flogging a dead horse

Flogging a dead horse is an idiom that means a particular effort is a waste of time as there will be no outcome, such as in the example of flogging a dead horse, which will not cause it to do any useful work.
برابر اصطلاح فارسی"آب در هاون کوبیدن"
به چَم "کار بیهوده انجام دادن"