By variational principle we obtain a system of differential equations and corresponding boundary conditions.
利用变分原理得到平衡微分方程组和相应的边界条件。
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。
On the basis of the energy-variational principle, the differential equations and boundary conditions of curved box girder are derived.
利用能量变分原理，推导出平面曲线箱梁的基本微分方程、边界条件；
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