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  • 1.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gupta, R.B.
    Periodic and chaotic behaviour of a threshold-limited two-degree-of-freedom system1993Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 165, nr 2, s. 305-327Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-degree-of-freedom impact oscillator with proportional damping is considered. The maximum displacement of one of the masses is limited to a threshold value by a rigid wall, which gives rise to a non-linearity in the system. Impacts between the mass and the wall are described by a coefficient of restitution. The behaviour of the system is rich and includes features like period doublings, period havings, jumps, chaos, etc. Periodic motions of the system are studied by analytical methods. The influence of system parameters such as damping, coefficient of restitution, distribution of masses and clearance, etc., is studied for some extreme values of these parameters. The stability of a class of periodic motions is investigated. Parameter ranges which result in stable periodic multiple impacts are identified. Application of the results to the design of impact tools is discussed.

  • 2.
    Byström, Berth-Ove
    et al.
    Luleå tekniska universitet.
    Nilsson, Anders
    Luleå tekniska universitet.
    Olsson, Erland
    Luleå tekniska universitet.
    Development of artificial hands for use in chain saw vibration measurement1982Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 82, nr 1, s. 111-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamic properties of the human hand were measured in the laboratory. The results were compared with those obtained by others and used to test three different hand model ideas. One of these was further developed and designed to fit in a test rig. Measurements were made on chain saws in the rig during cutting and with the chain running free. The results are compared to similar measurements on hand held chain saws. The hand model test results show good agreement with the hand held measurements but have much better repeatability.

  • 3.
    Edlund, G.
    et al.
    Luleå tekniska universitet.
    Wikander, G.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The visualization of modes in a circular cochlear model by hologram interferometry1978Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 59, nr 22, s. 299-303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work has been carried out to study the possibilities of using hologram interferometry to examine the mechanical behavior of the inner ear. The purpose was to make a model of the cochlea with a curved and stiff basilar membrane and to look for both travelling wave and standing wave patterns. The level of excitation is approximately the same as found in actual hearing when scaled to model dimensions and hence much lower than in most previous model studies. Also in contrast to previous studies, curvature effects are investigated

  • 4.
    Gupta, R. B.
    Luleå tekniska universitet.
    On optimum hammers and anvils1982Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 80, nr 2, s. 223-231Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Longitudinal elastic impact between a hammer and an anvil is studied with regard to maximizing the peak value of the impact force. For a given hammer, an appropriately chosen elastic anvil can generate a "maximax" impact force which is greater than the corresponding value for a rigid anvil. The improvements can be up to 50% for a class of hammer-anvil combinations. Such optimum combinations are determined for long, cylindrical hammers and finite conical anvils.

  • 5.
    Gupta, R.B.
    et al.
    Luleå tekniska universitet.
    Nilsson, L.
    Chalmers University of Technology.
    Elastic impact between a finite conical rod and a long cylindrical rod1978Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 60, nr 4, s. 555-563Artikel i tidskrift (Refereegranskat)
  • 6.
    Gustafsson, Göran
    Luleå tekniska universitet.
    Focusing of weak shock waves in a slightly elliptical cavity1987Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 116, nr 1, s. 137-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents theoretical work on the wave motion in an elliptical water jet generator. Such a device consists of a water filled elliptical cavity in which a shock wave is induced at one focus by a spark discharge. The shock converges to the other focus and via a convergent duct is allowed to reflect off a free surface of the liquid at the front of a nozzle, whereby a jet is emitted. The initial value problem of how a weak shock develops and how it is reflected from the walls of a cavity with small eccentricity is studied by using acoustic theory and a perturbation technique. In order to account for the distensibility of the wall material its admittance is introduced as a parameter. The validity of the results is extended to larger eccentricities by use of Padé approximants and by comparison with a geometrical acoustics solution to the same problem. The implications of the results on the design of the water jet generator are indicated.

