Assessment of Nonlinear Heave Damping Model for Spar With Heave Plate Using Free Decay Tests

2016 ◽  
Author(s):  
Mahesh J. Rao ◽  
S. Nallayarasu ◽  
S. K. Bhattacharyya
Keyword(s):  
Cfd Simulation ◽  
Linear Quadratic ◽  
Cfd Simulations ◽  
Free Decay ◽  
Linear Damping ◽  
Heave Plate ◽  
Decay Tests ◽  
Heave Motion ◽  
Damping Model ◽  
Quadratic Damping

Linear damping models have been used in the past for solving floating body dynamics, especially for simple geometries such as spar. However, due to the addition of heave damping elements to spar such as heave plate, complex flow around these elements may change the relationship between damping and velocity of the body to nonlinear. The damping plays a major role in accurate determination of motion response of spars, especially the heave. Free decay tests have been carried out for spar with and without heave plate in calm water condition. The Computational Fluid Dynamics (CFD) simulation of heave decay is carried out using ANSYS FLUENT and validated by free decay test results using scale models. Mesh convergence study has been conducted to determine the optimum mesh size. The heave motion obtained from CFD are used to derive the damping terms by matching the heave motion obtained using equation of motion by changing the damping term with linear, quadratic and the combination of linear and quadratic. The heave motion obtained from linear damping model matches well with that obtained from measured motion and CFD simulation for spar without heave plate. However, the linear / quadratic damping models alone are not suitable for spar with heave plate. Hence a combination of linear and quadratic damping model is proposed for spar with heave plate. The heave motion computed using a combination of linear and quadratic damping model matches well with that obtained from experimental studies and CFD simulations thus indicating the complexity of flow around heave plate in comparison to the spar alone. Further, the vortices around the spar models obtained from CFD simulations are also presented and discussed with regard to the higher order damping.

Hydrodynamic Properties of a Suction Can Oscillating Near the Free Surface

2009 ◽  
Author(s):  
C. Plummer ◽  
G. Macfarlane ◽  
Y. Drobyshevski
Keyword(s):  
Free Surface ◽  
Added Mass ◽  
Hydrodynamic Properties ◽  
Noticeable Effect ◽  
Sea Floor ◽  
Notable Effect ◽  
Free Decay ◽  
Decay Tests ◽  
Quadratic Damping ◽  
Motion Amplitude

Offshore operations often require heavy subsea equipment, such as suction piles or cans, to be lowered by a support vessel into the sea. A lifting device must have adequate capacity to withstand the dynamic loads generated by the motions of the vessel and the heave response of the structure. The objective of this study is to determine the added mass and damping of a suction can oscillating in heave near the free surface; knowledge of these hydrodynamic properties is required for the accurate prediction of the dynamic lift forces during the deployment. This project is a logical progression following two similar studies, which investigated these hydrodynamic properties for the suction can in the mid-water position and when approaching the seabed. All three studies involved the conduct of model tests to determine the hydrodynamic properties. Free decay tests were conducted at several heave frequencies, and the added mass, linear and quadratic damping components were determined. In addition, the effect of varying the percentage of open hatch area has been investigated. Test data demonstrates that the heave added mass is strongly dependent on the frequency of motion, and its values are significantly smaller than those measured in the unrestricted flow. From observations, there was no dependency on the motion amplitude, nor did the size of open hatches have notable effect on the added mass. It was observed that when the top plate of the structure was in contact with the free surface a mean “pull down” force appeared. This force is caused by the suction underneath the top plate when the can moves upwards. As opposed to the mid-water position and near the sea floor, the study indicates that the area of open hatches has no noticeable effect on the heave damping when the suction can is oscillating near the free surface.

scholarly journals Experimental and Computational Methodology for the Determination of Hydrodynamic Coefficients Based on Free Decay Test: Application to Conception and Control of Underwater Robots

Sensors ◽  
2019 ◽  
Vol 19 (17) ◽  
pp. 3631 ◽  
Author(s):  
Juan S. Cely ◽  
Roque Saltaren ◽  
Gerardo Portilla ◽  
Oz Yakrangi ◽  
Alejandro Rodriguez-Barroso
Keyword(s):  
Cfd Simulation ◽  
Low Cost ◽  
Water Channel ◽  
Hydrodynamic Coefficients ◽  
Underwater Robots ◽  
Free Decay ◽  
Test Application ◽  
Decay Test ◽  
Decay Tests ◽  
And Control

