In the present paper, an auxetic tape composed of modified star-shaped unit cells is used to filter the propagation of elastic waves in two-dimensional structures. The pattern of the designed bandgaps and their capability to mitigate wave propagation is experimentally and numerically studied. First, the architecture of the conventional star-shaped unit cell is introduced, and according to the Bloch’s theorem the phononic bandgaps are calculated for the one unit cell. The unit cells' dimensions are designed to provide a wide phononic bandgap over the low-frequency range of 400–1700 Hz. The geometry of the conventional star unit cell is modified toward two modified stars to enhance low-frequency bandgaps. These unit cells are then used as a filter tool in a two-dimensional panel, and they are numerically simulated using the finite element method. Excitation is locally applied to the panel, and a layer of phononic crystal surrounds its location. It is shown that the lattice band is capable of trapping waves inside the bounded area and can remarkably suppress the propagation of waves. Numerical results and the bandgap formation obtained from Bloch’s theorem are verified with the results measured from an experiment.

Cooling of the electrical vehicles’ battery is of crucial importance, as it affects the performance of the electrical power system, discharging duration, and subsequently their market acceptance. Present numerical work aims at analysing the improvement of the thermal management system by topological changes, which can be easily and affordably performed. The influence of AgO-water nanofluid with a volume fraction of 3% is also evaluated. A pack involving 10 cylindrical batteries with a constant heat flux is studied, which is merged by the nanofluid flow. Effects of changing the location of the inlet/outlet ports and inserting one or two plates to guide the fluid flow are assessed. The analysis was performed for a range of Reynolds number (based on the inlet pack diameter) from 1000 to 2000. It is shown that the topological modifications can improve the Nusselt number by more than 25%, while the Reynolds number rising from 1000 to 2000 makes a maximum increase of 30%. However, it follows a maximum 50% increment in the pressure drop. The proposed geometries indicate a more uniform temperature distribution compared to the simple cooling system without guiding plates by about 50%.

Metaplates, i.e. 2D extruded structures made by a periodic repetition of unit cells that exhibit a complete and wide 3D bandgap, are attracting increasing interest thanks to the variety of emerging applications. In this work, an innovative planar unit cell suitable for metaplates is proposed and optimized through a genetic algorithm, to achieve wide and low frequency bandgaps. Four objective functions are employed to show the potentiality of the proposed topology with respect to the state of the art. Metaplates obtained through the periodic repetition of the optimized unit cells are then simulated and experimentally tested. High performance metaplates, endowed e.g. with a nondimensional opening frequency of 0.0029 and bandgap width equal to 95%, are here obtained, thus opening the path to challenging applications also in the world of Micro-Electro-Mechanical Systems (MEMS).

Here, the elastic wave dispersion characteristics of a new circular-maze-shaped (CMS) phononic crystal are numerically and experimentally investigated. A parametric study is performed on the critical parameters of the unit cell, and the geometry effects on bandgaps formation are discussed. Then, applying the genetic algorithm approach integrated with the FE method, the geometric parameters of the unit cell are fine-tuned and optimized based on three objective functions consisting of the lowest, widest, and maximum summation of bandgaps. It is found that this novel architected phononic crystal, with its unique CMS scheme, can provide multiple, broad, and mutable bandgaps in the frequency range of 0 to 10 kHz. Over the frequency range, about 8215 Hz bandgap summation and a low band frequency of 184 Hz with a 95% bandgap ratio are achieved for the optimized case studies. Subsequently, one of the optimized unit cells is employed to develop a two-dimensional meta-plate as a filter tool to attenuate the bending vibration transmission through the meta-plate. The dynamic frequency response functions of the meta-plate are numerically and experimentally investigated, and the results are correlated to the bandgap diagram attained from Bloch's theory. It is observed that the meta-plate structure is capable of confining the elastic waves inside the specified region and can remarkably attenuate the propagation of elastic waves.

In this paper, elastic wave dispersion characteristics of two novel unit-cells are numerically and experimentally studied. Based on Bloch’s theorem for infinite cellular structures, the Eigen-frequency problem for the unit-cells is solved through a finite element scheme. These novel unit-cells are inspired from Maltese-Cross shape and named unit-cell I and II, while the unit-cell II is created from replacing side ligaments of unit-cell I with triangles. It is observed that these novel unit-cells are capable of providing over 200% phononic bandgap coverage factor over the low-frequency range of 0–12 kHz. Also, the effects of replacing side ligaments with triangles on shifting bandgap pattern to lower frequencies are investigated. The unit-cells are then utilized to construct a metaplate to filter two-dimensional wave’s propagation through the plate. The plate and its cellular segment are simulated with the finite element method, and they are fabricated through laser the cutting process. Frequency analysis is performed on the numerical and experimental models, and results are compared with the bandgaps obtained from periodic Bloch’s theorem. It is shown that a perfect match is observed between experimental and numerical results. The present study provides the practical application of new phononic crystals as a frequency tool to stop the propagation of elastic waves while the location of bandgaps can be tuned with the topology of unit-cells.

Geometry of cabins, corridors, and materials used in railway passenger carriages can play important roles in acoustic performance inside the rail cars. In order to evaluate the noise level inside a rail car, a hybrid method based on the ray-tracing and image-source techniques is employed. A parametric model is constructed based on the field experiment performed in a typical coach cabin namely Fadak train in Iranian Railway. An Omni-directional sound source inside the passenger carriage is employed inside the cabin once for an unequipped cabin and once for operational one. Acoustic parameters such as reverberation time (T30), Center time (Ts), and the sound pressure level have been calculated and results are validated with experimental acoustic measurements. The model is experimentally calibrated and then acoustics performance of the passenger coach is enhanced by modifying the materials and absorption coefficients against two dominant sound sources in low to middle speed ranges. It is found the simple recommendation can remarkably enhance the acoustic performance over a broad range of frequencies.