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Make drag coefficient explicit with consts; update bird masses

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This commit is contained in:
Ludvig Böklin 2021-05-18 20:18:31 +02:00
parent ac7221857c
commit 3b906cb024
3 changed files with 46 additions and 35 deletions
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12
common/src/comp/body.rs
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@ -184,8 +184,16 @@ impl Body {
},
Body::BipedSmall(_) => 50.0,
// Ravens are 0.69-2 kg, crows are 0.51 kg on average. Our birds are quite large
Body::BirdMedium(_) => 3.0,
// ravens are 0.69-2 kg, crows are 0.51 kg on average.
Body::BirdMedium(body) => match body.species {
bird_medium::Species::Chicken => 2.0, // ~✅ Red junglefowl are 1-1.5 kg
bird_medium::Species::Duck => 2.0,
bird_medium::Species::Eagle => 10.0, // ~✅ Steller's sea eagle are 5-9 kg
bird_medium::Species::Goose => 3.5, // ~✅ Swan geese are 2.8-3.5 kg
bird_medium::Species::Owl => 2.0,
bird_medium::Species::Parrot => 2.0,
bird_medium::Species::Peacock => 5.0,
},
Body::BirdLarge(_) => 50.0,
Body::Dragon(_) => 20_000.0,

48
common/src/comp/fluid_dynamics.rs
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@ -113,13 +113,12 @@ impl Body {
// All the coefficients come pre-multiplied by their reference area
0.5 * fluid_density
* v_sq
* wings
.and_then(|wings| match *wings {
Wings::Gliding {
* match wings {
Some(&Wings::Gliding {
aspect_ratio,
planform_area,
ori,
} => {
}) => {
if aspect_ratio > 25.0 {
tracing::warn!(
"Calculating lift for wings with an aspect ratio of {}. The \
@ -127,18 +126,14 @@ impl Body {
aspect_ratio
)
};
Some((aspect_ratio.min(24.0), planform_area, ori))
},
_ => None,
})
.map(|(ar, area, ori)| {
let ar = aspect_ratio.min(24.0);
// We have an elliptical wing; proceed to calculate its lift and drag
// aoa will be positive when we're pitched up and negative otherwise
let aoa = angle_of_attack(&ori, &rel_flow_dir);
// c_l will be positive when aoa is positive (we have positive lift,
// producing an upward force) and negative otherwise
let c_l = lift_coefficient(ar, area, aoa);
let c_l = lift_coefficient(ar, planform_area, aoa);
// lift dir will be orthogonal to the local relative flow vector.
// Local relative flow is the resulting vector of (relative) freestream
@ -162,22 +157,26 @@ impl Body {
ori.pitched_down(aoa_eff).up()
};
// drag coefficient due to lift
// drag coefficient
let c_d = {
// Oswald's efficiency factor (empirically derived--very magical)
// (this definition should not be used for aspect ratios > 25)
let e = 1.78 * (1.0 - 0.045 * ar.powf(0.68)) - 0.64;
// induced drag coefficient (drag due to lift)
let cdi = c_l.powi(2) / (PI * e * ar);
zero_lift_drag_coefficient(area)
zero_lift_drag_coefficient(planform_area)
+ self.parasite_drag_coefficient(wings)
+ c_l.powi(2) / (PI * e * ar)
+ cdi
};
debug_assert!(c_d.is_sign_positive());
debug_assert!(c_l.is_sign_positive() || aoa.is_sign_negative());
c_l * *lift_dir + c_d * *rel_flow_dir
})
.unwrap_or_else(|| self.parasite_drag_coefficient(wings) * *rel_flow_dir)
},
_ => self.parasite_drag_coefficient(wings) * *rel_flow_dir,
}
}
}
@ -192,7 +191,8 @@ impl Body {
// Cross-section, head/feet first
Body::BipedLarge(_) | Body::BipedSmall(_) | Body::Golem(_) | Body::Humanoid(_) => {
let dim = self.dimensions().xy().map(|a| a * 0.5);
0.7 * PI * dim.x * dim.y
const CD: f32 = 0.7;
CD * PI * dim.x * dim.y
},
// Cross-section, nose/tail first
@ -201,7 +201,7 @@ impl Body {
| Body::QuadrupedSmall(_)
| Body::QuadrupedLow(_) => {
let dim = self.dimensions().map(|a| a * 0.5);
let cd = if matches!(self, Body::QuadrupedLow(_)) {
let cd: f32 = if matches!(self, Body::QuadrupedLow(_)) {
0.7
} else {
1.0
@ -212,7 +212,7 @@ impl Body {
// Cross-section, zero-lift angle; exclude the wings (width * 0.2)
Body::BirdMedium(_) | Body::BirdLarge(_) | Body::Dragon(_) => {
let dim = self.dimensions().map(|a| a * 0.5);
let cd = if matches!(wings, Some(Wings::Folded) | None) {
let cd: f32 = if matches!(wings, Some(Wings::Folded) | None) {
0.7
} else {
// "Field Estimates of Body Drag Coefficient on the Basis of Dives in Passerine
@ -231,7 +231,8 @@ impl Body {
let dim = self.dimensions().map(|a| a * 0.5);
// "A Simple Method to Determine Drag Coefficients in Aquatic Animals",
// D. Bilo and W. Nachtigall, 1980
0.031 * PI * dim.x * 0.2 * dim.z
const CD: f32 = 0.031;
CD * PI * dim.x * 0.2 * dim.z
},
Body::Object(object) => match object {
@ -247,7 +248,8 @@ impl Body {
| object::Body::FireworkYellow
| object::Body::MultiArrow => {
let dim = self.dimensions().map(|a| a * 0.5);
0.02 * PI * dim.x * dim.z
const CD: f32 = 0.02;
CD * PI * dim.x * dim.z
},
// spherical-ish objects
@ -265,12 +267,14 @@ impl Body {
| object::Body::Pumpkin4
| object::Body::Pumpkin5 => {
let dim = self.dimensions().map(|a| a * 0.5);
0.5 * PI * dim.x * dim.z
const CD: f32 = 0.5;
CD * PI * dim.x * dim.z
},
_ => {
let dim = self.dimensions();
2.0 * (PI / 6.0 * dim.x * dim.y * dim.z).powf(2.0 / 3.0)
const CD: f32 = 2.0;
CD * (PI / 6.0 * dim.x * dim.y * dim.z).powf(2.0 / 3.0)
},
},

1
common/systems/src/phys.rs
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@ -26,7 +26,6 @@ use specs::{
use std::ops::Range;
use vek::*;
fn get_wings(character_state: Option<&CharacterState>) -> Option<Wings> {
match *character_state? {
CharacterState::Glide(states::glide::Data {