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Numrering	Referens	Omslagsbild	Hitta
1.	Boij, Susann, et al. (författare) Reflection of sound at area expansions in a flow duct 2003 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 260:3, s. 477-498 Tidskriftsartikel (refereegranskat)abstract An analytical model for scattering at area discontinuities and sharp edges in flow ducts and pipes is presented. The application we have in mind is large industrial duct systems, where sound attenuation by reactive and absorptive baffle silencers is of great importance. Such devices commonly have a rectangular cross-section, so the model is chosen as two-dimensional. Earlier solutions to this problem are reviewed in the paper. The modelling of the flow conditions downstream of the area expansion, with and without extended edges, and its implications for the resulting acoustic modes are discussed. Here, the scattering problem is solved with the Wiener–Hopf technique, and a Kutta condition is applied at the edge. The solution of the wave equation downstream of the expansion includes hydrodynamic waves, of which one is a growing wave. Theoretical results are compared with experimental data for the reflection coefficient for the plane wave, at frequencies below the cut-on for higher order modes. Influence of the interaction between the sound field and the flow field is discussed. A region where the reflection coefficient is strongly Strouhal number dependent is found.
2.	Byström, Berth-Ove, et al. (författare) Development of artificial hands for use in chain saw vibration measurement 1982 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 82:1, s. 111-117 Tidskriftsartikel (refereegranskat)abstract 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. (författare) The visualization of modes in a circular cochlear model by hologram interferometry 1978 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 59:2, s. 299-303 Tidskriftsartikel (refereegranskat)abstract 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., et al. (författare) Elastic impact between a finite conical rod and a long cylindrical rod 1978 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 60:4, s. 555-563 Tidskriftsartikel (refereegranskat)abstract Elastic impact between a truncated finite conical rod and a long cylindrical rod is studied (i) experimentally, (ii) analytically, by using one-dimensional wave theory to obtain a closed-form solution, and (iii) numerically, by using a three-dimensional axisymmetric finite element model. The results are compared for cones of different lengths but with the same end diameters. The agreement between the results from studies (i) and (iii) is very good in general. As expected, the deviation of the results of study (ii) from those of studies (i) and (iii) becomes increasingly apparent as the slenderness of the cones decreases.
5.	Gupta, R. B. (författare) On optimum hammers and anvils 1982 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 80:2, s. 223-231 Tidskriftsartikel (refereegranskat)abstract 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.
6.	Gustafsson, Göran (författare) Focusing of weak shock waves in a slightly elliptical cavity 1987 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 116:1, s. 137-148 Tidskriftsartikel (refereegranskat)abstract 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.	Knudsen, Jacob, et al. (författare) Dynamic stability of weakly damped oscillators with elastic impacts and wear 2003 Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 263:1, s. 175-204 Tidskriftsartikel (refereegranskat)abstract 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
8.	Lagerkvist, L., et al. (författare) Experimental determination of mechanical impedance through strain measurement on a conical rod 1982 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 85:4, s. 473-481 Tidskriftsartikel (refereegranskat)abstract 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
9.	Lagerkvist, L., et al. (författare) Mechanical impedance gauge based on measurement of strains on a vibrating rod 1982 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 80:3, s. 389-399 Tidskriftsartikel (refereegranskat)abstract 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
10.	Lagerkvist, L., et al. (författare) Mechanical impedance gauge based on measurement of strains on an impacted rod 1983 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 88:2, s. 225-231 Tidskriftsartikel (refereegranskat)abstract 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.
11.	Lundberg, Bengt, et al. (författare) Analysis of elastic waves in non-uniform rods from two-point strain measurement 1990 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 137:3, s. 483-493 Tidskriftsartikel (refereegranskat)abstract 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.
12.	Lundberg, Bengt, et al. (författare) Determination of mechanical material properties from the two-point response of an impacted linearly viscoelastic rod specimen 1988 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 126:1, s. 97-108 Tidskriftsartikel (refereegranskat)abstract 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.
13.	Lundberg, Bengt, et al. (författare) Impacor synthesis 1978 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 58:1, s. 5-14 Tidskriftsartikel (refereegranskat)abstract A method for synthesizing non-uniform, linearly elastic impactors which generate given impact forces on given targets is presented. The impactors are assumed to obey Webster's equation, and the targets are assumed to be linear with time-invariant properties. The method is illustrated by solving two synthesis problems concerned with the generation of exponential and ramp impact loads. The results are verified by solving the corresponding analysis problems.
