Enhancement of aircraft cabin comfort studies by coupling of models for human thermoregulation, internal radiation, and turbulent flows

Scientific enhancement of the analysis of thermal comfort aspects in aircraft cabins is the subject of the current investigation. For this purpose, three important processes are identified that play a significant role in thermal comfort, viz. the human response to its thermal environment which is also known as thermoregulation, the actual movement of air and heat inside aircraft cabins due to natural and forced convection, and heat transfer due to radiation. Three existing models have been adopted to describe these phenomena. In the current investigation, the behaviour of these three models is investigated in terms of modelling aspects and computational efficiency. Furthermore, a robust coupling of the models in a single simulation environment is described. Simulation results are shown for academic and real-life applications. It is concluded that a useful simulation environment has been obtained for studying aspects of the individual seat climate. Also, open issues in physical and computational aspects of the models are identified which can be addressed in future studies

Bounded analytic functions in the Dirichlet space

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46275/1/209_2005_Article_BF01163287.pd

Turbulence models for natural convection in side-heated enclosures

Applied Science

Covert Underwater Communication with Marine Mammal Sounds

Acoustic underwater communication is essential for the participation of friendly submersible vehicles in netcentric operations. To prevent interception of exchanged information and, not less important, detection of the submersibles in a hostile environment, the communication should be sufficiently ‘covert’. One approach is to hide the signal in the natural background noise. Another approach is to use local marine life sounds as a disguise for the transmitted information. Both approaches are subject of ongoing investigations at TNO. Progress on the latter approach will be the main topic of the current paper. The presented results have been obtained from a sea trial performed in littoral waters, where information was successfully exchanged between a surface ship and a submarine using modulated cetacean sounds, transmitted and recorded using existing sonar infrastructure. Pre-recorded cetacean sounds served as the basic carrier signal. Several modulation methods were tested by using them to encode short information patterns in the signal. Future efforts are directed at improvement of robustness, data rate and biological authenticity

On the Detection of Drifting Sea Mines using Ship Radar and Electro-Optical Systems

Small drifting objects can be a big threat to surface ships, especially when the objects are explosion hazards like sea mines that have become detached from their moorings. Timely detection of such objects is crucial in order to be able to perform adequate evasive manoeuvres. Due to the uncontrolled nature of drifting mines, permanent scanning of the horizon is required. On the other hand, these continual search activities should not have a significant operational impact on the ship’s mission. Therefore, automatic detection by time-interleaved use of existing surface radar and electro-optical systems from the ship’s mast seems attractive. However, what are the actual chances of such systems to detect a largely submerged sea mine at sufficient distance for representative weather conditions? This paper reports on the effectiveness of state-of-the-art surface radar and electro-optical systems as part of a ship’s organic MCM capability, based on literature study, theoretical considerations and sea trial results. Other possible approaches are discussed

On the Detection of Drifting Sea Mines using Above- and Underwater Sensors

Small drifting objects can be a big threat to surface ships, especially when the objects are explosion hazards like sea mines that have become detached from their moorings. Timely detection of such objects is crucial in order to be able to perform adequate evasive manoeuvres. However, the vertical position of drifting mines is a serious challenge for detection with both above- and underwater sensors, as the surface objects are usually only partly above and under water, and surface effects such as wave occlusion and scattering apply to both sides. On the other hand, above- and underwater sensors may complement each other as poor detection from above may imply good detection from below, and vice versa. This paper reports on sea trial results for the detection of drifting sea mines using a prototype surface-scanning infrared lidar from above and operational mine-hunting sonar systems from below. For the sonar experiments, both a forwardlooking hull-mounted sonar and an upward-looking self-propelled variable-depth sonar have been applied. Spherical exercise mines were used as mine-like objects, painted in a realistic warshot colour for the optical test

Adaptive turbo equalization for underwater acoustic communication

In this paper a multiband transceiver designed for underwater channels is presented. Multi-branch filtering at the receiver is used to leverage the diversity offered by a multi-scale multi-lag scenario. The multi-branch bank of filters is constructed by estimating scale and delay coefficients through an initial preamble composed by a maximum length sequence. An intelligent design of the pulse shaper at the transmitter and the receiver permits the reduction of the complexity of the equalization algorithm: the effective channel can be seen as a simple time-invariant finite impulse response filter possibly affected by a carrier frequency offset. Adaptive turbo equalization is chosen to deal with the high time-variability which characterizes many underwater channels and also to avoid the burden of estimating all parameters of the different paths. A phase locked loop and recursive least squares algorithm is implemented on each branch and for each subband which sweep the received sequence several times to refine decoding; in order to enhance the receiver performance the updating of the equalizer taps is obtained by making use of soft information provided as feedbacks from the turbo decoder. The proposed transceiver is tested on a realistic channel obtained by channel soundings performed in the Lyme Bay area, South England. Also comparisons with other existing turbo equalizer schemes are performed

Assessment of natural and anthropogenic sound sources and acoustic propagation in the North Sea

For a proper (national) implementation of the European Union’s ambitious Marine Strategy Framework Directive, it is required that the impact of anthropogenic activities on the North Sea environment is assessed thoroughly. One of the effects of the use of the North Sea by humans is the generation of underwater sound. Sound propagates over longer distances in water than in air. The impact of anthropogenic underwater sound sources could therefore be serious. At this time, there is insufficient information on the underwater sound environment in the North Sea to make an impact assessment. The information on anthropogenic sources of underwater sound, i.e. the sound characteristics and source levels, is by no means complete. Once this information becomes available, the next challenge is to predict correctly how the sound propagates in the shallow water of the North Sea, i.e. to find out the sound footprint of individual anthropogenic or natural sources of sound. The research reported on in this document aims at making an inventory of the existing knowledge on the underwater sound environment and identifying the gaps. In the next steps towards an impact assessment, there is insufficient information on the physiology and behaviour of the marine fauna of the North Sea. There is also a lack of knowledge on the effects of the various anthropogenic sources of sound on the ecosystem of the North Sea, both individually and cumulatively

Acoustic Channel Characterization in the Baltic Sea and in the North Sea

This paper reports results from the joint European project "UUV Covert Acoustic Communications" (UCAC), which aims at the establishment of a covert communication link between an Unmanned Underwater Vehicle (UUV) and a distant mother platform using acoustic telemetry. To this end, sea trials were carried out in 2006 and 2007 in two different areas in the Baltic and Norwegian North Sea. During the sea trials, acoustic and environmental data were obtained for the characterization of the acoustic channel-particularly the transmission loss and the channel impulse response-with the purpose of evaluating different (covert) acoustic communication schemes. A selection of these data is analyzed in the present pape

Natural and anthropogenic sources of sound in the North Sea

This paper summarises the progress made by TNO on describing the most significant natural and anthropogenic sound sources in the North Sea (Dutch sector). An assessment of their relative importance is made by estimating an annual energy budget, not neglecting that details of the sound distribution in frequency, time and space might be equally important. Our approach to propagation modelling of the noise sources in the shallow waters near the Dutch coast is explained. Example noise maps are presented. Validation of the noise predictions requires a capability for long-term noise monitoring. Suitable monitoring solutions are discussed