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  • 1.
    Albertson, Fredrik
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Acoustic source characterisation for non-linear in-duct sources2001Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Different ways to model acoustic in-duct sources have beenanalysed. Measurements were conducted on two diesel truckengines. It was found that for steady state oscillations, onecould linearise in the neighbourhood of a given linearisationpoint, i.e. engine speed, engine load and acoustic load. A morenon-linear source gave a smaller neighbourhood where thelinearisation was valid in comparison to the correspondingneighbourhood of amore linear source.

    Two different linearity tests have been proposed andanalysed. These tests are to be applied to systems where onlyoutput data is available. A method to increase the sensitivityof the linearity measure was also suggested.

    In order to model an acoustic in-duct source, one has tochoose if the model should be linear, non-linear or hybridlinear / non-linear. Hybrid methods were tested for a simplepiston-restriction system with satisfying results.

    Several of the hybrid methods were then tested and comparedto each other, quantitatively and qualitatively. It was foundthat the harmonic balance method, which is a steady statemethod, and the convolution method with a reflection functionwere the best for the present application. The calculationsconverged toward a solution for both methods in almost allcases. They furthermore gave similar results for the same testcase in the comparison.

    The results from the harmonic balance method were finallycompared to measurements. The accuracy was good in some cases,but worse in other

    A general conclusion from the results presented in thisthesis, would be that it is necessary to use non-linear sourcemodels in several cases. The receiving system could in mostapplications though be kept in the linear frequency domain forpredictions within engineering accuracy. The HBM and theconvolution method provide the coupling in the differentsituations that arise during design processes. Finally, amethodology in how an acoustic in-duct source can be analysedwas presented.

    Keywords:in-duct source, source characterisation,non-linear source, linearity test, hybrid method, IC-engine,muffler, coupling method

  • 2.
    Andersson, Evert
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Haggstrom, J
    Sima, M
    Stichel, Sebastian
    KTH, Tidigare Institutioner, Farkostteknik.
    Assessment of train-overturning risk due to strong cross-winds2004Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 218, nr 3, s. 213-223Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes the methodology for safety assessment related to the risk of a train overturning in strong cross-winds. As an example, this methodology is applied on the high-speed line Botniabanan being built for a maximum speed of 250 km/h in the northeast coastal region of Sweden. The process starts with a systematic identification of locations along the line having a potential high risk of overturning due to cross-winds. This is followed by a cross-disciplinary study. The first step is to estimate the probabilities of wind velocity and wind directions. The next step is aerodynamic computation of overturning forces and moments acting on relevant types of train. Further, the critical overturning wind velocity is determined by a multi-body simulation technique. Finally, the overturning accident frequency is calculated. The calculated risk is compared with generally accepted risk levels in modern train operation.

  • 3.
    Andreasson, Johan
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Laine, L
    Driving Dynamics for Hybrid Electric Vehicles Considering Handling and Control Architecture2004Ingår i: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 41, s. 497-506Artikel i tidskrift (Refereegranskat)
  • 4.
    Andreasson, Johan
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Laine, L
    Fredriksson, J
    Evaluation of a Generic Vehicle Motion Control Architecture2004Ingår i: Proceedings of World AutomotiveCongress FISITA, 2004Konferensbidrag (Refereegranskat)
  • 5. Beardmore, R. E.
    et al.
    Laister, R.
    Peplow, Andrew
    KTH, Tidigare Institutioner, Farkostteknik.
    Trajectories of a DAE near a pseudo-equilibrium2004Ingår i: Nonlinearity, ISSN 0951-7715, E-ISSN 1361-6544, Vol. 17, nr 1, s. 253-279Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a class of differential-algebraic equations (DAEs) defined by analytic nonlinearities and study its singular solutions. The main assumption used is that the linearization of the DAE represents a Kronecker index-2 matrix pencil and that the constraint manifold has a quadratic fold along its singularity. From these assumptions we obtain a normal form for the DAE where the presence of the singularity and its effects on the dynamics of the problem are made explicit in the form of a quasi-linear differential equation. Subsequently, two distinct types of singular points are identified through which there pass exactly two analytic solutions: pseudo-nodes and pseudo-saddles. We also demonstrate that a singular point called a pseudo-node supports an uncountable infinity of solutions which are not analytic in general. Moreover, akin to known results in the literature for DAEs with singular equilibria, a degenerate singularity is found through which there passes one analytic solution such that the singular point in question is contained within a quasi-invariant manifold of solutions. We call this type of singularity a pseudo-centre and it provides not only a manifold of solutions which intersects the singularity, but also a local flow on that manifold which solves the DAE.

