Try yourself:A vibrating machine is isolated from the floor using springs. If the ratio of excitation frequency of vibration of machine to the natural frequency of the isolation system is equal to 0.5, the transmissibility ratio of isolation is
Try yourself:In vibration isolation, which one of the following statements is NOT correct regarding Transmissibility (T)?
Try yourself:A machine of 250 kg mass is supported on springs of total stiffness 100 kN/m. Machine has an unbalanced rotating force of 350 N at speed of 3600 rpm. Assuming a damping factor of 0.15, the value of transmissibility ratio is
Try yourself:In a single degree of freedom underdamped spring-mass-damper system as shown in the figure, an additional damper, is added in parallel such that the system still remains underdamped. Which one of the following statements is ALWAYS true?
Try yourself:Consider the arrangement shown in the figure below where J is the combined polar mass moment of inertia of the disc and the shafts. k1 k2, k3 are the torsional stiffness of the respective shafts. The natural frequency of torsional oscillation of the disc is given by
Try yourself:A flexible rotor-shaft system comprises of a 10 kg rotor disc placed in the middle of a massless shaft of diameter 30 mm and length 500 mm between bearings (shaft is being taken massiess as the equivalent mass of the shaft is included in the rotor mass) mounted at the ends. The bearings are assumed to simulate simply supported boundary conditions. The shaft is made of steel for which the value of E is 2.1 × 1011 Pa. What is the critical speed of rotation of the shaft?
Here, m = 10 kg = mass of rotor d = diameter of shaft = 30 × 105 m l = length of shaft = 500 × 10–3 m E for steel =
2.1 × 1011 N/m2
Try yourself:A rotating disc of 1 m diameter has two eccentric masses of 0.5 kg each at radii of 50 mm and 60 mm at angular positions of 0° and 150°, respectively. A balancing mass of 0.1 kg is to be used to balance the rotor. What is the radial position of the balancing mass?
Along x- axis
Try yourself:The rotor shaft of a large electric motor supported between short bearings at both the ends shows a deflection of 1.8 mm in the middle of the rotor. Assuming the rotor to be perfectly balanced and supported at knife edges at both the ends, the likely critical speed (in rpm) of the shaft is
Alternately When speed of the shaft (w) is equal to natural speed of vibration, it is called critical speed (ωn)
Try yourself:If two nodes are observed at a frequency of 1800 rpm during whirling of simply supported long slender rotating shaft, the first critical speed of the shaft in rpm is