Hybrid isolation of structure-borne sound

Interior noise problems become more important due to the tendency to construct lighter vehicles. An important source for interior noise in a vehicle is the engine. The structural vibrations induced by the engine will transmit through the vehicle and will finally result in interior noise elsewhere in the vehicle, so-called structure-borne sound. To reduce the interior noise a solution is sought in a combination of passive and active isolation (hybrid isolation) of the engine. A project has been started to investigate this type of isolation and to develop experimentally validated numerical simulations for the design of hybrid isolation system. \ud This paper focuses on the numerical modelling approach for this type of problems. The model consists of a structural and a bounded acoustic part that are representative for a vehicle. The responses of both parts are determined efficiently with modal superposition. The controller design, necessary for the active part of the isolation, is performed with the optimal control theory that is based on minimization of a cost function. Different cost functions will be compared with each other with emphasis on the performance of the structural related cost functions (e.g. minimization of structural velocities) in comparison with the acoustical cost functions (e.g. minimization of sound pressures)

A new Determination of the Extragalactic Background of Diffuse Gamma Rays taking into account Dark Matter Annihilation

The extragalactic background (EGB) of diffuse gamma rays can be determined by subtracting the Galactic contribution from the data. This requires a Galactic model (GM) and we include for the first time the contribution of dark matter annihilation (DMA), which was previously proposed as an explanation for the EGRET excess of diffuse Galactic gamma rays above 1 GeV. In this paper it is shown that the newly determined EGB shows a characteristic high energy bump on top of a steeply falling soft contribution. The bump is shown to be compatible with a contribution from an extragalactic DMA signal from weakly interacting massive particles (WIMPs) with a mass between 50 and 100 GeV in agreement with the EGRET excess of the Galactic diffuse gamma rays and in disagreement with earlier analysis. The remaining soft contribution of the EGB is shown to resemble the spectra of the observed point sources in our Galaxy.Comment: 7 pages, 4 figures. Accepted by A&A, made Fig. 4 and table 1 consisten

Design of fibre reinforced PV concepts for building integrated applications

Fibre reinforced polymers present an interesting encapsulation medium for PV-modules. Glass fibres can provide increased strength and stiffness to thin polymer layers overcoming the brittleness and limited deformability of glass-panes. Glass fibre reinforced polymers allows for transparency over a broad range of the solar spectrum while the material properties and integral production processes create possibilities for novel product concepts with embedded PV technology. To explore such possibilities, innovative design methods were used to design novel PV product concepts for applications in the build environment.\ud In our paper three conceptual designs are presented; (1) a thin film module with an adjoining interconnection system functioning as structural element for geodetic roofing structures, (2) a PV lamella with single-axis tracking utilizing a linear concentration effect caused by the geometry of the product and the materials applied, and (3) a prepreg PV-material which allows for easy shaping during the production of PV modules with complex geometries. Each concept employs a specific PV technology and demonstrates a possible application aimed at a specific market. In this way we show the potential of integration of PV technology in fibre reinforced composites. The paper will be illustrated by concept renderings

Spontaneous electro-weak symmetry breaking and cold dark matter

In the standard model, the weak gauge bosons and fermions obtain mass after spontaneous electro-weak symmetry breaking, which is realized through one fundamental scalar field, namely Higgs field. In this paper we study the simplest scalar cold dark matter model in which the scalar cold dark matter also obtains mass through interaction with the weak-doublet Higgs field, the same way as those of weak gauge bosons and fermions. Our study shows that the correct cold dark matter relic abundance within $3\sigma$ uncertainty ($0.093 < \Omega_{dm} h^2 < 0.129$) and experimentally allowed Higgs boson mass ($114.4 \le m_h \le 208$ GeV) constrain the scalar dark matter mass within $48 \le m_S \le 78$ GeV. This result is in excellent agreement with that of W. de Boer et.al. ($50 \sim 100$ GeV). Such kind of dark matter annihilation can account for the observed gamma rays excess ($10\sigma$) at EGRET for energies above 1 GeV in comparison with the expectations from conventional Galactic models. We also investigate other phenomenological consequences of this model. For example, the Higgs boson decays dominantly into scalar cold dark matter if its mass lies within $48 \sim 64$ GeV.Comment: 4 Revtex4 pages, refs adde

Optimised Sound Absorbing Trim Panels for the Reduction of Aircraft Cabin Noise

The EU project FACE (Friendly Aircraft Cabin Environment) aims to improve the environmental comfort in aircraft cabins. As part of this project, this paper focuses on the reduction of noise in aircraft cabins. For modern aircraft flying at cruise conditions, this cabin noise is known to be dominated by turbulent boundary layer noise. The purpose of this work is to reduce the resulting sound pressure levels in the cabin by means of optimised sound absorbing trim panels with quarter-wave resonators. Sound absorption with quarter-wave resonators is mainly realised by dissipation of sound energy as a result of viscous and thermal losses. The viscothermal wave propagation of the air inside the resonators is efficiently and accurately described by the so-called low reduced frequency model. By optimisation of the dimensions of the resonators, desired sound absorption characteristics can be obtained for different specified frequency ranges. This means that the panels can be tailored to different positions in the aircraft cabin with different prevailing sound pressure levels. Results of optimisations for various frequency ranges show that a very good agreement is obtained between the desired and the calculated absorption curves. With the same optimisation procedure, panels have also been tuned for the dominant frequency range of a sound spectrum measured in a modern aircraft. Experimental validation of the numerically predicted optimal configurations, by means of impedance tube measurements, shows that a fairly good agreement is obtained between the numerical and experimental results

Prediction of mechanical fatigue caused by multiple random excitations

A simulation method is presented for the fatigue analysis of automotive and other products that are subjected to multiple random excitations. The method is denoted as frequency domain stress-life fatigue analysis and was implemented in the automotive industry at DAF Trucks N.V. in Eindhoven, The Netherlands. As an example case, a chassis part is analysed. The results of the analysis are consistent with fatigue cracks encountered during testing, which illustrates the effectiveness of the adopted method in the automotive industry