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Plants are usually considered static organisms, but they can perform a wide range of movements that can be a source of inspiration for robots. The roots’ growing motion is the most noteworthy since they are excellent diggers that can move in unstructured environments and navigate past barriers. Furthermore, root growth has a high energy efficiency since it penetrates the soil at its tip, adding new material without displacing the already grown portion, minimizing the energy dissipation due to friction and lowering the inertia. A robot inspired by the growth of roots could be used in search and rescue or environmental monitoring. The design of a soft robot inspired by root growth is presented in this article. The robot body consists of a cylindrical plastic membrane folded inside itself. The robot body is inflated, and its tip is everted, expanding its length as air is blown from the base. Velcro straps are placed on the membrane’s exterior surface to keep it folded. The head is positioned inside the tip, which houses the mechanism that controls the growth direction. It consists of housing for two balloons that are selectively inflated, and their expansion applies pressure on the exterior surface, opening the Velcro straps and determining the growth direction. The robot was constructed, and a kinematic model of its motion in the plane was created and compared with experimental data. The error in predicting the turning angle is only 5%, and the resulting predicted position differs on average by 55 mm on a total length of 850 mm.

Among all aquatic species, mantas and rays swim by flapping their pectoral fins; this motion is similar to other fishes in terms of efficiency, but it gives better maneuverability and agility in turning. The fin's motion is featured by a traveling wave going opposite to the forward motion, producing a force thanks to momentum conservation. This article aims at understanding the swimming dynamics of rays, focusing on energy efficiency. A computational fluid dynamics (CFD) model of the swimming motion of a cownose ray has been implemented in openfoam, simulating the acceleration of the fish from still to the steady-state velocity using an overset mesh. In this analysis, the one degree-of-freedom dynamics of forward swimming is solved together with the fluid velocity and pressure. The effect of frequency and wavelength of fin motion on thrust, power, and velocity has been investigated and an analysis of the vortices in the wake showed has been performed. The energy efficiency of a self-propelled body has been defined in a novel way and it has been calculated for different motion conditions. The results showed that batoid fishes swim with high energy efficiency and that they are a promising source of inspiration for biomimetic autonomous underwater vehicles.

This paper shows the design of an underwater autonomous robot. The challenges of this activity are mainly linked to motion design and to energy efficiency. Therefore, a bioinspired approach has been used. Batoid fishes swim moving their pectoral fins, they produce a wave travelling in the direction opposite to their motion, pushing water backwards and gaining thrust as a consequence of momentum conservation. The motion of the fin has been studied and reproduced with a series of articulated mechanisms. In this work the optimization of the mechanism’s geometry is described and the experimental results on the reconstructed fin are presented., https://youtu.be/72AKxWktQBI

The study of fish swimming is of great interest for engineers and researchers because the investigation of novel propulsion mechanisms is functional to the development of autonomous underwater vehicles. Among the different locomotion strategies adopted by fish species, the one characterizing the cownose ray is known to be very efficient. These fishes move their large pectoral fins and create a wave travelling in a direction opposite to the swimming direction. Thus, thanks to momentum conservation, the fish receives a propulsive thrust. This mechanism has been reproduced in a bioinspired robot mimicking a cownose ray, which has been designed and built. Before testing the robot underwater, some preliminary experiments in a small wind tunnel have been performed on a single fin. These tests are aimed at assessing the fluid dynamics of the fin shape and at verifying the effectiveness of this propulsive strategy. The fluid dynamic forces acting on the profile are measured with the fin still; the velocity of the incoming air is such that the Reynolds number is the same as for the fish swimming in water. Then, the propulsive strategy is tested with the fin in motion; the velocity of the incoming air is the same as the relative velocity of water for the fish during forward swimming, and several experiments were carried out with different frequencies and wavelengths of fin motion. Finally, having the fluids different densities, the measured forces and moments are scaled. These tests have confirmed that the cownose ray swimming strategy is effective and a relation between the measured forces with frequency and wavelength of fin motion has been found.

