The properties of composite materials are highly dependent on the fiber and matrix fraction and on the porosity resulting from micro voids. This paper addresses void content characterization and the constituent content of composite materials by resorting to a comparison of destructive and non-destructive methods. The work presents the detailed procedures of two destructive methods, using acid digestion of epoxy resins matrices, and compares their processes. It also presents the results of a non-destructive method, by means of Micro Computed Tomography (MicroCT). The results of both destructive and non-destructive methods are compared, and a recommendation is made based on the application and the type of composite being analyzed. The MicroCT showed better and more consistent results in detecting voids in the material, while the acid digestion tests provided better results about the fiber and matrix percentage. Exported results from the MicroCT scanning with actual locations of voids were used in numerical analysis, to examine the feasibility of using them, whether by developing models that map damage in the proximity of the void, or by developing models that predict the properties of the entire material with respect to the content, shape, and distribution in the material.

This paper outlines the design and testing process of the hull of a deep small Autonomous Underwater Vehicle (AUV), rated at 2000m depth. Many existing AUV pressure housings use aluminum or other isotropic traditional metals, instead of composites due to the complexities of the design of composites at such big load. The research at hand explains the process of design starting from setting the geometrical constraints for the design to mass production. To the best of the authors’ knowledge, none of the previous studies has presented such detailed description of the work. Carbon fiber reinforced epoxy material was chosen thanks to its high strength-to-weight ratio and similarity of its compressibility to sea water. Material characterization was performed to obtain the material properties under loading conditions using a modified method of the Combined Loading Compression testing technique. A specific fixture was designed and manufactured to test filament-wound tubes. An analytical model was developed using MATLAB, a finite element model was created using ABAQUS, and the results of the two models were compared. A set of recommendations was introduced for the stacking sequence to provide the lowest possible stresses, regardless on the diving depth of the vehicle. Afterwards, a quality control set of tests was conducted, including seawater absorption under high pressure and void analysis using destructive and non-destructive tests. Pilot samples were manufactured and tested in a pressure vessel, where it was cycle-tested and inspected using visual and ultrasonic testing. Other samples were fail-tested and showed a failure at ~93% of the expected failure load. Such range can be considered good to provide safe operation for the vehicle at the designated depth, given that the factor of safety included covers more than 7% of the failure load. The proposed design methodology has shown that CFRE can be safely used even at such high depths.

Buoyancy-driven underwater vehicles are key tools for obtaining data from the ocean. Underwater gliders and profiling floats, equipped with sensors, provide crucial information on ocean processes and climate changes. The Variable Buoyancy System (VBS) is a key element of these vehicles, and is in many cases the most complex and highest energy-consuming subsystem. Energy consumption directly determines a vehicle’s endurance and mission duration. This paper presents the design and testing of a miniature hydraulic VBS suitable for integration into small underwater vehicles and platforms. Previous VBS are reviewed, existing principles such as hydraulics and pneumatics are described, and an overview of their strengths and weaknesses is provided. The paper explains the concept and the components of the micro-hydraulic VBS, and provides experimental results from its testing in a pressure vessel up to 1000 m equivalent depth. All the components of the system were designed to be of low weight and small size in order to be used in small underwater vehicles such as gliders and profiling floats. The efficiency of the system is characterized for different operating conditions, and provides the basis for vehicle energy system design and endurance characterizations.

Defining the hydrodynamic properties of an underwater glider is a critical operation that should be properly optimized since it has a great impact on the vehicle’s efficiency. It also defines the allocated budget for the Variable Buoyancy System (VBS) of the glider. This paper describes the work performed to optimize the hydrodynamic forces, represented in the lift and drag forces of the vehicle, as well as optimizing the angle of attack that the vehicle should perform its cycles at. The approach used in the analysis is Computational Fluid Dynamics (CFD) by importing the 3D model of the glider to Ansys software. The best angle of attack is chosen based on the highest efficiency characterized by the lift-to-drag ratio. The polar charts of the vehicle are also drawn based on the vertical and horizontal components of the vehicle’s speed. The results are implemented in the calculations of the VBS of the vehicle, and the definitions of the general operation states of the vehicle.

Underwater gliders are power-efficient autonomous vehicles that can gather ocean data for extended periods. Small-sized underwater gliders may be more suitable for operation, deployment, and recovery using unmanned platforms in coastal areas. Designing a light compact underwater glider with a relatively compact battery and confined space makes the electronics hardware system design a significant challenge regarding compactness and power efficiency. This work presents an overview of the electronics system designed to fulfill these requirements.

This paper outlines the design and testing process of the hull of a deep small Autonomous Underwater Vehicle (AUV), rated at 2000m depth. Many existing AUV pressure housings use aluminum or other isotropic traditional metals, instead of composites due to the complexities of the design of composites at such big load. The research at hand explains the process of design starting from setting the geometrical constraints for the design to mass production. To the best of the authors’ knowledge, none of the previous studies has presented such detailed description of the work. Carbon fiber reinforced epoxy material was chosen thanks to its high strength-to-weight ratio and similarity of its compressibility to sea water. Material characterization was performed to obtain the material properties under loading conditions using a modified method of the Combined Loading Compression testing technique. A specific fixture was designed and manufactured to test filament-wound tubes. An analytical model was developed using MATLAB, a finite element model was created using ABAQUS, and the results of the two models were compared. A set of recommendations was introduced for the stacking sequence to provide the lowest possible stresses, regardless on the diving depth of the vehicle. Afterwards, a quality control set of tests was conducted, including seawater absorption under high pressure and void analysis using destructive and non-destructive tests. Pilot samples were manufactured and tested in a pressure vessel, where it was cycle-tested and inspected using visual and ultrasonic testing. Other samples were fail-tested and showed a failure at ∼93% of the expected failure load. Such range can be considered good to provide safe operation for the vehicle at the designated depth, given that the factor of safety included covers more than 7% of the failure load. The proposed design methodology has shown that CFRE can be safely used even at such high depths.