  • 7.
    Gustavsson, Rolf K.
    et al.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The influence of nonlinear magnetic pull on hydropower generator rotors2006Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 297, nr 3-5, s. 551-562Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In large electrical machines the electromagnetic forces can in some situations have a strong influence on the rotor dynamics. One such case is when the rotor is eccentrically displaced in the generator bore. A strong unbalanced magnetic pull will then appear in the direction of the smallest air-gap. In this paper, the influence of nonlinear magnetic pull is studied for a hydropower generator where the generator spider hub does not coincide with the centre of the generator rim. The generator model consists of a four-degree-of-freedom rigid body, which is connected to an elastic shaft supported by isotropic bearings. The influence of magnetic pull is calculated for the case when the generator spider hub deviates from the centre of the generator rim. A nonlinear model of the magnetic pull is introduced to the model by radial forces and transverse moments. In the numerical analysis input parameters typical for a 70 MW hydropower generator are used. Results are presented in stability and response diagrams. The results show that this type of rotor configuration can in some cases become unstable. Therefore, it is important to consider the distance between the centreline of generator spider hub and the centreline of generator rim

  • 8.
    Hosseini-Hashemi, Sh.
    et al.
    School of Mechanical Engineering, Iran University of Science and Technology, Narmak.
    Rezaee, V.
    School of Mechanical Engineering, Iran University of Science and Technology, Narmak.
    Atashipour, Seyed Rasoul
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Accurate free vibration analysis of thick laminated circular plates with attached rigid core2012Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, nr 25, s. 5581-5596Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper deals with the free vibration behavior of laminated transversely isotropic circular plates with axisymmetric rigid core attached at the center. The governing equations of motion are obtained based on Mindlin's first-order shear deformation plate theory. Two possible categories of vibration modes related to up-down translation of the core and wobbly rotation of the core about a diameter are studied. Accurate natural frequencies hitherto not reported in the literature are presented for a wide range of thickness-to-radius ratio, inner-to-outer radius ratio, mass and moment of inertia ratios of the core and various boundary conditions at the outer edge of the plate. Numerical results are compared with those of a three-dimensional finite element method (3-D FEM) to demonstrate the high accuracy and reliability of the current analysis.

  • 9.
    Isaksson, Anna
    et al.
    Luleå tekniska universitet.
    Saldner, Henrik
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Influence of enclosed air on vibration modes of a shell structure1995Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 187, nr 3, s. 451-466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments show that enclosed air in a thin walled structure affects some modes of vibration significantly. Air coupling between vibrating sides of the structure cannot (always) be neglected and frequencies cannot be predicted if calculations are performed as if in a vacuum. As a first attempt to include the enclosed air in a FE model of a violin body, the elastic properties of the air are modelled as a set of one dimensional non-interacting elastic members (columns of air) connecting opposite sides of the orthotropic shell structure. This admittedly oversimplified (but easy to formulate) model must be used with great care, since it neglects the three-dimensional wave behaviour of the enclosed air. A lower limit of allowed frequencies is that which corresponds to a wavelength in air which is much greater than a characteristic length of the object. For the violin this lower limit is less than about 600 Hz. Optical modal analysis of the real, physical, violin model has been performed by using electronic holography. Calculated modes of vibration are compared with experimental ones. For the lowest eigenmodes a good agreement between measured and calculated frequencies is reached despite the simple air model used. Modal shapes remain surprisingly unaffected. For some engineering calculations the simple one-dimensional model might be used.

  • 10.
    Jansson, Ida
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On the notion of a rotating fluid force induced by swirling flow2014Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 333, nr 25, s. 7076-7083Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Bently/Muszynska (B/M) model shows that oil whirl and oil whip are both self-sustained vibrations associated with two unstable modes of a rotor–fluid system. The model includes a rotating fluid damping and inertia force. In certain configurations, the rotating damping force overcomes the frictional internal damping of the rotor and pushes the rotor into a stable limit cycle of circular orbiting. Such a notion of a rotating fluid force is based on bulk-flow models of fluid-filled clearances that could be approximated as narrow since the tangential velocity of the fluid then translates to one angular velocity at a certain radial distance defined by an average radius. This paper scrutinizes the assumption of a rotating fluid inertia force and pinpoints the additional inertial effects of the swirling flow as the gap width increases. These effects are clarified by deriving the equation of motion of a body with a mass subjected to motion-induced fluid forces of a confined swirling flow. We show that the inertial effects of the swirling flow counteract the destabilizing effect of the rotating damping force. However, if the body mass is larger than the displaced fluid mass, instability follows. The frequency of the unstable mode is unchanged by the additional inertial effects and is always equal to the frequency of the damping that induces the instability.