Vibration analysis is recognized as a powerful tool for fault diagnosis and quality control of industrial machineries. Accelerometer signals can provide a measure of the majority of causes of inaccuracy in manufacturing processes and of components' faults, which can in turn affect the product quality. This paper provides a fault identification method based on time and frequency domain analysis. This method is applied to an automatic press machine for soft thermoplastic polymers. Pilot experiments conducted in laboratory conditions allowed to select the proper number and the position of the accelerometers, as well as the signal features needed for a preliminary threshold-based maintenance strategy.

Optimising the O&M activities related to the proprietary infrastructure assets is crucial for a company successful management. Nowadays this topic is gaining even major hype due to the accessibility of new technologies such as big data. Such reasons push the industrial market towards a pursue of effectiveness and efficiency of maintenance strategies. This work inserts itself in this context: born from a collaboration with a company involved in the sector of telecommunications, it aims at the determination of an heuristic model able to estimate, as far as their towers are concerned, the probability of a structural failure. The initial phase is about the analysis of the company’s database to identify the variables to be considered in the study. Then the focus is shifted on the research of a synthetic index that could summarise the contribution of the aforementioned parameters. Subsequently, a sensitivity analysis aimed at testing the robustness of such index is carried out, followed by a subdivision of the entirety of the assets into homogeneous clusters in terms of loads and structural properties. The clusterization is intended to feed the “risk” axis of a risk-impact matrix to be used to tailor the O&M best practices to apply to the fleet of communication towers. The predictive capability of such representation will be assessed performing physical checks on a number of towers sampled from the matrix.

Experimental activities on wind turbine models allow to speed up their design as well as the development of robust and effective control algorithms. Intending to have large information on load distribution on the blades, this work presents an experimental setup of a model wind turbine blade instrumented with two different types of optical fiber sensors (FOS). The first one is a traditional chain of Fiber Bragg Grating sensors, able to measure a large number of strain values; the second is based on Optical Backscatter Reflectometry (OBR), able to provide a continuous strain measurement. The experimental setup is calibrated to estimate load distribution along the blade and the two technologies are compared. The results of the experimental campaign suggest that optical fiber sensors could represent an interesting solution for real-time continuous load monitoring purposes.

Shape memory alloys (SMA) have long been explored as a semi-passive approach to mechanical energy dissipation particularly, but not exclusively, for application to vibration control. More recently, the integration of SMAs in composite materials has opened the opportunity to synthesize tunable composite structures exhibiting significantly enhanced energy dissipation characteristics and a certain degree of adaptability to different operating conditions. Despite the significant progress in the development and manufacturing of SMAs over the past several decades, the cost of common Ni-based alloys has remained an important factor hindering their widespread engineering application. The long-term goal of this research effort is to model, design, and fabricate shape-memory-alloy (SMA) meta-composites employing lower volume fractions of a more affordable Cu-based alloy, while still enabling enhanced and tunable dynamic properties. This paper summarizes recent progress in the development of the meta-composite platform and focuses on aspects involving both numerical modeling and fabrication of SMA materials. On the modeling side, particular emphasis is given to assess the ability to tune the dynamic performance of continuous SMA structures by exploiting the different phases and transformations of the alloy. On the other side, the material development effort focuses on the identification of the optimal chemical composition, mechanical and heat treatment processes. A combination of numerical and experimental results is presented to illustrate capabilities and opportunities presented by this material platform.

Although plants are usually seen as static organisms, they exhibit a wide range of movements that only in recent years have been considered as a source of inspiration for robots. The motion of roots is one of the most interesting, because they are extraordinary diggers, able to navigate in unstructured environments, finding their way around obstacles. Moreover, root growth is featured by high energy efficiency because they penetrate the soil adding new material at their tip, without moving the already grown part, preventing friction from dissipating energy and reducing the inertia. A robot inspired to roots’ growth could be employed in search and rescue operations or in environmental monitoring. In this work the design of a soft robot inspired to root’s growth is presented. The body of the robot consists of a cylindrical plastic membrane folded inside itself. When air is blown from the base, the body of the robot is inflated, and its tip is everted increasing its length. On the external surface some Velcro stripes are mounted, which keep the membrane folded. Inside the tip a head is mounted, where the mechanism controlling the direction of growth is placed. It consists of a housing for some balloons, which can be inflated selectively, and their expansion exerts a pressure on the external surface able to open the Velcro stripes. The direction of growth is controlled by selecting which balloon to inflate. The robot has been built and a kinematic model of its motion in the plane has been developed and compared with experimental results.

