scholarly journals Overview of active and passive systems for the turboprop modern generation

2018 ◽  
Author(s):  
Maurizio Arena ◽  
Massimo Viscardi
Keyword(s):  
Noise Source ◽  
Energy Levels ◽  
Low Frequency ◽  
Internal Noise ◽  
Angular Speed ◽  
Comfort Level ◽  
Design Parameters ◽  
Tonal Noise ◽  
Design Goal ◽  
New Generation

    Nowadays, one of the main marketing objectives of the new generation of turboprop aircrafts is the noise control to enhance the internal comfort. The propellers represent in fact the main noise source whose amplitude and frequencies depend on some design parameters such as its rotational angular speed, number of blades, power at shaft generating aircraft thrust and blades geometry. The higher energy levels are within the low-frequency region, corresponding in particular to the first blade passing frequency and its harmonics. The design goal is therefore to increase the passenger comfort level by controlling the propeller tonal noise and related vibrations. The present paper is aimed at discuss some relevant technological solutions to minimize the fuselage internal noise field at the passengers positions at each of the first three tones of the propeller load as well as due to other external aero-acoustic sources. 

Dynamic Analysis of Linke Hofmann Busch Coach and Determination of its Sensitive Design Parameters Considering Suspended Equipments

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
S.D. Singh ◽  
Rakesh Mathur ◽  
R.K. Srivastava
Keyword(s):  
Ride Comfort ◽  
Low Frequency ◽  
Comfort Level ◽  
Design Parameters ◽  
Bogie Frame ◽  
Long Wavelength ◽  
Stiffness And Damping ◽  
Sensitive Parameters ◽  
Track Irregularities

This study aims at dynamic behaviour of a Linke Hofmann Busch coach and its sensitive parameters against track irregularities considering various suspended equipment. The randomly distributed track irregularities characterized in terms of Indian Rail Road PSD standard are considered main source of excitation that produces undesired vibrations. The coach body and bogie frame subjected to 4 degree of freedom motions (bounce, lateral, roll and pitch) are modelled using finite element methodology where system matrices such as mass, stiffness and damping matrices are obtained for eigenvalue solution. Using modal parameters obtained as above and PSD of track irregularities, both vertical and lateral mean square acceleration responses (MSAR) are determined at various points of concern on coach body. It is observed that the vertical peak responses occur in low frequency range (0-10 Hz) which is caused by long wavelength irregularities of track that causes discomfort. It is also observed that constant peak lateral responses occur at still lower frequency as compared to vertical response which again causes discomfort to vehicle riders. This concludes that there is a further scope of improvement in comfort level with minor adjustments of suspended equipment of a LHB coach. A sensitivity analysis based on the partial derivatives against FRF displacement is conducted and most sensitive design parameters are obtained for optimization to improve ride comfort. It is suggested that if the mass of bio toilet tanks and relative position of battery box + transformer unit i.e. most sensitive parameters of suspended equipment are changed then the ride comfort can be improved

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

scholarly journals Estimation of the Noise Source Level of a Commercial Ship Using On-Board Pressure Sensors

2021 ◽  
Vol 11 (3) ◽  
pp. 1243
Author(s):  
Hongseok Jeong ◽  
Jeung-Hoon Lee ◽  
Yong-Hyun Kim ◽  
Hanshin Seol
Keyword(s):  
Noise Source ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Frequency Resolution ◽  
Source Strength ◽  
Recording Time ◽  
Source Level ◽  
The One ◽  
Hydrophone Array ◽  
Good Agreement

The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data.

scholarly journals Dynamic Line Rating—An Effective Method to Increase the Safety of Power Lines

2021 ◽  
Vol 11 (2) ◽  
pp. 492
Author(s):  
Levente Rácz ◽  
Bálint Németh
Keyword(s):  
Expert System ◽  
Electric Field ◽  
High Voltage ◽  
Low Frequency ◽  
Power Line ◽  
Power Lines ◽  
Design Parameters ◽  
Monitoring Methods ◽  
Limit Value ◽  
Potential Applications

Exceeding the electric field’s limit value is not allowed in the vicinity of high-voltage power lines because of both legal and safety aspects. The design parameters of the line must be chosen so that such cases do not occur. However, analysis of several operating power lines in Europe found that the electric field strength in many cases exceeds the legally prescribed limit for the general public. To illustrate this issue and its importance, field measurement and finite element simulation results of the low-frequency electric field are presented for an active 400 kV power line. The purpose of this paper is to offer a new, economical expert system based on dynamic line rating (DLR) that utilizes the potential of real-time power line monitoring methods. The article describes the expert system’s strengths and benefits from both technical and financial points of view, highlighting DLR’s potential for application. With our proposed expert system, it is possible to increase a power line’s safety and security by ensuring that the electric field does not exceed its limit value. In this way, the authors demonstrate that DLR has other potential applications in addition to its capacity-increasing effect in the high voltage grid.

