Showing papers by "Swedish Defence Research Agency published in 2009"
TL;DR: The review includes novel techniques, not yet tested in realistic environments, more mature technologies which have been tested outdoors in realistic environment as well as the most mature millimetre wave imaging technique.
Abstract: A review of standoff detection technologies for explosives has been made. The review is focused on trace detection methods (methods aiming to detect traces from handling explosives or the vapours surrounding an explosive charge due to the vapour pressure of the explosive) rather than bulk detection methods (methods aiming to detect the bulk explosive charge). The requirements for standoff detection technologies are discussed. The technologies discussed are mostly laser-based trace detection technologies, such as laser-induced-breakdown spectroscopy, Raman spectroscopy, laser-induced-fluorescence spectroscopy and IR spectroscopy but the bulk detection technologies millimetre wave imaging and terahertz spectroscopy are also discussed as a complement to the laser-based methods. The review includes novel techniques, not yet tested in realistic environments, more mature technologies which have been tested outdoors in realistic environments as well as the most mature millimetre wave imaging technique.
252 citations
TL;DR: The Populus Genome Integrative Explorer (PopGenIE), an integrated set of tools for exploring the Populus genome and transcriptome, significantly increases accessibility to Populus genomics resources and allows exploration of transcriptomics data without the need to learn or understand complex statistical analysis methods.
Abstract: * Populus has become an important model plant system. However, utilization of the increasingly extensive collection of genetics and genomics data created by the community is currently hindered by t ...
207 citations
TL;DR: Phylogenetic analyses suggest a North American origin for this B-radiation clade and multiple dispersal events between North America and Eurasia and indicates a complex transmission history for F. tularensis subsp.
Abstract: Francisella tularensis contains several highly pathogenic subspecies, including Francisella tularensis subsp. holarctica, whose distribution is circumpolar in the northern hemisphere. The phylogeography of these subspecies and their subclades was examined using whole-genome single nucleotide polymorphism (SNP) analysis, high-density microarray SNP genotyping, and real-time-PCR-based canonical SNP (canSNP) assays. Almost 30,000 SNPs were identified among 13 whole genomes for phylogenetic analysis. We selected 1,655 SNPs to genotype 95 isolates on a high-density microarray platform. Finally, 23 clade- and subclade-specific canSNPs were identified and used to genotype 496 isolates to establish global geographic genetic patterns. We confirm previous findings concerning the four subspecies and two Francisella tularensis subsp. tularensis subpopulations and identify additional structure within these groups. We identify 11 subclades within F. tularensis subsp. holarctica, including a new, genetically distinct subclade that appears intermediate between Japanese F. tularensis subsp. holarctica isolates and the common F. tularensis subsp. holarctica isolates associated with the radiation event (the B radiation) wherein this subspecies spread throughout the northern hemisphere. Phylogenetic analyses suggest a North American origin for this B-radiation clade and multiple dispersal events between North America and Eurasia. These findings indicate a complex transmission history for F. tularensis subsp. holarctica.
163 citations
TL;DR: The authors' observations suggest that despite an average nucleotide identity of >97%, F. tularensis and F. novicida have evolved as two distinct population lineages, the former characterized by clonal structure with weak purifying selection, the latter by more frequent recombination and strong purify selection.
Abstract: Francisella tularensis is a potent mammalian pathogen well adapted to intracellular habitats, whereas F. novicida and F. philomiragia are less virulent in mammals and appear to have less specialize ...
145 citations
TL;DR: The Vasco-Cirene program explores how strong air-sea interactions promoted by the shallow thermocline and high sea surface temperature in the Seychelles-Chagos temperature ridge results in marked variability at synoptic, intraseasonal, and interannual time scales.
Abstract: The Vasco-Cirene program explores how strong air-sea interactions promoted by the shallow thermocline and high sea surface temperature in the Seychelles-Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceanographic cruise collected oceanic, atmospheric, and air-sea flux observations in this region in January–February 2007. The contemporaneous Vasco field experiment complemented these measurements with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a mooring and 12 Argo profilers. Unusual conditions prevailed in the Indian Ocean during January and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles-Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward cur...
