signal. The latter procedure is applied to a model test case with extreme irregular wave events and resulting nonlinear global wave loads on a vertical cylinder (Stansberg, 1997), with the focus on higher-order ringing excitation. The purpose of the investigation is two-fold: 1) to validate the wave reconstruction procedure, and 2) to validate the resulting CFD ringing loads with the given waves. The results show generally good agreement both in the waves and in the loads; discrepancies found in the loads are considered to be mainly originating from corresponding uncertainties in the wave reconstruction. Wave breaking may be one source of uncertainty.

Computational Fluid Dynamics Reproduction of Nonlinear Loads on a Vertical Column During Extreme Irregular Wave Events

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Erin E. Bachynski ◽  
Csaba Pákozdi ◽  
Anders Östman ◽  
Carl Trygve Stansberg
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Vertical Cylinder ◽  
Test Case ◽  
Wave Loads ◽  
Reconstruction Procedure ◽  
Vertical Column ◽  
Irregular Wave ◽  
Wave Maker ◽  
The Waves

Recently, a method for numerical reproduction of measured irregular wave events has been developed. The measured motion of the wave maker flaps defines the wave kinematics at the boundary of the numerical simulation in order to generate the waves. When such data are not available, the control signal of the wave maker can, instead, be generated from a given free surface elevation following the same procedure as in model tests. This procedure is applied to a model test case with extreme irregular wave events and resulting nonlinear global wave loads on a vertical cylinder, focusing on higher-order ringing excitation. The purpose of the investigation is twofold: (1) to validate the wave reconstruction procedure and (2) to validate the resulting computational fluid dynamics (CFD) ringing loads with the given waves. In order to better understand the frequency content in the CFD-generated loads, wavelet analysis as well as the response of a single degree-of-freedom (SDOF) oscillator is examined and compared with the corresponding results for the third-order wave forcing based on the MacCamy–Fuchs (MF) and Faltinsen, Newman, Vinje (FNV) formulations. The results show generally good agreement between CFD and experiment both in the waves and in the loads; discrepancies found in the loads mainly originate from corresponding uncertainties in the wave reconstruction. Wave breaking may be one source of uncertainty. The MF + FNV formulation showed reasonable prediction of the maximum responses of an SDOF oscillator, but could not capture the loads well at all of the important frequencies.

Drilling Riser Model Tests for Software Verification

2016 ◽  
Author(s):  
Decao Yin ◽  
Halvor Lie ◽  
Massimiliano Russo ◽  
Guttorm Grytøyr
Keyword(s):  
Model Test ◽  
Software Verification ◽  
Cross Flow ◽  
Model Tests ◽  
Dynamic Responses ◽  
Wave Loads ◽  
Regular Wave ◽  
Marine Riser ◽  
Test Program ◽  
Irregular Wave

Marine drilling riser is subject to complicated environmental loads which include top motions due to Mobile Offshore Drilling Unit (MODU), wave loads and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling riser system, especially at the subsea well head (WH). Statoil and BP have carried out a comprehensive model test program on drilling riser in MARINTEK’s Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling riser behaviour under various environmental conditions by use of model test data. Six drilling riser configurations were tested, including different components such as Upper Flex Joint (UFJ), tensioner, marine riser, Lower Marine Riser Package (LMRP), Blow-Out Preventer (BOP), Lower Flex Joint (LFJ), buoyancy elements and seabed boundary model. The drilling riser models were tested in different load conditions: 1. Forced top motion tests 2. Regular wave test 3. Combined regular wave and towing test 4. Irregular wave test 5. Combined irregular wave and towing test 6. Towing test (VIV) Measurements were made of micro bending strains and accelerations along the riser in both In-Line (IL) and Cross-Flow (CF) directions. Video recordings were made both above and under water. In this paper, the test set-up and test program are presented. Comparisons of results between model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling riser model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between model test and RIFLEX simulation is promising.

