American Journal of Mechanical Engineering, 2017, Vol. 5, No. 6, 284-288 Available online at http://pubs.sciepub.com/ajme/5/6/10 ©Science and Education Publishing DOI:10.12691/ajme-5-6-10 Experimental Assumption of Steel Pipe Modal Parameters Using Common and Simplified Approach Martin Hagara * , Jozef Bocko Department of Applied Mechanics and Mechanical Engineering, Technical University of Košice, Faculty of Mechanical Engineering, Košice, Slovakia *Corresponding author: martin.hagara@tuke.sk Abstract The contribution deals with describing of two experimental approaches leading to assumption of modal parameters in a form of natural frequencies, mode shapes and damping of freely supported steel pipe. In the first approach, the model of the pipe was created in common way using planar elements. In the second one, the model of the pipe was simplified using line elements, which should lead to the increasing of time needed for realization of experimental investigation. The results obtained by both approaches as well as their pros and cons are described in the paper. Keywords: experimental modal analysis, natural frequencies, mode shapes, damping, pipe Cite This Article: Martin Hagara, and Jozef Bocko, “Experimental Assumption of Steel Pipe Modal Parameters Using Common and Simplified Approach.” American Journal of Mechanical Engineering, vol. 5, no. 6 (2017): 284-288. doi: 10.12691/ajme-5-6-10. 1. Introduction There are lot of problems in engineering praxis caused by a fact that mechanical structures work at frequencies, by which a phenomenon well known as resonance is occurred. The resonance increases the noise in the working environment or can even destroy the structure, if the damping elements are not able to absorb the raising magnitudes of vibration, what means that such phenomenon is de facto contrary. The aim of experimental modal analysis, known as modal testing, is to assume important dynamic characteristics of the structure in a form of natural frequencies, mode shapes and damping, called modal parameters. Its principle consists in the investigation of a relation between the vibration response ( ) Y f and the excitation ( ) X f at different locations of analyzed structure, known as frequency response function (FRF) [1,2] ( ) ( ) ( ) Y f H f X f = . (1) 2. Determination of FRF of Systems with One- and Multi-degree of Freedom Considering mechanical oscillator with viscous damping depicted in Figure 1. According to the second Newton’s law its motion can be expressed by () mu cu ku Ft + + =   . (2) Using Laplace transform eq. (2) leads to ( ) () () 2 ms cs kU s Fs + + = , (3) that can be adjusted to () () () 2 2 1/ 2 n n U s m H s Fs s s ζω ω = = + + , (4) where n k m ω = is the undamped angular frequency and 2 c mk ζ = is the damping ratio. Figure 1. Scheme of analyzed mechanical oscillator However, by the identification of dynamic system it is not possible to determine the frequency response function due to eq. (4), but it is necessary to find a ratio between the response and excitation spectrum. This function can be expressed using 2 s j j f ω π = = in a form ( ) ( ) ( ) 2 2 1/ . 2 n n U f m H f F f j ω ζω ω ω = = − + + (5) Eq. (5) can be adjusted to more practical form