Assoc. Prof. Mirosław Meissner, Ph.D., Dr. Habil., Eng. 

Doctoral thesis
1990  Generacja dźwięku o dyskretnej częstotliwości przy opływie wnęki głębokiej przez strumień gazu
 466 
Habilitation thesis
2000  Badania odpowiedzi układów rezonansowych na pobudzenie akustyczne i aerodynamiczne 
Supervision of doctoral theses
1.  20141127  Nowak Łukasz  Adaptive feedback control system for reduction of vibroacoustic emission  671  
2.  20121004  Raunmiagi Zygmunt (AM)  Metoda oceny stanu powierzchni stożkowych rozpylaczy paliwa silników okrętowych za pomocą emisji akustycznej  1081 
Recent publications
1.  Meissner M., Acoustics of small rectangular rooms: Analytical and numerical determination of reverberation parameters, APPLIED ACOUSTICS, ISSN: 0003682X, DOI: 10.1016/j.apacoust.2017.01.020, Vol.120, pp.111119, 2017 Abstract: A small rectangular room with hard walls has a number of acoustic flaws and the most serious drawback is a long reverberation time. A technique commonly used for improving room acoustics consists in increasing a sound absorption on a ceiling. In this study, the impact of acoustical treatment of a ceiling on reverberant properties of a small rectangular room was examined. Changes in the modal reverberation time due to this treatment were investigated by the analytical method. As was evidenced by calculations, the initial increase in a sound absorption on a ceiling causes a substantial decrease in the modal reverberation time and a treatment efficiency decreases with a further absorption increase. It was found also that for a room with hard walls statistical and wave theories give the same result as the modal reverberation time for oblique modes and the Sabine’s reverberation time are identical. A more detailed information about reverberant properties of a room was provided by the numerical method employing a backward integration of the squared room impulse response. Using this method, global and local reverberation parameters were determined. Numerical simulations discovered a quite good agreement between global and local reverberation time and high differences between global and local early decay time resulting from a nonlinear shape of a decay curve. Therefore, one can conclude that the global decay times characterize reasonably well a reverberation process in a late stage of sound decay but they are not correctly describe this process in an initial stage. Keywords:Small room acoustics, Modal expansion method, Room impulse response, Reverberation time, Early decay time Affiliations:
 
2.  Meissner M., Prediction of Reverberant Properties of Enclosures via a Method Employing a Modal Representation of the Room Impulse Response, ARCHIVES OF ACOUSTICS, ISSN: 01375075, DOI: 10.1515/aoa20160003, Vol.41, No.1, pp.2741, 2016 Abstract: A theoretical method has been presented to describe sound decay in enclosures and simulate the room impulse response (RIR) employed for prediction of the indoor reverberation characteristics. The method was based on a solution of wave equation with the form of a series whose timedecaying components represent responses of acoustic modes to an impulse sound source. For small sound absorption on room walls this solution was found by means of the method of variation of parameters. A decay function was computed via the timereverse integration of the squared RIR. Computer simulations carried out for a rectangular enclosure have proved that the RIR function reproduces the structure of a sound field in the initial stage of sound decay sufficiently well. They have also shown that bandlimitedness of the RIR has evident influence on the shape of the decay function and predicted decay times. Keywords:room acoustics, indoor reverberation, room impulse response, modal expansion method, decay times Affiliations:
 
3.  Meissner M., Numerical investigation of acoustic field in enclosures: Evaluation of active and reactive components of sound intensity, JOURNAL OF SOUND AND VIBRATION, ISSN: 0022460X, DOI: 10.1016/j.jsv.2014.10.043, Vol.338, pp.154168, 2015 Abstract: The paper focuses on a theoretical description and numerical evaluation of active and reactive components of sound intensity in enclosed spaces. As the study was dedicated to lowfrequency room responses, a modal expansion of the sound pressure was used. Numerical simulations have shown that the presence of energy vortices whose size and distribution depend on the character of the room response is a distinctive feature of the active intensity field. When several modes with frequencies close to a source frequency are excited, the vortices within the room are positioned irregularly. However, if the response is determined by one or two dominant modes, a regular distribution of vortices in the room can be observed. The irrotational component of the active intensity was found using the Helmholtz decomposition theorem. As was evidenced by numerical simulations, the suppression of the vortical flow of sound energy in the nearfield permits obtaining a clear image of the sound source. Keywords:room acoustics, modal analysis, sound intensity, energy vortex, stagnation point Affiliations:
 
