Active control of structural sound radiation is a promising technique to overcome the poor passive acoustic isolation performance of lightweight structures in the low-frequency region. Active structural acoustic control commonly aims at the suppression of the far-field radiated sound power. This paper is concerned with the active control of sound radiation into acoustic enclosures. Experimental results of a coupled rectangular plate-fluid system under stochastic excitation are presented. The amplitudes of the frequency-independent interior radiation modes are determined in real-time using a set of structural vibration sensors, for the purpose of estimating their contribution to the acoustic potential energy in the enclosure. This approach is validated by acoustic measurements inside the cavity. Utilizing a feedback control approach, a broadband reduction of the global acoustic response inside the enclosure is achieved.

Sustainable aviation fuels provide the opportunity to reduce the climate impact of air transport while avoiding a complete overhaul of the existing fleet. For Europe, the domestic production of sustainable...

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Can Urban Air Mobility (UAM) systems constitute viable and sustainable mobility solutions? This question has increasingly been concerning scientists, companies, policy makers, and authorities as more and more UAM vehicle concepts are seeing the light of day. In order to come closer to answering this question and to demonstrate the dependencies and impacts of the numerous parameters used to describe a highly complex system of a fleet of UAM vehicles operating in an urban environment, this paper employs a System of Systems (SoS) approach. A collaborative SoS framework with an agent-based simulation is introduced, which connects the UAM vehicle design, fleet performance, vertiport network, and reenergizing infrastructure with a Life-Cycle Assessment (LCA). The framework is used to simulate four exemplary UAM fleet-operation scenarios based on two cities and two operational modes, namely urban and suburban operations. Different vehicle design configurations, e.g. multirotor and lift + cruise vehicles, are evaluated in each scenario based on respectively realistic Concepts of Operations (CONOPS). Additionally, two different points in time, namely 2025 and 2050, are considered and assessed for powering the vehicles by taking into account the characteristics of batteries as well as the underlying electricity mix for their operation. Lithium nickel manganese cobalt oxide battery and lithium-sulfur (Li-S) batteries are considered. The SoS framework helps to asses various UAM metrics such as the average wait time for a passenger, the ideal number of aircraft needed for transporting all passengers within given time, the energy required on a vehicle and fleet level, sustainability metrics, e.g. the global warming potential associated with the energy carriers and many more. The capability to explore a wide design space and to visualize the dependencies between the system parameters and their impacts on different SoS metrics provides stakeholders with a helpful tool for their decision making.

The aviation sector is estimated to require a widespread deployment of sustainable fuels next to developments in aircraft technology and improvements in operations and infrastructure to efficiently reduce its climate impact. A possible pathway for more sustainable aviation fuels could be fuel production using hydrogen via water electrolysis with renewable energy followed by Fischer-Tropsch synthesis, also known as Power-to-Liquid (PtL). In order to investigate whether this fuel pathway contributes to the reduction in environmental impacts, we conduct an environmental Life Cycle Assessment (LCA) compared to fossil fuel for the use in a narrow-body shortto medium-haul aircraft fleet. Within the LCA, the focus lies on the phases of fuel production and operation of the aircraft’s life cycle. Unlike most LCA studies in aviation, the impacts of the flight emissions are computed based on the aircraft characteristics and considering the geographic position and altitude of the aircraft for a global route network. Since the aircraft design is not affected by the fuel types under investigation, the aircraft production and end-of-life phases are not considered in the LCA. This contribution shows the potential of PtL for aviation in a well-to-wake environmental sustainability analysis considering climate change and nine additional impact categories.