Reduction of Vibration and Noise Generated by Planetary Ring Gears in Helicopter Aircraft Transmissions

1973 ◽  
Vol 95 (4) ◽  
pp. 1149-1158 ◽  
Author(s):  
Thomas Chiang ◽  
R. H. Badgley
Keyword(s):  
High Frequency ◽  
Narrow Band ◽  
Vibration Energy ◽  
Ring Gear ◽  
Noise Sources ◽  
Rotor Drive ◽  
Design Changes ◽  
Planetary Ring ◽  
Gear Meshes ◽  
Very High

Rotor-drive gearboxes are major noise sources in helicopter aircraft. Narrow-band examination of this noise often indicates the presence of several or more very high, narrow noise peaks, which are located at gearbox mesh frequencies or their multiples. Important exceptions are sideband noise components, located so near the main signal component as to be indistinguishable except by very narrow band reduction. Noise of this type is most effectively treated through a systematic study of the flow of high-frequency vibration energy in the drive train. Such studies should examine the mechanism by which gear meshes generate vibrations, and the vibration response of the gearbox components which support the gears. Results of such calculations are presented for the planetary reduction ring-gear casing elements in the Boeing-Vertol CH-47 forward rotor-drive gearbox and the Bell UH-1D main rotor-drive gearbox. The calculations indicate logical reasons why noise is generated. Typical ring-gear casing design changes are examined for noise reduction.

REFLECTED AND TRANSMITTED FILTER FUNCTIONS FOR SIMPLE SUBSURFACE GEOMETRIES

Geophysics ◽  
1976 ◽  
Vol 41 (6) ◽  
pp. 1305-1317 ◽  
Author(s):  
M. Schoenberger ◽  
F. K. Levin
Keyword(s):  
Thin Layer ◽  
High Frequency ◽  
Narrow Band ◽  
Broad Band ◽  
Low Frequency ◽  
Single Layer ◽  
High Amplitude ◽  
Shadow Zone ◽  
Least Energy ◽  
Very High

A zone of sands embedded in shale acts as a filter, both in reflecting energy back to the surface and in transmitting energy to reflectors below them. For a single layer of sand, the reflection filter is periodic—reflecting no energy at some frequencies and more than either of the two individual interfaces at other frequencies. Separating the sand zone into two parts by inserting a thin layer of shale results in reflection filters which differ greatly from one another. The particular filter curve generated depends upon the location of the shale layer. A sand zone filters reflections from interfaces below the zone in a manner complementary to the reflection filter. Where the most energy is reflected, the least is transmitted; conversely, where the least energy is reflected, the most is transmitted. The models considered in this report could easily give rise to high‐amplitude reflections; but, unless the amplitudes were very high, there would be little filtering of deeper reflections. However, for very high‐amplitude reflections and narrow‐band data, little energy would be transmitted and a shadow zone would result. For very high‐amplitude shallow reflections and broad‐band data, a low‐frequency shallow reflection would cause high‐frequency deep reflections; a high‐frequency shallow reflection would cause low‐frequency deep reflections.

Experimental Investigation of very High Frequency Slot Antenna on M-60A-1 Tank

1977 ◽  
Author(s):  
D. V. Campbell ◽  
William Kennebeck ◽  
A. Zanella ◽  
Paul Sexton
Keyword(s):  
Experimental Investigation ◽  
High Frequency ◽  
Slot Antenna ◽  
Very High Frequency ◽  
Very High

A collision feedback based multiple access control protocol for very high frequency data exchange system in E-navigation

2021 ◽  
pp. 1-16
Author(s):  
Xu Hu ◽  
Bin Lin ◽  
Ping Wang ◽  
Hongguang Lyu ◽  
Tie-Shan Li
Keyword(s):  
Access Control ◽  
High Frequency ◽  
Multiple Access ◽  
Data Exchange ◽  
High Frequency Data ◽  
Frequency Data ◽  
Exchange System ◽  
Very High Frequency ◽  
Time Division ◽  
Very High

Abstract The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation.

scholarly journals Measurement of Electrical Properties of Superconducting YBCO Thin Films in the VHF Range