4.  Meissner M., Theoretical and Numerical Determination of LowFrequency Reverberant Characteristics of Coupled Rooms, JOURNAL OF VIBRATION AND ACOUSTICSTRANSACTIONS OF THE ASME, ISSN: 10489002, DOI: 10.1115/1.4029991, Vol.137, No.4, pp.04101319, 2015 Abstract: The main aim of room acoustics is to predict reverberant properties of enclosures from measured or numerically simulated room responses. In this paper, this issue was examined in lowfrequency range where acoustic characteristics of rooms are strongly frequency dependent due to differences in a modal damping. A theoretical description of a decaying sound field was based on a modal expansion of the sound pressure, and a reverberant response of the room was initiated by emission of Dirac delta time impulse or by switching off a timeharmonic source. Theoretical findings were employed to determine reverberant characteristics of a coupledroom system containing two connected rectangular subrooms. Simulation results have shown that a sound decay after steadystate harmonic excitation is strongly influenced by the sound frequency and due to large fluctuations in a decaying pressure; numerical techniques for smoothing decay curves are needed. Calculations also revealed that in some onethird octave bands, the decay function found via backward integration of squared room impulse response (RIR) changes very irregularly impeding a proper qualifying of nature of sound decay. Keywords:room acoustics, modal analysis, decay times, coupled rooms Affiliations:
 
5.  Meissner M., Sound Energy Field in a System of Coupled Rooms, ACTA PHYSICA POLONICA A, ISSN: 05874246, DOI: 10.12693/APhysPolA.125.A103, Vol.125, No.4A, pp.A103A107, 2014 Abstract: The paper presents a theoretical basis of calculations of the sound intensity in enclosed spaces and shows results of numerical visualization of the active intensity in a room with absorptive walls formed by two coupled rectangular subrooms. The study was focused on the lowfrequency range, therefore to describe the active and reactive intensities, the modal theory of room acoustics was applied. Space distribution of eigenfunctions, modal frequencies and modal damping coefficients were calculated numerically using the forced oscillator method (FOM) and the nite difference timedomain (FDTD) method. Based on theoretical and numerical results, the computer program has been developed to simulate the active intensity vector eld when the room is excited by a harmonic point source. Calculation data have shown that the active intensity was extremely sensitive to position of the source since at a fixed source frequency, different source locations always generate different distributions of characteristic objects of the active sound eld such as energy vortices and stagnation points. Because of complex room shape, the vortex centers are in most cases positioned irregularly inside the room. Almost regular arrangement of vortices was found only in the case when the source frequency was tuned to the frequencies of modes which were strongly localized in one of the subrooms. Keywords:room acoustics, coupled rooms, sound intensity, energy vortex, stagnation point Affiliations:
 
6.  Meissner M., Analytical and numerical study of acoustic intensity field in irregularly shaped room, APPLIED ACOUSTICS, ISSN: 0003682X, DOI: 10.1016/j.apacoust.2012.11.009, Vol.74, No.5, pp.661668, 2013 Abstract: The modal expansion method has been used to formulate expressions for real and imaginary parts of the complex sound intensity inside enclosures. Based on theoretical results, the computer program has been developed to simulate the acoustic intensity vector field inside the irregular room whose shape resembles the capital letter L. Calculation results have shown that a lowfrequency distribution of the acoustic intensity is strongly influenced by the modal localization and the characteristic objects in the active intensity field are energy vortices and saddle points positioned irregularly inside the room. It was found that for small sound damping the vortex centers lie exactly on the lines corresponding to zeros of the eigenfunction for a dominant mode. An increase in a sound attenuation results in the change of vortex positions and can cause the formation of new vortices. Finally, an influence of the wall impedance on the quantitative relation between the acoustic and reactive intensities was studied and it was concluded that for very small sound damping the behavior of the sound intensity is basically only oscillatory. Keywords:Room acoustics, Irregular room, Sound intensity, Energy vortex, Modal localization Affiliations:
 
