Study on Numerical Simulation of Jacket Launching Progress

2013 ◽  
Author(s):  
Lingzhi Xiong ◽  
Jianmin Yang ◽  
Xin Li ◽  
Xin Xu
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Scale Effect ◽  
Model Test ◽  
Hydrodynamic Force ◽  
Shallow Waters ◽  
Test Results ◽  
Physical Model Tests ◽  
Wave Basin ◽  
Similarity Law

Jacket type structures are widely used in shallow waters. The size of a jacket is determined by the dimensions of the deck and piles, as well as the environment loads. The jackets are usually transported with barges to the operation water after they have been fabricated in the shipyard, then the jackets slip into the water. Launch operation is the most hazardous stage during the installation of a jacket. The main purpose of this study is to evaluate the physical modeling test results for the launch, and compared to those of numerical simulation. It is found that there are some differences between the numerical simulations and physical model tests. The scale effect cannot be ignored in the prediction of the jacket launching process. The model test is based on the Froude similarity law, and the effect of Reynolds number is neglected. The drag coefficient depending on the Reynolds number plays a crucial role in determining the launch process. With different Reynolds number, the structure has different hydrodynamic force that results to different pitch angle, heave, launch time, acceleration and so on. Thus, a scale effect emerges when we convert the results of a wave basin model test to the prototype scale. This study also includes a sensitivity analysis about some key parameters in the launch process, such as initial barge trim and draft, frictions between barge and jacket.

Extrapolation of Propulsion Tests for Ships with Appendages and Complex Propulsors

2001 ◽  
Vol 38 (03) ◽  
pp. 145-157
Author(s):  
Jan Holtrop
Keyword(s):  
Scale Effect ◽  
Model Test ◽  
Test Results ◽  
Extrapolation Methods ◽  
Passive Components ◽  
Model Experiments

Prediction of ship powering is traditionally based on the results of model experiments. This paper covers the extrapolation of model test results for ships that may have a multitude of appendages and one or more complex propulsors. The major differences from conventional extrapolation methods are the application of the scale effect corrections to the model propulsion test, the treatment of the appendages and acknowledging the effects of the propeller load on the propulsion parameters. The last feature is considered essential to successfully handle complex propulsors with both rotating and passive components.

Collision Character Research for Semi-Submersible Through Model Test, Simplified Analytical and Numerical Simulation Method

2010 ◽  
Author(s):  
Zhiqiang Hu ◽  
Zhenhui Liu ◽  
Jo̸rgen Amdahl
Keyword(s):  
Numerical Simulation ◽  
Model Test ◽  
Simulation Method ◽  
Tension Force ◽  
Test Results ◽  
Buffer Effect ◽  
Mooring Lines ◽  
Column Structure ◽  
Collision Force ◽  
Energy Absorbing

The characters of the collision scenario when a semi-submersible is struck by a containership are studied in this paper, through the model test, simplified analytical method and numerical simulation. The model test is conducted in the Deepwater Offshore Basin in Shanghai Jiao Tong University. Two special devices are designed to fulfill the model test. One is Ship Launching Device, simplified as SLD, who can launch the striking ship with controllable velocity and in any horizontal direction. The other is Energy Absorbing Device, simplified as EAD, who can simulate the buffer effect of the column structure and collect the collision force as well. A numerical simulation is completed to get the approximate stiffness of the column structure, which is used to adjust the property of EAD. The motions of semi-submersible are obtained, and the collision force and the tension forces of mooring lines are also got. Collision scenario characters for semi-motion and tension force are summarized by the analysis of the model test results. The second collision phenomenon is observed. The collision force dominates the collision moment and the tension force of the mooring lines lags behind. A NTNU in-house program developed by analytical simplified method is also verified by the model test result. The comparison proves the feasibility of the program.

Numerical Seakeeping Simulation of Model Test Condition for Two-Ship Interaction in Waves

2007 ◽  
Author(s):  
Lin Li
Keyword(s):  
Numerical Simulation ◽  
Model Test ◽  
Current Paper ◽  
Free Motion ◽  
Test Results ◽  
Wave Excitation ◽  
Motion Constraints ◽  
Test Conditions ◽  
Motion Modes ◽  
Simulation Results

In order to validate the numerical prediction of two-ship interactions in waves, the model test calibration has to be conducted. However, motion constraints are usually applied when model tests are carried out for the measurement of wave excitation forces and moments in certain selected motion modes for both ships. Therefore, in current paper, a numerical seakeeping simulation of the model test conditions has been studied. Restraints in surge, sway and yaw, as well as the free motion modes in heave, roll and pitch have been all applied to both the ships, experimentally and numerically. The restraint forces and the unrestrained motions have been compared with the model test results and numerical simulation results. Fairly good agreements have been found.

