AAA??Jun. 28, 2013?3:15 AM ET Obama yet to have African legacy like predecessors By NEDRA PICKLERBy NEDRA PICKLER, Associated Press??
U.S. President Barack Obama, left, makes a toast during an official dinner with Senegalese President Macky Sall at the Presidential Palace on Thursday, June 27, 2013, in Dakar, Senegal. Obama is visiting Senegal, South Africa, and Tanzania on a week long trip. (AP Photo/Evan Vucci)
U.S. President Barack Obama, left, makes a toast during an official dinner with Senegalese President Macky Sall at the Presidential Palace on Thursday, June 27, 2013, in Dakar, Senegal. Obama is visiting Senegal, South Africa, and Tanzania on a week long trip. (AP Photo/Evan Vucci)
U.S. President Barack Obama looks out to sea through the 'Door of No Return,' at the slave house on Goree Island, in Dakar, Senegal, Thursday, June 27, 2013. Obama is calling his visit to a Senegalese island from which Africans were said to have been shipped across the Atlantic Ocean into slavery, a 'very powerful moment.' President Obama was in Dakar Thursday as part of a weeklong trip to Africa, a three-country visit aimed at overcoming disappointment on the continent over the first black U.S. president's lack of personal engagement during his first term. (AP Photo/Rebecca Blackwell)
President Barack Obama meets with a group of drummers that were playing music on his departure after taking a tour of Goree Island, Thursday, June 27, 2013, in Goree Island, Senegal. Goree Island is the site of the former slave house and embarkation point built by the Dutch in 1776, from which slaves were brought to the Americas. (AP Photo/Evan Vucci)
President Barack Obama meets with a group of drummers that were playing music on his departure after taking a tour of Goree Island, Thursday, June 27, 2013, in Goree Island, Senegal. Goree Island is the site of the former slave house and embarkation point built by the Dutch in 1776, from which slaves were brought to the Americas. (AP Photo/Evan Vucci)
DAKAR, Senegal (AP) ? President Barack Obama is receiving an enthusiastic welcome in Africa, even as he has yet to leave a lasting policy legacy on the scale of his two immediate predecessors.
Presidents Bill Clinton and George W. Bush passed innovative Africa initiatives while in the White House and passionately continue their development work in the region in their presidential afterlife.
Obama's efforts in Africa have not been so ambitious, despite his personal ties to the continent.
His first major tour of Africa as president is coming just now in his fifth year, while Bush and Clinton are frequent fliers to Africa. Bush even will be in Dar es Salaam, Tanzania, next week at the same time as Obama, although they have no plans to meet.
'Shields to Maximum, Mr. Scott'Public release date: 27-Jun-2013 [ | E-mail | Share ]
Contact: Faith Singer-Villalobos faith@tacc.utexas.edu 512-232-5771 University of Texas at Austin, Texas Advanced Computing Center
Researchers use TACC supercomputers to simulate orbital debris impacts on spacecraft and fragment impacts on body armor
We know it's out there, debris from 50 years of space exploration aluminum, steel, nylon, even liquid sodium from Russian satellites orbiting around the Earth and posing a danger to manned and unmanned spacecraft.
According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball (larger than 10 centimeters) in orbit, and about 500,000 pieces that are golf ball-sized (between one to 10 centimeters).
Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per secondroughly ten times faster than a speeding bullet!
"If a spacecraft is hit by orbital debris it may damage the thermal protection system," said Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, who studies impact dynamics both experimentally and through numerical simulations.
"Even if the impact is not on the main heat shield, it may still adversely affect the spacecraft. The thermal researchers take the results of impact research and assess the effect of a certain impact crater depth and volume on the survivability of a spacecraft during reentry," Fahrenthold said.
Only some of the collisions that may occur in low earth orbit can be reproduced in the laboratory. To determine the potential impact of fast-moving orbital debris on spacecraft and to assist NASA in the design of shielding that can withstand hypervelocity impacts Fahrenthold and his team developed a numerical algorithm that simulates the shock physics of orbital debris particles striking the layers of Kevlar, metal, and fiberglass that makes up a space vehicle's outer defenses.
Supercomputers enable researchers to investigate physical phenomenon that cannot be duplicated in the laboratory, either because they are too large, small, dangerous or in this case, too fast to reproduce with current testing technology.
