近似法

The formula can be used in approximate calculation of instable critical load of high pier in the design and construction.

本文利用能量原理的Ritz法，在对截面惯性矩变化作线性假定后，推导出变截面空心薄壁高墩失稳临界荷载近似计算公式，可用于设计施工中对高墩失稳临界荷载的近似计算。1中心压杆稳定理论及能量原理中心压杆的失稳问题是稳定问题中的一个最基本的问题。

In this paper, Galerkin method is employed. First, test functions to satisfy natural boundary conditions are selected. Then the approximate analytic formulations of the system frequency are derived. Meanwhile the approximate analytic formulation of the limit velocity is got.

采用直接法，首先选取满足自然边界条件的试函数，而后求出了系统固有频率的近似解析公式，同时也得到了极限流速的近似解析公式。

But the singularity location inversed by Born approximation inversion is false except the first interface.

本文第二章对Born近似反演算法进行了深入研究和分析，指出了Born近似反演存在的问题。

The given Branch and Bound method can find out the optimal solution of the problem in small size while the given GA implement can quickly find out the approximate optimal solution of the problem in large size. The given GA implement proves to be very effective by numerical experiments and examples.

对于问题的较小规模情形分支定界法能精确地求得最优解；对于问题的较大规模情形遗传算法能很快地求得近似最优解；算例及大量实验表明用遗传算法来求问题的近似解是成功的。

Calculus can be used to find approximate solutions to equations, in methods such as Newton's method , fixed point iteration , and linear approximation .

积分可以用来寻找近似解方程，在方法，如牛顿法，不动点迭代和线性近似。

By using function theoretic methods,the existence anduniqueness of the above problem are proved,which is generalization and devel-opment of related results.

先将其转化为一阶非线性椭圆型复方程的混合边值问题，然后使用Newton嵌入法得到了这一混合边值问题的近似解，并且在一定条件下给出了近似解的误差估计。

Then, on the basis of Atluri's work, a modified MLPG method is employed, in which the moving least squares approximation is used as a trial function and the Heaviside function is used as a test function of the weighted residual method.

然后基于Atluri等人的工作，采用移动最小二乘近似函数构造试函数，采用Heaviside函数作为加权残值法中的权函数，采用直接插值法施加本质边界条件而不采用罚函数法和拉格朗日乘子法。

The major implementations of the developed model include: Pseudo-spectral and finite-difference schemes are employed to approximate the spatial-differential operators in the horizontal and vertical directions, respectively. A second-order Runge-Kutta method is adopted to integrate in time for the velocity field and the free-surface elevation. The solenoidal condition of the velocity field is satisfied by solving the transformed pressure Poisson equation. A modified secant method is used to accelerate the iterative solution of the non-separable Poisson equation.

模式的主要数值方法包括：分别以拟频谱法以及二阶有限差分法近似控制方程与边界条件中的水平与垂直导数；以二阶Runge-Kutta法进行非稳态的自由液面位移与流场速度的时间积分；利用改良式割线叠代法求解计算区间中不可分离的压力Poisson方程式，以满足不可压缩流条件。

The book covers one-, two- and three dimensional problems which are solved by using exact and approximate analytical methods and numerical methods such as: the finite difference method, the finite volume method, the finite element method and the boundary method.

书中涵盖一，二和三是利用精确和近似分析方法和数值方法，如：有限差分法求解二维问题，有限体积法，有限元法和边界法。

It is different from the finite element method which uses the calculus of variation to construct the element-based approximate equilibrium equation. It does consider the equilibriums of forces on the inter-element boundary, which are neglected in the finite element method through the weak formulation.

这种方法跟有限元素法不同，因为有限元素法是采用变分法建立各个元素的近似平衡方程式，这种方法也考虑元素与元素相连接的边界上的力平衡条件，而在有限元素法的推导过程中我们忽略了这种条件。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。