  • 6.
    Berg, Mats
    KTH, Tidigare Institutioner, Farkostteknik.
    Understanding wear and profile changes of wheels and rails2004Ingår i: Proceedings of Conference on Advancing Practical Strategies for Wheel/Rail Interface Management, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 7.
    Berglund, Per-Olof
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Investigation of acoustic source characterisation and installation effects for small axial fans2003Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Fans are often used in equipment such as home appliances andelectronic equipment where the margin of profit is small butcustomers demands on a low noise level are high. Therefore,methods for predicting the noise emitted by an applicationincluding one or several fans are desirable in order toimprove, accelerate and reduce the cost of low-noise design.The Noise Shaping Technology (NST) has been developed withinthe EC-project NABUCCO in order to fulfil the aboverequirements on a prediction method. According to NST, thenoise source (not necessary a fan) is described by one orseveral noise descriptors, CSSs, and the correspondingtransmission paths through the structure described by one orseveral transfer functions, ACFs. In this thesis, theapplicability of NST is evaluated on a cabinet for electronicequipment where small axial cooling fans constitute the primarysources of the airborne sound.

    As an axial fan is a complex source of sound,simplifications are necessary when modelling its acousticproperties. Therefore, the sound radiation of an axial fan infree space was examined by expanding the generated soundpressure field into spherical harmonics. The conclusion on asource model for the cabinet example, where the fans are moreor less In-duct mounted, is a modified single axial dipole. Themodel is expected to be valid in the entire frequency range ofinterest except in the mid-frequency range where the modaldensity is low. In order to improve the source model in thisfrequency range, a future model based on a rotating dipole isproposed.

    The sound power of a small axial fan is measured in an ISO10302 test-rig. In order to take account of flow conditions,acoustically transparent ducts have been developed. These shallbe attached to the test-rig when measuring the sound power ofthe fan. A simple but practical method of how to correct thesound power for the baffling effect of the test-rig has alsobeen developed. Finally, the sound power can be converted intodipole force, which is the airborne CSS corresponding to thesingle axial dipole model.

    The corresponding airborne transfer function (ACF), i.e.,from dipole force at the source point to sound pressure at thereceiver point, is measured reciprocally by taking use ofLyamshevs reciprocity relation.

    From multiplication of the CSS and the ACF, the soundpressure can be predicted. The prediction shows quite goodagreement with the measured values.

    Keywords:axial fan, airborne sound, sourcecharacterisation, transmission path analysis, In-duct,spherical harmonics, rotating dipole, installation effects, ISO10302, flow conditions, baffling effect, acousticallytransparent ducts, Lyamshevs reciprocity relation, reciprocity,CSS, ACF, GSM, NST.

  • 8. Birgersson, F.
    et al.
    Ferguson, N. S.
    Finnveden, Svante
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Application of the spectral finite element method to turbulent boundary layer induced vibration of plates2003Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 259, nr 4, s. 873-891Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 9.
    Birgersson, F.
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Finnveden, Svante
    KTH, Tidigare Institutioner, Farkostteknik.
    Robert, G.
    Modelling turbulence-induced vibration of pipes with a spectral finite element method2004Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 278, nr 05-apr, s. 749-772Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 10.
    Blom, Peter
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Kari, Leif
    KTH, Tidigare Institutioner, Farkostteknik.
    Magneto-rheological rubber isolators in the audible frequency range2004Ingår i: Nordic Vibration Research, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 11.
    Boden, Hans
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Albertson, F.
    Linearity tests for in-duct acoustic one-port sources2000Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 237, nr 1, s. 45-65Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 12.
    Boden, Hans
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Sarin, S.
    Aeroacoustic research in Europe: The CEAS-ASC report on 1999 highlights2000Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 237, nr 3, s. 477-482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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).

