A preliminary experimental study on virtual sound barrier system

This paper describes an active sound control methodology based on difference potentials. The main feature of this methodology is its ability to automatically preserve "wanted" sound within a domain while cancelling "unwanted" noise from outside the domain. This method of preservation of the wanted sounds by active shielding control is demonstrated with various broadband and realistic sound sources such as human voice and music in multiple domains in a one-dimensional enclosure. Unlike many other conventional active control methods, the proposed approach does not require the explicit characterization of the wanted sound to be preserved. The controls are designed based on the measurements of the total field on the boundaries of the shielded domain only, which is allowed to be multiply connected. The method is tested in a variety of experimental cases. The typical attenuation of the unwanted noise is found to be about 20 dB over a large area of the shielded domain and the original wanted sound field is preserved with errors of around 1 dB and below through a broad frequency range up to 1 kHz.

https://usir.salford.ac.uk/18042/1/99D8Cd01.pdf

Multi-domain active sound control and noise shielding

Experimental study of noise emitted by propeller’s surface imperfections

Engine run-up tests are a part of routine aircraft maintenance at the Vancouver International Airport. A source of noise complaints is the Dash-8 aircraft, which emits low-frequency, tonal noise. Active noise control is a potentially cost-effective alternative to passive noise-control methods, which are ineffective at controlling low-frequency noise. Since the run-up tests are performed outdoors, the effects of outdoor conditions on the performance of an active control system must be considered. In this paper, the results of a preliminary investigation of the effects of realistic meteorological conditions and ground impedance on the performance of a single-channel active-control system are presented. Computer simulations of single-channel active control of a monopole source were performed using the Green’s-function parabolic-equation method. Different realistic atmospheric conditions, and reflective or soft ground, were used in the simulations. The results show that atmospheric refraction causes fluctuations in the noise attenuation achieved by a single-channel control system, and has the overall effect of decreasing its performance, making the system ineffective in some cases.

Effect of realistic grounds and atmospheric conditions on single-channel active control of outdoor sound propagation

Abstract Electric powertrains have different characteristics than conventional powertrains with combustion engines and require unconventional aircraft designs to evolve their full potential. Therefore, this paper describes a method to identify potential aircraft designs with electrified powertrains. Promising technology options in the fields of powertrain architecture, aerodynamic interactions, onboard systems and operating strategies were collected by the project partners of the LuFo project GNOSIS. The effect of the technology options on a commuter aircraft was evaluated in terms of global emissions ( $$\hbox {CO}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>CO</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> ), local emissions ( $$\text {NO}_{\text {X}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>NO</mml:mtext> <mml:mtext>X</mml:mtext> </mml:msub> </mml:math> and noise) and operating costs. The evaluation considers an entry into service in 2025 and 2050 and is based on the reference aircraft Beechcraft 1900D. Literature review and simplified calculations enabled the evaluation of the aerodynamic interactions, systems and operating strategies. A preliminary aircraft design tool assessed the different powertrain architectures by introducing the two parameters ’power hybridization’ and ’power split’. Afterwards, compatible technology options were compiled into technology baskets and ranked using the shortest euclidean distance to the ideal solution and the farthest euclidean distance to the worst solution (Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method). An analysis of the CS 23 regulations leads to a high-wing design and excluded the partial turbo-electric powertrain architecture with the gas turbine in the aircraft tail. For 2025, a partial turbo-electric powertrain with two additional electric driven wingtip propellers was selected. A serial hybrid powertrain, which uses a gas turbine or fuel cell in combination with a battery, powers distributed electric propulsors at the wing leading edge in 2050. In both scenarios, the aircraft design includes an electric environmental control system, an electric driven landing gear and electro-hydraulic actuators for the primary flight control and landing gear. 