Running hundreds of simulations on the Ranger, Lonestar and Stampede supercomputers at the Texas Advanced Computing Center, Fahrenthold and his students have assisted NASA in the development of ballistic limit curves that predict whether a shield will be perforated when hit by a projectile of a given size and speed. NASA uses ballistic limit curves in the design and risk analysis of current and future spacecraft.
Results from some of his group's impact dynamics research were presented at the April 2013 American Institute for Aeronautics and Astronautics' (AIAA) meeting, and have recently been published in the journals Smart Materials and Structures and International Journal for Numerical Methods in Engineering. In the paper presented at the AIAA conference, they showed in detail how different characteristics of a hypervelocity collision, such as the speed, impact angle, and size of the debris, could affect the depth of the cavity produced in ceramic tile thermal protection systems.
The development of these models is not just a shot in the dark. Fahrenthold's simulations have been tested exhaustively against real-world experiments conducted by NASA, which uses light gas guns to launch 'centimeter' size projectiles at speeds up to 10 kilometers per second. The simulations are evaluated in this speed regime to insure that they accurately capture the dynamics of hypervelocity impacts.
Validated simulation methods can then be used to estimate impact damage at velocities outside the experimental range, and also to investigate detailed physics that may be difficult to capture using flash x-ray images of experiments.
The simulation framework that Fahrenthold and his team developed employs a hybrid modeling approach that captures both the fragmentation of the projectiles their tendency to break into small shards that need to be caught and the shock response of the target, which is subjected to severe thermal and mechanical loads.
"We validate our method in the velocity regime where experiments can be performed, then we run simulations at higher velocities, to estimate what we think will happen at higher velocities," Fahrenthold explained. "There are certain things you can do in simulation and certain things you can do in experiment. When they work together, that's a big advantage for the design engineer."
Back on land, Fahrenthold and graduate student Moss Shimek extended this hybrid method in order to study the impact of projectiles on body armor materials in research supported by the Office of Naval Research. The numerical technique originally developed to study impacts on spacecraft worked well for a completely different application at lower velocities, in part because some of the same materials used on spacecraft for orbital debris protection, such as Kevlar, are also used in body armor.
According to Fahrenthold, this method offers a fundamentally new way of simulating fabric impacts, which have been modeled with conventional finite element methods for more than 20 years. The model parameters used in the simulation, such as the material's strength, flexibility, and thermal properties, are provided by experimentalists. The supercomputer simulations then replicate the physics of projectile impact and yarn fracture, and capture the complex interaction of the multiple layers of a fabric protection system some fragments getting caught in the mesh of yarns, others breaking through the layers and perforating the barrier.
"Using a hybrid technique for fabric modeling works well," Fahrenthold said. "When the fabric barrier is hit at very high velocities, as in spacecraft shielding, it's a shock-type impact and the thermal properties are important as well as the mechanical ones."
Moss Shimek's dissertation research added a new wrinkle to the fabric model by representing the various weaves used in the manufacture of Kevlar and ultra-high molecular weight polyethylene (another leading protective material) barriers, including harness-satin, basket, and twill weaves. Each weave type has advantages and disadvantages when used in body armor designed to protect military and police personnel. Layering the different weaves, many believe, can provide improved protection.
Fahrenthold and Shimek (currently a post-doctoral research associate at Los Alamos National Laboratory) explored the performance of various weave types using both experiments and simulations. In the November 2012 issue of the AIAA Journal, Shimek and Fahrenthold showed that in some cases the weave type of the fabric material can greatly influence fabric barrier performance.
"Currently body armor normally uses the plain weave, but research has shown that different weaves that are more flexible might be better, for example in extremity protection," Shimek said.
Shimek and Fahrenthold used the same numerical method employed for the NASA simulations to model a series of experiments on layered Kevlar materials, showing that their simulation results were within 15 percent of the experimental outcomes.
"Future body armor designs may vary the weave type through a Kevlar stack," Shimek said. "Maybe one weave type is better at dealing with small fragments, while others perform better for larger fragments. Our results suggest that you can use simulation to assist the designer in developing a fragment barrier which can capitalize on those differences."
What can researchers learn about the layer-to-layer impact response of a fabric barrier through simulation? Can body armor be improved by varying the weave type of the many layers in a typical fabric barrier? Can simulation assist the design engineer in developing orbital debris shields that better protect spacecraft? The range of engineering design questions is endless, and computer simulations can play an important role in the 'faster, better, cheaper' development of improved impact protection systems.