  • 11.
    Jönsson, P.
    et al.
    Luleå tekniska universitet.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Prediction of vehicle discomfort from transient vibrations2005Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 282, nr 3-5, s. 1043-1064Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vehicle manufacturers are continuously seeking to improve vibration comfort. In this paper, subjective responses from transient vibrations in a forklift were analyzed on the basis of ISO 2631-1 and a number of additional variables. The objectives were to define: the effect of different operating conditions and appropriate background variables of subjects on perceived motions; the development of model that describes perceived discomfort as a function of measured vibrations; and important frequencies for prediction of vibration discomfort. The experiment was based on 12 different operating conditions defined by the variables: vehicle speed, obstacle height and load conditions. Eleven professional drivers participated and their responses of overall discomfort were defined by a vector sum of three perceived motions: shaking, for-aft and up-down motions. The evaluation method, maximum transient vibration value as defined in ISO 2631-1 was found to be adequate in predicting vibration discomfort during a four second transient vibration exposure. By analysis of narrow frequency band spectra of vibrations several explanations for the test results are discussed. The best results were obtained using a prediction model based on accelerations in -octave bands of pitch vibrations.

  • 12.
    Karlberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Rotordynamical modelling of a fibre refiner during production2007Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 303, nr 3-5, s. 440-454Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A key component in panel board production is the fibre refiner, whose task is to break cellulose wood chips into slender fibres. This refining process takes place between a rotor and a stator, where a gap of around 0.5 mm is found. In the development of these refiners predicting the dynamics is important; hence, mathematical models are needed. For refiners and other applications like brakes, turbines, and compressors, the interaction between the rotor and the surrounding medium can in many situations be significant. In addition to external load, this interaction can also change the characteristics of the system, which should be considered in the design process. Today, there exists no validated load model for fibre refiner process. Hence, the aim of this paper is to suggest one.Measured axial force data were divided into a constant part and a superimposed oscillating part with different frequencies. For both parts a linear dependence on the gap between the stator and the rotor was assumed. Finally, a four degrees of freedom (dof) model was used to fit a pressure distribution to the axial force model.This process load model led to stiffness and external loads that can be both time dependant. If the pressure distribution only shows a radial variation along the refining zone, all the external loads except the axial one will vanish. The number of functions describing the stiffness parameters also decrease from eight to four. In one case, four stiffness coefficients vanish, whereas the remaining coefficients become constant. This occurs if the process load does not follow the angular vibrations and there is no gap dependence on the oscillating parts of the process load. Numerical simulations showed that by applying a specific process load model, the vibration orbit changed from the unbalance response by means of shape and vibration origin. The unstable domain was further increased when the process load model was applied.Measurements are necessary to select a realistic process model for a specific application. The derived model can be used in product development to choose suitable system parameters and thus to avoid dynamical problems.

  • 13.
    Karlberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Rotordynamical simulations of a fibre refiner during production2011Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 18/19, s. 4460-4473Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A key component in panel board production is the refiner, whose task is to break raw cellulose wood chips into slender fibres, done by a relative angular motion between stator and rotor. The main problem in predicting the dynamics of these machines is to model the complicated fibre breaking process, since the refining process leads to a three-phase flow (solid wood, water and steam) between the stator and rotor. By modelling the rotor as a rigid body, the process can only contribute by a resulting force and a resulting moment. Through this approach and axial force measurements, it has been shown that the refining process can be treated as a time dependent stiffness matrix and external load. The objective for this paper is to predict and explain dynamical characteristics of fibre refiners during production in such a way that the results can be used already at early stages of the product development process. Two different pressure distribution cases are studied, i.e. one axisymmetric with only radial variations and one non-axisymmetric. It is found that the axisymmetric case only excited forward modes, while the non-axisymmetric case excited all modes. The time dependent stiffness matrix resulted in unstable domains, but also in stable domains with intermittent high amplitudes.

