Helicopter Rotor Thickness Noise Control Using Unsteady Force Excitation

The low-frequency in-plane thickness noise generating from the displacement of air by rotating blades has an important influence on helicopter detection. An on-blade control technique to reduce thickness noise is developed in this paper based on the principle of sound field cancellation. Following the theoretical study on the mechanism of thickness noise reduction using in-plane unsteady force, a 2-m diameter rotor with an active trailing-edge winglet are designed and tested in a fully anechoic chamber. The winglet installed on the outboard blade is used to generate the unsteady force and anti-noise to counteract the thickness noise. The results demonstrate that effective reduction of thickness noise up to 3 dB is achieved in the front of the rotor when the winglet is under the one-harmonic control with 3 ° of deflection angle. Moreover, the experiments of frequency, amplitude, and phase scanning are carried out to study the parametric effects of winglet motions on noise reduction. The ability of noise reduction is proportional to the deflection amplitude of the winglet in each frequency. The control phase determines where noise can be reduced. There is an optimal phase angle at each frequency to minimize the noise at the observations, and it varies with different frequencies. The relationship among observation position, control phase, and frequency is derived, and the approximate expression of the optimal phase is presented.

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Suppression of the Hydrodynamic Noise Induced by the Horseshoe Vortex through Mechanical Vortex Generators

Applied Sciences ◽

10.3390/app9040737 ◽

2019 ◽

Vol 9 (4) ◽

pp. 737 ◽

Cited By ~ 1

Author(s):

Yongwei Liu ◽

Hongxu Jiang ◽

Yalin Li ◽

Dejiang Shang

Keyword(s):

Noise Reduction ◽

Noise Suppression ◽

Flow Direction ◽

Low Frequency ◽

Sound Field ◽

Leading Edge ◽

Horseshoe Vortex ◽

Vortex Generators ◽

Counter Rotation ◽

Hydrodynamic Noise

The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the flow field and the sound field of the three shapes of mechanical VGs: triangular, semi-circular, and trapezoidal. The triangular VGs with an angle of 30° to the flow direction achieved a better noise reduction. The optimum noise suppression is 8.93 dB, when the distance from the triangular VGs to the sail hull’s leading edge is 0.1c, where c is the chord length. The noise reduction mechanism is such that the mechanical VGs can destroy the formation of the horseshoe vortex at the origin and produce counter-rotation vortices to weaken its intensity. We created two steel models according to the simulation, and the experimental measurement was carried out in a gravity water tunnel. The measured results showed that the formation of the horseshoe vortex could be effectively inhibited by the triangular VGs. The results in our study can provide a new method for hydrodynamic noise suppression by flow control.

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Quasi-Periodic Control Technique for Minimizing Fuel Consumption During Record Vehicle Competition

Archive of Mechanical Engineering ◽

10.2478/meceng-2013-0012 ◽

2013 ◽

Vol 60 (2) ◽

pp. 185-197 ◽

Cited By ~ 2

Author(s):

Paweł Sulikowski ◽

Ryszard Maronski

Keyword(s):

Fuel Consumption ◽

Optimal Control Theory ◽

Slope Angle ◽

Control Technique ◽

Decision Variables ◽

Aeronautical Engineering ◽

The One ◽

Optimal Driving ◽

The Given ◽

Engine Power

The problem of the optimal driving technique during the fuel economy competition is reconsidered. The vehicle is regarded as a particle moving on a trace with a variable slope angle. The fuel consumption is minimized as the vehicle covers the given distance in a given time. It is assumed that the run consists of two recurrent phases: acceleration with a full available engine power and coasting down with the engine turned off. The most fuel-efficient technique for shifting gears during acceleration is found. The decision variables are: the vehicle velocities at which the gears should be shifted, on the one hand, and the vehicle velocities when the engine should be turned on and off, on the other hand. For the data of students’ vehicle representing the Faculty of Power and Aeronautical Engineering it has been found that such driving strategy is more effective in comparison with a constant speed strategy with the engine partly throttled, as well as a strategy resulting from optimal control theory when the engine is still active.

