DOI： 10.3397/1/376643

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DOI： 10.7567/JJAP.57.07LC09

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

The validity and applicability of an extended-reaction theoretical model, two local-reaction theoretical models and a finitedifference time-domain numerical model for outdoor sound propagation that take the ground reflection into account are tested varying the flow resistivity from 75 to 20 000kPa-s/m2. It was found from comparisons of the results that (1) the validity of the extended reaction model is confirmed under low flow resistivity, (2) the local reaction is a valid assumption for the tested grounds, (3) the two local reaction models agreed with each other and (4) the numerical model differed from the theoretical models under low source height, long range and high flow resistivity conditions.

DOI： 10.3130/aije.83.355

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Noise Control Engineering  

Wind is known to affect sound propagation outdoors. The effects become significant under a propagation distance of more than several tens of meters and makes impact on propagation of environmental noise in urban scale. Among such environmental noise, road traffic noise (RTN) is a primary noise source in most urban situations. Hence, prediction of the wind effects to the RTN propagation is important. In this paper, measurements of the wind effects to the RTN propagation are performed. Furthermore, calculations using theoretical models are compared with the measurement results. For measurements, an anemometer and microphones are placed along a line perpendicular to an embanked road with intense traffic with distances of 50–250 m from the road. Calculations simulating the measurements are performed using a theoretical model (Rasmussen, J. Sound Vib. 104, 321-335, 1986) and its modified models. The measured results show decrease of excess attenuation with increase of vector wind at middle and high frequencies, which is in line with known wind effects. However, an adverse effect is seen in a low frequency. A modified Rasmussen's model was able to reproduce the adverse wind effects, whereas other models were not.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Noise Control Engineering  

To predict acoustic environment in a realistic situation, it is desirable to measure acoustic properties of absorbing material surfaces and ground surfaces in-situ. Brandão et al. have published a comprehensive review of a number of in-situ measurement techniques of surface acoustic properties [Acta Acust. United Acust. 101, 443-463, 2015]. However, the review is hypothetical in that the techniques are compared on paper and not backed by actual measurements. In this study, three in-situ techniques are chosen from the review and comparative investigations through actual measurements are carried out. The measurement techniques chosen are those proposed in [J. Acoust. Soc. Am. 75, 382-389, 1984] (the Cramond technique), [J. Acoust. Soc. Am. 77, 1617-1618, 1985] (the Allard technique) and [Appl. Acoust. 66, 845-865, 2005] (the environmental anonymous (EA) technique). The Cramond and Allard techniques are chosen because they are considered as two of the origins of more modern techniques. The EA technique is chosen because the authors have been using for ground surface measurements. Measurements of surface impedance and absorption coefficient are carried out for sheets of polyester nonwoven, grass and compacted soil. Measurements of ground surface with low absorption are found to be difficult by the Cramond technique and the frequency interval of obtained results is difficult to make narrower than a few hundred Hz. The Allard technique is found to be unsuitable for indoor measurements but barely suitable for outdoor measurements where no reflected waves from walls or ceilings are present. The EA technique is found to produce reasonable results for both indoor and outdoor measurements.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：German Acoustical Society (DEGA)  

In our previous work, the effects of meteorological elements to the variance of the ground absorption coefficient have been modeled through a long-term in-situ measurement campaign but with remaining unexplained variations (Oshima et al., Inter-Noise 2015). The variations could be attributed to the uncertainty of the employed acoustic measurement technique, the EA method. The method was used because it requires only several portable loudspeakers and two microphones. In this work, the characteristics of the EA method in measuring the ground surface in-situ were systematically investigated by modeling the measurement process of the method. Using the model, the surface impedance and the absorption coefficient were calculated for oblique incidence conditions with varying incident angles and random incidence conditions with varying number of sound sources, averaging times and probability distributions of the incident angles. The results show that for the oblique incidence conditions, the imaginary part of the surface impedance becomes positive as the incident angle becomes larger. For the random incidence conditions, wide variance of the surface impedance is seen at low frequencies and slight variance of the absorption coefficient is seen at high frequencies with varying amount of oblique incident components.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Acoustical Society of Japan  

The applicability of the FMBEM to large outdoor problems was basically investigated. Conclusions are as follows. (i) The computational costs of the LF-FMBEM have no systematic relation with model size (root cell size) up to 1-km scale models. (ii) An increase in the root cell size directly increases the computational costs of the HF-FMBEM. (iii) It is much more inefficient in the HF-FMBEM to simply reduce the largest cell size used for computation with keeping high computational accuracy. (iv) An empirical formula proposed in Ref. [7] for the truncation number of infinite summation in the HF-FMBEM gives good values for high computational accuracy even in the range of kD ≤ 4
000, which corresponds to f ≤ 2
500 Hz with the root cell 200m on each side, if an appropriate value is chosen for its parameter.