/pdf/technology-selection-for-holistic-analysis-of-hybrid-5uq5ugcf.pdf

Technology selection for holistic analysis of hybrid-electric commuter aircraft

Engine run-ups are part of the regular maintenance schedule at Vancouver International Airport. The noise generated by the run-ups propagates into neighboring communities, disturbing the residents. Active noise control is a potentially cost-effective alternative to passive methods, such as enclosures. Propeller aircraft generate low-frequency tonal noise that is highly compatible with active control. This paper presents a preliminary investigation of the feasibility and effectiveness of controlling run-up noise from propeller aircraft using local active control. Computer simulations for different configurations of multi-channel active-noise-control systems, aimed at reducing run-up noise in adjacent residential areas using a local-control strategy, were performed. These were based on an optimal configuration of a single-channel control system studied previously. The variations of the attenuation and amplification zones with the number of control channels, and with source/control-system geometry, were stud...

Active local control of propeller-aircraft run-up noise.

Measurements were made of the characteristics of the noise radiated by a Beechcraft 1900D twin-propeller aircraft during engine run-up. The objective was to determine the feasibility of controlling this noise using active noise control. Total noise levels varied with aircraft heading from 103 to 112 dB (100 to 109 dBA) at 73 m from the aircraft. Noise directivity plots were generated. Levels at the nearest community 3 km away varied from 74 to 77 dB (62 to 66 dBA). Near the aircraft the noise spectra comprised a series of equally-high peaks at the 112-Hz fundamental frequency and its multiples. In the community, the three lowest peaks dominated the A-weighted spectrum, with higher-frequency peaks being progressively attenuated. A coherence analysis was performed on the noises measured at 73 m and 98 m from the aircraft. The insertion loss of a blast fence near the run-up area was estimated from run-up noise measurements made on both sides of the fence. The insertion loss varied from 4 to 13 dB and was greatest at mid frequencies.

/pdf/experimental-study-of-propeller-aircraft-run-up-noise-2fhdkpheah.pdf

Experimental study of propeller-aircraft run-up noise

The effectiveness of a control system on a directional dipole noise source was discussed. It was found that a primary source with a non-cylindrical radiation directivity affected the performance of the control system. The analysis showed that the control system worked more effectively when it was used to create quiet zones in the area with the strongest primary-radiation directivity.

/pdf/preliminary-investigation-of-active-control-of-dipole-noise-55j4zmra7z.pdf

Preliminary investigation of active control of dipole noise sources

Engine run-ups are part of the regular maintenance schedule at airports. The noise generated by the run-ups propagates into neighbouring communities, disturbing the residents. Active noise control is a potentially cost-effective alternative to passive methods, such as enclosures. Propeller aircraft generate low-frequency tonal noise that is highly compatible with active control. This paper presents a preliminary investigation of the feasibility and effectiveness of controlling run up noise from propeller aircraft using local active control. Computer simulations for different configurations of multi-channel active-noise-control systems, aimed at reducing run-up noise in adjacent residential areas using a local-control strategy, were performed. The variations of the attenuation and amplification zones with the number of control channels, and with the source/control-system geometry, were studied. The aircraft was modeled using one or two sources, with monopole or multipole radiation patters. Both free-field ...

Active local control of propeller-aircraft run-up noise

A multi-channel active-noise-control system can been used to create a large quiet zone in free-space when the noise source is on the symmetry axis of the control system. In this study, the efficiency of a multi-channel active-noise-control system is investigated numerically for the case of a noise source located at off-axis positions. It was found that both the location and the size of the quiet zone change significantly with the off-axis location of the noise source. The control system is still able to construct a large area of wavefront matching, and create a large quiet zone, when the off-axis shift of the noise source is within this range. There exists an off-axis range for which an optimally pre-arranged multiple-channel control system remains optimized. This range is expressed analytically in terms of the wavelength at the frequency of interest, and of the configuration of the control system.

/pdf/active-control-of-an-off-axis-noise-source-1kymtyu3e3.pdf

Jingnan Guo

Papers

Active local control of propeller-aircraft run-up noise.

Experimental study of propeller-aircraft run-up noise

Preliminary investigation of active control of dipole noise sources

Active local control of propeller-aircraft run-up noise

Active control of an off-axis noise source