Unstable issue

[Zheng0315]

After running this for 1 min, the wave motion becomes weird.

http://www.falstad.com/ripple/Ripple.html?rol=$+3+750+64+0+0+382+0.048828125%0AS+2+0+1+748+1+0+0.1166665+0+10+100+1+0%0Aw+0+473+300+553+300%0Aw+0+471+316+549+331%0Aw+0+466+331+540+361%0Aw+0+459+344+526+389%0Aw+0+449+357+506+413%0Aw+0+437+367+481+433%0Aw+0+423+374+454+448%0Aw+0+408+378+424+457%0Aw+0+393+380+393+460%0Aw+0+377+378+361+457%0Aw+0+362+374+331+448%0Aw+0+348+367+304+433%0Aw+0+336+357+279+413%0Aw+0+326+344+259+389%0Aw+0+319+331+245+361%0Aw+0+314+316+236+331%0Aw+0+313+300+233+300%0Aw+0+314+284+236+269%0Aw+0+319+269+245+239%0Aw+0+326+256+259+211%0Aw+0+336+243+279+187%0Aw+0+348+233+304+167%0Aw+0+362+226+331+152%0Aw+0+377+222+361+143%0Aw+0+393+220+393+140%0Aw+0+408+222+424+143%0Aw+0+423+226+454+152%0Aw+0+437+233+481+167%0Aw+0+449+243+506+187%0Aw+0+459+256+526+211%0Aw+0+466+269+540+239%0Aw+0+471+284+549+269%0A

[Patr1ck2005]

Some damping will greatly postpone this phenomemon, but seems it cant remove it. I guess it related to chaotic system or numerical problem?