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simulation.js
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'use strict';
function Simulation() { }
Simulation.prototype.metadata = [
{
label: 'Payload Design', params: [
{ name: 'r', type: 'float', label: 'r', default: 0.1, units: 'm', readonly: true},
{ name: 'C_d', type: 'float', label: 'C<sub>D</sub>', default: 0.5, nobreak: true, min: 0.2, max: 0.7, readonly: true},
{ name: 'C_derr', type: 'float', label: '±', default: 0.1, min: 0.05, max: 0.2 },
{ name: 'mean_m', type: 'float', label: 'm', default: 5, nobreak: true, min: 4, max: 9, readonly: true},
{ name: 'var_m', type: 'float', label: '±', default: 0.5, max: 1.0, min: 0.25},
],
}, {
label: 'Parachute Design', params: [
{ name: 'r_p', type: 'float', label: 'r<sub>p</sub>', default: 0.5, units: 'm', min: 0.25, max: 1.0, readonly: true},
{ name: 'C_dp', type: 'float', label: 'C<sub>Dp</sub>', default: 1.75, readonly: true},
{ name: 't_p', type: 'float', label: 't<sub>freefall</sub>', default: 9, units: 's', min: 0, max: 20},
{ name: 'mean_t_open', type: 'float', label: 't<sub>open</sub>', default: 4.5, nobreak: true, min: 1, max: 10},
{ name: 'var_t_open', type: 'float', label: '±', default: 2, min: 1, max: 4.0},
]
}, {
label: 'Initial Conditions', params: [
{ name: 'x', type: 'float', label: 'x', default: -320, units: 'm' },
{ name: 'y', type: 'float', label: 'y', default: 500, units: 'm' , readonly: true},
{ name: 'mean_v_x', type: 'float', label: 'v<sub>x</sub>', default: 50, nobreak: true, readonly: true},
{ name: 'var_v_x', type: 'float', label: '±', default: 1, min: 0.5, max: 2.0},
{ name: 'v_y', type: 'float', label: 'v<sub>y</sub>', default: 0, units: 'm/s' , readonly: true},
{ name: 'mean_w_x', type: 'float', label: 'w<sub>x</sub>', default: 0, nobreak: true, readonly: true},
{ name: 'var_w_x', type: 'float', label: '±', default: 2, readonly: true }
]
}, {
label: 'Mission Constraints', params: [
{ name: 'x_min', type: 'float', label: 'x<sub>min</sub>', default: -50, units: 'm', readonly: true },
{ name: 'x_max', type: 'float', label: 'x<sub>max</sub>', default: 50, units: 'm', readonly: true },
{ name: 'v_max', type: 'float', label: 'v<sub>max</sub>', default: 10, units: 'm/s', readonly: true },
{ name: 'F_max', type: 'float', label: 'F<sub>max</sub>', default: 300, units: 'N', readonly: true }
]
}, {
label: 'Monte Carlo', params: [
{ name: 'n_samp', type: 'int', label: 'Samples', default: 25000 }
]
}
];
Simulation.prototype.getLabel = function (name) {
this.metadata.forEach(function(group) {
group.params.forEach(function(param, i) {
if (name == param.name)
return group.params[i].label;
});
});
};
Simulation.prototype.run = function (params) {
var x = params.x, y = params.y,
v_x = params.v_x, v_y = params.v_y,
r = params.r, r_p = params.r_p,
C_d = params.C_d, C_dp = params.C_dp,
t_p = params.t_p, t_open = params.t_open,
w_x = params.w_x,
m = params.m;
var dt = 0.02;
var rho = 1.22, g = 9.8;
var trajectory = [ ];
var t = 0, p = 0, broken = 0; // parachute is closed at t=0
while (y > 0) {
if (params.save_trajectory === true)
trajectory.push({t: t, x: x, y: y, v_x: v_x, v_y: v_y, p: p, b: broken});