"We are trying to make fundamental improvements in numerical algorithms, and validate those algorithms against experiment," Fahrenthold concluded. "This can provide improved tools for engineering design, and allow simulation-based research to contribute in areas where experiments are very difficult to do or very expensive."
###
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AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
'Shields to Maximum, Mr. Scott'Public release date: 27-Jun-2013 [ | E-mail | Share ]
Contact: Faith Singer-Villalobos faith@tacc.utexas.edu 512-232-5771 University of Texas at Austin, Texas Advanced Computing Center
Researchers use TACC supercomputers to simulate orbital debris impacts on spacecraft and fragment impacts on body armor
We know it's out there, debris from 50 years of space exploration aluminum, steel, nylon, even liquid sodium from Russian satellites orbiting around the Earth and posing a danger to manned and unmanned spacecraft.
According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball (larger than 10 centimeters) in orbit, and about 500,000 pieces that are golf ball-sized (between one to 10 centimeters).
Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per secondroughly ten times faster than a speeding bullet!
"If a spacecraft is hit by orbital debris it may damage the thermal protection system," said Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, who studies impact dynamics both experimentally and through numerical simulations.
"Even if the impact is not on the main heat shield, it may still adversely affect the spacecraft. The thermal researchers take the results of impact research and assess the effect of a certain impact crater depth and volume on the survivability of a spacecraft during reentry," Fahrenthold said.
Only some of the collisions that may occur in low earth orbit can be reproduced in the laboratory. To determine the potential impact of fast-moving orbital debris on spacecraft and to assist NASA in the design of shielding that can withstand hypervelocity impacts Fahrenthold and his team developed a numerical algorithm that simulates the shock physics of orbital debris particles striking the layers of Kevlar, metal, and fiberglass that makes up a space vehicle's outer defenses.
Supercomputers enable researchers to investigate physical phenomenon that cannot be duplicated in the laboratory, either because they are too large, small, dangerous or in this case, too fast to reproduce with current testing technology.
Running hundreds of simulations on the Ranger, Lonestar and Stampede supercomputers at the Texas Advanced Computing Center, Fahrenthold and his students have assisted NASA in the development of ballistic limit curves that predict whether a shield will be perforated when hit by a projectile of a given size and speed. NASA uses ballistic limit curves in the design and risk analysis of current and future spacecraft.
Results from some of his group's impact dynamics research were presented at the April 2013 American Institute for Aeronautics and Astronautics' (AIAA) meeting, and have recently been published in the journals Smart Materials and Structures and International Journal for Numerical Methods in Engineering. In the paper presented at the AIAA conference, they showed in detail how different characteristics of a hypervelocity collision, such as the speed, impact angle, and size of the debris, could affect the depth of the cavity produced in ceramic tile thermal protection systems.
The development of these models is not just a shot in the dark. Fahrenthold's simulations have been tested exhaustively against real-world experiments conducted by NASA, which uses light gas guns to launch 'centimeter' size projectiles at speeds up to 10 kilometers per second. The simulations are evaluated in this speed regime to insure that they accurately capture the dynamics of hypervelocity impacts.
Validated simulation methods can then be used to estimate impact damage at velocities outside the experimental range, and also to investigate detailed physics that may be difficult to capture using flash x-ray images of experiments.
The simulation framework that Fahrenthold and his team developed employs a hybrid modeling approach that captures both the fragmentation of the projectiles their tendency to break into small shards that need to be caught and the shock response of the target, which is subjected to severe thermal and mechanical loads.
"We validate our method in the velocity regime where experiments can be performed, then we run simulations at higher velocities, to estimate what we think will happen at higher velocities," Fahrenthold explained. "There are certain things you can do in simulation and certain things you can do in experiment. When they work together, that's a big advantage for the design engineer."
Back on land, Fahrenthold and graduate student Moss Shimek extended this hybrid method in order to study the impact of projectiles on body armor materials in research supported by the Office of Naval Research. The numerical technique originally developed to study impacts on spacecraft worked well for a completely different application at lower velocities, in part because some of the same materials used on spacecraft for orbital debris protection, such as Kevlar, are also used in body armor.
