Effect of Particle Shape on Mechanical Behaviors of Rocks: A Numerical Study Using Clumped Particle Model

PubMed Central

Rong, Guan; Liu, Guang; Zhou, Chuang-bing

2013-01-01

Since rocks are aggregates of mineral particles, the effect of mineral microstructure on macroscopic mechanical behaviors of rocks is inneglectable. Rock samples of four different particle shapes are established in this study based on clumped particle model, and a sphericity index is used to quantify particle shape. Model parameters for simulation in PFC are obtained by triaxial compression test of quartz sandstone, and simulation of triaxial compression test is then conducted on four rock samples with different particle shapes. It is seen from the results that stress thresholds of rock samples such as crack initiation stress, crack damage stress, and peak stress decrease with the increasing of the sphericity index. The increase of sphericity leads to a drop of elastic modulus and a rise in Poisson ratio, while the decreasing sphericity usually results in the increase of cohesion and internal friction angle. Based on volume change of rock samples during simulation of triaxial compression test, variation of dilation angle with plastic strain is also studied. PMID:23997677

Effect of particle shape on mechanical behaviors of rocks: a numerical study using clumped particle model.

PubMed

Rong, Guan; Liu, Guang; Hou, Di; Zhou, Chuang-Bing

2013-01-01

Since rocks are aggregates of mineral particles, the effect of mineral microstructure on macroscopic mechanical behaviors of rocks is inneglectable. Rock samples of four different particle shapes are established in this study based on clumped particle model, and a sphericity index is used to quantify particle shape. Model parameters for simulation in PFC are obtained by triaxial compression test of quartz sandstone, and simulation of triaxial compression test is then conducted on four rock samples with different particle shapes. It is seen from the results that stress thresholds of rock samples such as crack initiation stress, crack damage stress, and peak stress decrease with the increasing of the sphericity index. The increase of sphericity leads to a drop of elastic modulus and a rise in Poisson ratio, while the decreasing sphericity usually results in the increase of cohesion and internal friction angle. Based on volume change of rock samples during simulation of triaxial compression test, variation of dilation angle with plastic strain is also studied.

Multi-rate, real time image compression for images dominated by point sources

NASA Technical Reports Server (NTRS)

Huber, A. Kris; Budge, Scott E.; Harris, Richard W.

1993-01-01

An image compression system recently developed for compression of digital images dominated by point sources is presented. Encoding consists of minimum-mean removal, vector quantization, adaptive threshold truncation, and modified Huffman encoding. Simulations are presented showing that the peaks corresponding to point sources can be transmitted losslessly for low signal-to-noise ratios (SNR) and high point source densities while maintaining a reduced output bit rate. Encoding and decoding hardware has been built and tested which processes 552,960 12-bit pixels per second at compression rates of 10:1 and 4:1. Simulation results are presented for the 10:1 case only.

Mental simulation of routes during navigation involves adaptive temporal compression

PubMed Central

Arnold, Aiden E.G.F.; Iaria, Giuseppe; Ekstrom, Arne D.

2016-01-01

Mental simulation is a hallmark feature of human cognition, allowing features from memories to be flexibly used during prospection. While past studies demonstrate the preservation of real-world features such as size and distance during mental simulation, their temporal dynamics remains unknown. Here, we compare mental simulations to navigation of routes in a large-scale spatial environment to test the hypothesis that such simulations are temporally compressed in an adaptive manner. Our results show that simulations occurred at 2.39x the speed it took to navigate a route, increasing in compression (3.57x) for slower movement speeds. Participant self-reports of vividness and spatial coherence of simulations also correlated strongly with simulation duration, providing an important link between subjective experiences of simulated events and how spatial representations are combined during prospection. These findings suggest that simulation of spatial events involve adaptive temporal mechanisms, mediated partly by the fidelity of memories used to generate the simulation. PMID:27568586

Effect of simulated sampling disturbance on creep behaviour of rock salt

NASA Astrophysics Data System (ADS)

Guessous, Z.; Gill, D. E.; Ladanyi, B.

1987-10-01

This article presents the results of an experimental study of creep behaviour of a rock salt under uniaxial compression as a function of prestrain, simulating sampling disturbance. The prestrain was produced by radial compressive loading of the specimens prior to creep testing. The tests were conducted on an artifical salt to avoid excessive scattering of the results. The results obtained from several series of single-stage creep tests show that, at short-term, the creep response of salt is strongly affected by the preloading history of samples. The nature of this effect depends upon the intensity of radial compressive preloading, and its magnitude is a function of the creep stress level. The effect, however, decreases with increasing plastic deformation, indicating that large creep strains may eventually lead to a complete loss of preloading memory.

Computational Simulation of Breast Compression Based on Segmented Breast and Fibroglandular Tissues on Magnetic Resonance Images

PubMed Central

Shih, Tzu-Ching; Chen, Jeon-Hor; Liu, Dongxu; Nie, Ke; Sun, Lizhi; Lin, Muqing; Chang, Daniel; Nalcioglu, Orhan; Su, Min-Ying

2010-01-01

This study presents a finite element based computational model to simulate the three-dimensional deformation of the breast and the fibroglandular tissues under compression. The simulation was based on 3D MR images of the breast, and the craniocaudal and mediolateral oblique compression as used in mammography was applied. The geometry of whole breast and the segmented fibroglandular tissues within the breast were reconstructed using triangular meshes by using the Avizo® 6.0 software package. Due to the large deformation in breast compression, a finite element model was used to simulate the non-linear elastic tissue deformation under compression, using the MSC.Marc® software package. The model was tested in 4 cases. The results showed a higher displacement along the compression direction compared to the other two directions. The compressed breast thickness in these 4 cases at 60% compression ratio was in the range of 5-7 cm, which is the typical range of thickness in mammography. The projection of the fibroglandular tissue mesh at 60% compression ratio was compared to the corresponding mammograms of two women, and they demonstrated spatially matched distributions. However, since the compression was based on MRI, which has much coarser spatial resolution than the in-plane resolution of mammography, this method is unlikely to generate a synthetic mammogram close to the clinical quality. Whether this model may be used to understand the technical factors that may impact the variations in breast density measurements needs further investigation. Since this method can be applied to simulate compression of the breast at different views and different compression levels, another possible application is to provide a tool for comparing breast images acquired using different imaging modalities – such as MRI, mammography, whole breast ultrasound, and molecular imaging – that are performed using different body positions and different compression conditions. PMID:20601773

Computational simulation of breast compression based on segmented breast and fibroglandular tissues on magnetic resonance images.

PubMed

Shih, Tzu-Ching; Chen, Jeon-Hor; Liu, Dongxu; Nie, Ke; Sun, Lizhi; Lin, Muqing; Chang, Daniel; Nalcioglu, Orhan; Su, Min-Ying

2010-07-21

This study presents a finite element-based computational model to simulate the three-dimensional deformation of a breast and fibroglandular tissues under compression. The simulation was based on 3D MR images of the breast, and craniocaudal and mediolateral oblique compression, as used in mammography, was applied. The geometry of the whole breast and the segmented fibroglandular tissues within the breast were reconstructed using triangular meshes by using the Avizo 6.0 software package. Due to the large deformation in breast compression, a finite element model was used to simulate the nonlinear elastic tissue deformation under compression, using the MSC.Marc software package. The model was tested in four cases. The results showed a higher displacement along the compression direction compared to the other two directions. The compressed breast thickness in these four cases at a compression ratio of 60% was in the range of 5-7 cm, which is a typical range of thickness in mammography. The projection of the fibroglandular tissue mesh at a compression ratio of 60% was compared to the corresponding mammograms of two women, and they demonstrated spatially matched distributions. However, since the compression was based on magnetic resonance imaging (MRI), which has much coarser spatial resolution than the in-plane resolution of mammography, this method is unlikely to generate a synthetic mammogram close to the clinical quality. Whether this model may be used to understand the technical factors that may impact the variations in breast density needs further investigation. Since this method can be applied to simulate compression of the breast at different views and different compression levels, another possible application is to provide a tool for comparing breast images acquired using different imaging modalities--such as MRI, mammography, whole breast ultrasound and molecular imaging--that are performed using different body positions and under different compression conditions.

The Use of DNS in Turbulence Modeling

NASA Technical Reports Server (NTRS)

Mansour, Nagi N.; Merriam, Marshal (Technical Monitor)

1997-01-01

The use of Direct numerical simulations (DNS) data in developing and testing turbulence models is reviewed. The data is used to test turbulence models at all levels: algebraic, one-equation, two-equation and full Reynolds stress models were tested. Particular examples on the development of models for the dissipation rate equation are presented. Homogeneous flows are used to test new scaling arguments for the various terms in the dissipation rate equation. The channel flow data is used to develop modifications to the equation model that take into account near-wall effects. DNS of compressible flows under mean compression are used in testing new compressible modifications to the two-equation models.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad/Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Gokcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Panel test articles included a metallic separation bolt imbedded in the compression-pad and heat shield materials, resulting in a circular protuberance over a flat plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.

Development of a multi-cycle shear-compression testing for the modeling of severe plastic deformation

NASA Astrophysics Data System (ADS)

Pesin, A.; Pustovoytov, D.; Lokotunina, N.

2017-12-01

The mechanism of severe plastic deformation comes from very significant shear strain. Shear-compression testing of materials is complicated by the fact that a state of large equivalent strain with dominant shear strain is not easily achievable. This paper presents the novel technique of laboratory simulation of severe plastic deformation by multi-cycle shear-compression testing at room temperature with equivalent strain e=1…5. The specimen consisted of a parallelepiped having an inclined gauge section created by two diametrically opposed semi-circular slots which were machined at 45°. Height of the specimen was 50 mm, section dimensions were 25×25 mm, gauge thickness was 5.0 mm and gauge width was 6.0 mm. The specimen provided dominant shear strain in an inclined gauge-section. The level of shear strain and equivalent strain was controlled through adjustment of the height reduction of the specimen, load application direction and number of cycles of shear-compression. Aluminium alloy Al-6.2Mg-0.7Mn was used as a material for specimen. FE simulation and analysis of the stress-strain state were performed. The microstructure of the specimen after multi-cycle shear-compression testing with equivalent strain e=1…5 was examined by optical and scanning electron microscope.

Analysis of non-destructive current simulators of flux compression generators.

PubMed

O'Connor, K A; Curry, R D

2014-06-01

Development and evaluation of power conditioning systems and high power microwave components often used with flux compression generators (FCGs) requires repeated testing and characterization. In an effort to minimize the cost and time required for testing with explosive generators, non-destructive simulators of an FCG's output current have been developed. Flux compression generators and simulators of FCGs are unique pulsed power sources in that the current waveform exhibits a quasi-exponential increasing rate at which the current rises. Accurately reproducing the quasi-exponential current waveform of a FCG can be important in designing electroexplosive opening switches and other power conditioning components that are dependent on the integral of current action and the rate of energy dissipation. Three versions of FCG simulators have been developed that include an inductive network with decreasing impedance in time. A primary difference between these simulators is the voltage source driving them. It is shown that a capacitor-inductor-capacitor network driving a constant or decreasing inductive load can produce the desired high-order derivatives of the load current to replicate a quasi-exponential waveform. The operation of the FCG simulators is reviewed and described mathematically for the first time to aid in the design of new simulators. Experimental and calculated results of two recent simulators are reported with recommendations for future designs.

Modeling of deformation behavior and texture evolution in magnesium alloy using the intermediate $$\\phi$$-model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Dongsheng; Ahzi, Said; M'Guil, S. M.

2014-01-06

The viscoplastic intermediate phi-model was applied in this work to predict the deformation behavior and texture evolution in a magnesium alloy, an HCP material. We simulated the deformation behavior with different intergranular interaction strengths and compared the predicted results with available experimental results. In this approach, elasticity is neglected and the plastic deformation mechanisms are assumed as a combination of crystallographic slip and twinning systems. Tests are performed for rolling (plane strain compression) of random textured Mg polycrystal as well as for tensile and compressive tests on rolled Mg sheets. Simulated texture evolutions agree well with experimental data. Activities of twinning and slip, predicted by the intermediatemore » $$\\phi$$-model, reveal the strong anisotropic behavior during tension and compression of rolled sheets.« less

A Numerical Simulation of a Normal Sonic Jet into a Hypersonic Cross-Flow

NASA Technical Reports Server (NTRS)

Jeffries, Damon K.; Krishnamurthy, Ramesh; Chandra, Suresh

1997-01-01

This study involves numerical modeling of a normal sonic jet injection into a hypersonic cross-flow. The numerical code used for simulation is GASP (General Aerodynamic Simulation Program.) First the numerical predictions are compared with well established solutions for compressible laminar flow. Then comparisons are made with non-injection test case measurements of surface pressure distributions. Good agreement with the measurements is observed. Currently comparisons are underway with the injection case. All the experimental data were generated at the Southampton University Light Piston Isentropic Compression Tube.

The use of direct numerical simulation data in turbulence modeling

NASA Technical Reports Server (NTRS)

Mansour, N. N.

1991-01-01

Direct numerical simulations (DNS) of turbulent flows provide a complete data base to develop and to test turbulence models. In this article, the progress made in developing models for the dissipation rate equation is reviewed. New scaling arguments for the various terms in the dissipation rate equation were tested using data from DNS of homogeneous shear flows. Modifications to the epsilon-equation model that take into account near-wall effects were developed using DNS of turbulent channel flows. Testing of new models for flows under mean compression was carried out using data from DNS of isotropically compressed turbulence. In all of these studies the data from the simulations was essential in guiding the model development. The next generation of DNS will be at higher Reynolds numbers, and will undoubtedly lead to improved models for computations of flows of practical interest.

High frequency dynamic engine simulation. [TF-30 engine

NASA Technical Reports Server (NTRS)

Schuerman, J. A.; Fischer, K. E.; Mclaughlin, P. W.

1977-01-01

A digital computer simulation of a mixed flow, twin spool turbofan engine was assembled to evaluate and improve the dynamic characteristics of the engine simulation to disturbance frequencies of at least 100 Hz. One dimensional forms of the dynamic mass, momentum and energy equations were used to model the engine. A TF30 engine was simulated so that dynamic characteristics could be evaluated against results obtained from testing of the TF30 engine at the NASA Lewis Research Center. Dynamic characteristics of the engine simulation were improved by modifying the compression system model. Modifications to the compression system model were established by investigating the influence of size and number of finite dynamic elements. Based on the results of this program, high frequency engine simulations using finite dynamic elements can be assembled so that the engine dynamic configuration is optimum with respect to dynamic characteristics and computer execution time. Resizing of the compression systems finite elements improved the dynamic characteristics of the engine simulation but showed that additional refinements are required to obtain close agreement simulation and actual engine dynamic characteristics.

Compressive and shear properties of commercially available polyurethane foams.

PubMed

Thompson, Mark S; McCarthy, Ian D; Lidgren, Lars; Ryd, Leif

2003-10-01

The shear properties of rigid polyurethane (PU-R) foams, routinely used to simulate cancellous bone, are not well characterized. The present assessment of the shear and compressive properties of four grades of Sawbones "Rigid cellular" PU-R foam tested 20 mm gauge diameter dumb-bell specimens in torsion and under axial loading. Shear moduli ranged from 13.3 to 99.7 MPa, shear strengths from 0.7 MPa to 4.2 MPa. Compressive yield strains varied little with density while shear yield strains had peak values with "200 kgm-3" grade. PU-R foams may be used to simulate the elastic but not failure properties of cancellous bone.

Simulated pressure denaturation thermodynamics of ubiquitin.

PubMed

Ploetz, Elizabeth A; Smith, Paul E

2017-12-01

Simulations of protein thermodynamics are generally difficult to perform and provide limited information. It is desirable to increase the degree of detail provided by simulation and thereby the potential insight into the thermodynamic properties of proteins. In this study, we outline how to analyze simulation trajectories to decompose conformation-specific, parameter free, thermodynamically defined protein volumes into residue-based contributions. The total volumes are obtained using established methods from Fluctuation Solution Theory, while the volume decomposition is new and is performed using a simple proximity method. Native and fully extended ubiquitin are used as the test conformations. Changes in the protein volumes are then followed as a function of pressure, allowing for conformation-specific protein compressibility values to also be obtained. Residue volume and compressibility values indicate significant contributions to protein denaturation thermodynamics from nonpolar and coil residues, together with a general negative compressibility exhibited by acidic residues. Copyright © 2017 Elsevier B.V. All rights reserved.