  • 14.
    Knudsen, Jacob
    et al.
    Luleå tekniska universitet.
    Massih, Ali R.
    Division of Materials Science, Malmö University.
    Dynamic stability of weakly damped oscillators with elastic impacts and wear2003Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 263, nr 1, s. 175-204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamics of non-linear oscillators comprising of a single-degree-of-freedom system and beams with elastic two-sided amplitude constraints subject to harmonic loads is analyzed. The beams are clamped at one end, and constrained against unilateral contact sites near the other end. The structures are modelled by a Bernoulli-type beam supported by springs using the finite element method. Rayleigh damping is assumed. Symmetric and elastic double-impact motions, both harmonic and sub-harmonic, are studied by way of a Poincaré mapping that relates the states at subsequent impacts. Stability and bifurcation analyses are performed for these motions, and domains of instability are delineated. Impact work rate, which is the rate of energy dissipation to the impacting surfaces, is evaluated and discussed. In addition, an experiment conducted by Moon and Shaw on the vibration of a cantilevered beam with one-sided amplitude constraining stop is modelled. Bifurcation observed in the experiment could be captured

  • 15.
    Knudsen, Jacob
    et al.
    Luleå tekniska universitet.
    Massih, A.R.
    Division of Materials Science, Malmö University.
    Impact oscillations and wear of loosely supported rod subject to harmonic load2004Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 278, nr 4-5, s. 1025-1050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The non-linear dynamic behaviour of a damped rod oscillator with elastic two-sided amplitude constraints is analyzed using finite element method. Symmetric and asymmetric elastic double-impact motions, both harmonic and sub-harmonic, are studied by way of a Poincaré mapping that relates the states at subsequent impacts. It is found that by increasing the forcing frequency (ω) for the beam at a certain frequency a stable period one motion turns into a stable period two motion without bifurcation and subsequently moves to an infinite number of solutions characteristic of chaotic behaviour through a cyclic fold bifurcation. By further increasing ω a series of windows in the bifurcation diagram (impact velocity vs. ω) comprising periodic solutions within the chaotic domain appear. The kinds of bifurcations involved are discussed. Furthermore, impact work-rate of the beam, i.e., the rate of energy dissipation to the impacting surfaces, is calculated. Computations show that the work-rate for asymmetric orbits is substantially higher than for symmetric orbits at or near the same frequency. For the vibro-impacting beam, under conditions that exhibit a stable attractor, calculation of work-rate allows prediction of the "lifetime" of the contacting beam due to fretting-wear damage by extending the stable branch and using the local gap between contacting surfaces as a control parameter

  • 16.
    Lagerkvist, L.
    et al.
    Luleå tekniska universitet.
    Lundberg, Bengt
    Luleå tekniska universitet.
    Mechanical impedance gauge based on measurement of strains on a vibrating rod1982Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 80, nr 3, s. 389-399Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An impedance gage based on measurement of strains at two different cross-sections of a vibrating rod is analyzed and tested. The gage rod, which may have variable characteristic impedance, is in contact with the object at one end and is driven by a harmonic vibrator at the other end. For conical and cylindrical rods explicit relations between point impedance and measured strains are derived. For a cylindrical gage rod of steel with length 800 mm, diameter 10 mm, and distance between strain gages 250 mm a fair agreement was generally obtained between experimental and theoretical point impedances of cylindrical test objects in the frequency range 50 Hz to 1. 7 kHz. Significant improvements in accuracy over that of the tested prototype are expected to be feasible

  • 17. Lagerkvist, L.
    et al.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental determination of mechanical impedance through strain measurement on a conical rod1982Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 85, nr 4, s. 473-481Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An impedance gauge based on measurement of strains at two different cross-sections of a conical gauge rod is tested. The gauge rod is in contact with the object at its narrow end while its wide end is driven by a harmonic vibrator. The length of the gauge rod is 260 mm and its end diameters are 9·8 mm and 20·1 mm. For cylindrical test objects a fair agreement is generally obtained between experimental and theoretical point impedances in the frequency range 50 Hz to 5 kHz. Further improvements in accuracy are expected to be feasible

  • 18.
    Lagerkvist, L.
    et al.
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mechanical impedance gauge based on measurement of strains on an impacted rod1983Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 88, nr 2, s. 225-231Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An impedance gauge based on measurement of strains at two cross-sections of a slender rod is studied. The gauge rod is in contact with the object at one end while it is impacted at the other end. The impedance is evaluated from the two strain signals by means of a two-channel FFT-analyzer and a desk-top computer. Gauge prototypes with cylindrical and conical geometries are tested in the frequency range 50 Hz to 5 kHz for cylindrical objects with known theoretical point impedances. Satisfactory agreement between experimental and theoretical impedances is obtained for both prototypes