  • 13.
    Bodén, Hans
    KTH, Tidigare Institutioner, Farkostteknik.
    APPLICATION OF LINEAR ACOUSTIC SOURCE DATA MEASUREMENT TECHNIQUES FOR TRUCK DIESEL ENGINES2004Ingår i: ICSV12-St Petersburg, 2004Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    IC-engines are known from previous studies to be non-linear sources of exhaust system noise. Never the less linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. In this paper results from experiments on truck Diesel engines are presented. A number of different techniques for extracting source data are tested and the linearity and time invariance is investigated. The results show that a linear time-invariant model can provide good results.

  • 14.
    Bodén, Hans
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Tonsa, M.
    AVL.
    Fairbrother, R.
    AVL.
    On extraction of IC-engine linear acoustic source data from non-linear simulations2004Ingår i: ICSV12-St Petersburg, 2004Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These tests are time consuming and expensive. It would therefore be of interest to extract the acoustic source data from existing 1-D CFD codes describing the engine gas exchange process. In this paper a comparison is made between results obtained applying the two-load technique to measurements on a truck Diesel engine and to 1-D CFD simulations of the same engine. The results show that it is possible to obtain reasonably accurate source data estimates from the simulations.

  • 15.
    Boij, Susann
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Nilsson, B.
    Växjö University, School of Mathematics and Systems Engineering, Sweden.
    Reflection of sound at area expansions in a flow duct2003Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 260, nr 3, s. 477-498Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 16.
    Boué, Mathieu
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Outdoor sound propagation under the influence of atmospheric turbulence2003Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 17.
    Carlbom, Pelle
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Carbody and Passengers in Rail Vehicle Dynamics2000Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The carbody plays an important role in rail vehicle dynamics.This thesis aims atdeveloping validated modelling methods tostudy its dynamics, how it is excited on trackand how itinteracts with the passengers. The primary interest is ridecomfort,considering vibrations up to 20 Hz. In this frequencyrange, the structural flexibility ofthe carbody is of majorconcern. The models are intended for use intime-domainsimulation, calling for small-sized models to reducecomputational time and costs. Keyparameters are proposed toselect carbody eigenmodes for inclusion in a flexiblemultibodymodel, and to quantify the interaction between passengers andcarbody.

    Extensive comparisons between measurements and correspondingsimulations arecarried out in a case study. On-track measurementsare performed to obtain operatingdeflection shapes and powerspectral densities of the accelerations in the carbody.Thecomplete vehicle is modelled using the pieces of softwareGENSYS (flexible multibodymodel) and ANSYS (finite element modelof the carbody). Actual, measured trackirregularities are used asinput. In order to investigate the influence of passengerload,experimental modal analysis of the carbody is performed withand without passengers.Also, amplitude dependence is examined.Simple models, based on human-body modelsfrom literature, of thepassenger-carbody system are proposed and validated.Verticalseating dynamics is considered. The models areimplemented and tested in the casestudy. Finally, ideas on modelreduction and approximation are presented and applied.

    The main conclusions drawn from the study are that

        the structural flexibility of the carbody must be takeninto account when predictingvertical vibration comfort. It ispossible to predict which carbody modes that willcontributemost to the vibrations.

        the carbody dynamical properties depend on the excitationamplitude.

        passengers and carbody interact significantly.- theproposed models describe the interaction quite well. Theproposed passenger-carbodymodel gives an upper boundary on theinteraction.

        the proposed passenger-seat-carbody model can be used tostudy the influence of theseat parameters on the interaction.This merits to be investigated further, however.

    Keywords: Carbody, Experimental modal analysis, Human-bodydynamics, Modelreduction, Multibody dynamics, Operatingdeflection shapes, Rail-vehicle dynamics,Ride comfort, Seatingdynamics, Structural dynamics.