14.	Matuk, Carlos (författare) Impact of a linearly elastic rod on a thin linearly viscoelastic target 1979 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 64:1, s. 45-55 Tidskriftsartikel (refereegranskat)abstract 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
15.	Ren, L.X. (författare) Experimental study of impact-induced vibrations of a simple viscoelastic column model 1985 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 99:1, s. 17-27 Tidskriftsartikel (refereegranskat)abstract 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
16.	Ren, L.X., et al. (författare) Impact-induced vibrations of a simple viscoelastic column model 1983 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 89:2, s. 261-272 Tidskriftsartikel (refereegranskat)abstract 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
17.	Sundin, Karl-Gustaf (författare) Performance test of a mechanical impedance gauge based on strain measurement on a rod 1985 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 102:2, s. 259-268 Tidskriftsartikel (refereegranskat)abstract 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.
18.	Ögren, Jan-Erik (författare) A Dynamic Ptotoelastic Study of Flexural Wave Generation in a Model of Percussive Drilling 1983 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 86:2, s. 243-252 Tidskriftsartikel (refereegranskat)abstract 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.
19.	Abadikhah, Hossein, 1987, et al. (författare) A hierarchy of dynamic equations for micropolar plates 2015 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 357, s. 427-436 Tidskriftsartikel (refereegranskat)abstract This work considers homogeneous isotropic micropolar plates adopting a power series expansion method in the thickness coordinate. Variationally consistent equations of motion and end boundary conditions are derived in a systematic fashion up to arbitrary order for extensional and flexural displacement cases. The plate equations are asymptotically correct to all studied orders. Numerical results are presented for various orders of the present method, other approximate theories as well as the exact three dimensional theory. The results illustrate that the present approach may render benchmark solutions provided higher order truncations are used, and act as engineering plate equations using low order truncation.
20.	Abadikhah, Hossein, 1987, et al. (författare) A hierarchy of dynamic equations for solid isotropic micropolar circular cylinders 2019 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 440, s. 70-82 Tidskriftsartikel (refereegranskat)abstract This work considers the derivation procedure and evaluation of dynamic equations for isotropic micropolar circular cylinders by adopting a power series expansion method in the radial coordinate. Variationally consistent equations of motion together with pertinent sets of boundary conditions are expressed in a systematic fashion up to arbitrary order. The numerical results cover eigenfrequencies, mode shapes and field distributions over cross sections for axisymmetric and flexural motion adopting different sets of end boundary conditions for equations of different truncation orders of the present method. The results illustrate that the present approach may render benchmark solutions provided that higher order equations are used, and act as accurate approximate engineering solution for lower order equations.
21.	Abdeljaber, Osama, et al. (författare) Active vibration control of flexible cantilever plates using piezoelectric materials and artificial neural networks 2016 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 363, s. 33-53 Tidskriftsartikel (refereegranskat)abstract The study presented in this paper introduces a new intelligent methodology to mitigate the vibration response of flexible cantilever plates. The use of the piezoelectric sensor/actuator pairs for active control of plates is discussed. An intelligent neural network based controller is designed to control the optimal voltage applied on the piezoelectric patches. The control technique utilizes a neurocontroller along with a Kalman Filter to compute the appropriate actuator command. The neurocontroller is trained based on an algorithm that incorporates a set of emulator neural networks which are also trained to predict the future response of the cantilever plate. Then, the neurocontroller is evaluated by comparing the uncontrolled and controlled responses under several types of dynamic excitations. It is observed that the neurocontroller reduced the vibration response of the flexible cantilever plate significantly; the results demonstrated the success and robustness of the neurocontroller independent of the type and distribution of the excitation force.
22.	Abdeljaber, Osama, et al. (författare) Optimization of chiral lattice based metastructures for broadband vibration suppression using genetic algorithms 2016 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 369, s. 50-62 Tidskriftsartikel (refereegranskat)abstract One of the major challenges in civil, mechanical, and aerospace engineering is to develop vibration suppression systems with high efficiency and low cost. Recent studies have shown that high damping performance at broadband frequencies can be achieved by incorporating periodic inserts with tunable dynamic properties as internal resonators in structural systems. Structures featuring these kinds of inserts are referred to as metamaterials inspired structures or metastructures. Chiral lattice inserts exhibit unique characteristics such as frequency bandgaps which can be tuned by varying the parameters that define the lattice topology. Recent analytical and experimental investigations have shown that broadband vibration attenuation can be achieved by including chiral lattices as internal resonators in beam-like structures. However, these studies have suggested that the performance of chiral lattice inserts can be maximized by utilizing an efficient optimization technique to obtain the optimal topology of the inserted lattice. In this study, an automated optimization procedure based on a genetic algorithm is applied to obtain the optimal set of parameters that will result in chiral lattice inserts tuned properly to reduce the global vibration levels of a finite-sized beam. Genetic algorithms are considered in this study due to their capability of dealing with complex and insufficiently understood optimization problems. In the optimization process, the basic parameters that govern the geometry of periodic chiral lattices including the number of circular nodes, the thickness of the ligaments, and the characteristic angle are considered. Additionally, a new set of parameters is introduced to enable the optimization process to explore non-periodic chiral designs. Numerical simulations are carried out to demonstrate the efficiency of the optimization process.
