Investigation of the effect of combustor cooling geometry on acoustic energy absorption

To control combustion instabilities occurring in LPP gas turbine combustors, several active and passive systems have been developed in recent years. The combustion chamber cooling geometry has the potential to influence instability feedback loops by absorbing acoustical energy inside the combustor. The design of the cooling liner and the geometry of the cooling plenum and the cooling air flow rate have a significant influence on the absorption characteristics of the system. This paper presents the results of a cold flow study which was carried out in the course of a comprehensive study on the influence of the cooling geometry on combustor thermoacoustics. Absorption characteristics of three different cooling liner geometries and non-perforated plates were determined over a frequency range from 50 Hz to 600 Hz for different cooling flow rates and different cooling plenum volumes. The experimental results compared well with results from a low order thermoacoustic network model. The acoustic energy absorption spectrum of a cooling liner with 90°-hole configuration was found to be strongly dependent on cooling flow rate and cooling plenum volume, whereas the absorption spectrum of cooling liners with 25°-holes were found to be strongly dependent on the cooling plenum volume, but less dependent on the cooling air flow rate. All cooling liner setups with perforations were capable of increased acoustic absorption over a broad band of frequencies compared to the case of non-perforated combustor walls. © 2010 by Johannes Schmidt.

Magnetic Hyperthermia With Fe(3)O(4) Nanoparticles: The Influence of Particle Size on Energy Absorption

We have studied the magnetic and power absorption properties of a series of magnetic nanoparticles (MNPs) of Fe(3)O(4) with average sizes < d > ranging from 3 to 26 rim. Heating experiments as a function of particle size revealed a strong increase in the specific power absorption (SPA) values for particles with < d > = 25-30 mn. On the other side saturation magnetization M(s) values of these MNPs remain essentially constant for particles with < d > above 10 rim, suggesting that the absorption mechanism is not determined by Ms. The largest SPA value obtained was 130 W/g, corresponding to a bimodal particle distribution with average size values of 17 and 26 nm.

Mechanical properties and energy absorption of ceramic particulate and resin-impregnation reinforced aluminium foams

The mechanical properties of aluminium foams can be improved by matrix reinforcement and resin-impregnation methods. In the present study, aluminium foams were reinforced by both ceramic particulate reinforcing of the aluminium matrix and resin-impregnating pores. The mechanical properties and the energy absorption of the reinforced aluminium foams were investigated by dynamic and quasi-static compression. Results indicated that the ceramic particle additions of CBN, SiC and B4C in aluminium foams increase the peak stress, elastic modulus and energy absorption of the aluminium foams, under both conditions of dynamic and quasi-static compression. Moreover, the aluminium foams with and without ceramic particle additions exhibited obvious strain rate sensitivity during dynamic compression. Furthermore, the resin-impregnation improves the mechanic properties and energy absorption of aluminium foams significantly. However, aluminium foams with resin-impregnation showed negligible strain rate sensitivity under dynamic compression. It is reported that both the ceramic particle addition and resin-impregnation can be effective techniques to improve the mechanical and the energy absorption properties of aluminium foams.

Strain rate effects on the energy absorption of rapidly manufactured composite tubes

As a result of recent increases in fuel prices and the growing number of accident fatalities, the two major concerns of the automotive industry and their customers are now occupant safety and fuel economy {1, 2]. Increasing the amount of energy and optimizing the manner in which energy is absorbed within vehicle crush zones can improve occupant survivability in the event of a crash, while fuel economy is improved through a reduction in weight.  Axial crush tests were conducted on tubular specimens of Carbon/Epoxy (Toray T700/G83C) and Glass/Polypropylene (Twintex). This paper presents results from the tests conducted at quasi-static rates at Deakin Unniversity, Victoria Australia, and intermediate rate tests performed at the Oak Ridge National Laboratory, Tennessee  USA.   The quasi-static tests were conducted at 10mm/min (1.67x10-4m/s) using 5 different forms of initiation. Tests at intermediate rates were performed at speeds of 0.25m/s, 0.5m/s, 0.75m/s 1m/s, 2m/s and 4m/s. Quasi-static tests of tubular specimens showed high specific energy absorption (SEA) values with 86 kJ/kg for Carbon/Epoxy specimens. The SEA of the Glass/Polypropylene specimens was measured to be 29 kJ/kg. Results from the intermediate test rates showed that SEA values did not fall below 55kJ/kg for carbon specimens or 35kJ/kg for the Glass/Polypropylene specimens. When compared with typical steel and aluminium, SEA values of 15 kJ/kg and 30kJ/kg respectively, the benefits of using composite materials in crash structures is apparent.                                                                     

