The most common approach for measuring the transmission loss of a muffler is to determine the incident power by decomposition theory and the transmitted power by the plane wave approximation assuming an anechoic termination. Unfortunately, it is difficult to construct a fully anechoic termination. Thus, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the twosource method. Both methods are demonstrated on two muffler types: (1) a simple expansion chamber and (2) a double expansion chamber with an internal connecting tube. For both cases, the measured transmission losses were compared to those obtained from the boundary element method. The measured transmission losses compared well for both cases demonstrating that transmission losses can be determined reliably without an anechoic termination. It should be noted that the two-load method is the easier to employ for measuring transmission loss. However, the two-source method can be used to measure both transmission loss and the fourpole parameters of a muffler.

The two-source method was used to measure the bulk properties (complex characteristic impedance and complex wavenumber) of sound-absorbing materials, and results were compared to those obtained with the more commonly used two-cavity method. The results indicated that the two-source method is superior to the two-cavity method for materials having low absorption. Several applications using bulk properties are then presented. These include: (1) predicting the absorptive properties of an arbitrary thickness absorbing material or (2) layered material and (3) using bulk properties for a multi-domain boundary element analysis.

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In this study, the perforated steel plates were demonstrated to exhibit high efficiency in protecting against small-caliber armor-piercing projectiles. The oblique hipped armor plates combined with the perforated steel plates acted as an armored vehicle exhaust vent protect against 7.62mm bullet. To enhance the efficiency of the vehicle exhaust, the numerical model was built, consisting of the hipped armor plate, the perforated steel plate and the bullet core. By performing a simple test, the efficiency of the model was verified. After the bullet penetrates the hipped armor plate, the shape of its core changed to be asymmetric. The sizes of the perforated steel plate were preliminarily designed in accordance with the statistical results of numerical simulation. Effects of the perforated steel thickness and the impacting positions on the residual bullet were ascertained. The results of this study were conducive to designing exhaust vents.