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  • 1.
    Ahlin, Kjell
    et al.
    Saven EduTech AB.
    Brandt, Anders
    Saven EduTech AB.
    A smart way to analyze dynamic data2003In: Sound & vibration, ISSN 1541-0161, no February, 20-22 p.Article in journal (Other academic)
    Abstract [en]

    In recent years MATLAB® has become a common software tool for general computational mathematics, in universities as well as in industry. In the field of noise and vibration analysis, MATLAB is very common in universities, but perhaps a little less common in the industrial world. In this article some ideas are presented on how MATLAB can be successfully used for analyzing experimental noise and vibration data. Through the introduction of toolboxes in this field, the less experienced user can take advantage of the powerful functionality of MATLAB, either as the main tool or as a complement to the many excellent menu driven systems available on the market. Some of the advantages and disadvantages of using MATLAB versus menu driven systems are also discussed.

  • 2.
    Ahlin, Kjell
    et al.
    Blekinge Institute of Technology.
    Brandt, Anders
    Axiom EduTech AB.
    Lagö, Thomas
    A New MATLAB Toolbox for Simulation and Parameter Identification of Nonlinear Mechanical Systems2007In: IMAC-XXV: A Conference & Exposition on Structural Dynamics, February 19 – 22, 2007, Orlando, Florida USA, 2007Conference paper (Refereed)
  • 3.
    Andersen, Michael Styrk
    et al.
    University of Southern Denmark, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    An alternative to the flutter derivatives2016In: BBAA VIII, 8th International Colloquium on Bluff Body Aerodynamics and Applications, Northeastern University, Boston, Massachusetts, USA, June 7-11, 2016: colloquium proceedings, Boston: Northeastern University, College of Engineering , 2016Conference paper (Refereed)
    Abstract [en]

    A new simplified framework to study flutter and assess the full scale flutter wind speed is suggested. The flutter instability problem is reduced from a problem involving 8 flutter derivatives to only 4 coefficients. With this method it is possible to estimate the self-excited forces with increased precision by using stability diagrams. Furthermore, the physical transparency of the aerodynamic damping and stiffness terms is increased because the development in vertical and torsional damping and stiffness is analysed instead of flutter derivatives.

  • 4.
    Andersen, Michael Styrk
    et al.
    University of Southern Denmark, Denmark.
    Johansson, Jens
    University of Southern Denmark, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Hansen, Svend Ole
    University of Southern Denmark, Denmark ; Svend Ole Hansen ApS, Denmark.
    Aerodynamic stability of long span suspension bridges with low torsional natural frequencies2016In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 120, 82-91 p.Article in journal (Refereed)
    Abstract [en]

    Classical flutter of suspended bridge decks can be avoided if the torsional frequencies are lower than the vertical. Wind tunnel tests of single boxes and twin box section models with torsional natural frequencies above and below the vertical frequency has been conducted. Flutter was avoided in all tests where the torsional frequency was lower than the vertical. But too low torsional stiffness caused large static displacements of the girder at medium–high wind speeds and steady state oscillations driven by a combination of torsional divergence and stalling behavior at the critical wind seed. In order to design aerodynamically stable suspension bridges with low torsional natural frequencies it is suggested to increase the mass moment of inertia and provide adequate torsional stiffness by the main cables spacing.

  • 5.
    Andrén, Linus
    et al.
    Blekinge Institute of Technology.
    Håkansson, Lars
    Blekinge Institute of Technology.
    Brandt, Anders
    Blekinge Institute of Technology.
    Claesson, Ingvar
    Blekinge Institute of Technology.
    Identification of dynamic properties of boring bar vibrations in a continuous boring operation2004In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, no 4, 869-901 p.Article in journal (Refereed)
    Abstract [en]

    Vibrations in internal turning operations are usually a cumbersome part of the manufacturing process. This article focuses on the boring bar vibrations. Boring bar vibrations in alloyed steel, stainless steel and cast iron have been measured in both the cutting speed direction and the cutting depth direction with the aid of accelerometers. The dynamic response of a boring bar seem to be a time varying process that exhibits non-linear behaviour. The process is influenced by non-stationary parameters that are not under the control of the operator or experimenter. The vibrations are clearly dominated by the first resonance frequency in one of the two directions of the boring bar. The problem with force modulation in rotary machinery, which appears as side band terms in the spectrum, is also addressed. Furthermore, the resonance frequencies of the boring bar are correlated to an Euler-Bernoulli beam model. 

