考察一个长度为 的均直简支梁系统，梁的横截面积为A，弹性模量为E，质量密度为 ，在离简支梁左边支点的 距离和 距离处 施加动态载荷-The mean length of study of a simply supported straight beam system, the beam cross-sectional area A, modulus of elasticity E, mass density, the left away from the simple beam and the