7.  Meissner M., Acoustic Behaviour of Lightly Damped Rooms, ACTA ACUSTICA UNITED WITH ACUSTICA, ISSN: 16101928, DOI: 10.3813/AAA.918663, Vol.99, No.5, pp.845847, 2013 Abstract: The analytical method has been developed to determine the acoustic behaviour of a lightly damped room excited by a sound source. Using the classical modal analysis, a solution of the wave equation was found as a sum of an infinite number of components representing individual responses of acoustic modes to the sound source. For weak sound absorption a general form of this solution was determined by means of the method of variation of parameters. From this solution the equations for the Green's function and the room impulse response were found. By employing the Green's function, the expressions describing a sound buildup and a sound decay for a harmonic excitation were derived. Keywords:room acoustics, wave equation, room impulse response, decay times Affiliations:
 
8.  Meissner M., Evaluation of Decay Times from Noisy Room Responses with PureTone Excitation, ARCHIVES OF ACOUSTICS, ISSN: 01375075, DOI: 10.2478/aoa20130006, Vol.38, No.1, pp.4754, 2013 Abstract: Reverberant responses are widely used to characterize acoustic properties of rooms, such as the early decay time (EDT) and the reverberation times T20 and T30. However, in real conditions a sound decay is often deformed by background noise, thus a precise evaluation of decay times from noisy room responses is the main problem. In this paper this issue is examined by means of numerical method where the decay times are estimated from the decay function that has been determined by nonlinear polynomial regression from a pressure envelope obtained via the discrete Hilbert transform. In numerical experiment the room responses were obtained from simulations of a sound decay for tworoom coupled system. Calculation results have shown that background noise slightly affects the evaluation of reverberation times T20 and T30 as long as the signaltonoise ratio (SNR) is not smaller than about 25 and 35 dB, respectively. However, when the SNR is close to about 20 and 30 dB, high overestimation of these times may occur as a result of bending up of the decay curve during the late decay. Keywords:room acoustics, reverberation, decay times, room response, background noise, coupled rooms Affiliations:
 
9.  Nowak Ł.J., Zieliński T.G., Meissner M., Active vibroacoustic control of plate structures with arbitrary boundary conditions, IPPT REPORTS, ISSN: 22993657, Vol.4a, pp.59, 2013 Abstract: The paper describes briefly some main aspects of the active feedback control system that has been developed and constructed for reduction of vibroacustic emission of vibrating plate structures with arbitrary boundary conditions. Relations between the forms and frequency of the vibrations induced by an external harmonic excitation and the distribution of the generated acoustic pressure field are investigated using the developed numerical model based on the Indirect Variational Boundary Element Method. The aim of the control is to minimize the sound pressure level in a given point of the ambient space. The system uses small, rectangleshaped piezoelectric transducers as both sensors and actuators. The transducers are connected in a number of independent feedback loops, and the feedback gains are the control parameters which are optimized using the developed optimal control algorithm. The constructed active system has been tested for the stability and control performance during experimental research performed in an anechoic chamber. Results of experiments are presented in the paper, proving a high level of noise reduction and a good agreement with numerical predictions. Keywords:Vibrating plate structures, Active feedback control system, Vibrational modes Affiliations:
 
10.  Meissner M., Acoustic energy density distribution and sound intensity vector field inside coupled spaces, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, ISSN: 00014966, Vol.132, No.1, pp.228238, 2012 Abstract: In this paper, the modal expansion method supported by a computer implementation has been used to predict steadystate distributions of the potential and kinetic energy densities, and the active and reactive sound intensities inside two coupled enclosures. The numerical study was dedicated to lowfrequency room responses. Calculation results have shown that the distribution of energetic quantities in coupled spaces is strongly influenced by the modal localization. Appropriate descriptors of the localization effect were introduced to identify localized modes. As was evidenced by numerical data, the characteristic objects in the active intensity field are vortices positioned irregularly inside the room. It was found that vortex centers lie exactly on the lines corresponding to zeros of the eigenfunction for a dominant mode. Finally, an impact of the wall impedance on the quantitative relationship between the active and reactive intensities was analyzed and it was concluded that for very small sound damping the behavior of the sound intensity inside the room space is essentially only oscillatory. Keywords:room acoustics, coupled rooms, acoustic energy density, active sound intensity, reactive sound intensity Affiliations:
 
