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.

Scenario development as a basis for formulating a research program on future agriculture: a methodological approach.

Abstract: To increase the awareness of society to the challenges of global food security, we developed five contrasting global and European scenarios for 2050 and used these to identify important issues for future agricultural research. Using a scenario development method known as morphological analysis, scenarios were constructed that took economic, political, technical, and environmental factors into account. With the scenarios as a starting point future challenges were discussed and research issues and questions were identified in an interactive process with stakeholders and researchers. Based on the outcome of this process, six socioeconomic and biophysical overarching challenges for future agricultural were formulated and related research issues identified. The outcome was compared with research priorities generated in five other research programs. In comparison, our research questions focus more on societal values and the role of consumers in influencing agricultural production, as well as on policy formulation and resolving conflicting goals, areas that are presently under-represented in agricultural research. The partly new and more interdisciplinary research priorities identified in Future Agriculture compared to other programs analyzed are likely a result of the methodological approach used, combining scenarios and interaction between stakeholders and researchers.

Large eddy simulation of CH4-air and C2H4-air combustion in a model annular gas turbine combustor

Abstract: Combustion instabilities are one of the major challenges in developing and operating propulsion and power generating gas-turbine engines More specifically, techniques for managing the increasingly stringent emissions regulations and efficiency demands have often given rise to thermo-acoustic instabilities, particularly for annular combustors operating in a lean premixed mode In this paper, we combine experimental and computational methods to examine unsteady gas turbine combustion in a full annular model gas turbine combustor installed at NTNU, operating both methane- and ethylene-air blends The experimental data consists of flame images, high-speed OH* chemiluminescence images, as well as pressure and heat-release time-series at discrete locations for the ethylene-air case The computational set-up consists of the 18 inlet tubes and swirlers, and the full annular combustor placed in a large external domain The computational model consists of a compressible finite rate chemistry LES model using skeletal methane-air and ethylene-air combustion chemistry The combustor is simulated in its self-excited state, without external forcing From the experiments and simulations the methane and ethylene cases are found to behave differently: The ethylene-air flames are much smaller than the methane-air flames, resulting in different interaction between adjacent flames The LES predictions show good qualitative agreement with the measurements in terms of instantaneous and time-averaged flame structure Comparing measured and predicted time-series of pressure and heat-release also shows good quantitative agreement with respect to the dynamics and structure for the ethylene-air case Investigating the predicted combustion dynamics using Proper Orthogonal Decomposition (POD) confirms the importance of the self-excited azimuthal mode on the behavior of the flame: the presence of nodes and anti-nodes of pressure induced fluctuations of the swirler mass-flow, which then, in turn, influence the heat-release These events occur shifted in time

Effects of sound exposure from a seismic airgun on heart rate, acceleration and depth use in free-swimming Atlantic cod and saithe.

Abstract: Airguns used for offshore seismic exploration by the oil and gas industry contribute to globally increasing anthropogenic noise levels in the marine environment. There is concern that the omnidirectional, high intensity sound pulses created by airguns may alter fish physiology and behaviour. A controlled short-term field experiment was performed to investigate the effects of sound exposure from a seismic airgun on the physiology and behaviour of two socioeconomically and ecologically important marine fishes: the Atlantic cod (Gadus morhua) and saithe (Pollachius virens). Biologgers recording heart rate and body temperature and acoustic transmitters recording locomotory activity (i.e. acceleration) and depth were used to monitor free-swimming individuals during experimental sound exposures (18-60 dB above ambient). Fish were held in a large sea cage (50 m diameter; 25 m depth) and exposed to sound exposure trials over a 3-day period. Concurrently, the behaviour of untagged cod and saithe was monitored using video recording. The cod exhibited reduced heart rate (bradycardia) in response to the particle motion component of the sound from the airgun, indicative of an initial flight response. No behavioural startle response to the airgun was observed; both cod and saithe changed both swimming depth and horizontal position more frequently during sound production. The saithe became more dispersed in response to the elevated sound levels. The fish seemed to habituate both physiologically and behaviourally with repeated exposure. In conclusion, the sound exposures induced over the time frames used in this study appear unlikely to be associated with long-term alterations in physiology or behaviour. However, additional research is needed to fully understand the ecological consequences of airgun use in marine ecosystems.

Absorber loading study in FOI 36.7 m 3 mode stirred reverberation chamber for pulsed power measurements

Abstract: A feasibility study was conducted to gain better understanding of the influence of different Q-values of a 36.7 m3 reverberation chamber. The chamber was loaded with different types and numbers of microwave absorbers. For different chamber Q-values, the lowest usable frequency for 200 uncorrelated stirrer positions the agreement with the expected exponential power distribution, the chamber time constant and field build up process, has been studied.