  • 6.
    Andrén, Linus
    et al.
    Blekinge Institute of Technology.
    Håkansson, Lars
    Blekinge Institute of Technology.
    Brandt, Anders
    Blekinge Institute of Technology.
    Claesson, Ingvar
    Blekinge Institute of Technology.
    Identification of motion of cutting tool vibration in a continuous boring operation: correlation to structural properties2004In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, no 4, 903-927 p.Article in journal (Refereed)
    Abstract [en]

    The internal turning operation has a history of being a cumbersome metal working process as vibration in boring operations is usually inevitable. In this article, the deflection shapes and/or mode shapes as well as the resonance frequencies of a boring bar have been put under scrutiny. Three methods have been used in order to investigate dynamic properties of a clamped boring bar: a theoretical Euler-Bernoulli beam model, an experimental modal analysis and an operating deflection shape analysis. The results indicate a correlation between the shapes of the deflection shapes and/or mode shapes produced by the three different analysis methods. On the other hand, the orientation of the forced deflection shapes and/or mode shapes and the resonance frequencies demonstrate differences between the three methods. During continuous cutting, it is demonstrated that the bending motion of the first two resonance frequencies is to a large extent in the cutting speed direction. (C) 2003 Elsevier Ltd. All rights reserved.

  • 7.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Damping Assessment of Light Wooden Assembly With and Without Damping Material2013In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 49, 434-447 p.Article in journal (Refereed)
    Abstract [en]

    Damping elastomers are often used in lightweight wooden constructions and are believed to have good sound insulating effects. In the present study the influence on the structural behaviour by using elastomer damping material (Sylomer®) in the joints, with particular respect to footsteps and floor vibrations, has been investigated. A full scale wooden mock-up was assembled with two different joint configurations and studied under free-free boundary conditions. In the first configuration, the joints between the floor and underlying walls were screwed together. In the second configuration the floor was resting free on top of ribs of elastomer damping material, equivalent to normal building practice when this material is used. Both configurations were analysed and evaluated using experimental modal analysis, in the frequency interval 10-115 Hz.

     

    The relative (viscous) damping ratios of the modes were found to be on average 1.2% for the screwed configuration and 2.1% for the configuration with elastomer damping material in the joints. The damping was found to vary significantly between modes in the elastomer case. It was found that at low frequencies damping was high for modes with large motion on the edge where the elastomer material was. At higher frequencies (above approx. 40 Hz), however, the damping for this configuration decreased. This is believed to be caused by a vibration isolation effect of the elastomer, decoupling the floor from the walls at higher frequencies.

     

    To assess the differences in vibration levels between the two configurations, mean acceleration levels of well spread points on the different building parts where computed and evaluated. It was found that above approximately 70 Hz, the mean vibration level in the elastomer configuration was significantly lower than for the screwed configuration. Below 70 Hz, however, for many frequencies the mean vibration level for the elastomer configuration was significantly higher than for the screwed configuration (as should be expected in vibration isolation). Problems with springiness and footsteps are due to loads in the frequency range of 10 to 50 Hz, this could indicate that elastomers, used as in the present study, could worsen these types of problems, although improving higher frequency acoustic performance.

  • 8.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Ekevid, Torbjörn
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    FE Modelling of Light Weight Wooden Assemblies: parameter study and comparison between analyses and experiments2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 73, 125-142 p.Article in journal (Refereed)
    Abstract [en]

    A finite element (FE) analysis of a model representing a mock-up structure previously investigated experimentally is investigated in this study. The aim is to make a correlation and calibration between test and analysis of the full scale wooden structure; both eigenmodes and acceleration levels are compared. Large scatter is found in material properties used for light weight wooden structures in literature. In this study, a parameter evaluation is therefore made to show how different properties influence the dynamic behaviour of the structure. It is shown that the wood beam material properties influence the behaviour of the light weight wooden structure FE model most.

    Two types of junctions are modelled and evaluated; a tied connection is used to simulate screwed junctions and spring/dashpot elements are used to represent elastomer junctions between the floor and the walls. The springs and dashpots used to model the elastomer in the junction work well in the bearing direction but need to be improved to obtain correct rotational stiffness, shear motion and friction. There are still many unknown parameters in a complex wooden structure that remain to be investigated. However, the results presented in this paper add data to be used for FE modelling of a complex wooden structure.

  • 9.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    ABRAVIBE – A MATLAB toolbox for noise and vibration analysis and teaching2011Other (Other academic)
    Abstract [en]

    The ABRAVIBE toolbox is a free, open MATLAB® /Octave toolbox for analysis of noise and vibration signals. It was developed to be both a tool for learning about vibrations, vibration analysis etc., and to be used as a tool for engineers, students, teachers, and researchers to analyze signals from vibration or acoustics applications.

    The ABRAVIBE toolbox provides tools for common acoustic and vibration analysis tasks, as well as numerous examples for learning this highly interesting, but sometimes perhaps difficult, topic. In terms of functionality the toolbox is similar to the largest commercial software packages. Parts of this toolbox should also appeal to anyone in the signal processing area who wishes to perform spectral analysis or frequency response estimation using FFT based methods.

    The ABRAVIBE toolbox was written as an accompanying toolbox for the book "Noise and Vibration Analysis: Signal Analysis and Experimental Procedures", by Anders Brandt. The book provides the theory basis for all functionality implemented in the toolbox.