var v = Math.sqrt((v_x - w_x) * (v_x - w_x) + v_y * v_y);
var F_d = -0.5 * rho * C_d * (Math.PI * r * r) * v * v;
var F_dp = -0.5 * rho * p * C_dp * (Math.PI * r_p * r_p) * v * v;
if (Math.abs(F_dp) > params.F_max)
broken = 1;
var a_x = -Math.abs(F_d + F_dp) / m * (v_x - w_x) / v;
var a_y = -g - Math.abs(F_d + F_dp) / m * v_y / v;
var a = Math.sqrt(a_x * a_x + a_y * a_y);
// dynamic step size
dt = Math.min(0.5, 0.02 + 2 / (a + 1));
if (Math.abs(t - t_p) < 1.1 * dt)
dt = 0.04;
// explicit euler time step
v_x = v_x + a_x * dt;
v_y = v_y + a_y * dt;
x = x + v_x * dt;
y = y + v_y * dt;
t = t + dt;
// update parachute open status
if (t < t_p || broken) p = 0;
else if (t > t_p + t_open) p = 1;
else p = Math.min(1, (t - t_p) / t_open);
}
// lerp to y = 0
x = x - y * v_x / v_y;
trajectory.push({t: t, x: x, y: 0, v_x: v_x, v_y: v_y, p: p, b: broken});
return trajectory;
}
Simulation.prototype.getSamples = function(params) {
var samples = {
w_x: new Float64Array(params.n_samp),
t_open: new Float64Array(params.n_samp),
C_d: new Float64Array(params.n_samp),
m: new Float64Array(params.n_samp),
v_x: new Float64Array(params.n_samp)
};
// want log normal with mean and variance
var mean = params.mean_t_open;
var variance = params.var_t_open;
// sample from Exp[N(mu, sigma2)]
var lognormal_params = function(mean, variance) {
var mu = Math.log(mean * mean / Math.sqrt(mean * mean + variance));
var sigma2 = 2 * Math.log(Math.sqrt(mean * mean + variance) / mean);
return {mu: mu, sigma2: sigma2};
};
var t_open_params = lognormal_params(params.mean_t_open, params.var_t_open);
var m_params = lognormal_params(params.mean_m, params.var_m);
for (var i = 0; i < params.n_samp; i++) {
samples.w_x[i] = Simulation.getNormal() * Math.sqrt(params.var_w_x) + params.mean_w_x;
samples.t_open[i] = Math.exp(Simulation.getNormal() * Math.sqrt(t_open_params.sigma2) + t_open_params.mu);
samples.C_d[i] = params.C_d + (Math.random() * 2 - 1) * params.C_derr;
samples.m[i] = Math.exp(Simulation.getNormal() * Math.sqrt(m_params.sigma2) + m_params.mu);
samples.v_x[i] = Simulation.getNormal() * Math.sqrt(params.var_v_x) + params.mean_v_x;
}
return samples;
};
Simulation.getNormal = function() {
var x, y, w;
do {
x = Math.random() * 2 - 1;
y = Math.random() * 2 - 1;
w = x * x + y * y;
} while (w >= 1.0)
return x * Math.sqrt(-2 * Math.log(w) / w);
};
Simulation.prototype.getDefault = function() {
var params = { };
this.metadata.forEach(function(paramGroup) {
paramGroup.params.forEach(function(param) {
params[param['name']] = param['default'];
});
});
return params;
};
Simulation.prototype.parse = function(params) {
var errors = [];
this.metadata.forEach(function(paramGroup) {
paramGroup.params.forEach(function(param) {
switch (param.type) {
case 'float': params[param.name] = parseFloat(params[param.name]); break;
case 'int': params[param.name] = parseInt(params[param.name]); break;
}
if (param.min != undefined && params[param.name] < param.min) {
errors.push(param.name + ' below minimum value of ' + param.min);
}
if (param.max != undefined && params[param.name] > param.max) {
errors.push(param.name + ' above maximum value of ' + param.max);
}
});
});
params.errors = errors;
return params;
};