scholarly journals Determination of Weak Knock Characteristics for Two-Stroke Spark Ignition UAV Engines Based on Mallat Decomposition Algorithm

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Jing Sheng ◽  
Yuping Zeng ◽  
Guoman Liu ◽  
Rui Liu
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Spark Ignition ◽  
Decomposition Algorithm ◽  
Frequency Noise ◽  
Frequency Signal ◽  
High Frequency Noise ◽  
Signal Component ◽  
Engine Vibration ◽  
Characteristic Domain

Two-stroke spark ignition (SI) unmanned aerial vehicle (UAV) engines do not allow heavy knock and require a certain knock safety margin. However, weak knock can help the engine increase power output and reduce fuel consumption. To accurately extract the knock characteristics of engine vibration signals under the condition of weak knock, a signal feature extraction method based on the Mallat decomposition algorithm was proposed. Mallat decomposition algorithm can decompose the signal into two parts: a low-frequency signal and a high-frequency noise signal. The decomposed high-frequency noise is eliminated, and the low-frequency signal is retained as the characteristic domain signal. Simulation results show the effectiveness of the proposed algorithm. The engine vibration signal of a two-stroke SI UAV engine was decomposed into the low-frequency signal and the high-frequency signal by the Mallat decomposition algorithm. The low-frequency signal is taken as the knock characteristic domain signal component, and the wavelet packet energy method is used to verify the correctness of the obtained signal component. The relative energy parameter is calculated by using the knock characteristic domain signal component, which can be used as the determination index of knock intensity. This method provides a reference for the weak knock control of two-stroke SI UAV engines.

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Effects of Noise Frequency on Performance and Annoyance for Women and Men

1981 ◽  
Vol 52 (2) ◽  
pp. 435-441 ◽  
Author(s):  
Kelli F. Key ◽  
M. Carr Payne
Keyword(s):  
Sex Differences ◽  
Magnitude Estimation ◽  
High Frequency ◽  
Ambient Noise ◽  
Direct Relationship ◽  
Low Frequency ◽  
Frequency Noise ◽  
Complex Task ◽  
High Frequency Noise ◽  
Noise Frequency

Effects of noise frequencies on both performance on a complex psychomotor task and annoyance were investigated for men ( n = 30) and women ( n = 30). Each subject performed a complex psychomotor task for 50 min. in the presence of low frequency noise, high frequency noise, or ambient noise. Women and men learned the task at different rates. Little effect of noise was shown. Annoyance ratings were subsequently obtained from each subject for noises of various frequencies by the method of magnitude estimation. High frequency noises were more annoying than low frequency noises regardless of sex and immediate prior exposure to noise. Sex differences in annoyance did not occur. No direct relationship between learning to perform a complex task while exposed to noise and annoyance by that noise was demonstrated.

Effect of Stimulus Duration on Localization of Direction of Noise Stimuli

1970 ◽  
Vol 13 (4) ◽  
pp. 826-838 ◽  
Author(s):  
Willard R. Thurlow ◽  
James R. Mergener
Keyword(s):  
Stimulus Duration ◽  
Head Movement ◽  
High Frequency ◽  
Thermal Noise ◽  
Low Frequency ◽  
Frequency Noise ◽  
Noise Sources ◽  
Minimum Duration ◽  
High Frequency Noise ◽  
Efficient Performance

Localization of the direction of bursts of thermal noise was measured for both high-frequency and low-frequency bands, as a function of duration of bursts. Durations of 0.3, 1, 2, and 5 sec were used. Subjects were free to move their heads to aid in localization. Subjects were not specially trained in sound localization. With increase in stimulus duration, perception of elevation was slightly improved for low-frequency noise, probably due to increased information from head movement. A minimum duration of the order of 2 sec appears necessary to allow subjects to achieve maximum performance (which still is not very good for these low-frequency stimuli). Perception of the elevation of the high-frequency noise sources we used was relatively good even at the briefest duration; however, variability of judgment was larger at the shorter durations. Perception of front-back source position was much improved for both low-frequency and high-frequency noise when stimulus duration was increased. The results are understandable in terms of the increased possibility for head movement with increase in stimulus duration. It appears that one should use a minimum stimulus duration of about 2 sec if one wishes subjects to approach their most efficient performance.

Evidence for the existence of locally-generated body waves in the short-period noise at the Large Aperture Seismic Array, Montana

1972 ◽  
Vol 62 (1) ◽  
pp. 13-29 ◽  
Author(s):  
H. M. Iyer ◽  
John H. Healy
Keyword(s):  
Statistical Analysis ◽  
Phase Velocity ◽  
High Frequency ◽  
Seismic Noise ◽  
Average Velocity ◽  
Low Frequency ◽  
Body Waves ◽  
Frequency Noise ◽  
High Frequency Noise ◽  
Short Period

Abstract The approximate hexagonal configuration of LASA subarrays enables their use as omnidirectional arrays. This property is used to study the phase velocity of short-period seismic noise at different frequencies. It is found that the noise in the low-frequency band consists mainly of surface waves traveling with average velocities in the range 3.0 to 3.5 km/sec. The high-frequency noise, in the band 0.45 to 1.0 Hz, has an average velocity of about 6.0 km/sec. It is quite likely that the high-frequency noise has the nature of locally-generated body waves. Statistical analysis of Pg velocities observed during a crustal refraction experiment at LASA lends support to this hypothesis.