23.	Abdeljaber, Osama, et al. (författare) Real-time vibration-based structural damage detection using one-dimensional convolutional neural networks 2017 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 388, s. 154-170 Tidskriftsartikel (refereegranskat)abstract Structural health monitoring (SHM) and vibration-based structural damage detection have been a continuous interest for civil, mechanical and aerospace engineers over the decades. Early and meticulous damage detection has always been one of the principal objectives of SHM applications. The performance of a classical damage detection system predominantly depends on the choice of the features and the classifier. While the fixed and hand-crafted features may either be a sub-optimal choice for a particular structure or fail to achieve the same level of performance on another structure, they usually require a large computation power which may hinder their usage for real-time structural damage detection. This paper presents a novel, fast and accurate structural damage detection system using 1D Convolutional Neural Networks (CNNs) that has an inherent adaptive design to fuse both feature extraction and classification blocks into a single and compact learning body. The proposed method performs vibration-based damage detection and localization of the damage in real-time. The advantage of this approach is its ability to extract optimal damage-sensitive features automatically from the raw acceleration signals. Large-scale experiments conducted on a grandstand simulator revealed an outstanding performance and verified the computational efficiency of the proposed real-time damage detection method.
24.	Afzal, Mohammad, 1987-, et al. (författare) A formulation of the Jacobian matrixfor 3D numerical friction contact model applied to turbine blade shroud contact Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modelling that eciently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for thecalculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3Drelative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite dierence method, with many points at the contact interface. Therefore,it also significantly reduces the overall computation time for the solution of the equations of motion,since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite dierence approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for aperiodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.
25.	Aggestam, Emil, 1992, et al. (författare) Multi-objective optimisation of transition zones between slab track and ballasted track using a genetic algorithm 2019 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 446, s. 91-112 Tidskriftsartikel (refereegranskat)abstract The vertical dynamic vehicle–track interaction in a transition between ballasted track and slab track is simulated in the time domain using an extended state-space vector approach. A complex-valued modal superposition technique is applied for the linear, time-invariant and non-periodic finite element model of the railway track. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. To reduce the risk of long-term degradation of track geometry due to ballast/subgrade settlement, the transition zone is designed to minimise the influence of the track stiffness gradient between the two different track forms. The methodology is demonstrated by minimising the maximum wheel–rail contact force and the maximum pressure between sleeper/panel and foundation, while the selected design variables are distributions of rail pad stiffness and sleeper spacing adjacent to the transition. From the solution of the optimisation problem, non-dominated fronts are obtained illustrating potential for a significant reduction of the dynamic loads. It is shown that the optimised design leads to a more uniform distribution of load on the foundation reducing the risk of differential track settlement. The influences of the length of the transition zone and direction of travel on the maximum dynamic loads are investigated. Prescribed irregularities in longitudinal level may be accounted for but have been neglected in the optimisation as the optimised design would be more influenced by the given irregularity than by the stiffness gradient.
26.	Aidanpää, Jan-Olov, et al. (författare) Periodic and chaotic behaviour of a threshold-limited two-degree-of-freedom system 1993 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 165:2, s. 305-327 Tidskriftsartikel (refereegranskat)abstract 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.