  • 10.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    ABRAVIBE - a toolbox for teaching and learning vibration analysis2013In: Sound & vibration, ISSN 1541-0161, no November, 12-17 p.Article in journal (Other academic)
    Abstract [en]

    A Matlab® toolbox has been developed as a tool for teaching and learning vibration engineering and vibration analysis. This free, open software will also run under GNU Octave, if an entirely free software platform is wanted, with a few functional limitations. The toolbox functionality includes simulation of mechanical models as well as advanced analysis such as time-series analysis, spectralanalysis, frequency response and correlation function estimation, modal parameter extraction, and rotating machinery analysis (order tracking). In this article, an overview of the functionality is given and recommended use in teaching is discussed.

  • 11.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Comparison and assessment of Methods to treat harmonics in Operational Modal Analysis2015In: Paper presented at ICEDyn 2015, International conference on structural engineering dynamics 2015, Lagos, Portugal, June 22-24, 2015, 2015Conference paper (Refereed)
  • 12.
    Brandt, Anders
    Blekinge Institute of Technology ; Saven EduTech AB.
    Introductory noise & vibration analysis2000Book (Other academic)
  • 13.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Lab Exercises for a Course on Mechanical Vibrations2014In: Special Topics in Structural Dynamics, Volume 6: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014 / [ed] Gary Foss & Christopher Niezrecki, Springer, 2014, Vol. 6, 15-20 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents some exercises designed to teach fundamental aspects of mechanical vibrations in general, and experimental techniques for vibration measurements in particular. Teaching students to become good experimentalists is a very difficult task, and is perhaps not even possible inside standard curricula. However, some fundamental aspects of experimental work must be taught, and can be included in a course on vibrations as well as in other courses. The first exercise is designed to teach the student how careful one has to be when applying vibration sensors to a structure, and is based on the repeatability of mass calibration measurements. This makes it a good exercise to base a discussion on experiment setup and repeatability issues etc. The second exercise is an exercise where an approximate single-degree-of-freedom (SDOF) system is investigated by some simple analytical calculations as well as by an experimental measurement. This exercise serves to demonstrate the rather abstract notion of SDOF, and also illustrate the applicability of a simplified model in a limited frequency range. Finally, a third exercise is made where modal analysis of a slalom ski using impact testing is used as a demonstration of more advanced vibration analysis.

  • 14.
    Brandt, Anders
    Blekinge Institute of Technology ; Saven EduTech AB.
    Ljud- och vibrationsanalys I2001Book (Other academic)
  • 15.
    Brandt, Anders
    Blekinge Institute of Technology ; Saven EduTech AB.
    Noise & Vibration Analysis III2003Book (Other academic)
  • 16.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Noise and vibration analysis: signal analysis and experimental procedures2011 (ed. 1)Book (Other academic)
    Abstract [en]

    Noise and Vibration Analysis is a complete and practical guide that combines both signal processing and modal analysis theory with their practical application in noise and vibration analysis. It provides an invaluable, integrated guide for practicing engineers as well as a suitable introduction for students new to the topic of noise and vibration. Taking a practical learning approach, Brandt includes exercises that allow the content to be developed in an academic course framework or as supplementary material for private and further study.

    • Addresses the theory and application of signal analysis procedures as they are applied in modern instruments and software for noise and vibration analysis
    • Features numerous line diagrams and illustrations
    • Accompanied by a web site at www.wiley.com/go/brandt with numerous MATLAB tools and examples.

    Noise and Vibration Analysis provides an excellent resource for researchers and engineers from automotive, aerospace, mechanical, or electronics industries who work with experimental or analytical vibration analysis and/or acoustics. It will also appeal to graduate students enrolled in vibration analysis, experimental structural dynamics, or applied signal analysis courses.

  • 17.
    Brandt, Anders
    Chalmers University of Technology.
    On Sound Transmission Characteristics of the Human Skull in vivo1989Report (Other academic)
  • 18.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Some Aspects of Time Domain Parameter Extraction Approaches For Operational Modal Analysis2013In: Paper presented at ICEDyn 2013, International conference on structural engineering dynamics 2013, Sesimbra, Portugal, June 17-19, 2013, 2013Conference paper (Refereed)
  • 19.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Some Cornerstones of Signal Analysis History2014In: Special Topics in Structural Dynamics, Volume 6: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014 / [ed] Gary Foss & Christopher Niezrecki, Springer, 2014, Vol. 6, 33-36 p.Conference paper (Refereed)
    Abstract [en]

    This brief paper contains a survey of some fundamental cornerstones to contemporary analysis of random signals. Being among the most important contributions to this field, the paper presents the background of the sampling theorem, as this is the foundation on which all modern data analysis rests. In addition, the background and history of the Fourier transform, the discrete Fourier transform (DFT), and, particularly, the fast Fourier transform (FFT) is given.

