Tag Archives: Numerical modeling

Computationally efficient modelling of dynamic soil-structure interaction of offshore wind turbines on gravity footings


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M. Damgaard, L.V. Andersen, and L.B. Ibsen – Renewable Energy, August 2014

Abstract

The formulation and quality of a computationally efficient model of offshore wind turbine surface foundations are examined. The aim is to establish a model, workable in the frequency and time domain, that can be applied in aeroelastic codes for fast and reliable evaluation of the dynamic structural response of wind turbines, in which the geometrical dissipation related to wave propagation into the subsoil is included. Based on the optimal order of a consistent lumped-parameter model obtained by the domain-transformation method and a weighted least-squares technique, the dynamic vibration response of a 5.0 MW offshore wind turbine is evaluated for different stratifications, environmental conditions and foundation geometries by the aeroelastic nonlinear multi-body code HAWC2. Analyses show that a consistent lumped-parameter model with three to five internal degrees of freedom per displacement or rotation of the foundation is necessary in order to obtain an accurate prediction of the foundation response in the frequency and time domain. In addition, the required static bearing capacity of surface foundations leads to fore–aft vibrations during normal operation of a wind turbine that are insensitive to wave propagating in the subsoil—even for soil stratifications with low cut-in frequencies. In this regard, utilising discrete second-order models for the physical interpretation of a rational filter puts special demands on the Newmark β-scheme, where the time integration in most cases only provides a causal response for constant acceleration within each time step.

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Filed under Modeling, Wind

A new time domain analysis of wave power


M.X. Wei and Z.G. Bai – Applied Mechanics and Materials, December, 2012

Abstract

The present frequency domain method of calculating wave power may not be accurate enough for calculating the incident wave power of a specific site, which is primary measurement for evaluating the efficiency of wave energy converters (WECs) and an alternative measure, the time domain method, is proposed. Three sites including two nearshore sites and one deepwater site at Chengshantou sea area were selected, and a sample wave parameters data set was obtained from wave model SWASH to demonstrate the application of these two methods. A comparison of the results of each method was also performed and two influential parameters used in calculation were analyzed. The results show that frequency domain method is very likely to overestimate the wave power at both deepwater and nearshore site. The time domain method proposed in this paper is believed to be more superior in calculating the incident wave power during a short term.

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Filed under Resource Characterization

Hydrokinetic assessment of the Kvichak River near Igiugig, Alaska, using a two-dimensional hydrodynamic model


H. Toniolo – Energy and Power Engineering, 2012

Abstract

Two-dimensional hydrodynamic simulations were performed on a monthly basis along 2.5 km of the Kvichak River near Igiugig in southwest Alaska, USA, to estimate flow conditions and to assess the hydrokinetic potential of the river reach. Instantaneous power density function along the computational domain was calculated. Study results indicate that two areas may be suitable for deploying turbines. The best option is located near the town, where the channel is relatively straight. A second possible site is located near the end of the study reach (approximately 2.3 km, along the river, from Lake Illiamna). Monthly-averaged velocities along the thalweg ranged from 1.7 to 2.7 m/s; and from 1.1 to 2 m/s at the upstream and downstream sites, respectively. Similarly, averaged values for the instantaneous power density, reduced by an extraction coefficient, were approximately 1500 and 5500 W/m2 during April and September, respectively, at the upstream site, as well as 400 and 2500 W/m2 for the same months at the downstream site. It was found that a previous resource assessment, which considered cross-sectionally averaged velocities, substantially underestimated the available power density along the river reach. Finally, the importance of having adequate bathymetric data is demonstrated by comparing field measurements with model simulations.

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Filed under Resource Assessment