Control Of Vibration Transmission Research Articles

The Control of Vibration Transmission from an Engine to its Resonant Base Structure

Engines and motors on board marine vessels are often mounted on flexible base supports. When the levels of vibration transmitted from such machines to the base structure are intolerable, vibration reduction techniques have to be used. In instances where machines are mounted via very stiff mounts to maintain shaft alignment, the transmission paths of the vibratory force are through the mounts. In such cases, active force cancellation at the mount locations using opposing controlled forces can be used. This paper discusses the use of frequency domain techniques to reduce the vibration with the H ∞ norm as a performance measure. The model of the system, identified using frequency response method is used in the design of the H ∞ controllers for active force cancellation. Two approaches were presented. Experimental results show a reduction of between 15 ~ 65% of the measured transmitted force at different mount locations when the machine is operated at a speed of about 1320 rpm. This frequency matches that of the machine-base system principal mode. Where the system response is not significant, reduction in transmitted force level is minimal. This limitation is the result of the control goal used in the design.

ANALYSIS AND CONTROL OF VIBRATIONAL POWER TRANSMISSION TO MACHINERY SUPPORTING STRUCTURES SUBJECTED TO A MULTI-EXCITATION SYSTEM, PART I: DRIVING POINT MOBILITY MATRIX OF BEAMS AND RECTANGULAR PLATES

The analysis and control of vibration transmission from a machine source to flexible beam- and plate-like supporting structures via the translational and rotational motions as well as the coupling between these motions are studied in these three companions papers. In these studies, co-located simultaneously acting sinusoidal force and moment excitations are assumed to act on the flexible supporting structures and the transmission of vibrational energy into the structures is expressed in terms of the time-averaged vibrational power. The driving point mobility functions of uniform beams and rectangular plates are derived in the first paper. The existence and contribution of the coupling mobility functions in the case of a multi-excitation system give rise to cancellation of vibrational power components. This observation forms the basis of the proposed vibration control technique, which is studied in the second paper. The experimental arrangements for validation of the cancellation of vibrational power components and the proposed vibration control technique with suitably designed force moment seatings are described in the third paper. The proposed vibration control technique is most suitable for the case of a low to medium constant speed machine mounted on a flexible supporting structure.

Enhanced vibration control of an ultrasonic cutting process

An ultrasonic cutting technique has been developed which transmits 20 kHz vibration from a piezoelectric transducer to a series of blades via a system of tuned horns. Problematic vibration behaviour exists due to the high modal density around the operating mode frequency. For this reason, an understanding of the mechanisms of non-tuned mode excitation and careful system design are essential for a successful cutting operation. This paper presents an investigation into the contributing influences of the ultrasonic generator signal to the vibration response of the cutting system components. Improvements in vibration performance are realised by obtaining a full vibration picture of the system and its components, which leads to enhanced control of vibration transmission to the cutting edge at the tuned frequency.

An experimental study of active control of vibration transmission in a cylindrical shell.

An experimental investigation of active control of vibratory power transmission in a semi‐infinite cylinder, using an array of electrodynamic shakers, is described. The cylinder was mounted vertically in a sand‐filled box (1 m in height) in an attempt to provide a semianechoic termination at one end. The other end was simply supported using a steel ring. The cylinder was excited near the simply supported end using a primary shaker. Control was implemented using three control shakers applied downstream from the primary shaker. Using three control shakers it is possible to achieve a 7‐dB reduction in power transmission. Although 7 dB was the maximum power reduction which could be obtained for the experimental equipment, the numerical simulation shows that on a large scale, a reduction of 30 dB could be obtained. Also, measurement of power transmission intensity in a cylinder using two accelerometers was investigated. The results indicate a means of simplifying power transmission measurements in large cylind...

Eigenmodes of quasicrystals

Recently, a new state of matter, referred to as quasicrystalline, was discovered. Previously, solids could be classified as crystalline, with periodic lattice spacing, or as glassy, with random site spacing. The new quasicrystal structures appear to have long‐range order, showing sharp peaks in the Fourier transform space as in a periodic system, but they also have properties that are impossible for any periodic structure, such as fivefold rotational symmetry. For periodic systems, Bloch's theorem may be used to understand physical properties such as wave transmission, and it is of current interest to learn if any such symmetry theorems apply to quasiperiodic systems. Rigorous theorems for one‐dimensional quasiperiodic patterns based on a Fibonacci sequence suggest that such a pattern may be useful in control of vibration transmission in rib‐stiffened plates. However, in two and higher dimensions, little is known about the consequences of quasiperiodic structure. Recently, acoustic measurements have been ...