  • 20.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Some educational vibration measurement exercises2016In: Sound & vibration, ISSN 1541-0161, no January, 12-14 p.Article in journal (Other academic)
    Abstract [en]

    Four exercises are presented to teach experimental vibration measurements: mass calibration; accelerometer mounting; singledegree-of-freedom vibration measurement and analysis; and fullscale experimental modal analysis.

  • 21.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    The ABRAVIBE Toolbox for Teaching Vibration Analysis and Structural Dynamics2013In: Special Topics in Structural Dynamics, Volume 6: Proceedings of the 31st IMAC, A Conference on Structural Dynamics, 2013 / [ed] Allemang, R., De Clerck, J., Niezrecki, C. & Wicks, A, Springer, 2013, Vol. 6, 131-141 p.Conference paper (Refereed)
    Abstract [en]

    Vibration analysis is a subject where students often find it hard to comprehend the fundamental theory. The fact that we have, in general, almost no intuition for dynamic phenomena, means that students need to explore various dynamic phenomena in order to grasp the subject. For this reason, a MATLAB toolbox (the ABRAVIBE toolbox) has been developed as an accompanying toolbox for the recent book “Noise and Vibration Analysis” by the author. This free, open software, published under GNU Public License, can be used with GNU Octave, if an entirely free software platform is wanted, with a few functional limitations. The toolbox includes functionality for simulation of mechanical models as well as advanced analysis such as time series analysis, spectral analysis, frequency response and correlation function estimation, modal parameter extraction, and rotating machinery analysis (order tracking). In this paper, an overview of the functionality is given and recommended use in teaching is discussed. It is also shown how the toolbox can be used for general vibration analysis using data from multichannel measurements. Finally, some laboratory exercises for structural dynamics teaching are discussed.

  • 22.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Unbiased Estimation of Frequency Response in the Presence of Input and Output Noise2011In: Modal Analysis Topics, Volume 3: Proceedings of the 29th IMAC, A Conference on Structural Dynamics, 2011 / [ed] Tom Proulx, Springer, 2011, Vol. 3, 299-305 p.Conference paper (Refereed)
    Abstract [en]

    Many attempts have been made on finding a frequency response estimator which minimizes the bias error in cases where both the input and output signals of a linear system are contaminated by extraneous noise, for example, Hv and Hs. It is wellknown that these estimators only minimize the bias error if the input and output extraneous noise spectra are known, which they are normally not. This paper describes how time domain averaging (cyclic averaging) of periodic excitation signals can be used to eliminate the bias due to both input and output extraneous noise. It is demonstrated by simulation results that asymptotically unbiased estimates of frequency response functions can be obtained by using time domain averaging and periodic random noise. Examples are given of both single-input/single-output (SISO) and of multiple-input/multiple-output (MIMO) systems. The fact that periodic excitation signals in this way can be used to eliminate the bias error in FRF estimates does not seem to have been recognized previously.

  • 23.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Ahlin, Kjell
    A digital filter method for forced response computation2003Conference paper (Refereed)
    Abstract [en]

    Transient forced response of mechanical structures is usually computed using time domain integration. This is often computationally costly, and the numerical precision and stability are concerns. In the present paper, a novel method based on modal superposition, using a new digital filter implementation, is presented. Poles and residues of the model are used as input data, which allows for using data from a finite element model, a lumped parameter model, or from experimental modal analysis. Modal damping can be used if the damping matrix is unknown. With the proposed method, the frequency dependant error can easily be computed, and can be chosen arbitrarily small by selecting proper sampling frequency (time increment). The method is applicable to all linear structures and can be used for stationary or transient input data. Simulation results show that the new method is superior to the alternative methods, at less computational cost.

  • 24.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Ahlin, Kjell
    A MATLAB Toolbox for Experimental Structural Dynamics2002Conference paper (Refereed)
  • 25.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Ahlin, Kjell
    A novel approach for computing time domain forced response2002Conference paper (Refereed)
  • 26.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    Sampling and time-domain analysis2010In: Sound & vibration, ISSN 1541-0161, no May, 13-17 p.Article in journal (Other academic)
    Abstract [en]

    Most noise and vibration measurement and analysis systems are able to record time history signals for subsequent processing. This article deals with some important aspects of recording and processing these data streams in order to maintain analysis integrity.