11.  Meissner M., The discrete Hilbert transform and its application to the analysis of reverberant decay of modal vibration in enclosures, JOURNAL OF VIBRATION AND CONTROL, ISSN: 10775463, DOI: 10.1177/1077546311420896, Vol.18, pp.15951606, 2012 Abstract: The Hilbert transform is an important tool for a signal analysis, and it has been widely used in many areas of science and technology. An application of this method to an analysis of reverberant decay of modal vibrations in enclosures enables a detection of a pressure envelope resulting in a more accurate prediction of a reverberation time. It is shown that the discrete Hilbert transform is not accurate in an envelope detection even for the moderately damped harmonic signals, and a generated error strongly depends on the ratio of a modal damping coefficient to a mode frequency. This inexactness is due to the fact that for exponentially decaying harmonic signals the Bedrosian identity is not satisfied. In order to increase the accuracy of the envelope prediction, appropriate modifications of discrete signals corresponding to different kinds of modes are proposed. This method is successfully tested in the multimode case using discrete signals simulating a reverberant response of two coupled rooms. Keywords:Hilbert transform, modal vibrations, reverberation time, room acoustics Affiliations:
 
12.  Meissner M., Accuracy issues of discrete Hilbert transform in identification of instantaneous parameters of vibration signals, ACTA PHYSICA POLONICA A, ISSN: 05874246, Vol.121, No.1A, pp.A164167, 2012 Abstract: In the paper, an accuracy of the discrete Hilbert transform method in a detection of amplitude and frequency of vibration signals has been examined. This issue was studied for sinusoidal damped vibrations often encountered in practical applications. It has been shown that an inexactness of the Hilbert transform generates fictitious oscillations of amplitude and frequency. For small damping of vibrations these oscillations were significant only at both ends of a discrete signal. An error induced by a numerical algorithm was especially severe for strongly damped vibrations because it manifested itself by a large overestimation of amplitude and erroneous jumps of frequency. To reduce the error generated by the Hilbert transform method, the appropriate modification of discrete signal was proposed. Keywords:vibration signals, discrete Hilbert transform, Bedrosian theorem Affiliations:
 
13.  Meissner M., Numerical modelling of coupled rooms: evaluation of decay times via method employing Hilbert transform, ACTA PHYSICA POLONICA A, ISSN: 05874246, Vol.119, pp.10311034, 2011 Abstract: In the paper, a usefulness of the Hilbert transform in a computer modelling of reverberant behaviour of rooms is demonstrated for the enclosure consisting of two coupled subrooms. In numerical simulations a decay of the sound pressure is computed and the Hilbert transform methodology is used to determine an envelope of this decay. Calculation results have shown that, because of the mode localization, a distribution of absorbing material has a great influence on decay times evaluated from changes in the pressure envelope. For example, when a difference between the sound damping in subrooms is large, the localization effect is responsible for a creation of a nonlinear decay of the sound pressure level characterized by rapid early and slow late sound decays. Keywords:room acoustics, reverberant behaviour of rooms, coupled rooms, Hilbert transform Affiliations:
 
14.  Meissner M., Examination of the effect of a sound source location on the steadystate response of a tworoom coupled system, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.36, pp.761775, 2011 Abstract: In this paper, the computer modelling application based on the modal expansion method is developed to study the influence of a sound source location on a steadystate response of coupled rooms. In the research, an eigenvalue problem is solved numerically for a room system consisting of two rectangular spaces connected to one another. A numerical procedure enables the computation of shape and frequency of eigenmodes, and allows one to predict the potential and kinetic energy densities in a steadystate. In the first stage, a frequency room response for several source positions is investigated, demonstrating large deformations of this response for strong and weak modal excitations. Next, a particular attention is given to studying how the changes in a source position influence the room response when a source frequency is tuned to a resonant frequency of a strongly localized mode. Keywords:coupled room system, steadystate room response, potential and kinetic energy densities, localization of modes Affiliations:
 
