Vibration Behavior Of Structure Research Articles

Engineering Analysis on Vibration Characteristics of Merchant Vessels with Theoretical and Onboard Test Approaches

Recent development of ship design, such as flexible hull structures with somewhat light ship weight in terms of larger/longer/wider principal particulars and long-stroke diesel engine of high brake horsepower, has been demonstrated dramatically. Nevertheless, this kind of ship design concept harmfully degrades system stability of electronic instrumentation and operating performance of human beings in sea service. Therefore practical prediction on structural vibration behavior of designed vessels is of primary concern and has to be taken into account at the preliminary design stage. Two theoretical approaches, preliminary prediction by empirical formula and numerical solutions by finite-element technique (matrix analysis methodology), are briefly reviewed. An onboard test system for structural vibration measurement is developed and comprehensively described. In fact, a standard procedure of data acquisition and analysis system for structural vibration measurement is already set up to deal with several kinds of vibration research work in practical engineering fields. Natural frequencies of vibration behavior for a 1200 TEU container vessel are checked out by preliminary prediction of empirical formula and measurement data from onboard tests. Moreover, a comparison study by finite-element analysis and full-scale measurement is also performed on vibration characteristics of hull structures. The amplitude of vibration acceleration induced by unbalanced moment of the main engine is calculated for any point of hull at the resonance condition and the installation of an electrical balancer onboard is taken into account for vibration countermeasures also. All approximate predictions, compared with onboard test results, are found to meet with an acceptable level of engineering accuracy. The practical package of approximate approaches in both theoretical and onboard test aspects to investigate vibration characteristics of structures, for instance, hull, machinery, piping, and shafting system, in universal service is quite reliable and easily performed on portable computers for extensive engineering applications.

The receptance sensitivity and the effect of concentrated mass inserts on the modal balance of spindle-bearing systems

In this paper, it is shown how the receptance of a modified system can be described in terms of the receptance of the unmodified system. Furthermore, a receptance sensitivity analysis is introduced to show the effects of design changes on the dynamic performance of vibrating structures. The spindle-bearing system is chosen as a good target for investigation with respect to machine tool's performance. The sensitivity analysis carried out shows the effect of concentrated mass inserrts on its dynamic behaviour. The concept of modal flexibility sharing is chosen as a good measure of modal balance of the vibrating structure. Therefore, a technique is introduced based on the aforementioned method to achieve such state of modal balance by means of some mass inserts. The results obtained lead one to think that such a procedure can be employed to optimise the vibration behaviour of structures in general and machine tools in particular.

The receptance modification strategy of a complex vibrating system

The introduction of computers into engineering has played a significant role in solving vibration problems of great complexity. This paper is concerned with introducing a new method in calculating the effect of structural modification on the vibration characteristics of a mechanical structure. A modification strategy is introduced based on Kron's method of “tearing”. In this method the receptance of the modified system is found in terms of the receptance of the unmodified system. The usefulness and versatility of the proposed method is reflected not only, in its ability to handle modifications regardless of their magnitude and locations but also in its power to retain the information concerning the unmodified structure and hence enabling the user to refer back to the original data whenever needed. The results obtained leads one to think that such modification procedure can be employed to optimize the vibration behaviour of structures.