27.	Al-Najjar, Basim, 1954- (författare) Accuracy, effectiveness and improvement of Vibration-based Maintenance in Paper Mills : Case Studies 2000 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 229:2, s. 389-410 Tidskriftsartikel (refereegranskat)abstract Many current vibration-based maintenance (VBM) policies for rolling element bearings do not use as much as possible of their useful lives. Evidence and indications to prolong the bearings’ mean effective lives by using more accurate diagnosis and prognosis are confirmed when faulty bearing installation, faulty machinery design, harsh environmental condition and when a bearing is replaced as soon as its vibration level exceeds the normal. Analysis of data from roller bearings at two paper mills suggests that longer bearing lives can be safely achieved by increasing the accuracy of the vibration data. This paper relates bearing failure modes to the observed vibration spectra and their development patterns over the bearings’ lives. A systematic approach, which describes the objectives and performance of studies in two Swedish paper mills, is presented. Explanations of the mechanisms behind some frequent modes of early failure and ways to avoid them are suggested. It is shown theoretically, and partly confirmed by the analysis of (unfortunately incomplete) data from two paper mills over many years, that accurate prediction of remaining bearing life requires: (a) enough vibration measurements, (b) numerate records of operating conditions, (c) better discrimination between frequencies in the spectrum and (d) correlation of (b) and (c). This is because life prediction depends on precise knowledge of primary, harmonic and side band frequency amplitudes and their development over time. Further, the available data, which are collected from relevant plant activities, can be utilised to perform cyclic improvements in diagnosis, prognosis, experience and economy.
28.	Alberdi-Muniain, Ane, et al. (författare) Direct energy flow measurement in magneto-sensitive vibration isolator systems 2012 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 331:9, s. 1994-2006 Tidskriftsartikel (refereegranskat)abstract The effectiveness of highly nonlinear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber components applied in a vibration isolation system is experimentally investigated by measuring the energy flow into the foundation. The energy flow, including both force and velocity of the foundation, is a suitable measure of the effectiveness of a real vibration isolation system where the foundation is not perfectly rigid. The vibration isolation system in this study consists of a solid aluminium mass supported on four magneto-sensitive rubber components and is excited by an electro-dynamic shaker while applying various excitation signals, amplitudes and positions in the frequency range of 20-200 Hz and using magneto-sensitive components at zero-field and at magnetic saturation. The energy flow through the magneto-sensitive rubber isolators is directly measured by inserting a force transducer below each isolator and an accelerometer on the foundation close to each isolator. This investigation provides novel practical insights into the potential of using magneto-sensitive material isolators in noise and vibration control, including their advantages compared to traditional vibration isolators. Finally, nonlinear features of magneto-sensitive components are experimentally verified.
29.	Albertson, F., et al. (författare) Comparison of different methods to couple nonlinear source descriptions in the time domain to linear system descriptions in the frequency domain - Application to a simple valveless one-cylinder cold engine 2006 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 291:05-mar, s. 963-985 Tidskriftsartikel (refereegranskat)abstract In duct acoustics the fundamental sound generating mechanisms must often be described by nonlinear time domain models. A linear frequency domain model is in many cases sufficient for describing the sound propagation in the connected duct system. This applies both for fluid machines such as IC-engines and compressors and for musical wind instruments. Methods for coupling a nonlinear source description to a linear system description have been proposed by several authors. In this paper some of those methods are compared concerning accuracy, calculation time and the possibility to perform parametric studies. The model problem used is a simple piston-restriction system connected to a linear system with varying complexity. The piston and restriction are considered as the source part and are modelled nonlinearly.
30.	Alenius, Emma, et al. (författare) Large eddy simulations of acoustic-flow interaction at an orifice plate 2015 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 345, s. 162-177 Tidskriftsartikel (refereegranskat)abstract The scattering of plane waves by an orifice plate with a strong bias flow, placed in a circular or square duct, is studied through large eddy simulations and dynamic mode decomposition. The acoustic-flow interaction is illustrated, showing that incoming sound waves at a Strouhal number of 0.43 trigger a strong axisymmetric flow structure in the orifice in the square duct, and interact with a self-sustained axisymmetric oscillation in the circular duct orifice. These structures then generate a strong sound, increasing the acoustic energy at the frequency of the incoming wave. The structure triggered in the square duct is weaker than that present in the circular duct, but stronger than structures triggered by waves at other frequencies. Comparing the scattering matrix with measurements, there is a good agreement. However, the results are found to be sensitive to the inflow, where the self-sustained oscillation in the circular duct simulation is an artefact of an axisymmetric, undisturbed inflow. This illustrates a problem with using an undisturbed inflow for studying vortex-sound effects, and can be of interest when considering musical instruments, where the aim is to get maximum amplification of specific tones. Further, it illustrates that at the frequency where an amplification of acoustic energy is found for the orifice plate, the flow has a natural instability, which is suppressed by non-axisymmetry and incoming disturbances.
