The growth of undersea exploration is pushing both the length and the complexity of propeller-driven autonomous underwater vehicles (AUVs) missions, leading to more stringent energy requirements. One approach to decrease the energy consumption of a hovering capable AUV is to use variable buoyancy systems (VBS) as a complement to the propeller actuators. These devices only require energy consumption during limited periods of time, taking into advantage the fact that whenever buoyancy is different from zero, the vehicle will continuously ascend or descend. Nevertheless, literature is scarce regarding the choice of the type of the VBS and of its constitutive elements, and regarding their effects on the energy required for buoyancy changes. This work presents structured and detailed static models of electromechanical and electrohydraulic VBSs that allow the calculation of the power required to actuate them. Based on the VBS desired characteristics and on manufacturer's data, the power consumption in each element of the VBS can be pinpointed to determine critical elements. Furthermore, a direct energy comparison with propeller-based solutions can be performed, allowing an easy evaluation of the energy gains provided by the VBS in different scenarios. This work also presents the preliminary development of an electromechanical and electrohydraulic VBS for an existing AUV at the University of Porto, Porto, Portugal. Based on the developed VBS and the developed model, numerical examples are provided for typical mission profiles. It is shown that the use of a VBS in the case of the existing AUV at the University of Porto leads to considerable energetic improvements.

中文翻译：

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悬停有能力的车辆的基于可变浮力或螺旋桨的系统：能量比较

水下勘探的增长推动了螺旋桨驱动的自动水下航行器（AUV）任务的持续时间和复杂性，从而导致对能源的要求更加严格。减少具有悬停功能的AUV的能量消耗的一种方法是使用可变浮力系统（VBS）作为螺旋桨致动器的补充。这些设备仅在有限的时间段内消耗能量，从而充分利用了这样的事实，即只要浮力不为零，车辆就会连续上升或下降。然而，关于VBS类型及其组成元素的选择以及它们对浮力变化所需能量的影响的文献很少。这项工作提出了机电和电动液压VBS的结构化且详细的静态模型，该模型可以计算驱动它们的功率。根据VBS所需的特性和制造商的数据，可以精确确定VBS每个元素中的功耗以确定关键元素。此外，可以与基于螺旋桨的解决方案进行直接能量比较，从而可以轻松评估VBS在不同情况下提供的能量增益。这项工作还介绍了在葡萄牙波尔图的波尔图大学为现有AUV进行的电动机械和电动液压VBS的初步开发。基于已开发的VBS和已开发的模型，为典型任务配置文件提供了数值示例。