  • 27.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    Lagö, Thomas
    Acticut International, USA.
    Noise and vibration measurement system basics2006In: Sound & vibration, ISSN 1541-0161, no April, 9-10 p.Article in journal (Other academic)
  • 28.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Berardengo, Marta
    University of Parma, Italy.
    Manzoni, Stefano
    Polytechnic University of Milan, Italy.
    Cigada, Alfredo
    Polytechnic University of Milan, Italy.
    Harmonic scaling of mode shapes for operational modal analysis2016In: The 28th International Conference on Noise and Vibration Engineering 2016 (ISMA 2016): proceedings of a meeting held 19-21 September 2016, Leuven, Belgium. Including USD 2016, Leuven: Katholieke Universiteit Leuven, Department of Mechanical Engineering , 2016Conference paper (Refereed)
  • 29.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Brincker, Rune
    University of Southern Denmark, Denmark.
    Impact Excitation Processing for Improved Frequency Response Quality2010In: Structural Dynamics, Volume 3: Proceedings of the 28th IMAC, A Conference on Structural Dynamics, 2010 / [ed] Tom Proulx, Springer, 2010, Vol. 3, 89-95 p.Conference paper (Refereed)
    Abstract [en]

    Impact excitation is the most common excitation type for measurements of frequency response functions for modal analysis and other purposes. The method used is almost always based on setting the data acquisition system up with triggering, fixed FFT analysis settings, and then using an accept/reject step where each impact is either accepted if the impact seems good, or rejected if it contained some error such as double impacts or overload. This method has several drawbacks that often lead to non-optimal frequency responses. In this paper, an improved method based on time recording of all signals and subsequent post processing is proposed. The data acquisition part is made easier with the proposed method, while at the same time the importance of a skilled operator is reduced. It is shown on a real test structure that the quality of the resulting frequency responses can be significantly improved (measured by the coherence function) compared to the traditional method, and at the same time the total acquisition time can be shortened. An automatic optimization procedure which allows for fully automated post processing is proposed.

  • 30.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Brincker, Rune
    Aarhus University, Denmark.
    Integrating time signals in frequency domain: comparison with time domain integration2014In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 58, 511-519 p.Article in journal (Refereed)
    Abstract [en]

    Integrating sampled time signals is a common task in signal processing. In this paper we investigate the performance of two straightforward integration methods: (i) integration in the frequency domain by a discrete Fourier transform (DFT), division by jω followed by inverse DFT (IDFT) back to the time domain, and (ii) a method using a weighted overlap-add (WOLA) technique which is developed in the paper. These two methods are compared with two time domain methods: (a) the trapezoidal rule, and (b) an optimized IIR filter. It is shown that the intuitive method of a straightforward DFT/IDFT is a very good method which is recommended for data lengths exceeding 16 K samples, provided data are short enough to allow a single DFT. The IIR filter integration is shown to have very similar accuracy and can also be recommended. The WOLA integration method is shown to perform well in most cases for steady-state conditions. For cases with short transients it should, however, be avoided. A signal integrated by the WOLA method is further shown to be incoherent with the signal before integration. This suggests that the WOLA method should be avoided in cases where coherence between the signals before and after integration is important. It is also demonstrated by a simulation example that integration by the trapezoidal rule should be avoided, as it gives biased results, particularly for higher frequencies.

  • 31.
    Brandt, Anders
    et al.
    Axiom EduTech.
    Brincker, Rune
    Ahlin, Kjell
    Welsh Averaging method revisited2006Conference paper (Refereed)
  • 32.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Håkansson, Bo
    Chalmers University of Technology.
    Stenfelt, Stefan
    Chalmers University of Technology.
    Properties of Bone Conduction Hearing2006Conference paper (Refereed)
    Abstract [en]

    Bone conduction sound, the transmission of sound as vibrations in the skull bone, is used in several areas, forexample for hearing aids, in audiometry, and in communication systems. The bone-anchored hearing aid (BAHA)has been commercially available for many years. This device utilizes titanium screws attached to the skull bonepenetrating the soft tissues thus providing a rigid attachment to the skull bone. Subjects equipped with suchtitanium screws have proven important for investigation of bone conducted sound and in the present paper anoverview of some results from different studies on such patients is given. Included are results from investigationsof resonance frequencies, propagation delays, and transcranial (cross-skull) attenuation.

  • 33.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Håkansson, Bo
    Chalmers University of Technology.
    Stenfelt, Stefan
    Chalmers University of Technology.
    Tjellström, Anders
    ENT Department, Sahlgrenska Hospital.
    Transcranial Attenuation Measured by a Laser Doppler Vibrometer1996Conference paper (Refereed)
  • 34.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Håkansson, Lars
    Blekinge Institute of Technology .
    Claesson, Ingvar
    Blekinge Institute of Technology .
    Cyclostationary Analysis of Boring Bar Vibrations2004Conference paper (Refereed)
    Abstract [en]

    Internal turning or boring operation is a common metal working process that is usually associated with vibration problems. The vibration problems in internal turning considerably influence important factors such as surface quality, productivity, production costs, etc. In order to gain further understanding of the dynamic metal cutting process, an important early step is to thoroughly classify the vibrations. Boring bar vibrations have previously been proven to be nonstationary when analyzed with traditional methods. For vibrations originating in a combination of a rotating workpiece and random material inhomogeneities, it can be anticipated that the vibrations have cyclostationary properties. Methods for analysis of cyclostationary signals have rendered an increasing interest in the past decade, especially in the telecommunications field. However, very little has been published on the use of these methods in vibration applications. In this paper we show there is strong statistical evidence of cyclostationary behavior in vibrations on an operating boring bar. Methods for estimating the cyclic autocorrelation function and cyclic spectrum for sampled data are developed and results are compared. Some preliminary results from implementing these methods on operating boring bar vibrations are also presented.