138 citations
TL;DR: The present study supports the suggestion of the subendocortical layer as a transitional zone, which can readily be transformed into trabecular bone in response to immobilization, and confirms that endocorticals circumference can account for the different amounts of bone loss in the tibia.
112 citations
TL;DR: It is demonstrated that Hfq promotes resistance to several cellular stresses and appears to be a new pleiotropic regulator of virulence in F. tularensis, acting mostly as a repressor, in contrast to the other regulators identified so far.
Abstract: Francisella tularensis is a highly infectious pathogen that infects animals and humans, causing tularemia. The ability to replicate within macrophages is central for virulence and relies on expression of genes located in the Francisella pathogenicity island (FPI), as well as expression of other genes. Regulation of FPI-encoded virulence gene expression in F. tularensis involves at least four regulatory proteins and is not fully understood. Here we studied the RNA-binding protein Hfq in F. tularensis and particularly the role that it plays as a global regulator of gene expression in stress tolerance and pathogenesis. We demonstrate that Hfq promotes resistance to several cellular stresses (including osmotic and membrane stresses). Furthermore, we show that Hfq is important for the ability of the F. tularensis vaccine strain LVS to induce disease and persist in organs of infected mice. We also demonstrate that Hfq is important for stress tolerance and full virulence in a virulent clinical isolate of F. tularensis, FSC200. Finally, microarray analyses revealed that Hfq regulates expression of numerous genes, including genes located in the FPI. Strikingly, Hfq negatively regulates only one of two divergently expressed putative operons in the FPI, in contrast to the other known regulators, which regulate the entire FPI. Hfq thus appears to be a new pleiotropic regulator of virulence in F. tularensis, acting mostly as a repressor, in contrast to the other regulators identified so far. Moreover, the results obtained suggest a novel regulatory mechanism for a subset of FPI genes.
107 citations
TL;DR: It is demonstrated that the RVF VLPs are highly immunogenic and confer protection against RVFV infection in mice and the test groups, the vaccinated mice did not exhibit any side effects, and the lack of anti-nucleocapsid protein antibodies serologically distinguished vaccinated animals from experimentally infected animals.
96 citations
TL;DR: House dust mites are well‐known as a source of indoor aeroallergens and for causing allergic airway diseases, but there is limited knowledge regarding such activity among non‐proteolytic HDM allergens.
Abstract: BACKGROUND: House dust mites (HDM) are well-known as a source of indoor aeroallergens and for causing allergic airway diseases Some proteolytic HDM allergens are known to activate respiratory epit
93 citations
TL;DR: In this article, spontaneous Raman spectroscopy was used to identify explosives at distances of up to 55 in using an outdoors test field and performing experiments under varying weather conditions such as rain or snowfall or bright sunshine.
Abstract: Standoff identification of explosives at distances of up to 55 in has been performed by applying spontaneous Raman spectroscopy. This work has been focused on detection in a realistic environment, using an outdoors test field and performing experiments under varying weather conditions such as rain- or snowfall or bright sunshine. The instrumentation, based on a 532 nm pulsed laser source combined with gated detection, proved the performance insensitive to weather variations. Investigated HMEs and precursors were TATP, HMTD, HP, MEKP, NM, NB, and IPN; all in bulk quantities. The time needed for acquiring spectra was typically between single pulse (5 ns) and 10 s. Detection through green and brown glass bottles and PET bottles were tried and found viable. (Less)
91 citations
TL;DR: This study gives an overview of the state-of-the-art methods to decompose an image into a number of IMFs and a residue image with a minimum number of extrema points, together with the use of the method.
