Autonomous Underwater Vehicles (AUVs) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time, they are usually powered by lithium-ion secondary batteries, which have insufficient specific energies. In order for this technology to achieve a mature state, increased endurance is required. Fuel cell power systems have been identified as an effective means to achieve this endurance but no implementation in a commercial device has yet been realized. This paper summarizes the current state of development of the technology in this field of research. First, the most adequate type of fuel cell for this application is discussed. The prototypes and design concepts of AUVs powered by fuel cells which have been developed in the last few years are described. Possible commercial and experimental fuel cell stack options are analyzed, examining solutions adopted in the analogous aerial vehicle applications, as well as the underwater ones, to see if integration in an AUV is feasible. Current solutions in oxygen and hydrogen storage systems are overviewed and energy density is objectively compared between battery power systems and fuel cell power systems for AUVs. A couple of system configuration solutions are described including the necessary lithium-ion battery hybrid system. Finally, some closing remarks on the future of this technology are given. OPEN ACCESSEnergies 2014, 7 4677

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Shipbuilding with steel elements has changed little over the past 100 years. The introduction of hybrid materials has led to certain changes in construction methodology and in the calculation of structure and fabrication in shipyards. This study assesses a welded/adhesively joint used as a primary element union. It is made of steel and is used with a hybrid panel that is easy to manufacture and install at a low cost. To define the geometry of the joint, topological optimization of a symmetrical clamp-shaped steel part is carried out, attaching the hybrid panel with a structural adhesive. The geometric shape resulting from this optimization is analysed with a finite element model by means of a non-linear cohesive zone model simulation, minimizing the Von Mises stresses. The numerical result is compared to a destructive laboratory test. The result is analysed using the digital image correlation technique, making the following validations: in the adhesive-bonded area, no damage was found; the structural failure begins in the area near the embedded end; and there is an absence of cracks since no debonding of the structural adhesive takes place, confirming the obtained design by numerical simulation.

Fibre-metal hybrid laminates combine layers of metal with laminates made of composites -polymeric matrix reinforced with glass-fibre woven fabric. Interface behaviour plays a fundamental role in the overall properties of the hybrid material, especially in the failure mode by debonding buckiing of the outermost metal layer. A proper measurement of adhesive fracture energy is required so as to avoid this early failure mechanism during bending. Tapered double cantilever beam test and dissimilar mixed-mode bending test have been used in obtaining mode I and II contributions to the adhesive fracture energy. Data reduction for elastomeric adhesives has been modified in order to account for the variation in compliance during the test due to nonlinear behaviour of the material.Keywords adhesive; DMMB; debonding buckiing; fracture; hybrid material; TDCB.NOMENCLATURE a = crack length B, c = loading configuration parameters C = compliance D¿ = metal píate bending stiffness D s = composite laminate bending stiffness £¡j = elastic modulus of the i^ material along the^'th direction f x = distributed load G a a = adhesive shear elasticity modulus G = strain energy reléase rate G c = adhesive fracture energy Gi c = adhesive fracture energy in mode I Gi c i = adhesive fracture energy in mode I for initiation of crack growth Gi ca = adhesive fracture energy in mode I for arrest of crack growth Giic = adhesive fracture energy in mode II G* = adhesive fracture energy threshold for stable crack growth h = test fixture height H\¡ = hybrid laminate thickness H¿ = metal píate thickness H s = composite laminate thickness K\ = stress-intensity factors kx = tangential spring constant kz = normal spring constant L = specimen length m = tapered test fixture constant m x = distributed moment load N x = membrane forcé P¡ = applied loads P\ = partial load contributing to mode I P n = partial load contributing to mode II P° = buckling load pEUL _ £ u i er buckling load q = distributed load t = adhesive thickness a¡ = axial displacements Vi = displacements w\ = transverse displacements W = specimen thickness a, p = fractions of the forcé acting in each test specimen arm k, n,a> = constants with dimensión of length v[/ = mode-mixity angle X = crack length correction for crack tip rotation n = total potential energy Q,¿ = debonded metal píate región S2 dk = adhering metal píate región Q, s = debonded composite laminate región S2 sk = adhering composite laminate región

Autonomous Underwater Vehicles (AUV's) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time they are usually powered by lithium-ion secondary batteries, which have insufficient specific energy. In order for this technology to achieve a mature state increased endurance is required. Fuel cell power systems have been identified as an effective means to achieve this endurance but no implementation in a commercial device has yet been realized. This paper summarizes the current state of development of the technology in this field of research. First, the most adequate type of fuel cell for this application is discussed. The prototypes and design concepts of AUV's powered by fuel cells which have been developed in the last few years are described. Possible commercial and experimental fuel cell stack options are analyzed, examining solutions adopted in the analogous aerial vehicle and automotive applications as well as the underwater ones, to see if integration in an AUV is feasible. Current solutions in oxygen and hydrogen storage systems are overviewed and specific energy is objectively compared between battery power systems and fuel cell power systems for AUV's. A couple of system configuration solutions are described including the necessary lithium-ion battery hybrid system. Finally, some closing remarks on the future of this technology are given.