144 research outputs found
TeraWatt North Atlantic spectral wave model input files (for MIKE 21)
No full textNORTH ATLANTIC MIKE 21 MODEL INPUT FILES
This submission includes the input files for the North Atlantic spectral wave model that is described in [1,2]. It formed part of the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 &
EP/K012851/1 respectively).
The input files require the MIKE 21 modelling suite to run, available commercially from https://www.mikepoweredbydhi.com/; they were created and validated using the 2014 edition. Input files are being stored instead of outputs as per RCUK guidelines due to the size of the output files.
For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]).
[1] V. Venugopal and R. Nemalidinne, ‘Wave resource assessment for Scottish waters using a large scale North Atlantic spectral wave model’, Renewable Energy, vol. 76, no. Supplement C, pp. 503–525, Apr. 2015.
[2] V. Venugopal, R. Nemalidinne, and A. Vögler, ‘Numerical modelling of wave energy resources and assessment of wave energy extraction by large scale wave farms’, Ocean & Coastal Management, Mar. 2017.See readme.txt
WEST ORKNEY MIKE 21 MODEL INPUT FILES
No full textThis submission includes the input files for the West Orkney spectral wave sub-model that is described in [1]. It formed part of the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 & EP/K012851/1 respectively). The input files require the MIKE 21 modelling suite to run, available commercially from https://www.mikepoweredbydhi.com/; they were created and validated using the 2014 edition. Input files are being stored instead of outputs as per RCUK guidelines due to the size of the output files. Versions of the simulation were run for present (2010) and future (2050) climate, and with and without wave energy extraction by wave energy convertors (WECs). All four resulting scenarios are included here. For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]).Venugopal, Vengatesan; Waldman, Simon. (2017). WEST ORKNEY MIKE 21 MODEL INPUT FILES, 2010 [dataset]. School of Engineering, University of Edinburgh. http://dx.doi.org/10.7488/ds/2217
Numerical modelling of full scale tidal turbines using the actuator disc approach
Get PDFIn recent years, the actuator disc approach which employs the Reynolds-Averaged
Navier-Stokes (RANS) solvers has been extensively applied in wind and tidal energy
field to estimate the wake of a horizontal axis turbine. This method is simpler to administer
and requires moderate computational resources in modelling a tidal turbines rotor.
Nonetheless, the use of actuator disc approximation in predicting the performance
of tidal devices has been limited to studies involving an extremely small disc (e.g.
rotor diameter of 0.1 meter). The drawback of a small scale actuator disc model is the
overestimation of essential parameters such as the mesh density and the resolution of
the vertical layers, making them impractical to be replicated in a regional scale model.
Hence, this study aims to explore the methodology on implementation of the Three-
Dimensional (3D) actuator disc-RANS model in an ocean scale simulation. Additionally,
this study also aspires to examine the sensitivity of the applied momentum source
term and its validity in representing full-size tidal devices. Nonetheless, before the
effectiveness of an actuator disc in a regional model can be tested, tidal flow models
for the area of interest needed to be set up first. This was essential for two reasons: (a) to
ensure accurate hydrodynamic flow conditions at the deployment site were replicated,
(b) to give confidence in the outputs produced by the regional scale actuator disc
simulations, since in-situ turbine measurement data from a real deployment site were
difficult to source.
This research was undertaken in two stages; in the first stage, a numerical model which
can simulate the tidal flow conditions of the deployment sites was constructed, and, in
the second stage, the actuator disc method which is capable of modelling an array of
real scale-sized tidal turbines rotors has been implemented.
In the first stage, tidal flow simulations of the Pentland Firth and Orkney Waters
(PFOW) were conducted using two distinct open-source software – Telemac3D, which
is a finite element based numerical model, and Delft3D, which is a finite difference
based model. Detailed methodologies in developing a 3D tidal flow model for the
PFOW using both numerical models were presented, where their functionality, as well
as limitations were explored. In the calibration and validation processes, both models
demonstrated excellent comparison against the measured data. However, Telemac3D
was selected for further modelling of the actuator disc considering the model’s capability
to perform parallel computing, together with its flexibility to combine both
structured and unstructured mesh.