  • 35.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Kjær, Christopher
    University of Southern Denmark, Denmark.
    Flipping the classroom for a class on experimental vibration analysis2016In: Rotating Machinery, Hybrid Test Methods, Vibro-Acoustics & Laser Vibrometry, Volume 8: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 2016 / [ed] James De Clerck & David S. Epp, Springer, 2016, Vol. 8, 155-159 p.Conference paper (Refereed)
    Abstract [en]

    Flipped classroom is a relatively new teaching form in higher education which is aimed at improving the learning process by engaging students in pre-class video activities fostering more active discussions between lecturer and student in-class. The concept is that the students watch recorded lectures (lower-order thinking skills) at home prior to class. During the class the students work on assignments and discuss the course content which can make better use of the teacher as a facilitator, so the focus can be on the more difficult things (higher-order cognitive skills) in the course content. In the present paper, the design and implementation using the flipped classroom technique for a course on experimental vibration analysis is presented. Some important experiences are discussed and an evaluation of student experiences is presented. The outcome is that the teaching technique is relatively time consuming to implement, but that the students appreciate being able to watch the lectures at their own pace and having more time working with the difficult things together with the teacher. Also, it turned out that the way the videos were used was very different among different students.

  • 36.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech AB.
    Actual Accuracy in Flight Data Collection and Analysis2005Conference paper (Refereed)
    Abstract [en]

    In aerospace applications it is often vital to understand what is happening when analyzing sound and vibration data and what total accuracy one receives. The tradition has been to spend money on yearly calibration of sensors and part of the measurement equipment, but not on the software used for analysis of the data collected by these sensors. While the sensors might be accurate to a percentage level, erroneous analysis procedures can give arbitrarily high errors! Usually, there is no “calibration option” or “benchmark” for sound and vibration analysis software. This paper will present some common pitfalls and what can happen if the user is not aware how the software is handling the data, or even worse, the code was not correctly implemented in the first place. Some real life examples of the latter and suggested solutions to avoid such harmful situations will be presented. Also, some good guidelines for aerospace data collection and analysis, with focus on sound and vibration applications, will be discussed.

  • 37.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech Inc, USA.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    MATLAB Toolboxes for Advanced Noise and Vibration Analysis2005Conference paper (Refereed)
  • 38.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech AB.
    Ahlin, Kjell
    Blekinge Institute of Technology .
    Summary of Spectrum Estimators for Vibration Signals and Their Errors2004Conference paper (Refereed)
  • 39.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech Inc, USA.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    Using MATLAB for Advanced Noise and Vibration Analysis2004Conference paper (Refereed)
    Abstract [en]

    Commercial tools for measurement and analysis of noise and vibration signals have traditionally been very expensive. In the last decade, however, multi-channel measurement systems have become relatively inexpensive. The analysis functionality in most inexpensive instruments is limited. Therefore, many companies are using alternatives for post processing of measurement results. Matlab is a platform that is popular for this purpose and which offers many advantages over dedicated, menu driven systems. The open functions in Matlab assure flexibility and the possibility to modify functions for specific needs. In addition, a command based programming environment provides for traceability and quality assurance, including qualification of used algorithms, important aspects particularly in the aerospace industry. In the past, basic functions for signal analysis and vibration analysis have had to be developed before taking full advantage of the Matlab platform. In this paper we present a new suite of toolboxes that turn Matlab into state-of-the-art software for noise and vibration analysis. The toolboxes presented here have been well proven in applications in aerospace industry. Parts of the toolboxes are provided as freeware, and everyone is encouraged to download this from Internet.

  • 40.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech Inc, USA.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    Tuma, Jiri
    Ostrava-Poruba, Czech Republic.
    Main principles and limitations of current order tracking methods2005In: Sound & vibration, ISSN 1541-0161, no March, 19-22 p.Article in journal (Other academic)
    Abstract [en]

    Order tracking is a widely used tool for analysis of vibrations generated in vehicle drivetrain components, since many vibrations are related to engine RPMs. In recent years, offline order tracking has become suitable due to enhanced computer speeds. Many methods, some patented, for both online and offline order tracking have been presented over the years. This article reviews some basic ideas behind current methods and compares their main advantages and limitations. Some basic time-frequency concepts and time window effects are reviewed. Questions on suitable tachometers and their number of pulses per revolution are also addressed. The possibility of processing RPM dependent data without tachometers is also discussed.