According to Fahrenthold, this method offers a fundamentally new way of simulating fabric impacts, which have been modeled with conventional finite element methods for more than 20 years. The model parameters used in the simulation, such as the material's strength, flexibility, and thermal properties, are provided by experimentalists. The supercomputer simulations then replicate the physics of projectile impact and yarn fracture, and capture the complex interaction of the multiple layers of a fabric protection system some fragments getting caught in the mesh of yarns, others breaking through the layers and perforating the barrier.
"Using a hybrid technique for fabric modeling works well," Fahrenthold said. "When the fabric barrier is hit at very high velocities, as in spacecraft shielding, it's a shock-type impact and the thermal properties are important as well as the mechanical ones."
Moss Shimek's dissertation research added a new wrinkle to the fabric model by representing the various weaves used in the manufacture of Kevlar and ultra-high molecular weight polyethylene (another leading protective material) barriers, including harness-satin, basket, and twill weaves. Each weave type has advantages and disadvantages when used in body armor designed to protect military and police personnel. Layering the different weaves, many believe, can provide improved protection.
Fahrenthold and Shimek (currently a post-doctoral research associate at Los Alamos National Laboratory) explored the performance of various weave types using both experiments and simulations. In the November 2012 issue of the AIAA Journal, Shimek and Fahrenthold showed that in some cases the weave type of the fabric material can greatly influence fabric barrier performance.
"Currently body armor normally uses the plain weave, but research has shown that different weaves that are more flexible might be better, for example in extremity protection," Shimek said.
Shimek and Fahrenthold used the same numerical method employed for the NASA simulations to model a series of experiments on layered Kevlar materials, showing that their simulation results were within 15 percent of the experimental outcomes.
"Future body armor designs may vary the weave type through a Kevlar stack," Shimek said. "Maybe one weave type is better at dealing with small fragments, while others perform better for larger fragments. Our results suggest that you can use simulation to assist the designer in developing a fragment barrier which can capitalize on those differences."
What can researchers learn about the layer-to-layer impact response of a fabric barrier through simulation? Can body armor be improved by varying the weave type of the many layers in a typical fabric barrier? Can simulation assist the design engineer in developing orbital debris shields that better protect spacecraft? The range of engineering design questions is endless, and computer simulations can play an important role in the 'faster, better, cheaper' development of improved impact protection systems.
"We are trying to make fundamental improvements in numerical algorithms, and validate those algorithms against experiment," Fahrenthold concluded. "This can provide improved tools for engineering design, and allow simulation-based research to contribute in areas where experiments are very difficult to do or very expensive."
###
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?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
'Shields to Maximum, Mr. Scott'Public release date: 27-Jun-2013 [ | E-mail | Share ]
Contact: Faith Singer-Villalobos faith@tacc.utexas.edu 512-232-5771 University of Texas at Austin, Texas Advanced Computing Center
Researchers use TACC supercomputers to simulate orbital debris impacts on spacecraft and fragment impacts on body armor
We know it's out there, debris from 50 years of space exploration aluminum, steel, nylon, even liquid sodium from Russian satellites orbiting around the Earth and posing a danger to manned and unmanned spacecraft.
According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball (larger than 10 centimeters) in orbit, and about 500,000 pieces that are golf ball-sized (between one to 10 centimeters).
Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per secondroughly ten times faster than a speeding bullet!
"If a spacecraft is hit by orbital debris it may damage the thermal protection system," said Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, who studies impact dynamics both experimentally and through numerical simulations.
"Even if the impact is not on the main heat shield, it may still adversely affect the spacecraft. The thermal researchers take the results of impact research and assess the effect of a certain impact crater depth and volume on the survivability of a spacecraft during reentry," Fahrenthold said.
Only some of the collisions that may occur in low earth orbit can be reproduced in the laboratory. To determine the potential impact of fast-moving orbital debris on spacecraft and to assist NASA in the design of shielding that can withstand hypervelocity impacts Fahrenthold and his team developed a numerical algorithm that simulates the shock physics of orbital debris particles striking the layers of Kevlar, metal, and fiberglass that makes up a space vehicle's outer defenses.
Supercomputers enable researchers to investigate physical phenomenon that cannot be duplicated in the laboratory, either because they are too large, small, dangerous or in this case, too fast to reproduce with current testing technology.