DOI： 10.1250/ast.37.87

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACOUSTICAL SOC AMER AMER INST PHYSICS  

Knowledge of distinct effects of moisture content and air volume on acoustic properties of soil is sought to predict the influence of human activities such as cultivation on acoustic propagation outdoors. This work used an impedance tube with the two-thickness method to investigate such effects. For a constant moisture weight percentage, the magnitude of the characteristic impedance became smaller and the absorption coefficient became higher with increase of the air space ratio. For a constant air space ratio, the absorption coefficient became larger and the magnitude of the propagation constant became smaller with increasing moisture weight percentage. (C) 2015 Acoustical Society of America

DOI： 10.1121/1.4929736

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACOUSTICAL SOC AMER AMER INST PHYSICS  

Comparisons of finite-difference time-domain sound propagation simulations over real-life urban topography with scale-model experimental measurements are performed. A 1:100 scale model for the measurements and full-scale input geometry for the simulations are created by using digital geographic datasets. The sound pressure levels obtained by the measurements and simulations resulted in approximately 2 dB of root mean square error in the 125 and 250 Hz octave bands, and 4 dB in 500 Hz. Visualizations of a low-frequency sound propagation case by the measurement and simulation clearly show the wave phenomena caused by buildings and natural terrain. (C) 2014 Acoustical Society of America

DOI： 10.1121/1.4879672

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本建築学会  

A conventional selection criterion of room air conditioners based on rated performance is considered suboptimal from the standpoint of energy efficiency. In order to help consumers evaluate energy performance, annual performance factor (APF) was introduced in the 2005 revision of JIS C 9612. However, APF assumes thermal environment of Tokyo, which makes regional deviation of APF remain unknown. In the present study, rated coefficients of performance (COPs) and market prices of year 2012 models of air conditioners are collected. From the collection, APFs are calculated at nine representative cities in Japan to quantify regional characteristics of APF.

DOI： 10.3130/aijt.20.187

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With the recent progresses in computer performance and simulation techniques, it is becoming feasible to apply full three-dimensional wave-based numerical simulation techniques to large-scale problems of real-life sound propagation outdoors. In the present paper, a reconstruction technique for real-life urban geometries with full reproduction of the roof shapes and for the ground profiles using digital geographic information is presented. Also, a generation technique for the uniform rectilinear grid used in finite-difference time-domain simulations is presented. The types of geographic dataset used for the reconstruction are a digital surface model and a two-dimensional building outline map. For comparison, another geometry with flat building roofs, which is the type of geometry used in former noise-mapping studies using empirical models, is created. Comparison of the results of finitedifference time-domain acoustic simulations performed over the geometries shows sound pressure level differences above and behind buildings. The maximum level difference of 10 dB in magnitude indicates the necessity of proper reconstruction of the roof shapes in real-life urban acoustic simulations. © 2014 The Acoustical Society of Japan.

DOI： 10.1250/ast.35.108

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Australian Acoustical Society  

We have calculated the flow-induced sound pressure field using Lighthill's acoustic analogy by means of an acoustic boundary element method (BEM). For this calculation, firstly, an unsteady flow field is calculated using a computational fluid dynamics (CFD) solver. Then acoustic sources are extracted from the result and transformed into the frequency domain. Finally, these are used as quadrupole acoustic sources in the acoustic BEM model. In the BEM calculation, because some of the CFD grid points exist quite close to the BEM elements, for example 100 times smaller than the element length, so the contribution from the sources must be evaluated quite preciously. To achieve this, the elemental integration of the source contribution is introduced. We have validated the procedure (CFD/BEM approach) by comparing with an experimental data. The first validation is a comparison of the acoustic pressure generated by a low Mach number flow past a 3D circular cylinder. The second validation is a comparison of the acoustic pressure induced by a low Mach number flow in a bending duct. Finally the transmitting acoustic pressure which is originally induced by a flow through an elastic structure is calculated by the structural-acoustic coupled model.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Australian Acoustical Society  