Abstract: Image empirical mode decomposition (IEMD) is an empirical mode decomposition concept used in Hilbert–Huang transform (HHT) expanded into two dimensions for the use on images. IEMD provides a tool for image processing by its special ability to locally separate superposed spatial frequencies. The tendency is that the intrinsic mode functions (IMFs) other than the first are low-frequency images. In this study we give an overview of the state-of-the-art methods to decompose an image into a number of IMFs and a residue image with a minimum number of extrema points, together with the use of the method. Ideas and open problems are presented.
TL;DR: The oxime-pyridinium ring structure is determined, which shows that the oxime group of HI-6 can form a hydrogen-bond network to the sarin isopropyl ether oxygen, and a water molecule is able to form a Hydrogen bond to the catalytic histidine residue and subsequently deprotonates the oximes for reactivation.
Abstract: Organophosphonates such as isopropyl metylphosphonofluoridate (sarin) are extremely toxic as they phosphonylate the catalytic serine residue of acetylcholinesterase (AChE), an enzyme essential to humans and other species. Design of effective AChE reactivators as antidotes to various organophosphonates requires information on how the reactivators interact with the phosphonylated AChEs. However, such information has not been available hitherto because of three main challenges. First, reactivators are generally flexible in order to change from the ground state to the transition state for reactivation; this flexibility discourages determination of crystal structures of AChE in complex with effective reactivators that are intrinsically disordered. Second, reactivation occurs upon binding of a reactivator to the phosphonylated AChE. Third, the phosphorous conjugate can develop resistance to reactivation. We have identified crystallographic conditions that led to the determination of a crystal structure of the sarinnonaged-conjugated mouse AChE in complex with [(E)-[1-[(4-carbamoylpyridin-1-ium-1-yl)methoxymethyl]pyridin-2-ylidene]methyl]-oxoazanium dichloride (HI-6) at a resolution of 2.2 A. In this structure, the carboxyamino-pyridinium ring of HI-6 is sandwiched by Tyr124 and Trp286, however, the oxime-pyridinium ring is disordered. By combining crystallography with microsecond molecular dynamics simulation, we determined the oxime-pyridinium ring structure, which shows that the oxime group of HI-6 can form a hydrogen-bond network to the sarin isopropyl ether oxygen, and a water molecule is able to form a hydrogen bond to the catalytic histidine residue and subsequently deprotonates the oxime for reactivation. These results offer insights into the reactivation mechanism of HI-6 and design of better reactivators.
TL;DR: Some advanced concepts for gated viewing are presented, including spectral diversity illumination techniques, non-line-of-sight imaging, indirect scene illumination, and in particular setups in bistatic configurations, which contribute to a reduced dazzling risk and to observer convertness.
Abstract: Some advanced concepts for gated viewing are presented, including spectral diversity illumination techniques, non-line-of-sight imaging, indirect scene illumination, and in particular setups in bistatic configurations. By using a multiple-wavelength illumination source target speckles could be substantially reduced, leading to an improved image quality and enhanced range accuracy. In non-line-of-sight imaging experiments we observed the scenery through the reflections in a window plane. The scene was illuminated indirectly as well by a diffuse reflection of the laser beam at different nearby objects. In this setup several targets could be spotted, which, e.g., offers the capability to look around the corner in urban situations. In the presented measuring campaigns the advantages of bistatic setups in comparison with common monostatic configurations are discussed. The appearance of shadows or local contrast enhancements as well as the mitigation of retroreflections supports the human observer in interpreting the scene. Furthermore a bistatic configuration contributes to a reduced dazzling risk and to observer convertness.
TL;DR: It is shown that reintroduction of the two deleted regions restores virulence of LVS in a mouse infection model to a level indistinguishable from that of virulent type B strains.