  • 19. Ljunggren, Fredrik
    et al.
    Wang, Junye
    Luleå tekniska universitet.
    Ågren, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Human vibration perception from single- and dual-frequency components2007Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 300, nr 1-2, s. 13-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper covers three different studies with respect to human perception of vertical vibrations. Although the amplitudes and frequencies throughout the experiments are set to match those that might occur in lightweight floor constructions, the results can be seen as general. A motion simulator generates signals from 5 to 31.5 Hz and the test subjects receive the vibrations sitting on a wooden chair. In the first study, the absolute threshold values from sinusoidal signals are determined. The results agree reasonably well with those found from other similar studies. In study number two, threshold values are determined in the presence of an 8 Hz base component. The threshold values were generally found to be higher than those obtained in the first study, except in the case of 10 Hz which due to beating effect gave an even lower threshold level than when the signal was played alone. The third study is about annoyance from dual sinusoidal vibrations, always including a base signal of 8 Hz at fixed amplitude. In similarity with study two, test persons reported to be more annoyed as the second signal component gets close to the base frequency and, naturally, they also got more annoyed as the amplitude increased.

  • 20.
    Lundberg, Bengt
    et al.
    Luleå tekniska universitet.
    Blanc, R.H.
    Laboratoire de Mecanique et d'Acoustique.
    Determination of mechanical material properties from the two-point response of an impacted linearly viscoelastic rod specimen1988Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 126, nr 1, s. 97-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theoretical basis is established for a general way of determining mechanical material properties from the measured response to impact at two different cross-sections of a linearly viscoelastic rod specimen. The measured quantities can be either strains or particle velocities. Explicit results are provided for two special cases, the first corresponding to a pre-existing method and the second to a new method. The results obtained under various conditions with the same material are in good agreement. The two methods usefully complement each other as well as other methods in a frequency range of approximately 20 Hz-20 kHz.

  • 21.
    Lundberg, Bengt
    et al.
    Luleå tekniska universitet.
    Carlsson, J.
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Analysis of elastic waves in non-uniform rods from two-point strain measurement1990Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 137, nr 3, s. 483-493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is established which permits evaluation of the histories of normal force and particle velocity at an arbitrary cross-section E of a non-uniform linearly-elastic rod from measured strain histories at two different cross-sections, A and B. Other quantities at E, such as stress, strain, displacement, acceleration and power transmission, can be determined in terms of the evaluated normal force and particle velocity. The method is an extension of that developed by Lundberg and Henchoz for uniform rods. Theoretical results, based on one-dimensional elastic wave theory, are provided for the general case as well as for cases of piecewise constant characteritic impedance. Experimental tests with different configurations of non-uniform rods and strain gauges show that the normal force histories determined at E with the present method (from measured strains at A and B) agree well with those obtained through direct strain measurement at E.

  • 22.
    Lundberg, Bengt
    et al.
    Luleå tekniska universitet.
    Lesser, Martin
    Luleå tekniska universitet.
    Impacor synthesis1978Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 58, nr 1, s. 5-14Artikel i tidskrift (Refereegranskat)
  • 23.
    Lundberg, Bengt
    et al.
    Luleå tekniska universitet.
    Ödeen, Sven
    Luleå tekniska universitet.
    In Situ Determination Of The Complex Modulus From Strain Measurements On An Impacted Structure1993Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 167, nr 3, s. 413-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is proposed for in situ determination of the complex modulus of a member of an impact-loaded structure. The modulus was obtained in terms of strains measured at three different cross-sections of a uniform part of the member, by using one-dimensional theory. The potential of the method was examined for a cylindrical polypropylene bar mounted as a member in each of two simple frame structures, and the modulus was obtained in the frequency range of 500 Hz to 3 kHz. For comparison, the modulus was also determined from tests on the same member, dismounted from the structures, by using a different method based on measurement of end-point accelerations. The results obtained from the in situ tests on the two frame structures and from the tests on the dismounted member are in fair agreement. The larger scatter in the results of the in situ tests is probably explained by a lower signal-to-noise ratio due to the use of strain gauges rather than accelerometers and to differences in excitation.