In Inter-Noise 2013, the authors presented a study comparing acoustic propagation measurements over a 1:100 scale model of a real-life urban topography and large-scale three-dimensional finite-difference time- domain simulations. The results were presented in octave-band sound pressure levels. As a sequel to the 2013 paper, this paper compares the results in time domain. The waveforms of acoustic pulse propagation are computed by inverse filtering the source responses of an electric spark generator of the measurements and a Gaussian pulse of the simulation. The results show excellent matches at line-of-sight and single diffraction receiver positions in overall waveform structure, especially in arrival times of the diffracted and reflected pulses. The arrival time matched even after 0.7 s of traveling time. However, major discrepancies are observed at a receiver position which is affected by a combination of double diffraction and multiple reflections and positions affected by deep triple diffractions. Furthermore, in such positions, the simulated waveforms are found to have more energy in higher frequency. The discrepancies are possibly attributed to the use of rigid surfaces in the simulation and the lack of air absorption correction in the measured data processing.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The procedure of sound propagation calculation employing the linearized Euler (LE) model has been known to be complex because the procedure requires a chaining of two distinct simulations, namely a fluid dynamics simulation (CFD) in order to solve the background flow field, and a succeeding sound propagation simulation using the LE model over the flow field. The complexity is considered one of the main reasons why the most of the applications of the model remain in investigations assuming highly abstract geometries. In the study, a streamlined workflow is established for LE simulations over a complex urban terrain with its reconstruction utilizing digital geographic models which provide building outline maps and digital surface elevation information. Focus is given to automatic geometry reconstruction and mesh generations of realistic urban terrain. Subsequent processes of CFD and LE simulations are validated through comparisons with published results of wind-tunnel tests and with theoretical solutions. The workflow is deployed to an actual urban terrain of Nagaoka, Japan. The present technique generates a good reconstruction of urban geometry and subsequent split-hexahedral unstructured grid for CFD software and uniform structured mesh for finite-difference LE simulation. The numerical experiments show differences of up to 5 dB between sound pressure levels obtained by the present reconstruction technique and those by a flat-roof geometry. Also, the wind effects are mostly representable in terms of the source-observation point distance in spite of the complex urban configuration. Subtle wind effects of less than 0.5 dB are observed in crosswind condition as well. (c) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.apacoust.2013.05.006

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本建築学会  

This paper describes particle image velocimetry (PIV) air flow measurements in a room model of scale 1:0
the model has inlets and outlets across its width. The PIV measurements use three types of tracer particles: water mist, oil mist, and metal powder. The air flow distribution and turbulence intensity are measured by PIV with metal powder tracers in four combinations of inlet and outlet positions. The results are as follows
(1) Among the three tracer particles, metal powder yields the best air flow measurements in the 1:10·scale room model. (2) To obtain uniform luminance, an appropriate tracer particle concentration and increased laser output are required. (3) When the inlet and outlet are located midway across the scale model, the air flow velocity in the room in nearly symmetrical. In this case, air enters straight through the inlet, is sucked into the outlet, and is largely discharged. The air not discharged from the outlet collides with the side-wall of the outlet to forms a symmetrical vortex area.

DOI： 10.3130/aije.78.631

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本建築学会  

One of the effects of the 2011 Tohoku earthquake and the subsequent power disruptions was an increased demand for electricity. As a result, there have been societal efforts to reduce electricity usage and to provide electrical power more equitably. Private power generation by a fuel cell cogeneration system (FCCGS) recently proposed for home use is expected to advance the efficient utilization of primary energy sources and contribute to energy conservation. In this paper, we present the results of a case study on peak electricity demand by modeling the district served by the Tohoku Electric Power Company. The study analyzes the effects on peak power demand if residences in the district were equipped with FCCGSs. For this study, we assume that the FCCGSs are installed in groups of 100,000 units. The groups are composed of FCCGS units with different rated outputs whose hours of operation throughout the day are distributed among the groups. Power supply, primary energy consumption, and CO2 emission amounts both before and after the installation of FCCGSs are recorded in order to quantify the cut in peak demand for electricity. The results of the study demonstrate that peak demand can be cut if FCCGSs are installed in 5% or less (in winter) and about 25% (in summer) of all the private residences in the district served by Tohoku Electric Power Company.

DOI： 10.3130/aije.78.639

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本建築学会  

It has been known that the road traffic noise propagation is affected by the wind. However, not so many studies deal with the effect in conjunction with microscopic wind conditions. In the present study wind conditions around a road embankment and their influence on sound propagation were investigated by two-point simultaneous measurements of noise and wind velocity in an open suburban area. Results show that (1) the wake turbulence by the embankment affects variance in received sound pressure levels, (2) the wind velocity component parallel to the road could also be affecting sound propagation.

DOI： 10.3130/aije.78.317

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本建築学会  

The effect of improving indoor environment by the cross ventilation, the rate to discharge thermal energy by the ventilation is larger than the reduction effects of SET* by indoor air flow. In this study, the relationship between the difference of indoor temperature and outdoor temperature by the effect of ventilation will be less than 1°C and the opening area of windows ratio are calculated for a simple and the standerd AIJ detached house model. The relationship between the air change rate, opening area of windows conditions and cross ventilation performance of the detached house is clarified. The results are as follows
(1) When air change rate is 20 times/h, the inside air temperature becomes nearly equal to the outside air temperature due to the discharge thermal energy by the ventilation. (2) The opening area of windows ratio tends to be high in the inland, and it tends to be low in the city along the sea in Japan. (3) Results of standard AIJ detached house model, the opening area of windows ratio with which ventilation rate is 20 times/h becomes a low value of feasibility. The opening area of windows ratio with which ventilation rate is 10 times/h becomes a values that may be realized.

