ATTENUATING AMPLITUDE OF PULSATING PRESSURE IN A LOWPRESSUREHYDRAULIC SYSTEM BY AN ADAPTIVE HELMHOLTZ RESONATOR, ACTA UNIVERSITATIS OULUENSIS C Tec h n i c a 3 5 4

The adaptive Helmholtz resonator for decreasing harmonic pulsating pressure in a low-pressure\nhydraulic system is presented in this study. Adaptivity is executed by both open loop and closed\nloop controls so that continuous -20dB attenuation of the peak-to-peak value of the amplitude of\npressure is reached.\nThe study begins by a theory review including the theory of effective bulk modulus, sound\nvelocity measurements, adjustable dynamic vibration absorbers and control methods of dynamic\nvibration absorbers. The main target of the paper, the Helmholtz resonator, is presented in its own\nchapter, albeit it is noted to be one application of the dynamic vibration absorber. The review is\ncompleted by the analytical model of the hydraulic pipe with a T-filter or Helmholtz resonator.\nAfter the theory review, the test equipment and its characteristics are presented. The main parts\nof the test equipment were a main pipe and an adjustable Helmholtz resonator, which were both\ndeveloped for this study. Certain properties of the hydraulic oils used were determined\nexperimentally to increase understanding of the system.\nThe experimental section includes sound velocity measurements, sonic bulk modulus\ndefinitions, measurements of the resonant frequencies of the adaptive Helmholtz resonator in the\ntest equipment, and tests of the open loop and closed loop control of the resonator. Control is\nverified to maintain -20dB attenuating of pressure pulsations in the system.\nThe presented Helmholtz resonator and controls are available for installation into a hydraulic\nsystem to damp out harmonic vibrations at low frequency. For example, the roll in the size press\nof a paper machine might become excited to vibrate at its resonance frequency after the paper wad\nhas washed through the nip. In that case, tuned Helmholtz resoAnators in the hydraulic cylinders of\nthe size press would damp out the pulsating pressures, and if the resonators are adaptive, as\npresented in this study, they can operate in a wider frequency range.

ISBN-10:
978-951-42-6159-6
Kieli:
eng.
Sivumäärä:
154 s.
Tekijät:
Kela Lari
Tuotekoodi 013961
20,00 €