Running hundreds of simulations on the Ranger, Lonestar and Stampede supercomputers at the Texas Advanced Computing Center, Fahrenthold and his students have assisted NASA in the development of ballistic limit curves that predict whether a shield will be perforated when hit by a projectile of a given size and speed. NASA uses ballistic limit curves in the design and risk analysis of current and future spacecraft.
Results from some of his group's impact dynamics research were presented at the April 2013 American Institute for Aeronautics and Astronautics' (AIAA) meeting, and have recently been published in the journals Smart Materials and Structures and International Journal for Numerical Methods in Engineering. In the paper presented at the AIAA conference, they showed in detail how different characteristics of a hypervelocity collision, such as the speed, impact angle, and size of the debris, could affect the depth of the cavity produced in ceramic tile thermal protection systems.
The development of these models is not just a shot in the dark. Fahrenthold's simulations have been tested exhaustively against real-world experiments conducted by NASA, which uses light gas guns to launch 'centimeter' size projectiles at speeds up to 10 kilometers per second. The simulations are evaluated in this speed regime to insure that they accurately capture the dynamics of hypervelocity impacts.
Validated simulation methods can then be used to estimate impact damage at velocities outside the experimental range, and also to investigate detailed physics that may be difficult to capture using flash x-ray images of experiments.
The simulation framework that Fahrenthold and his team developed employs a hybrid modeling approach that captures both the fragmentation of the projectiles their tendency to break into small shards that need to be caught and the shock response of the target, which is subjected to severe thermal and mechanical loads.
"We validate our method in the velocity regime where experiments can be performed, then we run simulations at higher velocities, to estimate what we think will happen at higher velocities," Fahrenthold explained. "There are certain things you can do in simulation and certain things you can do in experiment. When they work together, that's a big advantage for the design engineer."
Back on land, Fahrenthold and graduate student Moss Shimek extended this hybrid method in order to study the impact of projectiles on body armor materials in research supported by the Office of Naval Research. The numerical technique originally developed to study impacts on spacecraft worked well for a completely different application at lower velocities, in part because some of the same materials used on spacecraft for orbital debris protection, such as Kevlar, are also used in body armor.
According to Fahrenthold, this method offers a fundamentally new way of simulating fabric impacts, which have been modeled with conventional finite element methods for more than 20 years. The model parameters used in the simulation, such as the material's strength, flexibility, and thermal properties, are provided by experimentalists. The supercomputer simulations then replicate the physics of projectile impact and yarn fracture, and capture the complex interaction of the multiple layers of a fabric protection system some fragments getting caught in the mesh of yarns, others breaking through the layers and perforating the barrier.
"Using a hybrid technique for fabric modeling works well," Fahrenthold said. "When the fabric barrier is hit at very high velocities, as in spacecraft shielding, it's a shock-type impact and the thermal properties are important as well as the mechanical ones."
Moss Shimek's dissertation research added a new wrinkle to the fabric model by representing the various weaves used in the manufacture of Kevlar and ultra-high molecular weight polyethylene (another leading protective material) barriers, including harness-satin, basket, and twill weaves. Each weave type has advantages and disadvantages when used in body armor designed to protect military and police personnel. Layering the different weaves, many believe, can provide improved protection.
Fahrenthold and Shimek (currently a post-doctoral research associate at Los Alamos National Laboratory) explored the performance of various weave types using both experiments and simulations. In the November 2012 issue of the AIAA Journal, Shimek and Fahrenthold showed that in some cases the weave type of the fabric material can greatly influence fabric barrier performance.
"Currently body armor normally uses the plain weave, but research has shown that different weaves that are more flexible might be better, for example in extremity protection," Shimek said.
Shimek and Fahrenthold used the same numerical method employed for the NASA simulations to model a series of experiments on layered Kevlar materials, showing that their simulation results were within 15 percent of the experimental outcomes.
"Future body armor designs may vary the weave type through a Kevlar stack," Shimek said. "Maybe one weave type is better at dealing with small fragments, while others perform better for larger fragments. Our results suggest that you can use simulation to assist the designer in developing a fragment barrier which can capitalize on those differences."
What can researchers learn about the layer-to-layer impact response of a fabric barrier through simulation? Can body armor be improved by varying the weave type of the many layers in a typical fabric barrier? Can simulation assist the design engineer in developing orbital debris shields that better protect spacecraft? The range of engineering design questions is endless, and computer simulations can play an important role in the 'faster, better, cheaper' development of improved impact protection systems.