A Study on Exhaust Muffler Using Counter-Phase Counteract

2014 ◽  
Vol 986-987 ◽  
pp. 810-813
Author(s):  
Ying Li Shao
Keyword(s):  
Mathematical Model ◽  
Experimental Validation ◽  
Noise Source ◽  
Low Frequency ◽  
Frequency Noise ◽  
Expansion Chamber ◽  
Band Noise ◽  
Exhaust Noise ◽  
Perforated Pipe ◽  
The Mathematical Model

The exhaust noise, which falls into low-frequency noise, is the dominant noise source of a diesel engines and tractors. The traditional exhaust silencers, which are normally constructed by combination of expansion chamber, and perforated pipe or perforated board, are with high exhaust resistance, but poor noise reduction especially for the low-frequency band noise. For this reason, a new theory of exhaust muffler of diesel engine based on counter-phase counteracts has been proposed. The mathematical model and the corresponding experimental validation for the new exhaust muffler based on this theory were performed.

scholarly journals Development of a Novel Double-Ring Deployable Mesh Antenna

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Yan Xu ◽  
Fuling Guan ◽  
Xian Xu ◽  
Hongjian Wang ◽  
Yao Zheng
Keyword(s):  
Low Frequency ◽  
Design Concept ◽  
Design Parameters ◽  
Accuracy Measurement ◽  
Double Ring ◽  
Reflective Surface ◽  
Final Design ◽  
Geometric Relationship ◽  
Relationship Of ◽  
Adjustment Test

This paper addresses a type of deployable mesh antenna consisting of the double-ring deployable truss edge frame and the cable net reflector. The structural design concept of the deployable antennas is presented. The deployable truss is designed and the geometric relationship of each strut length is formulated. Two types of radial truss elements are described and compared. The joint pattern and the active cables of the final design concept are determined. The pattern of the cable net is the three-orientation grid. Two connection schemes between the reflector and the deployable edge frame are investigated. The design parameters and the shape adjustment mechanism of this cable net are determined. The measurement test technologies of the antennas on the ground including test facilities, deployment test, and measurement and adjustment test are proposed. The antenna patterns are analyzed based on the real surfaces of the reflector obtained by the reflective surface accuracy measurement. The tests and analytic results indicated that the accuracy of the reflective surface is high and is suitable for low-frequency communication.

scholarly journals Pipeline Compressor Redesign With the Consideration of Both Noise and Performance

2000 ◽  
Author(s):  
Yuri I. Biba ◽  
Zheji Liu ◽  
D. Lee Hill
Keyword(s):  
High Efficiency ◽  
Aerodynamic Characteristics ◽  
The Body ◽  
Design Parameters ◽  
Original Design ◽  
Tonal Noise ◽  
Experimental Performance ◽  
Expected Performance ◽  
Computational Fluid Dynamics Cfd ◽  
And Performance

A complete effort to redesign the aerodynamic characteristics of a single-stage pipeline compressor is presented. The components addressed are the impeller, diffuser region, and the volute. The innovation of this effort stems from the simultaneous inclusion of both the noise and aerodynamic performance as primary design parameters. The final detailed flange-to-flange analysis of the new components clearly shows that the operating range is extended and the tonal noise driven by the impeller is reduced. This is accomplished without sacrificing the existing high efficiency of the baseline machine. The body of the design effort uses both Computational Fluid Dynamics (CFD) and vibro-acoustics technology. The predictions are anchored by using the flange-to-flange analysis of the original design and its experimental performance data. By calculating delta corrections and assuming that these deltas are approximately the same for the new design, the expected performance is extrapolated.

scholarly journals What internal noise source limits peripheral vision?

2017 ◽  
Vol 17 (10) ◽  
pp. 775
Author(s):  
Denis Pelli ◽  
Hörmet Yiltiz
Keyword(s):  
Peripheral Vision ◽  
Noise Source ◽  
Internal Noise

Characteristics of Low-Frequency Horizontal Noise of Ocean-Bottom Seismic Data

2021 ◽  
Author(s):  
Chao An ◽  
Chen Cai ◽  
Lei Zhou ◽  
Ting Yang
Keyword(s):  
Water Waves ◽  
Noise Source ◽  
Random Noise ◽  
Low Frequency ◽  
Ocean Bottom ◽  
Coherent Noise ◽  
Infragravity Waves ◽  
Low Frequencies ◽  
Bottom Currents ◽  
Ocean Bottom Seismographs

Abstract Horizontal records of ocean-bottom seismographs are usually noisy at low frequencies (< 0.1 Hz). The noise source is believed to be associated with ocean-bottom currents that may tilt the instrument. Currently horizontal records are mainly used to remove the coherent noise in vertical records, and there has been little literature that quantitatively discusses the mechanism and characteristics of low-frequency horizontal noise. In this article, we analyze in situ ocean-bottom measurements by rotating the data horizontally and evaluating the coherency between different channels. Results suggest that the horizontal noise consists of two components, random noise and principle noise whose direction barely changes in time. The amplitude and the direction of the latter are possibly related to the intensity and direction of ocean-bottom currents. Rotating the horizontal records to the direction of the principle noise can largely suppress the principle noise in the orthogonal horizontal channel. In addition, the horizontal noise is incoherent with pressure, indicating that the noise source is not ocean surface water waves (infragravity waves). At some stations in shallow waters (<300 m), horizontal noise around 0.07 Hz is found to be linearly proportional to the temporal derivative of pressure, which is explained by forces of added mass due to infragravity waves.

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