In the second stage, to examine the actuator disc’s accuracy in modelling a full size
tidal device, the momentum source term was initially applied in an idealised channel
study, where the presence of a 20-meter diameter turbine was simulated for both
single and array configurations. The following parameters were investigated: (i) size
of the unstructured mesh utilised in the computational domain, (ii) variation in disc’s
thickness, (iii) resolution of the imposed structured grid to represent turbine’s enclosure,
(iv) variation in the vertical layers, and (v) influence of hydrostatic and non-hydrostatic
formulations on the models’ outputs. It is to be noted that the turbine’s
support structures have not been included in the modelling.
The predicted velocities and computed turbulence intensities from the models were
compared against laboratory measurement data sourced from literature, where excellent
agreement between the model outputs and the data from literature was observed.
In essence, these studies highlighted the efficiency and robustness of the applied momentum
source term in replicating the wake profiles and turbulence characteristics
downstream of the disc, hence providing credence in implementing the actuator disc
method for a regional scale application.
Subsequently, the validated actuator disc method was applied to the Inner Sound region
of the Pentland Firth to simulate arrays of up to 32 tidal turbine rotors. The wake
development, flow interactions with the rotor arrays, and flow recovery at the Inner
Sound region have been successfully mapped. Also, this study highlighted the importance
of employing optimal numerical margins, specifically for the structured grid and
horizontal planes, as both parameters were relevant in defining the disc’s swept area. As
published materials on the implementation of actuator disc approach within a regional
scale model is still scarce, it was aspired that this work could provide some evidence,
guidance and examples of suggested best practice in effort to fill the research gap in
modelling tidal turbine arrays using the actuator disc approach
TeraWatt North Atlantic spectral wave model input files (for MIKE 21)
No full textNORTH ATLANTIC MIKE 21 MODEL INPUT FILES This submission includes the input files for the North Atlantic spectral wave model that is described in [1,2]. It formed part of the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 & EP/K012851/1 respectively). The input files require the MIKE 21 modelling suite to run, available commercially from https://www.mikepoweredbydhi.com/; they were created and validated using the 2014 edition. Input files are being stored instead of outputs as per RCUK guidelines due to the size of the output files. For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]). [1] V. Venugopal and R. Nemalidinne, ‘Wave resource assessment for Scottish waters using a large scale North Atlantic spectral wave model’, Renewable Energy, vol. 76, no. Supplement C, pp. 503–525, Apr. 2015. [2] V. Venugopal, R. Nemalidinne, and A. Vögler, ‘Numerical modelling of wave energy resources and assessment of wave energy extraction by large scale wave farms’, Ocean & Coastal Management, Mar. 2017.Venugopal, Vengatesan. (2017). TeraWatt North Atlantic spectral wave model input files (for MIKE 21), 2010 [dataset]. School of Engineering, University of Edinburgh. http://dx.doi.org/10.7488/ds/2216
MIKE 21 West Orkney Monthly Hs Summary Outputs
No full textMIKE 21 WEST ORKNEY MONTHLY Hs SUMMARY OUTPUTS
This collection of netCDF format files contains monthly summary outputs of significant wave height (Hs) from the West of Orkney MIKE 21 spectral wave model described in [1]. For each month the mean Hs and the values of the 5,10,20...,90,95th percentiles are given for each cell in the model.
The model was designed to study the effects on wave height of both wave energy extraction and climate change.
Four scenarios are included: Present day (2010) with and without wave energy convertors, and future climate (~2050) with and without wave energy convertors. See [1] for more detail on present-day; a future publication will describe the future version.
This model was developed under the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 & EP/K012851/1 respectively). The data archived here are being used within the EcoWatt project for ongoing ecological studies.
For the input files for the model used to produce these outputs, please see submission "WEST ORKNEY MIKE 21 MODEL INPUT FILES" in this repository.
For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]).
