Challenges in the Silent Aircraft engine design

The Silent Aircraft Initiative goal is to design an aircraft that is imperceptible above background noise outside the airport boundary. The aircraft that fulfils this objective must also be economically competitive with conventional aircraft of the future and therefore fuel consumption and mechanical reliability are key considerations for the design. To meet these ambitious targets, a multi-fan embedded turbofan engine with boundary layer ingestion has been proposed. This configuration includes several new technologies including a variable area nozzle, a complex high-power transmission system, a Low Pressure turbine designed for low-noise, an axial-radial HP compressor, advanced acoustic liners and a low-speed fan optimized for both cruise and off-design operation. These technologies, in combination, enable a low-noise and fuel efficient propulsion system but they also introduce significant challenges into the design. These challenges include difficulties in predicting the noise and performance of the new components but there are also challenges in reducing the design risks and proving that the new concepts are realizable. This paper presents the details of the engine configuration that has been developed for the Silent Aircraft application. It describes the design approach used for the critical components and discusses the benefits of the new technologies. The new technologies are expected to offer significant benefits in noise reduction without compromising fuel burn. However, more detailed design and further research are required to fully control the additional risks generated by the system complexity.

The silent base flow and the sound sources in a laminar jet.

An algorithm to compute the silent base flow sources of sound in a jet is introduced. The algorithm is based on spatiotemporal filtering of the flow field and is applicable to multifrequency sources. It is applied to an axisymmetric laminar jet and the resulting sources are validated successfully. The sources are compared to those obtained from two classical acoustic analogies, based on quiescent and time-averaged base flows. The comparison demonstrates how the silent base flow sources shed light on the sound generation process. It is shown that the dominant source mechanism in the axisymmetric laminar jet is "shear-noise," which is a linear mechanism. The algorithm presented here could be applied to fully turbulent flows to understand the aerodynamic noise-generation mechanism.

The Silent Period of Evidence Integration in Fast Decision Making

In a typical experiment on decision making, one out of two possible stimuli is displayed and observers decide which one was presented. Recently, Stanford and colleagues (2010) introduced a new variant of this classical one-stimulus presentation paradigm to investigate the speed of decision making. They found evidence for "perceptual decision making in less than 30 ms". Here, we extended this one-stimulus compelled-response paradigm to a two-stimulus compelled-response paradigm in which a vernier was followed immediately by a second vernier with opposite offset direction. The two verniers and their offsets fuse. Only one vernier is perceived. When observers are asked to indicate the offset direction of the fused vernier, the offset of the second vernier dominates perception. Even for long vernier durations, the second vernier dominates decisions indicating that decision making can take substantial time. In accordance with previous studies, we suggest that our results are best explained with a two-stage model of decision making where a leaky evidence integration stage precedes a race-to-threshold process. © 2013 Rüter et al.

Aerodynamic noise from a poroelastic trailing edge with implications for the silent flight of owls

The interaction of a turbulent eddy with a semi-infinite, poroelastic edge is examined with respect to the effects of both elasticity and porosity on the efficiency of scattered aerodynamic noise. The scattering problem is solved using the Wiener-Hopf technique for constant plate properties to identify their scaling dependence on the resulting aerodynamic noise, including the dependence on flight velocity, where special attention is paid to the limiting cases of rigid, porous and elastic, impermeable plate conditions. Results from these analyses attempt to address how trailing edge noise may be mitigated by porosity and seek to deepen the understanding of how owls hunt in acoustic stealth. © 2012 by Justin W. Jaworski and Nigel Peake. Published by the American Institute of Aeronautics and Astronautics, Inc.

Cross-Border Unitization and Joint Development Agreements: An International Law Perspective

Okoye, Adaeze, et al, 'Cross-Border Unitization and Joint Development Agreements: An International Law Perspective', Houston Journal of International Law (2007) 29(2) pp.355-425 RAE2008

From clonal selection to immune networks: induction of silent idiotypes.

Journal Article

From Lomé to economic partnership agreements in Africa

The development of coherent and effective relations with other regions and countries is one of the most challenging tasks faced by the European Union. This original volume explores the EU’s engagement with the global South, focusing on three controversial policy areas: economic cooperation, development cooperation, and conflict management. A discussion of the EU’s interregional model—which promotes interaction with regions rather than nation-states—provides a backdrop for case studies of EU policies with regard to Africa, Asia, and Latin America. While disclosing the tensions and overlaps between the EU’s foreign policies and those of its member states, the authors also highlight an increasing trend toward successful policy coordination.

Penalties on car rental agreements

Examines the Cambridge County Court ruling in Volkswagen Financial Services (UK) Ltd v Ramage on whether a clause in a car hire contract which allowed the finance company, upon repudiation of the contract after the hirer fell into arrears, to claim compensation equivalent to the lost future rental payments was unenforceable as a penalty clause, rather than being a reasonable pre-estimate of actual loss. Refers to case law including the Court of Appeal ruling in Anglo Auto Finance Co v James in considering the differing losses which would occur during the course of the hire term according to the natural depreciation of the value of the car. Notes the reasoning of the Court on: (1) contracts of hire compared with hire purchase agreements; (2) the comparative position of the parties and the freedom to contract elsewhere; and (3) the reasonable prediction of future losses.

Oral agreements: estoppel, constructive trusts and restitution

Analyses the House of Lords judgment in Cobbe v Yeoman's Row Management Ltd in relation to claims by the prospective purchaser under an oral agreement for sale of a block of flats based on proprietary estoppel, a constructive trust and common law restitution brought against the owner of the property who sought to resile from the agreement after the purchaser had, at considerable expense, obtained planning permission to redevelop the property in reliance on assurances given by the owner that if permission was granted the sale would be honoured.

Electroreduction of N-methylphthalimide in room temperature ionic liquids under insonated and silent conditions

The selective electroreduction N-methylphthalimide to 3-hydroxy-2-methyl-isoindolin-1-one has been performed in ionic liquids using phenol as a proton donor under silent and ultrasonic conditions. A significant increase in the rate of electroreduction is shown using ultrasonic activation and in addition high current efficiencies were observed. Some decomposition of the ionic liquid was found to have occurred under exposure to ultrasound. © 2004 Elsevier B.V. All rights reserved.