DOI： 10.3130/aije.78.277

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Language：English   Publishing type：Research paper (scientific journal)  

There has been carried out a number of experimental studies with regard to wind effects to outdoor sound propagation. Most of the studies deal with propagation from steady-state point source such as a loudspeaker in case of field measurements. However, wind effects to more realistic sources, such as road traffic noise sources which are considered to be time-varying line sources, are hardly known in public literature. In the present study, the wind effects to acoustic propagation from a straight road with intense traffic to an open and flat field were investigated through field measurements in order to specifically illustrate the effects of such sources. Two measurement points were placed at 40 m and 140 m distance from the subject road. The results show that (1) The standard deviations of sound pressure levels (SPLs) at the measurement points were around 2 dB for both receiver distances. (2) The effect of perpendicular component of wind velocity to the road direction was slightly stronger than the ASJ Model which was mostly derived from point-source experiments. (3) The effect of source time-variance was effectively taken out by taking the difference in SPLs at the nearby and distant measurement points, in which case the standard deviations of the excess attenuation were reduced to around 1.3 dB. (4) Slight tendency of coherence magnitude of sound pressure between the receivers converging to zero with increasing turbulent kinetic energy is observed in 125 Hz and 250 Hz bands. Meanwhile, the effect of parallel wind velocity component to the road still remained unclear and thus requires further investigations. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.apacoust.2012.07.003

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Language：English   Publishing type：Research paper (scientific journal)  

The article examines time-domain outdoor acoustic simulation of a real-life area using land cover classification identified by airborne hyperspectral imagery. In order to solve the identification problem, the authors presented a classification technique of using airborne hyperspectral imagery for land cover types in a real-life area. The simulation employs a porous-medium model for the solution of acoustic absorption by the surfaces. A validation of the porous-medium model through comparisons with exact solutions is given. The results are compared with those obtained assuming perfectly reflecting surfaces. The source is a coherent linear Gaussian pulse with a full width at half maximum of 1.25m and an amplitude of 1 Pa placed on a road, assuming a road traffic noise source.

DOI： 10.1250/ast.34.364

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Language：English   Publishing type：Research paper (scientific journal)  

The article presents a possible land cover classification estimation technique specialized for acoustic simulations using high-accuracy hyperspectral imaging data through a case study using a Nagaoka sample. The image was obtained by PASCO Corp. on 5 June 2004 using the Airborne Imaging Spectroradiometer for Application (AISA), which is a hyperspectral sensor with a 1m spatial resolution developed by Spectral Imaging Ltd. The image data comprise 67 bands, covering both the visible and a part of near-infrared wavelengths from 400 nm to 1,000 nm. Spectral band widths are equally spaced by 8-9 nm. The spectrum value at each picture element indicates a normalized spectral reflectance, which is calculated based on the spectral radiance of the ground surface and the sun observed simultaneously. The land cover classification that should be estimated is determined by referring to ASJ RTN-Model 2008 in the first step to discuss classification methods.

DOI： 10.1250/ast.34.367

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OAL-Osterreichischer Arbeitsring fur Larmbekampfung  

On Inter-Noise 2011, one of the authors presented a finite-difference time-domain simulation technique of outdoor sound propagation problems over a reconstructed geometry of a real-life urban area using digital geographic information. However, the technique has not been validated against a real-life or a scale model experiment. Of the two, a scale model experiment allows precise controls over problem geometry and experimental conditions. In the present study, a geometry of a real-life urban area in Kanagawa, Japan is reconstructed using three types of digital geographic information: A digital surface model, a digital elevation model and a building outline dataset. A 1:100 scale model of the geometry is created from the geometry by a combination of numerically controlled machining of the terrain and handicrafts of the buildings. Experiments are carried out to measure shieldings and diffractions by the buildings and the terrain. In parallel with the experiments, large scale finite-difference time-domain simulations are performed over the same geometry and conditions using a supercomputer. Comparisons of the experimental and the simulation results show good agreements at low frequencies. However, notable differences are observed at shadow zones of the buildings in high frequencies and at street canyons where multiple reflections occur.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The fast multipole boundary element method (FMBEM) has been well known as a highly efficient BEM with the use of the fast multipole method (FMM). In the present paper, an efficient technique for plane-symmetric acoustic problems is proposed in the framework of an FMBEM based on the original multipole expansion theory (FMBEM for low-frequency problems: LF-FMBEM). Presented here are concrete computational procedures, which are based on the symmetries among multipole expansion coefficients for a plane-symmetric sound field produced by monopole or dipole sources. The proposed technique is straightforwardly applicable to a variety of formulations for the BEM, such as hypersingular, Burton-Miller, and indirect formulations. Numerical results show an ideal improvement of computational efficiency, with the proposed technique reducing both the computation time and required memory to about 1/2(nsym) of those using the standard LF-FMBEM, where n(sym) is the number of planes of symmetry. (c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.enganabound.2012.04.006

