36 lines
1.6 KiB
C++
36 lines
1.6 KiB
C++
#include "RK4AdvectionKernel.h"
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#include "interpolate.h"
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using namespace std;
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RK4AdvectionKernel::RK4AdvectionKernel(std::shared_ptr<UVGrid> grid): grid(grid) { }
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std::pair<double, double> RK4AdvectionKernel::advect(int time, double latitude, double longitude) const {
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auto [u1, v1] = bilinearinterpolate(*grid, time, latitude, longitude);
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// lon1, lat1 = (particle.lon + u1*.5*particle.dt, particle.lat + v1*.5*particle.dt);
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double lon1 = longitude + metreToDegrees(u1 * 0.5*DT);
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double lat1 = latitude + metreToDegrees(v1 * 0.5*DT);
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// (u2, v2) = fieldset.UV[time + .5 * particle.dt, particle.depth, lat1, lon1, particle]
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auto [u2, v2] = bilinearinterpolate(*grid, time + 0.5 * DT, lat1, lon1);
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// lon2, lat2 = (particle.lon + u2*.5*particle.dt, particle.lat + v2*.5*particle.dt)
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double lon2 = longitude + metreToDegrees(u2 * 0.5 * DT);
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double lat2 = latitude + metreToDegrees(v2 * 0.5 * DT);
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// (u3, v3) = fieldset.UV[time + .5 * particle.dt, particle.depth, lat2, lon2, particle]
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auto [u3, v3] = bilinearinterpolate(*grid, time + 0.5 * DT, lat2, lon2);
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// lon3, lat3 = (particle.lon + u3*particle.dt, particle.lat + v3*particle.dt)
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double lon3 = longitude + metreToDegrees(u3 * DT);
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double lat3 = latitude + metreToDegrees(v3 * DT);
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// (u4, v4) = fieldset.UV[time + particle.dt, particle.depth, lat3, lon3, particle]
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auto [u4, v4] = bilinearinterpolate(*grid, time + DT, lat3, lon3);
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double lonFinal = longitude + metreToDegrees((u1 + 2 * u2 + 2 * u3 + u4) / 6.0 * DT);
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double latFinal = latitude + metreToDegrees((v1 + 2 * v2 + 2 * v3 + v4) / 6.0 * DT);
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return {latFinal, lonFinal};
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}
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