15.  Meissner M., Simulation of acoustical properties of coupled rooms using numerical technique based on modal expansion, ACTA PHYSICA POLONICA A, ISSN: 05874246, Vol.118, No.1, pp.123127, 2010 Abstract: In the present study, the acoustic characteristics of coupled rooms were investigated using the computer modelling application based on the modal expansion method. A numerical procedure enables the computation of shape and frequency of eigenmodes, and allows one to predict sound decay times at any point of a room space. Results of numerical simulation have shown that along with a change in a coupling area the effect of a mode degeneration appeared and there are two main reasons for this. First, a mode degeneration is associated with a convergence of frequencies of neighbouring modes with a decrease of coupling area. Another reason for the mode degeneration are variations in a sequence of modes with a change in the coupling area. It was demonstrated that in the coupled rooms several modes exhibit a considerable localization. A degree of mode localization was described theoretically by the “existence surface” of mode and it was found that the localization phenomenon has a great effect on the reverberation process because for some absorbing material distributions it caused the double–slope decay characterized by steep initial and slow late sound decays. Affiliations:
 
16.  Meissner M., Effect of crosssectional area discontinuities in closed hardwalled duct on frequency of longitudinal modes, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.35, No.3, pp.421435, 2010 Abstract: A simple analytical method is developed to estimate frequencies of longitudinal modes in closed hardwalled ducts with discontinuities in a crosssectional area. The approach adopted is based on a general expression for the acoustic impedance for a plane wave motion in a duct and conditions of impedance continuity at duct discontinuities. Formulae for mode frequencies in a form of transcendental equations were found for one, two and three discontinuities in a duct crosssection. An accuracy of the method was checked by a comparison of analytic predictions with calculation data obtained by use of numerical implementation based on the forced oscillator method with a finite difference algorithm. Keywords:longitudinal duct modes, discontinuity in duct crosssection, contraction ratio Affiliations:
 
17.  Meissner M., Spectral characteristics and localization of modes in acoustically coupled enclosures, ACTA ACUSTICA UNITED WITH ACUSTICA, ISSN: 16101928, DOI: 10.3813/AAA.918152, Vol.95, No.2, pp.300305, 2009 Abstract: In this paper spectral characteristics and a mode localization in acoustically coupled enclosures were studied numerically. In a theoretical model a lowfrequency limit was considered where eigenmodes are weakly damped, thus they were approximated by normal acoustic modes for rigid room walls. The effect of acoustic coupling on the mode frequency, the integrated density of states (IDOS) and the existence surface of modes were investigated for several coupling areas. Numerical results indicate that a decrease in coupling area causes a decrease of IDOS and results in a stronger localization of modes. Keywords:coupled rooms, spectral characteristics, localization of modes Affiliations:
 
18.  Janczur R., Walerian E.M., Meissner M., Czechowicz M., Application of simulation program to specific urban situation, APPLIED ACOUSTICS, ISSN: 0003682X, DOI: 10.1016/j.apacoust.2008.11.002, Vol.70, No.7, pp.973985, 2009 Abstract: In the paper, the simulation program predicting the sound level has been applied to one of buildings neighbouring a road. In the simulation are considered: geometry of road surroundings, the shape of the investigated building façade including, road geometry (number of lanes and their positions) and traffic structure (vehicle flow rates and their average speeds). Adjustable accuracy in an urban system modelling allows finding the model which is adequate to the real system. For the model of the accuracy limited by the simulation error due to vehicle speed estimation, by comparison with the field measurement, the model validation range has been established. Based on the simulation adjustable accuracy, possibilities of the validation range extension have been analysed. Keywords:simulation, traffic noise, noise protecting means Affiliations:
 
19.  Meissner M., Computer modelling of coupled spaces: variations of eigenmodes frequency due to a change in coupling area, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.34, No.2, pp.157168, 2009 Abstract: Acoustically coupled spaces have recently been drawing more and more attention in the architectural acoustics community, thus a determination of shapes and frequencies of eigenmodes in these room systems from computerbased models has become increasingly significant. In this investigation, an eigenvalue problem was solved numerically for a simple room system consisting of two connected rectangular spaces. In a numerical procedure, the forced oscillator method with a finite difference algorithm was applied. In order to determine the influence of irregularity of system shape on eigenmodes frequency, a modal behaviour in the coupled spaces was studied for several sizes of coupling area. Calculation results have shown that with the exception of a fundamental mode, the changes in resonant frequencies were relatively small. However, an increase in a system irregularity led to a coincidence of frequencies of neighbouring modes and variations in a sequence of modes on a frequency axis, which both contributed to a degeneration of eigenmodes. Keywords:coupled spaces, modal analysis, degenerate modes, mode localization Affiliations:
 