Model Test Comparisons of TLP, Spar-buoy and Semi-submersible Floating Offshore Wind Turbine Systems

2012 ◽  
Author(s):  
Richard W. Kimball ◽  
Andrew J. Goupee ◽  
Alexander J. Coulling ◽  
Habib J. Dahger
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Model Test ◽  
Functional Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Floating Offshore Wind Turbine ◽  
Power Spectral ◽  
Wave Basin ◽  
Modeling Code

Results of wave basin tests on three 1/50th scale floating wind turbine systems tested at the MARIN model basin are presented. The tests included a fully functional model wind turbine and a novel wind machine to produce swirl free inflow at a turbulence intensity of about 5%. Simultaneous stochastic wind and waves as well as multidirectional sea conditions were tested. This paper presents the experimental work as well as validation comparisons to NREL’s FAST floating offshore wind turbine dynamic modeling code. The paper also discusses the testing methodology and presents means to more closely match full scale performance at the low-Reynolds number operation regimes of the model test. Analyses presented include response amplitude operator and power spectral density plots for the spar-buoy, tensionleg platform and semi-submersible designs. The results presented for the systems highlight both turbine response effects and second-order wave diffraction forcing effects.

Determining Side-by-Side Current Loads Using CFD and Model Tests

2016 ◽  
Author(s):  
Arjen Koop
Keyword(s):  
Reynolds Number ◽  
Model Test ◽  
Full Scale ◽  
Test Results ◽  
Model Scale ◽  
Moment Coefficient ◽  
The Difference ◽  
The Moment ◽  
Good Agreement ◽  
Shielding Effects

When two vessels are positioned close to each other in a current, significant shielding or interaction effects can be observed. In this paper the current loads are determined for a LNG carrier alone, a Shuttle tanker alone and both vessels in side-by-side configuration. The current loads are determined by means of tow tests in a water basin at scale 1:60 and by CFD calculations at model-scale and full-scale Reynolds number. The objective of the measurements was to obtain reference data including shielding effects. CFD calculations at model-scale Reynolds number are carried out and compared with the model test results to determine the capability of CFD to predict the side-by-side current load coefficients. Furthermore, CFD calculations at full-scale Reynolds number are performed to determine the scale effects on current loads. We estimate that the experimental uncertainty ranges between 3% and 5% for the force coefficients CY and CMZ and between 3% and 10% for CX. Based on a grid sensitivity study the numerical sensitivity is estimated to be below 5%. Considering the uncertainties mentioned above, we assume that a good agreement between experiments and CFD calculations is obtained when the difference is within 10%. The best agreement between the model test results and the CFD results for model-scale Reynolds number is obtained for the CY coefficient with differences around 5%. For the CX coefficient the difference can be larger as this coefficient is mainly dominated by the friction component. In the model tests this force is small and therefore difficult to measure. In the CFD calculations the turbulence model used may not be suitable to capture transition from laminar to turbulent flow. A good agreement (around 5% difference) is obtained for the moment coefficient for headings without shielding effects. With shielding effects larger differences can be obtained as for these headings a slight deviation in the wake behind the upstream vessel may result in a large difference for the moment coefficient. Comparing the CFD results at full-scale Reynolds number with the CFD results at model-scale Reynolds number significant differences are found for friction dominated forces. For the CX coefficient a reduction up to 50% can be observed at full-scale Reynolds number. The differences for pressure dominated forces are smaller. For the CY coefficient 5–10% lower values are obtained at full-scale Reynolds number. The moment coefficient CMZ is also dominated by the pressure force, but up to 30% lower values are found at full-scale Reynolds number. The shielding effects appear to be slightly smaller at full-scale Reynolds number as the wake from the upstream vessel is slightly smaller in size resulting in larger forces on the downstream vessel.

Investigation Into Float-Over Installations of Minimal Platforms by Hydrodynamic Model Testing

2005 ◽  
Author(s):  
J. Xia ◽  
S. Hayne ◽  
G. Macfarlane ◽  
D. Field ◽  
Y. Drobyshevski
Keyword(s):  
Model Test ◽  
Load Transfer ◽  
Test Results ◽  
Numerical Predictions ◽  
Wave Basin ◽  
Transfer Operation ◽  
Response Amplitude Operators ◽  
Jack Up ◽  
Standard Software ◽  
Insight Into

