Arpan Gupta

A quasi two-dimensional model for sound attenuation by the sonic crystals

Sound propagation in the sonic crystal (SC) along the symmetry direction is modeled by sound propagation through a variable cross-sectional area waveguide. A one-dimensional (1D) model based on the Webster horn equation is used to obtain sound attenuation through the SC. This model is compared with two-dimensional (2D) finite element simulation and experiment. The 1D model prediction of frequency band for sound attenuation is found to be shifted by around 500 Hz with respect to the finite element simulation. The reason for this shift is due to the assumption involved in the 1D model. A quasi 2D model is developed for sound propagation through the waveguide. Sound pressure profiles from the quasi 2D model are compared with the finite element simulation and the 1D model. The result shows significant improvement over the 1D model and is in good agreement with the 2D finite element simulation. Finally, sound attenuation through the SC is computed based on the quasi 2D model and is found to be in good agreement with the finite element simulation. The quasi 2D model provides an improved method to calculate sound attenuation through the SC.

A review on sonic crystal, its applications and numerical analysis techniques

This paper presents a review study on sonic crystal, their development and present status. The paper also focuses on some of the applications of sonic crystal and numerical methods to study these crystals. Sonic crystals are periodic arrangement of scatterers, whose interaction with acoustic waves leads to the formation of band gap. Band gap are regions of frequencies where the sound propagation is significantly restricted from the sonic crystal. This property is used in many applications such as sound barrier, frequency filter, acoustic imaging etc. The paper presents a review of all these applications. Further the paper presents some of the numerical methods used to calculate the band gap formation in sonic crystal.

Sound propagation in two-dimensional waveguide with circular wavefront

Sound propagation through a waveguide is generally modeled by the Webster horn equation which assumes a planar pressure wavefront. However, most of the sources are non-planar in nature. In this work, a 1-D model is derived for sound propagation through a 2-D waveguide with circular wavefront. The model is derived from the 2-D Helmholtz equation using the weighted residual method. The model assumes a uniform pressure across the angular coordinate at a given radial distance. A 2-D finite element model is used to validate the results for different waveguide geometries and it shows good agreement.

Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation

Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the complex wave numbers, which give the decay constants. The decay constant is used to predict the sound attenuation of the evanescent wave in the finite sonic crystal. The theoretical prediction is verified with experimental measurements.

Parametric Study on Rectangular Sonic Crystal

Sonic crystals are periodic structures made of sound hard scatterers which attenuate sound in a range of frequencies. For an infinite periodic structure, this range of frequencies is known as band gap, and is determined by the geometric arrangement of the scatterers. In this paper, a parametric study on rectangular sonic crystal is presented. It is found that geometric spacing between the scatterers in the direction of sound propagation affects the center frequency of the band gap. Reducing the geometric spacing between the scatterers in the direction perpendicular to the sound propagation helps in better sound attenuation. Such rectangular arrangement of scatterers gives better sound attenuation than the regular square arrangement of scatterers. The model for parametric study is also supported by some experimental results.

Mechanical response of femur bone to bending load using finite element method

Bending load is often encountered in femur bone (thigh bone) particularly in the case of lateral impact. Femur fracture is quite usual in pedestrians. It generally occurs because of bending of femur bone due to lateral impact. In order to prevent fractures in walkers and vehicle passengers from accidents, it is significant to study the bending behavior of femur bone. Femur bone is one of the most commonly fractured bones in human body as it is one of the longest and largest bones. In this work, mechanical response of femur bone to bending load is studied by the help of finite element simulation. For a given critical load, deflection, von Mises stresses and bending stresses have been obtained. For the critical bending moment of 200 N-m, the maximum von Mises stresses reaches up to 131.3 MPa, and the maximum deflection is found to be 1.8 cm. The Von Mises stress must be less than the yield stress of the material; otherwise it could lead to fracture of the bone.

Effect of periodic structure on sound propagation

In this study, propagation of acoustic wave through a periodic structure has been analyzed. Such a periodic structure has been found to attenuate sound significantly in certain frequency bands, and therefore it can be used as a frequency filter and sound barrier. Experiments were performed to measure the sound attenuation by the periodic structure made of acrylic cylinders. The experimental results were compared with a simulation study using the finite element method, and they are in good agreement. The benefit of such structure is that it is light weight compared to the solid barriers, and it can be tailored according to the frequency of the sound source to be attenuated.

Exhaust Heat Recovery Using Thermoelectric Generators: A Review

With the major concern to increase the efficiency of internal combustion (IC) engines, various technologies and innovations have been implemented to improvise efficiency and reduction of emissions. Since 60–70% of the energy produced during combustion is rejected as heat through exhaust and coolant channels, it is important to recover that waste heat. Numerous technologies have been invented and applied to the diesel engine unit to harness the waste heat. One such is the use of solid-state device thermoelectric generator (TEG). In the late 1980s, many automobile manufacturers implemented automotive exhaust thermoelectric generators (AETEGs) in their respective vehicles, and since then, the work on AETEGs has picked at gradual pace. Advantages of using TEG are its noise-free operation, low failure rate and lack of moving components. However, it is not a very popular solution due to the low energy conversion efficiency (~6–8%) of thermoelectric modules and the incompetence to produce high power at low-temperature gradient. Engineers and researchers are basically working for improving the conversion efficiency of TEG modules by developing and doping semiconductors and optimization of the AETEG system to utilize and recover maximum heat available from the exhaust line by designing efficient heat exchanger systems, thus trying to improve its feasibility. This chapter covers the wide spectrum of feasibility of application of TEG modules in diesel engines with possible ways to utilize the generated power.

Reverberation time improvement of lecture auditorium: A case study:

In this study, reverberation time of a lecture auditorium has been analyzed experimentally and analytically. It is well-known fact that reverberation time affects the speech intelligibility and hence should be within the range of possible optimum values. Experiments were performed to calculate the reverberation time of a lecture auditorium constructed at Indian Institute of Technology Mandi (IIT Mandi), for different internal conditions such as furniture and curtains. Experimental results were compared with the theoretically calculated values of reverberation time. It is found that acoustic performance of the lecture auditorium has significantly improved using curtains on the windows and furniture. For further improvement, it has also been suggested to use the carpet on the floor of the auditorium. The theoretical value of reverberation time is also calculated to show the improvement which can be achieved using carpet. The effect of audience on reverberation time has also been studied theoretically.

Enhancing the sound transmission loss through acoustic double panel using sonic crystal and porous material

Acoustic panels are widely used for sound insulation in various applications. Sound transmission loss (STL) through the panel is due to a change in acoustic impedance as sound travels from one medium to another. In double panels, STL further increases due to multiple reflections in air cavity. Recently the sonic crystal (SC) has emerged as an interesting research topic which provides sound attenuation in specific frequency bands. The present paper aims at combining the property of a SC with the acoustic panel for enhancing the STL through the double panel. Initially, an analytical method is developed to obtain the STL through the double panel. Further finite element (FE) simulations are performed using acoustic structure interaction to obtain the STL through the double panel which is in good agreement with the analytical predictions. The SC, along with the double panel, is analyzed using the FE method for the combined effect of both sound attenuators. Further, glass wool is considered as a filler material between the double panel as well as between the double panel and the SC assembly. It is found that the combined structure of the double panel and the SC with glass wool as filler gives the best STL for all different cases for the same external dimensions.