A side branch silencer which is one of the reactive-type silencers is effective for the reduction of periodical sound. It is often used to reduce noise such as those due to pulsation pressure. This is especially effective for noise generating a single frequency. However, an effective frequency range is comparatively narrow obliging the silencer to be enlarged as a countermeasure of low frequency sound. This may cause problems concerning installation space. In order to develop a side branch silencer which is effective at low frequency ranges, a side branch with the finite impedance at the end was made and examined. As a result, it was clarified that this side branch was useful for low frequency noise.

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Aerodynamic noise is a major source of wayside noise generated by high-speed railway vehicles, and thus it is important to reduce this phenomenon. For this purpose, a new aerodynamic noise reduction method that involves covering the surface of objects with particular porous materials has been developed. To verify its aerodynamic noise reduction effects, wind tunnel tests using cylinders and high-speed pantographs were conducted. Field tests using the high-speed pantograph were also conducted. The results indicated that aerodynamic noise generated from the cylinders and the high-speed pantographs was reduced by the application of porous materials, thus confirming the effectiveness of this method. An advantage of this method is that it is possible to reduce aerodynamic noise with little modification of object shape. Furthermore, separate wind tunnel tests also demonstrated the effectiveness of the method in reducing aerodynamic noise in combination with simplifying the shape to allow easier material processing.

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Boilers and heat exchangers are widely used in various plants such as power and chemical plants. However, unexpected high level sounds are generated when these plants are operated and it becomes a serious problem. This kind of problem is called acoustic resonance. In addition, it has been considered that resonance generates when the frequency of the vortex shedding behind the tube bank coincides with the natural frequency of the duct system. However, it has also been thought of as a self-sustained tone. In general, the self-excited phenomenon arises when the exciting energy becomes greater than the dissipating energy. In this paper, in order to clarify the mechanism of the self-sustained tone experimentally, we tried to find the origin of the instability by changing the number of tube rows and acoustic damping. As a result, it was found that the self-sustained tone generates when the number of tube rows increases and the acoustic damping decreases.

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In automobile head-on collisions, some part of occupant's kinetic energy is transferred to the vehicle through a seat belt. The high ratio of the transferred energy is advantageous in protecting the occupant. This phenomenon is called “ride down effect”. In order to design a car body structure with consideration of the ride down effect, the dynamic relation between the occupant deceleration, which is an important injury criteria, and the automotive body structure must be investigated. This paper intends to clarify the dynamic theory of the ride down effect by means of an experimental model with two degrees of freedom consisting of a vehicle and an occupant. In addition, the relationship between the index of the ride down effect and the occupant deceleration was experimentally investigated. The experimental results show good coincidence with the theoretical predictions. It was found that a car body structure with stiffness featured in “hard in the initial stage of collision and soft later” is able to reduce the maximum occupant deceleration.

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A composite material was produced using bamboo fiber soaked into biodegradable poly(vinyl alcohol). To enhance the wettability of specimen, corona discharge was conducted as pre-treatments. The pre-treated specimen was soaked into the poly(vinyl alcohol), then it was compressed and fixed in a airtight atmosphere. Young's modulus in the length direction and in-plane and out-of-plane shear moduli of the composite material were measured by flexural vibration method, whereas Young's modulus and bending strength were measured by static bending tests. The bending strength of the composite satisfied that of sheathing board, which is determined in the Japanese Industrial Standards as JIS A 5905. Nevertheless, the shear modulus in the thickness direction was so small that it should be improved.

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Porous aluminum is lightweight with high specific strength and high energy absorptivity. By applying porous aluminum as a multifunctional material in automobiles, improved collision safety and fuel efficiency can be realized. As a new method of manufacturing porous aluminum with high productivity and a low cost, the authors proposed a method utilizing friction stir processing, i.e., friction stir processing route precursor method (FSP route precursor method). In this study, porous aluminum is manufactured by the FSP route precursor method while varying the amount of added alumina, the holding temperature and holding time. On the basis of the experimental results, the effects of these manufacturing conditions on the porosity and pore structure are investigated. It is shown that porous aluminum with porosity up to 80% can be realized by optimizing the amount of added alumina, the holding temperature and holding time.

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In recent years, production of biogas by an anaerobic digestion method has been reconsidered as an alternative means for producing clean fuel. Thus, research on various aspects of biogas production by anaerobic digestion has become important for its widespread utilization. One of the important aspects is energy balance of the process. The energy balance is affected by a heat demand, whereas the heat demand is affected by ambient temperature. In the present study, in order to clarify the effect of ambient temperature on the energy balance of anaerobic digestion, typical municipal sewage sludge anaerobic digestion in an actual wastewater treatment plant was adopted as analysis model and was studied under various temperature conditions. It was found that the heat demand for heating the sludge was temperature-dependent and that 26∼39% of the total amount of heat demand was heat losses from digester tanks. From the energy balance, it was found that net energy can be produced by the anaerobic digestion in any region and season in Japan, and this shown that it has a possiblity to be a new energy resource. It was also shown that, when ambient temperature became closer to the digestion temperature, more efficient anaerobic digestion can be obtained. These results were confirmed by indexes of energy balance that were defined in this study, with notable proportional relations being found between indexes and ambient temperature. Ratio of energy of heat demand to biogas produced had an inverse proportional relation with ambient temperature, whereas ratio of energy of net energy to biogas produced had a proportional relation, and ranges of these values in all of Japan were 0.13∼0.44 and 0.45∼0.84, respectively.

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