Abstract: A disadvantage of several old vaccines is that the genetic events resulting in the attenuation are often largely unknown and reversion to virulence cannot be excluded. In the 1950s, a live vaccine strain, LVS, was developed from a type B strain of Francisella tularensis, the causative agent of tularemia. LVS, which is highly attenuated for humans but still virulent for mice by some infection routes, has been extensively studied and found to protect staff from laboratory-acquired tularemia. The efforts to improve biopreparedness have identified a demand for a vaccine against tularemia. Recently the rapid progress in genomics of different Francisella strains has led to identification of several regions of differences (RDs). Two genes carried within RDs, pilA, encoding a putative type IV pilin, and FTT0918, encoding an outer membrane protein, have been linked to virulence. Interestingly, LVS has lost these two genes via direct repeat-mediated deletions. Here we show that reintroduction of the two deleted regions restores virulence of LVS in a mouse infection model to a level indistinguishable from that of virulent type B strains. The identification of the two attenuating deletion events could facilitate the licensing of LVS for use in humans.
TL;DR: The appearance of Rift Valley fever associated clinical signs were significantly decreased among the DNA vaccinated mice and further adjustment of this strategy may result in full protection against Rift Valley Fever.
Abstract: Affecting both livestock and humans, Rift Valley Fever is considered as one of the most important viral zoonoses in Africa However, no licensed vaccines or effective treatments are yet available for human use Naked DNA vaccines are an interesting approach since the virus is highly infectious and existing attenuated Rift Valley Fever virus vaccine strains display adverse effects in animal trials In this study, gene-gun immunisations with cDNA encoding structural proteins of the Rift Valley Fever virus were evaluated in mice The induced immune responses were analysed for the ability to protect mice against virus challenge Immunisation with cDNA encoding the nucleocapsid protein induced strong humoral and lymphocyte proliferative immune responses, and virus neutralising antibodies were acquired after vaccination with cDNA encoding the glycoproteins Even though complete protection was not achieved by genetic immunisation, four out of eight, and five out of eight mice vaccinated with cDNA encoding the nucleocapsid protein or the glycoproteins, respectively, displayed no clinical signs of infection after challenge In contrast, all fourteen control animals displayed clinical manifestations of Rift Valley Fever after challenge The appearance of Rift Valley Fever associated clinical signs were significantly decreased among the DNA vaccinated mice and further adjustment of this strategy may result in full protection against Rift Valley Fever
TL;DR: A mobile system for sampling of atmospheric xenon was transported to the Republic of South Korea (ROK) in an attempt to detect possible emissions of radioxenon in the region from a presumed test as discussed by the authors.
Abstract: Following the claimed nuclear test in the Democratic People’s Republic of Korea (DPRK) on October 9, 2006, and a reported seismic event, a mobile system for sampling of atmospheric xenon was transported to the Republic of South Korea (ROK) in an attempt to detect possible emissions of radioxenon in the region from a presumed test. Five samples were collected in the ROK during October 11–14, 2006 near the ROK–DPRK border, and thereafter transported to the Swedish Defense Research Agency (FOI) in Stockholm, Sweden, for analysis. Following the initial measurements, an automatic radioxenon sampling and analysis system was installed at the same location in the ROK, and measurements on the ambient atmospheric radioxenon background in the region were performed during November 2006 to February 2007. The measured radioxenon concentrations strongly indicate that the explosion in October 9, 2006 was a nuclear test. The conclusion is further strengthened by atmospheric transport models. Radioactive xenon measurement was the only independent confirmation that the supposed test was in fact a nuclear explosion and not a conventional (chemical) explosive.
TL;DR: The channel capacity of this model is derived, and numerical examples are given for some useful sets of model parameters.
Abstract: Middleton's class A interference model has properties that make it possible to represent a wide class of interference signals. By choice of model parameters, interference signals ranging from pure Gaussian distributed to pure impulsive interference can be modelled. These properties make the model very useful for a large variety of applications. However, an expression for the channel capacity of the class A interference channel has not yet been published. The channel capacity of this model is derived, and numerical examples are given for some useful sets of model parameters.