  • 18.
    Carlbom, Pelle
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Track-induced structural vibrations in rail vehicle car bodies: modelling, simulation and measurements1998Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 19.
    Carlsson, Martin
    KTH, Tidigare Institutioner, Farkostteknik.
    Aeroelastic model design using an integrated optimization approach2004Ingår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, nr 6, s. 1523-1526Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An elastic wind-tunnel model was designed with an internal carbon fiber/epoxy composite beam as primary structure and with prescribed static and dynamic behavior. The sequential stiffness and mass design approach was used in order to find a design with resonably representative properties. The integrated stiffness and mass design optimization was shown to improve the quality of the model significantly. It was found that the stiffness and frequency objectives did not cause any significant problem, but the mode shape matching was more involved.

  • 20.
    Cederholm, Alex
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Analysis of acoustic reflection and transmission properties of a rubber coated steel plate2001Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 21.
    Chaar, Nizar
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Berg, Mats
    KTH, Tidigare Institutioner, Farkostteknik.
    Experimental and numerical modal analyses of a loco wheelset2004Ingår i: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 41, nr Suppl., s. 597-606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wheelset structural flexibility is believed to have a major influence on the vehicle-track dynamics. Several studies have related the structural flexibility of the wheelset to fluctuations of wheel-rail forces, rail and wheel corrugation, etc. This paper reports part of an ongoing project that studies the effects of wheelset structural flexibility on the vehicle-track dynamics. The paper focuses on experimental and numerical modal analyses of a loco wheelset in the frequency range of 0-500 Hz. Major issues related to modal analyses and modelling of wheelset are presented along with respective results. The results from numerical modal analysis were in good agreement with those obtained from the experiment. In addition, the wheelset had fairly low eigenfrequencies. Reduced versions of the generated wheelset model will be used in coming work in on-track numerical simulations in order to determine the effects of wheelset structural flexibility on the vehicle-track dynamics. Results from these simulations will be validated against existing experimental on-track results.

  • 22.
    Coja, Michael
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Kari, Leif
    KTH, Tidigare Institutioner, Farkostteknik.
    A new computational method based on waveguides for modeling of preload nonlinear effects on cylindrical vibration isolators2004Ingår i: Nordic Seminar on Computational Mechanics, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 23.
    Coja, Michael
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Kari, Leif
    KTH, Tidigare Institutioner, Farkostteknik.
    A self similarity audio-frequency stiffness model of pre-compressed vibration isolators2004Ingår i: Nordic Vibration Research, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 24. Cronander, C.
    et al.
    Ringertz, Ulf
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Closed loop roll control using aeroelastic information2000Ingår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 4, nr 7, s. 481-494Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mathematical model of the rolling dynamics of a flexible wing is derived by experimental measurements and 3D potential flow analysis. Based on the mathematical model which includes one aeroelastic parameter, control laws are designed which almost completely eliminate the problem of reduced aileron efficiency for increasing airspeed. Finally, the control laws are tested on the model in the wind tunnel, and good correlation with computer simulations is achieved, except when a structural mode is excited.

  • 25.
    Dahlberg, Erik
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Commercial vehicle roll and yaw stability1999Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 26.
    Dahlberg, Erik
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Commercial Vehicle Stability - Focusing on Rollover2001Doktorsavhandling, monografi (Övrigt vetenskapligt)
  • 27.
    Dalenbring, Mats
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Methods for experimental estimation of anelastic material properties2001Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 28.
    Dalenbring, Mats
    KTH, Tidigare Institutioner                               , Farkostteknik.
    On experimental material damping estimation based on vibration response models and hybride modal analysis2000Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 29.
    Ekman, Philip
    KTH, Tidigare Institutioner                               , Farkostteknik.
    On the radiation and diffraction of waves from a ship in beam seas at Fn=02001Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 30.
    Elnady, T.
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Bodén, H.
    KTH, Tidigare Institutioner, Farkostteknik.
    Glav, R.
    KTH, Tidigare Institutioner, Farkostteknik.
    Application of the point matching method to model circumferentially segmented non-locally reacting liners2001Ingår i: 7th AIAA/CEAS Aeroacoustics Conference and Exhibit, 2001Konferensbidrag (Refereegranskat)
    Abstract [en]