Membrane filtration device for studying compression of fouling layers in membrane bioreactors

PubMed Central

Bugge, Thomas Vistisen; Larsen, Poul; Nielsen, Per Halkjær; Christensen, Morten Lykkegaard

2017-01-01

A filtration devise was developed to assess compressibility of fouling layers in membrane bioreactors. The system consists of a flat sheet membrane with air scouring operated at constant transmembrane pressure to assess the influence of pressure on resistance of fouling layers. By fitting a mathematical model, three model parameters were obtained; a back transport parameter describing the kinetics of fouling layer formation, a specific fouling layer resistance, and a compressibility parameter. This stands out from other on-site filterability tests as model parameters to simulate filtration performance are obtained together with a characterization of compressibility. Tests on membrane bioreactor sludge showed high reproducibility. The methodology’s ability to assess compressibility was tested by filtrations of sludges from membrane bioreactors and conventional activated sludge wastewater treatment plants from three different sites. These proved that membrane bioreactor sludge showed higher compressibility than conventional activated sludge. In addition, detailed information on the underlying mechanisms of the difference in fouling propensity were obtained, as conventional activated sludge showed slower fouling formation, lower specific resistance and lower compressibility of fouling layers, which is explained by a higher degree of flocculation. PMID:28749990

Full-Scale System for Quantifying Loads and Leak Rates of Seals for Space Applications

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H., Jr.; Steinetz, Bruce M.; Daniels, Christopher C.; Wasowski, Janice L.; Robbie, Malcolm G.; Erker, Arthur H.; Drlik, Gary J.; Mayer, John J.

2010-01-01

NASA is developing advanced space-rated vacuum seals in support of future space exploration missions to low-Earth orbit and other destinations. These seals may be 50 to 60 in. (127 to 152 cm) in diameter and must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions to the International Space Station or the Moon. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them during docking or mating, and seal adhesion forces must be low to allow two mated systems to separate when required. NASA Glenn Research Center has developed a new test apparatus to measure leak rates and compression and adhesion loads of candidate full-scale seals under simulated thermal, vacuum, and engagement conditions. Tests can be performed in seal-on-seal or seal-on-flange configurations at temperatures from -76 to 140 F (-60 to 60 C) under operational pressure gradients. Nominal and off-nominal mating conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features of the test apparatus as well as techniques used to overcome some of the design challenges.

Compression simulations of plant tissue in 3D using a mass-spring system approach and discrete element method.

PubMed

Pieczywek, Piotr M; Zdunek, Artur

2017-10-18

A hybrid model based on a mass-spring system methodology coupled with the discrete element method (DEM) was implemented to simulate the deformation of cellular structures in 3D. Models of individual cells were constructed using the particles which cover the surfaces of cell walls and are interconnected in a triangle mesh network by viscoelastic springs. The spatial arrangement of the cells required to construct a virtual tissue was obtained using Poisson-disc sampling and Voronoi tessellation in 3D space. Three structural features were included in the model: viscoelastic material of cell walls, linearly elastic interior of the cells (simulating compressible liquid) and a gas phase in the intercellular spaces. The response of the models to an external load was demonstrated during quasi-static compression simulations. The sensitivity of the model was investigated at fixed compression parameters with variable tissue porosity, cell size and cell wall properties, such as thickness and Young's modulus, and a stiffness of the cell interior that simulated turgor pressure. The extent of the agreement between the simulation results and other models published is discussed. The model demonstrated the significant influence of tissue structure on micromechanical properties and allowed for the interpretation of the compression test results with respect to changes occurring in the structure of the virtual tissue. During compression virtual structures composed of smaller cells produced higher reaction forces and therefore they were stiffer than structures with large cells. The increase in the number of intercellular spaces (porosity) resulted in a decrease in reaction forces. The numerical model was capable of simulating the quasi-static compression experiment and reproducing the strain stiffening observed in experiment. Stress accumulation at the edges of the cell walls where three cells meet suggests that cell-to-cell debonding and crack propagation through the contact edge of neighboring cells is one of the most prevalent ways for tissue to rupture.

XS: a FASTQ read simulator.

PubMed

Pratas, Diogo; Pinho, Armando J; Rodrigues, João M O S

2014-01-16

The emerging next-generation sequencing (NGS) is bringing, besides the natural huge amounts of data, an avalanche of new specialized tools (for analysis, compression, alignment, among others) and large public and private network infrastructures. Therefore, a direct necessity of specific simulation tools for testing and benchmarking is rising, such as a flexible and portable FASTQ read simulator, without the need of a reference sequence, yet correctly prepared for producing approximately the same characteristics as real data. We present XS, a skilled FASTQ read simulation tool, flexible, portable (does not need a reference sequence) and tunable in terms of sequence complexity. It has several running modes, depending on the time and memory available, and is aimed at testing computing infrastructures, namely cloud computing of large-scale projects, and testing FASTQ compression algorithms. Moreover, XS offers the possibility of simulating the three main FASTQ components individually (headers, DNA sequences and quality-scores). XS provides an efficient and convenient method for fast simulation of FASTQ files, such as those from Ion Torrent (currently uncovered by other simulators), Roche-454, Illumina and ABI-SOLiD sequencing machines. This tool is publicly available at http://bioinformatics.ua.pt/software/xs/.

Implementation of 3D spatial indexing and compression in a large-scale molecular dynamics simulation database for rapid atomic contact detection.

PubMed

Toofanny, Rudesh D; Simms, Andrew M; Beck, David A C; Daggett, Valerie

2011-08-10

Molecular dynamics (MD) simulations offer the ability to observe the dynamics and interactions of both whole macromolecules and individual atoms as a function of time. Taken in context with experimental data, atomic interactions from simulation provide insight into the mechanics of protein folding, dynamics, and function. The calculation of atomic interactions or contacts from an MD trajectory is computationally demanding and the work required grows exponentially with the size of the simulation system. We describe the implementation of a spatial indexing algorithm in our multi-terabyte MD simulation database that significantly reduces the run-time required for discovery of contacts. The approach is applied to the Dynameomics project data. Spatial indexing, also known as spatial hashing, is a method that divides the simulation space into regular sized bins and attributes an index to each bin. Since, the calculation of contacts is widely employed in the simulation field, we also use this as the basis for testing compression of data tables. We investigate the effects of compression of the trajectory coordinate tables with different options of data and index compression within MS SQL SERVER 2008. Our implementation of spatial indexing speeds up the calculation of contacts over a 1 nanosecond (ns) simulation window by between 14% and 90% (i.e., 1.2 and 10.3 times faster). For a 'full' simulation trajectory (51 ns) spatial indexing reduces the calculation run-time between 31 and 81% (between 1.4 and 5.3 times faster). Compression resulted in reduced table sizes but resulted in no significant difference in the total execution time for neighbour discovery. The greatest compression (~36%) was achieved using page level compression on both the data and indexes. The spatial indexing scheme significantly decreases the time taken to calculate atomic contacts and could be applied to other multidimensional neighbor discovery problems. The speed up enables on-the-fly calculation and visualization of contacts and rapid cross simulation analysis for knowledge discovery. Using page compression for the atomic coordinate tables and indexes saves ~36% of disk space without any significant decrease in calculation time and should be considered for other non-transactional databases in MS SQL SERVER 2008.

Implementation of 3D spatial indexing and compression in a large-scale molecular dynamics simulation database for rapid atomic contact detection

PubMed Central

2011-01-01

Background Molecular dynamics (MD) simulations offer the ability to observe the dynamics and interactions of both whole macromolecules and individual atoms as a function of time. Taken in context with experimental data, atomic interactions from simulation provide insight into the mechanics of protein folding, dynamics, and function. The calculation of atomic interactions or contacts from an MD trajectory is computationally demanding and the work required grows exponentially with the size of the simulation system. We describe the implementation of a spatial indexing algorithm in our multi-terabyte MD simulation database that significantly reduces the run-time required for discovery of contacts. The approach is applied to the Dynameomics project data. Spatial indexing, also known as spatial hashing, is a method that divides the simulation space into regular sized bins and attributes an index to each bin. Since, the calculation of contacts is widely employed in the simulation field, we also use this as the basis for testing compression of data tables. We investigate the effects of compression of the trajectory coordinate tables with different options of data and index compression within MS SQL SERVER 2008. Results Our implementation of spatial indexing speeds up the calculation of contacts over a 1 nanosecond (ns) simulation window by between 14% and 90% (i.e., 1.2 and 10.3 times faster). For a 'full' simulation trajectory (51 ns) spatial indexing reduces the calculation run-time between 31 and 81% (between 1.4 and 5.3 times faster). Compression resulted in reduced table sizes but resulted in no significant difference in the total execution time for neighbour discovery. The greatest compression (~36%) was achieved using page level compression on both the data and indexes. Conclusions The spatial indexing scheme significantly decreases the time taken to calculate atomic contacts and could be applied to other multidimensional neighbor discovery problems. The speed up enables on-the-fly calculation and visualization of contacts and rapid cross simulation analysis for knowledge discovery. Using page compression for the atomic coordinate tables and indexes saves ~36% of disk space without any significant decrease in calculation time and should be considered for other non-transactional databases in MS SQL SERVER 2008. PMID:21831299

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H., Jr.

2014-01-01

NASA is developing advanced space-rated elastomeric seals to support future space exploration missions to low Earth orbit, the Moon, near Earth asteroids, and other destinations. This includes seals for a new docking system and vehicle hatches. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them, and seal adhesion forces must be low to allow the sealed interface to be separated when required (e.g., during undocking or hatch opening). NASA Glenn Research Center has developed a number of unique test fixtures to measure the leak rates and compression and adhesion loads of candidate seal designs under simulated thermal, vacuum, and engagement conditions. Tests can be performed on fullscale seals with diameters on the order of 50 in., subscale seals that are about 12 in. in diameter, and smaller specimens such as O-rings. Test conditions include temperatures ranging from -238 to 662degF (-150 to 350degC), operational pressure gradients, and seal-on-seal or seal-on-flange mating configurations. Nominal and off-nominal conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features and capabilities of each type of test apparatus and provides an overview of advanced seal development activities at NASA Glenn.

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H.

2014-01-01

NASA is developing advanced space-rated elastomeric seals to support future space exploration missions to low Earth orbit, the Moon, near Earth asteroids, and other destinations. This includes seals for a new docking system and vehicle hatches. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them, and seal adhesion forces must be low to allow the sealed interface to be separated when required (e.g., during undocking or hatch opening). NASA Glenn Research Center has developed a number of unique test fixtures to measure the leak rates and compression and adhesion loads of candidate seal designs under simulated thermal, vacuum, and engagement conditions. Tests can be performed on full-scale seals with diameters on the order of 50 in., subscale seals that are about 12 in. in diameter, and smaller specimens such as O-rings. Test conditions include temperatures ranging from -238 to 662 F (-150 to 350 C), operational pressure gradients, and seal-on-seal or seal-on-flange mating configurations. Nominal and off-nominal conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features and capabilities of each type of test apparatus and provides an overview of advanced seal development activities at NASA Glenn.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Gokcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Each panel test article included a metallic separation bolt imbedded in Orion compression-pad and heatshield materials, resulting in a circular protuberance over a flat plate. The protuberances produce complex model flowfields, containing shock-shock and shock-boundary layer interactions, and multiple augmented heating regions on the test plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad/Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Goekcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Each panel test article included a metallic separation bolt imbedded in Orion compression-pad and heatshield materials, resulting in a circular protuberance over a flat plate. The protuberances produce complex model flowfields, containing shock-shock and shock-boundary layer interactions, and multiple augmented heating regions on the test plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the nonequilibrium flowfield in the facility nozzle, test box, and flowfield over test articles, and comparisons with the measured calibration data.

Predicting the sinkage of a moving tracked mining vehicle using a new rheological formulation for soft deep-sea sediment

NASA Astrophysics Data System (ADS)

Xu, Feng; Rao, Qiuhua; Ma, Wenbo

2018-03-01

The sinkage of a moving tracked mining vehicle is greatly affected by the combined compression-shear rheological properties of soft deep-sea sediments. For test purposes, the best sediment simulant is prepared based on soft deep-sea sediment from a C-C poly-metallic nodule mining area in the Pacific Ocean. Compressive creep tests and shear creep tests are combined to obtain compressive and shear rheological parameters to establish a combined compressive-shear rheological constitutive model and a compression-sinkage rheological constitutive model. The combined compression-shear rheological sinkage of the tracked mining vehicle at different speeds is calculated using the RecurDyn software with a selfprogrammed subroutine to implement the combined compression-shear rheological constitutive model. The model results are compared with shear rheological sinkage and ordinary sinkage (without consideration of rheological properties). These results show that the combined compression-shear rheological constitutive model must be taken into account when calculating the sinkage of a tracked mining vehicle. The combined compression-shear rheological sinkage decrease with vehicle speed and is the largest among the three types of sinkage. The developed subroutine in the RecurDyn software can be used to study the performance and structural optimization of moving tracked mining vehicles.

Characterization of cell mechanical properties by computational modeling of parallel plate compression.

PubMed

McGarry, J P

2009-11-01

A substantial body of work has been reported in which the mechanical properties of adherent cells were characterized using compression testing in tandem with computational modeling. However, a number of important issues remain to be addressed. In the current study, using computational analyses, the effect of cell compressibility on the force required to deform spread cells is investigated and the possibility that stiffening of the cell cytoplasm occurs during spreading is examined based on published experimental compression test data. The effect of viscoelasticity on cell compression is considered and difficulties in performing a complete characterization of the viscoelastic properties of a cell nucleus and cytoplasm by this method are highlighted. Finally, a non-linear force-deformation response is simulated using differing linear viscoelastic properties for the cell nucleus and the cell cytoplasm.

Column compression strength of tubular packaging forms made from paper

Treesearch

Thomas J. Urbanik; Sung K. Lee; Charles G. Johnson

2006-01-01

Tubular packaging forms fabricated and shaped from rolled paper are used as reinforcing corner posts for major appliances packaged in corrugated containers. Tests of column compression strength simulate the expected performance loads from appliances stacked in warehouses. Column strength depends on tube geometry, paper properties, basis weight, and number of...

Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars

DOE PAGES

Liu, Yue; Li, Nan; Mariyappan, Arul Kumar; ...

2017-06-07

Basal slip and {01more » $$\\bar{1}$$2} twinning are two major plastic deformation mechanisms in hexagonal closed-packed magnesium. Here in this paper, we quantify the critical stresses associated with basal slip and twinning in single-crystal and bi-crystal magnesium samples by performing in situ compression of micropillars with different diameters in a scanning electron microscope. The micropillars are designed to favor either slip or twinning under uniaxial compression. Compression tests imply a negligible size effect related to basal slip and twinning as pillar diameter is greater than 10 μm. The critical resolved shear stresses are deduced to be 29 MPa for twinning and 6 MPa for basal slip from a series of micropillar compression tests. Employing full-field elasto-visco-plastic simulations, we further interpret the experimental observations in terms of the local stress distribution associated with multiple twinning, twin nucleation, and twin growth. Our simulation results suggest that the twinning features being studied should not be close to the top surface of the micropillar because of local stress perturbations induced by the hard indenter.« less

Deformation behaviors of peat with influence of organic matter.

PubMed

Yang, Min; Liu, Kan

2016-01-01

Peat is a kind of special material rich in organic matter. Because of the high content of organic matter, it shows different deformation behaviors from conventional geotechnical materials. Peat grain has a non-negligible compressibility due to the presence of organic matter. Biogas can generate from peat and can be trapped in form of gas bubbles. Considering the natural properties of peat, a special three-phase composition of peat is described which indicates the existence of organic matter and gas bubbles in peat. A stress-strain-time model is proposed for the compression of organic matter, and the surface tension effect is considered in the compression model of gas bubbles. Finally, a mathematical model has been developed to simulate the deformation behavior of peat considering the compressibility of organic matter and entrapped gas bubbles. The deformation process is the coupling of volume variation of organic matter, gas bubbles and water drainage. The proposed model is used to simulate a series of peat laboratory oedometer tests, and the model can well capture the test results with reasonable model parameters. Effects of model parameters on deformation of peat are also analyzed.

Compression of thick laminated composite beams with initial impact-like damage

NASA Technical Reports Server (NTRS)

Breivik, N. L.; Guerdal, Z.; Griffin, O. H., Jr.

1992-01-01

While the study of compression after impact of laminated composites has been under consideration for many years, the complexity of the damage initiated by low velocity impact has not lent itself to simple predictive models for compression strength. The damage modes due to non-penetrating, low velocity impact by large diameter objects can be simulated using quasi-static three-point bending. The resulting damage modes are less coupled and more easily characterized than actual impact damage modes. This study includes the compression testing of specimens with well documented initial damage states obtained from three-point bend testing. Compression strengths and failure modes were obtained for quasi-isotropic stacking sequences from 0.24 to 1.1 inches thick with both grouped and interspersed ply stacking. Initial damage prior to compression testing was divided into four classifications based on the type, extent, and location of the damage. These classifications are multiple through-thickness delaminations, isolated delamination, damage near the surface, and matrix cracks. Specimens from each classification were compared to specimens tested without initial damage in order to determine the effects of the initial damage on the final compression strength and failure modes. A finite element analysis was used to aid in the understanding and explanation of the experimental results.

Assessment of compressive failure process of cortical bone materials using damage-based model.