TL;DR: It was hypothesized that nutrient-rich environments, with strong protozoan predation, favour the occurrence of the tularaemia bacterium, and high nutrient conditions in combination with high abundances of nanoflagellates were found to favour F. tularensis ssp.
TL;DR: In this paper, the synthesis of trans-di(arylalkynyl)diphosphine platinum(II) complexes bearing trialkoxysilane groups was described, as well as the preparation of siloxane-based hybrid materials from organometall materials.
Abstract: The synthesis of trans-di(arylalkynyl)diphosphine platinum(II) complexes bearing trialkoxysilane groups is described, as well as the preparation of siloxane-based hybrid materials from organometall ...
TL;DR: The batch leaching test used for waste characterization substantially underestimated As solubility that could occur under water-saturated (anaerobic) conditions, and other techniques than Fe-stabilization of As containing soil should be considered.
TL;DR: The results indicate that early single-dose treatment with dexamethasone protects against long-term effects observed 2–4 weeks after melphalan exposure, as indicated by reduced lymphocytic response in airways and decreased collagen deposition.
Abstract: The pathogenesis of lung injury by exposure to highly toxic sulfur and nitrogen mustards involves alkylating damage of the respiratory epithelium followed by an acute inflammatory response and lung edema. The acute phase is followed by long-term respiratory complications characterized by bronchitis, lung fibrosis, and airway hyperreactivity. In this study, we utilized a mouse model for airway inflammation induced by inhalation exposure to the alkylating nitrogen mustard melphalan, in order to investigate possible beneficial treatment effects by the corticosteroid dexamethasone. In addition, we investigated therapeutic efficacy of liposome-encapsuled vitamin E, an antioxidant formulation previously shown to be efficient in counteracting inflammatory conditions. Influx of inflammatory cells to airways, edema formation, and expression of different cytokines were analyzed 6 and 18 hours after exposure to melphalan. In order to evaluate long-term lung effects, we also investigated collagen deposition and accumulation of lymphocytes at 2 and 4 weeks after exposure. A single intraperitoneal injection of dexamethasone (10 mg/kg body weight) 1 hour after melphalan exposure significantly reduced interleukin (IL)-1 and IL-6 in bronchoalveolar lavage fluid (BALF) and diminished the acute airway inflammation. Our results also indicate that early single-dose treatment with dexamethasone protects against long-term effects observed 2-4 weeks after melphalan exposure, as indicated by reduced lymphocytic response in airways and decreased collagen deposition. Furthermore, our results indicate that also vitamin E (50 mg/kg) reduces acute inflammatory cell influx, and suppresses collagen formation in lung tissue, indicating that this drug could be used in combination with corticosteroids for protection against chemical-induced lung injury.
TL;DR: Investigation of lymphocyte subtypes in bronchoalveolar lavage fluid finds CD8+ T cell activation was found in COPD, supporting the contention that this T cell subset may play a role in the pathogenesis of COPD.
Abstract: The mechanisms behind airway inflammation in chronic obstructive pulmonary disease (COPD) are still not well understood. Here we investigated lymphocyte subtypes in bronchoalveolar lavage fluid, li ...
TL;DR: In the CAWAPI project, nine groups participated in the Cranked Arrow Wing Aerodynamics Project International (CAWAPI) project have contributed steady and unsteady viscous simulations of a full-scale, semi-span model of the F-16XL aircraft as discussed by the authors.
Abstract: Nine groups participating in the Cranked Arrow Wing Aerodynamics Project International (CAWAPI) project have contributed steady and unsteady viscous simulations of a full-scale, semi-span model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations were computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models of different complexity with no topology information required and which overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation (DES) and its successor delayed detached-eddy simulation (DDES) have been used to compute the time accurate flow development. Common structured and unstructured grids as well as individually-adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction and boundary velocity profiles at subsonic speeds. The physical modeling, steady or unsteady, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time it cannot be determined how much each part contributes to the whole. Overall it can be said that the technology readiness of CFD-simulation technology for the study of vehicle performance has matured since 2001 such that it can be used today with a reasonable level of confidence for complex configurations.
