说明：  给出了 Gassmann 方程的假设，针对如何应用 Gassmann 方程进行流体替换及注意事项给出说明，并给出了明确的方法和计算步骤。
(Given the assumptions of the Gassmann equation for how to apply the Gassmann equation fluid replacement and precautions given instructions, and gives a clear method and calculation steps.)