蛇皮走位

model new

model domain extent -10 10

wall generate box -5 5

wall generate box -5 1 -1 1

ball create position 0 -4 radius 1
ball attribute density 2e3
[bp=ball.find(1)]
def update_ball_vel
time=mech.time total
ball.vel.x(bp)=1
ball.vel.y(bp)=1
if time>4 then
ball.vel.x(bp)=-1
endif
end
model mechanical timestep fix 1e-4
fish callback add @update_ball_vel -1.0

model solve time 8