  • 24.
    Lundström, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Dynamic consequences of electromagnetic pull due to deviations in generator shape2007Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 301, nr 1-2, s. 207-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results from earlier measurements on hydropower generators have indicated relatively large eccentricities and shape deviations in the rotor and stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The UMP force can produce large vibrations which can be dangerous to the machine. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained through the law of energy conservation. The target of the paper is to analyse the dynamics of a generator due to shape deviations in the rotor and stator. As rotor-model, a balanced Jeffcott rotor is used. A linearization of the UMP indicates the importance of considering the nonlinear effects. The stability of some attractors are analysed and the generator dynamics are further investigated by simulating the basin of attraction. The magnitudes are approximately obtained when the shape deviations become dangerous for the generator. It is concluded which shape deviations that are more dangerous than others. In hydropower generator maintenance the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and estimate the stability and robustness by simulations.

  • 25.
    Magnevall, M.
    et al.
    AB Sandvik Coromant, Sandviken.
    Josefsson, A.
    Blekinge Institute of Technology.
    Ahlin, K.
    Blekinge Institute of Technology.
    Broman, Göran
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Nonlinear structural identification by the "Reverse Path" spectral method2012Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 131, nr 4, s. 938-946Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When dealing with nonlinear dynamical systems, it is important to have efficient, accurate and reliable tools for estimating both the linear and nonlinear system parameters from measured data. An approach for nonlinear system identification widely studied in recent years is "Reverse Path". This method is based on broad-band excitation and treats the nonlinear terms as feedback forces acting on an underlying linear system. Parameter estimation is performed in the frequency domain using conventional multiple-input-multiple-output or multiple-input-single-output techniques. This paper presents a generalized approach to apply the method of "Reverse Path" on continuous mechanical systems with multiple nonlinearities. The method requires few spectral calculations and is therefore suitable for use in iterative processes to locate and estimate structural nonlinearities. The proposed method is demonstrated in both simulations and experiments on continuous nonlinear mechanical structures. The results show that the method is effective on both simulated as well as experimental data.

  • 26.
    Matuk, Carlos
    Luleå tekniska universitet.
    Impact of a linearly elastic rod on a thin linearly viscoelastic target1979Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 64, nr 1, s. 45-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of linearly elastic rod on a thin linearly viscoelastic target which rests on a rigid foundation is considered. The behaviour of the target is quasi-static. The special case of a cylindrical linearly elastic rod impacting on a thin Kelvin target is studied in detail and the maximum impact force, the coefficient of restitution and the energy absorption of the target are determined

  • 27.
    Mei, C.
    et al.
    Department of Mechanical Engineering, University of Michigan.
    Mace, B.R.
    Institute of Sound and Vibration Research, University of Southampton.
    Jones, Richard W.
    Luleå tekniska universitet.
    Hybrid wave/mode active vibration control2001Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 247, nr 5, s. 765-784Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A hybrid approach to active vibration control is described in this paper. It combines elements of both wave and mode approaches to active control and is an attempt to improve on the performance of these approaches individually. In the proposed hybrid approach, wave control is first applied at one or more points in the structure. It is designed on the basis of the local behaviour of the structure and is intended to absorb vibrational energy, especially at higher frequencies. Then modal control is applied, being designed on the basis of the modified global equations of motion of the structure-plus-wave controller. These are now normally non-self-adjoint. Since the higher order modes are relatively well damped, hybrid control improves the model accuracy and the robustness of the system and gives better broadband vibration attenuation performance. Hybrid wave/mode active vibration control is described with specific reference to the control of a cantilever beam: The particular case considered is that of collocated, point force/sensor feedback wave control combined with modal control designed using pole placement. Numerical and experimental results are presented

  • 28.
    Ren, L.X.
    Luleå tekniska universitet.
    Experimental study of impact-induced vibrations of a simple viscoelastic column model1985Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 99, nr 1, s. 17-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The longitudinal and transverse displacements of an almost axially impacted two-degree-of-freedom viscoelastic cantilever column model have been determined experimentally. Cases for various ratios of natural frequencies of transverse to longitudinal vibrations and for different small angles of incidence have been investigated. The results obtained are compared with results of theoretical analysis. Good agreement is found

