There has been increasing interest in numerical simulations of fragmentation of expanding warheads in 3D.Accordingly there is a pressure on developers of leading commercial codes,such as LS-DYNA.AUTODYN and IMPETUS Af...There has been increasing interest in numerical simulations of fragmentation of expanding warheads in 3D.Accordingly there is a pressure on developers of leading commercial codes,such as LS-DYNA.AUTODYN and IMPETUS Afea.to implement the reliable fracture models and the efficient solution techniques.The applicability of the Johnson—Cook strength and fracture model is evaluated by comparing the fracture behaviour of an expanding steel casing of a warhead with experiments.The numerical codes and different numerical solution techniques,such as Eulerian,Lagrangian.Smooth particle hydrodynamics(SPH).and the corpuscular models recently implemented in IMPETUS Afea are compared.For the same solution techniques and material models we find that the codes give similar results.The SPH technique and the corpuscular technique are superior to the Eulerian technique and the Lagrangian technique(with erosion) when it is applied to materials that have fluid like behaviour such as the explosive and the tracer.The Eulerian technique gives much larger calculation time and both the Lagrangian and Eulerian techniques seem to give less agreement with our measurements.To more correctly simulate the fracture behaviours of the expanding steel casing,we applied that ductility decreases with strain rate.The phenomena may be explained by the realization of adiabatic shear bands.An implemented node splitting algorithm in IMPETUS Afea seems very promising.展开更多
We examine the ricochet and penetration behavior in sand, water and gelatin by steel spheres, 7.62 mm APM2 and 25 mm projectiles. A threshold impact angle(critical angle) exists beyond which ricochet cannot occur. The...We examine the ricochet and penetration behavior in sand, water and gelatin by steel spheres, 7.62 mm APM2 and 25 mm projectiles. A threshold impact angle(critical angle) exists beyond which ricochet cannot occur. The Autodyn simulation code with the smooth particle hydrodynamic(SPH) method and Impetus Afea Solver with the corpuscular model are used and the results are compared with experimental and analytical results. The resistance force in sand for spheres was proportional to a term quadratic in velocity plus a term linear in velocity. The drag coefficient for the quadratic term was 0.65. The Autodyn and Impetus Afea codes simulate too large penetration due to the lack of a linear velocity resistance force. Critical ricochet angles were consistent with analytical results in the literature. In ballistic gelatin at velocities of 50–850 m/s a drag coefficient of 0.30 fits the high speed camera recordings if a linear velocity resistance term is included. However, only a quadratic velocity resistance force with drag coefficient that varies with the Reynolds number also fits the measurements. The simulation of a sphere in water with Autodyn showed too large drag coefficient. The 7.62 mm APM2 core simulations in sand fit reasonable well for both codes. The 25 mm projectile ricochet simulations in sand show consistency with the high speed camera recordings. Computer time was reduced by one to two orders of magnitudes when applying the Impetus Afea Solver compared to Autodyn code due to the use of the graphics processing units(GPU).展开更多
For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testin...For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.展开更多
3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the directio...3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the direction of velocity of center of mass.The expectation of a randomly distributed projected area is commonly used for fragments that tumble(random rotation)during flight.We forecast a model where the expected drag coefficient is dependent of shape and Mach number.Rotation or tumbling only affects the expected projected area.Models of projected areas during tumbling and rotation are presented.An examination of the data by Mc Cleskey(1988)indicates that the volume of the fragment to the power of2/3 is a better parameter to characterize the drag coefficient of the fragments than the maximum projected area.Hydrocode simulations are used to verify results and to study projected area and drag coefficient of fragments.展开更多
Sedimentary rocks cover-73% of the Earth's surface and metamorphic rocks account for approximately91% of the crust by volume. Understanding the average behavior and variability of heat production for these rock ty...Sedimentary rocks cover-73% of the Earth's surface and metamorphic rocks account for approximately91% of the crust by volume. Understanding the average behavior and variability of heat production for these rock types are vitally important for developing accurate models of lithospheric temperature. We analyze the heat production of ～204,000 whole rock geochemical data to quantify how heat production of these rocks varies with respect to chemistry and their evolution during metamorphism. The heat production of metaigneous and metasedimentary rocks are similar to their respective protoliths. Igneous and metaigneous samples increase in heat production with increasing SiO_2 and K_2 O, but decrease with increasing FeO, MgO and CaO. Sedimentary and metasedimentary rocks increase in heat production with increasing Al_2 O_3, FeO, TiO_2, and K_2 O but decrease with increasing CaO. For both igneous and sedimentary rocks, the heat production variations are largely correlated with processes that affect K_2 O concentration and covary with other major oxides as a consequence. Among sedimentary rocks,aluminous shales are the highest heat producing(2.9 μW^(-3)) whereas more common iron shales are lower heat producing(1.7 μW m^(-3)). Pure quartzites and carbonates are the lowest heat producing sedimentary rocks. Globally, there is little definitive evidence for a decrease in heat production with increasing metamorphic grade. However, there remains the need for high resolution studies of heat production variations within individual protoliths that vary in metamorphic grade. These results improve estimates of heat production and natural variability of rocks that will allow for more accurate temperature models of the lithosphere.展开更多
Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosoci...Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosocial work situation of staff working with people with cognitive restrictions and to identify predictors for their job satisfaction and workability. A cross sectional study was performed. Method: The Questionnaire Psycho Social Nordic (QPS-Nordic questionnaire) was used. Results: The results showed that the majority of the staff working with people with cognitive restrictions were satisfied with their job, but musculoskeletal symptoms were described by 40%. Decision demands at work were high compared to quantitative and learning demands. Musculoskeletal symptoms were related to low ability to master the work, low job control and high job demands. Symptoms from the neck region were correlated to stress. A low level of neck pain was related to a high level of job satisfaction. Predictors for workability were positive challenges in work and not being hindered by musculoskeletal symptoms in work. Predictors for job satisfaction were mastery, workability and not having pain during the last 7 days. Conclusion: Due to the relatively small sample the results should be interpreted with caution. The results indicated that positive challenges in work and not being hindered by musculoskeletal disorders predicted workability in this group and that mastery, workability and not having pain during the last 7 days predicted job satisfaction.展开更多
Purpose: The inflammatory response in acute anterior uveitis (AU) is believed to be primarily mediated by autoreactive Tcells. We wanted to evaluate whether t he T-cell activation marker CD40 ligand is involved in the...Purpose: The inflammatory response in acute anterior uveitis (AU) is believed to be primarily mediated by autoreactive Tcells. We wanted to evaluate whether t he T-cell activation marker CD40 ligand is involved in the AU immunopathogenesi s. Methods: We evaluated the expression of the CD40 ligand on CD4+T-cells, CD8 +T-cells and CD19+B-cells on peripheral blood mononuclear cells using flow c ytometry in six patients with unilateralAU, six patientswith monosymptomatic opt ic neuritis (ON) as inflammatory controls, and in six healthy controls. The ex v ivo induction of the CD40 ligand on T-cells in patients and controls was also s tudied. Results: A significantly higher expression of the CD40 ligand on both CD 4+(p< 0.05)-and CD8+(p< 0.05) T-cells in patients with AU compared to ON pat ients and healthy controls was found. There was a significantly higher induction of the CD40 ligand on CD8+T-cells in AU patients compared to ON patients and healthy controls (p < 0.01). No differences in the B-cell population were obser ved between the three groups. Conclusion: Patients with AU had increased express ion of the CD40 ligand on T-cells in the blood and expressed higher levels of t he CD40 ligand when stimulated, compared to ophthalmological inflammatory contro ls and healthy controls. The data suggest that the CD40 ligand is involved in th e development of AU.展开更多
文摘There has been increasing interest in numerical simulations of fragmentation of expanding warheads in 3D.Accordingly there is a pressure on developers of leading commercial codes,such as LS-DYNA.AUTODYN and IMPETUS Afea.to implement the reliable fracture models and the efficient solution techniques.The applicability of the Johnson—Cook strength and fracture model is evaluated by comparing the fracture behaviour of an expanding steel casing of a warhead with experiments.The numerical codes and different numerical solution techniques,such as Eulerian,Lagrangian.Smooth particle hydrodynamics(SPH).and the corpuscular models recently implemented in IMPETUS Afea are compared.For the same solution techniques and material models we find that the codes give similar results.The SPH technique and the corpuscular technique are superior to the Eulerian technique and the Lagrangian technique(with erosion) when it is applied to materials that have fluid like behaviour such as the explosive and the tracer.The Eulerian technique gives much larger calculation time and both the Lagrangian and Eulerian techniques seem to give less agreement with our measurements.To more correctly simulate the fracture behaviours of the expanding steel casing,we applied that ductility decreases with strain rate.The phenomena may be explained by the realization of adiabatic shear bands.An implemented node splitting algorithm in IMPETUS Afea seems very promising.
文摘We examine the ricochet and penetration behavior in sand, water and gelatin by steel spheres, 7.62 mm APM2 and 25 mm projectiles. A threshold impact angle(critical angle) exists beyond which ricochet cannot occur. The Autodyn simulation code with the smooth particle hydrodynamic(SPH) method and Impetus Afea Solver with the corpuscular model are used and the results are compared with experimental and analytical results. The resistance force in sand for spheres was proportional to a term quadratic in velocity plus a term linear in velocity. The drag coefficient for the quadratic term was 0.65. The Autodyn and Impetus Afea codes simulate too large penetration due to the lack of a linear velocity resistance force. Critical ricochet angles were consistent with analytical results in the literature. In ballistic gelatin at velocities of 50–850 m/s a drag coefficient of 0.30 fits the high speed camera recordings if a linear velocity resistance term is included. However, only a quadratic velocity resistance force with drag coefficient that varies with the Reynolds number also fits the measurements. The simulation of a sphere in water with Autodyn showed too large drag coefficient. The 7.62 mm APM2 core simulations in sand fit reasonable well for both codes. The 25 mm projectile ricochet simulations in sand show consistency with the high speed camera recordings. Computer time was reduced by one to two orders of magnitudes when applying the Impetus Afea Solver compared to Autodyn code due to the use of the graphics processing units(GPU).