  • 41.
    Brandt, Anders
    et al.
    Axiom EduTech AB.
    Lagö, Thomas
    Axiom EduTech AB.
    Ahlin, Kjell
    Blekinge Institute of Technology.
    Tuma, Jiri
    Ostrava-Poruba, The Czech Republic.
    Main Principles and Limitations of Current Order Tracking Methods2005Conference paper (Refereed)
  • 42.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Linderholt, Andreas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    A Periodogram-Based Method for Removing Harmonics in Operational Modal Analysis2012In: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012): Proceedings of a meeting held 17-19 September 2012, Leuven, Belgium. Including USD 2012 / [ed] P. Sas, S. Jonckheere & D. Moens, Leuven: Katholieke Universiteit Leuven, Department of Mechanical Engineering , 2012, 2625-2634 p.Conference paper (Refereed)
    Abstract [en]

    In many cases where operational modal analysis is of interest, harmonic components are disturbing the estimation of modal parameters. Sometimes the harmonics can be included in the parameter estimation process and subsequently removed (because the damping values become unrealistically low). However, this is difficult if a natural frequency is very close to, or coincides with, a harmonic. In this paper we investigate a recently proposed method for removing harmonics when estimating spectral densities for operational modal analysis. The method is essentially based on removing the harmonics in a periodogram, prior to estimating the spectral density by smoothing the same periodogram. This makes it a very time efficient method, as the harmonic removal is integrated into the spectral analysis process. To produce data for testing the method, a finite element dynamic model representing a wind turbine was created. The MATLAB-based finite element code CALFEM was used to achieve a flexible description of the tower. An aerodynamic force representation excited the rotating structure. An unbalance in one of the blades was introduced to produce a harmonic at the rotation speed of the turbine. To validate the efficiency of the harmonic removal, modal parameters were estimated using simulated data prior to, and after, removing the harmonics. The results show that the harmonic removal with the proposed method is efficient.

  • 43.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Singhal, RajCanadian Space Agency, Canada.
    Shock & Vibration, Aircraft/Aerospace, Energy Harvesting, Acoustics & Optics, Volume 9: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 20162016Collection (editor) (Other academic)
    Abstract [en]

    Shock Vibration, Aircraft /Aerospace, Energy Harvesting, Acoustics Optics, Volume 9. Proceedings of the 34th IMAC, A Conference and Exposition on Dynamics of Multiphysical Systems: From Active Materials to Vibroacoustics, 2016, the ninth volume of ten from the Conference brings together contributions to this important area of research and engineering. The collection presents early fi ndings and case studies on fundamental and applied aspects of Structural Dynamics, including papers on:• Energy Harvesting• Adaptive Support• Shock Calibration• Operating Data Applications• Aerospace Testing Techniques• Aircraft /Aerospace Applications• Joints• Acoustics & Optics• Other Sensing

  • 44.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Sturesson, Per-Olof
    Volvo Car Corp., Sweden.
    Ristinmaa, Matti
    Lund University.
    Test analysis verification exercise using open software2014In: Sound & vibration, ISSN 1541-0161, no June, 13-16 p.Article in journal (Other academic)
    Abstract [en]

    Teaching the topic of structural dynamics in any engineering field is a true challenge due to the wide span of the underlying subjects like mathematics, mechanics (both rigid-body and continuum mechanics), numerical analysis, random data analysis and physical understanding. In this article we present a pedagogical example of using experimental modal analysis to verify and calibrate a finite-element model using free, open-source software.

  • 45.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Vaarning, Claus
    University of Southern Denmark, Denmark.
    A Comparison of Non-Parametric Techniques for FRF Estimation Using Pure Random Excitation2012In: Topics in Modal Analysis I, Volume 5: Proceedings of the 30th IMAC, A Conference on Structural Dynamics, 2012 / [ed] R. Allemang, J. De Clerck, C. Niezrecki & J.R. Blough, Springer, 2012, 523-534 p.Conference paper (Refereed)
    Abstract [en]

    It is often remarked that pure random noise cannot, or should not, be used for estimating frequency response on lightly damped structures. The reason given is that the bias errors caused by leakage would “deform” the estimated FRF in an unsuitable way for modal parameter processing. In this paper, traditional coherence-based methods are compared with the recently proposed local polynomium method. It is demonstrated that the bias error can be made arbitrarily small but that it requires rather long FFT blocksize, relative to what is needed with other excitation signals, such as burst random or periodic excitation signals. A main conclusion is that, while pure random is an inferior excitation signal for synthetic excitation, in cases where there is no choice, such as wind or traffic loaded structures, low-bias FRFs can very well be estimated, provided the measurement time can be long enough.

