| 1. |
- Johansson, Sven, et al.
(författare)
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A Novel Multiple-Reference, Multiple-Channel, Normalized Filtered-X LMS Algorithm for Active Control of Propeller-Induced Noise in Aircraft Cabins
- 1998
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Konferensbidrag (refereegranskat)abstract
- The dominating cabin noise in propeller aircraft consists essentially of strong tonal components at harmonics of the Blade Passage Frequency (BPF) of the propellers. In order to efficiently reduce such low frequency periodic noise, it is advisable to employ an Active Noise Control (ANC) system based on a feedforward controller. This paper presents a set of normalized complex Filtered-X Least-Mean-Square (FX LMS) algorithms. By using different variants of normalization factors the convergence rate, the tracking performance and the steady-state noise attenuation can be improved. The algorithms presented are based either on a single normalization factor for the whole control system (global normalized FX LMS algorithm), or several individual normalization factors (reference-individual FX LMS algorithm) or the novel actuator-individual FX LMS algorithm. The evaluation is performed on noise recorded during flight in the cabin of a Dornier 328, a twin-engine propeller aircraft.
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| 2. |
- Johansson, Sven, et al.
(författare)
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Algoritmer för aktiv bullerundertryckning i propellerflygplan
- 1997
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Konferensbidrag (refereegranskat)abstract
- I många praktiska tillämpningar generas buller av roterande maskiner, t.ex. av kompressorer, fläktar, motorer och propellrar. Detta buller består huvudsakligen av periodiska komponenter, grundton med tillhörande övertoner. Vid denna typ av tillämpningar där bullret är lågfrekvent och periodiskt är det lämpligt att använda aktiv bullerreglering. Aktiva system baserade på framkopplad reglerteknik har visat sig ge en bra undertryckning av denna typ av buller. Ett framkopplat reglersystem behöver en synkroniseringssignal från den buller alstrande källan. Denna signal används sedan för att generera referenssignaler innehållande de frekvenser man vill undertrycka. Med hjälp av referenssignalerna generar reglersystemet ett ljudfält som är lika starkt som bullret och i motfas med detta. På detta sätt erhålls en reducering av bullret. För att ställa in den adaptiva regulatorn så att bästa möjliga undertryckning erhålls används reglermikrofoner som mäter det erhållna ljudtrycket. För att erhålla god undertryckning är det viktigt att referenssignalerna är väl korrelerade med bullret. I applikationer där endast en eller flera korrelerade källor bidrar till bullret räcker det att använda ett reglersystem baserat på en synkroniseringssignal, dvs ett enreferenssystem. Är det flera okorrelerade bullerkällor är det emellertid nödvändigt att använda en synkroniseringssignal från varje källa för att erhålla effektiv bullerundertryckning, dvs ett flerreferenssystem. I propellerflygplan härrör bullret huvudsakligen från propellrarna och de dominerande frekvenskomponenterna kan relateras till propellrarnas bladpassagefrekvenser (BPF) samt deras övertoner. Idag är de flesta tvåmotoriga flygplan utrustade med en synkroniseringsenhet, som synkroniserar propellrarnas varvtal. När propellrarna är synkroniserade kan de betraktas som fullständigt korrelerade, vilket medför att ett enreferenssystem kan användas för att åstadkomma en effektiv bullerundertryckning. I situationer där propellrarna är osynkroniserade skiljer sig propellrarnas varvtal åt och propellrarna kan nu betraktas som två okorrelerade källor. I dessa fall bör ett flerreferenssystem användas, eftersom denna regulatortyp kan följa varvtalsförändringar hos båda propellrarna. I denna presentation görs en jämförelse mellan prestanda för ett enreferenssystem och ett flerreferenssystem. Utvärderingen görs för två olika flygsituationer, synkroniserade respektive osynkroniserade propellrar.
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| 3. |
- Johansson, Sven, et al.
(författare)
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Evaluation of a Multiple- versus a Single-Reference MIMO ANC Algorithm on Dornier 328 Test Data Set
- 1998
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Konferensbidrag (refereegranskat)abstract
- In many applications, such as in propeller aircraft, the dominating noise is periodic. Successful reduction of the periodic noise components can be achieved by using an Active Noise Control (ANC) system based on feedforward techniques. In this paper, a comparison between the performance of single--reference (single-tacho) and multiple--reference (twin-tacho) feedforward control systems is presented. The comparison is made for two different flight conditions, both with and without synchronized propellers. The evaluation results show that a multiple--reference controller provides better performance than a single--reference controller when a slight deviation exists in the propeller synchronization.
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| 4. |
- Johansson, Sven, et al.