  • 29.
    Ren, L.X.
    et al.
    Luleå tekniska universitet.
    Lundberg, Bengt
    Luleå tekniska universitet.
    Impact-induced vibrations of a simple viscoelastic column model1983Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 89, nr 2, s. 261-272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-degree-of-freedom model for an almost-axially impacted viscoelastic cantilever column is analyzed. The impact load is produced by a mass striking the free end of the column. Under the assumption of small displacements two second-order non-linear ordinary differential equations for the coupled longitudinal and transverse vibrations of the column are derived. In the absence of damping these equations of motion are reduced to Mathieu's equation through the use of a perturbation method. The excitation parameters are (i) the natural frequency of small amplitude transverse vibrations of the undamped column and (ii) the initial velocity of the end of the column

  • 30.
    Runnemalm, Anna
    Luleå tekniska universitet.
    Standing waves in a rectangular sound box recorded by TV holography1999Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 224, nr 4, s. 689-707Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple but informative whole-field method to visualize standing waves in air enclosures is presented. The integrated sound pressure field distribution of standing-wave patterns inside a rectangular, air-filled transparent box is measured using ordinary TV holography (also called ESPI or DSPI). The phase distribution of the sound pressure is measured by using the more complicated, phase-modulated TV holography technique. Standing waves in the box are excited by a loudspeaker. The structural vibration amplitude distribution of the walls of the same box (operational deflection shapes, ODSs) are measured at the same frequencies as the standing waves with the same optical technique. The pressure maps obtained and the corresponding structural ODSs are of great pedagogical value and can be used to verify numerical models, etc. Standing-wave patterns in non-rectangular enclosures, as the sound box of a guitar, illustrates the usefulness of the method.

  • 31.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Lambourg, C.
    Ecole Nationale Supérieure des Télécommunications.
    Chaigne, A.
    Ecole Nationale Supérieure des Télécommunications.
    Transient sound fields from inpacted plates: comparison between numerical simulations and experiments1999Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 221, nr 3, s. 471-190Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A comparison between measured and simulated transient acoustic fields generated by a thin rectangular impacted steel plate is reported. The plate vibration is modelled in the time domain using a finite difference scheme of second-order in time and fourth-order in space (2-4 scheme) and the radiated acoustic pressure is obtained by solving numerically the Rayleigh integral equation by using a simple Boundary Element Method (trapezoidal rule). The simulated results are evaluated in the form of the spatial pressure distribution at times short-after the impact excitation. The measurements are performed using an optical method: pulsed two-reference-beam holographic interferometry. Results in the form of 2-D projections of the acoustic pressure field are obtained and compared with the simulations. A high degree of similarity is found between the measured and simulated sound fields.

  • 32.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Performance test of a mechanical impedance gauge based on strain measurement on a rod1985Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 102, nr 2, s. 259-268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An impedance gauge based on measurement of strains at two cross sections of a slender rod has been tested on practical objects. Sensitive semiconductor strain gauges are used and the impact force necessary for excitation is therefore low. Measurements were conducted with the gauge held in contact with the test objects by hand and excited by light strokes from a hammer. With this technique impedances in the transverse direction of beams were measured in the frequency range 20 Hz to 2 kHz. Similar measurements were also conducted with a conventional impedance head for comparison. From the results of the measurements it is concluded that the performance of the impedance gauge is good under the prevailing experimental conditions.

  • 33.
    Sundin, Karl-Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Åhrström, Bert-Olof
    Method for investigation of frictional properties at impact loading1999Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 222, nr 4, s. 669-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the assessment of lubricant performance and also in various other contact applications it is of importance to know the frictional qualities of a surface. Under quasi-static conditions, normal and frictional forces are measured using force transducers but the task is more difficult when loads are transient. The experimental method presented in this paper is based on the analysis of propagating waves in a beam, due to an impact on the end surface. The impact is oblique and therefore a transverse as well as a normal force is generated. The normal force history is measured from the axial non-dispersive wave using strain gauges. Transverse force and bending moment both generate dispersive flexural waves. From the FFT of two transverse acceleration histories, the frictional force at the end of the rod is evaluated using beam theory. The relation between normal and frictional force histories displays the frictional properties at the impact. Preliminary results are presented

