Takumi Asakura

Finite-Difference Time-Domain Analysis of Sound Insulation Performance of Wall Systems

A prediction method for the sound insulation of walls by vibro-acoustical numerical analysis using the finite-difference time-domain (FDTD) method is described. In order to accurately predict the sound insulation performance of walls, numerical modeling of the vibration energy loss of walls in the vibration analysis is necessary. In this study, the energy loss at the boundary part of the plates and the internal damping of the plates are modeled and the sound transmission loss of glass plates and plasterboard walls is calculated. A reasonable agreement is found between the calculation and measurement results and the applicability of the numerical analysis is confirmed.

Prediction of low-frequency structure-borne sound in concrete structures using the finite-difference time-domain method

Due to limitations of computers, prediction of structure-borne sound remains difficult for large-scale problems. Herein a prediction method for low-frequency structure-borne sound transmissions on concrete structures using the finite-difference time-domain scheme is proposed. The target structure is modeled as a composition of multiple plate elements to reduce the dimensions of the simulated vibration field from three-dimensional discretization by solid elements to two-dimensional discretization. This scheme reduces both the calculation time and the amount of required memory. To validate the proposed method, the vibration characteristics using the numerical results of the proposed scheme are compared to those measured for a two-level concrete structure. Comparison of the measured and simulated results suggests that the proposed method can be used to simulate real-scale structures.

Noise reduction by eaves/louvers attached on façade of high-rise buildings

The authors have been investigating noise reduction effects of several types of eaves/louvers attached on facade of high-rise buildings. The eaves are originally used for the aim of shading of solar radiation or as structures for fire-proofing in Japan, but the devices can also provide high effectiveness of noise reduction against road traffic. The authors have revealed such effects through wave-based numerical analyses, scale model experiments and in-situ experiment. The eaves attached on the facade work as either noise shielding materials or noise reflectors, so inclined eaves at higher rooms have more effectiveness of noise reduction. The effectiveness varies with protrusion length of the eave, inclination angle, height of the room and so on. In this paper, such results of our investigation on noise reduction by eaves and louvers will be presented.

Visualization of acoustic resonance phenomena using Kundt’s dust figure method

It is very effective to visualize a sound field for intuitive understanding of various acoustic phenomena, especially for acoustic education. The most famous and classical visualization technique is the Kundt’s dust‐tube method contrived by August Adolph Kundt. He devised this experimental technique to determine the sound velocity in the air by observing the mode pattern of a standing wave excited in a glass tube. The technique can be applied to various other acoustic resonance phenomena. In Japan, Sato and Koyasu applied this technique to a two‐dimensional room acoustic model experiment in which the effect of the shape of a reverberation room on the normal modes was examined. Referring to these experiments, the authors made experimental equipment to visualize acoustic resonance phenomena for an educational purpose. In our experiment, two types of two‐dimensional boxes with hard surface were prepared. In these boxes, normal modes in a closed sound field and the Helmholtz resonance phenomena, which are essential and important for architectural acoustics, can be visualized. These physical experiments are visually impressive on students in architectural courses and therefore the experiment is efficiently used in architectural acoustic courses.

Finite-difference time-domain analysis of the vibration characteristics of building structures using a dimension-reduced model

In order to accurately predict the vibration characteristics of buildings, wave-based numerical methods are effective from the viewpoint of the modeling accuracy of the physical mechanism and the detailed geometries of the simulated field. However, because of the performance of current PCs, the prediction of real-scale problems remains difficult. In order to address such problems, we herein propose a vibration simulation method for a beam-plate structure using a dimension-reduced modeling method. The target structure is modeled as a composite structure consisting of two-dimensional plate elements and one-dimensional beam elements, which are coupled based on the implicit finite-difference approximation scheme. By applying such a low-dimensional element, a faster simulation that requires less memory, as compared with a three-dimensional discretization scheme, is made available. To validate the method, the vibration characteristics obtained by the proposed scheme are compared to the measured results for mode...

Acoustic Property Simulation for Building Components

This chapter shows practical examples of numerical simulation results for acoustical characteristics of building elements, such as the sound absorption, sound-scattering, and sound insulation performance. Additionally, radiation characteristics of speaker systems are also treated. In each section, methodologies and numerical modeling schemes of the simulation, and the calculated results for practical cases are illustrated. The results are validated through comparison with the measurement results, and the applicability of the numerical methods is discussed.

Noise Propagation Simulation

This chapter shows examples of numerical analyses on various noise propagation problems including outdoor noise propagation, noise barriers, depressed roads, building facades, building windows, and floor impact sound. In each section, considering the features of each problem, methodology of applying the simulation techniques presented in Part I to the practical problem is introduced and the calculated results are illustrated. Some of the calculated results are compared with measured ones and the applicability and efficiency of the analysis method are discussed.

Finite-Difference Time-Domain Method

In this chapter, analysis of sound and vibration using the Finite-Difference Time-Domain method (FDTD method) is illustrated. In Sect. 2.1, the fundamentals of the FDTD method are described. In the FDTD method, several error factors caused by discretization of sound field are pointed out. As methods to solve such problems, in Sect. 2.2, the compact finite difference is described in detail. The FDTD method can not only be applied to acoustic problem of air-borne sound, but also vibroacoustic problems such as a floor impact sound and a sound insulation problem through a wall structure. In Sect. 2.3, therefore, application of the FDTD method to vibroacoustic problems is focused on, and the theoretical background and its numerical formulation are described in detail.