PubMed

Ng, Theng Pin; R Koloor, S S; Djuansjah, J R P; Abdul Kadir, M R

2017-02-01

The main failure factors of cortical bone are aging or osteoporosis, accident and high energy trauma or physiological activities. However, the mechanism of damage evolution coupled with yield criterion is considered as one of the unclear subjects in failure analysis of cortical bone materials. Therefore, this study attempts to assess the structural response and progressive failure process of cortical bone using a brittle damaged plasticity model. For this reason, several compressive tests are performed on cortical bone specimens made of bovine femur, in order to obtain the structural response and mechanical properties of the material. Complementary finite element (FE) model of the sample and test is prepared to simulate the elastic-to-damage behavior of the cortical bone using the brittle damaged plasticity model. The FE model is validated in a comparative method using the predicted and measured structural response as load-compressive displacement through simulation and experiment. FE results indicated that the compressive damage initiated and propagated at central region where maximum equivalent plastic strain is computed, which coincided with the degradation of structural compressive stiffness followed by a vast amount of strain energy dissipation. The parameter of compressive damage rate, which is a function dependent on damage parameter and the plastic strain is examined for different rates. Results show that considering a similar rate to the initial slope of the damage parameter in the experiment would give a better sense for prediction of compressive failure. Copyright © 2016 Elsevier Ltd. All rights reserved.

Magnetic Compression Experiment at General Fusion with Simulation Results

NASA Astrophysics Data System (ADS)

Dunlea, Carl; Khalzov, Ivan; Hirose, Akira; Xiao, Chijin; Fusion Team, General

2017-10-01

The magnetic compression experiment at GF was a repetitive non-destructive test to study plasma physics applicable to Magnetic Target Fusion compression. A spheromak compact torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped inner flux conserver, and an insulating outer wall. External coil currents keep the CT off the outer wall (levitation) and then rapidly compress it inwards. The optimal external coil configuration greatly improved both the levitated CT lifetime and the rate of shots with good compressional flux conservation. As confirmed by spectrometer data, the improved levitation field profile reduced plasma impurity levels by suppressing the interaction between plasma and the insulating outer wall during the formation process. We developed an energy and toroidal flux conserving finite element axisymmetric MHD code to study CT formation and compression. The Braginskii MHD equations with anisotropic heat conduction were implemented. To simulate plasma / insulating wall interaction, we couple the vacuum field solution in the insulating region to the full MHD solution in the remainder of the domain. We see good agreement between simulation and experiment results. Partly funded by NSERC and MITACS Accelerate.

StirMark Benchmark: audio watermarking attacks based on lossy compression

NASA Astrophysics Data System (ADS)

Steinebach, Martin; Lang, Andreas; Dittmann, Jana

2002-04-01

StirMark Benchmark is a well-known evaluation tool for watermarking robustness. Additional attacks are added to it continuously. To enable application based evaluation, in our paper we address attacks against audio watermarks based on lossy audio compression algorithms to be included in the test environment. We discuss the effect of different lossy compression algorithms like MPEG-2 audio Layer 3, Ogg or VQF on a selection of audio test data. Our focus is on changes regarding the basic characteristics of the audio data like spectrum or average power and on removal of embedded watermarks. Furthermore we compare results of different watermarking algorithms and show that lossy compression is still a challenge for most of them. There are two strategies for adding evaluation of robustness against lossy compression to StirMark Benchmark: (a) use of existing free compression algorithms (b) implementation of a generic lossy compression simulation. We discuss how such a model can be implemented based on the results of our tests. This method is less complex, as no real psycho acoustic model has to be applied. Our model can be used for audio watermarking evaluation of numerous application fields. As an example, we describe its importance for e-commerce applications with watermarking security.

Constitutive Soil Properties for Mason Sand and Kennedy Space Center

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.

2011-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle (CEV). This report provides constitutive material models for two soil conditions at Kennedy Space Center (KSC) and four conditions of Mason Sand. The Mason Sand is the test sand for LaRC s drop tests and swing tests of the Orion. The soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LSDYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The soil models are intended to be specific to the soil conditions they were tested at. The two KSC models represent two conditions at KSC: low density dry sand and high density in-situ moisture sand. The Mason Sand model was tested at four conditions which encompass measured conditions at LaRC s drop test site.

Real-Time Mobile Device-Assisted Chest Compression During Cardiopulmonary Resuscitation.

PubMed

Sarma, Satyam; Bucuti, Hakiza; Chitnis, Anurag; Klacman, Alex; Dantu, Ram

2017-07-15

Prompt administration of high-quality cardiopulmonary resuscitation (CPR) is a key determinant of survival from cardiac arrest. Strategies to improve CPR quality at point of care could improve resuscitation outcomes. We tested whether a low cost and scalable mobile phone- or smart watch-based solution could provide accurate measures of compression depth and rate during simulated CPR. Fifty health care providers (58% intensive care unit nurses) performed simulated CPR on a calibrated training manikin (Resusci Anne, Laerdal) while wearing both devices. Subjects received real-time audiovisual feedback from each device sequentially. Primary outcome was accuracy of compression depth and rate compared with the calibrated training manikin. Secondary outcome was improvement in CPR quality as defined by meeting both guideline-recommend compression depth (5 to 6 cm) and rate (100 to 120/minute). Compared with the training manikin, typical error for compression depth was <5 mm (smart phone 4.6 mm; 95% CI 4.1 to 5.3 mm; smart watch 4.3 mm; 95% CI 3.8 to 5.0 mm). Compression rates were similarly accurate (smart phone Pearson's R = 0.93; smart watch R = 0.97). There was no difference in improved CPR quality defined as the number of sessions meeting both guideline-recommended compression depth (50 to 60 mm) and rate (100 to 120 compressions/minute) with mobile device feedback (60% vs 50%; p = 0.3). Sessions that did not meet guideline recommendations failed primarily because of inadequate compression depth (46 ± 2 mm). In conclusion, a mobile device application-guided CPR can accurately track compression depth and rate during simulation in a practice environment in accordance with resuscitation guidelines. Copyright © 2017 Elsevier Inc. All rights reserved.

Loading simulation of lumbar spine vertebrae during a compression test using the finite elements method and trabecular bone strength properties, determined by means of nanoindentations.

PubMed

Bouzakis, K D; Mitsi, S; Michailidis, N; Mirisidis, I; Mesomeris, G; Maliaris, G; Korlos, A; Kapetanos, G; Antonarakos, P; Anagnostidis, K

2004-06-01

The mechanical strength properties of lumbar spine vertebrae are of great importance in a wide range of applications. Herein, through nanoindentations and appropriate evaluation of the corresponding results, trabecular bone struts stress-strain characteristics can be determined. In the frame of the present paper, an L2 fresh cadaveric vertebra, from which posterior elements were removed, was subjected to compression. With the aid of developed finite elements method based algorithms, the cortical shell and the cancellous core bulk elasticity moduli and stresses were determined, whereas the tested vertebra geometrical model used in these algorithms was considered as having a compound structure, consisting of the cancellous bone surrounded by the cortical shell. Moreover nanoindentations were conducted and an appropriate evaluation method of the obtained results was applied to extract stress-strain curves of individual lumbar spine vertebra trabecular bone struts. These data were used in the mathematical description of the vertebrae compression test. The vertebral cancellous bone structure was simulated by a beam elements network, possessing an equivalent porosity and different stiffnesses in vertical and horizontal direction. Thus, the measured course of the compression load versus the occurring specimen deformation was verified.

Design of bunch compressing system with suppression of coherent synchrotron radiation for ATF upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, Yichao; Fedurin, Mikhail; Stratakis, Diktys

2015-05-03

One of the operation modes for Accelerator Test Facility (ATF) upgrade is to provide high peak current, high quality electron beam for users. Such operation requires a bunch compressing system with a very large compression ratio. The CSR originating from the strong compressors generally could greatly degrade the quality of the electron beam. In this paper, we present our design for the entire bunch compressing system that will limit the effect of CSR on the e-beam’s quality. We discuss and detail the performance from the start to end simulation of such a compressor for ATF.

Atomic Oxygen Exposure of Polyimide Foam for International Space Station Solar Array Wing Blanket Box

NASA Technical Reports Server (NTRS)

Finckenor, M. M.; Albyn, K. C.; Watts, E. W.

2006-01-01

Onorbit photos of the International Space Station (ISS) solar array blanket box foam pad assembly indicate degradation of the Kapton film covering the foam, leading to atomic oxygen (AO) exposure of the foam. The purpose of this test was to determine the magnitude of particulate generation caused by low-Earth orbital environment exposure of the foam and also by compression of the foam during solar array wing retraction. The polyimide foam used in the ISS solar array wing blanket box assembly is susceptible to significant AO erosion. The foam sample in this test lost one-third of its mass after exposure to the equivalent of 22 mo onorbit. Some particulate was generated by exposure to simulated orbital conditions and the simulated solar array retraction (compression test). However, onorbit, these particles would also be eroded by AO. The captured particles were generally <1 mm, and the particles shaken free of the sample had a maximum size of 4 mm. The foam sample maintained integrity after a compression load of 2.5 psi.

Ensemble sea ice forecast for predicting compressive situations in the Baltic Sea

NASA Astrophysics Data System (ADS)

Lehtiranta, Jonni; Lensu, Mikko; Kokkonen, Iiro; Haapala, Jari

2017-04-01

Forecasting of sea ice hazards is important for winter shipping in the Baltic Sea. In current numerical models the ice thickness distribution and drift are captured well, but compressive situations are often missing from forecast products. Its inclusion is requested by the shipping community, as compression poses a threat to ship operations. As compressing ice is capable of stopping ships for days and even damaging them, its inclusion in ice forecasts is vital. However, we have found that compression can not be predicted well in a deterministic forecast, since it can be a local and a quickly changing phenomenon. It is also very sensitive to small changes in the wind speed and direction, the prevailing ice conditions, and the model parameters. Thus, a probabilistic ensemble simulation is needed to produce a meaningful compression forecast. An ensemble model setup was developed in the SafeWIN project for this purpose. It uses the HELMI multicategory ice model, which was amended for making simulations in parallel. The ensemble was built by perturbing the atmospheric forcing and the physical parameters of the ice pack. The model setup will provide probabilistic forecasts for the compression in the Baltic sea ice. Additionally the model setup provides insight into the uncertainties related to different model parameters and their impact on the model results. We have completed several hindcast simulations for the Baltic Sea for verification purposes. These results are shown to match compression reports gathered from ships. In addition, an ensemble forecast is in preoperational testing phase and its first evaluation will be presented in this work.

Mechanical abuse simulation and thermal runaway risks of large-format Li-ion batteries

NASA Astrophysics Data System (ADS)

Wang, Hsin; Lara-Curzio, Edgar; Rule, Evan T.; Winchester, Clinton S.

2017-02-01

Internal short circuit of large-format Li-ion pouch cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ∼40% maximum compressive loading force during the pinch test. The cell was twisted about 5° to the side by horizontally pulling a wire attached to the anode tab. The combined torsion-compression force created small failure at the separator yet allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4-6 cells at each state-of-charge (SOC). Commercially available 18 Ahr LiFePO4 (LFP) and 25 Ahr Li(NiMnCo)1/3O2 (NMC) cells were tested, and a thermal runaway risk (TRR) score system was used to evaluate the safety of the cells under the same testing conditions. The aim was to provide the cell manufacturers and end users with a tool to compare different designs and safety features.

Redistribution of Welding Residual Stresses of Crack Tip Opening Displacement Specimen by Local Compression.

PubMed

Kim, Young-Gon; Song, Kuk-Hyun; Lee, Dong-Hoon; Joo, Sung-Min

2018-03-01

The demand of crack tip opening displacement (CTOD) test which evaluates fracture toughness of a cracked material is very important to ensure the stability of structure under severe service environment. The validity of the CTOD test result is judged using several criterions of the specification standards. One of them is the artificially generated fatigue pre-crack length inside the specimen. For acceptable CTOD test results, fatigue pre-crack must have a reasonable sharp crack front. The propagation of fatigue crack started from the tip of the machined notch, which might have propagated irregularly due to residual stress field. To overcome this problem, test codes suggest local compression method, reversed bending method and stepwise high-R ratio method to reduce the disparity of residual stress distribution inside the specimen. In this paper, the relation between the degree of local compression and distribution of welding residual stress has been analyzed by finite element analyses in order to determine the amount of effective local compression of the test piece. Analysis results show that initial welding residual stress is dramatically varied three-dimensionally while cutting, notch machining and local compressing due to the change of internal restraint force. From the simulation result, the authors find that there is an optimum amount of local compression to modify regularly for generating fatigue pre-crack propagation. In the case of 0.5% compressions of the model width is the most effective for uniforming residual stress distribution.

Remote Sensing Image Quality Assessment Experiment with Post-Processing

NASA Astrophysics Data System (ADS)

Jiang, W.; Chen, S.; Wang, X.; Huang, Q.; Shi, H.; Man, Y.

2018-04-01

This paper briefly describes the post-processing influence assessment experiment, the experiment includes three steps: the physical simulation, image processing, and image quality assessment. The physical simulation models sampled imaging system in laboratory, the imaging system parameters are tested, the digital image serving as image processing input are produced by this imaging system with the same imaging system parameters. The gathered optical sampled images with the tested imaging parameters are processed by 3 digital image processes, including calibration pre-processing, lossy compression with different compression ratio and image post-processing with different core. Image quality assessment method used is just noticeable difference (JND) subject assessment based on ISO20462, through subject assessment of the gathered and processing images, the influence of different imaging parameters and post-processing to image quality can be found. The six JND subject assessment experimental data can be validated each other. Main conclusions include: image post-processing can improve image quality; image post-processing can improve image quality even with lossy compression, image quality with higher compression ratio improves less than lower ratio; with our image post-processing method, image quality is better, when camera MTF being within a small range.

High-Speed Photography of Detonation Propagation in Dynamically Precompressed Liquid Explosives

NASA Astrophysics Data System (ADS)

Petel, O. E.; Higgins, A. J.; Yoshinaka, A. C.; Zhang, F.

2007-12-01

The propagation of detonation in shock-compressed nitromethane was observed with a high-speed framing camera. The test explosive, nitromethane, was compressed by a reverberating shock wave to pressures as high as 10 GPa prior to being detonated by a secondary detonation event. The pressure and density in the test explosive prior to detonation were determined using two methods: manganin stress gauge measurements and LS-DYNA simulations. The velocity of the detonation front was determined from consecutive frames and correlated to the density of the reverberating shock-compressed explosive prior to detonation. Observing detonation propagation under these non-ambient conditions provides data which can be useful in the validation of equation of state models.

Constitutive Soil Properties for Cuddeback Lake, California and Carson Sink, Nevada

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.; Gildea, Martin L.; T'Kindt, Casey M.

2008-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle. This report provides constitutive material modeling properties for four soil models from two dry lakebeds in the western United States. The four soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples from the lakebeds. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LS-DYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The four soil models are intended to be specific only to the two lakebeds discussed in the report. The Cuddeback A and B models represent the softest and hardest soils at Cuddeback Lake. The Carson Sink Wet and Dry models represent different seasonal conditions. It is possible to approximate other clay soils with these models, but the results would be unverified without geotechnical tests to confirm similar soil behavior.

An Experimental Study of Shear-Dominated Failure in the 2013 Sandia Fracture Challenge Specimen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corona, Edmundo; Deibler, Lisa Anne; Reedlunn, Benjamin

2015-04-01

This report presents an experimental study motivated by results obtained during the 2013 Sandia Fracture Challenge. The challenge involved A286 steel, shear-dominated compression specimens whose load-deflection response contained a load maximum fol- lowed by significant displacement under decreasing load, ending with a catastrophic fracture. Blind numerical simulations deviated from the experiments well before the maximum load and did not predict the failure displacement. A series of new tests were conducted on specimens machined from the original A286 steel stock to learn more about the deformation and failure processes in the specimen and potentially improve future numerical simulations. The study consistedmore » of several uniaxial tension tests to explore anisotropy in the material, and a set of new tests on the compression speci- men. In some compression specimen tests, stereo digital image correlation (DIC) was used to measure the surface strain fields local to the region of interest. In others, the compression specimen was loaded to a given displacement prior to failure, unloaded, sectioned, and imaged under the microscope to determine when material damage first appeared and how it spread. The experiments brought the following observations to light. The tensile tests revealed that the plastic response of the material is anisotropic. DIC during the shear- dominated compression tests showed that all three in-plane surface strain components had maxima in the order of 50% at the maximum load. Sectioning of the specimens revealed no signs of material damage at the point where simulations deviated from the experiments. Cracks and other damage did start to form approximately when the max- imum load was reached, and they grew as the load decreased, eventually culminating in catastrophic failure of the specimens. In addition to the steel specimens, a similar study was carried out for aluminum 7075-T651 specimens. These specimens achieved much lower loads and displacements, and failure occurred very close to the maximum in the load-deflection response. No material damage was observed in these specimens, even when failure was imminent. In the future, we plan to use these experimental results to improve numerical simu- lations of the A286 steel experiments, and to improve plasticity and failure models for the Al 7075 stock. The ultimate goal of our efforts is to increase our confidence in the results of numerical simulations of elastic-plastic structural behavior and failure.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlanderer, Stefan C., E-mail: stefan.schlanderer@unimelb.edu.au; Weymouth, Gabriel D., E-mail: G.D.Weymouth@soton.ac.uk; Sandberg, Richard D., E-mail: richard.sandberg@unimelb.edu.au

This paper introduces a virtual boundary method for compressible viscous fluid flow that is capable of accurately representing moving bodies in flow and aeroacoustic simulations. The method is the compressible extension of the boundary data immersion method (BDIM, Maertens & Weymouth (2015), ). The BDIM equations for the compressible Navier–Stokes equations are derived and the accuracy of the method for the hydrodynamic representation of solid bodies is demonstrated with challenging test cases, including a fully turbulent boundary layer flow and a supersonic instability wave. In addition we show that the compressible BDIM is able to accurately represent noise radiation frommore » moving bodies and flow induced noise generation without any penalty in allowable time step.« less

The dynamic properties behavior of high strength concrete under different strain rate

NASA Astrophysics Data System (ADS)

Abdullah, Hasballah; Husin, Saiful; Umar, Hamdani; Rizal, Samsul

2005-04-01

This paper present a number experimental data and numerical technique used in the dynamic behavior of high strength concrete. A testing device is presented for the experimental study of dynamic behavior material under high strain rates. The specimen is loaded by means of a high carbon steel Hopkinson pressure bar (40 mm diameter, 3000 mm long input bar and 1500 mm long out put bar) allowing for the testing of specimen diameter is large enough in relation to the size of aggregates. The other method also proposed for measuring tensile strength, the measurement method based on the superposition and concentration of tensile stress wave reflected both from the free-free ends of striking bar and the specimen bar. The compression Hopkinson bar test, the impact tensile test of high strength concrete bars are performed, together with compression static strength test. In addition, the relation between break position under finite element simulation and impact tensile strength are examined. The three-dimensional simulation of the specimen under transient loading are presented and comparisons between the experimental and numerical simulation on strain rate effects of constitutive law use in experimental are study.