  • 34.
    Wu, L.
    et al.
    Luleå tekniska universitet.
    Ågren, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    A study of the initial decay rate of two-dimensional vibrating structures in relation to estimates of loss factor1997Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 206, nr 5, s. 663-684Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this study was to obtain a better understanding of the process of the initial decay of energy in relation to the estimates of damping loss factor; to investigate the spatial variation of the initial decay rate in order to obtain more reliable estimates of damping loss factor from the decay rate method; and to compare the spatial averages and spatial variation of damping loss factor between the decay rate method and the power input method. The initial decay rate of energy was experimentally investigated on uniform plates. The energy mean free path time was introduced as a factor to characterize the lower limit of a decay interval for fitting an initial decay slope, and to determine the initial point of a decay curve. It is concluded that the initial decay slopes can sometimes be determined within a very short decay interval (e.g., less than 10 dB) provided that the corresponding time interval is larger or much larger than the energy mean free path time. Additionally. the effect of the direct field on the initial decay can be ignored provided that the response point is far enough from the drive point. An analysis of the spatial variation of initial decay rate showed that an increase in the number of modes per band, and light and moderate damping can reduce the spatial variation. High damping may increase the spatial variation. For a frequency band with more modes, fewer response points need to be used to obtain a stable estimation of spatial variance. It was confirmed that the damping loss factor determined from the decay rate method was in general in good agreement with the power input method. The comparison of the spatial variances of damping loss factor between the two methods showed that the decay rate method gives a more reliable estimate of the damping loss factor of the plates. It is concluded that the decay rate method is to be preferred to the power input method when determining the damping loss factor of a system.

  • 35. Xin, Tao
    et al.
    Gao, Liang
    Reducing slab track vibration into bridge using elastic materials in high speed railway2011Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 10, s. 2237-2248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the problem of vibration transmission from slab track structures into bridge is studied by theoretical analysis. A vehicle–track–bridge coupling system dynamics model is established based on a multibody dynamics theory and a finite element method. The system model consists of vehicle model, track–bridge model and wheel/rail interaction model. The vehicle model is established based on the multibody dynamics theory, and the tack–bridge model is established by the finite element method. The vehicle model and track–bridge model are coupled through wheel/rail interaction model, and the track irregularities are included. The system dynamic responses are calculated, and the effectiveness of elastic materials in vibration reducing is discussed. The results demonstrate that elastic materials like slab mat layer inserted between slab track and bridge can reduce vibration transmitted from track into the bridge. Some suggestions for the design and application of slab mat are provided in the end of the paper.

  • 36.
    Ödeen, Sven
    et al.
    Luleå tekniska universitet.
    Lundberg, Bengt
    Determination of complex modulus from measured end-point accelerations of an impacted rod specimen1993Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 165, nr 1, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is presented for determination of the complex modulus of a linearly viscoelastic material from measured end-point accelerations of an impact-loaded rod specimen. An iterative numerical scheme was used. An approximate analytical solution was also established for the case of small accelerometer mass relative to the specimen mass. Tests were carried out at room temperature for polypropylene, with relatively high losses, and polyamide 6, with relatively low losses. Tests were also performed at temperatures between 20 and 140°C for the former material. Valid results were obtained in the approximate frequency range of 400 Hz to 200 kHz with specimen diameters between 11 and 21 mm, and specimen lengths between 200 and 800 mm. For polypropylene these results are in good agreement with those obtained by using a different method developed by Blanc. For polyamide 6, however, there was some disagreement for the imaginary part of the complex modulus. The method was convenient to use at elevated temperatures as well as at room temperature. It should be suitable for fast routine testing of materials provided that the losses are not too low.

  • 37.
    Ögren, Jan-Erik
    Luleå tekniska universitet.
    A Dynamic Ptotoelastic Study of Flexural Wave Generation in a Model of Percussive Drilling1983Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 86, nr 2, s. 243-252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The development of the percussive drilling machine has led to a situation where the drill steel itself has become a major noise source. A qualitative theory for the generation of this noise is presented. In this theory the longitudinal drilling pulse is partially converted to flexural motion by non-symmetric boundary conditions. The technique of stress optics combined with high speed photography is used in conjunction with Araldite models of the drill steel to verify the above conjectures. The models are then used to demonstrate the importance of the clamping conditions in preventing the growth of noise producing motions of the drill steel. It is also shown that the Araldite models give a reasonable representation of the stress wave pattern in a true drill steel, at least for the time period associated with the first few passes of the primary stress wave pattern and its reflexions.

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