Metamaterials are pushing the limits of traditional materials and are fascinating frontiers in scientific innovation. Mechanical metamaterials (MMs) are a category of metamaterials that display properties and performances that cannot be realized in conventional materials. Exploring the mechanical properties and various aspects of vibration and damping control is becoming a crucial research area. Their geometries have intricate features inspired by nature, which make them challenging to model and fabricate. The fabrication of MMs has become possible because of the emergence of additive manufacturing (AM) technology. Mechanical vibrations in engineering applications are common and depend on inertia, stiffness, damping, and external excitation. Vibration and damping control are important aspects of MM in vibrational environments and need to be enhanced and explored. This comprehensive review covers different vibration and damping control aspects of MMs fabricated using polymers and other engineering materials. Different morphological configurations of MMs are critically reviewed, covering crucial vibration aspects, including bandgap formation, energy absorption, and damping control to suppress, attenuate, isolate, and absorb vibrations. Bandgap formation using different MM configurations is presented and reviewed. Furthermore, studies on the energy dissipation and absorption of MMs are briefly discussed. In addition, the vibration damping of various lattice structures is reviewed along with their analytical modeling and experimental measurements. Finally, possible research gaps are highlighted, and a general systematic procedure to address these areas is suggested for future research. This review paper may lay a foundation for young researchers intending to start and pursue research on additive-manufactured MM lattice structures for vibration control applications.

Unmanned underwater vehicles (UUVs) have become increasingly popular in recent years due to their use in various applications. The motivations for using UUVs include the exploration of difficult and dangerous underwater environments, military tasks in mine detection, intelligence gathering and surveillance, the inspection of offshore oil and gas infrastructure in the oil and gas industry, scientific research for studying marine life, and the search and rescue of missing persons or submerged airplanes or boats in underwater environments. UUVs offer many advantages in achieving the desired applications with increased safety, efficiency, and cost-effectiveness. However, there are also several challenges associated with their communication, navigation, power requirements, maintenance, and payload limitations. These types of vehicles are also prone to various disturbances caused by currents of the ocean, propulsion systems, and unmolded uncertainties. Practically, it is a challenging task to design a controller that will ensure optimal performance under these conditions. Therefore, the control system design is of prime importance in the overall development of UUVs. Also, the UUV controller receives input from different sensors, and the data from these sensors are used by the controller to perform different tasks. The control systems of UUVs should take into account all uncertainties and make them stable so that all sensors can perform optimally. This paper presents a complete review of different control system design algorithms for UUVs. The basic logic designs of several control system algorithms are also presented. A comparison is made based on reliability, robustness, precession, and the ability of the controller to handle the nonlinearity that is faced by UUVs during their missions. Simulation and experimental results are thoroughly studied to gain insight into each algorithm. The advantages and disadvantages of each algorithm are also presented, which will facilitate the selection of a suitable algorithm for the control system design of UUVs.

About nine million barrels of gasoline are consumed daily by automobile engines. Out of this, roughly 2.25 million barrels are effectively used by the engine to generate power, whereas the rest is wasted due to engine inefficiencies. There is a dire need to bring up a more efficient engine, since even an effort for a 1% increase in efficiency would result in savings of almost $6 million daily worldwide. In this study, first, a conventional poppet valve engine configuration for a 70cc engine was analyzed. Then, based on the engine efficiency contributing parameters, a novel Independent Rotary Valve (IRV) engine configuration was proposed. The proposed engine configuration was analyzed for the same 70cc engine. The LOTUS Engine software was used for the thermodynamic investigation of intake valve closing angle for getting maximum values of volumetric efficiency, brake power, and brake torque at different speeds and intake valve closing angles. It has been found that the proposed engine configuration resulted in approximately 1.165% increase in thermal efficiency by a decrease in air-fuel mixture pumping work. In addition, a 13% increase in volumetric efficiency, a 13% increase in brake torque, and an 18% increase in brake power were found, through the use of independent valve actuation. Also, an increase in mechanical efficiency is expected, due to the added simplicity of the proposed IRV as compared to the conventional poppet valve system. This increase has been verified analytically and by numerical modeling performed in ANSYS FLUENT. The proposed IRV engine configuration is thus a more efficient, more powerful, less complicated, more stable, and an environmentally safer engine.