Design Lab viva-voice questions For experiments 1-4 Vibration: It is a term that describes oscillations in a mechanical system. OR periodic back-andforth motion of the particles of an elastic body or medium, commonly resulting when almost any physical system is displaced from its equilibrium condition and allowed to respond to the forces that tend to restore equilibrium. Frequency: number of cycles per seconds, Hz (Hertz). For a body undergoing simple harmonic motion, the number of vibrations it makes per unit time. For a series of waves, the number of waves that pass a particular point per unit time. Frequency = 1/Period -or- Period = 1/Frequency hertz (Hz): unit of frequency; one vibration per second is 1Hz Natural Frequency: -When no external force acts on the system after giving it an initial displacement, the body vibrates is called natural frequency. Or A frequency at which an elastic object naturally tends to vibrate, so that minimum energy is required to produce a forced vibration or to continue vibration at that frequency. Amplitude: For a wave or vibration, the maximum displacement on either side of the equilibrium (midpoint) position. Period: The time required for a vibration or a wave to make a complete cycle Forced Vibration: The setting up of vibrations in an object by a vibrating force. What are the different types of vibration? Following are the types the different types of vibration 1. Free & forced vibration 2. Linear & non-linear vibration 3. Damped & Undamped vibration 4. Deterministic & random vibration 5. Longitudinal, transverse & Torsional vibration 6. Transient vibration. State some reasons/causes for vibration? Following are some reasons/causes for vibration 1. Unbalanced centrifugal forces in the system. 2. Elastic nature of the system. 3. External excitation applied on the system. 4. Winds may cause vibrations 5. & Vibrations of certain systems such as electricity lines, telephone lines, etc., What are the methods used to eliminate vibration in system? 1. Removing external excitation, if possible. 2. Using shock absorbers. 3. Dynamic absorbers. 4. Resting the system on proper vibration isolators.
DAMPING RATIO: The damping ratio is a dimensionless measure describing how oscillations in a system decay after a disturbance. OR it can be defined as the ratio of the damping coefficient in the system's differential equation to the critical damping coefficient:
mass system is completely lossless, the mass would oscillate indefinitely, UN DAMPED: Where the spring – mass with each bounce of equal height to the last. This hypothetical case is called undamped.
OVER DAMPED: If the system contained high losses, for example if the spring – mass experiment were conducted in a viscous fluid, the mass could slowly return to its rest position without ever overshooting. This case is called overdamped. UNDER DAMPED: Commonly, the mass tends to overshoot its starting position, and then return, overshooting again. With each overshoot, some energy in the system is dissipated, and the oscillations die towards zero. This case is called underdamped. CRITICAL DAMPING: Between the overdamped and underdamped cases, there exists a certain level of damping at which the system will just fail to overshoot and will not make a single oscillation. This case is called critical damping. LOGARITHMIC DECREMENT: The logarithmic decrement is the natural log of the ratio of the amplitudes of any two successive peaks. Experiment no-5, whirling of shaft Resonance: When the external forcing frequency co-insides with the natural frequency is called Resonance.OR Resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. Frequencies at which the response amplitude is a relative maximum are known as the system's resonant frequencies, or resonance frequencies. Critical speed: The speed at which Resonance occurs is called critical speed. Or Rotation shafts tend to vibrate violently at certain speed called critical speed. What are the causes for the failure of shaft? 1. Eccentricity in mounting. 2. Non-uniform distribution of material. 3. Shaft if self may bend. 4. Manufacturing defects. What are the other names for critical speed? Whirling, whipping and critical speed. Experiment no-7, Calibration of circular disc under diametric compression Wavelength: the distance between successive identical parts of a wave Polarization: the alignment of the electric vectors that make up electromagnetic radiation. Such waves of aligned vibrations are said to be polarized. Stress Optic law: The theory which relates changes in the indices of refraction of a material (exhibiting temporary bobble refraction) to the material is called stress optic law. Photo elasticity : The property shown by certain transparent solids, esp. glass and plastics, of producing double refraction when put under tension or compression, thus permitting stress analysis of models of parts this is called photo elasticity.
The application of photoelastici Non-contact optical method for determining stresses and load paths in components or structures
coating
2D investigation
3D investigati
Impact Testing Assembly Stress Analysis Glass Inspection Flaw Detection Residual Stress Analysis FEA Model Verification
Residual Stress in Glass
Name the different arrangement made for finding stress by optical method. Plane polariscope arrangement and circular polariscope arrangement. Plane polariscope arrangement: arrangement without quarter wave plates. st nd circular polariscope arrangement: arrangement with 1 & 2 quarter wave plates.
Name some important photo elastic modal materials. 1. Araldite-B 2. Araldite-D 3. Catalin 4. Urethane 5. Glass
Ideal properties of photo elastic materials are
6. Gelatin 7. Rubber 8. Crystons 9. Fused Silica 10. Epoxy resines
1. 2. 3. 4. 5.
Transparency Sensitivity Linearity Isotropy & homogeneity Creep
6. High modulus of rigidity 7. High ultimate strength 8. Temperature sensitivity 9. Machinability 10. Residual stress
Experiment no-8, Gyroscope Gyroscope: A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum Mechanically, a gyroscope is a spinning wheel or disk in which the axle is free to assume any orientation.
The right hand Thumb(screw) rule can be used when a direction must be determined based upon a rotational direction, or vice versa. It is best illustrated using a diagram.
The axis is 'grasped' in the right hand, the fingers curl round in the direction of positive rotation and the thumb is orientated in the positive direction. Therefore if the direction of rotation is know the fingers can be curled in this orientation and the thumb will point in the positive direction, and vice versa. Name some applications in which gyroscope effect acts. Automobiles, planes and ships. What is Gyroscopic effect on aeroplane? gyroroscope effect will usefull in determining the direction in wich the aeroplane nose and tale will move while taking a turn in either direction like left or right ...it have several conditions...like if we are noticing from the rare side(back side) whn the plan take a left cut ..and the rotter of the plan is moving in the clockwise direction..then the nose get up and the tail goes down...because of the active and reavtive gyroscopic couple fore which are acting in opposite direction and equal in magnitude... (2)-if plan takes a right turn in the same conditions the action of the tail and nose will be the vice versa of the 1st result... if rotter in moving in anticlock wise direction...then the result 1st and 2nd will be the vice versa ... (3)-condition 2nd...if we notice it from the front the all results are oppsite...for e.g if plane turns left then the nose get down and tail gets down in direction ......so nw u can get all result by transforming them into the jst opposite to the results of the condition 1st...results