Energy absorption and crushing behaviour of foam-filled aluminium tubes

The crushing behaviour and energy absorption of foam filled aluminium tubular structures were investigated using the quasi-static compressive tests. The crushing behaviour of the tubular structures changed due to foam filling. The energy absorption of the foam filled tubular structures was improved significantly. Foam filling caused an interaction effect between the tube and the foam during progressive crushing, leading to an increase in the mean crushing load compared to that of the foam or tube itself. This interaction effect might be affected by several parameters such as the density of the foam, the properties of both the foam material and tube material, and the thickness and outer diameter of the tube. In particular, the interaction effect essentially depended on the ratio of the mean crushing force of the foam to that of the tube.

Compressive properties and energy absorption of hollow sphere aluminium

Manufactured cellular aluminums have been developed for a wide range of automotive applications where weight savings, improved safety, crashworthiness and comfort are required. The plateau deformation behavior of cellular aluminums under compressive loading makes this new class of lightweight materials suitable for energy absorption and comes close to ideal impact absorbers. In the present study, aluminum hollow hemispheres were firstly processed by pressing. Hollow sphere aluminum samples with a body-centered cubic (BCC) packing were then fabricated by bonding together single hollow spheres, which were prepared by adhering together hollow hemispheres. Hollow sphere aluminum samples with various kinds of sphere wall thicknesses of 0.1 mm, 0.3 mm and 0.5 mm but the same outside diameter of 4 mm were investigated by compressive tests. The effects of the sphere wall thickness on the mechanical properties and energy absorption characteristics were investigated.

Compressive behavior and energy absorption of constructed cellular aluminum

The defoThe deformation behaviors and energy absorption characteristics of constructed cellular aluminums were investigated by compressive tests. Constructed cellular aluminum specimens with two kinds of thickness in the cold-pressed panel and various numbers of layers bonded together have been tested. The plateau stress and the energy absorption have been measured and furthermore, the deformation behaviors have been evaluated. Results indicate that superior mechanical properties with constructed cellular aluminums can be achieved when the distribution of material at cell level is properly selected. Excellent energy absorption per unit mass can be obtained by only changing the thickness of the original aluminum sheet.nnation behaviors and energy absorption characteristics of constructed cellular aluminums were investigated by compressive tests. Constructed cellular aluminum specimens with two kinds of thickness in the cold-pressed panel and various numbers of layers bonded together have been tested. The plateau stress and the energy absorption have been measured and furthennore, the defonnation behaviors have been evaluated. Results indicate that superior mechanical properties with constructed cellular aluminums can be achieved when the distribution of material at cell level is properly selected. Excellent energy absorption per unit mass can be obtained by only changing the thickness of the original aluminum sheet.

Strain rate effects on the energy absorption of rapidly manufactured composite tubes

Quasi-static and intermediate rate axial crush tests were conducted on tubular specimens of Carbon/Epoxy (Toray T700/G83C) and Glass/Polypropylene (Twintex). The quasi-static tests were conducted at 10 mm/min (1.67 x 10¯⁴ m/s); five different crush initiators were used. Tests at intermediate rates were performed at speeds of 0.25, 0.5, 0.75, 1, 2, and 4m/s. Modes of failure and specific energy absorption (SEA) values were studied. The highest SEA measured was 86 kJ/kg. This value was observed using Carbon/Epoxy samples at quasi static rates with a 45° chamfer initiator. The highest energy absorption for Twintex tubes was observed to be 57.56 kJ/kg during 45° chamfer initiated tests at 0.25 m/s. Compared with steel and aluminium, SEA values of 15 and 30 kJ/kg, respectively, the benefits of using composite materials in crash structures become apparent.

Impact response and energy absorption of aluminium foam-filled tubes

The effect of foam fillers on the impact behaviour and energy absorption of an aluminium tube is investigated. Both experimental test and computational simulation are employed in current study. For comparison, hollow tubes and foams are also tested, respectively. Foam filler is found to be ineffective in increasing the crushing loads of the composite tubes over the simple superposition of the crushing loads of hollow tube and foam. Also, foam filler increases the tendency for the concertina mode of folding. The foam fillers of tubes additionally result in increasing the SAE values over those of hollow tubes.