Sander M. Calisal

Application of Bubnov-Galerkin formulation to orthogonal grid generation

Abstract A Bubnov-Galerkin formulation is used to solve an elliptic grid generation system by using linear and quadratic isoparametric elements. Good orthogonality characteristics are obtained for symmetric and non-symmetric physical domains using both complete boundary correspondence or a combination of Dirichlet and Neuman boundary conditions. The method exhibits excellent stability and requires a low number of iterations to attain convergence. Results are compared with those presented in (E. D. Chikliwala and Y. C. Yortsos, J. Comput. Phys. , 57 , 391, 1985).

Hydrodynamic coefficients for vertical composite cylinders

Abstract An efficient method of calculation for vertical, composite cylinders at finite depth is presented. Hydrodynamic coefficients calculated by this method are compared with numerical results obtained by a surface element method.

Estimating Power Output from a Tidal Current Turbine Farm with First-order Approximation of Hydrodynamic Interaction between Turbines

This article presents a numerical approach to estimate power output from a tidal current turbine farm with first-order approximation of hydrodynamic interactions between multiple turbines. An example study is conducted by using this approach to design a tidal current turbine farm in an ideal site with the objective of maximizing the power output of the farm by optimizing the turbine distribution in the site. The results suggest that the maximum power output of a farm can be significantly improved with the utilization of the constructive hydrodynamic interaction between turbines. Limitation of this approach is discussed at the end.

Preliminary Results of a Vortex Method for Stand-Alone Vertical Axis Marine Current Turbine

Tidal power technology has been dwarfed once to take hold in the late 1970’s, because the early generations were expensive at small scale and some applications (such as barrages) had negative environmental impacts. In a similar working manner as a wind turbine, a tidal current turbine has been recognized as a promising ocean energy conversion device in the past two decades. However, the industrialization process is still slow. One of the important reasons is lack of comprehensive turbine hydrodynamics analysis which can not only predict turbine power but also assess impacts on the surrounding areas. Although a lot can be learned from the marine propeller or the wind turbine studies, a systematic hydrodynamics analysis on a vertical axis tidal current turbine has not been reported yet. In this paper, we employed vortex method to calculate the performance of stand-alone vertical axis tidal turbine in term of power efficiency, torque and forces. This method focuses on power prediction, hydrodynamics analysis and design, which can provide information for turbines distribution planning in a turbine farm and other related studies, which are presented in Li and Calisal (2007), a companion paper in the conference. In this method, discrete vortex method is the core for numerical calculation. Free vortex wake structure, nascent vortex and vortex decay mechanism are discussed in detail. Good agreements in turbine efficiency comparison are obtained with both the newly-designed tidal turbine test in a towing tank and early wind turbine test.© 2007 ASME

Modeling the Energy Output from an In-Stream Tidal Turbine Farm

This paper is based on a recent paper presented in the 2007 IEEE SMC conference by the same authors, discussing an approach to predicting energy output from an instream tidal turbine farm. An in-stream tidal turbine is a device for harnessing energy from tidal currents in channels, and functions in a manner similar to a wind turbine. A group of such turbines distributed in a site is called an in-stream tidal turbine farm which is similar to a wind farm. Approaches to estimating energy output from wind farms cannot be fully transferred to study tidal farms, however, because of the complexities involved in modeling turbines underwater. In this paper, we intend to develop an approach for predicting energy output of an in-stream tidal turbine farm. The mathematical formulation and basic procedure for predicting power output of a stand-alone turbine is presented, which includes several highly nonlinear terms. In order to facilitate the computation and utilize the formulation for predicting power output from a turbine farm, a simplified relationship between turbine distribution and turbine farm energy output is derived. A case study is then conducted by applying the numerical procedure to predict the energy output of the farms. Various scenarios are implemented according to the environmental conditions in Seymour Narrows, British Columbia, Canada. Additionally, energy cost results are presented as an extension.