20.  Meissner M., Application of Hilbert transformbased methodology to computer modelling of reverberant sound decay in irregularly shaped rooms, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.34, No.4, pp.491506, 2009 Abstract: A study into the application of the Hilbert transform in numerical simulations of reverberant sound decay in irregularly shaped enclosures is presented. It is shown that there are some limitations in the use of this integral transform to exponentially decaying harmonic signals because the integration result consists not only of a signal, which differs from the original one by a phase shift of pi/2, but also of a decaying nonoscillating signal occurring due to the fact that a spectrum of exponential function is unbounded. An initial amplitude of this signal is directly proportional to the ratio between a damping coefficient and a mode frequency, thus for lightly damped rooms, where this ratio is much smaller than unity, it can be neglected. Results of numerical simulation carried out for Lshaped enclosure indicate that the Hilbert transform is a useful tool in calculating instantaneous properties of reverberant sound, especially an envelope of the sound pressure level. It is of special importance in the case of irregularly shaped rooms, where a deviation from the exponential sound decay often occurs because of differences between reverberant responses for particular modes. Keywords:Hilbert transform, analytic signal, irregularly shaped enclosures, reverberant room response, reverberation time, early and late decay times Affiliations:
 
21.  Meissner M., Influence of wall absorption on lowfrequency dependence of reverberation time in room of irregular shape, APPLIED ACOUSTICS, ISSN: 0003682X, DOI: 10.1016/j.apacoust.2007.02.004, Vol.69, No.7, pp.583590, 2008 Abstract: In this paper, a modal analysis was used to describe a reverberation phenomenon in a room of complex shape. A theoretical model was limited to low sound frequencies, when eigenmodes are lightly damped, thus they may be approximated by uncoupled normal acoustic modes of a hardwalled room. A utility of this method was demonstrated in a numerical example where the enclosure in a form of two coupled rooms was considered. A reverberation time was evaluated from a time decay of spatial root mean square pressure, the overall measure of room pressure. The results of calculations, performed for three different distributions of absorbing materials on room walls, showed how various location of the material can effect a dependence of the reverberation time on a frequency of sound source. Keywords:coupled enclosures, modal analysis, reverberation time Affiliations:
 
22.  Meissner M., Influence of absorbing material distribution on double slope sound decay in Lshaped room, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.33, No.4S, pp.159164, 2008 Abstract: The sound decay process in Lshaped room was the subject of this investigation. The room with walls covered by the low absorbent material constituted the initial configuration for the study. To decrease a reverberation time, alterations of acoustic room properties were carried out by adding a high absorbent material on lateral room walls. Two different material configurations were considered and their effects on a double slope sound decay were analysed. In order to predict the behaviour of decay curve, a numerical implementation based on the wave theory was applied. A space distribution of eigenfunctions was computed using the forced oscillator method with a finite difference algorithm. Numerical results have demonstrated that an introduction of high absorbent material on selected room walls may cause an intense double slope effect. It is characterized by rapid initial and slow late decays, thus the decay curve exhibits socalled a “sagging” appearance. It was found also that a phenomenon of mode localization is an important factor in modifying the double slope sound decay. Keywords:coupled rooms, modal analysis, reverberation, double slope effect, localization of eigenmodes Affiliations:
 
23.  Meissner M., Computational studies of steadystate sound field and reverberant sound decay in a system of two coupled rooms, CENTRAL EUROPEAN JOURNAL OF PHYSICS, ISSN: 18951082, DOI: 10.2478/s1153400700167, Vol.5, No.3, pp.293312, 2007 Abstract: The acoustical properties of an irregularly shaped room consisting of two connected rectangular subrooms were studied. An eigenmode method supported by a numerical implementation has been used to predict acoustic characteristics of the coupled system, such as the distribution of the sound pressure in steadystate and the reverberation time. In the theoretical model a lowfrequency limit was considered. In this case the eigenmodes are lightly damped, thus they were approximated by normal acoustic modes of a hardwalled room. The eigenfunctions and eigenfrequencies were computed numerically via application of a forced oscillator method with a finite difference algorithm. The influence of coupling between subrooms on acoustic parameters of the enclosure was demonstrated in numerical simulations where different distributions of absorbing materials on the walls of the subrooms and various positions of the sound source were assumed. Calculation results have shown that for large differences in the absorption coefficient in the subrooms the effect of modal localization contributes to peaks of RMS pressure in steadystate and a large increase in the reverberation time. Keywords:coupled rooms, modal analysis, reverberation time, modes localization Affiliations:
 