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Noise Reduction Effect of Superhydrophobic Surfaces with Streamwise Strip of Channel Flow

Applied Sciences ◽

10.3390/app11093869 ◽

2021 ◽

Vol 11 (9) ◽

pp. 3869

Author(s):

Chen Niu ◽

Yongwei Liu ◽

Dejiang Shang ◽

Chao Zhang

Keyword(s):

Reynolds Number ◽

Drag Reduction ◽

Noise Reduction ◽

Channel Flow ◽

Superhydrophobic Surface ◽

Sound Field ◽

Flow Noise ◽

Slip Boundary ◽

Eddy Simulation ◽

Reduction Effect

Superhydrophobic surface is a promising technology, but the effect of superhydrophobic surface on flow noise is still unclear. Therefore, we used alternating free-slip and no-slip boundary conditions to study the flow noise of superhydrophobic channel flows with streamwise strips. The numerical calculations of the flow and the sound field have been carried out by the methods of large eddy simulation (LES) and Lighthill analogy, respectively. Under a constant pressure gradient (CPG) condition, the average Reynolds number and the friction Reynolds number are approximately set to 4200 and 180, respectively. The influence on noise of different gas fractions (GF) and strip number in a spanwise period on channel flow have been studied. Our results show that the superhydrophobic surface has noise reduction effect in some cases. Under CPG conditions, the increase in GF increases the bulk velocity and weakens the noise reduction effect. Otherwise, the increase in strip number enhances the lateral energy exchange of the superhydrophobic surface, and results in more transverse vortices and attenuates the noise reduction effect. In our results, the best noise reduction effect is obtained as 10.7 dB under the scenario of the strip number is 4 and GF is 0.5. The best drag reduction effect is 32%, and the result is obtained under the scenario of GF is 0.8 and strip number is 1. In summary, the choice of GF and the number of strips is comprehensively considered to guarantee the performance of drag reduction and noise reduction in this work.

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Analysis of the Influence of Different Bionic Structures on the Noise Reduction Performance of the Centrifugal Pump

Sensors ◽

10.3390/s21030886 ◽

2021 ◽

Vol 21 (3) ◽

pp. 886

Author(s):

Cui Dai ◽

Chao Guo ◽

Yiping Chen ◽

Liang Dong ◽

Houlin Liu

Keyword(s):

Flow Field ◽

Noise Reduction ◽

Centrifugal Pump ◽

Great Influence ◽

Frequency Doubling ◽

Sound Field ◽

Internal Flow ◽

Test System ◽

Centrifugal Pumps ◽

External Characteristics

The strong noise generated during the operation of the centrifugal pump harms the pump group and people. In order to decrease the noise of the centrifugal pump, a specific speed of 117.3 of the centrifugal pump is chosen as a research object. The bionic modification of centrifugal pump blades is carried out to explore the influence of different bionic structures on the noise reduction performance of centrifugal pumps. The internal flow field and internal sound field of bionic blades are studied by numerical calculation and test methods. The test is carried out on a closed pump test platform which includes external characteristics and a flow noise test system. The effects of two different bionic structures on the external characteristics, acoustic amplitude–frequency characteristics and flow field structure of a centrifugal pump, are analyzed. The results show that the pit structure has little influence on the external characteristic parameters, while the sawtooth structure has a relatively great influence. The noise reduction effect of the pit structure is aimed at the wide-band noise, while the sawtooth structure is aimed at the discrete noise of the blade-passing frequency (BPF) and its frequency doubling. The noise reduction ability of the sawtooth structure is not suitable for high-frequency bands.

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Posturography with head movements in the assessment of balance in chronic unilateral vestibular lesions

Scientific Reports ◽

10.1038/s41598-021-85745-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Magdalena Janc ◽

Mariola Sliwinska-Kowalska ◽

Piotr Politanski ◽

Marek Kaminski ◽

Magdalena Jozefowicz-Korczynska ◽

...

Keyword(s):

High Reliability ◽

Low Frequency ◽

Random Order ◽

Head Movements ◽

Canal Paresis ◽

Eyes Closed ◽

Static Posturography ◽

Unstable Surface ◽

Novel Method ◽

The One

AbstractThe aim of our study was to validate the method of head-shake static posturography (HS-posturography) in healthy individuals and to establish the value of this novel method in the diagnostics of patients with unilateral vestibular lesion (UV). The study included 202 participants divided into two groups, one consisting of 133 patients with canal paresis CP > 19% and one of 69 healthy subjects. Participant was tested according to the standard protocol of static posturography (SP), and with head movements of 0.3 Hz (HS 40), 0.6 Hz (HS 70) in random order controlled by a metronome. HS-posturography revealed a similar repeatability and internal consistency as the standard posturography. In patients with UV, 4th condition revealed higher sensitivity (74%) and specificity (71%) in HS 40 than in the standard posturography (67%, 65% respectively) and HS 70 (54%, 70% respectively). Static posturography and HS- posturography revealed a high reliability of the testing method. The head movements added to static posturography improve the sensitivity and specificity of the method in group with vestibular impairment. The most important test for that purpose seems to be the one on unstable surface with the eyes closed, with low frequency of head movements.