(författare)
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Evaluation of Multiple Reference Active Noise Control Algorithms on Dornier 328 Aircraft Data
- 1999
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Ingår i: IEEE transactions on speech and audio processing. - New York : IEEE Signal Processing Society. - 1063-6676. ; 7:4, s. 473-477
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Tidskriftsartikel (refereegranskat)abstract
- This correspondence presents an evaluation of multiple-reference adaptive algorithms. Two LMS-types and a Newton-type algorithm are considered. The special structure of the adaptive filtering problem implies that the Newton-type algorithm can be implemented with the same numerical complexity as LMS-type algorithms. The concept of a fast filtered-x Newton algorithm is thus introduced.
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| 5. |
- Lagö, Thomas L, et al.
(författare)
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Active vibration reduction in a light high speed train bogie
- 1998
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Konferensbidrag (refereegranskat)abstract
- Vibration induced sound in the car of a light high speed train is of great interest since the light structure makes it more resonant. Low weight is important and and the aim is to decrease the weight of future trains significantly, compared to the X2000. Classical sound attenuation techniques are good for higher frequencies but active techniques are more suitable when lowering the low frequency induced noise in the car. This work therefore addresses a problem that is likely to occur in future trains, due to the decreased weight. The sleepers are a dominant excitation source for this case, and this implies a periodic excitation of 85 Hz when the train is running at 200 km/h. The sleeper frequency excitation will be an even larger problem when the car has a lower weight as well. This paper describes an active vibration isolation, or damping, where the goal is to reduce the sound inside the car due to the sleeper frequency excitation not the vibrations levels. Four actuators have been used and both an AVC as well as an ASAC control strategy has been tested and the results are presented. Tests have been performed on a full scale train in a lab as well as on track at approximately 200 km/h.
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| 6. |
- Lagö, Thomas L, et al.
(författare)
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Evaluation of Field Tests for a MIMO ANC System Used in a Fishing Boat
- 1997
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Konferensbidrag (refereegranskat)abstract
- The sound levels in the sleeping quarters and the mess-room of fishing boats are sometimes too high. It is especially important to keep the sound levels down since the crew have to spend several days on the boat. This implies a long exposure time to low frequency noise. Even during sleep the crew does not have a hearing rest. It is therefore of interest to decrease sound levels in specific areas to give the crew hearing rest. The advantage with an ANC system is that it can be used as a retrofit kit, and the installation does not force the owner to keep the boat in the harbor for long times, compared to a passive treat of the noise problem. In order to evaluate how much sound level decrease it is possible to achieve, a volumetric ANC system has been tested. The typical fishing boat is equipped with one main engine. The engine is typically mounted using a passive isolation, but this does not decrease the sound levels enough. A brief review and discussion of the background noise situation are made in this paper. Since the boat has one engine, a single reference, multiple input, multiple output active noise control system, SR-MIMO ANC, was used using loudspeakers and microphones and an adaptive system based on a DSP. The SR-MIMO ANC system consists of one reference signal, four loudspeakers and six microphones. The results from a field test are presented in the paper and the results are commented.
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| 7. |
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| 8. |
- Sjösten, Per, et al.
(författare)
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Active Vibration Control on a Light High Speed Train : Preliminary Results
- 1997
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Konferensbidrag (refereegranskat)abstract
- Active vibration control has been utilized in an attempt to reduce vibration on a high-speed traincar. The purpose of this experiment was to investigate the possibilities of preventing vibrationsfrom the bogie to excite the car and to produce tonal noise components within the car. Theprimary source of excitation was the variation in rail stiffness due to the sleepers.This work addresses a problem that is likely to occur in future trains, where the structures arelighter and have less internal damping. Periodic excitation from the sleepers is expected tointroduce tonal components that are clearly audible within the car. Decreasing the weight of thestructure will be necessary in future very high-speed trains to save energy and reduce rail wear.The bogie that was used in the experiments described here weights approximately 40% less thanthe standard bogie used in the ABB X2000 today.
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| 9. |
- Sjösten, Per, et al.
(författare)
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Evaluation field tests of a multiple reference ANC system in a small patrol boat
- 1997
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Konferensbidrag (refereegranskat)abstract
- A common problem in small vessels is the high levels of low frequency sound, usually produced by the engines and/or the propellers. Due to the low frequency character of the noise, the primary concern is usually not the potential risk of hearing damage, but the masking effect that reduces speech intelligibility. Another aspect is loss of sleep due to noise, which increases the potential risk for accidents during work onboard caused by tiredness. For this reason, a multiple reference, multiple input, multiple output active control system was implemented and tested in a small patrol boat. The boat was 13 meters long and powered by two 800 hp MTU Diesel engines. The primary tonal components in the drivers cabin were reduced by 20 dB.
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| 10. |
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