文摘For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.
文摘3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the direction of velocity of center of mass.The expectation of a randomly distributed projected area is commonly used for fragments that tumble(random rotation)during flight.We forecast a model where the expected drag coefficient is dependent of shape and Mach number.Rotation or tumbling only affects the expected projected area.Models of projected areas during tumbling and rotation are presented.An examination of the data by Mc Cleskey(1988)indicates that the volume of the fragment to the power of2/3 is a better parameter to characterize the drag coefficient of the fragments than the maximum projected area.Hydrocode simulations are used to verify results and to study projected area and drag coefficient of fragments.
基金supported by Australian Government Research Training Program Scholarship
文摘Sedimentary rocks cover-73% of the Earth's surface and metamorphic rocks account for approximately91% of the crust by volume. Understanding the average behavior and variability of heat production for these rock types are vitally important for developing accurate models of lithospheric temperature. We analyze the heat production of ～204,000 whole rock geochemical data to quantify how heat production of these rocks varies with respect to chemistry and their evolution during metamorphism. The heat production of metaigneous and metasedimentary rocks are similar to their respective protoliths. Igneous and metaigneous samples increase in heat production with increasing SiO_2 and K_2 O, but decrease with increasing FeO, MgO and CaO. Sedimentary and metasedimentary rocks increase in heat production with increasing Al_2 O_3, FeO, TiO_2, and K_2 O but decrease with increasing CaO. For both igneous and sedimentary rocks, the heat production variations are largely correlated with processes that affect K_2 O concentration and covary with other major oxides as a consequence. Among sedimentary rocks,aluminous shales are the highest heat producing(2.9 μW^(-3)) whereas more common iron shales are lower heat producing(1.7 μW m^(-3)). Pure quartzites and carbonates are the lowest heat producing sedimentary rocks. Globally, there is little definitive evidence for a decrease in heat production with increasing metamorphic grade. However, there remains the need for high resolution studies of heat production variations within individual protoliths that vary in metamorphic grade. These results improve estimates of heat production and natural variability of rocks that will allow for more accurate temperature models of the lithosphere.
文摘Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosocial work situation of staff working with people with cognitive restrictions and to identify predictors for their job satisfaction and workability. A cross sectional study was performed. Method: The Questionnaire Psycho Social Nordic (QPS-Nordic questionnaire) was used. Results: The results showed that the majority of the staff working with people with cognitive restrictions were satisfied with their job, but musculoskeletal symptoms were described by 40%. Decision demands at work were high compared to quantitative and learning demands. Musculoskeletal symptoms were related to low ability to master the work, low job control and high job demands. Symptoms from the neck region were correlated to stress. A low level of neck pain was related to a high level of job satisfaction. Predictors for workability were positive challenges in work and not being hindered by musculoskeletal symptoms in work. Predictors for job satisfaction were mastery, workability and not having pain during the last 7 days. Conclusion: Due to the relatively small sample the results should be interpreted with caution. The results indicated that positive challenges in work and not being hindered by musculoskeletal disorders predicted workability in this group and that mastery, workability and not having pain during the last 7 days predicted job satisfaction.
文摘Purpose: The inflammatory response in acute anterior uveitis (AU) is believed to be primarily mediated by autoreactive Tcells. We wanted to evaluate whether t he T-cell activation marker CD40 ligand is involved in the AU immunopathogenesi s. Methods: We evaluated the expression of the CD40 ligand on CD4+T-cells, CD8 +T-cells and CD19+B-cells on peripheral blood mononuclear cells using flow c ytometry in six patients with unilateralAU, six patientswith monosymptomatic opt ic neuritis (ON) as inflammatory controls, and in six healthy controls. The ex v ivo induction of the CD40 ligand on T-cells in patients and controls was also s tudied. Results: A significantly higher expression of the CD40 ligand on both CD 4+(p< 0.05)-and CD8+(p< 0.05) T-cells in patients with AU compared to ON pat ients and healthy controls was found. There was a significantly higher induction of the CD40 ligand on CD8+T-cells in AU patients compared to ON patients and healthy controls (p < 0.01). No differences in the B-cell population were obser ved between the three groups. Conclusion: Patients with AU had increased express ion of the CD40 ligand on T-cells in the blood and expressed higher levels of t he CD40 ligand when stimulated, compared to ophthalmological inflammatory contro ls and healthy controls. The data suggest that the CD40 ligand is involved in th e development of AU.