24.  Meissner M., Analysis of nonexponential sound decay in an enclosure composed of two connected rectangular subrooms, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.32, No.4S, pp.213220, 2007 Abstract: Acoustically coupled rooms have recently been drawing more and more attention in the architectural acoustics community. Determination of decay times in these coupled rooms from computerbased models has become increasingly significant. In computational modelling of coupled enclosures the geometrical acoustics methods do not apply at lower frequencies, and models must account for the wavenature of sound fields, especially modal effects. In this investigation a combination of modal analysis with finitedifference algorithm was used to predict a decay in the sound field energy in an enclosure composed of two connected rectangular subrooms. Random incidence absorption coefficients inside subrooms have been modified in this study to create different configurations of absorbing materials on subrooms walls. When one of these subrooms was much more absorbent than the other one, calculation results have shown that, at any frequencies, there existed both the initial sudden and the late slow decrease in the sound field energy. This effect was characterized by two metrics: early decay time (EDT) and late decay time (LDT) determined from a sound level decay from –50 to –60 dB. The analysis of numerical data confirmed that the most influential factor in realizing the nonexponential sound decay is a phenomenon of eigenmodes localization. Keywords:coupled rooms, reverberation, doublesloped sound decay, localization of modes Affiliations:
 
25.  Janczur R., Walerian E.M., Meissner M., Czechowicz M., Influence of vehicle noise emission directivity on sound level distribution in a canyon street. Part II: Experimental verification, APPLIED ACOUSTICS, ISSN: 0003682X, DOI: 10.1016/j.apacoust.2005.12.003, Vol.67, pp.659679, 2006 Abstract: In the paper, predictions of relative sound level distribution on building facades in citycentres obtained by using the simulation PROP11 program are compared with measurements. The simulation involves the geometry of surrounding buildings, road geometry (number of lanes and their positions) and traffic structure (vehicle flow rates and their average speeds). The agreement between measurement and simulation results is tested for different directivity characteristics of an equivalent point source representing the vehicles. Keywords:predicted sound level in builtup area, vehicle noise emission directivity Affiliations:
 
26.  Meissner M., The effect of modal localization on reverberant energy decay in a case of two acoustically coupled rooms, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.31, pp.239245, 2006 Abstract: In the paper a modal analysis was used to describe a reverberation phenomenon in an irregularly shaped room. A theoretical model was limited to low sound frequencies, when eigenmodes are lightly damped, thus they may be approximated by normal acoustic modes of a hardwalled room. A utility of this method was demonstrated in a numerical example where the room in a form of two acoustically coupled rectangular subrooms was considered. A reverberation time was evaluated individually for each subroom from time decay of acoustic pressure amplitude for different distributions of absorbing materials of room walls and various positions of sound source under the condition that a total room absorption remained constant. Calculation results have shown a great influence of modes localization on a reverberant energy decay for a large difference between the absorption coefficients of walls in subrooms, because in this case for frequencies of some localized modes a substantial increase in the reverberation time was observed. Keywords:room acoustics, modal analysis, reverberation time, modes localization Affiliations:
 
27.  Meissner M., The response of Helmholtz resonator to external excitation. Part II: flowinduced resonance, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.30, No.1, pp.5771, 2005 Abstract: In the paper a phenomenon of sound production in a resonator driven by an air jet has been investigated. Measurements of sound spectra at the closed end of the resonator cavity were performed to determine the influence of the jet velocity on the frequency and amplitude of excited acoustic oscillations. It was found that in the sound generation process two ranges of the jet velocity could be distinguished where different variations of the oscillation frequency with the growing jet velocity were observed. After the onset of oscillation the frequency increased fast with growing jet velocity and the frequency increment was directly proportional to a value of jet velocity. At higher flow velocities an increase in the frequency was still observed, but the frequency growth was much smaller. The experiment has shown also that due to an excitation of mechanical vibrations of the resonator elements a rapid change in the oscillation frequency occurred. Finally, the experimental data were compared to calculation results to examine the accuracy of the theoretical model, in which a force driving the resonator was predicted from the vortex sound theory and the resonator was modelled by an equivalent impedance circuit. Keywords:sound generation, flowinduced resonance, acoustic resonators Affiliations:
 