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Language：English   Publishing type：Research paper (international conference proceedings)  

There are a lot of studies on calculation methods for outdoor sound propagation. In Japan, ASJ RTN-Model 2008 has been widely known and used for prediction of road traffic noise. However, due to the fact that many of these methods are energy-based ones, the application range and the problem types to which they are applicable are limited and considerably complicated. With this background, we have studied on wave-based calculation methods for outdoor sound propagation in large area. In the present paper, we perform a basic investigation for prediction of propagation in large area using the fast multipole BEM (FMBEM). As a first study, here we use the FMBEM for low-frequency problems (LFFMBEM). We investigate the effect of the size, shape, and distribution of analysis objects on the computational accuracy and efficiency, keeping the number of unknowns almost fixed. Numerical results show that the LF-FMBEM can calculate 1-km-size problems without losing computational accuracy and efficiency, if the analysis frequency is in the application range of the method.

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Language：Japanese   Publisher：公益社団法人 空気調和・衛生工学会  

In recent years, the use of BIM for commercial applications of architecture has been increasing. BIM is used for planning, schematic design, working drawing, maintenance, management, and so on. When CFD simulation is performed for developing the design of air-conditioning systems, it is usually required to define the geometry of HVAC systems and boundary conditions such as the value of airflow velocity at the supply opening. If BIM is employed, such data as well as information can be extracted from BIM into the simulation in the form of "CFD parts." "Subcommittee of Integration of BIM and Modularization of Elements for CFD," which is a part of "The Society of Heating, Air-Conditioning and Sanitary Engineers of Japan," is deciding the data formats and the guidelines for the use of BIM, and is promoting it. This paper shows the current situation of research involving BIM. The data coupling of BIM between thermal load calculation and CFD simulation has been examined in one of the activities of "Integrating BIM Working Group," which is a part of the committee.

DOI： 10.18948/shase.36.174_15

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Language：English   Publishing type：Research paper (international conference proceedings)  

There has been a number of experimental, theoretical and numerical studies regarding wind effects on outdoor sound propagation, most of which focus on propagation from steady-state point source such as a loudspeaker in case of field measurements. However on the other hand, wind effect studies on more realistic sources, such as road traffic noise sources which are considered to be timevarying line sources, are hardly known in public literature. In the study, the wind effects to acoustic propagation from a straight road with intense traffic to a at and open field is investigated through a series of field measurements to specifically illustrate the effects of such sources. The results show that 1) The standard deviations of SPLs at the measurement points were around 2 dB regardless of the distance from the road, 2) The effect of perpendicular component of wind velocity to the road direction was slightly stronger than the ASJ Model which was mostly derived from point-source experiments. 3) The effect of source time-variance was effectively taken out by taking the difference in SPLs at the nearby and distant measurement points, in which case the standard deviations of the excess attenuation were reduced to around 1.4 dB. Meanwhile, the effect of parallel wind velocity component to the road still remained unclear in the study and thus requires further investigations.

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Language：English   Publishing type：Research paper (international conference proceedings)  

The fast multipole boundary element method (FMBEM) has been known as a highly-efficient BEM with the use of the fast multipole method (FMM). There are two types of FMBEM: FMBEM in which the well-known high-frequency diagonal form is employed (FMBEM for high frequency problems: HF- FMBEM), and FMBEM based on the original multipole expansion theory (FMBEM for low-frequency problems: LF-FMBEM). In the present paper, an efficient technique is proposed to deal with plane- symmetric acoustic problems in the framework of the LF-FMBEM. Firstly, symmetrical relations among multipole expansion coefficients for a plane-symmetric sound field produced by monopole/dipole sources are derived from the properties of the spherical harmonics. These relations enable limiting the calculation of multipole and local expansion coefficients to 1/2, 1/4, or 1/8-space, when one, two, or three planes of symmetry exist. Based on these relations, the outline of computational procedures for the LF-FMBEM for plane-symmetric acoustic problems is presented. The computational efficiency of this technique is validated through a numerical experiment. Copyright © (2011) by the Institute of Noise Control Engineering.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The fast multipole boundary element method (FMBEM), which is an efficient BEM that uses the fast multipole method (FMM), is known to suffer from instability at low frequencies when the well-known high-frequency diagonal form is employed. In the present paper, various formulations for a low-frequency FMBEM (LF-FMBEM), which is based on the original multipole expansion theory, are discussed; the LF-FMBEM can be used to prevent the low-frequency instability. Concrete computational procedures for singular, hypersingular, Burton-Miller, indirect (dual BEM), and mixed formulations are described in detail. The computational accuracy and efficiency of the LF-FMBEM are validated by performing numerical experiments and carrying out a formal estimation of the efficiency. Moreover, practically appropriate settings for numerical items such as truncation numbers for multipole/local expansion coefficients and the lowest level of the hierarchical cell structure used in the FMM are investigated; the differences in the efficiency of the LF-FMBEM when different types of formulations are used are also discussed.