Impacts of compression on crystallization behavior of freeze-dried amorphous sucrose.

PubMed

Imamura, Koreyoshi; Nomura, Mayo; Tanaka, Kazuhiro; Kataoka, Nobuhide; Oshitani, Jun; Imanaka, Hiroyuki; Nakanishi, Kazuhiro

2010-03-01

An amorphous matrix comprised of sugar molecules is used as excipient and stabilizing agent for labile ingredients in the pharmaceutical industry. The amorphous sugar matrix is often compressed into a tablet form to reduce the volume and improve handling. Herein, the effect of compression on the crystallization behavior of an amorphous sucrose matrix was investigated. Amorphous sucrose samples were prepared by freeze-drying and compressed under different conditions, followed by analyses by differential scanning calorimetry, isothermal crystallization tests, X-ray powder diffractometry, Fourier transform infrared spectroscopy (FTIR), and gas pycnometry. The compressed sample had a lower crystallization temperature and a shorter induction period for isothermal crystallization, indicating that compression facilitates the formation of the critical nucleus of a sucrose crystal. Based on FTIR and molecular dynamics simulation results, the conformational distortion of sucrose molecules due to the compression appears to contribute to the increase in the free energy of the system, which leads to the facilitation of critical nucleus formation. An isothermal crystallization test indicated an increase in the growth rate of sucrose crystals by the compression. This can be attributed to the transformation of the microstructure from porous to nonporous, as the result of compression. 2009 Wiley-Liss, Inc. and the American Pharmacists Association

Vapor compression distiller and membrane technology for water revitalization

NASA Technical Reports Server (NTRS)

Ashida, A.; Mitani, K.; Ebara, K.; Kurokawa, H.; Sawada, I.; Kashiwagi, H.; Tsuji, T.; Hayashi, S.; Otsubo, K.; Nitta, K.

1987-01-01

Water revitalization for a space station can consist of membrane filtration processes and a distillation process. Water recycling equipment using membrane filtration processes was manufactured for ground testing. It was assembled using commercially available components. Two systems for the distillation are studied: one is absorption type thermopervaporation cell and the other is a vapor compression distiller. Absorption type thermopervaporation, able to easily produce condensed water under zero gravity, was investigated experimentally and through simulated calculation. The vapor compression distiller was studied experimentally and it offers significant energy savings for evaporation of water.

Vapor compression distiller and membrane technology for water revitalization.

PubMed

Ashida, A; Mitani, K; Ebara, K; Kurokawa, H; Sawada, I; Kashiwagi, H; Tsuji, T; Hayashi, S; Otsubo, K; Nitta, K

1987-01-01

Water revitalization for a space station can consist of membrane filtration processes and a distillation process. Water recycling equipment using membrane filtration processes was manufactured for ground testing. It was assembled using commercially available components. Two systems for the distillation are studied; one is an absorption type thermopervaporation cell and the other is a vapor compression distiller. Absorption type thermopervaporation able to easily produce condensed water under zero gravity was investigated experimentally and through simulated calculation. The vapor compression distiller was studied experimentally and it offers significant energy savings for evaporation of water.

Optimization of the dynamic behavior of strongly nonlinear heterogeneous materials

NASA Astrophysics Data System (ADS)

Herbold, Eric B.

New aspects of strongly nonlinear wave and structural phenomena in granular media are developed numerically, theoretically and experimentally. One-dimensional chains of particles and compressed powder composites are the two main types of materials considered here. Typical granular assemblies consist of linearly elastic spheres or layers of masses and effective nonlinear springs in one-dimensional columns for dynamic testing. These materials are highly sensitive to initial and boundary conditions, making them useful for acoustic and shock-mitigating applications. One-dimensional assemblies of spherical particles are examples of strongly nonlinear systems with unique properties. For example, if initially uncompressed, these materials have a sound speed equal to zero (sonic vacuum), supporting strongly nonlinear compression solitary waves with a finite width. Different types of assembled metamaterials will be presented with a discussion of the material's response to static compression. The acoustic diode effect will be presented, which may be useful in shock mitigation applications. Systems with controlled dissipation will also be discussed from an experimental and theoretical standpoint emphasizing the critical viscosity that defines the transition from an oscillatory to monotonous shock profile. The dynamic compression of compressed powder composites may lead to self-organizing mesoscale structures in two and three dimensions. A reactive granular material composed of a compressed mixture of polytetrafluoroethylene (PTFE), tungsten (W) and aluminum (Al) fine-grain powders exhibit this behavior. Quasistatic, Hopkinson bar, and drop-weight experiments show that composite materials with a high porosity and fine metallic particles exhibit a higher strength than less porous mixtures with larger particles, given the same mass fraction of constituents. A two-dimensional Eulerian hydrocode is implemented to investigate the mechanical deformation and failure of the compressed powder samples in simulated drop-weight tests. The calculations indicate that the dynamic formation of mesoscale force chains increase the strength of the sample. This is also apparent in three-dimensional finite element calculations of drop-weight test simulations using LS-Dyna despite a higher granular bulk coordination number, and an increased mobility of individual grains.

A Semi-implicit Method for Time Accurate Simulation of Compressible Flow

NASA Astrophysics Data System (ADS)

Wall, Clifton; Pierce, Charles D.; Moin, Parviz

2001-11-01

A semi-implicit method for time accurate simulation of compressible flow is presented. The method avoids the acoustic CFL limitation, allowing a time step restricted only by the convective velocity. Centered discretization in both time and space allows the method to achieve zero artificial attenuation of acoustic waves. The method is an extension of the standard low Mach number pressure correction method to the compressible Navier-Stokes equations, and the main feature of the method is the solution of a Helmholtz type pressure correction equation similar to that of Demirdžić et al. (Int. J. Num. Meth. Fluids, Vol. 16, pp. 1029-1050, 1993). The method is attractive for simulation of acoustic combustion instabilities in practical combustors. In these flows, the Mach number is low; therefore the time step allowed by the convective CFL limitation is significantly larger than that allowed by the acoustic CFL limitation, resulting in significant efficiency gains. Also, the method's property of zero artificial attenuation of acoustic waves is important for accurate simulation of the interaction between acoustic waves and the combustion process. The method has been implemented in a large eddy simulation code, and results from several test cases will be presented.

FEM simulation of the die compaction of pharmaceutical products: influence of visco-elastic phenomena and comparison with experiments.

PubMed

Diarra, Harona; Mazel, Vincent; Busignies, Virginie; Tchoreloff, Pierre

2013-09-10

This work studies the influence of visco-elastic behavior in the finite element method (FEM) modeling of die compaction of pharmaceutical products and how such a visco-elastic behavior may improve the agreement between experimental and simulated compression curves. The modeling of the process was conducted on a pharmaceutical excipient, microcrystalline cellulose (MCC), by using Drucker-Prager cap model coupled with creep behavior in Abaqus(®) software. The experimental data were obtained on a compaction simulator (STYLCAM 200R). The elastic deformation of the press was determined by performing experimental tests on a calibration disk and was introduced in the simulation. Numerical optimization was performed to characterize creep parameters. The use of creep behavior in the simulations clearly improved the agreement between the numerical and experimental compression curves (stresses, thickness), mainly during the unloading part of the compaction cycle. For the first time, it was possible to reproduce numerically the fact that the minimum tablet thickness is not obtained at the maximum compression stress. This study proves that creep behavior must be taken into account when modeling the compaction of pharmaceutical products using FEM methods. Copyright © 2013 Elsevier B.V. All rights reserved.

Development of laboratory test methods to replace the simulated high-temperature grout fluidity test : [summary].

DOT National Transportation Integrated Search

2014-06-01

Concretes remarkable role in construction depends on its marriage with reinforcing steel. Concrete is very strong in compression, but weak in tension, so reinforcing steel is added to increase tensile strength, yielding structural components capab...

The benefits of a simplified method for CPR training of medical professionals: a randomized controlled study.

PubMed

Allan, Katherine S; Wong, Natalie; Aves, Theresa; Dorian, Paul

2013-08-01

We developed and tested a training method for basic life support incorporating defibrillator feedback during simulated cardiac arrest (CA) to determine the impact on the quality and retention of CPR skills. 298 subjects were randomized into 3 groups. All groups received a 2h training session followed by a simulated CA test scenario, immediately after training and at 3 months. Controls used a non-feedback defibrillator during training and testing. Group 1 was trained and tested with an audiovisual feedback defibrillator. During training, Group 1 reviewed quantitative CPR data from the defibrillator. Group 2 was trained as per Group 1, but was tested using the non-feedback defibrillator. The primary outcome was difference in compression depth between groups at initial testing. Secondary outcomes included differences in rate, depth at retesting, compression fraction, and self-assessment. Groups 1 and 2 had significantly deeper compressions than the controls (35.3 ± 7.6 mm, 43.7 ± 5.8 mm, 42.2 ± 6.6 mm for controls, Groups 1 and 2, P=0.001 for Group 1 vs. controls; P=0.001 for Group 2 vs. controls). At three months, CPR depth was maintained in all groups but remained significantly higher in Group 1 (39.1 ± 9.9 mm, 47.0 ± 7.4 mm, 42.2 ± 8.4 mm for controls, Groups 1 and 2, P=0.001 for Group 1 vs. control). No significant differences were noted between groups in compression rate or fraction. A simplified 2h training method using audiovisual feedback combined with quantitative review of CPR performance improved CPR quality and retention of these skills. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Mechanical properties and mechanism of single crystal Cu pillar by in situ TEM compression and molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Lin, Kai-Peng; Fang, Te-Hua; Lin, Ying-Jhin

2018-02-01

In this study, we investigate the mechanical properties of single-crystal copper (Cu) nanopillars. Critical deformation variations of Cu-nanopillared structures are estimated using in situ transmission electron microscopy compression tests and molecular dynamics simulations. The Young’s moduli of Cu nanopillars with diameters of 2-6 nm were 90.20-124.47 GPa. The contact stiffnesses of the Cu nanopillars with diameters of 400 and 500 nm were 1.33 and 3.86 N m-1, respectively; the Poisson’s ratios for these nanopillars were 0.32 and 0.33. The yield strength of the nanopillars varied from 0.25 GPa at 500 nm to 0.42 GPa at 400 nm; the yield strength of single-crystal Cu nanopillars decreased with increasing diameter. The values of the indented hardness of the Cu block were 0.27 and 1.06 GPa, respectively. Through experimental work and molecular dynamics simulations, we demonstrate that Cu nanopillars exhibit internal stress transmission during compression. When compression reaches the maximum strain, it can be observed that Cu slips. Our results are useful for understanding the mechanical properties, contact, and local deformation of Cu nanopillars.

End-to-end communication test on variable length packet structures utilizing AOS testbed

NASA Technical Reports Server (NTRS)

Miller, Warner H.; Sank, V.; Fong, Wai; Miko, J.; Powers, M.; Folk, John; Conaway, B.; Michael, K.; Yeh, Pen-Shu

1994-01-01

This paper describes a communication test, which successfully demonstrated the transfer of losslessly compressed images in an end-to-end system. These compressed images were first formatted into variable length Consultative Committee for Space Data Systems (CCSDS) packets in the Advanced Orbiting System Testbed (AOST). The CCSDS data Structures were transferred from the AOST to the Radio Frequency Simulations Operations Center (RFSOC), via a fiber optic link, where data was then transmitted through the Tracking and Data Relay Satellite System (TDRSS). The received data acquired at the White Sands Complex (WSC) was transferred back to the AOST where the data was captured and decompressed back to the original images. This paper describes the compression algorithm, the AOST configuration, key flight components, data formats, and the communication link characteristics and test results.

Assessment of chemistry models for compressible reacting flows

NASA Astrophysics Data System (ADS)

Lapointe, Simon; Blanquart, Guillaume

2014-11-01

Recent technological advances in propulsion and power devices and renewed interest in the development of next generation supersonic and hypersonic vehicles have increased the need for detailed understanding of turbulence-combustion interactions in compressible reacting flows. In numerical simulations of such flows, accurate modeling of the fuel chemistry is a critical component of capturing the relevant physics. Various chemical models are currently being used in reacting flow simulations. However, the differences between these models and their impacts on the fluid dynamics in the context of compressible flows are not well understood. In the present work, a numerical code is developed to solve the fully coupled compressible conservation equations for reacting flows. The finite volume code is based on the theoretical and numerical framework developed by Oefelein (Prog. Aero. Sci. 42 (2006) 2-37) and employs an all-Mach-number formulation with dual time-stepping and preconditioning. The numerical approach is tested on turbulent premixed flames at high Karlovitz numbers. Different chemical models of varying complexity and computational cost are used and their effects are compared.

Basic life support: evaluation of learning using simulation and immediate feedback devices1.

PubMed

Tobase, Lucia; Peres, Heloisa Helena Ciqueto; Tomazini, Edenir Aparecida Sartorelli; Teodoro, Simone Valentim; Ramos, Meire Bruna; Polastri, Thatiane Facholi

2017-10-30

to evaluate students' learning in an online course on basic life support with immediate feedback devices, during a simulation of care during cardiorespiratory arrest. a quasi-experimental study, using a before-and-after design. An online course on basic life support was developed and administered to participants, as an educational intervention. Theoretical learning was evaluated by means of a pre- and post-test and, to verify the practice, simulation with immediate feedback devices was used. there were 62 participants, 87% female, 90% in the first and second year of college, with a mean age of 21.47 (standard deviation 2.39). With a 95% confidence level, the mean scores in the pre-test were 6.4 (standard deviation 1.61), and 9.3 in the post-test (standard deviation 0.82, p <0.001); in practice, 9.1 (standard deviation 0.95) with performance equivalent to basic cardiopulmonary resuscitation, according to the feedback device; 43.7 (standard deviation 26.86) mean duration of the compression cycle by second of 20.5 (standard deviation 9.47); number of compressions 167.2 (standard deviation 57.06); depth of compressions of 48.1 millimeter (standard deviation 10.49); volume of ventilation 742.7 (standard deviation 301.12); flow fraction percentage of 40.3 (standard deviation 10.03). the online course contributed to learning of basic life support. In view of the need for technological innovations in teaching and systematization of cardiopulmonary resuscitation, simulation and feedback devices are resources that favor learning and performance awareness in performing the maneuvers.

In Vivo Investigation of the Effectiveness of a Hyper-viscoelastic Model in Simulating Brain Retraction

NASA Astrophysics Data System (ADS)

Li, Ping; Wang, Weiwei; Zhang, Chenxi; An, Yong; Song, Zhijian

2016-07-01

Intraoperative brain retraction leads to a misalignment between the intraoperative positions of the brain structures and their previous positions, as determined from preoperative images. In vitro swine brain sample uniaxial tests showed that the mechanical response of brain tissue to compression and extension could be described by the hyper-viscoelasticity theory. The brain retraction caused by the mechanical process is a combination of brain tissue compression and extension. In this paper, we first constructed a hyper-viscoelastic framework based on the extended finite element method (XFEM) to simulate intraoperative brain retraction. To explore its effectiveness, we then applied this framework to an in vivo brain retraction simulation. The simulation strictly followed the clinical scenario, in which seven swine were subjected to brain retraction. Our experimental results showed that the hyper-viscoelastic XFEM framework is capable of simulating intraoperative brain retraction and improving the navigation accuracy of an image-guided neurosurgery system (IGNS).

Implementation of Slater Boundary Condition into OVERFLOW

NASA Astrophysics Data System (ADS)

Duncan, Sean

Bleed is one of the primary methods of controlling the flow within a mixed compression inlet. In this work the Slater boundary condition, first applied in WindUS, is implemented in OVERFLOW. Further, a simulation using discrete holes is run in order to show the differences between use of the boundary condition and use of the bleed hole geometry. Recent tests at Wright Patterson Air Force Base seek to provide a baseline for study of mixed compression inlets. The inlet used by the Air Force Research Laboratory is simulated in the modified OVERFLOW. The results from the experiment are compared to the CFD to qualitatively assess the accuracy of the simulations. The boundary condition is shown to be robust and viable in studying bleed.

