% A loose, lightly damped net, struck hard: energy cascades from the struck
% low modes to high ones over tens of milliseconds.
%
% Compared with drum.m, the springs are stretched only 0.5% at rest, so the
% stretching caused by the motion itself is large relative to the rest
% tension, and the high modes ring about twice as long (T60 1.6 s rather
% than 0.75 s near 2 kHz), so they keep their energy long enough to pass
% it on. Turn on "small-strike reference" to hear and measure the
% difference from the same strike at small amplitude.

R = 0.15;
a = 0.01;
sigma = 0.25;
T = 2000;
strain = 0.005;

[pos, tri, rim] = bp_hexdisk(R, a);
E = bp_edges(tri);
f0 = T * a / sqrt(3);
k = f0 / (strain * a);

sys.pos = pos;
sys.mass = sigma * (sqrt(3)/2) * a^2;
sys.pinned = rim;
sys.springs = bp_springs(pos, E, k, f0);
[sys.friction, sys.dashpots] = bp_decay(pos, sys.mass, sys.springs, [200 3; 2000 1.6]);

hit.t = 0;
hit.beads = bp_near(pos, [0.05 0 0], 0.03);
hit.force = [0 0 -12];       % peak force per bead (N); try 1 to 50
hit.duration = 1e-3;
sys.hits = hit;

sys.listen = struct('beads', bp_near(pos, [-0.04 0.03 0], 0), 'dir', [0 0 1]);
sys.duration = 1.5;

fprintf('%d beads, %d springs, %d struck\n', size(pos, 1), size(E, 1), numel(hit.beads));