    Acoustic liners are widely used to attenuate sound waves inside the aircraft jet engines. Previous research has proved that segmenting the liner and the positioning of the liner segments affect the attenuation characteristics of the liner. The combined effect of circumferentially segmented and non-locally reacting liners received little attention. The aim of this work is to investigate these effects, and to compare the properties of circumferentially segmented duct liners with those of uniform liners, in order to identify any potential benefits of circumferentially segmented liners. A new technique is proposed here; the point-matching method. Briefly, it is a straightforward numerical method based on a closed form ansatz, which fulfils the governing equations and is matched to the boundary conditions point-wise. A code, previously developed for automobile applications, is used to obtain the wave numbers of the different modes, from which the transmission loss for each mode can be calculated at the desired range of frequencies. An infinite cylindrical duct of diameter 40 cms was chosen to apply different non-locally (bulk) reacting liner configurations on. It was found that the existence of hard surfaces in a lined duct and their arrangement greatly affect the behavior of each mode and the energy distribution among them.

  • 31.
    Elnady, Tamer
    KTH, Tidigare Institutioner                               , Farkostteknik.
    On the use of liners to reduce aircraft jet engine noise2002Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 32.
    Ericson, Anna
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Ship and cargo models for studying the risk of cargo shiftning in waves2000Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 33. Facian, Amparo
    et al.
    Nilsson, Anders
    KTH, Tidigare Institutioner, Farkostteknik.
    Feng, Leping
    KTH, Tidigare Institutioner, Farkostteknik.
    Nilsson, Eva
    KTH, Tidigare Institutioner, Farkostteknik.
    Propagation of structure-borne sound in silencers used in power plants2004Ingår i: The 11th International Congress on Sound and Vibration, 2004, s. 1069-1076Konferensbidrag (Refereegranskat)
  • 34.
    Feng, Leiping
    KTH, Tidigare Institutioner                               , Farkostteknik.
    An experimental method for vibrational insertion loss of mechanical joints2001Ingår i: Acustica, ISSN 0001-7884, Vol. 87, nr 2, s. 191-198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental method is presented in this paper to determine vibro-acoustic properties of mechanical joints. A new quantity, vibrational insertion loss, which is the vibration reduction introduced by a joint and is used to describe vibro-acoustic performance of a mechanical joint in a finite system, is introduced. Two test-rigs are manufactured and tested for planar and non-planar joints. Results show that for well-defined joints, repeatability and reproducibility of the suggested parameter less than 2 dB can be achieved. Comparisons are also made between the vibrational insertion loss and the vibration level difference. It is illustrated that the vibration level difference can only detect the change of modal behaviour of the system, while the vibrational insertion loss can be used to detect both changes of modal behaviour and of system damping introduced by the insertion of the joint.

  • 35.
    Feng, Leiping
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Vibrational insertion loss of traditional and smart joints2001Ingår i: Acustica, ISSN 0001-7884, Vol. 87, nr 2, s. 199-205Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vibrational insertion loss of selected traditional and smart joints are investigated experimentally with the test-rigs presented in reference [1, 2]. The influences of various factors such as spacing between fasteners, overlap, bonding materials are examined. The relation between system damping and the damping introduced by the joint is discussed. For smart joints, comparison is also made with the transmission loss of elastic interlayer in order to understand the mechanism. At low frequencies the main positive effect of a joint is damping. When the frequency is higher, the joint start to separate the system and other factors such as stiffness and weight become more important. Maximum damping does not coincide with the maximum vibrational insertion loss. In order to achieve best vibro-acoustic performance and structure integrity, it is better to use different joint techniques in different frequency bands, since the insertion loss is frequency dependent.

  • 36.
    Feng, Leiping
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Liu, M. H.
    Nilsson, A.
    Experimental study of structure-borne sound transmission loss of mechanical joints2001Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 110, nr 3, s. 1391-1397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mechanical joint is one of the most effective ways to reduce the transmission of structure-borne sound. In order to increase the transmission loss, heavily damped joints are often used, which, in many cases, will reduce the structure integrity and hence can only be used in limited cases. In this study attention is focused on a type of resonant joint, i.e., a joint which will increase the transmission loss but will not reduce the structure integrity. The study is based on experiments in a one-dimensional structure. It is found that by adjusting the overlap of the joint, the transmission loss of 30 dB can be obtained at a certain frequency range without adding any dissipative materials. The mechanism of this high transmission loss is the cantilever-type resonance. The resonant frequency can be predicted precisely. The influence of extra dissipative material is investigated. The performance of the same joint in a finite structure is also examined by using the concept of vibrational insertion loss. When there is a certain damping in a finite system, a rather high insertion loss can still be achieved by using the above-mentioned joint, but the resonant frequency is shifted to higher end. It seems that the effective length of the cantilever is shortened by the finiteness.

