User/tanmaythakral/67 create fluid force computation class #76
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| def calculate_attack_angle(self, apparent_velocity: NDArray, orientation: Scalar) -> Scalar: | ||
| """Calculates the angle of attack formed between the orientation angle of the medium | ||
| and the direction of the apparent velocity, bounded between 0 and 180 degrees. | ||
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| Args: | ||
| apparent_velocity (NDArray): The apparent (relative) velocity between the fluid and | ||
| the medium, expressed in meters per second (m/s). | ||
| orientation (Scalar): The orientation angle of the medium in degrees. | ||
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| Returns: | ||
| Scalar: The angle of attack formed between the orientation angle of the medium and | ||
| the direction of the apparent velocity, expressed in degrees | ||
| and bounded between 0 and 180 degrees. | ||
| """ |
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This function behavior can be slightly improved: the angle of attack should be bounded between [-180, 180). In practice, it is more common to use this symmetric range. Mapping to [0, 180] can cause arbitrary results. For example,
apparent_wind = [0,0]
orientation =
Then,
apparent_wind = [0,0]
orientation =
Mapping to [0, 180] would also yield
You can use the function boat_simulator.common.utils.bound_to_180 in our utils package to map to a symmetric range.
One more thing as well: whenever you are using Euler Angles, always define the angle convention:
- Where is 0 degrees location?
- Do angles increase clockwise or counterclockwise?
In this case, we use 0 degrees on the positive x-axis and increasing counterclockwise (CCW) for the boat simulator.
| @@ -37,6 +43,32 @@ def __init__( | |||
| self.__areas = areas | |||
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We only use a constant area. Switch your implementation to use a single area rather than interpolating areas
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will switch to single area
| drag_coefficient = np.interp( | ||
| attack_angle, self.__drag_coefficients[:, 0], self.__drag_coefficients[:, 1] | ||
| ) | ||
| area = np.interp(attack_angle, self.__areas[:, 0], self.__areas[:, 1]) |
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As per my previous comment, let's use a constant area for our implementation
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will switch to single area.
| # Calculate the lift and drag forces | ||
| lift_force_magnitude = ( | ||
| 0.5 * self.__fluid_density * lift_coefficient * area * (velocity_magnitude**2) | ||
| ) | ||
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| drag_force_magnitude = ( | ||
| 0.5 * self.__fluid_density * drag_coefficient * area * (velocity_magnitude**2) | ||
| ) |
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These can probably be abstracted into a separate function
| # Rotate the lift and drag forces by 90 degrees to obtain the lift and drag forces | ||
| # Rotate counter clockwise in 1st and 3rd quadrant, and clockwise in 2nd and 4th quadrant | ||
| # 0 otherwise | ||
| drag_force_direction = (apparent_velocity) / velocity_magnitude |
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If I recall correctly, you are only rotating the lift by 90 degrees. To be clear, I understand that you do indeed rotate the drag as an intermediate step, but lift is rotated by 90 degrees relative to drag.
I might also rename this variable to denote this as the drag unit vector
| print(lift_force, drag_force) | ||
| print(calculate_magnitude(lift_force), calculate_magnitude(drag_force)) |
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When you're finished debugging, any print statements should be removed from test functions
| def test_calculate_attack_angle( | ||
| apparent_velocity, orientation, expected_angle, medium_force_setup | ||
| ): |
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Great test suite so far. A few suggestions for some more tests:
- Try using orientations that fall outside of the typical expected range (negative numbers, larger than 360, etc.)
| def test_compute_forces( | ||
| medium_force_setup, orientation, expected_lift, expected_drag, apparent_velocity | ||
| ): |
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Some suggestions on additional tests:
- Testing with an apparent velocity with a magnitude other than 44
- Testing with an orientation other than 0
- Try testing with orientations that might lie outside the expected range (negative, larger than 360, etc.)
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The NASA simulator only has values for velocity 44m/s. Will need to manually develop tests in this case.
Will do but the NASA sim only provides me with magnitude so it'll still have the same magnitudes in these cases. (Cant test direction)
| area = np.interp(attack_angle, self.__areas[:, 0], self.__areas[:, 1]) | ||
| return lift_coefficient, drag_coefficient, area | ||
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| def draw_boat(ax, position, orientation): |
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Does this function belong in this class?
| def visualize_forces( | ||
| self, apparent_velocity, lift_force, drag_force, position=[0, 0], orientation=0 | ||
| ): |
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Does this function belong in this class?
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