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  • 1. Claesson, Ingvar
    et al.
    Håkansson, Lars
    Adaptive Active Control of Machine-Tool Vibration In a Lathe1998Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 3, nr 4, s. 155-162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the turning operation the relative dynamic motion between cutting tool and workpiece, or vibration, is a frequent problem, which affects the result of the machining, and in particular, the surface finish. Tool life is also influenced by vibration. Noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. With proper machine design, i.e. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. However, by active control of machine-tool vibration, a further reduction of the dynamic motion between cutting tool and workpiece can be achieved. It was found that adaptive feedback control of tool vibration in the cutting speed direction, based on the filtered-x LMS-algorithm, enables a reduction in vibration, by up to 40 dB at 1.5 kHz, and by approximately 40 dB at 3 kHz. It was also observed that the introduction of leakage in the filtered-x LMS-algorithm improved the stability properties of the feedback control system. A significant improvement in the workpiece surface was observed and a substantial improvement in the acoustic noise level was obtained with adaptive control.

  • 2. Claesson, Ingvar
    et al.
    Nilsson, Andreas
    GSM TDMA Frame Rate Internal Active Noise Cancellation2003Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 8, nr 3, s. 159-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A common problem in the world's most widely-used cellular telephone system, the GSM system, is the interfering signal generated by the switching nature of TDMA cellular telephony in handheld and other terminals. Signals are sent as chunks of data, speech frames, equivalent to 160 samples of data corresponding to 20 ms at sampling rate of 8 kHz. This paper describes a study of two different software solutions designed to suppress such interference internally in the mobile handset. The methods are 1) notch filtering, which is multiplicative in frequency, and 2) subtractive noise cancellation, which is an alternative method employing correlators. The latter solution is a straigtforward, although somewhat unorthodox, application of "in-wire" active noise control. Since subtraction is performed directly in the time domain, and we have access to the state of the mobile, it is also possible to consider a recurring pause in the interference caused by the idle frame in the transmission, when the mobile listens to other base stations communicating. More complex control algorithms, based on the state of the communication between the handset and the base station, can be utilised.

  • 3.
    Håkansson, Lars
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    The Fourier Transform in Sound and Vibration2015Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, ISSN 1027-5851, Vol. 20, nr 4, s. 190-190Artikkel i tidsskrift (Fagfellevurdert)
  • 4. Johansson, Sven
    et al.
    Håkansson, Lars
    Persson, Per
    Claesson, Ingvar
    Active Control of Lateral Vibrations in a Railway Carriage2002Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 7, nr 4, s. 195-210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As trains are continually designed for higher and higher speeds the problems of railway carriage vibration are on the increase. Lateral vibrations in a railway carriage are noticeable to passengers if the vibration frequencies are lower than approximately 20 Hz. Below this frequency discomfort is a common problem for the passengers and below approximately 1 Hz motion sickness is a problem. The passive solution of stiffening the carriage chassis to shift the vibrational frequencies higher up results in inflated manufacturing and running costs, and opposes higher travel speeds due to increased weight. Semi-passive solutions such as modifying the structural dynamics of the carriage body by decoupling heavy underfloor equipment do not reduce the vibrations sufficiently. However, by appending a multi-reference feedforward active vibration control system, one way expect a substantial reduction in the lateral vibration level. Using a dynamic computer model of a railway carriage simulating the lateral vibration, and using as input bogie acceleration data measured on a running train, multiple-input/single-output coherence spectra were shown to constitute a suitable set of reference signals for an active control system. Control simulations based on the Feedforward Multiple-Input/Single-Output Filtered-x LMS Algorithm are carried out using different reference signal combinations. The control results indicate lateral vibration attenuation on the order of 15dB at the objective frequency of 10Hz.

  • 5. Johansson, Sven
    et al.
    Sjösten, Per
    Nordebo, Sven
    Claesson, Ingvar
    Comparison of Multiple- and Single-Reference MIMO Active Noise Control Approaches Using Data Measured in a Dornier 328 Aircraft2000Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 5, nr 4, s. 77-88Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an active noise control system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple-reference control system is usually required. This type of system allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. The present paper addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single-reference controller is sufficient, the performance of a single- versus twin-reference control algorithm is evaluated in a comparative study. The study is performed as a computer simulation (off-line evaluation) using real-life data recorded in a Dornier 328 under different flight conditions. The results demonstrate that the twin-reference controller performs better than the single-reference whenever there is a slight deviation in the rotational speed of the two propellers. The paper also treats the generation of reference signals. The approach presented is based on a fixed sampling rate and uses a sliding FFT filtering technique.