[1] V. Venugopal, R. Nemalidinne, and A. Vögler, ‘Numerical modelling of wave energy resources and assessment of wave energy extraction by large scale wave farms’, Ocean & Coastal Management, Mar. 2017
MIKE 21 West Orkney Monthly Hs Summary Outputs
No full textMIKE 21 WEST ORKNEY MONTHLY Hs SUMMARY OUTPUTS This collection of netCDF format files contains monthly summary outputs of significant wave height (Hs) from the West of Orkney MIKE 21 spectral wave model described in [1]. For each month the mean Hs and the values of the 5,10,20...,90,95th percentiles are given for each cell in the model. The model was designed to study the effects on wave height of both wave energy extraction and climate change. Four scenarios are included: Present day (2010) with and without wave energy convertors, and future climate (~2050) with and without wave energy convertors. See [1] for more detail on present-day; a future publication will describe the future version. This model was developed under the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 & EP/K012851/1 respectively). The data archived here are being used within the EcoWatt project for ongoing ecological studies. For the input files for the model used to produce these outputs, please see submission "WEST ORKNEY MIKE 21 MODEL INPUT FILES" in this repository. For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]). [1] V. Venugopal, R. Nemalidinne, and A. Vögler, ‘Numerical modelling of wave energy resources and assessment of wave energy extraction by large scale wave farms’, Ocean & Coastal Management, Mar. 2017.Waldman, Simon; Venugopal, Vengatesan. (2017). MIKE 21 West Orkney Monthly Hs Summary Outputs, 2010 [dataset]. School of Engineering, University of Edinburgh. http://dx.doi.org/10.7488/ds/2218
WEST ORKNEY MIKE 21 MODEL INPUT FILES
No full textThis submission includes the input files for the West Orkney spectral wave sub-model that is described in [1]. It formed part of the TeraWatt and EcoWatt2050 EPSRC projects (grant numbers EP/J010170/1 & EP/K012851/1 respectively).
The input files require the MIKE 21 modelling suite to run, available commercially from https://www.mikepoweredbydhi.com/; they were created and validated using the 2014 edition. Input files are being stored instead of outputs as per RCUK guidelines due to the size of the output files.
Versions of the simulation were run for present (2010) and future (2050) climate, and with and without wave energy extraction by wave energy convertors (WECs). All four resulting scenarios are included here.
For further information please contact Dr. Vengatesan Venugopal, School of Engineering, University of Edinburgh ([email protected]).See readme.txt
Hydrodynamic performance of free surface semicircular breakwaters
Get PDFDifferent types of breakwaters have been developed in the past for the protection of valuable coastal
property, commercial activity and beach morphology. Among these, gravity-type breakwaters are the
most common and provide good surface wave attenuation. However, these breakwaters are not always
suitable due to their adverse impact on the coastal environment. To alleviate the problem, free surface
breakwaters with a variety of caisson designs have been proposed and developed. The main
advantages of such breakwaters are low capital cost, freedom from silting and scouring, short
construction period, circulation of water beneath the breakwater and exertion of relatively low
hydrodynamic forces on the structure as compared to conventional breakwaters. However, complete
tranquillity on the lee side is not likely to occur due to wave energy transfer through the permeable
parts of the breakwater. The degree of wave attenuation primarily depends on the configuration of the
breakwater, the water depth and the incident wave conditions. The hydrodynamic performance of such
free surface breakwaters is the subject of this thesis.
Semicircular breakwaters mounted on a low-crested rubble mound structure were successfully built
for harbour protection in Japan and China. However, the concept of having semicircular structures as
free surface breakwaters has not yet been explored by the research community. As a result, this
research is initiated with the aim of developing a free surface semicircular breakwater (SCB) that
would serve as an anti-reflection barrier and provide reasonably good wave protection to coastal and
marine infrastructures. To meet this research goal, a free surface SCB models were constructed and
tested in a wave flume under various wave conditions. The experiments were conducted in three
stages. For the first stage, the SCB model was initially tested without any perforations on the curved
surface (i.e. a solid SCB) for different depths of immersion from the still water level in the wave
flume. For the second stage, the front curved wall of the model was subsequently perforated with
rectangular openings of different dimensions, producing front wall porosity of 9, 18 and 27%.
Following this, two rows of rectangular openings near the crest of the rear curved wall were provided
so as to facilitate water infiltration and escape of the run-up waves. For the third stage, additional
effort was made to extend the draft of the breakwater by adding a wave screen at the front or/and rear.