31.	Allam, Sabry, et al. (författare) Acoustic modelling and testing of diesel particulate filters 2005 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 288:02-jan, s. 255-273 Tidskriftsartikel (refereegranskat)abstract The use of Diesel Particulate Filters (DPFs) on automobiles to reduce the harmful effects of diesel exhaust gases is becoming a standard in many countries. Although the main purpose of a DPF is to reduce harmful emission of soot particles it also affects the acoustic emission. This paper presents a first attempt to describe the acoustic behavior of DPFs and to present models which allow the acoustic two-port to be calculated. The simplest model neglects wave propagation and treats the filter as an equivalent acoustic resistance modeled via a lumped impedance element. This simple model gives a constant frequency-independent transmission loss and agrees within I dB with measured data on a typical filter (length 250 mm) up to 200-300 Hz (at 20 degrees C). In the second model, the ceramic filter monolith is described as a system of coupled porous channels carrying plane waves. The coupling between the channels through the porous walls is described via Darcy's law. This model gives a frequency-dependent transmission loss and agrees well with measured data in the entire plane wave range.
32.	Allam, Sabry, et al. (författare) Investigation of damping and radiation using full plane wave decomposition in ducts 2006 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 292:05-mar, s. 519-534 Tidskriftsartikel (refereegranskat)abstract A general plane wave decomposition procedure that determines both the wave amplitudes (or the reflection coefficient) and the wavenumbers is proposed for in-duct measurements. To improve the quality of the procedure, overdetermi nation and a nonlinear least-squares procedure is used. The procedure has been tested using a six microphone array, and used for accurate measurements of the radiation from an open unflanged pipe with flow. The experimental results for the reflection coefficient magnitude and the end correction have been compared with the theory of Munt. The agreement is very good if the maximum speed rather than the average is used to compare measurements and theory. This result is the first complete experimental validation of the theory of Munt [Acoustic transmission properties of a jet pipe with subsonic jet flow, 1: the cold jet reflection coefficient, Journal of Sound and Vibration 142(3) (1990) 413-436]. The damping of the plane wave (the imaginary part of the wavenumber) could also be obtained from the experimental data. It is found that the damping increases strongly, compared with the damping for a quiescent fluid.. when the acoustic boundary layer becomes thicker than the viscous sublayer. This finding is in agreement with a few earlier measurements and is also in agreement with a theoretical model proposed by Howe [The damping of sound by wall turbulent sheer layers, Journal of Acoustic Society, of America 98(3) (1995) 1723-17301. The results reported here are the first experimental verifications of Howe's model. It is found that the model works well typically up to a normalized acoustic boundary layer thickness delta(+)(A) of 30-40. For values of A a delta(+)(A) less than 10, corresponding to higher frequencies or lower flow speeds, the model proposed by Dokumaci [A note on A transmission of sound in a wide pipe with mean flow and viscothermal attenuation, Journal of Sound and Vibration 208(4) (1997) 653-655] is also in good agreement with the experimental data.
33.	Allam, Sabry, et al. (författare) Sound propagation in an array of narrow porous channels with application to diesel particulate filters 2006 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 291:05-mar, s. 882-901 Tidskriftsartikel (refereegranskat)abstract In an earlier work the authors have presented a 1-D acoustic model for diesel particulate filters (DPFs). One shortcoming of this first model is the approximate treatment of the viscous and thermal losses along the narrow channels. In the present paper this issue is analyzed in more detail, by solving the convective acoustic wave equations for two neighboring channels simplified in the manner of the Zwikker and Kosten theory. From the solution the acoustic two-port has been calculated to predict the sound transmission losses for an entire DPF unit. The theoretical results are compared with experimental data for clean filter units at room temperature and the agreement is very good and better, in particular for very small Mach numbers, than for the earlier presented 1-D model. A modified 1-D model using the classical (exact) Kirchhoff solution for a plane wave in a narrow tube is also presented. This modified 1-D model is in close agreement with the predictions of the new model. Furthermore, the earlier proposed 1-D model, which assumes isothermal sound propagation, works satisfactorily up to 800-1000Hz for a typical filter at operating (hot) conditions.
34.	Alvelid, Magnus, 1962 (författare) Optimal position and shape of applied damping material 2008 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 310:4-5, s. 947-965 Tidskriftsartikel (refereegranskat)abstract The frequency averaged transverse vibration levels of a plate with a harmonic excitation is minimized by optimizing the position and shape of attached passive constrained layer damping. A modified gradient method is used in the finite-element context to successively add pieces of constrained damping layers at the elemental positions showing the steepest gradient of the goal function as a result of the treatment. The coding is done in MATLAB and different stop conditions can be included so as to set limits for the cost or weight that can be spent on the treatment of the structure. It is demonstrated that for a square plate, only a few iterations are needed to reduce the average vibration level with up to 18 dB by covering less than 30 percent of the surface with a sandwich type applied damping material. For an industrial example, measurements show that the solution proposed by the optimization procedure will decrease the vibration levels for the two dominant modes of vibrations with 3-4 dB, by covering 3.4 percent of the surface with a single-sided constraining layer type applied damping material. (C) 2007 Elsevier Ltd. All rights reserved.