Hydrodynamic coefficients are essential for the development of underwater robots; in particular, for their design and navigation control. To obtain these coefficients, several techniques exist. These methods are usually experimental, but, more recently, some have been designed by a combination of experiments with computational methods based on Computational Fluid Dynamics (CFD). One method for obtaining the hydrodynamic coefficients of an ROV (Remote Operated Vehicle) is by using an experimental PMM (Planar Motion Mechanism) or CWC (Circular Water Channel); however, the use of these experimental infrastructures is costly. Therefore, it is of interest to obtain these coefficients in other ways, for example, by the use of simple experiments. The Free Decay Test is an ideal type of experiment, as it has a low cost and is simple to implement. In this paper, two different free decay tests were carried out, to which three different methods for obtaining coefficients were applied. They were compared with results obtained by CFD simulation to conduct a statistical analysis in order to determine their behaviours. It was possible to obtain values of the drag and added mass coefficients for the models analysed, where the values were obtained for an Underwater Drone Robot (UDrobot).

scholarly journals OC6 Phase Ia: CFD Simulations of the Free-Decay Motion of the DeepCwind Semisubmersible

Energies ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 389
Author(s):  
Lu Wang ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Jang Kim ◽  
Zhi-Rong Shen ◽  
...  
Keyword(s):  
Damping Ratio ◽  
International Energy Agency ◽  
Offshore Wind ◽  
Cfd Simulations ◽  
Energy Agency ◽  
Equivalent Damping ◽  
Damping Coefficients ◽  
Hydrodynamic Damping ◽  
Free Decay ◽  
Quadratic Damping

Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free-decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid-fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertainties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge-decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction-type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid-fidelity models.

Scale Effects on Heave Plates for Floating Offshore Wind Turbines

2018 ◽  
Author(s):  
Ana Bezunartea-Barrio ◽  
Sergio Fernandez-Ruano ◽  
Adolfo Maron-Loureiro ◽  
Enrique Molinelli-Fernandez ◽  
Francisco Moreno-Buron ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Scale Effects ◽  
Added Mass ◽  
Offshore Wind ◽  
Forced Oscillations ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Heave Plate ◽  
Decay Tests ◽  
Heave Motion

An essential aspect of experimental campaigns in ocean basins is the extrapolation of results to prototype scale. In the case of “spar” or semi-submersible platforms for floating wind turbines, it is customary to use heave plates that reduce the heave motion and/or tune its period. As part of the Hiprwind project, it was decided to study the scale effects on the hydrodynamics of these elements. To this aim, models of one column of the platform, equipped with a plain heave plate, were built. This model is a simplified representation of the actual one, which incorporates an edge vertical flap. The scales were 1:20, 1:27.6, and 1:45.45, with the former leading to added mass values of the order of 300kg, becoming one of the largest model for which experiments with heave oscillations have been carried out. Decay tests starting from various amplitudes and forced oscillations tests were performed at a range of frequencies and operational and extreme KCs (range of motion). Results related to these tests will be discussed in the paper.

scholarly journals Two-phase CFD simulation of the monodyspersed suspension hydraulic behaviour in the tank apparatus from a circulatory pipe

2008 ◽  
Vol 10 (1) ◽  
pp. 22-27 ◽  
Author(s):  
Roch Plewik ◽  
Piotr Synowiec ◽  
Janusz Wójcik
Keyword(s):  
Cfd Simulation ◽  
Fluidised Bed ◽  
Cfd Simulations ◽  
Two Phase ◽  
Hydraulic Behaviour ◽  
Hydraulic Conditions ◽  
The One ◽  
Cfd Method ◽  
Multi Phase ◽  
The Ideal

Two-phase CFD simulation of the monodyspersed suspension hydraulic behaviour in the tank apparatus from a circulatory pipe The hydrodynamics in fluidized-bed crystallizers is studied by CFD method. The simulations were performed by a commercial packet of computational fluid dynamics Fluent 6.x. For the one-phase modelling (15), a standard k-ε model was applied. In the case of the two-phase flows the Eulerian multi-phase model with a standard k-ε method, aided by the k-ε dispersed model for viscosity, has been used respectively. The collected data put a new light on the suspension flow behaviour in the annular zone of the fluidised bed crystallizer. From the presented here CFD simulations, it clearly issues that the real hydraulic conditions in the fluidised bed crystallizers are far from the ideal ones.