  • 6. Larsson, Martin
    et al.
    Johansson, Sven
    Claesson, Ingvar
    Håkansson, Lars
    A Module Based Active Noise Control System for Ventilation Systems, Part I: Influence of Measurement Noise on the Performance and Convergence of the Filtered-x LMS Algorithm2009Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 14, nr 4, s. 188-195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low noise level is an essential feature when installing ventilation systems today. To achieve attenuation over a broad frequency range, the passive silencers traditionally used to attenuate ventilation noise can be combined with an active noise control (ANC) system. To insure reliable operation and desirable levels of attenuation when applying ANC to duct noise, it is highly important to be able to suppress the contamination of the microphone signals due to the turbulent pressure fluctuations arising as the microphones are exposed to the airflow in the duct. This paper is the first in a series of two, that treats the problem of turbulence induced noise originating from the airflow inside the ducts. Part I is concerned with theoretical and experimental investigations of the influence of the turbulence induced noise on the adaptive algorithm in the ANC system. Part II is concerned with design and investigations of microphone installations for turbulence suppression and results concerning the performance of an ANC system with the different microphone installations are presented. Some of the results were obtained at an acoustic laboratory according to an ISO-standard. The attenuation achieved with ANC was approximately 15-25 dB between 50-315 Hz even for airflow speeds up to 20 m/s.

  • 7. Larsson, Martin
    et al.
    Johansson, Sven
    Claesson, Ingvar
    Håkansson, Lars
    A Module Based Active Noise Control System for Ventilation Systems, Part II: Performance Evaluation2009Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 14, nr 4, s. 196-206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To utilize the full noise attenuation potential of an active noise control (ANC) system applied to duct noise, it is important to be able to minimize the turbulence induced noise in the microphone signals. This is the second paper in a series of two, that treats the problem of turbulence induced noise originating from the airflow inside the ducts, when applying ANC to ducts. Part I contains theoretical and experimental investigations of the influence of the turbulence induced noise on the filtered-x LMS algorithm used in the ANC system. Part II (the present paper) is concerned with design and investigations of microphone installations which produces a sufficient amount of turbulence suppression while also meeting industry requirements. These requirements are, for example, that the microphone installations should be based on standard ventilation parts, and that they should be easily installed and maintained. Furthermore, results concerning the performance of an ANC system with different microphone installations are presented. Some of the results were obtained at an acoustic laboratory according to an ISO standard. The attenuation achieved with ANC was approximately 15-25 dB between 50-315 Hz even for airflow speeds up to 20 m/s.

  • 8. Smirnova, Tatiana
    et al.
    Åkesson, Henrik
    Håkansson, Lars
    Dynamic Modeling of a Boring Bar Using Theoretical and Experimental Engineering Methods Part 1: Distributed-Parameter System Modeling and Experimental Modal Analysis2009Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 14, nr 3, s. 124-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Boring bar vibration is a common problem during internal turning operations and is a major problem for the manufacturing industry. High levels of boring bar vibration generally occur at frequencies related to the first two fundamental bending modes of a boring bar. This is the first of two companion papers that summarize the theoretical and experimental work carried out concerning modeling of dynamic properties of boring bars. This paper introduces the Timoshenko beam theory for the modeling of clamped boring bars. Also, the traditional Euler-Bernoulli beam theory is applied. These continuous system methods have been utilized to produce fixed-free beam models of the clamped boring bar. In order to improve accuracy of dynamic models of clamped boring bars, the modeling of the boring bar clamping is addressed by means of multi-span beam models with pinned boundary conditions. The derived boring bar models have also been compared with results obtained by means of experimental modal analysis, conducted on the actual boring bar clamped in a lathe. The multi-span beam boring bar models display higher correlation with experimental modal analysis results as compared to fixed-free beam models. For the fixed-free beams the Timoshenko model results in the highest correlation with the experimental results. On the other hand, the interval in frequency and the orientation of the two fundamental modes demonstrate differences, particularly between the continuous system models and the experimental results.

  • 9. Smirnova, Tatiana
    et al.
    Åkesson, Henrik
    Håkansson, Lars
    Dynamic Modeling of a Boring Bar Using Theoretical and Experimental Engineering Methods Part 2: Finite Element Modeling and Sensitivity Analysis2009Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 14, nr 3, s. 134-142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This is the second of two companion papers that summarize the theoretical and experimental work carried out concerning modeling of dynamic properties of boring bars. This paper introduces the finite element method for the modeling of clamped boring bars. The “3-D” FE models of the system boring bar – clamping house as well as the “1-D” FE models of the clamped boring bar were derived. In particular, the modeling of the boring bar clamping is addressed. Dynamic properties predicted based on the developed FE models of the clamped boring bar were compared with the ones estimated by means of experimental modal analysis conducted on the actual boring bar clamped in the lathe. The “3-D” FE models display substantially higher correlation with the experimental modal analysis results compared to the “1-D” FE models. A “3-D” FE model of the boring bar – clamping house manages to model the distance in frequency and the orientation of the two fundamental modes to a large extent. The importance of the modeling of the boring bar boundary conditions for the accuracy of dynamic models of boring bars is demonstrated. The sensitivity of the natural frequency estimates produced by means of the FE and the continuous system (presented in Part 1) boring bar models with respect to variations in material density and Young’s elastic modulus has been addressed.