Burial Process of a Seismic Station by Moving Dunes in Tarim Basin

2020 ◽  
Vol 91 (5) ◽  
pp. 2936-2941
Author(s):  
Xiaofeng Liang ◽  
Sicheng Zuo ◽  
Shilin Li ◽  
Yongge Feng
Keyword(s):  
High Frequency ◽  
Noise Level ◽  
Seismic Station ◽  
Low Frequency ◽  
Seismic Signal ◽  
Frequency Noise ◽  
Temperature Record ◽  
Environment Change ◽  
Broadband Seismometer ◽  
High Frequency Noise

Abstract A temporary seismometer vault was buried by a moving sand dune in the Taklimakan Desert at northwestern China in October 2019. The dune gradually covered the solar panel and the power supply to the seismic station was subsequently cut off. Here, we show that the burial process can be diagnosed according to the temperature record from the thermometer in the data-logger, an ultra-low-frequency seismic signal, and the change of high-frequency noise level from the continuous seismograms recorded by the broadband seismometer. The ultra-low-frequency seismic signal reflects the thermoelastic effect of the suspension spring in the seismometer corresponding to the temperature gradient in the sensor vault. At the same time, the variation of high-frequency noise level correlates well with the temperature profile and the ultra-low-frequency seismic signal, indicating the ground wind intensity. The peak frequency shifts and their different responses on three-component waveforms for the high-frequency noise might reflect the distance from the moving dunes to the station and their moving directions. This observation shows a potential usage of continuous seismograms to study rapid environment change around a temporary seismic station.

Effect of Perforated Tabs on the Noise Field of an Axisymmetric Jet

2013 ◽  
Vol 307 ◽  
pp. 250-256
Author(s):  
G. Fayaaz Hussain ◽  
Afthab Shaban Nasser ◽  
Mohammad Mohiudeen Nawaz ◽  
Bikash Kumar Mondal ◽  
N. Karthikeyan
Keyword(s):  
High Frequency ◽  
Supersonic Jet ◽  
Low Frequency ◽  
Frequency Noise ◽  
Noise Levels ◽  
Convergent Nozzle ◽  
High Frequency Noise ◽  
Axisymmetric Jet ◽  
Underexpanded Jets ◽  
Mach Numbers

Effect of triangular tabs with circular perforations on the acoustic far-field of an axisymmetric jet issued from a convergent nozzle of exit diameter of 30.16 mm was studied for both subsonic and sonic underexpanded cases. It was found that the noise in the low frequency range (Strouhal number < 0.29) reduced in both subsonic and supersonic jet mach numbers with a penalty in high frequency noise. OASPL plots showed that overall noise levels in subsonic jets increased due to the introduction of tabs except for far downstream angles where the noise levels reduced by 2 dB. Overall noise levels in underexpanded jets decreased in all directions and at all jet mach numbers without the penalty of high frequency noise. Comparison between tabs without perforation and perforated tabs showed that both the tabs were equally effective.

On the resonance sound generated in a vehicle cabin moving at low speed due to breaking force

2021 ◽  
Vol 263 (3) ◽  
pp. 3817-3823
Author(s):  
Zhe Li ◽  
Ryo Kiyotaki ◽  
Osamu Terashima ◽  
Vinay Poddar ◽  
Takashi Murakami
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Frequency Noise ◽  
Wheel Surface ◽  
High Frequency Noise ◽  
Transfer Path ◽  
Rotation Direction ◽  
Vehicle Cabin ◽  
Vibrational Acceleration ◽  
Transfer Path Analysis

To improve the comfortability in a vehicle cabin, unwanted noise which is recognized as an allophone generated from automobile wheels was experimentally studied to investigate its generation mechanism and to develop its reduction countermeasures. In this experiment, simultaneous measurements of sound pressure and vibrational acceleration of the wheel surface were performed. Then, frequency analysis, vibrational modal analysis and operational transfer path analysis were performed by using measured data. The results show that this kind of noise started in a low frequency first and then became higher. Furthermore, the high-frequency noise was mainly generated by vibrational acceleration at its center and near the rim when the wheel spoke gets close to the brake caliper. The high-frequency noise is around 250Hz, 750Hz, 1000Hz and 1250Hz, and the wheel spoke easily gets vibration and resonance mainly from around 750Hz and 1000Hz. Vibration at 750Hz occurs on the side of the wheel spoke in the rotation direction, while vibration at 1000Hz occurs at the midpoint of the wheel spoke. The closer to the brake caliper, louder noise was generated at the wheel spoke.

Calculation Error's Correction of Three-Component Geomagnetic Field's Marine Survey

2013 ◽  
Vol 756-759 ◽  
pp. 323-326
Author(s):  
Xing Le Zhu ◽  
Chang Han Xiao ◽  
Zhen Ning Yao
Keyword(s):  
Wavelet Transform ◽  
High Frequency ◽  
Geomagnetic Field ◽  
Low Frequency ◽  
Frequency Component ◽  
Frequency Noise ◽  
Calculation Error ◽  
High Frequency Noise ◽  
Multi Scale ◽  
Simulation Results

In order to eliminate calculation error, wavelet transform is used to remove noise when navigational data is used to calculate truth-value of three-component geomagnetic field. By introducing Euler attitude rotation matrix, the computing value of geomagnetic vector is decomposed by multi-scale wavelet transform in each frequency. The high-frequency noise is removed and the accurate value of geomagnetic field can be got by rebuilding low-frequency component. Simulation results indicate that the calculated value is identical with setting value and has high precision, which means the method has great applied importance and instructional significance for practical measurement of marine three-component geomagnetic field.

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