Anders Goude

Net load variability in Nordic countries with a highly or fully renewable power system

Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Full ...

Adaptive fast multipole methods on the GPU

We present a highly general implementation of fast multipole methods on graphics processing units (GPUs). Our two-dimensional double precision code features an asymmetric type of adaptive space discretization leading to a particularly elegant and flexible implementation. All steps of the multipole algorithm are efficiently performed on the GPU, including the initial phase, which assembles the topological information of the input data. Through careful timing experiments, we investigate the effects of the various peculiarities of the GPU architecture.

Dynamic Stall Modeling for the Conditions of Vertical Axis Wind Turbines

Unsteady aerodynamics imposes additional demands on the modeling of vertical axis wind turbines. Large variations in the angles of attack of the blades cause force oscillations, which can lead to the fatigue-associated problems. Therefore, an accurate estimation of the dynamic loads is essential for the vertical axis wind turbines design. Dynamic stall modeling is in focus because it represents complex phenomena associated with the unsteady flow conditions. The purpose of the study is to find a suitable dynamic stall model for the vertical axis wind turbine conditions. Three versions of the Leishman–Beddoes model are explicitly presented. Additional modifications are implemented for the model to work when the angles of attack change sign and have high amplitudes. All the model parameters are presented. The model is assessed against measured data. The conditions for the simulation tests are close to the vertical axis wind turbine operational conditions. A version of the model, originally designed for low M...

Numerical Simulation of a Farm of Vertical Axis Marine Current Turbines

Two computationally fast fluid mechanical models for vertical axis turbines are the streamtube and the vortex model. The streamtube model is the fastest, allowing three-dimensional modeling of the turbine, but lacks a proper time-dependent description of the flow through the turbine. The vortex model used is two-dimensional, but gives a more complete time-dependent description of the flow. Effects of a velocity profile and the inclusion of struts have been investigated with the streamtube model. Simulations with an inhomogeneous velocity profile predict that the power coefficient of a vertical axis turbine is relatively insensitive to the velocity profile. For the struts, structural mechanic loads have been computed and the calculations show that if turbines are designed for high flow velocities, additional struts are required, reducing the efficiency for lower flow velocities.Turbines in channels and turbine arrays have been studied with the vortex model. The channel study shows that smaller channels give higher power coefficients and convergence is obtained in fewer time steps. Simulations on a turbine array were performed on five turbines in a row and in a zigzag configuration, where better performance is predicted for the row configuration. The row configuration was extended to ten turbines and it has been shown that the turbine spacing needs to be increased if the misalignment in flow direction is large.A control system for the turbine with only the rotational velocity as input has been studied using the vortex model coupled with an electrical model. According to simulations, this system can obtain power coefficients close to the theoretical peak values. This control system study has been extended to a turbine farm. Individual control of each turbine has been compared to a less costly control system where all turbines are connected to a mutual DC bus through passive rectifiers. The individual control performs best for aerodynamically independent turbines, but for aerodynamically coupled turbines, the results show that a mutual DC bus can be a viable option.Finally, an implementation of the fast multipole method has been made on a graphics processing unit (GPU) and the performance gain from this platform is demonstrated.

Simulating Pitching Blade With Free Vortex Model Coupled With Dynamic Stall Model for Conditions of Straight Bladed Vertical Axis Turbines

This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies. An existing dynamic stall model was investigated and further modified for the conditions of the VAWT operation. This model was coupled with a streamtube model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube model has been improved compared to its previous versions. The dynamic stall model was further modified by coupling it with a free vortex model. The new model has become less dependent on empirical constants and has shown an improved accuracy. Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified.The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved vortex model has been validated against the data from the new measurements. The model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented vortex model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.

Dynamic autotuning of adaptive fast multipole methods on hybrid multicore CPU and GPU systems

Dynamic autotuning of adaptive fast multipole methods on hybrid multicore CPU and GPU systems

Frequency analysis of tangential force measurements on a vertical axis wind turbine

This paper presents experimental results of the torque ripple obtained from a three bladed 12 kW experimental H-rotor prototype. The measurements are performed by means of load cells installed on t ...

Experimental demonstration of performance of a vertical axis marine current turbine in a river

An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measure ...

Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines

Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicul ...

Wind Energy Converters and Photovoltaics for Generation of Electricity after Natural Disasters

Abstract During recovery and reconstruction after a natural disaster, an autonomous power supply might be needed for an extended period of time. In this work, the feasibility of using small‐scale wind power and battery storage for power supply is evaluated and compared with systems containing photovoltaics. The investment cost per yearly produced and for an optimized energy system supplying small loads (2 or 20 KW peak) has been calculated for 32 sites, predominantly in frica and the iddle ast. The sites represent foreign activities of the wedish ivil ontingencies gency at the end of 2012. Since wind speed measurement series often have a lot of missing data, autoregressive moving average models were trained and used to generate hourly time series of wind speed. This methodology proved robust, even when data availability was very low or when measurements were only taken every third hour. The results of the simulations show that photovoltaic/battery systems outperform wind/battery systems at all evaluated sites. This can be explained by lower investment cost per yearly produced and smoother daily/weekly power output over the year for the photovoltaic system. The proportion of wind power for optimized systems comprising wind, photovoltaics and battery bank is generally very low and the system cost is almost identical to the corresponding photovoltaic/battery systems. In conclusion, at lower latitudes and with little time for a proper wind measurement campaign, photovoltaics should be the primary candidate for replacing or complementing conventional diesel generators.