Weak Coupling Strategy for Multi-Physics CFD Simulation in Engineering Problems

2011 ◽  
Author(s):  
Makoto Yamamoto ◽  
Masaya Suzuki
Keyword(s):  
Strong Coupling ◽  
Time Scale ◽  
Weak Coupling ◽  
Particle Deposition ◽  
Cfd Simulation ◽  
The Other ◽  
Cfd Simulations ◽  
Sand Erosion ◽  
Coupling Strategy ◽  
The Difference

Multi-Physics CFD Simulation will be one of key technologies in various engineering fields. There are two strategies to simulate a multi-physics phenomenon. One is “Strong Coupling”, and the other is “Weak Coupling”. Each can be employed, based on time-scales of physics embedded in a problem. That is, when a time-scale of one physics is nearly same as that of the other physics, we have to use Strong Coupling to take into account the interaction between two physics. On the other hand, when one time-scale is quite different from the other one, Weak Coupling can be applied. Considering the present computer performance, Strong Coupling is difficult to be used in engineering design processes now. Therefore, we are focusing on Weak Coupling, and it has been applied to a number of multi-physics CFD simulations in engineering. We have successfully simulated sand erosion, ice accretion, particle deposition, electro-chemical machining and so on, with using Weak Coupling method. In the present study, the difference between strong and weak couplings is briefly described, and two examples of our multi-physics CFD simulations are expressed. The numerical results indicate that Weak Coupling strategy is promising in a lot of multi-physics CFD simulations.

The Impact of Predried Lignite Cofiring With Hard Coal in an Industrial Scale Pulverized Coal Fired Boiler

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Halina Pawlak-Kruczek ◽  
Robert Lewtak ◽  
Zbigniew Plutecki ◽  
Marcin Baranowski ◽  
Michal Ostrycharczyk ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Bituminous Coal ◽  
Cfd Simulation ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Industrial Scale ◽  
Hard Coal ◽  
Cfd Simulations ◽  
Reference Case ◽  
The Impact

The paper presents the experimental and numerical study on the behavior and performance of an industrial scale boiler during combustion of pulverized bituminous coal with various shares of predried lignite. The experimental measurements were carried out on a boiler WP120 located in CHP, Opole, Poland. Tests on the boiler were performed during low load operation and the lignite share reached over to 36% by mass. The predried lignite, kept in dedicated separate bunkers, was mixed with bituminous coal just before the coal mills. Computational fluid dynamic (CFD) simulation of a cofiring scenario of lignite with hard coal was also performed. Site measurements have proven that cofiring of a predried lignite is not detrimental to the boiler in terms of its overall efficiency, when compared with a corresponding reference case, with 100% of hard coal. Experiments demonstrated an improvement in the grindability that can be achieved during co-milling of lignite and hard coal in the same mill, for both wet and dry lignite. Moreover, performed tests delivered empirical evidence of the potential of lignite to decrease NOx emissions during cofiring, for both wet and dry lignite. Results of efficiency calculations and temperature measurements in the combustion chamber confirmed the need to predry lignite before cofiring. Performed measurements of temperature distribution in the combustion chamber confirmed trend that could be seen in the results of CFD. CFD simulations were performed for predried lignite and demonstrated flow patterns in the combustion chamber of the boiler, which could prove useful in case of any further improvements in the firing system. CFD simulations reached satisfactory agreement with the site measurements in terms of the prediction of emissions.

scholarly journals Bilge Keel Induced Roll Damping of an FPSO With Sponsons

2016 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Trygve Kristiansen ◽  
Christopher Hutchison ◽  
Hanne Bakksjø
Keyword(s):  
Free Surface ◽  
Two Dimensions ◽  
The Body ◽  
Proximity Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Free Decay ◽  
Strip Theory ◽  
Decay Tests ◽  
Bilge Keel

The bilge keel induced roll damping of an FPSO with sponsons is investigated numerically and experimentally. The influence of the bilge keel size, on the roll damping is studied. Free decay tests of a three-dimensional ship model, for three different bilge keel sizes are used to determine roll damping coefficients. The dependency of the quadratic roll damping coefficient to the bilge keel height and the vertical location of the rotation center is studied using CFD. A Navier-Stokes solver based on the Finite Volume Method is adopted for solving the laminar flow of incompressible water around a section of the FPSO undergoing forced roll oscillations in two-dimensions. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. An averaged center of rotation is estimated by comparing the results of the numerical calculations and the free decay tests. The obtained two-dimensional damping coefficients are extrapolated to 3D by use of strip theory argumentations and compared with the experimental results. It is shown that this simplified approach can be used for evaluating the bilge keel induced roll damping with efficiency, considering unconventional ship shapes and free-surface proximity effects.

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