Swedish Defence Research Agency

About: Swedish Defence Research Agency is a government organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Radar & Synthetic aperture radar. The organization has 1413 authors who have published 2731 publications receiving 56083 citations. The organization is also known as: Totalförsvarets forskningsinstitut.

LES MODELING OF COMBUSTION APPLICATIONS USING OpenFOAM

Abstract: Predictive modeling of turbulent combustion is important for the development of IC engines, air-breathing engines, furnaces and for the understanding of afterburning be- hind explosive blasts. Significant advances in modeling non-reactive turbulent flows are now possible with the development of Large Eddy Simulation (LES) in which the large en- ergetic scales of the flow are resolved on the grid whilst modeling the effects of the small scales. Here we discuss the use of combustion LES in predictive modeling of propulsion and afterburning behind explosive blasts. The LES models used are described in some de- tail and are validated against laboratory data - of which results from two cases are pre- sented. These validated LES models are then applied to an annular multi-burner gas tur- bine combustor, a simplified scramjet combustor and condensed phase explosive TNT air blast, for which some additional experimental data is available. For these cases good agreement with the available reference data is obtained, and the LES predictions are used to elucidate the flow physics in such devices to further enhance our knowledge of these propulsion systems. Particular attention is focused on the influence of the combustion chemistry, turbulence-chemistry interaction, self-ignition, flameholding burner-to-burner interactions and combustion oscillations and instabilities.

Human thermoregulatory function during exercise and immersion after 35 days of horizontal bed-rest and recovery

Abstract: The present study evaluated the effect of 35 days of experimental horizontal bed-rest on exercise and immersion thermoregulatory function. Fifteen healthy male volunteers were assigned to either a Control (n = 5) or Bed-rest (n = 10) group. Thermoregulatory function was evaluated during a 30-min bout of submaximal exercise on a cycle ergometer, followed immediately by a 100-min immersion in 28 degrees C water. For the Bed-rest group, exercise and immersion thermoregulatory responses observed post-bed-rest were compared with those after a 5 week supervised active recovery period. In both trials, the absolute work load during the exercise portion of the test was identical. During the exercise and immersion, we recorded skin temperature, rectal temperature, the difference in temperature between the forearm and third digit of the right hand (DeltaT(forearm-fingertip))--an index of skin blood flow, sweating rate from the forehead, oxygen uptake and heart rate at minute intervals. Subjects provided ratings of temperature perception and thermal comfort at 5-min intervals. Exercise thermoregulatory responses after bed-rest and recovery were similar. Subjective ratings of temperature perception and thermal comfort during immersion indicated that subjects perceived similar combinations of Tsk and Tre to be warmer and thermally less uncomfortable after bed-rest. The average (SD) exercise-induced increase in Tre relative to resting values was not significantly different between the Post-bed-rest (0.4 (0.2) degrees C) and Recovery (0.5 (0.2) degrees C) trials. During the post-exercise immersion, the decrease in Tre, relative to resting values, was significantly (P < 0.05) greater in the Post-bed-rest trial (0.9 (0.5) degrees C) than after recovery (0.4 (0.3) degrees C). DeltaT(forearm-fingertip) was 5.2 (0.9) degrees C and 5.8 (1.0) degrees C at the end of the post-bed-rest and recovery immersions, respectively. The gain of the shivering response (increase in VO(2) relative to the decrease in Tre; VO(2)/Tre) was 1.19 l min(-1) degrees C(-1) in the Recovery trial, and was significantly attenuated to 0.51 l min(-1) degrees C(-1) in the Post-bed-rest trial. The greater cooling rate observed in the post-bed-rest trial is attributed to the greater heat loss and reduced heat production. The former is the result of attenuated cold-induced vasoconstriction and enhanced sweating rate, and the latter a result of a lower shivering VO(2) response.

Intensity variations using a quantized spatial light modulator for nonmechanical beam steering

Abstract: A liquid-crystal spatial light modulator (SLM) can be used to alter the phase of the wavefront to achieve a deflection or a change in the shape of a laser beam. Ideal blazed gratings have perfect diffraction efficiency, and all the light is deflected. Encoded onto a pixelated spatial light modulator, however, the spatial limitations and phase quantization result in a stepped, nonideal blazed grating and decreased diffraction efficiency. The far-field intensity distribution was measured for different deflection angles using 4 and 32 phase levels. The result has been analyzed and used to construct a simple model of the studied SLM. Simulations of the far field based on this model show good agreement with the experimental results.