scholarly journals WAVE LOADS ON HORIZONTAL CYLINDERS

1978 ◽  
Vol 1 (16) ◽  
pp. 147
Author(s):  
P. Holmes ◽  
J.R. Chaplin
Keyword(s):  
Oscillatory Flow ◽  
Vertical Plane ◽  
Vertical Cylinder ◽  
Irregular Waves ◽  
Wave Loads ◽  
Incident Flow ◽  
Cylinder Axis ◽  
Straight Line ◽  
Horizontal Cylinders ◽  
Wave Induced

The problem of predicting wave induced loads on cylinders is an enormously complex one. It is clear from the scatter present in most experimental determinations of force coefficients that there are many individual factors which influence the mechanisms of flow induced loading. Among these are some, for instance Reynolds number, separation and periodic vortex shedding, which are inter-related and whose influences cannot be studied in isolation. Others, such as shear flow, irregular waves and free surface effects, can at least be eliminated in the laboratory, in order to approach an understanding of the more fundamental characteristics of the flow. A vertical cylinder in uniform waves experiences an incident flow field which can be described in terms of rotating velocity and acceleration vectors, always in the same vertical plane, containing also the cylinder axis, whose magnitudes are functions of time and of position along the length of the cylinder. Some of the essential features of this flow can be studied under two-dimensional oscillatory conditions, in which either the cylinder or the fluid is oscillated relative to the other along a straight line (planar oscillatory flow). The incident velocity and acceleration vectors are then always concurrent, normal to the cylinder axis, and oscillating in magnitude with time.

Model Tests of a Spar-Type Floating Wind Turbine Under Wind/Wave Loads

2015 ◽  
Author(s):  
Fei Duan ◽  
Zhiqiang Hu ◽  
Jin Wang
Keyword(s):  
Wind Turbine ◽  
Model Test ◽  
Wind Wave ◽  
Wave Model ◽  
Offshore Structures ◽  
Model Tests ◽  
Wave Loads ◽  
Scaled Model ◽  
Floating Wind Turbine ◽  
Wave Effects

Wind power has great potential because of its clean and renewable production compared to the traditional power. Most of the present researches for floating wind turbine rely on the hydro-aero-elastic-servo simulation codes and have not been exhaustively validated yet. Thus, model tests are needed and make sense for its high credibility to master the kinetic characters of floating offshore structures. The characters of kinetic responses of the spar-type wind turbine are investigated through model test research technique. This paper describes the methodology for wind/wave model test that carried out at Deepwater Offshore Basin in Shanghai Jiao Tong University at a scale of 1:50. A Spar-type floater was selected to support the wind turbine in this test and the model blade was geometrically scaled down from the original NREL 5 MW reference wind turbine blade. The detail of the scaled model of wind turbine and the floating supporter, the test set-up configuration, the mooring system, the high-quality wind generator that can create required homogeneous and low turbulence wind, and the instrumentations to capture loads, accelerations and 6 DOF motions are described in detail, respectively. The isolated wind/wave effects and the integrated wind-wave effects on the floating wind turbine are analyzed, according to the test results.

Reproduction of Monopile Ringing Events in Reduced-Duration Model Tests

2017 ◽  
Author(s):  
Erin E. Bachynski ◽  
Trygve Kristiansen
Keyword(s):  
Time Windows ◽  
Full Scale ◽  
Offshore Wind ◽  
Maximum Deviation ◽  
Wave Loads ◽  
Traditional Practice ◽  
Hydrodynamic Loads ◽  
Offshore Wind Turbines ◽  
Irregular Wave ◽  
Structural Responses

Monopile support structures for offshore wind turbines may experience ringing-type responses in steep wave conditions. In order to experimentally capture the statistical distribution of the hydrodynamic loads and structural responses, traditional practice is to generate many 3-hour (full scale) realizations of the relevant sea states. An experimental campaign at 1:48 scale was carried out in the Lilletanken wave tank at NTNU/MARINTEK in order to examine the possibility of using shorter time windows to recreate irregular wave ringing events. Wave elevations and hydrodynamic loads on a rigid vertical circular cylinder in 27 m water depth were measured for a variety of 3-hour, 450 s (7.5-minute), 800 s (13.3-minute), 1150 s (19.2-minute), and 1500 s (25-minute) wave realizations, where all durations are listed in full scale. Wavelet transformations and a single degree-of-freedom oscillator were used to investigate the magnitude and repeatability of the high-frequency content of the wave loads. Large variations in the repeatability were seen among events. On average, the repeatability in the ringing response was 4.2 % for 3-hour tests, while 13.3-minute tests reproduced the same events within 9.1 %. The maximum deviation was, nonetheless, much higher when only 13.3 minutes were used.

