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Experimental Identification of Dynamic Balancing of Rigid and Flexible Rotors
Published in Rajiv Tiwari, Rotor Systems: Analysis and Identification, 2017
If the rotor experiences no deformations or has appreciably small displacements, i.e. it remains a rigid rotor, the balancing procedure discussed earlier is effective. Once the rotor bends while approaching a critical speed, the bend centerline whirls around and additional centrifugal forces are set up and the rigid rotor balancing becomes ineffective (sometimes rigid rotor balancing worsens bending mode whirl amplitude). Two different techniques are generally employed: the (i) modal balancing technique (Bishop and Gladwell, 1959; Gnilka, 1983) and (ii) influence coefficient method (Drechsler, 1980). These will be described in detail in a subsequent section. However, initially some basic concepts are described related to the flexible rotor unbalance distribution and underlying equilibrium equations are considered that need to be satisfied for the balancing of flexible rotors.
Faults in Machines (1)
Published in Arthur W. Lees, Vibration Problems in Machines, 2020
It is here that the importance of the distinction between rigid and flexible rotors becomes clear since a rigid rotor, balanced in two planes, will be balanced for all speeds. This is clear in modal terms since all the modes (i.e. two rigid body modes) have been balanced. With a flexible rotor however, this will not be the case as other modes assume importance with increasing rotor speed. Of course, there is no such thing as a truly rigid rotor, but the criterion is based on the closeness of the first flexural free–free natural frequency to the running range. The state of balance of a flexible rotor must be considered at its speed of operation.
Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
A rigid rotor can be balanced at a speed less than operating speed and generally provide acceptable performance. This slow-speed balance is best accomplished in a dynamic balancing machine. Instructions provided by each balance machine manufacturer provide adequate balancing procedures.
A new rotor balancing method using amplitude subtraction and its performance analysis with phase angle measurement-based rotor balancing method
Published in Australian Journal of Mechanical Engineering, 2020
The operation of the mass redistribution balancer is based on the motion of correction masses along two perpendicular axes fixed to the rotating system (Hassan 1995). For rigid rotor balancing two methods are available, e.g. the conversional cradle balancing machine method (off-site or of field balancing) and the modern influence coefficients method (on-site or field balancing). Similarly, for the flexible rotor two basic methods are available, e.g. the modal balancing method and the influence coefficient method. In general, the rigid rotor can be balanced by putting correction masses in two balancing planes, however, in flexible rotor case, it can be balanced by N balancing planes, where N is the number of flexible modes need to be balanced. Sometimes, it is suggested to balance flexible rotor by (N + 2) balancing planes (i.e. to balance rigid rotor modes by two planes at low speeds and flexible rotor modes by N planes at high speeds) (Louis 1987; Amogh, Hande, and Kadam 2015). The selection of balancing method will depend on several factors such as unbalance configuration, length-to-diameter ratio, balance speed compared to operating speed, rotor flexibility and amount of cross-effect. Different methods of rotor balancing requires different trial runs (number of times the machine has to stop) so as to place trial weights and measure vibration amplitude (Christenson, Tonnesen, and Lund 1976). Any method which balances the rotor in less number of trials is considered to be the efficient one because stopping machine results in more energy consumption and reduction in machine life. There are various static and dynamic balancing methods depending upon type of rotor (Kiran, Diwakar, and Satyanarayana 2012).