Model-Scale and Full-Scale CFD Calculations for Current Loads on Semi-Submersible

2011 ◽  
Author(s):  
Arjen Koop ◽  
Alexei Bereznitski
Keyword(s):  
Wind Tunnel ◽  
Scale Effects ◽  
Full Scale ◽  
Grid Resolution ◽  
Wind Tunnel Experiments ◽  
Force Coefficients ◽  
Model Scale ◽  
Coarse Grids

In this paper results of CFD calculations with the MARIN in-house code ReFRESCO are presented for the JBF-14000 Semi-Submersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semi-submersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the model-scale current loads on a semi-submersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semi-submersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Full-scale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for model-scale and full-scale. The use of coarse grids can lead to misleading conclusions. On average the full-scale values are approximately 15–20% lower than for model-scale. However, larger differences for a number of angles do exist.

A New Method of Modeling Underexpanded Exhaust Plumes for Wind Tunnel Aerodynamic Testing

1989 ◽  
Vol 111 (4) ◽  
pp. 748-754
Author(s):  
V. Salemann ◽  
J. M. Williams
Keyword(s):  
Wind Tunnel ◽  
Free Stream ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Full Scale ◽  
New Method ◽  
Thrust Coefficient ◽  
Model Scale ◽  
Exhaust Plumes

A new method for modeling hot underexpanded exhaust plumes with cold model scale plumes in aerodynamic wind tunnel testing has been developed. The method is applicable to aeropropulsion testing where significant interaction between the exhaust and the free stream and aftbody may be present. The technique scales the model and nozzle external geometry, including the nozzle exit area, matches the model jet to free-stream dynamic pressure ratio to full-scale jet to free-stream dynamic pressure ratio, and matches the model thrust coefficient to full-scale thrust coefficient. The technique does not require scaling of the internal nozzle geometry. A generalized method of characteristic computer code was used to predict the plume shapes of a hot (γ = 1.2) half-scale nozzle of area ratio 3.2 and of a cold (γ = 1.4) model scale nozzle of area ratio 1.3, whose pressure ratio and area ratio were selected to satisfy the above criteria and other testing requirements. The plume shapes showed good agreement. Code validity was checked by comparing code results for cold air exhausting into a quiescent atmosphere to pilot surveys and shadowgraphs of model nozzle plumes taken in a static facility.

A study on the influence of hull wake on model scale cavitation and noise tests for a fast twin screw vessel with inclined shaft

2017 ◽  
Vol 232 (3) ◽  
pp. 307-330
Author(s):  
Giorgio Tani ◽  
Michele Viviani ◽  
Diego Villa ◽  
Marco Ferrando
Keyword(s):  
Scale Effects ◽  
Full Scale ◽  
Ship Wake ◽  
Radiated Noise ◽  
Wake Field ◽  
Model Scale ◽  
Propeller Noise ◽  
Twin Screw ◽  
Long Time ◽  
The Impact

The study of ship underwater radiated noise is nowadays a topic of great and largely recognized importance. This is due to the fact that in the last decades, the problem of the impact of anthropogenic noise on marine life has been addressed with higher emphasis, giving rise to different efforts aimed to the analysis of its effects on different organisms and, in parallel, to means for the reduction of shipping noise. In this context, attention is focused on the propeller noise, which, in cavitating conditions, may represent the most important noise source of the ship. The propeller noise has been studied for long time with different approaches. One of the most effective approaches is represented by model scale testing in cavitation tunnels or similar facilities. Despite having been adopted for several years, radiated noise experiments in model scale are usually affected by significant scale effects and technical issues. One of these aspects is represented by the correct modelling of the propeller inflow; different techniques are adopted, depending on the facility, in order to reproduce a certain target wake. One of the main problems is to define this target wake, which should in principle coincide with the ship wake; as it is well known, it is usually derived from model scale towing tank measurements, with the necessity for the prediction of the full-scale wake field. Starting from the outcomes of a previous work on the influence of different approaches for the prediction of the full-scale wake field for a single screw ship, in this work, attention is focused on the case of a fast twin screw vessel, analysing the different issues which may be connected to this hull form.