Preferred Compression Speed for Speech and Music and Its Relationship to Sensitivity to Temporal Fine Structure.

PubMed

Moore, Brian C J; Sęk, Aleksander

2016-09-07

Multichannel amplitude compression is widely used in hearing aids. The preferred compression speed varies across individuals. Moore (2008) suggested that reduced sensitivity to temporal fine structure (TFS) may be associated with preference for slow compression. This idea was tested using a simulated hearing aid. It was also assessed whether preferences for compression speed depend on the type of stimulus: speech or music. Twenty-two hearing-impaired subjects were tested, and the stimulated hearing aid was fitted individually using the CAM2A method. On each trial, a given segment of speech or music was presented twice. One segment was processed with fast compression and the other with slow compression, and the order was balanced across trials. The subject indicated which segment was preferred and by how much. On average, slow compression was preferred over fast compression, more so for music, but there were distinct individual differences, which were highly correlated for speech and music. Sensitivity to TFS was assessed using the difference limen for frequency at 2000 Hz and by two measures of sensitivity to interaural phase at low frequencies. The results for the difference limens for frequency, but not the measures of sensitivity to interaural phase, supported the suggestion that preference for compression speed is affected by sensitivity to TFS. © The Author(s) 2016.

Pre-compression volume on flow ripple reduction of a piston pump

NASA Astrophysics Data System (ADS)

Xu, Bing; Song, Yuechao; Yang, Huayong

2013-11-01

Axial piston pump with pre-compression volume(PCV) has lower flow ripple in large scale of operating condition than the traditional one. However, there is lack of precise simulation model of the axial piston pump with PCV, so the parameters of PCV are difficult to be determined. A finite element simulation model for piston pump with PCV is built by considering the piston movement, the fluid characteristic(including fluid compressibility and viscosity) and the leakage flow rate. Then a test of the pump flow ripple called the secondary source method is implemented to validate the simulation model. Thirdly, by comparing results among the simulation results, test results and results from other publications at the same operating condition, the simulation model is validated and used in optimizing the axial piston pump with PCV. According to the pump flow ripples obtained by the simulation model with different PCV parameters, the flow ripple is the smallest when the PCV angle is 13°, the PCV volume is 1.3×10-4 m3 at such operating condition that the pump suction pressure is 2 MPa, the pump delivery pressure 15 MPa, the pump speed 1 000 r/min, the swash plate angle 13°. At the same time, the flow ripple can be reduced when the pump suction pressure is 2 MPa, the pump delivery pressure is 5 MPa,15 MPa, 22 MPa, pump speed is 400 r/min, 1 000 r/min, 1 500 r/min, the swash plate angle is 11°, 13°, 15° and 17°, respectively. The finite element simulation model proposed provides a method for optimizing the PCV structure and guiding for designing a quieter axial piston pump.

Constitutive Soil Properties for Unwashed Sand and Kennedy Space Center

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.; Gildea, Martin L.; T'Kindt, Casey M.

2008-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle. This report provides constitutive material models for one soil, unwashed sand, from NASA Langley's gantry drop test facility and three soils from Kennedy Space Center (KSC). The four soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LS-DYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The four soil models are intended to be specific to the soil conditions discussed in the report. The unwashed sand model represents clayey sand at high density. The KSC models represent three distinct coastal sand conditions: low density dry sand, high density in-situ moisture sand, and high density flooded sand. It is possible to approximate other sands with these models, but the results would be unverified without geotechnical tests to confirm similar soil behavior.

Biomechanics of the Proximal Radius Following Drilling of the Bicipital Tuberosity to Mimic Cortical Button Distal Biceps Repair Technique.

PubMed

Oak, Nikhil R; Lien, John R; Brunfeldt, Alexander; Lawton, Jeffrey N

2018-05-01

A fracture through the proximal radius is a theoretical concern after cortical button distal biceps fixation in an active patient. The permanent, nonossified cortical defect and medullary tunnel is at risk during a fall eliciting rotational and compressive forces. We hypothesized that during simulated torsion and compression, in comparison with unaltered specimens, the cortical button distal biceps repair model would have decreased torsional and compressive strength and would fracture in the vicinity of the bicipital tuberosity bone tunnel. Sixteen fourth-generation composite radius Sawbones models were used in this controlled laboratory study. A bone tunnel was created through the bicipital tuberosity to mimic the exact bone tunnel, 8 mm near cortex and 3.2 mm far cortex, made for the BicepsButton distal biceps tendon repair. The radius was then prepared and mounted on either a torsional or compression testing device and compared with undrilled control specimens. Compression tests resulted in average failure loads of 9015.2 N in controls versus 8253.25 N in drilled specimens ( P = .074). Torsional testing resulted in an average failure torque of 27.3 Nm in controls and 19.3 Nm in drilled specimens ( P = .024). Average fracture angle was 35.1° in controls versus 21.1° in drilled. Gross fracture patterns were similar in compression testing; however, in torsional testing all fractures occurred through the bone tunnel in the drilled group. There are weaknesses in the vicinity of the bone tunnel in the proximal radius during biomechanical stress testing which may not be clinically relevant in nature. In cortical button fixation, distal biceps repairs creates a permanent, nonossified cortical defect with tendon interposed in the bone tunnel, which can alter the biomechanical properties of the proximal radius during compressive and torsional loading.

Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

PubMed

Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

2017-01-01

Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

Experimental Characterization of the Energy Absorption of Functionally Graded Foam Filled Tubes Under Axial Crushing Loads

NASA Astrophysics Data System (ADS)

Ebrahimi, Saeed; Vahdatazad, Nader; Liaghat, Gholamhossein

2018-03-01

This paper deals with the energy absorption characterization of functionally graded foam (FGF) filled tubes under axial crushing loads by experimental method. The FGF tubes are filled axially by gradient layers of polyurethane foams with different densities. The mechanical properties of the polyurethane foams are firstly obtained from axial compressive tests. Then, the quasi-static compressive tests are carried out for empty tubes, uniform foam filled tubes and FGF filled tubes. Before to present the experimental test results, a nonlinear FEM simulation of the FGF filled tube is carried out in ABAQUS software to gain more insight into the crush deformation patterns, as well as the energy absorption capability of the FGF filled tube. A good agreement between the experimental and simulation results is observed. Finally, the results of experimental test show that an FGF filled tube has excellent energy absorption capacity compared to the ordinary uniform foam-filled tube with the same weight.

The Lateral Compressive Buckling Performance of Aluminum Honeycomb Panels for Long-Span Hollow Core Roofs

PubMed Central

Zhao, Caiqi; Zheng, Weidong; Ma, Jun; Zhao, Yangjian

2016-01-01

To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS)), lateral compression tests and finite element analyses were employed in this study to examine the lateral compressive buckling performance of this new type of honeycomb panel with different length-to-thickness ratios. The results led to two main conclusions: (1) Under the experimental conditions that were used, honeycomb panels with the same planar dimensions but different thicknesses had the same compressive stiffness immediately before buckling, while the lateral compressive buckling load-bearing capacity initially increased rapidly with an increasing honeycomb core thickness and then approached the same limiting value; (2) The compressive stiffnesses of test pieces with the same thickness but different lengths were different, while the maximum lateral compressive buckling loads were very similar. Overall instability failure is prone to occur in long and flexible honeycomb panels. In addition, the errors between the lateral compressive buckling loads from the experiment and the finite element simulations are within 6%, which demonstrates the effectiveness of the nonlinear finite element analysis and provides a theoretical basis for future analysis and design for this new type of spatial structure. PMID:28773567

Evaluation of multidensity orthotic materials used in footwear for patients with diabetes.

PubMed

Foto, J G; Birke, J A

1998-12-01

Selected combinations of multidensity orthotic materials were tested under simulated walking conditions found in the forefoot of diabetic patients. Materials were compared for therapeutic effectiveness by their stress/strain properties and dynamic compression set. Results showed that all of the multidensity materials experienced losses in performance throughout the testing period of 100,000 cycles, with the greatest losses occurring within the first 10,000 cycles. Of the materials tested, Poron + Plastazote #2 and Spenco + Microcel Puff Lite had the highest dynamic material strain and the lowest dynamic compression set over 100,000 cycles. In comparison, these are better multidensity combinations than the others tested to use as therapeutic orthoses in footwear for diabetic patients.

Mechanical Abuse Simulation and Thermal Runaway Risks of Large-Format Li-ion Batteries

DOE PAGES

Wang, Hsin; Lara-Curzio, Edgar; Rule, Evan; ...

2017-01-11

Internal short circuit of large-format Li-ion cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ~40% maximum compressive loading force during the pinch test. The cell was twisted about 5 degrees to the side by horizontally pulling a wire attached to the anode tab. The combined torsion-compression force created small enough failure at the separator and allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4-6 cells at each state-of-charge (SOC). The 18 Ah LiFePO 4 (LFP)more » and 25 Ah Li(NiMnCo) 1/3O 2 (NMC) cells were tested and the thermal runaway risk (TRR) score system was used to evaluate the safety risk of the cells under the same testing conditions. The aim is to provide the cell manufacturers and end users a tool to compare different designs and safety features.« less

Mechanical Abuse Simulation and Thermal Runaway Risks of Large-Format Li-ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hsin; Lara-Curzio, Edgar; Rule, Evan

Internal short circuit of large-format Li-ion cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ~40% maximum compressive loading force during the pinch test. The cell was twisted about 5 degrees to the side by horizontally pulling a wire attached to the anode tab. The combined torsion-compression force created small enough failure at the separator and allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4-6 cells at each state-of-charge (SOC). The 18 Ah LiFePO 4 (LFP)more » and 25 Ah Li(NiMnCo) 1/3O 2 (NMC) cells were tested and the thermal runaway risk (TRR) score system was used to evaluate the safety risk of the cells under the same testing conditions. The aim is to provide the cell manufacturers and end users a tool to compare different designs and safety features.« less

The development of a performance-enhancing additive for vapor-compression heat pumps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grzyll, L.R.; Scaringe, R.P.; Gottschlich, J.M.

1997-12-31

This paper describes the testing results of a vapor-compression heat pump operating with HFC-134a refrigerant and a performance-enhancing additive. Preliminary bench-top testing of this additive, when added to polyolester (POE) lubricant and HFC-134a refrigerant, showed surprising enhancements to system COP. To further investigate this finding, the authors designed and fabricated a vapor-compression heat pump test stand for the 3--5 ton range. The authors investigated the effect of different concentrations of this additive on various system performance parameters such as cooling capacity, compressor power requirement, pressure ratio, compressor pressure difference, compressor isentropic efficiency, refrigerant flow rate, and heat exchanger performance. Themore » authors investigated various heat source and heat sink conditions to simulate air-conditioning and heat pump operating conditions. To investigate the effect of this additive on compressor lubrication and life, the authors performed compressor life tests (with scroll and reciprocating compressors), and had lubrication wear tests performed with various concentrations of the additive in the POE lubricant.« less

A preliminary investigation of inlet unstart effects on a high-speed civil transport concept

NASA Technical Reports Server (NTRS)

Domack, Christopher S.

1991-01-01

Vehicle motions resulting from a supersonic mixed-compression inlet unstart were examined to determine if the unstart constituted a hazard severe enough to warrant rejection of mixed-compression inlets on high-speed civil transport (HSCT) concepts. A simple kinematic analysis of an inlet unstart during cruise was performed for a Mach 2, 4, 250-passenger HSCT concept using data from a wind-tunnel test of a representative configuration with unstarted inlets simulated. A survey of previously published research on inlet unstart effects, including simulation and flight test data for the YF-12, XB-70, and Concorde aircraft, was conducted to validate the calculated results. It was concluded that, when countered by suitable automatic propulsion and flight control systems, the vehicle dynamics induced by an inlet unstart are not severe enough to preclude the use of mixed-compression inlets on an HSCT from a passenger safety standpoint. The ability to provide suitable automatic controls appears to be within the current state of the art. However, the passenger startle and discomfort caused by the noise, vibration, and cabin motions associated with an inlet unstart remain a concern.

Structural materials from lunar simulants through thermal liquefaction

NASA Technical Reports Server (NTRS)

Desai, Chandra S.; Girdner, Kirsten

1992-01-01

Thermal liquefaction that allows development of intermediate ceramic composites from a lunar simulant with various admixtures is used to develop structural materials for construction on the moon. Bending and compressive properties of resulting composites are obtained from laboratory tests and evaluated with respect to the use of three different types and fibers.

An experimental study of the effects of bodyside compression on forward swept sidewall compression inlets ingesting a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Rodi, Patrick E.

1993-01-01

Forward swept sidewall compression inlets have been tested in the Mach 4 Blowdown Facility at the NASA Langley Research Center to study the effects of bodyside compression surfaces on inlet performance in the presence of an incoming turbulent boundary layer. The measurements include mass flow capture and mean surface pressure distributions obtained during simulated combustion pressure increases downstream of the inlet. The kerosene-lampblack surface tracer technique has been used to obtain patterns of the local wall shear stress direction. Inlet performance is evaluated using starting and unstarting characteristics, mass capture, mean surface pressure distributions and permissible back pressure limits. The results indicate that inlet performance can be improved with selected bodyside compression surfaces placed between the inlet sidewalls.

Design of a CO2 Twin Rotary Compressor for a Heat Pump Water Heater

NASA Astrophysics Data System (ADS)

Ahn, Jong Min; Kim, Woo Young; Kim, Hyun Jin; Cho, Sung Oug; Seo, Jong Cheun

2010-06-01

For a CO2 heat pump water heater, one-stage twin rotary compressor has been designed. As a design tool, computer simulation program for the compressor performance has been made. Validation of the simulation program has been carried out for a bench model compressor in a compressor calorimeter. Cooling capacity and the compressor input power were reasonably well compared between the simulation and the calorimeter test. Good agreement on P-V diagram between the simulation and the test was also obtained. With this validated compressor simulation program, parametric study has been performed to arrive at optimum dimensions for the compression chamber.

Experimental study on foam coverage on simulated longwall roof.

PubMed

Reed, W R; Zheng, Y; Klima, S; Shahan, M R; Beck, T W

2017-01-01

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique's potential for longwall shield dust control.

Experimental study on foam coverage on simulated longwall roof

PubMed Central

Reed, W.R.; Zheng, Y.; Klima, S.; Shahan, M.R.; Beck, T.W.

2018-01-01

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique’s potential for longwall shield dust control. PMID:29563765

Enriched Air Nitrox Breathing Reduces Venous Gas Bubbles after Simulated SCUBA Diving: A Double-Blind Cross-Over Randomized Trial.

PubMed

Souday, Vincent; Koning, Nick J; Perez, Bruno; Grelon, Fabien; Mercat, Alain; Boer, Christa; Seegers, Valérie; Radermacher, Peter; Asfar, Pierre

2016-01-01

To test the hypothesis whether enriched air nitrox (EAN) breathing during simulated diving reduces decompression stress when compared to compressed air breathing as assessed by intravascular bubble formation after decompression. Human volunteers underwent a first simulated dive breathing compressed air to include subjects prone to post-decompression venous gas bubbling. Twelve subjects prone to bubbling underwent a double-blind, randomized, cross-over trial including one simulated dive breathing compressed air, and one dive breathing EAN (36% O2) in a hyperbaric chamber, with identical diving profiles (28 msw for 55 minutes). Intravascular bubble formation was assessed after decompression using pulmonary artery pulsed Doppler. Twelve subjects showing high bubble production were included for the cross-over trial, and all completed the experimental protocol. In the randomized protocol, EAN significantly reduced the bubble score at all time points (cumulative bubble scores: 1 [0-3.5] vs. 8 [4.5-10]; P < 0.001). Three decompression incidents, all presenting as cutaneous itching, occurred in the air versus zero in the EAN group (P = 0.217). Weak correlations were observed between bubble scores and age or body mass index, respectively. EAN breathing markedly reduces venous gas bubble emboli after decompression in volunteers selected for susceptibility for intravascular bubble formation. When using similar diving profiles and avoiding oxygen toxicity limits, EAN increases safety of diving as compared to compressed air breathing. ISRCTN 31681480.

Novel Data Reduction Based on Statistical Similarity

DOE PAGES

Lee, Dongeun; Sim, Alex; Choi, Jaesik; ...