28.  Meissner M., Influence of room geometry on lowfrequency modal density, spatial distribution of modes and their damping, ARCHIVES OF ACOUSTICS, ISSN: 01375075, Vol.30, pp.205210, 2005 Abstract: Acoustical properties of two rooms of irregular shapes have been investigated theoretically by a system of eigenmodes, which for low frequencies and weak losses on walls can be well approximated by a system of normal acoustic modes of hard wall room. The eigenfunctions and eigenfrequencies were determined numerically with an application of the forced oscillator method with a finite difference algorithm. It was found that a geometrical irregularity has three main effects. First, the lowfrequency modal density is changed. Second, some of eigenmodes are localized, thus for particular frequencies a vibration amplitude will be enhanced locally inside the room. Third, the acoustic energy losses inside the room are increased with the amplitude of vibration on walls. Keywords:room acoustics, modal analysis, eigenfunctions, modal density, modes localization Affiliations:
 
29.  Meissner M., Badania odpowiedzi układów rezonansowych na pobudzenie akustyczne i aerodunamiczne (Praca habilitacyjna), Prace IPPT  IFTR Reports, ISSN: 22993657, No.8, pp.1233, 1998  
30.  Meissner M., Oscylacje samowzbudne w rurociągu z zamkniętymi odgałęzieniami, Prace IPPT  IFTR Reports, ISSN: 22993657, No.18, pp.140, 1994  
31.  Meissner M., Zjawisko nieliniowości przy oddziaływaniu ciśnienia akustycznego na rezonator Helmholtza, Prace IPPT  IFTR Reports, ISSN: 22993657, No.19, pp.150, 1994  
32.  Meissner M., Ranachowski Z., Generacja i propagacja wzorcowych impulsów emisji akustycznej, Prace IPPT  IFTR Reports, ISSN: 22993657, No.36, pp.147, 1992  
33.  Meissner M., Generacja dźwięku o dyskretnej częstotliwości przy opływie wnęki głębokiej przez strumień gazu (Praca doktorska), Prace IPPT  IFTR Reports, ISSN: 22993657, No.8, pp.1144, 1991 
List of chapters in recent monographs
1. 498  Meissner M., Postępy Akustyki 2016, rozdział: Improving acoustics of hardwalled rectangular room by ceiling treatment with absorbing material, Polskie Towarzystwo Akustyczne, Oddział Warszawski, Warszawa, Poland, pp.413424, 2016 
2. 499  Meissner M., Postępy Akustyki 2016, rozdział: Wavebased method for simulating small room acoustics, Polskie Towarzystwo Akustyczne, Oddział Warszawski, Warszawa, Poland, pp.425436, 2016 
3. 408  Meissner M., Progress of Acoustics, rozdział: Numerical Analysis of Sound Decay Process in Acoustically Coupled Spaces, Polskie Towarzystwo Akustyczne, pp.497508, 2015 
4. 190  Meissner M., Renewable energy: innovative technologies and new ideas, rozdział: Acoustics of irregular rooms in buildings: lowfrequency mathematical modelling and numerical simulation, Warsaw University of Technology (Warsaw), Chwieduk D., Domański R., Jaworski M. (Eds.), pp.265272, 2008 
Editor of monographs
1. 500  Meissner M.^{♦}, Postępy Akustyki 2016, Polskie Towarzystwo Akustyczne, Oddział Warszawski, Warszawa, Poland, pp.1682, 2016 
Conference papers
Patents
Numer/data zgłoszenia patentowego Ogłoszenie o zgłoszeniu patentowym  Twórca / twórcy Tytuł Kraj i Nazwa uprawnionego z patentu  Numer patentu Ogłoszenie o udzieleniu patentu  

396560 20111006 BUP 08/13 20130415  Raunmiagi Z.^{♦}, Ranachowski Z., Meissner M. Sposób i urządzenie do oceny stanu technicznego rozpylacza paliwa, do silnika z samoczynnym zapłonem PL, Akademia Morska w Szczecinie  217570 WUP 07/14 20140731 