  • 46.
    Brincker, Rune
    et al.
    Aarhus School of Engineering, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Estimating Low-Bias Frequency Response Using Random Decrement2011In: Modal Analysis Topics, Volume 3: Proceedings of the 29th IMAC, A Conference on Structural Dynamics, 2011, Springer, 2011, Vol. 3, 497-502 p.Conference paper (Refereed)
    Abstract [en]

    It is well known that in order to minimize the influence of leakage bias in frequency response function (FRF) estimates, smooth windows should be applied in the FFT processing. It is also normal practice to use self windowing excitation signals whenever possible. However, in many cases FRFs have to be estimated on systems where the excitation signal cannot be altered. Since random data can be compressed in a random decrement function, and since this procedure introduces a natural window, using this technique significantly reduces the influence of leakage bias, and thus, can be used as an alternative to Welch based estimates in cases where the signals involved are random. This means that almost bias-free FRF estimates can be obtained from stationary random excitation. In the paper it is shown how the random decrement technique can be applied to process the time series, and the level of bias on the FRF is estimated and compared to normal Welch based FRF estimates.

  • 47.
    Brincker, Rune
    et al.
    University of Southern Denmark, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    FFT Integration of Time Series Using an Overlap-add Technique2010In: Structural Dynamics, Volume 3: Proceedings of the 28th IMAC, A Conference on Structural Dynamics, 2010 / [ed] Tom Proulx, Springer, 2010, Vol. 3, 1467-1474 p.Conference paper (Refereed)
    Abstract [en]

    Many times in vibration problems it is of importance to be able to integrate signals. Well known cases are Operational Deflection Shapes and earth quake problems where the displacements often need to be estimated from acceleration time series. When digital signals are integrated some classical problems arise; one of these is numerical noise introduced by the inaccurate integration algorithms resulting in large errors in the low frequency region leading to large DC drift. These problems are normally dealt with by using high pass filters that often introduce additional implementation problems like instability and amplitude/phase distorting problems. In this paper an FFT based procedure is introduced.

  • 48.
    Brincker, Rune
    et al.
    University of Southern Denmark, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Random Decrement Signal Processing of Modal Impact Test Data2010In: Structural Dynamics, Volume 3: Proceedings of the 28th IMAC, A Conference on Structural Dynamics, 2010 / [ed] Tom Proulx, Springer, 2010, Vol. 3, 1453-1459 p.Conference paper (Refereed)
    Abstract [en]

    When performing modal impact tests on mechanical systems many practioners utilize hardware based digital signal processors to rapidly estimate average spectral properties from a set of repeated impact and response time traces. However, if the complete set of time traces is saved as is commonly done when performing impact tests on civil structures then more generalized analysis and triggering conditions can be used to process the dataset. One such more general triggering condition can be referred to as random decrement signal processing. In this paper it is explained and illustrated how random decrement signal processing can be used to accept double hit impact and overlapping responses and it is shown that in many cases, the estimated transfer function are estimated with higher accuracy then using traditional triggering/averaging techniques.

  • 49.
    Brincker, Rune
    et al.
    Aarhus School of Engineering, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Time Synchronization by Modal Correlation2011In: 4th International Operational Modal Analysis Conference (IOMAC), Istanbul, Turkey, May 9-11, 2011, International Operational Modal Analysis Conference (IOMAC) , 2011Conference paper (Refereed)
    Abstract [en]

    It is often difficult to synchronize OMA sensors when the distance between sensors is large. Sometimes GPS can be used for synchronization, but not always since GPS require visibility of a certain number of satellites. Other times cables or radio signals can be used, however, in some cases a direct synchronization is difficult or impossible. The focus of this paper is on synchronizing sensors by using the modal response of the considered structure. The technique assumes that only a single mode is present in the signal, and that the phase relationship between the different measurement points is known. The background for the technique is introduced and it is illustrated on response data from the Great Belt Bridge.

  • 50.
    Brincker, Rune
    et al.
    University of Southern Denmark, Denmark.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Bolton, Bob
    University of Southern Denmark, Denmark.
    Calibration and Processing of Geophone Signals for Structural Vibration Measurements2010In: Structural Dynamics, Volume 3: Proceedings of the 28th IMAC, A Conference on Structural Dynamics, 2010 / [ed] Tom Proulx, Springer, 2010, Vol. 3, 1375-1379 p.Conference paper (Refereed)
    Abstract [en]

    Geophones are highly sensitive motion transducers that have been used by seismologists and geophysicists for decades. The conventional geophone's ratio of cost to performance, including noise, linearity and dynamic range is unmatched by advanced modern accelerometers. However, the problem of this sensor is that it measures velocity, and that the linear frequency range is limited to frequencies above the natural frequency, typically at 4-12 Hz. In this paper an instrument is presented based on geophone technology. The sensor is aimed at low vibration level measurements on large civil structures, thus the problem of correcting the bad frequency response becomes essential. The instrument is based on a digitally wired system principle where time synchronization is obtained by GPS, and a good frequency response is secured by calibration and subsequent correction using inverse filtering techniques.

12 1 - 50 of 72
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