Maneuvering Behavior of Ships in Irregular Waves

2013 ◽  
Author(s):  
Renato Skejic ◽  
Odd M. Faltinsen
Keyword(s):  
Deep Water ◽  
Cross Flow ◽  
Irregular Waves ◽  
Scale Model ◽  
Wave Loads ◽  
Ship Maneuvering ◽  
Slender Body Theory ◽  
Statistical Point ◽  
Irregular Wave ◽  
Mmg Model

Ship maneuvering in waves is analyzed by using a unified seakeeping and maneuvering two-time scale model in irregular sea that has been applied by Skejic and Faltinsen [1] for regular waves. The irregular wave effects are accounted for by Newman’s [2] approximation of the slow-drift 2nd order wave loads valid for deep water (Faltinsen [3], Pinkster [29]). The modular type maneuvering model (MMG model) based on Söding’s [4] nonlinear slender-body theory is used for the maneuvering analysis. Forces and moments due to rudder, propeller, and viscous cross-flow are accounted for as presented by Skejic and Faltinsen [1] and Yasukawa [5, 6]. In particular, the behavior of the propulsive coefficients (the thrust deduction and wake fraction) in waves (Faltinsen et al. [7], Faltinsen and Minsaas [8]) are discussed from the perspective of ship maneuvering characteristics in both regular and irregular wave environments. The unified model of seakeeping and maneuvering for deep-water irregular waves is validated for the ‘S7-175’ (‘SR 108’) container ship in calm water and regular deep-water wave scenarios by comparison with experimental results by Yasukawa [5, 6]. The maneuvering model is applied to a ‘MARINER’ ship performing turning maneuver in irregular waves. The obtained results of the ships main maneuvering parameters are discussed from a statistical point of view.

scholarly journals WAVES INDUCED BY NON-PERMANENT PADDLE MOVEMENTS

1972 ◽  
Vol 1 (13) ◽  
pp. 35 ◽  
Author(s):  
C. Campos Moraes ◽  
F. Silveira Ramos ◽  
M. Mendes De Carvalho
Keyword(s):  
Experimental Study ◽  
Gain Function ◽  
Surface Motion ◽  
Irregular Wave ◽  
Input And Output ◽  
Wave Maker

In a flume equipped with an irregular wave maker the motion of the paddle and the resulting waves may be thought of respectively as input and output of a system which, if linear, is for some purposes described by the so-called gain function. A theoretical and experimental study of this function is carried out ma king use of paddle movements that produce transient surface motion.

scholarly journals Horizontal Wave Pressures on the Crown Wall of Rubble Mound Breakwater under Non-Breaking Condition

2021 ◽  
Vol 33 (6) ◽  
pp. 321-332
Author(s):  
Jong-In Lee ◽  
Geum Yong Lee ◽  
Young-Taek Kim
Keyword(s):  
Physical Model ◽  
Model Test ◽  
Efficient Solution ◽  
Physical Model Test ◽  
Wave Loads ◽  
Wave Pressure ◽  
Practical Design ◽  
Horizontal Wave ◽  
Series Of Experiments ◽  
Rubble Mound

The crown wall with parapet on top of the rubble mound breakwater represents a relatively economic and efficient solution to reduce the wave overtopping discharge. However, the inclusion of parapet leads to increased wave pressure on the crown wall. The wave pressure on the crown wall is investigated by physical model test. To design the crown wall the wave loads should be available, and the horizontal wave pressure is still unclear. Regarding to the horizontal wave pressure on the crown wall, a series of experiments were conducted by changing the rubble mound type structure and the wave conditions. Based on these results, pressure modification factors of Goda’s (1974, 2010) formula have been suggested, which can be applicable for the practical design of the crown wall of the rubble-mound breakwater covered by tetrapods.

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