  • 10. Winberg, Mathias
    et al.
    Johansson, Sven
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Active Vibration Isolation in Ships: A Pre-Analysis of Sound and Vibration Problems2005Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 10, nr 4, s. 175-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Engine-induced sound and vibration levels in boats for professional and leisure use are in many cases unacceptably high in terms of comfort and environmental disturbance. Classical methods for passive treatment are normally less efficient due to the low frequency content and often lead to a substantial increase in weight. The requirements for lower weight which would increase the maximum speed of the boat as well as improve fuel economy have to be considered. More efficient vibration damping methods must therefore be found. With, for example, active engine mounts, it is possible to achieve a decrease in the vibrations even for cases when the hull is not very stiff. This is especially important in marine applications, since the engines are usually mounted on flexible and light structures. The project Active Vibration Isolation In Ships (AVIIS) aims at investigating the effects of using a type of Active Noise and Vibration Control system (ANVC) in this type of marine application. This article presents the analysis of the sound and vibration problems in one particular leisure boat from an ANVC point of view. A very thorough investigation is carried out, the main noise and vibration sources are established as well as the transmission paths of the noise into the boat. Answers are found from this investigation as to where the actuators should be positioned, which kind of ANVC approach that would be preferable to use and the expected interior noise reduction. This is the kind of pre-analysis that is needed for a complex structure such as found in a marine vessel for the successful implementation of ANVC. An optimized engine mount was also designed and evaluated resulting in a 10 dBA saloon sound level reduction compared to the standard engine mounts. Additionally, with the optimized engine mounts, the vibration levels at the hull were also reduced by up to 15 dB at the main harmonic components. This paper also presents a feasible way to estimate the performance of a potential active control system based on feedforward narrowband control of engine and propeller harmonics. Secondary sources inertial mass actuators are proposed and for error sensors, accelerometers or microphones or a combination of the two are used. In the low frequency range, below 300 Hz, a further reduction of engine orders and propeller BPFs in the order of 5-10 dB are predicted.

  • 11. Winberg, Mathias
    et al.
    Johansson, Sven
    Lagö, Thomas L
    Claesson, Ingvar
    A New Passive/Active Hybrid Headset for a Helicopter Application1999Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 4, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. In addition, pilots are likely to suffer from damage to their hearing due to the high sound levels in the headset produced to overcome the noise caused by increased speaker levels. A feasible approach is to reduce the low frequency noise by using active techniques combined with a method for reducing the noise in the intercom microphone signal, with lower speaker levels as a result. Helicopter noise consists of tonal components embedded in broadband noise. In order to achieve an efficient attenuation of the primary noise inside the headset, a combination of a digital feedforward controller and an analog feedback controller is employed. Spectral Subtraction is used to suppress the background noise in speech signals. This paper evaluates a combination of the two techniques and their application to real data.

  • 12. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Claesson, Ingvar
    Håkansson, Lars
    On the Development of a Simple and Robust Active Control System for Boring Bar Vibration in Industry2007Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 12, nr 4, s. 139-152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vibration in internal turning is a problem in the manufacturing industry. A digital adaptive controller for the active control of boring bar vibration may not be a suficient solution to the problem. The inherent delay in a digital adaptive controller delays control authority and may result in tool failure when the load applied by the workpiece on the tool changes abruptly, e.g. in the engagement phase of the cutting edge. A robust analog controller, based on a lead-lag compensator, with simple adjustable gain and phase, suitable for the industry application, has been developed. Also, the basic principle of an active boring bar with embedded actuator is addressed. The performance and robustness of the developed controller has been investigated and compared with an adaptive digital controller based on the feedback filtered-x algorithm. In addition, this paper takes into account those variations in boring bar dynamics which are likely to occur in industry; for example, when the boring bars is clamped in a lathe. Both the analog and the digital controller manage to reduce the boring bar vibration level by up to approximately 50 dB.

  • 13. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Estimation and Simulation of the Nonlinear Dynamic Properties of a Boring Bar2011Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 16, nr 1, s. 35-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, an initial investigation of the nonlinear dynamic properties of clamped boring bars is carried out. Two nonlinear, single-degree-of-freedom models with different softening spring nonlinearities are introduced for modeling the nonlinear dynamic behavior of the fundamental bending mode in the cutting speed direction of a boring bar. Also, two different methods for the simulation of nonlinear models are used. The dynamic behavior in terms of frequency response function estimates for the nonlinear models and the experimental modal analysis of the clamped boring bar is compared. Similar resonance frequency shift behavior for varying excitation force levels is observed for both the nonlinear models and the actual boring bar.

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