Effects of towing tank walls on the performance of a Vertical Axis Turbine

The effect of towing tank walls on the performance of a vertical axis turbine has been investigated. A discrete vortex method combined with a panel method has been used to calculate the power coefficient of the turbine running in a towing tank. Higher power coefficients are obtained for the turbine when it is running in towing tank, in comparison to the case for a turbine running in an open free stream. The amount of increase in power coefficient depends on the proximity of the wall to the turbine; the closer the walls are to the turbine, a higher power coefficient is calculated for the turbine.

A numerical approach to resistance reduction of displacement vessels using parabolic waterlines

Abstract The addition of parabolic side bulbs at the ships midbody can significantly reduce the wave-making resistance of a vessel. The parabolic bulbs are strategically placed to create a wave pattern that interacts with the shoulder wave system of the base hull at the desired speed range. This concept was first successfully tested on a coaster tanker and then extended to the UBC series hull, a series typical of Canadian West Coast fishing vessels. Systematic tow tank experiments revealed that while parabolization decreases the total resistance (due to a drop in the wave making resistance) the form factor suffered an increase. An integral boundary method solver and a two-dimensional RANS solver both showed that the increase in viscous resistance was mostly due to an increase in viscous pressure drag. The parabolization concept was subsequently extended to a high-speed NPL trimaran, to determine whether resistance reduction using parabolic side bulbs could be achieved for a slender multihull vessel. A Rankine source panel method was used to predict the wave-making characteristics of the trimaran, and an Integral Boundary Layer solver and a RANS solver were used to calculate the viscous drag. A parametric study, varying the size and location of bulbs, was first performed on the centre hull to identify beneficial bulb arrangements. The study was then extended to the trimaran to evaluate the additional wave interactions caused by the outriggers. Experimental work validated the numerically predicted wave interactions, as well as the change in viscous drag. Based on the numerical work, a modified NPL trimaran hull form was designed that reduced the total resistance of the vessel by up to 6% in the design speed range.

A Numerical Study on Squat of a Wigley Hull

A numerical study is conducted to calculate the squat for a wigley hull. An approach based on slender body theory is used to convert the three dimensional ship problem into a series of two dimensional problems in cross sections from bow to stern (solved sequentially in time). A boundary element method is used to compute the flow potential at every cross section. The ship squat is calculated from the pressure integration over the hull. Numerical results for the Wigley hull is presented and compared with the experimental results.Copyright

The Effect of Ducting on the Performance of a Vertical Axis Tidal Turbine

The effect of ducting on the performance of a vertical axis tidal turbine is studied. The calculation of the output power is done using a commercial code and a discrete vortex method. The results show that duct can highly boost the performance of the turbine in comparison to a turbine running in an open free stream. Increasing the output power along with providing a structure for mooring of the turbine introduces ducting as one of the best ways to make a reliable and efficient tidal turbine.Copyright

A Procedure for Predicting Energy From a Tidal Turbine Farm

A tidal current turbine is a device for harnessing energy from tidal current. A group of tidal current turbines, distributed schematically at a site, is called a tidal turbine farm. A tidal turbine farm has to be located in a confined channel or a straight where consistent high-velocity tidal current flow is available for the cost-effectiveness concern. This narrow geographical condition poses challenges for turbine farm planners to distribute turbines strategically. Turbines’ distribution in a farm affects power generation efficiency and the resultant tidal unit power cost. In this paper, we propose a procedure for predicting energy generation from a tidal turbine farm by investigating the optimal distribution of turbines at a given site. The objective of optimizing the turbines distribution is to maximize the power output efficiency. To fulfill this, we conducted a systematic analysis on power generation from a tidal turbine farm to identify the key factors affecting the optimal tidal turbines distribution with an emphasis on the turbines’ hydrodynamics analysis and briefed the turbine working principle. As a companion paper to Li and Calisal (2007) which discusses the principle of a stand alone turbine, turbine configuration and interactions (i.e. angle of attack, turbine relative distance and turbine size) are extended here. The main assumption of this discussion is that vortex shedding impact is the dominant factor causing the turbine efficiency loss. Considering the turbine design principle, a simplified relationship between turbines distribution and turbine farm efficiency is formulated. Then, numerical simulation results are presented for a given site in British Columbia together with extended general solution.Copyright