The idea of using float-over installations for minimal facilities platforms was shown to offer significant advantages, especially when coupled with a substructure installed by a jack-up rig. Recently, float-over installations of minimal facilities have been conducted by the cantilevered method by ICON Engineering Pty Ltd (ICON). The operation involves the platform topsides being loaded and transported to site on a barge, skidded over the barge bow, and lowered onto the jacket. The paper presents results of a research project undertaken by the Australian Maritime College (AMC) in conjunction with ICON, with the objective to investigate motions of a barge and loads exerted on the jacket when the two are docked together for a smooth load transfer operation. The model of an installation barge has been tested in the AMC wave basin and response amplitude operators of the barge motions have been determined for both the free floating and docked conditions. A range of wave periods and heights has been investigated. Model test results have been used to verify numerical predictions used in the design, and to get insight into uncertainties, which may otherwise be difficult to assess using standard software.

Investigation on Reasons for Possible Difference Between VIM Response in the Field and in Model Tests

2016 ◽  
Author(s):  
Arjen Koop ◽  
Jaap de Wilde ◽  
André Luís Condino Fujarra ◽  
Oriol Rijken ◽  
Samuel Linder ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Fatigue Damage ◽  
Model Test ◽  
Scale Effects ◽  
Model Tests ◽  
Full Scale ◽  
Strong Impact ◽  
Numerical Verification ◽  
Field Observations ◽  
Test Results

Floating offshore structures, such as production semi-submersibles and spars, can exhibit significant in-line and transverse oscillatory motions under current conditions. When caused by vortex shedding from the floater, such motions are generally called Vortex-Induced Motions (VIM). For semi-submersibles these motions could have a strong impact on the fatigue life of mooring and riser systems. Some field development studies indicate that the VIM induced fatigue damage for larger diameter Steel Catenary Risers (SCRs) can have a magnitude equal to or larger than the wave-induced fatigue damage. The VIM phenomenon for multi-column floaters is characterized by complex interactions between the flow and the motions of the floater. Presently, model tests are the preferred method to predict the VIM response of a multi-column floater. However, several studies indicate that the observed VIM response in the field is less than what is observed in model test campaigns: typical model test results are very conservative. Using such test results in the development of mooring and riser design can easily result in very conservative designs which can have a significant impact on mooring and riser cost, or even affect SCR selection and/or feasibility. The primary objective of the VIM JIP was to increase the physical insight into the VIM phenomenon. This knowledge is then used to address possible areas that could explain the differences between the results from model tests and field observations. To address these objectives, the JIP focused on model testing and CFD studies. A key segment of the JIP was the use of identical semi-submersible hull geometries for the numerical and experimental studies thereby facilitating the interpretation of the various response comparisons. The JIP identified that a CFD model, at model-scale Reynolds number, can reasonably well reproduce the VIM response observed in model tests. However, to have confidence in the CFD results extensive numerical verification studies have to be carried out. The effect of external damping was investigated in model tests and in CFD calculations. Both the numerical and experimental results show that external damping significantly reduces the VIM response. Comparisons between CFD results at model- and full-scale Reynolds number indicate that Froude scaling is applicable, with minor scale effects identified on the amplitudes of the VIM motions. Changing the mass ratio of the floater has a small influence on the VIM response. Experimentally it was found that VIM response under inline or transverse waves is slightly smaller than without the presence of waves and is wave heading and wave height dependent. The presence of waves does not explain the observed differences between model test results and field observations. The effect of unsteady current on the VIM response is minimal. Based on the results from the JIP it is concluded that increased external damping reduces the VIM response. The questions that remain are if the increased external damping is actually present in full-scale conditions and if the mooring and riser systems provide the required damping to reduce the VIM amplitudes.

Comments on Compressor Efficiency Scaling With Reynolds Number and Relative Roughness

1989 ◽  
Author(s):  
Terry Wright
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Friction Factor ◽  
Model Test ◽  
Large Scale ◽  
Recent Literature ◽  
Test Results ◽  
Relative Roughness ◽  
Scaling Algorithms ◽  
Compressor Efficiency

The background and literature on scaling of model test results to predict the performance of large scale turbomachines are presented and discussed in the context of both industry restrictions and recent improvements in analytical rigor and accuracy of scaling algorithms. The variety and disparity of methods developed before about 1970 is illustrated and plausible explanation is offered to account for the broad differences. The more recent literature is considered and the older exponential algorithms for scaling are reconciled with the current methods based on friction factor correlations. A simpler form is developed in terms of either exponential or friction factor formulations which includes the influence of Reynolds Number, relative roughness and fixed, friction-independent losses. This method is compared to the recently developed algorithms and to experimental data taken from the literature.

Sign in / Sign up

Export Citation Format

Share Document