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A COMPARATIVE STUDY OF DESIGN AND PERFORMANCE OF FREE OR FORCE VIBRATION APPARATUS

BSTRACT

This seminar report is on a comparative study of design and performance of free and forced vibration apparatus. This work described the vibrometer and accelerometer apparatus. The work discusses the designs, performance and features of both free and forced vibrations. Also the analysis of comparative study was carryout in order to state the similarities and dissimilarities of free vibration apparatus and forced vibration apparatus.

CHAPTER ONE:

INTRODUCTION

BACKGROUND OF THE STUDY

Vibration is a mechanical phenomenon whereby oscillationsoccur about an equilibrium point. Vibration can be desirable: for example, the motion of a tuning fork, the reed in a woodwind instrument or harmonica, a mobile phone, or the cone of aloudspeaker. In many cases, however, vibration is undesirable, wasting energy and creating unwanted sound. For example, the vibrational motions of engines, electric motors, or any mechanical device in operation are typically unwanted. Such vibrations could be caused by imbalances in the rotating parts, uneven friction, or the meshing of gear teeth. Careful designs usually minimize unwanted vibrations (Rivin, 2010).

Vibration can be classified to either be free or forced vibration. Free vibration occurs when a mechanical system is set in motion with an initial input and allowed to vibrate freely. Examples of this type of vibration is hitting a tuning fork and letting it ring. The mechanical system vibrates at one or more of its natural frequencies and damps down to motionlessness. While forcedvibration is when a time-varying disturbance (load, displacement or velocity) is applied to a mechanical system. The disturbance can be a periodic and steady-state input, a transient input, or a random input. The periodic input can be a harmonic or a non-harmonic disturbance. Examples of this type of vibration include a washing machine shaking due to an imbalance or transportation vibration caused by an engine or uneven road (Inman, 2014).

Free and forced vibration can be measured using vibration measuring apparatus. These apparatus can be designed and their performance depends on solely the quality of the design. Vibration apparatus are used for measuring the magnitude of vibration. Some of the vibration apparatus are vibrometer, accelerometer, seismometer, etc. Accelerometers are used to record forced vibrations, while seismometers are used to detect free vibrations. A recording device, called a seismograph, records the relative motion between the mass and the unit, producing a record of the movement. Modern seismometers utilize electronic circuits to measure the electrical voltage created by this motion rather than mechanical means (Macinante, 2013). These modern devices are capable of detecting vibrations as small as semidiurnal gravitational tide movements and distances almost as small as atomic spacing.

In view of the above this work intends to present a comparative study of design and performance of free and forced vibration apparatus.

OBJECTIVES OF THE STUDY

The aim of this work is to present a study on a comparative study of design and performance of free and forced vibration.

The specific objectives are as follows;

1. To examine the cause of vibration of free and forced vibration

2. To investigate apparatus used for measuring free and forced vibration

3. To carryout a comparative study of design and performance of free and forced vibration apparatus.

JUSTIFICATION OF THE STUDY

In reading books and technical papers on vibration including the previous paragraph, engineering students are usually left with the impression that all vibrations are detrimental because most publicized work discusses vibration reduction in one form or another. But vibrations can also be beneficial. For instance, many different types of mining operations rely on sifting vibrations through which different sized particles are sorted using vibrations. In nature, vibrations are also used by all kinds of different species in their daily lives. Orb web spiders, for example, use vibrations in their webs to detect the presence of flies and other insects as they struggle after being captured in the web for food. The reason that mechanical systems vibrate freely is because energy is exchanged between the system’s inertial (masses) elements and elastic (springs) elements. Free vibrations usually cease after a certain length of time because damping elements in systems dissipate energy as it is converted back-and-forth between kinetic energy and potential energy.