1,691 research outputs found
Research on Low Frequency Noise Caused by Beat Vibration of Rotary Compressor
The discontinuity of low frequency noise caused by beat frequency vibration of rotary compressor is studied in this paper. Based on beat frequency theoretical analysis, a finite element model is established to simulate the electromagnetic harmonics. And the contributions of various compressor motor designs to beat frequency vibration are investigated, so the motor optimization design schemes are obtained. The tests show that the method proposed in the paper is effective to improve low frequency noise of the compressor
Numerical and Experimental Research of Noise Reduction due to Low Frequency Pressure Fluctuation of Rotary Compressor
In order to reduce the noise level due to the low frequency pressure fluctuation associated with a rotary compressor, the noise mechanism and noise reduction solutions were conducted by using numerical and experimental methods. A 1D simulation model was established and a sensitivity analysis was conducted for the parameters associated with the low frequency pressure fluctuation of the rotary compressor. Then, a 3D CFD simulation model corresponding to the operation procedure of the rotary compressor was established and the working process of the rotary compressor was simulated. At the same time, the low frequency pressure fluctuation and the noise spectral characteristic were measured by using a refrigerant test fixture established in this work. Based on numerical and experimental research results, several noise reduction solutions and basic methods to restrain the low frequency pressure fluctuation were proposed and verified by using experimental method. A good improvement for the noise performance due to the low frequency pressure fluctuation was obtained. The work in this paper provides a reference and a foundation for the improvement of the noise due to the low frequency pressure fluctuation associated with rotary compressors
Chiral symmetry analysis and rigid rotational invariance for the lattice dynamics of single-wall carbon nanotubes
In this paper, we provide a detailed expression of the vibrational potential
for the lattice dynamics of the single-wall carbon nanotubes (SWCNT) satisfying
the requirements of the exact rigid translational as well as rotational
symmetries, which is a nontrivial generalization of the valence force model for
the planar graphene sheet. With the model, the low frequency behavior of the
dispersion of the acoustic modes as well as the flexure mode can be precisely
calculated. Based upon a comprehensive chiral symmetry analysis, the calculated
mode frequencies (including all the Raman and infrared active modes),
velocities of acoustic modes and the polarization vectors are systematically
fitted in terms of the chiral angle and radius, where the restrictions of
various symmetry operations of the SWCNT are fulfilled
Raman and Infra-red properties and layer dependence of the phonon dispersions in multi-layered graphene
The symmetry group analysis is applied to classify the phonon modes of
-stacked graphene layers (NSGL's) with AB- and AA-stacking, particularly
their infra-red and Raman properties. The dispersions of various phonon modes
are calculated in a multi-layer vibrational model, which is generalized from
the lattice vibrational potentials of graphene to including the inter-layer
interactions in NSGL's. The experimentally reported red shift phenomena in the
layer number dependence of the intra-layer optical C-C stretching mode
frequencies are interpreted. An interesting low frequency inter-layer optical
mode is revealed to be Raman or Infra-red active in even or odd NSGL's
respectively. Its frequency shift is sensitive to the layer number and
saturated at about 10 layers.Comment: enlarged versio
A lattice dynamical treatment for the total potential energy of single-walled carbon nanotubes and its applications: relaxed equilibrium structure, elastic properties, and vibrational modes of ultra-narrow tubes
In this paper, we proposed a lattice dynamic treatment for the total
potential energy for single-walled carbon nanotubes (SWCNT's) which is, apart
from a parameter for the non-linear effects, extracted from the vibrational
energy of the planar graphene sheet. Based upon the proposal, we investigated
systematically the relaxed lattice configuration for narrow SWCNT's, the strain
energy, the Young's modulus and Poisson ratio, and the lattice vibrational
properties respected to the relaxed equilibrium tubule structure. Our
calculated results for various physical quantities are nicely in consistency
with existing experimental measurements. Particularly, we verified that the
relaxation effect brings the bond length longer and the frequencies of various
optical vibrational modes softer; Our calculation provides the evidence that
the Young's modulus of armchair tube exceeds that of the planar graphene sheet,
and the large diameter limits of the Young's modulus and Poisson ratio are in
agreement with the experimental values of the graphite; The calculated radial
breathing modes for the ultra narrow tubes with diameter range between 0.2 -
0.5 nm coincide the experimental results and the existing {\it ab initio}
calculations with satisfaction; For narrow tubes of diameter 2 nm, the
calculated frequencies of optical modes in tubule tangential plane as well as
those of radial breathing modes are also in good agreement with the
experimental measurement. In addition, our calculation shows that various
physical quantities of relaxed SWCNT's can actually be expanded in terms of the
chiral angle defined for the correspondent ideal SWCNT's.Comment: 9 pages, 7 figure
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