The screen porosity was 25, 40 and 50%.
The hydrodynamic characteristics of the SCB models were investigated in both regular and irregular
seas through a series of systematic experimental programme. The water surface elevations were
measured at different locations upstream and downstream of the models to determine the coefficients
of wave transmission (CT), reflection (CR) and energy dissipation (CL) as well as the wave climate
coefficients in front and inside the breakwater chamber. The horizontal wave forces exerted on the
SCB models and the wave screen(s) were also measured and subsequently normalised to yield the
force coefficients in the analysis. These hydrodynamic coefficients for the respective test cases are
presented and discussed in this thesis.
The experimental results revealed that even though the solid SCB was a better wave attenuator than
the perforated ones, it produced a considerable amount of wave reflection. The perforated SCB with
9% porosity of the front wall (denoted as SCB9) outperformed the other perforated breakwater
models; however, it produced high wave transmission when the draft was limited and subjected to
longer period waves. Hence, wave screens were added to further enhance the performance of the
SCB9. The SCB9 with double screens of 25% porosity was found to provide the highest hydraulic
performance.
Empirical equations were developed using a multiple regression technique to provide design formulae
for wave transmission, wave reflection and horizontal wave forces. The proposed empirical equations
showed good agreement with the experimental data. These equations are intended to be of direct use
to engineers in predicting the hydrodynamic performance of free surface SCBs. However, sensible
engineering judgement must be taken while using these equations as they are based on small scale
laboratory tests
Computational fatigue assessment of mooring chains accounting for residual stresses
Get PDFMooring chains are used to keep dynamically floating structures on a fixed geographical
position within a specified tolerance. Chains for permanent moorings have been traditionally
used by the Oil and Gas industry for Floating Production Storage and Offloading (FPSO) and
have recently found application in the Offshore Renewable Energy Industry, as for example in
mooring floating wind turbines. For both industries, the failure of the mooring can give rise to
large accidents with devastating economic losses as well as drastic environmental
consequences. During the last decade, the increasing number of mooring incidents has rise to
concern among Oil and Gas companies. In most of these incidents, chain links were the root
cause, and fatigue the main damage mechanism.
This research aims to investigate the fatigue of mooring chains from a global approach. That
is, to follow the life cycle of a mooring chain, which is mainly composed of two stages:
manufacturing, and service life. The fatigue of mooring chains has been studied using the Dang
Van fatigue criterion. Dang Van fatigue criterion and critical plane methods are a set of fatigue
criteria that have proven to be accurate, and account for complex phenomena (for example nonproportionality
of the loading, mean load effects, among others); however, they have a complex
mathematical formulation which involves solving optimization problems, and therefore such
methods carry substantial computational overhead if they are applied to an industrial
component with complex geometry. The research of this thesis is divided in three main parts.
In the first part, different numerical methods are reviewed for solving the optimization
problems faced when applying critical plane methods and Dang Van fatigue criterion. The best
performing method for applying the Dang Van fatigue criterion is identified.
In the second part, the residual stress field after the manufacturing of a chain is predicted by
means of Finite Element Analysis (FEA). Relevant manufacturing steps are modelled. A
qualitative validation using data from the literature is presented.
Finally, using the numerical method identified in the first part for applying Dang Van fatigue
criterion, and the residual stress prediction derived in the second part, the computational fatigue
assessment of mooring chains is performed. Two different loading modes have been studied,
tension and twisting. The first one is the nominal loading mode; however current standards do
not account for the effect of the mean load. The influence of mean load is assessed, and a
simplified fatigue assessment method implementing Dang Van fatigue criterion is proposed.
The accuracy of the proposed method is proven by comparing the predictions with full scale
fatigue testing carried out in sea water at TWI Ltd as part of a Joint Industry Program (JIP).
The second loading mode (twisting) is not fully accounted for in the standards; the fatigue
analysis predicts cracks at locations that do not correspond with fatigue breakage locations
under tension loading or Out-of-Plane Bending (OPB). The predicted fatigue crack initiation
locations match very well with cracks found in chains recovered from the field after more than
15 years in service
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