给出系统的时间积分等式，并由此等式导出类能量方程、类维里定理、一个积分变分原理和一个微分变分原理。
A power-like equation, a Virial-like theorem, an integral variational principle and a differential variational principle for the system are deduced by using the time-integral identity.
本文应用哈密顿变分原理较简捷地建立了厚梁横向振动的微分方程。
The differential equation for transverse vibration in thick beam is easily established by applying the Hamilton's variance principle.
根据地下水的连续方程和变分原理建立渗流场微分方程。
Based on the continuity equation of ground water and the variation principle, the seepage differential equation can be acquired.
利用变分原理得到平衡微分方程组和相应的边界条件。
By variational principle we obtain a system of differential equations and corresponding boundary conditions.
本文由费马原理的变分形式，导出光线微分方程。
Ray equation is derived from Fermat's principle in variation form.
该方法不用一般的变分原理，可适用任意变系数正定和非正定偏微分方程。利用这一方法得到一个新的八节点四边形平面应力单元。
It doesn't need the variational principle and can be applied to solve non-positive or positive definite partial differential equations with arbitrary variable coefficient.
该方法不用一般的变分原理，可适用任意变系数正定和非正定偏微分方程。利用这一方法得到一个新的八节点四边形平面应力单元。
It doesn't need the variational principle and can be applied to solve non-positive or positive definite partial differential equations with arbitrary variable coefficient.
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