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

Applied Sciences ◽

10.3390/app11031243 ◽

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.

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Shape Factors in Low‐Frequency Noise Reduction

The Journal of the Acoustical Society of America ◽

10.1121/1.2144182 ◽

1967 ◽

Vol 42 (5) ◽

pp. 1202-1203

Author(s):

J. Ronald Bailey ◽

Franklin D. Hart

Keyword(s):

Noise Reduction ◽

Low Frequency ◽

Frequency Noise ◽

Low Frequency Noise ◽

Shape Factors

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Handling Nonlinearity in an Ensemble Kalman Filter: Experiments with the Three-Variable Lorenz Model

Monthly Weather Review ◽

10.1175/mwr-d-11-00313.1 ◽

2012 ◽

Vol 140 (8) ◽

pp. 2628-2646 ◽

Cited By ~ 39

Author(s):

Shu-Chih Yang ◽

Eugenia Kalnay ◽

Brian Hunt

Keyword(s):

Kalman Filter ◽

Ensemble Kalman Filter ◽

Linear Models ◽

Low Frequency ◽

Lorenz Model ◽

Outer Loop ◽

Nonlinear Growth ◽

Ensemble Mean ◽

Ensemble Transform Kalman Filter ◽

The One

Abstract An ensemble Kalman filter (EnKF) is optimal only for linear models because it assumes Gaussian distributions. A new type of outer loop, different from the one used in 3D and 4D variational data assimilation (Var), is proposed for EnKF to improve its ability to handle nonlinear dynamics, especially for long assimilation windows. The idea of the “running in place” (RIP) algorithm is to increase the observation influence by reusing observations when there is strong nonlinear error growth, and thus improve the ensemble mean and perturbations within the local ensemble transform Kalman filter (LETKF) framework. The “quasi-outer-loop” (QOL) algorithm, proposed here as a simplified version of RIP, aims to improve the ensemble mean so that ensemble perturbations are centered at a more accurate state. The performances of LETKF–RIP and LETKF–QOL in the presence of nonlinearities are tested with the three-variable Lorenz model. Results show that RIP and QOL allow LETKF to use longer assimilation windows with significant improvement of the analysis accuracy during periods of high nonlinear growth. For low-frequency observations (every 25 time steps, leading to long assimilation windows), and using the optimal inflation, the standard LETKF RMS error is 0.68, whereas for QOL and RIP the RMS errors are 0.47 and 0.35, respectively. This can be compared to the best 4D-Var analysis error of 0.53, obtained by using both the optimal long assimilation windows (75 time steps) and quasi-static variational analysis.

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Stream Selector’s Control System Based on High-Precision Incremental Encoder

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.303-306.1657 ◽

2013 ◽

Vol 303-306 ◽

pp. 1657-1660

Author(s):

Zhi Guang Zhang ◽

Wei Hu ◽

Xiao Qiong Li ◽

Xue Fei Lv ◽

Min Ping Zhang ◽

...

Keyword(s):

Control System ◽

Power Consumption ◽

High Precision ◽

Position Control ◽

High Reliability ◽

Dc Motor ◽

Step Motor ◽

Low Power Consumption ◽

Incremental Encoder ◽

The One

For the precision rotor position control of stream selector, a control system based on direct current motor (DC motor) has been constructed. The DC motor, with a high-precision incremental encoder used as the driving force, was assembled with the stream selector rotor through a shaft coupling. Following the motor rotation, the encoder generated two-channel quadrature pulses and one channel index pulses. An ultralow-power consumption microcontroller (msp430f2232) received theses pulses and calculated them. The position of the slot was determined by the number of pulses counted from the index pulse. Operator can set and monitored the slot positions of five stream selectors simultaneously through the program which was written with LabVIEW on the host computer. This module featured high reliability and low power consumption compared with the one driven by step motor. Beyond that, it was much smaller and lighter.

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