5 research outputs found
Flow-induced vibration of an underwater lazy wave cable in unidirectional current
Full text linkThis paper describes measurements of the flow-induced vibration of an instrumented model cable in a lazy wave configuration immersed in unidirectional currents in the 2 m deep FloWave Fa- cility at the University of Edinburgh. The cable model, designed to represent a dynamic power cable used in offshore renewable energy structures for electricity transmission, has an external diameter (D) of 31 mm and a mass ratio of 1.22. The current speed was varied from 0.1 to 0.9 m/s and its direction was set at 0, 90, and 180 degrees relative to the initial longitudinal axis of the cable. An underwater Qualisys motion capture system measured the in-line (IL) and cross-flow (CF) displacement components at 36 locations along the length of the submerged cable. Local displacements, response frequencies, and travelling wave modes are determined for reduced velocity Ur ε (5.29, 47.69), and Reynolds number Re ε (103, 104). It is found that the root mean square (RMS) values of the displacement components exhibited an increasing trend with reduced velocity reaching 0.40D in the in-line direction and 0.45D in the cross-flow direction. For reduced velocity in the range from 5.29 to 10.58, the cable exhibited single frequency vibrations. For Ur > 10.58, the cable experienced broad-banded, multi-frequency responses. Along the cable, certain locations were found to execute distinct circular, elliptical, nearly linear, and figure-of-eight orbits at low Ur. A sudden phase shift was observed along the cable length, related to unsteady vortex-induced vibration (VIV), which effectively prevented lock-in occurring at high Ur
Numerical Investigation of Breaking Focused Waves and Forces on Coastal Deck Structure with Girders
No full textIn the present study, breaking focused wave groups were simulated using open-source Computational Fluid Dynamics model REEF3D in order to investigate the breaking wave impact on scaled (1:10) two-dimensional coastal deck structure with girder. The effect of environmental parameters, such as bottom slope and wave steepness on the breaking and geometric properties of high-crested spilling breakers, was investigated. The effect of the wave breaking location on the impact forces acting on the deck structure located at different airgap positions was studied for three wave impact scenarios: (i) when the wave breaking starts, (ii) when a slightly overturning crest is formed, and (iii) when the wave breaks and a fully overturning crest is formed just before hitting the preceding trough. The peak horizontal impact force was found to be higher when the wave breaks ahead of the structure and the overturning wave crest hits the deck positioned above the still water level. Additionally, the peak vertical impact force attains the peak when the deck is placed at the still water level for different stages of breaking. The peak horizontal impact force shows a parabolic trend, whereas the peak vertical impact forces show a decreasing linear trend with an increase in airgap. Finally, force coefficients are derived for calculating the peak impact force on deck with girders subjected to high-crested spilling breakers
Effect of Girder Spacing and Depth on the Solitary Wave Impact on Coastal Bridge Deck for Different Airgaps
Full text linkCoastal bridge damage has become a severe issue of concern in the recent past with the destruction of a considerable number of bridges under the impact of waves during tsunami and storm surges. These events have become more frequent, with waves reaching the bridge deck and causing upliftment and destruction. Past studies have demonstrated the establishment of various theoretical equations which works well for the submerged deck and regular wave types but show much scatter and uncertainty in case of a deck that is above still water level (SWL). The present study aims to generate a solitary wave to represent an extreme wave condition like a tsunami in the numerical wave tank modeled using the open source computational fluid dynamics (CFD) model REEF3D and to study the vertical impact force on the coastal bridge deck. A parametric study is carried out for increasing wave heights, girders spacing and depth for varying airgaps to analyze the effect of these parameters on the peak vertical impact force. It is observed that increasing the girder spacing and girder depth is effective in reducing the peak vertical impact force for the cases considered
Numerical Simulation and Analysis of Phase Focused Breaking and Non-Breaking Wave Impact on Fixed Offshore Platform Deck
No full textVIV-induced strain on a lazy wave dynamic marine power cable in a steady current
Full text linkMarine power cables are commonly used to transfer electricity from offshore renewable energy (ORE) devices to shore. Such cables are susceptible to fatigue failure due to flow-induced vibration. We present results from physical model tests conducted at Edinburgh University’s FloWave wave-current facility on an instrumented flexible cable in a lazy wave configuration subjected to a steady, unidirectional current. The Reynolds number was subcritical, ranging from 3,100 to 24,800. Bending strain was measured at seven locations along the length of the cable and the results are presented in terms of cable curvature. The data analysis shows that, currents propagating normal to the longitudinal axis of the cable caused large local variations in curvature. The maximum variation in curvature occurred near the touchdown zone and at the sag bend. Repeated high-amplitude cyclic loading was observed in currents directed at angles within ± 30o normal to the longitudinal axis of the cable. Significant shifts in peak frequency and spectral energy distribution were evident with increasing reduced velocity. At certain locations along the cable, the strain frequency corresponded to a Strouhal number of 0.127 - 0.144, whereas very low peak strain frequencies occurred elsewhere. The strain behaviour was sensitive to the current speed and direction relative to the orientation of the cable. Mono-frequency strain responses occurred at lower reduced velocity and multi-frequency responses at higher reduced velocity