2016-07-18

Applications such as scientific simulations and power grid monitoring are generating so much data quickly that compression is essential to reduce storage requirement or transmission capacity. To achieve better compression, one is often willing to discard some repeated information. These lossy compression methods are primarily designed to minimize the Euclidean distance between the original data and the compressed data. But this measure of distance severely limits either reconstruction quality or compression performance. In this paper, we propose a new class of compression method by redefining the distance measure with a statistical concept known as exchangeability. This approach reduces the storagemore » requirement and captures essential features, while reducing the storage requirement. In this paper, we report our design and implementation of such a compression method named IDEALEM. To demonstrate its effectiveness, we apply it on a set of power grid monitoring data, and show that it can reduce the volume of data much more than the best known compression method while maintaining the quality of the compressed data. Finally, in these tests, IDEALEM captures extraordinary events in the data, while its compression ratios can far exceed 100.« less

The evaluation of upper body muscle activity during the performance of external chest compressions in simulated hypogravity

NASA Astrophysics Data System (ADS)

Krygiel, Rebecca G.; Waye, Abigail B.; Baptista, Rafael Reimann; Heidner, Gustavo Sandri; Rehnberg, Lucas; Russomano, Thais

2014-04-01

BACKGROUND: This original study evaluated the electromyograph (EMG) activity of four upper body muscles: triceps brachii, erector spinae, upper rectus abdominis, and pectoralis major, while external chest compressions (ECCs) were performed in simulated Martian hypogravity using a Body Suspension Device, counterweight system, and standard full body cardiopulmonary resuscitation (CPR) mannequin. METHOD: 20 young, healthy male subjects were recruited. One hundred compressions divided into four sets, with roughly six seconds between each set to indicate 'ventilation', were performed within approximately a 1.5 minute protocol. Chest compression rate, depth and number were measured along with the subject's heart rate (HR) and rating of perceived exertion (RPE). RESULTS: All mean values were used in two-tailed t-tests using SPSS to compare +1 Gz values (control) versus simulated hypogravity values. The AHA (2005) compression standards were maintained in hypogravity. RPE and HR increased by 32% (p < 0.001) and 44% (p = 0.002), respectively, when ECCs were performed during Mars simulation, in comparison to +1 Gz. In hypogravity, the triceps brachii showed significantly less activity (p < 0.001) when compared with the other three muscles studied. The comparison of all the other muscles showed no difference at +1 Gz or in hypogravity. CONCLUSIONS: This study was among the first of its kind, however several limitations were faced which hopefully will not exist in future studies. Evaluation of a great number of muscles will allow space crews to focus on specific strengthening exercises within their current training regimes in case of a serious cardiac event in hypogravity.

Biomechanical analysis of tension band fixation for olecranon fracture treatment.

PubMed

Kozin, S H; Berglund, L J; Cooney, W P; Morrey, B F; An, K N

1996-01-01

This study assessed the strength of various tension band fixation methods with wire and cable applied to simulated olecranon fractures to compare stability and potential failure or complications between the two. Transverse olecranon fractures were simulated by osteotomy. The fracture was anatomically reduced, and various tension band fixation techniques were applied with monofilament wire or multifilament cable. With a material testing machine load displacement curves were obtained and statistical relevance determined by analysis of variance. Two loading modes were tested: loading on the posterior surface of olecranon to simulate triceps pull and loading on the anterior olecranon tip to recreate a potential compressive loading on the fragment during the resistive flexion. All fixation methods were more resistant to posterior loading than to an anterior load. Individual comparative analysis for various loading conditions concluded that tension band fixation is more resilient to tensile forces exerted by the triceps than compressive forces on the anterior olecranon tip. Neither wire passage anterior to the K-wires nor the multifilament cable provided statistically significant increased stability.

Determining Tension-Compression Nonlinear Mechanical Properties of Articular Cartilage from Indentation Testing.

PubMed

Chen, Xingyu; Zhou, Yilu; Wang, Liyun; Santare, Michael H; Wan, Leo Q; Lu, X Lucas

2016-04-01

The indentation test is widely used to determine the in situ biomechanical properties of articular cartilage. The mechanical parameters estimated from the test depend on the constitutive model adopted to analyze the data. Similar to most connective tissues, the solid matrix of cartilage displays different mechanical properties under tension and compression, termed tension-compression nonlinearity (TCN). In this study, cartilage was modeled as a porous elastic material with either a conewise linear elastic matrix with cubic symmetry or a solid matrix reinforced by a continuous fiber distribution. Both models are commonly used to describe the TCN of cartilage. The roles of each mechanical property in determining the indentation response of cartilage were identified by finite element simulation. Under constant loading, the equilibrium deformation of cartilage is mainly dependent on the compressive modulus, while the initial transient creep behavior is largely regulated by the tensile stiffness. More importantly, altering the permeability does not change the shape of the indentation creep curves, but introduces a parallel shift along the horizontal direction on a logarithmic time scale. Based on these findings, a highly efficient curve-fitting algorithm was designed, which can uniquely determine the three major mechanical properties of cartilage (compressive modulus, tensile modulus, and permeability) from a single indentation test. The new technique was tested on adult bovine knee cartilage and compared with results from the classic biphasic linear elastic curve-fitting program.

Numerical simulation of a relaxation test designed to fit a quasi-linear viscoelastic model for temporomandibular joint discs.

PubMed

Commisso, Maria S; Martínez-Reina, Javier; Mayo, Juana; Domínguez, Jaime

2013-02-01

The main objectives of this work are: (a) to introduce an algorithm for adjusting the quasi-linear viscoelastic model to fit a material using a stress relaxation test and (b) to validate a protocol for performing such tests in temporomandibular joint discs. This algorithm is intended for fitting the Prony series coefficients and the hyperelastic constants of the quasi-linear viscoelastic model by considering that the relaxation test is performed with an initial ramp loading at a certain rate. This algorithm was validated before being applied to achieve the second objective. Generally, the complete three-dimensional formulation of the quasi-linear viscoelastic model is very complex. Therefore, it is necessary to design an experimental test to ensure a simple stress state, such as uniaxial compression to facilitate obtaining the viscoelastic properties. This work provides some recommendations about the experimental setup, which are important to follow, as an inadequate setup could produce a stress state far from uniaxial, thus, distorting the material constants determined from the experiment. The test considered is a stress relaxation test using unconfined compression performed in cylindrical specimens extracted from temporomandibular joint discs. To validate the experimental protocol, the test was numerically simulated using finite-element modelling. The disc was arbitrarily assigned a set of quasi-linear viscoelastic constants (c1) in the finite-element model. Another set of constants (c2) was obtained by fitting the results of the simulated test with the proposed algorithm. The deviation of constants c2 from constants c1 measures how far the stresses are from the uniaxial state. The effects of the following features of the experimental setup on this deviation have been analysed: (a) the friction coefficient between the compression plates and the specimen (which should be as low as possible); (b) the portion of the specimen glued to the compression plates (smaller areas glued are better); and (c) the variation in the thickness of the specimen. The specimen's faces should be parallel to ensure a uniaxial stress state. However, this is not possible in real specimens, and a criterion must be defined to accept the specimen in terms of the specimen's thickness variation and the deviation of the fitted constants arising from such a variation.

A Comparison of Ignition Characteristics of Diesel Fuels as Determined in Engines and in a Constant-volume Bomb

NASA Technical Reports Server (NTRS)

Selden, Robert F

1939-01-01

Ignition-lag data have been obtained for seven fuels injected into heated, compressed air under conditions simulating those in a compression-ignition engine. The results of the bomb tests have been compared with similar engine data, and the differences between the two sets of results are explained in terms of the response of each fuel to variations in air density and temperature.

Simulation of breast compression in mammography using finite element analysis: A preliminary study

NASA Astrophysics Data System (ADS)

Liu, Yan-Lin; Liu, Pei-Yuan; Huang, Mei-Lan; Hsu, Jui-Ting; Han, Ruo-Ping; Wu, Jay

2017-11-01

Adequate compression during mammography lowers the absorbed dose in the breast and improves the image quality. The compressed breast thickness (CBT) is affected by various factors, such as breast volume, glandularity, and compression force. In this study, we used the finite element analysis to simulate breast compression and deformation and validated the simulated CBT with clinical mammography results. Image data from ten subjects who had undergone mammography screening and breast magnetic resonance imaging (MRI) were collected, and their breast models were created according to the MR images. The non-linear tissue deformation under 10-16 daN in the cranial-caudal direction was simulated. When the clinical compression force was used, the simulated CBT ranged from 2.34 to 5.90 cm. The absolute difference between the simulated CBT and the clinically measured CBT ranged from 0.5 to 7.1 mm. The simulated CBT had a strong positive linear relationship to breast volume and a weak negative correlation to glandularity. The average simulated CBT under 10, 12, 14, and 16 daN was 5.68, 5.12, 4.67, and 4.25 cm, respectively. Through this study, the relationships between CBT, breast volume, glandularity, and compression force are provided for use in clinical mammography.

A high-compression electron gun for C6+ production: concept, simulations and mechanical design

NASA Astrophysics Data System (ADS)

Mertzig, Robert; Breitenfeldt, M.; Mathot, S.; Pitters, J.; Shornikov, A.; Wenander, F.

2017-07-01

In this paper we report on simulations and the mechanical design of a high-compression electron gun for an Electron Beam Ion Source (EBIS) dedicated for production of high intensity and high repetition rate pulses of bare carbon ions for injection into linac-based hadron therapy facilities. The gun is presently under construction at CERN to be retrofitted into the TwinEBIS test bench for experimental studies. We describe the design constraints, show results of numeric simulations and report on the mechanical design featuring several novel ideas. The reported design makes use of combined-function units with reduced number of mechanical joints that were carefully controlled and tuned during the manufacturing phase. The simulations addressed a wide range of topics including the influence of thermal effects, focusing optics, symmetry-breaking misalignments and injection into a full 5 T field.

On time discretizations for the simulation of the batch settling-compression process in one dimension.

PubMed

Bürger, Raimund; Diehl, Stefan; Mejías, Camilo

2016-01-01

The main purpose of the recently introduced Bürger-Diehl simulation model for secondary settling tanks was to resolve spatial discretization problems when both hindered settling and the phenomena of compression and dispersion are included. Straightforward time integration unfortunately means long computational times. The next step in the development is to introduce and investigate time-integration methods for more efficient simulations, but where other aspects such as implementation complexity and robustness are equally considered. This is done for batch settling simulations. The key findings are partly a new time-discretization method and partly its comparison with other specially tailored and standard methods. Several advantages and disadvantages for each method are given. One conclusion is that the new linearly implicit method is easier to implement than another one (semi-implicit method), but less efficient based on two types of batch sedimentation tests.

COMPRESSIVE FATIGUE IN TITANIUM DENTAL IMPLANTS SUBMITTED TO FLUORIDE IONS ACTION

PubMed Central

Ribeiro, Ana Lúcia Roselino; Noriega, Jorge Roberto; Dametto, Fábio Roberto; Vaz, Luís Geraldo

2007-01-01

The aim of this study was to assess the influence of a fluoridated medium on the mechanical properties of an internal hexagon implant-abutment set, by means of compression, mechanical cycling and metallographic characterization by scanning electronic microscopy. Five years of regular use of oral hygiene with a sodium fluoride solution content of 1500 ppm were simulated, immersing the samples in this medium for 184 hours, with the solutions being changed every 12 hours. Data were analyzed at a 95% confidence level with Fisher's exact test. After the action of fluoride ions, a negative influence occurred in the mechanical cycling test performed in a servohydraulic machine (Material Test System-810) set to a frequency of 15 Hz with 100,000 cycles and programmed to 60% of the maximum resistance of static compression test. The sets tended to fracture by compression on the screw, characterized by mixed ruptures with predominance of fragile fracture, as observed by microscopy. An evidence of corrosion by pitting on sample surfaces was found after the fluoride ions action. It may be concluded that prolonged contact with fluoride ions is harmful to the mechanical properties of commercially pure titanium structures. PMID:19089148

Modeling of video compression effects on target acquisition performance

NASA Astrophysics Data System (ADS)

Cha, Jae H.; Preece, Bradley; Espinola, Richard L.

2009-05-01

The effect of video compression on image quality was investigated from the perspective of target acquisition performance modeling. Human perception tests were conducted recently at the U.S. Army RDECOM CERDEC NVESD, measuring identification (ID) performance on simulated military vehicle targets at various ranges. These videos were compressed with different quality and/or quantization levels utilizing motion JPEG, motion JPEG2000, and MPEG-4 encoding. To model the degradation on task performance, the loss in image quality is fit to an equivalent Gaussian MTF scaled by the Structural Similarity Image Metric (SSIM). Residual compression artifacts are treated as 3-D spatio-temporal noise. This 3-D noise is found by taking the difference of the uncompressed frame, with the estimated equivalent blur applied, and the corresponding compressed frame. Results show good agreement between the experimental data and the model prediction. This method has led to a predictive performance model for video compression by correlating various compression levels to particular blur and noise input parameters for NVESD target acquisition performance model suite.

Effects of video compression on target acquisition performance

NASA Astrophysics Data System (ADS)

Espinola, Richard L.; Cha, Jae; Preece, Bradley

2008-04-01

The bandwidth requirements of modern target acquisition systems continue to increase with larger sensor formats and multi-spectral capabilities. To obviate this problem, still and moving imagery can be compressed, often resulting in greater than 100 fold decrease in required bandwidth. Compression, however, is generally not error-free and the generated artifacts can adversely affect task performance. The U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate recently performed an assessment of various compression techniques on static imagery for tank identification. In this paper, we expand this initial assessment by studying and quantifying the effect of various video compression algorithms and their impact on tank identification performance. We perform a series of controlled human perception tests using three dynamic simulated scenarios: target moving/sensor static, target static/sensor static, sensor tracking the target. Results of this study will quantify the effect of video compression on target identification and provide a framework to evaluate video compression on future sensor systems.

Effects of hot compression deformation temperature on the microstructure and properties of Al-Zr-La alloys

NASA Astrophysics Data System (ADS)

Yue, Xian-hua; Liu, Chun-fang; Liu, Hui-hua; Xiao, Su-fen; Tang, Zheng-hua; Tang, Tian

2018-02-01

The main goal of this study is to investigate the microstructure and electrical properties of Al-Zr-La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al3Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.

Mechanical and structural characteristics of the new BONE-LOK cortical-cancellous internal fixation device.

PubMed

Cachia, Victor V; Culbert, Brad; Warren, Chris; Oka, Richard; Mahar, Andrew

2003-01-01

The purpose of this study was to evaluate the structural and mechanical characteristics of a new and unique titanium cortical-cancellous helical compression anchor with BONE-LOK (Triage Medical, Inc., Irvine, CA) technology for compressive internal fixation of fractures and osteotomies. This device provides fixation through the use of a distal helical anchor and a proximal retentive collar that are united by an axially movable pin (U.S. and international patents issued and pending). The helical compression anchor (2.7-mm diameter) was compared with 3.0-mm diameter titanium cancellous screws (Synthes, Paoli, PA) for pullout strength and compression in 7# and 12# synthetic rigid polyurethane foam (simulated bone matrix), and for 3-point bending stiffness. The following results (mean +/- standard deviation) were obtained: foam block pullout strength in 12# foam: 2.7-mm helical compression anchor 70 +/- 2.0 N and 3.0-mm titanium cancellous screws 37 +/- 11 N; in 7# foam: 2.7-mm helical compression anchor 33 +/- 3 N and 3.0-mm titanium cancellous screws 31 +/- 12 N. Three-point bending stiffness, 2.7-mm helical compression anchor 988 +/- 68 N/mm and 3.0-mm titanium cancellous screws 845 +/- 88 N/mm. Compression strength testing in 12# foam: 2.7-mm helical compression anchor 70.8 +/- 4.8 N and 3.0-mm titanium cancellous screws 23.0 +/- 3.1 N, in 7# foam: 2.7-mm helical compression anchor 42.6 +/- 3.2 N and 3.0-mm titanium cancellous screws 10.4 +/- 0.9 N. Results showed greater pullout strength, 3-point bending stiffness, and compression strength for the 2.7-mm helical compression anchor as compared with the 3.0-mm titanium cancellous screws in these testing models. This difference represents a distinct advantage in the new device that warrants further in vivo testing.

Possibilities of rock constitutive modelling and simulations

NASA Astrophysics Data System (ADS)

Baranowski, Paweł; Małachowski, Jerzy

2018-01-01

The paper deals with a problem of rock finite element modelling and simulation. The main intention of authors was to present possibilities of different approaches in case of rock constitutive modelling. For this purpose granite rock was selected, due to its wide mechanical properties recognition and prevalence in literature. Two significantly different constitutive material models were implemented to simulate the granite fracture in various configurations: Johnson - Holmquist ceramic model which is very often used for predicting rock and other brittle materials behavior, and a simple linear elastic model with a brittle failure which can be used for simulating glass fracturing. Four cases with different loading conditions were chosen to compare the aforementioned constitutive models: uniaxial compression test, notched three-point-bending test, copper ball impacting a block test and small scale blasting test.

A new constitutive model for simulation of softening, plateau, and densification phenomena for trabecular bone under compression.

PubMed

Lee, Chi-Seung; Lee, Jae-Myung; Youn, BuHyun; Kim, Hyung-Sik; Shin, Jong Ki; Goh, Tae Sik; Lee, Jung Sub

2017-01-01

A new type of constitutive model and its computational implementation procedure for the simulation of a trabecular bone are proposed in the present study. A yield surface-independent Frank-Brockman elasto-viscoplastic model is introduced to express the nonlinear material behavior such as softening beyond yield point, plateau, and densification under compressive loads. In particular, the hardening- and softening-dominant material functions are introduced and adopted in the plastic multiplier to describe each nonlinear material behavior separately. In addition, the elasto-viscoplastic model is transformed into an implicit type discrete model, and is programmed as a user-defined material subroutine in commercial finite element analysis code. In particular, the consistent tangent modulus method is proposed to improve the computational convergence and to save computational time during finite element analysis. Through the developed material library, the nonlinear stress-strain relationship is analyzed qualitatively and quantitatively, and the simulation results are compared with the results of compression test on the trabecular bone to validate the proposed constitutive model, computational method, and material library. Copyright © 2016 Elsevier Ltd. All rights reserved.