  • 37.
    Feng, Leiping
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Nilsson, A.
    KTH, Tidigare Institutioner, Farkostteknik.
    Kari, Leif
    KTH, Tidigare Institutioner, Farkostteknik.
    New designs of sandwich engine foundations1998Ingår i: International Conference on Sandwich Construction, 1998, s. 289-300Konferensbidrag (Refereegranskat)
  • 38.
    Feng, Leiping
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Nilsson, A.
    KTH, Tidigare Institutioner, Farkostteknik.
    Kari, Leif
    KTH, Tidigare Institutioner, Farkostteknik.
    Vibration of engine foundations1997Ingår i: Modern Practice in Stress and Vibration Analysis / [ed] M D Gilchrist, Rotterdam: Balkema, 1997, s. 311-316Konferensbidrag (Refereegranskat)
  • 39.
    Feng, Leping
    KTH, Tidigare Institutioner, Farkostteknik.
    A modified honeycomb panel to increase sound transmission loss2003Ingår i: Proceedings of the Tenth International Congress on Sound and Vibration:  , 2003, s. 4549-4554Konferensbidrag (Refereegranskat)
    Abstract [en]

    Honeycomb panels are widely used in aviation industry because of the properties of lightweight and high bending stiffness. However, the sound transmission loss of the panel is often low since the coincident frequency of the panel usually lies below 2 kHz. Previous results show that a single-faced honeycomb panel may acoustically perform much better, especially when it is combined with absorptive materials. This idea is further developed to overcome drawbacks. An improved concept of honeycomb panel is presented, which keeps the basic properties of a honeycomb panel, while the coincident phenomenon in audible frequency is avoided. The theoretical consideration behind this design is discussed. The idea is then tested experimentally. The weighted apparent sound reduction index of the modified honeycomb panel is 4 dB higher than an ordinary honeycomb panel with similar surface density.

  • 40.
    Feng, Leping
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Liu, B.
    On low frequency sound insulation of lightweight structures2004Ingår i: Proceedings of the Eleventh International Congress on Sound and Vibration, 2004, s. 2425-2432Konferensbidrag (Refereegranskat)
  • 41.
    Finnveden, Svante
    KTH, Tidigare Institutioner, Farkostteknik.
    Finite element techniques for the evaluation of energy flow parameters: Keynote Lecture2000Konferensbidrag (Refereegranskat)
    Abstract [en]

    In applications of Statistical Energy Analysis (SEA) to complex engineering structures, procedures for the calculation of the SEA parameters are frequently unavailable. This note discusses two Finite Element techniques for identification of energy flow parameters: a waveguide and a modal approach.

  • 42.
    Finnveden, Svante
    et al.
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Pinnington, R. J.
    A velocity method for estimating dynamic strain and stress in pipes2000Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 229, nr 1, s. 147-182Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A velocity method for estimating dynamic strain and stress in pipe structures is investigated. With this method, predicted or measured spatial average vibration velocity and theoretically derived strain factors are used to estimate maximum strain at the ends of pipes. Theoretical investigation shows that the strain at a point is limited by an expression proportional to the square root of the strain energy density, which in turn is related to its cross-sectional average. For a reverberant field or for an infinite pipe, the average strain energy density is proportional to the mean square velocity. Upon this basis, the non-dimensional strain factor is defined as the maximum strain times the ratio of the sound velocity to the spatial root mean square vibration velocity. Measurements are made confirming that this is a descriptive non-dimensional number. Using a spectral finite element method, numerical experiments are made varying the pipe parameters and considering all 16 homogeneous boundary conditions. While indicating possible limitations of the method when equipment is mounted on pipes, the experiments verify the theoretical results. The velocity method may become useful in engineering practice for assessments of fatigue life.