35.	Ashwear, Nasseradeen, 1968-, et al. (författare) Reducing effects from environmental temperature on the natural frequencies of tensegrity structures 2024 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. Tidskriftsartikel (populärvet., debatt m.m.)abstract n vibration health monitoring, dynamic properties such as natural frequencies and mode shapes are used as tools for assessing the structures health condition.~They are, however, also affected by environmental conditions like wind, humidity and temperature changes. Of particular importance is the change of the environmental temperature, and it is the most commonly considered environmental variable that influences the vibration health monitoring algorithms.~This paper discusses how the tensegrity structures can be designed such that some of their lowest natural frequencies are less sensitive to the temperature changes. A genetic algorithm is used to solve the optimization problem. In the form-finding stage, an asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution, particularly when a symmetric self-stress vector is chosen.
36.	Avci, Onur, et al. (författare) Wireless and real-time structural damage detection : a novel decentralized method for wireless sensor networks 2018 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 424, s. 158-172 Tidskriftsartikel (refereegranskat)abstract Being an alternative to conventional wired sensors, wireless sensor networks (WSNs) are extensively used in Structural Health Monitoring (SHM) applications. Most of the Structural Damage Detection (SDD) approaches available in the SHM literature are centralized as they require transferring data from all sensors within the network to a single processing unit to evaluate the structural condition. These methods are found predominantly feasible for wired SHM systems; however, transmission and synchronization of huge data sets in WSNs has been found to be arduous. As such, the application of centralized methods with WSNs has been a challenge for engineers. In this paper, the authors are presenting a novel application of 1D Convolutional Neural Networks (1D CNNs) on WSNs for SDD purposes. The SDD is successfully performed completely wireless and real-time under ambient conditions. As a result of this, a decentralized damage detection method suitable for wireless SHM systems is proposed. The proposed method is based on 1D CNNs and it involves training an individual 1D CNN for each wireless sensor in the network in a format where each CNN is assigned to process the locally-available data only, eliminating the need for data transmission and synchronization. The proposed damage detection method operates directly on the raw ambient vibration condition signals without any filtering or preprocessing. Moreover, the proposed approach requires minimal computational time and power since 1D CNNs merge both feature extraction and classification tasks into a single learning block. This ability is prevailingly cost-effective and evidently practical in WSNs considering the hardware systems have been occasionally reported to suffer from limited power supply in these networks. To display the capability and verify the success of the proposed method, large-scale experiments conducted on a laboratory structure equipped with a state-of-the-art WSN are reported.
37.	Backström, Daniel, et al. (författare) Modelling the vibration of sandwich beams using frequency dependent parameters 2007 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 300:3-5, s. 589-611 Tidskriftsartikel (refereegranskat)abstract Various types of sandwich beams with foam or honeycomb cores are currently used in the industry, indicating the need for simple methods describing the dynamics of these complex structures. By implementing frequency-dependent parameters, the vibration of sandwich composite beams can be approximated using simple fourth-order beam theory. A higher-order sandwich beam model is utilized in order to obtain estimates of the frequency-dependent bending stiffness and shear modulus of the equivalent Bernoulli-Euler and Timoshenko models. The resulting predicted eigenfrequencies and transfer accellerance functions are compared to the data obtained from the higher-order model and from measurements.
38.	Bengtsson, Johanna, 1974, et al. (författare) Evaluations of effects due to low-frequency noise in a low demanding work situation 2004 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 278:1-2, s. 83-99 Tidskriftsartikel (refereegranskat)abstract Noise sources with a dominating content of low frequencies (20-200 Hz) are found in many occupational environments. This study aimed to evaluate effects of moderate levels of low-frequency noise on attention, tiredness and motivation in a low demanding work situation. Two ventilation noises at the same A-weighted sound pressure level of 45 dB were used: one of a low-frequency character and one of a flat frequency character (reference noise). Thirty-eight female subjects worked with six performance tasks for 4 h in the noises in a between-subject design. Most of the tasks were monotonous and routine in character. Subjective reports were collected using questionnaires and cortisol levels were measured in saliva. The major finding in this study was that low-frequency noise negatively influenced performance on two tasks sensitive to reduced attention and on a proof-reading task. Performances of tasks aimed at evaluating motivation were not significantly affected. The difference in work performance was not reflected by the subjective reports. No effect of noise was found on subjective stress or cortisol levels.
