Source code for opentidalfarm.turbines.thrust_turbine

from .base_turbine import BaseTurbine
from .controls import Controls
from dolfin import *

[docs]class ThrustTurbine(BaseTurbine): """ Create a turbine that is modelled as a bump of bottom friction. In addition this turbine implements cut in and out speeds for the power production. This turbine introduces a non-linearity, which is handled explicitly. """ def __init__(self, friction=1.0, diameter=20., swept_diameter=20., c_t_design=0.6, cut_in_speed=1, cut_out_speed=2.5, water_depth = None, upwind_correction=True, minimum_distance=None, controls=Controls(position=True)): # Check for a given minimum distance. if minimum_distance is None: minimum_distance=diameter*1.5 # Initialize the base class. super(ThrustTurbine, self).__init__(friction=friction, diameter=diameter, minimum_distance=minimum_distance, controls=controls, thrust=True) # To parametrise a square 2D plan-view turbine to characterise a # realistic tidal turbine with a circular swept area in the section # plane we assume that the specified 2D turbine diameter is equal to the # circular swept diameter self.swept_diameter = swept_diameter self.c_t_design = c_t_design self.cut_in_speed = cut_in_speed self.cut_out_speed = cut_out_speed self.upwind_correction = upwind_correction # Check that the parameter choices make some sense - these won't break # the simulation but may give unexpected results if the choice isn't # understood. if self.swept_diameter != self.diameter: log(INFO, 'Warning - swept_diameter and plan_diameter are not equal') if self.friction != 1.0: log(INFO, 'Warning - for accurate parametrisation friction should \ be set to 1') swept_area = pi * (swept_diameter/2)**2 plan_area = diameter**2 # We can bundle all this up into a constant (i.e. independent of u) in # a stunning display of imaginative thinking we will call this the # turbine_parametrisation_constant self.turbine_parametrisation_constant = 0.5 * swept_area / \ ((self._unit_bump_int/4) * plan_area) if upwind_correction: # This is a correction for the fact that C_t (c_t_design) # is defined as the thrust coefficient relative to the *upstream* # velocity. Since the drag term is computed from the local depth-averaged # velocity (which is lower) we need to compensate for this. The theory # behind this is explained in if water_depth is None: raise ValueError("The water_depth needs to be specifed for the upwind correction") # the "numerical" cross-section this is the cross section over which # the drag is effectively applied effective_area = diameter*water_depth self.turbine_parametrisation_constant *= 4./(1.+sqrt(1-swept_area/effective_area*self.c_t_design))**2
[docs] def less_than_cut_out(self, u_mag): """ The function describing the thrust coefficient for velocities < cut_out_speed """ return self.c_t_design * ((tanh(10*(u_mag-self.cut_in_speed))+1)/2)
[docs] def greater_than_cut_out(self, u_mag): """ The function describing the thrust coefficient for velocities > cut_out_speed """ return self.c_t_design * (self.cut_out_speed / u_mag)
[docs] def compute_C_t(self, u_mag): """ Return C_t as a function of u_mag """ return conditional(gt(u_mag, self.cut_out_speed), self.greater_than_cut_out(u_mag), self.less_than_cut_out(u_mag))