DOI： 10.1142/S0218396X10004243

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Language：English   Publishing type：Research paper (international conference proceedings)  

The fast multipole BEM (FMBEM), which is well known as an efficient BEM with the use of the fast multipole method (FMM), has been studied a lot in the field of acoustics. However, studies on energy decay fields particularly in porous materials are hardly seen since the assumed medium in many of the FMBEM studies is limited to the air. We have already proposed a setting for FMBE analyses of porous material fields and validated the setting through numerical experiments with simple-shaped models (Y. Yasuda, et al., Inter-Noise 2008). In the present paper, the FMBEM with a domain decomposition approach is applied to a complex-shaped room that includes porous-type sound absorbers. Numerical results by the standard BEM and by the FMBEM with the proposed setting agree well. Moreover, the FMBEM shows much more rapid convergence of iterative solutions than the standard BEM.

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Language：English   Publishing type：Research paper (international conference proceedings)  

The fast multipole boundary element method (FMBEM), which is an efficient BEM with the use of the fast multipole method (FMM), is known to have instability at low frequencies when the well-known diagonal form for translation of multipole/local coefficients is employed. To overcome this problem, we have already developed a low-frequency FMBEM (LF-FMBEM), which is based on the original multipole expansion theory with translation techniques proposed by Gumerov and Duraiswami for avoiding the low-frequency instability. In the present paper, the degenerate boundary formulation, which is often referred to as the dual BEM, is discussed in the framework of the LF-FMBEM. The degenerate boundary formulation enables not only analyzing degenerate boundary models which have unknowns on both sides of the boundaries, but also avoiding well-known fictitious eigenfrequency difficulties for exterior problems. A concrete computational procedure of the LF-FMBEM based on the degenerate boundary formulation is described in details, which results in O(N) operation counts and memory requirements. The computational accuracy and efficiency are validated through numerical experiments. Moreover, practically appropriate numerical settings on truncation numbers for multipole/local expansion coefficients and the lowest level for the hierarchical cell structure used in the FMM are investigated. Numerical results and computational efficiency of the LF-FMBEM are compared with those of the high-frequency FMBEM (HF-FMBEM), in which the diagonal form is employed. Copyright © (2010) by the International Congress on Acoustics.

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Language：English   Publishing type：Research paper (international conference proceedings)  

There are an increasing number of reports about applications of fast multipole algorithms to large-scale boundary element sound field analyses. However, Rokhlin's diagonal translation theory, adopted to most of the algorithms due to its efficiency for translating multipole coefficients, is at the same time known to cause numerical instability at low frequencies. One way to avoid the instability is to purposely degrade its efficiency and accuracy, while another is to prepare meshes with different element densities for the same geometry, each of which is optimal for certain frequency ranges. As neither is thought to be practical for large-scale complex problems, we address the issue by another translation theory proposed by Gumerov and Duraiswami, especially meant to be used for low-frequency ranges. Further, we apply the fast multipole algorithm based on this translation theory to the boundary element method. The procedure will be validated and tested against a conventional fast multipole algorithm under a single common mesh per problem in terms of timing, accuracy and stability.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The convergence behavior of the Krylov subspace iterative solvers towards the systems with the 3D acoustical BEM is investigated through numerical experiments. The fast multipole BEM, which is an efficient BEM based on the fast multipole method, is used for solving problems with up to about 100,000 DOF. It is verified that the convergence behavior of solvers is much affected by the formulation of the BEM (singular, hypersingular, and Burton-Miller formulation), the complexity of the shape of the problem, and the sound absorption property of the boundaries. In BiCG-like solvers, GPBiCG and BiCGStab2 have more stable convergence than others, and these solvers are useful when solving interior problems in basic singular formulation. When solving exterior problems with greatly complex shape in Burton-Miller formulation, all solvers hardly converge without preconditioning, whereas the convergence behavior is much improved with ILU-type preconditioning. In these cases GMRes is the fastest, whereas CGS is one of the good choices, when taken into account the difficulty of determining the timing of restart for GMRes. As for calculation for rigid thin objects in hypersingular formulation, much more rapid convergence is observed than ordinary interior/exterior problems, especially using BiCG-like solvers.