Development of real time abdominal compression force monitoring and visual biofeedback system

NASA Astrophysics Data System (ADS)

Kim, Tae-Ho; Kim, Siyong; Kim, Dong-Su; Kang, Seong-Hee; Cho, Min-Seok; Kim, Kyeong-Hyeon; Shin, Dong-Seok; Suh, Tae-Suk

2018-03-01

In this study, we developed and evaluated a system that could monitor abdominal compression force (ACF) in real time and provide a surrogating signal, even under abdominal compression. The system could also provide visual-biofeedback (VBF). The real-time ACF monitoring system developed consists of an abdominal compression device, an ACF monitoring unit and a control system including an in-house ACF management program. We anticipated that ACF variation information caused by respiratory abdominal motion could be used as a respiratory surrogate signal. Four volunteers participated in this test to obtain correlation coefficients between ACF variation and tidal volumes. A simulation study with another group of six volunteers was performed to evaluate the feasibility of the proposed system. In the simulation, we investigated the reproducibility of the compression setup and proposed a further enhanced shallow breathing (ESB) technique using VBF by intentionally reducing the amplitude of the breathing range under abdominal compression. The correlation coefficient between the ACF variation caused by the respiratory abdominal motion and the tidal volume signal for each volunteer was evaluated and R 2 values ranged from 0.79 to 0.84. The ACF variation was similar to a respiratory pattern and slight variations of ACF ranges were observed among sessions. About 73-77% average ACF control rate (i.e. compliance) over five trials was observed in all volunteer subjects except one (64%) when there was no VBF. The targeted ACF range was intentionally reduced to achieve ESB for VBF simulation. With VBF, in spite of the reduced target range, overall ACF control rate improved by about 20% in all volunteers except one (4%), demonstrating the effectiveness of VBF. The developed monitoring system could help reduce the inter-fraction ACF set up error and the intra fraction ACF variation. With the capability of providing a real time surrogating signal and VBF under compression, it could improve the quality of respiratory tumor motion management in abdominal compression radiation therapy.

Simulations of free shear layers using a compressible k-epsilon model

NASA Technical Reports Server (NTRS)

Yu, S. T.; Chang, C. T.; Marek, C. J.

1991-01-01

A two-dimensional, compressible Navier-Stokes equations with a k-epsilon turbulence model are solved numerically to simulate the flows of compressible free shear layers. The appropriate form of k and epsilon equations for compressible flows are discussed. Sarkar's modeling is adopted to simulate the compressibility effects in the k and epsilon equations. The numerical results show that the spreading rate of the shear layers decreases with increasing convective Mach number. In addition, favorable comparison was found between the calculated results and Goebel and Dutton's experimental data.

Simulations of free shear layers using a compressible kappa-epsilon model

NASA Technical Reports Server (NTRS)

Yu, S. T.; Chang, C. T.; Marek, C. J.

1991-01-01

A two-dimensional, compressible Navier-Stokes equation with a k-epsilon turbulence model is solved numerically to simulate the flow of a compressible free shear layer. The appropriate form of k and epsilon equations for compressible flow is discussed. Sarkar's modeling is adopted to simulate the compressibility effects in the k and epsilon equations. The numerical results show that the spreading rate of the shear layers decreases with increasing convective Mach number. In addition, favorable comparison was found between the calculated results and experimental data.

Graphs of Soil Mechanics Tests in Orbit

NASA Technical Reports Server (NTRS)

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Compression Strength of Sulfur Concrete Subjected to Extreme Cold

NASA Technical Reports Server (NTRS)

Grugel, Richard N.

2008-01-01

Sulfur concrete cubes were cycled between liquid nitrogen and room temperature to simulate extreme exposure conditions. Subsequent compression testing showed the strength of cycled samples to be roughly five times less than those non-cycled. Fracture surface examination showed de-bonding of the sulfur from the aggregate material in the cycled samples but not in those non-cycled. The large discrepancy found, between the samples is attributed to the relative thermal properties of the materials constituting the concrete.

In Vivo Investigation of the Effectiveness of a Hyper-viscoelastic Model in Simulating Brain Retraction

PubMed Central

Li, Ping; Wang, Weiwei; Zhang, Chenxi; An, Yong; Song, Zhijian

2016-01-01

Intraoperative brain retraction leads to a misalignment between the intraoperative positions of the brain structures and their previous positions, as determined from preoperative images. In vitro swine brain sample uniaxial tests showed that the mechanical response of brain tissue to compression and extension could be described by the hyper-viscoelasticity theory. The brain retraction caused by the mechanical process is a combination of brain tissue compression and extension. In this paper, we first constructed a hyper-viscoelastic framework based on the extended finite element method (XFEM) to simulate intraoperative brain retraction. To explore its effectiveness, we then applied this framework to an in vivo brain retraction simulation. The simulation strictly followed the clinical scenario, in which seven swine were subjected to brain retraction. Our experimental results showed that the hyper-viscoelastic XFEM framework is capable of simulating intraoperative brain retraction and improving the navigation accuracy of an image-guided neurosurgery system (IGNS). PMID:27387301

Numerical simulation of unmanned aerial vehicle under centrifugal load and optimization of milling and planing

NASA Astrophysics Data System (ADS)

Chen, Yunsheng; Lu, Xinghua

2018-05-01

The mechanical parts of the fuselage surface of the UAV are easily fractured by the action of the centrifugal load. In order to improve the compressive strength of UAV and guide the milling and planing of mechanical parts, a numerical simulation method of UAV fuselage compression under centrifugal load based on discrete element analysis method is proposed. The three-dimensional discrete element method is used to establish the splitting tensile force analysis model of the UAV fuselage under centrifugal loading. The micro-contact connection parameters of the UAV fuselage are calculated, and the yield tensile model of the mechanical components is established. The dynamic and static mechanical model of the aircraft fuselage milling is analyzed by the axial amplitude vibration frequency combined method. The correlation parameters of the cutting depth on the tool wear are obtained. The centrifugal load stress spectrum of the surface of the UAV is calculated. The meshing and finite element simulation of the rotor blade of the unmanned aerial vehicle is carried out to optimize the milling process. The test results show that the accuracy of the anti - compression numerical test of the UAV is higher by adopting the method, and the anti - fatigue damage capability of the unmanned aerial vehicle body is improved through the milling and processing optimization, and the mechanical strength of the unmanned aerial vehicle can be effectively improved.

Stability Analysis of Intertank Formed Skin/Stringer Compression Panel with Simulated Damage

NASA Technical Reports Server (NTRS)

Harper, David W.; Wingate, Robert J.

2012-01-01

The External Tank (ET) is a component of the Space Shuttle launch vehicle that contains fuel and oxidizer. During launch, the ET supplies the space shuttle main engines with liquid hydrogen and liquid oxygen. In addition to supplying fuel and oxidizer, it is the backbone structural component of the Space Shuttle. It is comprised of a liquid hydrogen (LH2) tank and a liquid oxygen (LOX) tank, which are separated by an Intertank. The Intertank is a stringer-stiffened cylindrical structure with hat-section stringers that are roll formed from aluminum-lithium alloy Al-2090. Cracks in the Intertank stringers of the STS-133 ET were noticed after a November 5, 2010 launch attempt. The cracks were approximately nine inches long and occurred on the forward end of the Intertank (near the LOX tank), along the fastener line, and were believed to have occurred while loading the ET with the cryogenic propellants. These cracks generated questions about the structural integrity of the Intertank. In order to determine the structural capability of the Intertank with varying degrees of damage, a finite element model (FEM) simulating a 1995 compression panel test was analyzed and correlated to test data. Varying degrees of damage were simulated in the FEM, and non-linear stability analyses were performed. The high degree of similarity between the compression panel and the Intertank provided confidence that the ET Intertank would have similar capabilities.

Material Characterization and Computer Model Simulation of Low Density Polyurethane Foam Used in a Rodent Traumatic Brain Injury Model

PubMed Central

Zhang, Liying; Gurao, Manish; Yang, King H.; King, Albert I.

2011-01-01

Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou’s impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou’s impact device, has not been fully characterized. The foam used in Marmarou’s device was tested at seven strain rates ranging from quasi-static to dynamic (0.014 ~ 42.86 s−1) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam. PMID:21459114

Material characterization and computer model simulation of low density polyurethane foam used in a rodent traumatic brain injury model.

PubMed

Zhang, Liying; Gurao, Manish; Yang, King H; King, Albert I

2011-05-15

Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou's impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou's impact device, has not been fully characterized. The foam used in Marmarou's device was tested at seven strain rates ranging from quasi-static to dynamic (0.014-42.86 s⁻¹) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam. Copyright © 2011 Elsevier B.V. All rights reserved.

Fragmentation modeling of a resin bonded sand

NASA Astrophysics Data System (ADS)

Hilth, William; Ryckelynck, David

2017-06-01

Cemented sands exhibit a complex mechanical behavior that can lead to sophisticated models, with numerous parameters without real physical meaning. However, using a rather simple generalized critical state bonded soil model has proven to be a relevant compromise between an easy calibration and good results. The constitutive model formulation considers a non-associated elasto-plastic formulation within the critical state framework. The calibration procedure, using standard laboratory tests, is complemented by the study of an uniaxial compression test observed by tomography. Using finite elements simulations, this test is simulated considering a non-homogeneous 3D media. The tomography of compression sample gives access to 3D displacement fields by using image correlation techniques. Unfortunately these fields have missing experimental data because of the low resolution of correlations for low displacement magnitudes. We propose a recovery method that reconstructs 3D full displacement fields and 2D boundary displacement fields. These fields are mandatory for the calibration of the constitutive parameters by using 3D finite element simulations. The proposed recovery technique is based on a singular value decomposition of available experimental data. This calibration protocol enables an accurate prediction of the fragmentation of the specimen.

Contribution of actin filaments to the global compressive properties of fibroblasts.

PubMed

Ujihara, Yoshihiro; Nakamura, Masanori; Miyazaki, Hiroshi; Wada, Shigeo

2012-10-01

Actin filaments are often regarded as tension-bearing components. Here, we examined the effects of actin filaments on global compressive properties of cells experimentally and numerically. Fibroblasts were harvested from the patellar tendon of a mature Japanese white rabbit and treated with cytochalasin D to depolymerize the actin filaments. Intact cells and cells with disrupted actin filaments were subjected to the compressive tests. Each floating cell was held between the cantilever and compressive plates and compressed by moving the compressive plate with a linear actuator to obtain a load-deformation curve under quasi-static conditions. The experimental results demonstrated that the initial stiffness of a cell with disrupted actin filaments decreased by 51%. After the experiments, we simulated the compressive test of cells with/without bundles of actin filaments. A bundle of actin filaments was modeled as a tension-bearing component that generates a force based on Hooke's law only when it was elongated. By contrast, if it was shortened, it was assumed to exert no force. The computational results revealed that the alignment of bundles of actin filaments significantly affected the cell stiffness. In addition, the passive reorientation of bundles of actin filaments perpendicular to the compression induced an increase in the resistance to the vertical elongation of a cell and thereby increased the cell stiffness. These results clearly indicated that bundles of actin filaments contribute to the compressive properties of a cell, even if they are tension-bearing components. Copyright © 2012 Elsevier Ltd. All rights reserved.

Model test on partial expansion in stratified subsidence during foundation pit dewatering

NASA Astrophysics Data System (ADS)

Wang, Jianxiu; Deng, Yansheng; Ma, Ruiqiang; Liu, Xiaotian; Guo, Qingfeng; Liu, Shaoli; Shao, Yule; Wu, Linbo; Zhou, Jie; Yang, Tianliang; Wang, Hanmei; Huang, Xinlei

2018-02-01

Partial expansion was observed in stratified subsidence during foundation pit dewatering. However, the phenomenon was suspected to be an error because the compression of layers is known to occur when subsidence occurs. A slice of the subsidence cone induced by drawdown was selected as the prototype. Model tests were performed to investigate the phenomenon. The underlying confined aquifer was generated as a movable rigid plate with a hinge at one end. The overlying layers were simulated with remolded materials collected from a construction site. Model tests performed under the conceptual model indicated that partial expansion occurred in stratified settlements under coordination deformation and consolidation conditions. During foundation pit dewatering, rapid drawdown resulted in rapid subsidence in the dewatered confined aquifer. The rapidly subsiding confined aquifer top was the bottom deformation boundary of the overlying layers. Non-coordination deformation was observed at the top and bottom of the subsiding overlying layers. The subsidence of overlying layers was larger at the bottom than at the top. The layers expanded and became thicker. The phenomenon was verified using numerical simulation method based on finite difference method. Compared with numerical simulation results, the boundary effect of the physical tests was obvious in the observation point close to the movable endpoint. The tensile stress of the overlying soil layers induced by the underlying settlement of dewatered confined aquifer contributed to the expansion phenomenon. The partial expansion of overlying soil layers was defined as inversed rebound. The inversed rebound was induced by inversed coordination deformation. Compression was induced by the consolidation in the overlying soil layers because of drainage. Partial expansion occurred when the expansion exceeded the compression. Considering the inversed rebound, traditional layer-wise summation method for calculating subsidence should be revised and improved.

Mechanical characterization of human brain tissue.

PubMed

Budday, S; Sommer, G; Birkl, C; Langkammer, C; Haybaeck, J; Kohnert, J; Bauer, M; Paulsen, F; Steinmann, P; Kuhl, E; Holzapfel, G A

2017-01-15

Mechanics are increasingly recognized to play an important role in modulating brain form and function. Computational simulations are a powerful tool to predict the mechanical behavior of the human brain in health and disease. The success of these simulations depends critically on the underlying constitutive model and on the reliable identification of its material parameters. Thus, there is an urgent need to thoroughly characterize the mechanical behavior of brain tissue and to identify mathematical models that capture the tissue response under arbitrary loading conditions. However, most constitutive models have only been calibrated for a single loading mode. Here, we perform a sequence of multiple loading modes on the same human brain specimen - simple shear in two orthogonal directions, compression, and tension - and characterize the loading-mode specific regional and directional behavior. We complement these three individual tests by combined multiaxial compression/tension-shear tests and discuss effects of conditioning and hysteresis. To explore to which extent the macrostructural response is a result of the underlying microstructural architecture, we supplement our biomechanical tests with diffusion tensor imaging and histology. We show that the heterogeneous microstructure leads to a regional but not directional dependence of the mechanical properties. Our experiments confirm that human brain tissue is nonlinear and viscoelastic, with a pronounced compression-tension asymmetry. Using our measurements, we compare the performance of five common constitutive models, neo-Hookean, Mooney-Rivlin, Demiray, Gent, and Ogden, and show that only the isotropic modified one-term Ogden model is capable of representing the hyperelastic behavior under combined shear, compression, and tension loadings: with a shear modulus of 0.4-1.4kPa and a negative nonlinearity parameter it captures the compression-tension asymmetry and the increase in shear stress under superimposed compression but not tension. Our results demonstrate that material parameters identified for a single loading mode fail to predict the response under arbitrary loading conditions. Our systematic characterization of human brain tissue will lead to more accurate computational simulations, which will allow us to determine criteria for injury, to develop smart protection systems, and to predict brain development and disease progression. There is a pressing need to characterize the mechanical behavior of human brain tissue under multiple loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We perform a sequence of experimental tests on the same brain specimen to characterize the regional and directional behavior, and we supplement our tests with DTI and histology to explore to which extent the macrostructural response is a result of the underlying microstructure. Results demonstrate that human brain tissue is nonlinear and viscoelastic, with a pronounced compression-tension asymmetry, and we show that the multiaxial data can best be captured by a modified version of the one-term Ogden model. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Test code for the assessment and improvement of Reynolds stress models

NASA Technical Reports Server (NTRS)

Rubesin, M. W.; Viegas, J. R.; Vandromme, D.; Minh, H. HA

1987-01-01

An existing two-dimensional, compressible flow, Navier-Stokes computer code, containing a full Reynolds stress turbulence model, was adapted for use as a test bed for assessing and improving turbulence models based on turbulence simulation experiments. To date, the results of using the code in comparison with simulated channel flow and over an oscillating flat plate have shown that the turbulence model used in the code needs improvement for these flows. It is also shown that direct simulation of turbulent flows over a range of Reynolds numbers are needed to guide subsequent improvement of turbulence models.

Comparison and Tensorial Formulation of Inelastic Constitutive Models of Salt Rock Behaviour and Efficient Numerical Implementatio

NASA Astrophysics Data System (ADS)

Nagel, T.; Böttcher, N.; Görke, U. J.; Kolditz, O.