  • 43.
    Forsén, Anders
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Heavy vehicle ride and endurance1999Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 44.
    Förstberg, Johan
    KTH, Tidigare Institutioner, Farkostteknik.
    Ride comfort and motion sickness in tilting trains2000Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents a systematic study of human responses to different motions and strategies of car body tilt control regarding ride comfort, working/reading ability and motion sickness on high-speed tilting trains. Experiments with test subjects were performed in a tilting train on curved track as well as in a moving vehicle simulator. The study is multi-disciplinary, combining knowledge and methods from the fields of railway technology, human factors and vestibular science.

    The main experiment in a tilting train was performed with about 75 seated test subjects, mainly students from Linköping University, making three test runs. In total, these subjects participated in about 210 individual test rides, each with a duration of about 3 hours. Additional tests on comfort disturbances with pushbutton technique have been reported in the project. The simulator experiments used a total of about 75 subjects, making some 320 test rides each of about 30 minutes duration. Test motions consisted of combinations of horizontal (lateral) acceleration and roll acceleration, together with either roll or horizontal acceleration. Rate of change of horizontal acceleration (jerk) and roll velocity were of the same order of magnitude as in a tilting train environment, but horizontal acceleration alone was about half the magnitude. Horizontal and vertical vibrations from a tilting train were added to the test motions, and train seats and interior train noise were also introduced to create a "train feeling".

    Test designs and methodology have been developed during the course of the experiments. The test subjects answered questionnaires, four times per test run in the train experiment and each 5 minute in the simulator experiment. The investigated variables were: estimated average ride comfort, estimated ability to work or read, and occurrence of symptoms of motion sickness (dizziness, nausea and not feeling well). Lateral and vertical accelerations together with roll motions were monitored and recorded for later evaluation.

    Results from the train experiments show that the estimated average ride comfort was about 4 on a 5-degree scale, which indicates “good”. Results also show that a reduced tilt compensation of the lateral acceleration while curving together with a reduced tilt velocity of the car body reduce the provocation of motion sickness. However, a reduction in tilt compensation may produce an increased number of comfort disturbances due to lateral acceleration in the car body. Regression analysis shows that motion doses from roll acceleration may be used to predict the incidence of motion sickness.

    The simulator experiments show that the primary sources of provocation of nausea and motion sickness are the motion doses from roll and lateral acceleration in the horizontal plane. The study proposes a hypothesis and a model of provocation of motion sickness. It is shown that motion sickness has a time decay, or leakage. A model for this leakage is proposed.

    The determinative types of motion for provocation of nausea and motion sickness in tilting trains are identified and future tilting train and/or simulator experiments are proposed in order to further investigate their influence.

  • 45.
    Garme, Karl
    KTH, Tidigare Institutioner                               , Farkostteknik.
    Time-domain model for high-speed vessels in head seas2000Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 46.
    Glav, R.
    KTH, Tidigare Institutioner, Farkostteknik.
    On acoustic modelling of silencers1994Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 47.
    Glav, R
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Bodén, Hans
    KTH, Tidigare Institutioner, Farkostteknik.
    Åbom, Mats
    KTH, Tidigare Institutioner, Farkostteknik.
    An acoustic model for automobile catalytic converters1988Konferensbidrag (Refereegranskat)
  • 48.
    Grisell, Bengt
    KTH, Tidigare Institutioner, Farkostteknik.
    Bol Tyter - Tyterskär 20032004Rapport (Övrig (populärvetenskap, debatt, mm))
  • 49.
    Grisell, Bengt
    KTH, Tidigare Institutioner, Farkostteknik.
    Rapport avseende sanering av den ryska ön Tyterskär i Finska viken samt öns omgivande vattenområden 19992000Rapport (Övrig (populärvetenskap, debatt, mm))
  • 50.
    Grisell, Bengt
    KTH, Tidigare Institutioner, Farkostteknik.
    Slutrapport avseende upprensning 1996 av Stora och Lilla Rågö samt Odensholm med omgivande vattenområden, i Estland1997Rapport (Övrig (populärvetenskap, debatt, mm))
1234 1 - 50 av 151
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