65 research outputs found
Wave energy assessment and wind correlation for the north region of Scotland, hindcast resource and calibration, investigating for improvements of physical model for adaptation to temporal correlation
A 35 year high-resolution wave atlas for nearshore energy production and economics at the Aegean Sea
Wave data analysis for a semi-sheltered site in the Inner Hebrides of Scotland suitable for small scale WEC development
Characterising the wave power potential of the Scottish coastal environment
The study focuses around the energetic waters of Scotland that has expressed high interest in the development of wave energy farms. There are only a few long-term suitable studies characterising coastal locations. A detail coastal resource assessment is provided, focusing on wave energy and site characterisation. Mean nearshore energy content in the Western coasts is ≥50 kW/m and on the East ≈10 kW/m. Monthly and seasonal analyses outline available resource and annual variations. Availability of production is also examined, West coastlines present higher levels, however, depending on resource and wave converters operational range significant differences are shown. Availability levels on the East coastline are low ≈40% due to lower wave heights, while Western locations record consistently over 80% at both scenarios examined. Results discuss the potential applicability of favourable wave converters, and characteristics which achieve maximum utilisation based on the local environment
Hydrodynamic force coefficients for rectangular cylinders in waves and currents
The research into hydrodynamic loading on ocean structures is concentrated mostly
on circular cross section members and relatively limited work has been carried out on
wave loading on rectangular sections, particularly in waves and currents. This
research work is therefore carried out focussing on the evaluation of hydrodynamic
force coefficients for sharp edged rectangular cylinders of various cross-sections
(aspect ratios), subjected to waves and currents. Three cylinders with three different
cross-sections are constructed and tested vertically, as surface piercing and
horizontally, as fully submerged with the cylinder axis parallel to the wave crests.
The aspect ratios considered for this investigation are 1.0, 112, 2/1, 3/4 and 4/3. The
length of each cylinder is 2000mm. The sectional loadings are measured on a 100mm
section, which is located at the mid-length of the cylinder. The forces are measured
using a force measuring system, which consists of load cells, capable of measuring
wave and current forces. The in-line & transverse forces (for vertical cylinders) and
horizontal & vertical forces (for horizontal cylinders) have been measured. For
horizontal cylinder, to study the effect of depth of variation on submergence of the
cylinder, the tests are carried out for two depths of submergence.
The experiments are carried out at the Hydrodynamic Laboratory, Department of
Naval Architecture and Ocean Engineering, University of Glasgow. The tests are
carried out in a water depth of 2.2m with regular and random waves for low
Keulegan-Carpenter (KC) number up to 4.5 and the Reynolds number varied from
6.397xl03 to 1.18xl05
• The combined wave and current effect has been produced by
towing the cylinders in regular waves, along and opposite to the wave direction at
speeds of ± 0.1 mis, ± 0.2 mls and ± 0.3 mls. Based on Morison's equation, the
relationship between inertia and drag coefficients are evaluated and are presented as a
function of KC number for various values of frequency parameter, {3.
For the vertical cylinders, the drag coefficients decrease and inertia coefficients
increase with increase in KC number up to the range of KC tested for all the
cylinders. For the horizontally submerged cylinders, the drag coefficients showed a
similar trend to vertical cylinders, whereas the inertia coefficients decrease with
increase in KC number for all the cylinders. This reduction in inertia force is
attributed to the presence of a circulating flow [Chaplin (1984)] around the cylinders.
The random wave results are consistent with regular wave results and the measured
and computed force spectrum compares quite well.
While computing the force coefficients in the case of combined waves and currents,
only the wave particle velocity is used, as the inclusion of current velocity tends to
produce unreliable drag force coefficients. For vertical cylinders, the drag and the
inertia coefficients in combined waves and currents are lower than the drag and the
inertia coefficients obtained in waves alone. For horizontal cylinders the drag
coefficients are larger than those obtained for waves alone and the inertia coefficients
are smaller than those measured in waves alone.
The Morison's equation with computed drag and inertia coefficients has been found
to predict the measured forces well for smaller KC numbers. However, the
comparison between measured and computed positive peak forces indicate that the
computed forces are underestimated. It is suggested that if the wave particle
kinematics are directly measured, this discrepancy between measured and computed
forces might well be reduced.
Wave excitation forces are also reported in non-dimensional forms in the diffraction
regime, using 3D-Green function method. Wave induced pressure distribution around
the cylinder in regular waves have been measured and are reported as normalised
pressures. Wave run-up on the cylinder surfaces has been measured and simple
empirical formulae are presented for run-up calculations on the cylinder surfaces. The
results of this investigation show that the cylinder aspect ratio plays major role on
hydrodynamic force coefficients, dynamic pressure distribution and on wave run-up
on cylinder surfaces
Dynamic analysis of a multi-column TLP floating offshore wind turbine with tendon failure scenarios
On the Variation of Turbulence in a High-Velocity Tidal Channel
This study presents the variation in turbulence parameters derived from site measurements at a tidal energy test site. Measurements were made towards the southern end of the European Marine Energy Centre’s tidal energy test site at the Fall of Warness (Orkney, Scotland). Four bottom mounted divergent-beam Acoustic Doppler Current Profilers (ADCPs) were deployed at three locations over an area of 2 km by 1.4 km to assess the spatial and temporal variation in turbulence in the southern entrance to the channel. During the measurement campaign, average flood velocities of 2 ms−1 were recorded with maximum flow speeds of 3 ms−1 in the absence of significant wave activity. The velocity fluctuations and turbulence parameters show the presence of large turbulent structures at each location. The easternmost profiler located in the wake of a nearby headland during ebb tide, recorded flow shielding effects that reduced velocities to almost zero and produced large turbulence intensities. The depth-dependent analysis of turbulence parameters reveals large velocity variations with complex profiles that do not follow the standard smooth shear profile. Furthermore, turbulence parameters based on data collected from ADCPs deployed in a multi-carrier frame at the same location and time period, show significant differences. This shows a large sensitivity to the make and model of ADCPs with regards to turbulence. Turbulence integral length scales were calculated, and show eddies exceeding 30 m in size. Direct comparison of the length scales derived from the streamwise velocity component and along-beam velocities show very similar magnitudes and distributions with tidal phase
- …