Development of a Scaled-Down Floating Wind Turbine for Offshore Basin Testing

2014 ◽  
Author(s):  
Erik-Jan de Ridder ◽  
William Otto ◽  
Gert-Jan Zondervan ◽  
Fons Huijs ◽  
Guilherme Vaz
Keyword(s):  
Wind Turbine ◽  
Wind Velocity ◽  
Scaling Laws ◽  
Scale Effects ◽  
Model Testing ◽  
Model Tests ◽  
Full Scale ◽  
Pitch Control ◽  
Model Scale ◽  
Floating Wind Turbine

In the last years MARIN has been involved in an increasing number of projects for the offshore wind industry. New techniques in model testing and numerical simulations have been developed in this field. In this paper the development of a scaled-down wind turbine operating on a floating offshore platform, similar to the well-known 5MW NREL wind turbine is discussed. To simulate the response of a floating wind turbine correctly it is important that the environmental loads due to wind, waves and current are in line with full scale. For dynamic similarity on model scale, Froude scaling laws are used successfully in the Offshore industry for the underwater loads. To be consistent with the underwater loads, the winds loads have to be scaled according to Froude as well. Previous model tests described by Robertson et al [1] showed that a geometrically-scaled turbine generated a lower thrust and power coefficient with a Froude-scaled wind velocity due to the strong Reynolds scale effects on the flow. To improve future model testing, a new scaling method for the wind turbine blades was developed originally by University of Maine, and here improved and applied. In this methodology, the objective is to obtain power and thrust coefficients which are similar to the full-scale turbine in Froude-scaled wind. This is obtained by changing the geometry of the blades in order to provide thrust equality between model and full scale, and can therefore be considered as a “performance scaling”. This method was then used to design and construct a new MARIN Stock Wind Turbine (MSWT) based on the NREL 5MW wind turbine blade, including an active blade pitch control to simulate different blade pitch control systems. MARIN’s high-quality wind setup in combination with the new model scale stock wind turbine was used for testing the GustoMSC Tri-Floater semi-submersible as presented in Figure 1, including an ECN active blade pitch control algorithm. From the model tests it was concluded that the measured thrust versus wind velocity characteristics of the new MSWT were in line with the full scale prediction and with CFD (Computational Fluid Dynamics) results.

Analysis of U-Type Anti-Roll Tank Using URANS: Sensitivity and Validation

2014 ◽  
Author(s):  
Maarten Kerkvliet ◽  
Guilherme Vaz ◽  
Nicolas Carette ◽  
Michiel Gunsing
Keyword(s):  
Free Surface ◽  
Full Scale ◽  
Grid Resolution ◽  
Experimental Results ◽  
Green Water ◽  
Roll Motion ◽  
Time Step ◽  
Roll Damping ◽  
Maximum Acceleration ◽  
Model Scale

The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.

scholarly journals Comparing flyover noise measurements to full-scale nose landing gear wind tunnel experiments for regional aircraft

2017 ◽  
Author(s):  
Roberto Merino Martinez ◽  
Eleonora Neri ◽  
Mirjam Snellen ◽  
John Kennedy ◽  
Dick Simons ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Landing Gear ◽  
Full Scale ◽  
Wind Tunnel Experiments ◽  
Noise Measurements

Numerical Simulation of Wind Pressure Distribution on Structure Roofs with Suspension Solar Panels

2010 ◽  
Vol 163-167 ◽  
pp. 3943-3946
Author(s):  
Ying Zhou ◽  
Qi Lin Zhang
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Pressure Distribution ◽  
3D Model ◽  
Distribution Coefficients ◽  
Full Scale ◽  
Wind Pressure ◽  
Solar Panels ◽  
Wind Tunnel Experiments ◽  
Load Effect

This paper presents the results of full-scale numerical wind tunnel tests of wind pressure on structure roofs with suspension solar panels. Solar roof project is popularized in this century. Solar panels are suspended above the structure roof. So the wind load effect on the structure roof is varied. The wind tunnel experiments are often expensive. A 3D model is introduced and solved using ADINA. The wind pressure distribution coefficients are calculated.

The Spinning of Aeroplanes

1927 ◽  
Vol 31 (199) ◽  
pp. 619-688 ◽  
Author(s):  
L. W. Bryant ◽  
S. B. Gates
Keyword(s):  
Wind Tunnel ◽  
Preliminary Report ◽  
Full Scale ◽  
Wind Tunnel Experiments ◽  
Research Committee ◽  
Stability And Control ◽  
The Subject ◽  
Ready Access ◽  
The Stability ◽  
And Control

We should like to preface our essay on the subject of spinning by mentioning the circumstances under which our investigations were carried out and the sources of our information. The Panel of the Aeronautical Research Committee which has been appointed to deal with all questions connected with the stability and control of aeroplanes was requested in 1924 to consider the urgent problems connected with the alarming accidents due to certain machines failing to retover from a spin. After the issue of a preliminary report on the situation by the Panel, the writers of this paper were asked to go into the whole question as far as existing information from full-scale and wind tunnel experiments would permit. We have had ready access to all available data, coming chiefly from Farnborough on the full-scale side, and from the N.P.L. on the model side.

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