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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
If the body that rotates about a fixed axis is at rest and if the moments of the weights about the center of the rotating shaft are zero, we say that the system is statically balanced. When the body starts rotating, the moment due to D'Alembert forces, ma→, around the center of gravity of the system may not sum to zero; the system is not dynamically balanced. Rotating machinery strives to have its systems dynamically balanced to reduce the reaction forces at the bearings and consequently their wearing. Counterweights are added such that the total D'Alembert forces of the original bodies and the weights sum to zero. In its most general case, the motion of a rigid body in space can be solved only through numerical integration, except for very few simple problems, such as gyroscopic motion.
Seals and Packing
Published in Don Renner, Hands-On Water/Wastewater Equipment Maintenance, 2017
11.77 To increase seal life, the manufacturers make a balanced style seal. The term balanced does not refer to static or dynamic balancing that reduces rotational vibration. Instead, the balancing reduces hydraulic pressure on the seal face during operation. This hydraulic balancing is accomplished by reducing the rear area of the seal face that is exposed to internal pressure from the fluid being pumped. Although the coil spring maintains pressure on the rotating element, hydraulic pressure has a greater effect.
Vibration Control
Published in Haym Benaroya, Mark Nagurka, Seon Han, Mechanical Vibration, 2017
Haym Benaroya, Mark Nagurka, Seon Han
When an unacceptable vibration problem occurs, it must be decided how it is best solved. Three methods can be identified. In every case, the first effort should be to reduce the vibration input from the source. If, for example, the vibration is attributed to imbalance in a rotating machine, the machine should be balanced as carefully as possible. If the vibration stems from misalignment of bearings, the bearings should be aligned or replaced. The first step is simply to address the source of the problem through proper operation.
Optimal design of support parameters for minimum force transmissibility of a flexible rotor based on H∞ and H2 optimization methods
Published in Engineering Optimization, 2018
Hamidreza Heidari, Pedram Safarpour
In rotating machinery such as turbojet engines, compressors and turbines, the rotors often encounter large forces transmitted to the support structure. The problem becomes more severe as machinery is designed to be lighter and, hence, more flexible. Large force transmissibility may be due to several causes and may be roughly grouped under the headings of synchronous and non-synchronous response. Synchronous response is usually associated with unbalance in the rotor. This unbalance may result from either the manufacturing process or the assembly of the components. Even if a rotor is well balanced initially, the balance degrades with rotor use. Thermal gradients can cause warping of the shaft. Erosion of compressor or turbine blades can alter the balance of the rotor. Therefore, in the design of machinery provisions should be made so that the increase of unbalance with operation will not overload the bearings or cause excessive rotor amplitudes.