"We are trying to make fundamental improvements in numerical algorithms, and validate those algorithms against experiment," Fahrenthold concluded. "This can provide improved tools for engineering design, and allow simulation-based research to contribute in areas where experiments are very difficult to do or very expensive."
###
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AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
'Shields to Maximum, Mr. Scott'Public release date: 27-Jun-2013 [ | E-mail | Share ]
Contact: Faith Singer-Villalobos faith@tacc.utexas.edu 512-232-5771 University of Texas at Austin, Texas Advanced Computing Center
Researchers use TACC supercomputers to simulate orbital debris impacts on spacecraft and fragment impacts on body armor
We know it's out there, debris from 50 years of space exploration aluminum, steel, nylon, even liquid sodium from Russian satellites orbiting around the Earth and posing a danger to manned and unmanned spacecraft.
According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball (larger than 10 centimeters) in orbit, and about 500,000 pieces that are golf ball-sized (between one to 10 centimeters).
Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per secondroughly ten times faster than a speeding bullet!
"If a spacecraft is hit by orbital debris it may damage the thermal protection system," said Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, who studies impact dynamics both experimentally and through numerical simulations.
"Even if the impact is not on the main heat shield, it may still adversely affect the spacecraft. The thermal researchers take the results of impact research and assess the effect of a certain impact crater depth and volume on the survivability of a spacecraft during reentry," Fahrenthold said.
Only some of the collisions that may occur in low earth orbit can be reproduced in the laboratory. To determine the potential impact of fast-moving orbital debris on spacecraft and to assist NASA in the design of shielding that can withstand hypervelocity impacts Fahrenthold and his team developed a numerical algorithm that simulates the shock physics of orbital debris particles striking the layers of Kevlar, metal, and fiberglass that makes up a space vehicle's outer defenses.
Supercomputers enable researchers to investigate physical phenomenon that cannot be duplicated in the laboratory, either because they are too large, small, dangerous or in this case, too fast to reproduce with current testing technology.
Running hundreds of simulations on the Ranger, Lonestar and Stampede supercomputers at the Texas Advanced Computing Center, Fahrenthold and his students have assisted NASA in the development of ballistic limit curves that predict whether a shield will be perforated when hit by a projectile of a given size and speed. NASA uses ballistic limit curves in the design and risk analysis of current and future spacecraft.
Results from some of his group's impact dynamics research were presented at the April 2013 American Institute for Aeronautics and Astronautics' (AIAA) meeting, and have recently been published in the journals Smart Materials and Structures and International Journal for Numerical Methods in Engineering. In the paper presented at the AIAA conference, they showed in detail how different characteristics of a hypervelocity collision, such as the speed, impact angle, and size of the debris, could affect the depth of the cavity produced in ceramic tile thermal protection systems.
The development of these models is not just a shot in the dark. Fahrenthold's simulations have been tested exhaustively against real-world experiments conducted by NASA, which uses light gas guns to launch 'centimeter' size projectiles at speeds up to 10 kilometers per second. The simulations are evaluated in this speed regime to insure that they accurately capture the dynamics of hypervelocity impacts.
Validated simulation methods can then be used to estimate impact damage at velocities outside the experimental range, and also to investigate detailed physics that may be difficult to capture using flash x-ray images of experiments.
The simulation framework that Fahrenthold and his team developed employs a hybrid modeling approach that captures both the fragmentation of the projectiles their tendency to break into small shards that need to be caught and the shock response of the target, which is subjected to severe thermal and mechanical loads.
"We validate our method in the velocity regime where experiments can be performed, then we run simulations at higher velocities, to estimate what we think will happen at higher velocities," Fahrenthold explained. "There are certain things you can do in simulation and certain things you can do in experiment. When they work together, that's a big advantage for the design engineer."
Back on land, Fahrenthold and graduate student Moss Shimek extended this hybrid method in order to study the impact of projectiles on body armor materials in research supported by the Office of Naval Research. The numerical technique originally developed to study impacts on spacecraft worked well for a completely different application at lower velocities, in part because some of the same materials used on spacecraft for orbital debris protection, such as Kevlar, are also used in body armor.
