Module 5 : Numerical Techniques

Lecture 1 : Review of numerical methods: Root finding and Solution of Deferential Equations

 

Here, and are the Young modulus, moment of inertia, mass density, area of cross-section, length of the cantilever beam and damping factor of the system and respectively, are used as integration variables. The following non-dimensional parameters are used in the further analysis.

, , , , , , , , and .

Also, the eigenfunction for a cantilever beam with a tip mass is given by

(5.1.11)

One may determine from the following equation.

.............................. (5.1.12)

One may note that the coefficients of the temporal equation can be obtained by first finding the roots of the characteristic equation (5.1.12) and there by finding the integration to which also requires numerical differentiation. Following numerical methods may be used for finding the roots of the characteristic equation.

Let us consider a function . According to method of bisection one should choose two values of x for example and such that, one of the functional value should be positive and other should be negative. Now the next point is obtain by interval halving, i.e., . The root is now assumed to lie between and if their functional values are of opposite sign. Otherwise, it will lie between and . The next point is obtained by halving the interval and the procedure is repeated till obtain a root having the functional value within a very close tolerance.

In Newton's method which is also known as Newton-Raphson's method one finds the derivative to obtain the root. As shown in Fig. (5.1.2), the actual solution is . Choosing as the guess value of the root