DOI： 10.1142/S0218396X07003470

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Language：Japanese   Publisher：Architectural Institute of Japan  

Iterative solvers are widely used for solving large systems of linear equations, and applied to the systems obtained with the acoustical FEM and BEM. In the present paper, the convergence behavior of the Krylov subspace iterative solvers towards the systems with the 3-D acoustical fast muftipole BEM, an efficient BEM based on the fast multipole algorithm, is investigated through numerical experiments. The convergence behavior of solvers is much affected by the formulation of the BEM (basic form (BF), normal derivative form (NDF) and Burton-Miller formulation), the complexity of the shape of the problem, and the sound absorption property of the boundaries. In BiCG-like solvers, GPBiCG and BiCGStab2 converge more stable than others, and these solvers are useful when solving interior problems using BF. When solving exterior problems with greatly complex shape using Burton-Miller formulation, all solvers hardly converge without preconditioning, whereas the convergence behavior is much improved with ILU-type preconditioning. In these cases GMRes is the fastest, whereas CGS is one of the good choices, when taken into account the difficulty of determining the timing of restart for GMRes. As for calculation for thin objects using NDF, much more rapid convergence is observed than ordinary interior/exterior problems, especially using BiCG-like solvers.

DOI： 10.3130/aije.71.15_3

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Other Link： http://hdl.handle.net/10191/18374

Language：Japanese   Publisher：日本建築学会  

Finite-difference time-domain (FDTD) acoustic simulation technique in generalized curvilinear coordinates using contravariant velocity and pressure as variables for two-step leapfrog time marching scheme is presented. The technique excels the conventional generalized curvilinear technique using contravariant velocity, covariant velocity and pressure as variables for three-step time marching, especially in that normal acoustic impedance boundary conditions which are indispensable in practical application are also presented. Validation of the technique through comparison against orthogonal FDTD with staircasing applied in irregularly-shaped sound field shows suppressions of phase error in initial time marching stage and diffusion from staircased boundaries.

DOI： 10.3130/aije.71.9_1

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Language：Japanese   Publisher：日本建築学会  

Estimation technique of aerodynamic sound radiation from a cylindrical body using results of partial-span CFD computation is presented. The technique replaces the calculation of Curie equation in Lighthill-Curle computational aeroacoustics technique, and is based on Morse-Ingard's and Goldstein's theory and coherence model function. The validation of the model function and the technique through wind-tunnel experiment results 1) measured coherence between surface fluid forces on the body surface shows good agreement with the model function, and 2) reasonable agreement is obtained between measured SPL at a receiving point and estimated SPL using the technique.

DOI： 10.3130/aije.70.15_8

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Language：English   Publisher：ACOUSTICAL SOCIETY OF JAPAN  

DOI： 10.1250/ast.24.139

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10572443

Language：English   Publisher：ACOUSTICAL SOCIETY OF JAPAN  

DOI： 10.1250/ast.24.100

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10572430

Language：English   Publisher：ACOUSTICAL SOCIETY OF JAPAN  

DOI： 10.1250/ast.22.367

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10572254

Language：Japanese   Publisher：Architectural Institute of Japan  

Quantitative methods for predicting aeroacoustic noise radiated from balusters of buildings have been expected as a tool for its effective reduction. We applied a numerical method of solution based on Lighthill-Curle equation. As a basic step, we attempted to predict characteristics of the sound radiated by airflow around a row of square cylinders at Reynolds number 1000 by 2-dimensional analysis. We also made a comparison of solutions of an isolated cylinder wake flow at the same Reynolds number by 2- and 3-dimensional analyses, as a preparation for further improvement of the method.

DOI： 10.3130/aija.65.7_3

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Other Link： http://hdl.handle.net/10191/18380

To date, numerical simulation for sound wave propagation has been widely investigated as a result of advances in?computer?technology.?For?acoustic imaging?and prediction, the development of accurate and effective?analysis?methods in time domain has become an important technical issue. The constrained?interpolation?profile (CIP) method, a novel low-dispersive numerical scheme, is a type of method of characteristics (MOC) employing a co-located grid system. In our past study, we have applied the CIP method to solving the linearized?sound propagation?equation.?MOC is the calculation method which transforms governing?equations?of acoustic field into advection?equationsto solve the acoustic fields. Therefore, the method should be suitable for solving?sound propagationconsidering the background flow?effect,?e.g., prediction of sound noise environment generated from a propulsion system of aircrafts or rockets. In the study, we proposed and examined the calculation method of?sound propagation?in an arbitrary background flow using CIP method. We made a numerical comparison between proposed method and the linearized Euler?equations?(LEE) method. The presentation has clarified that the CIP method is more accurate and effective for solving?sound propagation?in a strong and/or heterogeneous background flow.