According to Fahrenthold, this method offers a fundamentally new way of simulating fabric impacts, which have been modeled with conventional finite element methods for more than 20 years. The model parameters used in the simulation, such as the material's strength, flexibility, and thermal properties, are provided by experimentalists. The supercomputer simulations then replicate the physics of projectile impact and yarn fracture, and capture the complex interaction of the multiple layers of a fabric protection system some fragments getting caught in the mesh of yarns, others breaking through the layers and perforating the barrier.
"Using a hybrid technique for fabric modeling works well," Fahrenthold said. "When the fabric barrier is hit at very high velocities, as in spacecraft shielding, it's a shock-type impact and the thermal properties are important as well as the mechanical ones."
Moss Shimek's dissertation research added a new wrinkle to the fabric model by representing the various weaves used in the manufacture of Kevlar and ultra-high molecular weight polyethylene (another leading protective material) barriers, including harness-satin, basket, and twill weaves. Each weave type has advantages and disadvantages when used in body armor designed to protect military and police personnel. Layering the different weaves, many believe, can provide improved protection.
Fahrenthold and Shimek (currently a post-doctoral research associate at Los Alamos National Laboratory) explored the performance of various weave types using both experiments and simulations. In the November 2012 issue of the AIAA Journal, Shimek and Fahrenthold showed that in some cases the weave type of the fabric material can greatly influence fabric barrier performance.
"Currently body armor normally uses the plain weave, but research has shown that different weaves that are more flexible might be better, for example in extremity protection," Shimek said.
Shimek and Fahrenthold used the same numerical method employed for the NASA simulations to model a series of experiments on layered Kevlar materials, showing that their simulation results were within 15 percent of the experimental outcomes.
"Future body armor designs may vary the weave type through a Kevlar stack," Shimek said. "Maybe one weave type is better at dealing with small fragments, while others perform better for larger fragments. Our results suggest that you can use simulation to assist the designer in developing a fragment barrier which can capitalize on those differences."
What can researchers learn about the layer-to-layer impact response of a fabric barrier through simulation? Can body armor be improved by varying the weave type of the many layers in a typical fabric barrier? Can simulation assist the design engineer in developing orbital debris shields that better protect spacecraft? The range of engineering design questions is endless, and computer simulations can play an important role in the 'faster, better, cheaper' development of improved impact protection systems.
"We are trying to make fundamental improvements in numerical algorithms, and validate those algorithms against experiment," Fahrenthold concluded. "This can provide improved tools for engineering design, and allow simulation-based research to contribute in areas where experiments are very difficult to do or very expensive."
###
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AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
MONTREAL - Why are there going to be Downton Abbey-branded wines? Because the world is full of suckers.
A big Bordeaux producer, Dulong Grands Vins, will make the stuff for Wines That Rock, a U.S. marketer. ?These are wines the Crawley family would have been proud to serve at Downton,? WTR co-owner Bill Zysblat told thedrinksbusiness.com, keeping a straight face all the while.
By coincidence, Paul Giamatti is about to join the Downton cast. You?ll recall that Giamatti made his name in the 2004 wine-centric movie Sideways.
Downton Abbey red and white wines are to be sold in the U.S. and Canada, although I won?t hold my breath until the SAQ lists it.
- - -
In Dallas, a white suit once owned by Col. Harland Sanders, founder of Kentucky Fried Chicken, has fetched $21,500 at an auction. The buyer was KFC Japan?s president, Masao (Charlie) Watanabe.
The suit came with a certificate of provenance: Sanders gave it to a friend, about 35 years ago, to wear as a Halloween costume.
Sanders ? who was once in the U.S. army but was never an officer ? died in 1980, at age 90.
- - -
Quote of the day: Julia Louis-Dreyfus, 52, tells Health mag about appearance and aging:
?Getting older, it?s like, ?Yeah, this is who I am, (bad word) off,? as opposed to, ?This is who I am, I?m sorry.?
?You know, there?s something about getting older and owning who you are that is a good thing.?
- - -
Model/entrepreneur/TV host Heidi Klum broke up with singer Seal in January 2012. Now she?s undergoing removal of the tattoo she got to feel closer to him.
It?s an abstract design ? she said something about initials, but it looks random to me ? on the inside of her right arm, below the elbow.
People mag noted that recent photos show the marking has faded away; they asked, and sure enough, she?s having it erased.