TL;DR: In this article, the authors investigated mental workload in basic civil aviation training and found that the increase of workload starts in advance of an unexpected event in the simulator where it seems to be of a preparatory nature, whereas in the aircraft it is more connected to management of the situation.
Abstract: This study investigated mental workload in basic civil aviation training. Heart rate, eye movement, and subjective ratings from 11 students were collected during simulator and aircraft sessions. Results show high correspondence in psychophysiological reactions between the sessions. For some flight segments, heart rate was consistently lower in the simulator, suggesting higher mental workload in the aircraft. Differences in heart rate during rejected takeoff and engine failure indicate that the increase of workload starts in advance of an “unexpected” event in the simulator where it seems to be of preparatory nature, whereas in the aircraft it is more connected to management of the situation.
TL;DR: Using a combination of classical and shotgun proteome analyses, several proteins that accumulated in fractions enriched for membrane-associated proteins in the dsbA mutant are identified as substrate candidates for the DsbA disulfide oxidoreductase as well as being responsible for the virulence attenuation of the dSBA mutant.
Abstract: Francisella tularensis (F. tularensis) is highly infectious for humans via aerosol route and untreated infections with the highly virulent subsp. tularensis can be fatal. Our knowledge regarding key virulence determinants has increased recently but is still somewhat limited. Surface proteins are potential virulence factors and therapeutic targets, and in this study, we decided to target three genes encoding putative membrane lipoproteins in F. tularensis LVS. One of the genes encoded a protein with high homology to the protein family of disulfide oxidoreductases DsbA. The two other genes encoded proteins with homology to the VacJ, a virulence determinant of Shigella flexneri. The gene encoding the DsbA homologue was verified to be required for survival and replication in macrophages and importantly also for in vivo virulence in the mouse infection model for tularemia. Using a combination of classical and shotgun proteome analyses, we were able to identify several proteins that accumulated in fractions enriched for membrane-associated proteins in the dsbA mutant. These proteins are substrate candidates for the DsbA disulfide oxidoreductase as well as being responsible for the virulence attenuation of the dsbA mutant.
TL;DR: In this paper, a 20-GHz radio frequency microelectromechanical system (RF MEMS)-based electrically switchable antenna on a quartz substrate was demonstrated with a single-pole double-throw (SPDT) switch router network on a 21 mm times 8 mm chip.
Abstract: This letter demonstrates a 20-GHz radio frequency microelectromechanical system (RF MEMS)-based electrically switchable antenna on a quartz substrate Two quasi-Yagi antenna elements are monolithically integrated with a single-pole double-throw (SPDT) MEMS switch router network on a 21 mm times 8 mm chip Electrical beam steering between two opposite directions is achieved using capacitive MEMS SPDT switches in the router Port impedance and radiation patterns are studied numerically and experimentally Measured results show that the switched beam antenna features a 27% impedance bandwidth (S11 = -10 dB), a gain of 46 dBi, and a front-to-back ratio of 14 dB at 20 GHz when the control voltage is applied to one of the switch pairs of the SPDT switch
TL;DR: In this paper, the potential for the transportation sector to develop in a way that is consistent with long-term climate targets is discussed, and the question is whether technical measures will be sufficient for reaching longterm climate goals.
TL;DR: In this paper, the authors present a case study on the future vulnerability to climate change of the Swedish railway transport system and its adaptive capacity, based on interviews with key personnel within the Swedish Rail Administration.