39.	Berggren, Eric, et al. (författare) Identification of Substructure Properties of Railway Tracks by Dynamic Stiffness Measurements and Simulations 2010 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:19, s. 3999-4016 Tidskriftsartikel (refereegranskat)abstract A new vehicle has been developed to measure dynamic vertical track stiffness while in motion. This technique allows the resonance behaviour of the track below 50 Hz to be measured. Soft soils like clay and peat are the main causes of resonance below 20 Hz. By means of simulation studies with the software VibTrain, soft soil resonance behaviour may be characterized using a few key parameters originating from track stiffness measurements, such as the minimum phase delay and corresponding frequency of the receptance transfer function. Statistical models are built to relate these key parameters with substructure properties, such as embankment thickness, shear wave velocity and thickness of the soft soil layer using pattern recognition methods. Two case studies are used to show the methodology, and the results are verified using Ground Penetration Radar (GPR) measurements and borehole investigations. Models are also developed from the statistical relationship between GPR-data and stiffness measurements. It is shown that embankment thickness is the easiest quantity to estimate, but indicative results are also presented for the other quantities (shear wave velocity and thickness of soil layer).
40.	Besselink, Bart, et al. (författare) A comparison of model reduction techniques from structural dynamics, numerical mathematics and systems and control 2013 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:19, s. 4403-4422 Forskningsöversikt (refereegranskat)abstract In this paper, popular model reduction techniques from the fields of structural dynamics, numerical mathematics and systems and control are reviewed and compared. The motivation for such a comparison stems from the fact that the model reduction techniques in these fields have been developed fairly independently. In addition, the insight obtained by the comparison allows for making a motivated choice for a particular model reduction technique, on the basis of the desired objectives and properties of the model reduction problem. In particular, a detailed review is given on mode displacement techniques, moment matching methods and balanced truncation, whereas important extensions are outlined briefly. In addition, a qualitative comparison of these methods is presented, hereby focusing both on theoretical and computational aspects. Finally, the differences are illustrated on a quantitative level by means of application of the model reduction techniques to a common example.
41.	Billger, Dag V. J., 1969, et al. (författare) The imbedding equations for the Timoshenko beam 1998 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 209, s. 609-634 Tidskriftsartikel (refereegranskat)abstract Wave reflection in a Timoshenko beam is treated, using wave splitting and the imbedding technique. The beam is assumed to be inhomogeneous and restrained by a viscoelastic suspension. The viscoelasticity is characterized by constitutive relations that involve the past history of deflection and rotation of the beam through memory functions of the suspension. By applying wave splitting, the propagating fields are decomposed into left- and right-moving parts. An integral representation of the split fields in impulse responses is presented. This representation gives the reflected and transmitted fields as convolutions of the incident field with the reflection and transmission kernels, respectively. The kernels are independent of the incident field and depend only on the material properties. Invariant imbedding is used to obtain equations for these kernels. In general, the kernels contain discontinuities for which transport equations are derived and solved. Some numerical solutions are presented for the reflection by a homogeneous beam suspended on two separated, semi-infinite layers of continuously distributed, viscoelastically damped, local acting springs.
42.	Birgersson, F., et al. (författare) A spectral super element for modelling of plate vibration. Part 1 : general theory 2005 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 287:02-jan, s. 297-314 Tidskriftsartikel (refereegranskat)abstract The dynamic response of vibrating structures is studied with a proposed merger of the standard finite element method with the more computationally efficient spectral finite element method. First a plate structure is modelled with a newly developed spectral super element. Then this element is coupled to other parts that can have a more complex geometry and are modelled entirely with conventional finite elements. Some numerical examples are given to illustrate and validate the developed method and studies of numerical stability are also presented. In an accompanying paper the predicted and measured response of a turbulence excited aircraft panel are compared.
43.	Birgersson, F., et al. (författare) A spectral super element for modelling of plate vibration. Part 2 : turbulence excitation 2005 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 287:02-jan, s. 315-328 Tidskriftsartikel (refereegranskat)abstract In the accompanying paper, the suitability of a spectral super element to predict the response to point force excitation, was demonstrated. This paper expands the element formulation to also include distributed forces, which is useful when studying distributed excitation. First the sensitivity function, i.e. the structural response to a travelling pressure wave, is found. This sensitivity function and a wavenumber frequency description of the wall pressure are then used to predict the response of a turbulence excited panel in a numerically efficient way. The predictions were validated by a conventional finite element method and also compared to measurements.