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3360
Author(s):  
Yakir Dahan ◽  
Eldad Holdengreber ◽  
Elichai Glassner ◽  
Oz Sorkin ◽  
Shmuel E. Schacham ◽  
...  
Keyword(s):  
Thin Films ◽  
Theoretical Model ◽  
Quality Factor ◽  
High Frequency ◽  
Unit Length ◽  
Superconducting Thin Films ◽  
Electrical Parameters ◽  
Very High Frequency ◽  
Production Constraints ◽  
Very High

A new measurement technique of electrical parameters of superconducting thin films at the Very High Frequency (VHF) range is described, based on resonators with microstrip (MS) structures. The design of an optimal resonator was achieved, based on a thorough theoretical analysis, which is required for derivation of the exact configuration of the MS. A theoretical model is presented, from which an expression for the attenuation of a MS line can be derived. Accordingly, simulations were performed, and an optimal resonator for the VHF range was designed and implemented. Production constraints of YBa2Cu3O7 (YBCO) limited the diameter of the sapphire substrate to 3″. Therefore, a meander configuration was formed to fit the long λ/4 MS line on the wafer. By measuring the complex input reflection coefficients of a λ/4 resonator, we extracted the quality factor, which is mainly affected by the dielectric and conductor attenuations. The experimental results are well fitted by the theoretical model. The dielectric attenuation was calculated using the quasi-static analysis of the MS line. An identical copper resonator was produced and measured to compare the properties of the YBCO resonator in reference to the copper one. A quality factor of ~6·105 was calculated for the YBCO resonator, three orders of magnitude larger than that of the copper resonator. The attenuation per unit length of the YBCO layer was smaller by more than five orders of magnitude than that of the copper.

Da eine oder mehrere betroffen …

2020 ◽  
Vol 48 (1) ◽  
pp. 47-100
Author(s):  
Melitta Gillmann
Keyword(s):  
High Frequency ◽  
Formal Language ◽  
Subordinate Clause ◽  
Matrix Clause ◽  
Very High Frequency ◽  
Corpus Study ◽  
Causal Relations ◽  
Legal Texts ◽  
The Matrix ◽  
Very High

AbstractBased on a corpus study conducted using the GerManC corpus (1650–1800), the paper sketches the functional and sociosymbolic development of subordinate clause constructions introduced by the subjunctor da ‘since’ in different text genres. In the second half of the 17th and the first half of the 18th century, the da clauses were characterized by semantic vagueness: Besides temporal, spatial and causal relations, the subjunctor established conditional, concessive, and adversative links between clauses. The corpus study reveals that different genres are crucial to the readings of da clauses. Spatial and temporal usages, for example, occur more often in sermons than in other genres. The conditional reading, in contrast, strongly tends to occur in legal texts, where it displays very high frequency. This could be the reason why da clauses carry indexical meaning in contemporary German and are associated with formal language. Over the course of the 18th century, the causal usages increase in all genres. Surprisingly, these causal da clauses tend to be placed in front of the matrix clause despite the overall tendency of causal clauses to follow the matrix clause.

scholarly journals Sintering, Microstructure, and Dielectric Properties of Copper Borates for High Frequency LTCC Applications

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4017
Author(s):  
Dorota Szwagierczak ◽  
Beata Synkiewicz-Musialska ◽  
Jan Kulawik ◽  
Norbert Pałka
Keyword(s):  
Dielectric Properties ◽  
Dielectric Permittivity ◽  
High Frequency ◽  
Ceramic Materials ◽  
Sintering Behavior ◽  
Terahertz Time Domain Spectroscopy ◽  
Very High Frequency ◽  
X Ray ◽  
Low Dielectric ◽  
Very High

New ceramic materials based on two copper borates, CuB2O4 and Cu3B2O6, were prepared via solid state synthesis and sintering, and characterized as promising candidates for low dielectric permittivity substrates for very high frequency circuits. The sintering behavior, composition, microstructure, and dielectric properties of the ceramics were investigated using a heating microscope, X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy, and terahertz time domain spectroscopy. The studies revealed a low dielectric permittivity of 5.1–6.7 and low dielectric loss in the frequency range 0.14–0.7 THz. The copper borate-based materials, owing to a low sintering temperature of 900–960 °C, are suitable for LTCC (low temperature cofired ceramics) applications.

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