Abstract: The current variability in weather and climate is posing a challenge for transport infrastructure. However, during the past decade the need to adapt to a changing climate has attracted increasing attention. This paper summarises a case study on the future vulnerability to climate change of the Swedish railway transport system and its adaptive capacity. The combination of a long time horizon in planning and an expected increasing demand for rail traffic raises many questions regarding how adaptation to climate change can be accounted for in future planning, design and management of railways. The case study was essentially based on interviews with key personnel within the Swedish Rail Administration. Views on vulnerability and adaptation to climate change were documented, and the need for improved methods to assess the vulnerability and adaptive capacity related to climate change for the Swedish railways was addressed. The conclusions of the paper are addressed to the European railway context at large. Firstly, systematic mapping of current climate vulnerabilities and their consequences is important in order to guide the implementation of adaptation measures. Secondly, climate change should be considered in the early stages of planning and included in risk and vulnerability assessments. In assessing future conditions with the aim of prioritising adaptation measures, current methodologies should be complemented with more future-orientated tools. When designing adaptation measures, the effects of potential goal conflicts should also be assessed, in order to avoid the implementation of counter-productive measures. The possibility of creating synergies with climate mitigation goals and other environmental goals should also be investigated.
05 Jan 2009
TL;DR: The paper focuses on the implementation of the line-implicit scheme starting from an explicit multigrid flow solver and on the application of it, and the gain is quantified in terms of reduction of iterations and CPU time.
Abstract: A line-implicit Runge-Kutta time stepping scheme is derived, implemented and applied. It is applied to fluid flow problems governed by the Navier-Stokes equations on stretched unstructured grids. The flow equations are integrated implicitly in time along structured lines in regions where the grid is stretched, typically in the boundary layer, and explicitly elsewhere. The integration technique is introduced for steady state problems with the intention to speed up the rate of convergence. It is extended to unsteady problems by a dual time stepping approach. The paper focuses on the implementation of the line-implicit scheme starting from an explicit multigrid flow solver and on the application of it. Numerical results are presented for test cases in two and three dimensions for inviscid and viscous flow problems. The line-implicit time integration convergence rates are compared to pure explicit convergence rates and the gain is quantified in terms of reduction of iterations and CPU time. All presented test cases show improved convergence rates. The gain is highest for the three dimensional test cases for which reductions of up to 75% of the computing time is obtained.
TL;DR: In this article, the authors compare the performance of three different computational fluid dynamics codes using a common unstructured grid for steady and unsteady viscous flow simulations of a full-scale, semispan, and full-span model of the F-16XL-1 aircraft.
Abstract: Steady and unsteady viscous flow simulations of a full-scale, semispan, and full-span model of the F-16XL-1 aircraft are performed with three different computational fluid dynamics codes using a common unstructured grid. Six different flight conditions are considered. They represent Reynolds and Mach number combinations at subsonic speeds, with and without sideslip. The steady computations of the flow at these flight conditions are made with several Reynolds-averaged Navier-Stokes turbulence models of different complexity. Detached-eddy simulation, delayed detached-eddy simulation, and an algebraic hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation model are used to quantify unsteady effects at the same flight conditions. The computed results are compared with flight-test data in the form of surface pressures, skin friction, and boundary-layer velocity profiles. The focus of the comparison is on turbulence modeling effects and effects of unsteadiness. The overall agreement with flight data is good, with no clear trend as to which physical modeling approach is superior for this class of flow. The Reynolds-averaged Navier-Stokes turbulence models perform well in predicting the flow in an average sense. However, some of the flow conditions involve locally unsteady flow over the aircraft, which are held responsible for the scatter between the different turbulence modeling approaches. The detached-eddy simulations are able to quantify the unsteady effects, although they are not consistently better than the Reynolds-averaged Navier-Stokes turbulence models in predicting the flow in an average sense in these flow regions. Detached-eddy simulation fails to predict boundary-layer profiles consistently over a range of flow regimes, with delayed detached-eddy simulation and hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation models offering a remedy to recover some of the predictive capabilities of the underlying Reynolds-averaged Navier-Stokes turbulence model. Nonetheless, the confidence in the predictive capabilities of the computational fluid dynamics codes with regard to complex vortical flowfields around high-performance aircraft of this planform increased significantly during this study.