Centrifugal Pendulum Vibration Absorbers-Theory and PraetioeReciprocating mechanical systems, such as pumps and compressors, present a nonuniform dynamic load to the driving motor. These load variations and their interactions with the dynamic characteristics of the motor result in dynamic torque variations on the rotor which have very significant harmonic components. These torque variations contribute to undesirable dynamic loading of the mounting frame and subsequent transmission of vibrations and noise into the supporting structure. Centrifugal pendulum absorbers offer an excellent means for the elimination of the effects of some of these torque harmonics. Since most reciprocating machinery operates over a speed range depending on load conditions, the centrifugal absorber is an excellent means for insuring that the suppression of vibrations is insensitive to speed and local conditions. While the virtues of centrifugal absorbers are well known as are the differential equations describing the dynamics of the absorbers, the literature does not address the case of real absorbers with distributed mass properties. This paper presents a derivation of the equations of motion for the rotor and the distributed mass pendulum, along with those insights and techniques necessary for the practical design of a centrifugal pendulum system. The tuning of the pendulum is discussed along with damping requirements.A case study is presented where a set of pendulums is employed on the rotor of an air compressor driven by a close-coupled electric induction motor. In the case study, first and second harmonic rotor torques (30 percent and 9 percent, respectively, of the average rotor torque) are eliminated with 3.77 lb and 0.83 lb pendulums in a 3-horsepower, 875 rpm machine.
A simple, theoretically based time domain model for the propagation of small, arbitrary signals in a finite, circular, fluid transmission line is developed. A recent simple theoretical solution for the step response at a downstream point in a semi-infinite fluid line is combined with a two-port representation of a finite line. The major feature of this finite line model is two “filters” which represent a convolution of their arbitrary inputs with the unit impulse response at the equivalent location in a semi-infinite line. Experimental tests are reported which further verify the simple semi-infinite line solution and verify the response of several example systems containing finite lines. The models developed herein show good agreement with experiment. The major anomaly noted was an amplitude dependence in the experimental response for signals larger than one percent of the bulk modulus of the fluid. Since the theory represents a linearized, small perturbation model, such disagreement might have been anticipated and is viewed as a limitation, rather than invalidation, of the model. Finally, quantitative comparisons are made between the proposed model and those in current use.
One of the most important components in simulating track-train dynamics is the mathematical model of the connection between two cars, the draft gear-coupler combination. In this paper an automatic parameter identification technique is presented which can be used to generate a nonlinear functional relationship of dynamic draft gear characteristics using experimental data.
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