DOI： 10.1121/1.4970286

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this study, we present a fundamental examination on analysis of extremely low frequency sound waves caused by tsunami. We show a numerical visualization of sound wave propagation using finite-difference time-domain (FDTD) method considering altitude data of the islands of Japan. We made a numerical estimation of the properties of the 3-D sound wave propagation, and evaluate the modeling of tsunami-induced sound waves, compared with the observed data.

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Other Link： http://www.aij.or.jp/paper/detail.html?productId=396491

Language：Japanese   Publisher：Acoustical Society of Japan  

DOI： 10.20697/jasj.69.8_407

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Language：Japanese   Publisher：日本流体力学会  

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Language：Japanese   Publisher：日本騒音制御工学会  

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A standardization of modularized CFD elements for architectural environmental designs is under way at a SHASE committee. In the heart of the works is a draft of standardized XML-based format which is intended to provide architectural elements such as air-conditioning inlets and outlets as computational boundary conditions for CFD. Even in the early stage of the format definitions, it should be noted that verifying how the proposed format works through actual implementations to production-level CFD software is important. In this paper, the implementations are attempted and tested with the four software: FlowDesigner, STREAM, WindPerfectDX and OpenFOAM.

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In this study, we present a fundamental examination on analysis of extremely low frequency sound waves caused by tsunami. We show a numerical visualization of sound wave propagation using finite-difference time-domain (FDTD) method considering altitude data of the islands of Japan. We made a numerical estimation of the properties of the 3-D sound wave propagation, and evaluate the modeling of tsunami-induced sound waves, compared with the observed data.

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屋外において、音の伝搬は風の影響を受けるとされ、音の伝搬と風の関係について様々な研究が行われている。しかしながら、主要な環境騒音の一つである道路交通騒音に対する風の影響についての研究は少なく、少ないながらも風速に関しては1点でのみ測定が行われている。本研究では2点で風速の測定を行い、騒音伝搬への影響を調べることで1点での測定に基づいた気流効果モデルよりも精密なモデルの構築を試みる。

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Recently, the fast multipole method (FMM), originally proposed by V. Rokhlin, has been applied as a fast method for large-DOF potential problems in a variety of fields. In the fields of acoustics, especially those of architectural acoustics and noise control, the authors have studied on a BEM accelerated by the FMM (FMBEM) for Helmholtz equation. In these fields, development of efficient methods is much important because objects dealt with are large, such as buildings and civil engineering structures. In this paper, outline of our studies for multi-purpose FMBEM in the fields of architectural acoustics and noise control are presented: specifically, on formulations for various types of problems, on an efficient technique for plane-symmetrical problems, on domain decomposition and structural-acoustical coupled problems, on a technique to deal with porous materials, on convergence behavior of iterative solvers, etc. Numerical results in these fields are also shown.

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A standardization of modularized CFD elements for architectural environmental designs is under way at a SHASE committee. In the heart of the works is a draft of standardized XML-based format which is intended to provide architectural elements such as air-conditioning inlets and outlets as computational boundary conditions for CFD. Even in the early stage of the format definitions, it should be noted that verifying how the proposed format works through actual implementations to production-level CFD software is important. In this paper, the implementations are attempted and tested with the four software: FlowDesigner, STREAM, WindPerfectDX and OpenFOAM.

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時間領域有限差分(FDTD)法で不整形音場解析を行う場合,従来は境界形状を直交直線格子で分割するために階段近似が行われてきた.しかしながら階段近似による解析誤差が知られており,境界面に適合した格子分割が可能な一般曲線座標系の導入がより適切な状況が存在すると考えられる.そこで本報告では,近年提案されている一般曲線座標系を導入した反変速度-圧力交互時間進行によるFDTD音場解析手法を2次元で実装し,台形音場および不整形残響室音場の解析例を通して本手法が有効な手法となり得ることを示す.

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コンクリート構造物の加振応答計測による欠陥部の的確な検出方法の確立を目的とし, 既往研究[1]で用いられた模擬試験体を解析対象とした有限要素法による数値的検討を行った.既往実験で得られた振動変位振幅の複雑な振動姿態は試験体の固有振動によることを明らかにし, 近接した2測定点間で得られる複素振動変位実部の差分値の比較が比較的簡易な欠陥検出に有望との結果を得た.測定時の雑音への耐性の検証および無限要素の導入による開領域での検討が課題である.

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