Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Natural frequency


Effect of Cracks on the Natural Frequency of Cylindrical Shell Structures

Marwah . A. Husain; Mohsin A. Al-shammari

Engineering and Technology Journal, 2020, Volume 38, Issue 12, Pages 1808-1817
DOI: 10.30684/etj.v38i12A.1513

Shell structures are liable to different kinds of defects and damage like cracking and corrosion which may destroy their structural safety and affect the service life. The cracks' effects are significant considerations in the design of cylindrical shell structures as they influence the vibration characteristics and safety. This present work is an experimental study on the free vibration analysis of a cylindrical shell involving circumferential surface crack. The influence of the ratio of shell’s radius to a shell’s thickness (R/h)of the shell structure, crack length in the shell, crack depth in the shell, crack location of the shell, and crack orientation in the shell are investigated under a clamped - clamped and simply supported boundary conditions at each end in the shell. Results showed that the minimum impact of the crack is at the angle of crack 75, and the circumferential fissure has more effect than a longitudinal fissure, In addition to this, under SS-SS, C-C the natural frequency will decrease if the fissure is located in the middle of the shell is greater than other locations. but when crack animated across in the ends of the limits the decrease in the natural frequency under C-C only. Results were compared with the literature there was a close agreement.

Finite Element Analysis of Suppression the Vibration of Dish Using Closed Loop Control System

Nahedh Mahmood Ali

Engineering and Technology Journal, 2016, Volume 34, Issue 8, Pages 1499-1513

A closed loop simulation is used for minimizing of undemanding vibration caused in the dish system. The finite element method is used to model the closed loop control via ANSYS- APDL. In this paper the Bezier function for surface modeling to get the best modeling points for dish is used. A designed surface is represented by sufficient control points, using these control points, the surface has been represented depending on Bezier technique to generate reliable and near-optimal dish surface. The required equations are generated to apply the surfaces and curves efficiently using MATLAP program, then exported to ANSYS to perform closed loop vibration analysis. It can be concluded that the closed loop control system with gain (Kp=4, Ki=1, Kd=0.1) suppression the vibration of the dish with 98% with different thickness and materials of dish. Also the natural frequencies and the mode shapes of the dish is evaluated. Three materials (pure copper, pure aluminum and steel) each with different thickness is taken for the dish (0.8, 0.9, 1, 1.1 and 1.2) mm and for each thickness the responses and the natural frequencies are determined for six modes. The effect of the thickness’s variation on natural frequencies for each material was studied. It can be observed that natural frequency is direct proportional with the thickness of the dish.

Vibration Analysis of Laminated Composites Using Experimental and Genetic Algorithms Optimization Technique

Nabil Hassan Hadi; Kayser Aziz Ameen

Engineering and Technology Journal, 2012, Volume 30, Issue 18, Pages 3192-3218

In this paper, damage detection for different types of defects (delamination, crack
and hole) in the composite laminate plate and cylindrical shell be used to characterize
the vibration behavior experimentally which used two types of load (plus and sine
load) to find the frequency response. To this end, some plates and cylindrical shells
are made using hand-lay-up process. Glass fiber is used as a reinforcement in the
form of bidirectional fabric and general purpose polyester resin as matrix for the
composite material of plates and cylindrical shells. From the results, the damage
detection by using the Genetic algorithms is investigated. Also, these experiments are
used to validate the results of free vibration obtained from the finite elements
program.