岩本 宏之

<p>Noise countermeasures are an important engineering problem, and acoustic analysis methods for noise prediction and reduction have been widely studied. In general acoustic analysis, the temperature of the air is often assumed to be constant. However, the temperature gradient of the space may have a large effect on the sound pressure. For example, in a thermoacoustic engine, the sound is generated when the air vibrates due to the temperature gradient inside the pipe. Applying this effect may reduce noise by using the temperature distribution. Therefore, the purpose of this study is to formulate an acoustic space with a temperature gradient using a concentrated mass model. This model is consisted of the masses, springs and dampers. In addition, the relationship between temperature gradient and sound pressure is analyzed. In this paper, as a first step, a model using a linear spring is constructed, and the validity of the proposed model is confirmed by numerical calculation for a cylindrical pipe.</p>

<p>In active noise control<tt>，</tt>if total acoustic power is minimized<tt>，</tt>absorption and blowout of acoustic energy around the control source are balanced<tt>，</tt>and a zero power phenomenon occurs in which the time average of control power becomes zero. In this study, we aim at generalization of this phenomenon, the sound source is regarded as a flat plate structure embedded in an infinite baffle, and the generation condition of the zero power phenomenon is considered. First, we will clarify the reciprocity when the zero power phenomenon occurs in the case of three point sources. Next, the reciprocity of the zero power condition is clarified based on the control law derived from the sound sources emitted from the three flat plate structures.</p>

<p>This paper is concerned with active control of acoustic radiation power of a multi-walled structure. In the past literature, optimal control of acoustic radiation power for a double-walled structure in which both walls of the acoustic space are surrounded by flexible walls has been studied. It has been clarified that the reduction level of an actively controlled doublewalled structure is greater than that of an actively controlled one-walled structure in the sense of sound transmission control. Thus, the number of flexible walls have an impact on the control effect. However, research on modelling and control of a triple or more walled structure have not sufficiently done. Therefore, this paper presents how to model and control a triple walled structure.<tt> </tt>First, in order to facilitate further numerical analysis of multiple-walled structures, we model triple-walled structures using block inverse matrices, which is different from the conventional method. Next, the validity of the theory using the block inverse matrix is verified by comparing with the result of the numerical analysis for the triple-walled structure in the previous research. Finally, we verify the optimal control of acoustic radiation power by two control elements in a triple-walled structure from the numerical perspective, comparing its characteristics with the case of control by one control element.</p>

<p>In active noise control，if total acoustic power is minimized，absorption and blowout of acoustic energy around the control source are balanced，and a zero power phenomenon occurs in which the time average of control power becomes zero. In this research，we aim at generalization of the said phenomenon，and consider the generation condition of the zero power phenomenon in the case of multiple control sound sources. Next，based on the derived control rules，we will clarify the change in acoustic power due to the increase in the number of sound sources and the position from the viewpoint of numerical analysis. Finally，the zero power control law in the case of expanding the control sound source to n control sources is derived.Numerical analysis using the derived control law to prove importance.</p>

<p>This paper is concerned with active control of acoustic radiation power of a multi-walled structure. In the past literature, optimal control of acoustic radiation power for a double-walled structure in which both walls of the acoustic space are surrounded by flexible walls has been studied. It has been clarified that the reduction level of an actively controlled double-walled structure is greater than that of an actively controlled one-walled structure in the sense of sound transmission control. Thus, the number of flexible walls have an impact on the control effect. However, research on modelling and control of a triple or more walled structure have not sufficiently done. Therefore, this paper presents how to model and control a triple walled structure. First, the target structure is analytically modelled by using modal coupling method that utilizes modal amplitudes of the uncoupled subsystems. Next, the optimal control law for minimizing the acoustic radiation power of the triple wall structure is derived by using the elementary radiator method which calculates the acoustic radiation power based on the minute and divided elements of the panel. Finally, numerical simulations of the control system are conducted, confirming the effectiveness of the proposed method.</p>