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How the movie business works: In 2008, Liam Neeson made a movie called Taken ? ex-CIA man?s daughter gets kidnapped and sold into sex slavery, and he gets her back the hard way.
Personally, I?d rather watch paint dry, but the picture cost $25 million and grossed 11 times that amount. Neeson, who has some pride, didn?t want to do a sequel, but 20th Century Fox and something called EuropaCorp offered him 15 million good reasons; he did it, and that picture, on a $45 million budget, grossed $376 million, well more than the first one.
Who among us will be surprised to learn that Neeson wants more money to do it again? He got it, too: Deadline.com reports that he will accept $20 million for No. 3. Famke Janssen and Maggie Grace still need to be re-signed, but that will happen, Deadline suggests.
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So, Armie Hammer, what was it like working with Johnny Depp on this Lone Ranger movie? That?s what Hollywoodlife.com asked the actor. His answer: ?Terrible! Hated it, hate him and never want to see him again in my life!?
Then, perhaps fearing Depp is irony-impaired, Hammer added this: ?No, it was great!?
You might say the day is never really done in consumer technology news. Your workday, however, hopefully draws to a close at some point. This is the Daily Roundup on Engadget, a quick peek back at the top headlines for the past 24 hours -- all handpicked by the editors here at the site. Click on through the break, and enjoy.
June 26, 2013 ? Further evidence of climate change shifting atmospheric circulation in the southern Australian-New Zealand region has been identified in a new study.
The study, in the Nature journal Scientific Reports, demonstrates that mid-latitude high pressure zones (30oS-45oS) are being pushed further into the Southern Ocean by rising global temperatures associated with greenhouse warming. This is despite more frequent occurrences of strong El Ni?os in recent decades, which should have drawn the high pressure zones in the opposite direction toward the equator.
"What we are seeing," says study lead author, Mr Guojian Wang "is a 'tug of war' between stronger El Ni?os driving the winds north and the greenhouse gas-warming effect driving the winds south."
Mr Wang, said the result confirms the robustness of the Southern Hemisphere circulation changes over the past three to four decades as the global temperature rose, "so much so that it overode the influence from strong El Ni?os during this period."
Study co-author, Dr Wenju Cai said the most conspicuous change is a rising sea level pressure in the mid-latitude bands and a decreasing sea level pressure over the Southern high latitudes (55o-70oS), a pattern referred to as the Southern Annular Mode. The changing pressures indicate a poleward or southward expansion of the tropical and subtropical atmospheric zones.
In turn, this indicates that over the long-term, there is a relationship between a rising global mean temperature and an upward trend of the Southern Annular Mode.
"The research reinforces our past work that climate change is altering Southern Hemisphere circulation and increases our confidence in this conclusion," Dr Cai said.
Dr Cai has previously reported on changes in atmospheric circulation that have been shifting and strengthening the Pacific Ocean winds poleward and in turn strengthening the ocean circulation, pushing the East Australian Current further south down the Australian coast.
He said during El Ni?o, the warmer ocean releases heat to the atmosphere and global average temperatures increase. At the same time, warm ocean surface temperatures along the equator cause the tropical and subtropical atmospheric belts to move toward the equator, generating a 'negative' phase of the Southern Annular Mode.
"On year-to-year time scales, higher global temperatures are associated with a negative phase of the Mode but over the past 35 years, when El Ni?o has been strong and conducive to a negative trend, we are seeing an opposite trend with the circulation systems moving southward impacting on regional climate," he said.
The project was funded through the Australian Climate Change Science Program.
It's probably not a huge stretch to say that Samsung's Galaxy S 4 running stock Android was the biggest surprise to come out of Google I/O last month. The handset -- officially called Samsung Galaxy S 4 Google Play edition -- is now on sale in the Play store for $649 alongside a special version of the HTC One. Spec-wise, the phone is identical to AT&T's 16GB model and supports the same bands (including LTE). It's powered by Qualcomm's 1.9GHz quad-core Snapdragon 600 processor with 2GB or RAM and features a 5-inch 1080p Super AMOLED display, 13-megapixel camera with flash, removable 2600mAh Li-ion battery and microSD expansion. While we briefly handled the phone at I/O, it wasn't until yesterday that we got to spend some quality time with it. Hit the break for our first impressions and hands-on video.
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Public release date: 27-Jun-2013
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