Among all aquatic species, mantas and rays swim by oscillating their pectoral fins; this motion is similar to other fishes in term of efficiency, but it gives better agility in turning with respect to fishes moving their caudal fin. The fin motion is featured by a travelling wave going opposite to the forward motion, producing a force thanks to momentum conservation. Another contribution to the generation of thrust is given by the generation of a vortex in correspondence of the leading edge of the fin, which pulls the fish forward thanks to the lower pressure in its centre. In literature these contributions have been highlighted, but it remains to understand which one of these two mechanisms is prevailing according to different conditions of swimming, how they affect each other and what is the influence of the two on energetical efficiency. The object of this activity is to investigate how thrust generation is influenced by geometrical characteristics of the fin, such as size, geometry and flexibility and by parameters of motion, such as speed, amplitude and frequency of fin oscillation and velocity of the travelling wave. A CFD model of the fish has been implemented in OpenFOAM, not only confirming that both upstroke and downstroke contribute positively to the forward movement according to the momentum conservation principle, but also highlighting the formation of a leading-edge vortex enhancing thrust generation. The description of how thrust generation is linked to motion parameters is simulated also coupling the CFD with a multibody to simulate the whole motion in its complexity.

The increasing availability of small size and low cost sensors is orienting the world of smart structures towards a deep integration of a large number of these devices. This makes possible a more accurate knowledge of the dynamics of the structure, even if it requires the ability to manage an increasing number of information, potentially not consistent. In applications of vibration suppression, this circumstance must be avoided as measurements are used as a feedback in the control loop and therefore they can potentially capable of altering the stability of the controlled system and, in any case, to limit its performance. This work proposes a new algorithm for the automatic identification of inconsistent measurements due to sensors malfunctions, noise, wrong calibrations, etc. The approach is based on an innovative sliding mode observer that has been designed to seek faults and to avoid false positive results. The algorithm has been numerically and experimentally tested on a composite smart structure with 15 Fiber Bragg grating sensors embedded. Tests have been carried out considering different faults. Results confirm the effectiveness of the approach and allows to always identify faulty sensors.

A huge problem in cruise ships is related to undesired noise and vibrations generated by engines and exhaust stacks. Reduction or suppression of ship noise has traditionally been implemented by passive means, such as by the use of vibration isolation mounts, flexible pipe-work, and interior acoustic absorbing materials. However. while passive devices are effective mostly for attenuating high-frequency noise, they are generally ineffective to suppress low-frequency vibrations. The paper deals with the design of an active standalone device to suppress vibrations on cruise ships funnels. The device can work independently and, matched with others through a decentralized control, can dissipate most of the kinetic energy of the system, thus limiting the propagation of vibration and improving comfort on surroundings.

An investigation on fatigue crack growth monitoring of bonded joints has been conducted employing a novel carbon nanotube (CNT) adhesive film, chosen for their proven exceptional properties for sensing purposes. Single lap shear fatigue tests have been carried out at a 7 kN load, load ratio 0.1 and 10 Hz frequency. A correlation between the electrical response of the adhesive joints and the fatigue crack growth has been established by means of voltage acquisition through the thickness in combination with crack length monitoring by microscopy analysis. Three phases can be distinguished during the fatigue tests: phase one without crack initiation with a steady electrical response; phase two in which cracks start propagating, with a slight increase of the electrical resistance, and phase three, corresponding to final propagation to failure with a drastic increase of the electrical resistance. A correlation between the electrical response, the estimated crack area and the measured edge-crack size is achieved, allowing to get a deeper understanding of crack growth phenomenon as a function of the number of cycles. Thus, the potential and the applicability of the proposed technique for monitoring crack growth in lap joint fatigue tests have been demonstrated.