44.	Birgersson, F., et al. (författare) Application of the spectral finite element method to turbulent boundary layer induced vibration of plates 2003 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 259:4, s. 873-891 Tidskriftsartikel (refereegranskat)abstract The spectral finite element method and equally the dynamic stiffness method use exponential functions as basis functions. Thus it is possible to find exact solutions to the homogeneous equations of motion for simple rod, beam, plate and shell structures. Normally, this restricts the analysis to elements where the excitation is at the element ends. This study removes the restriction for distributed excitation, that in particular has an exponential spatial dependence, by the inclusion of the particular solution in the set of basis functions. These elementary solutions, in turn, build up the solution for an arbitrary homogeneous random excitation. A numerical implementation for the vibration of a plate, excited by a turbulent boundary layer flow, is presented. The results compare favourably with results from conventional modal analysis.
45.	Birgersson, Fredrik, et al. (författare) Application of the spectral finite element method to turbulent boundary layer induced vibrations of plates 2003 Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 259, s. 873-891 Tidskriftsartikel (refereegranskat)
46.	Birgersson, F., et al. (författare) Modelling turbulence-induced vibration of pipes with a spectral finite element method 2004 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 278:05-apr, s. 749-772 Tidskriftsartikel (refereegranskat)abstract The vibration of pipes is studied here using the Arnold-Warburton theory for thin shells and a simplified theory valid in a lower frequency regime. The vibrational response is described numerically with the spectral finite element method (SFEM), which uses the exact solutions of the equations of motion as basis functions. For turbulence excitation, the set of basis functions was extended to include particular solutions, which model a spatially distributed excitation. An efficient numerical solution to homogeneous random excitation is presented and the results compare favourably with wind tunnel measurements.
47.	Blom, Peter, et al. (författare) A non-linear constitutive audio frequency magneto-sensitive rubber model including amplitude, frequency and magnetic field dependence. 2011 Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:5, s. 947-954 Tidskriftsartikel (refereegranskat)abstract A novel constitutive model of magneto-sensitive rubber in the audible frequency range is presented. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. Prior to creating the model assumptions based on experimental observations concerning these components are formulated. The first observation is that not only does the rubber display a strong amplitude dependence even for small strains, but also the magnetic sensitivity is strongly amplitude dependent. The second and third are, respectively, that the elastic component is magneto-sensitive, whereas the viscoelastic dependence on magnetic induction appears to be small. Thus, the model is developed from these assumptions and parameters are optimized with respect to experimental values for one case and subsequently validated for others; a very good agreement is obtained.
48.	Boden, Hans, et al. (författare) Aeroacoustic research in Europe : the CEAS-ASC report on 1999 highlights 2000 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 237:3, s. 477-482 Tidskriftsartikel (refereegranskat)abstract This paper is a report on the highlights of aeroacoustics research and development in Europe in 1999, compiled from the information provided to the Aeroacoustics Specialists Committee (ASC) of the Confederation of European Aerospace Societies (CEAS). CEAS presently comprises the national Aerospace Societies of France (AAAF), Germany (DGLR), Italy (AIDAA), The Netherlands (NVvL), Spain (AIAE), Sweden (FTEF), Switzerland (SVFW) and the United Kingdom (RaeS).
49.	Bodén, Hans, et al. (författare) Aeroacoustics research in Europe : The CEAS-ASC report on 2012 highlights 2013 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:25, s. 6617-6636 Forskningsöversikt (refereegranskat)abstract The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.
50.	Boden, Hans, et al. (författare) Linearity tests for in-duct acoustic one-port sources 2000 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 237:1, s. 45-65 Tidskriftsartikel (refereegranskat)abstract Acoustic one-port source data are commonly used to predict the plane wave sound generation in duct and pipe systems connected to fluid machines. The source data are usually determined experimentally, which assumes that linear time-invariant system theory can be used. Since some machines such as IC-engines and compressors generate very high sound levels in the connecting ducts or pipes it is of interest to investigate whether the assumption of linearity is justified. Linearity tests for linear system identification when both input and output signals can be measured are common in the literature. In the case when only the output signal can be measured linearity tests are not so readily found. This paper presents two different linearity coefficients for determining whether an acoustic one-port source under test is linear. Their sensitivity to random noise and their ability to detect non-linearities are investigated by simulations and measurements on several types of machines.

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