2014-12-01

The design process of geotechnical installations includes the application of numerical simulation tools for safety assessment, dimensioning and long term effectiveness estimations. Underground salt caverns can be used for the storage of natural gas, hydrogen, oil, waste or compressed air. For their design one has to take into account fluctuating internal pressures due to different levels of filling, the stresses imposed by the surrounding rock mass, irregular geometries and possibly heterogeneous material properties [3] in order to estimate long term cavern convergence as well as locally critical wall stresses. Constitutive models applied to rock salt are usually viscoplastic in nature and most often based on a Burgers-type rheological model extended by non-linear viscosity functions and/or plastic friction elements. Besides plastic dilatation, healing and damage are sometimes accounted for as well [2]. The scales of the geotechnical system to be simulated and the laboratory tests from which material parameters are determined are vastly different. The most common material testing modalities to determine material parameters in geoengineering are the uniaxial and the triaxial compression tests. Some constitutive formulations in widespread use are formulated based on equivalent rather than tensorial quantities valid under these specific test conditions and are subsequently applied to heterogeneous underground systems and complex 3D load cases. We show here that this procedure is inappropriate and can lead to erroneous results. We further propose alternative formulations of the constitutive models in question that restore their validity under arbitrary loading conditions. For an efficient numerical simulation, the discussed constitutive models are integrated locally with a Newton-Raphson algorithm that directly provides the algorithmically consistent tangent matrix for the global Newton iteration of the displacement based finite element formulation. Finally, the finite element implementations of the proposed constitutive formulations are employed to simulate an underground salt cavern used for compressed air energy storage with OpenGeoSys [1]. Transient convergence and stress fields are evaluated for typical fluctuating operation pressure regimes.

Evaluation of a method for enhancing interaural level differences at low frequencies.

PubMed

Moore, Brian C J; Kolarik, Andrew; Stone, Michael A; Lee, Young-Woo

2016-10-01

A method (called binaural enhancement) for enhancing interaural level differences at low frequencies, based on estimates of interaural time differences, was developed and evaluated. Five conditions were compared, all using simulated hearing-aid processing: (1) Linear amplification with frequency-response shaping; (2) binaural enhancement combined with linear amplification and frequency-response shaping; (3) slow-acting four-channel amplitude compression with independent compression at the two ears (AGC4CH); (4) binaural enhancement combined with four-channel compression (BE-AGC4CH); and (5) four-channel compression but with the compression gains synchronized across ears. Ten hearing-impaired listeners were tested, and gains and compression ratios for each listener were set to match targets prescribed by the CAM2 fitting method. Stimuli were presented via headphones, using virtualization methods to simulate listening in a moderately reverberant room. The intelligibility of speech at ±60° azimuth in the presence of competing speech on the opposite side of the head at ±60° azimuth was not affected by the binaural enhancement processing. Sound localization was significantly better for condition BE-AGC4CH than for condition AGC4CH for a sentence, but not for broadband noise, lowpass noise, or lowpass amplitude-modulated noise. The results suggest that the binaural enhancement processing can improve localization for sounds with distinct envelope fluctuations.

The Fire Resistance Performance of Recycled Aggregate Concrete Columns with Different Concrete Compressive Strengths

PubMed Central

Dong, Hongying; Cao, Wanlin; Bian, Jianhui; Zhang, Jianwei

2014-01-01

In order to ascertain the fire resistance performance of recycled aggregate concrete (RAC) components with different concrete compressive strengths, four full-scaled concrete columns were designed and tested under high temperature. Two of the four specimens were constructed by normal concrete with compressive strength ratings of C20 and C30, respectively, while the others were made from recycled coarse aggregate (RCA) concrete of C30 and C40, respectively. Identical constant axial forces were applied to specimens while being subjected to simulated building fire conditions in a laboratory furnace. Several parameters from the experimental results were comparatively analyzed, including the temperature change, vertical displacement, lateral deflection, fire endurance, and failure characteristics of specimens. The temperature field of specimens was simulated with ABAQUS Software (ABAQUS Inc., Provindence, RI, USA) and the results agreed quite well with those from the experiments. Results show that the rate of heat transfer from the surface to the interior of the column increases with the increase of the concrete’s compressive strength for both RAC columns and normal concrete columns. Under the same initial axial force ratio, for columns with the same cross section, those with lower concrete compressive strengths demonstrate better fire resistance performance. The fire resistance performance of RAC columns is better than that of normal concrete columns, with the same concrete compressive strength. PMID:28788279

The Fire Resistance Performance of Recycled Aggregate Concrete Columns with Different Concrete Compressive Strengths.

PubMed

Dong, Hongying; Cao, Wanlin; Bian, Jianhui; Zhang, Jianwei

2014-12-08

In order to ascertain the fire resistance performance of recycled aggregate concrete (RAC) components with different concrete compressive strengths, four full-scaled concrete columns were designed and tested under high temperature. Two of the four specimens were constructed by normal concrete with compressive strength ratings of C20 and C30, respectively, while the others were made from recycled coarse aggregate (RCA) concrete of C30 and C40, respectively. Identical constant axial forces were applied to specimens while being subjected to simulated building fire conditions in a laboratory furnace. Several parameters from the experimental results were comparatively analyzed, including the temperature change, vertical displacement, lateral deflection, fire endurance, and failure characteristics of specimens. The temperature field of specimens was simulated with ABAQUS Software (ABAQUS Inc., Provindence, RI, USA) and the results agreed quite well with those from the experiments. Results show that the rate of heat transfer from the surface to the interior of the column increases with the increase of the concrete's compressive strength for both RAC columns and normal concrete columns. Under the same initial axial force ratio, for columns with the same cross section, those with lower concrete compressive strengths demonstrate better fire resistance performance. The fire resistance performance of RAC columns is better than that of normal concrete columns, with the same concrete compressive strength.

Pulse compression favourable aperiodic infrared imaging approach for non-destructive testing and evaluation of bio-materials

NASA Astrophysics Data System (ADS)

Mulaveesala, Ravibabu; Dua, Geetika; Arora, Vanita; Siddiqui, Juned A.; Muniyappa, Amarnath

2017-05-01

In recent years, aperiodic, transient pulse compression favourable infrared imaging methodologies demonstrated as reliable, quantitative, remote characterization and evaluation techniques for testing and evaluation of various biomaterials. This present work demonstrates a pulse compression favourable aperiodic thermal wave imaging technique, frequency modulated thermal wave imaging technique for bone diagnostics, especially by considering the bone with tissue, skin and muscle over layers. In order to find the capabilities of the proposed frequency modulated thermal wave imaging technique to detect the density variations in a multi layered skin-fat-muscle-bone structure, finite element modeling and simulation studies have been carried out. Further, frequency and time domain post processing approaches have been adopted on the temporal temperature data in order to improve the detection capabilities of frequency modulated thermal wave imaging.

Biomechanical analysis of fixation of middle third fractures of the clavicle.

PubMed

Drosdowech, Darren S; Manwell, Stuart E E; Ferreira, Louis M; Goel, Danny P; Faber, Kenneth J; Johnson, James A

2011-01-01

This biomechanical study compares four different techniques of fixation of middle third clavicular fractures. Twenty fresh-frozen clavicles were randomized into four groups. Each group used a different fixation device (3.5 Synthes reconstruction plate, 3.5 Synthes limited contact dynamic compression plate, 3.5 Synthes locking compression plate, and 4.5 DePuy Rockwood clavicular pin). All constructs were mechanically tested in bending and torque modes both with and without a simulated inferior cortical defect. Bending load to failure was also conducted. The four groups were compared using an analysis of variance test. The plate constructs were stiffer than the pin during both pure bending and torque loads with or without an inferior cortical defect. Bending load to failure with an inferior cortical defect revealed that the reconstruction plate was weaker compared with the other three groups. The limited contact and locking plates were stiffer than the reconstruction plate but demonstrated statistical significance only with the cortical defect. As hypothesized, the 3.5 limited contact dynamic compression plate and 3.5 locking compression plate demonstrated the greatest resistance to bending and torque loads, especially in the presence of simulated comminution of a middle third clavicular fracture. The reconstruction plate demonstrated lower stiffness and strength values compared with the other plates, especially with a cortical defect, whereas the pin showed poor resistance to bending and torque loads in all modes of testing. This information may help surgeons to choose the most appropriate method of fixation when treating fractures of the middle third of the clavicle.

Evaluation of Subgrid-Scale Models for Large Eddy Simulation of Compressible Flows

NASA Technical Reports Server (NTRS)

Blaisdell, Gregory A.

1996-01-01

The objective of this project was to evaluate and develop subgrid-scale (SGS) turbulence models for large eddy simulations (LES) of compressible flows. During the first phase of the project results from LES using the dynamic SGS model were compared to those of direct numerical simulations (DNS) of compressible homogeneous turbulence. The second phase of the project involved implementing the dynamic SGS model in a NASA code for simulating supersonic flow over a flat-plate. The model has been successfully coded and a series of simulations has been completed. One of the major findings of the work is that numerical errors associated with the finite differencing scheme used in the code can overwhelm the SGS model and adversely affect the LES results. Attached to this overview are three submitted papers: 'Evaluation of the Dynamic Model for Simulations of Compressible Decaying Isotropic Turbulence'; 'The effect of the formulation of nonlinear terms on aliasing errors in spectral methods'; and 'Large-Eddy Simulation of a Spatially Evolving Compressible Boundary Layer Flow'.

Evaluation of simulation-based training on the ability of birth attendants to correctly perform bimanual compression as obstetric first aid.

PubMed

Andreatta, Pamela; Gans-Larty, Florence; Debpuur, Domitilla; Ofosu, Anthony; Perosky, Joseph

2011-10-01

Maternal mortality from postpartum hemorrhage remains high globally, in large part because women give birth in rural communities where unskilled (traditional birth attendants) provide care for delivering mothers. Traditional attendants are neither trained nor equipped to recognize or manage postpartum hemorrhage as a life-threatening emergent condition. Recommended treatment includes using uterotonic agents and physical manipulation to aid uterine contraction. In resource-limited areas where Obstetric first aid may be the only care option, physical methods such as bimanual uterine compression are easily taught, highly practical and if performed correctly, highly effective. A simulator with objective performance feedback was designed to teach skilled and unskilled birth attendants to perform the technique. To evaluate the impact of simulation-based training on the ability of birth attendants to correctly perform bimanual compression in response to postpartum hemorrhage from uterine atony. Simulation-based training was conducted for skilled (N=111) and unskilled birth attendants (N=14) at two regional (Kumasi, Tamale) and two district (Savelugu, Sene) medical centers in Ghana. Training was evaluated using Kirkpatrick's 4-level model. All participants significantly increased their bimanual uterine compression skills after training (p=0.000). There were no significant differences between 2-week delayed post-test performances indicating retention (p=0.52). Applied behavioral and clinical outcomes were reported for 9 months from a subset of birth attendants in Sene District: 425 births, 13 postpartum hemorrhages were reported without concomitant maternal mortality. The results of this study suggest that simulation-based training for skilled and unskilled birth attendants to perform bi-manual uterine compression as postpartum hemorrhage Obstetric first aid leads to improved applied procedural skills. Results from a smaller subset of the sample suggest that these skills could potentially lead to improved clinical outcomes and additional study is merited. Copyright © 2011 Elsevier Ltd. All rights reserved.

Analysis of direct-drive capsule compression experiments on the Iskra-5 laser facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gus'kov, S. Yu.; Demchenko, N. N.; Zhidkov, N. V.

2010-09-15

We have analyzed and numerically simulated our experiments on the compression of DT-gas-filled glass capsules under irradiation by a small number of beams on the Iskra-5 facility (12 beams) at the second harmonic of an iodine laser ({lambda} = 0.66 {mu}m) for a laser pulse energy of 2 kJ and duration of 0.5 ns in the case of asymmetric irradiation and compression. Our simulations include the construction of a target illumination map and a histogram of the target surface illumination distribution; 1D capsule compression simulations based on the DIANA code corresponding to various target surface regions; and 2D compression simulationsmore » based on the NUTCY code corresponding to the illumination conditions. We have succeeded in reproducing the shape of the compressed region at the time of maximum compression and the reduction in neutron yield (compared to the 1D simulations) to the experimentally observed values. For the Iskra-5 conditions, we have considered targets that can provide a more symmetric compression and a higher neutron yield.« less

Space environmental effects on graphite-epoxy compressive properties and epoxy tensile properties

NASA Technical Reports Server (NTRS)

Fox, Derek J.; Sykes, George F., Jr.; Herakovich, Carl T.

1987-01-01

This study characterizes the effects of electron radiation and temperature on a graphite-epoxy composite material. Compressive properties of the T300/934 material system were obtained at -250 F (-157 C), room temperature, and 250 F (121 C). Tensile specimens of the Fiberite 934 epoxy resin were fabricated and tested at room temperature and 250 F (121 C). Testing was conducted in the baseline (nonirradiated) and irradiated conditions. The radiation exposure was designed to simulate 30 year, worst-case exposure in geosynchronous Earth orbit. Mechanical properties tended to degrade at elevated temperature and improve at cryogenic temperature. Irradiation generally degraded properties at all temperatures.

Femtosecond timing-jitter between photo-cathode laser and ultra-short electron bunches by means of hybrid compression

NASA Astrophysics Data System (ADS)

Pompili, R.; Anania, M. P.; Bellaveglia, M.; Biagioni, A.; Castorina, G.; Chiadroni, E.; Cianchi, A.; Croia, M.; Di Giovenale, D.; Ferrario, M.; Filippi, F.; Gallo, A.; Gatti, G.; Giorgianni, F.; Giribono, A.; Li, W.; Lupi, S.; Mostacci, A.; Petrarca, M.; Piersanti, L.; Di Pirro, G.; Romeo, S.; Scifo, J.; Shpakov, V.; Vaccarezza, C.; Villa, F.

2016-08-01

The generation of ultra-short electron bunches with ultra-low timing-jitter relative to the photo-cathode (PC) laser has been experimentally proved for the first time at the SPARC_LAB test-facility (INFN-LNF, Frascati) exploiting a two-stage hybrid compression scheme. The first stage employs RF-based compression (velocity-bunching), which shortens the bunch and imprints an energy chirp on it. The second stage is performed in a non-isochronous dogleg line, where the compression is completed resulting in a final bunch duration below 90 fs (rms). At the same time, the beam arrival timing-jitter with respect to the PC laser has been measured to be lower than 20 fs (rms). The reported results have been validated with numerical simulations.

Mechanical characterization and modeling of sponge-reinforced hydrogel composites under compression.

PubMed

Wu, Lei; Mao, Guoyong; Nian, Guodong; Xiang, Yuhai; Qian, Jin; Qu, Shaoxing

2018-05-30

Load-bearing applications of hydrogels call for materials with excellent mechanical properties. Despite the considerable progress in developing tough hydrogels, there is still a requirement to prepare high-performance hydrogels using simple strategies. In this paper, a sponge-reinforced hydrogel composite is synthesized by combining poly(acrylamide) (PAAm) hydrogel and polyurethane (PU) sponge. Uniaxial compressive testing of the hydrogel composites reveals that both the compressive modulus and the strength of the hydrogel composites are much higher than those of the PAAm hydrogel or sponge. In order to predict the compressive modulus of the hydrogel composite, we develop a theoretical model that is validated by experiments and numerical simulations. The present work may guide the design and manufacture of hydrogel-based composite materials, especially for biomaterial scaffolds and soft transducers.

Generation and Analysis of Subpicosecond Double Electron Bunch at the Brookhaven Accelerator Test Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babzien, M.; Kusche, K.; Yakimenko, V.

2011-08-09

Two compressed electron beam bunches from a single 60-MeV bunch have been generated in a reproducible manner during compression in the magnetic chicane - 'dog leg' arrangement at ATF. Measurements indicate they have comparable bunch lengths ({approx}100-200 fs) and are separated in energy by {approx}1.8 MeV with the higher-energy bunch preceding the lower-energy bunch by 0.5-1 ps. Some simulation results for analyzing the double-bunch formation process are also presented.

Density Fluctuations in the Solar Wind Driven by Alfvén Wave Parametric Decay

NASA Astrophysics Data System (ADS)

Bowen, Trevor A.; Badman, Samuel; Hellinger, Petr; Bale, Stuart D.

2018-02-01

Measurements and simulations of inertial compressive turbulence in the solar wind are characterized by anti-correlated magnetic fluctuations parallel to the mean field and density structures. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures, kinetic ion-acoustic waves, as well as the MHD slow-mode. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising and suggestive of a local driving process. One possible candidate for the generation of compressive fluctuations in the solar wind is the Alfvén wave parametric instability. Here, we test the parametric decay process as a source of compressive waves in the solar wind by comparing the collisionless damping rates of compressive fluctuations with growth rates of the parametric decay instability daughter waves. Our results suggest that generation of compressive waves through parametric decay is overdamped at 1 au, but that the presence of slow-mode-like density fluctuations is correlated with the parametric decay of Alfvén waves.

Fuel containment and damage tolerance in large composite primary aircraft structures. Phase 2: Testing

NASA Technical Reports Server (NTRS)

Sandifer, J. P.; Denny, A.; Wood, M. A.

1985-01-01

Technical issues associated with fuel containment and damage tolerance of composite wing structures for transport aircraft were investigated. Material evaluation tests were conducted on two toughened resin composites: Celion/HX1504 and Celion/5245. These consisted of impact, tension, compression, edge delamination, and double cantilever beam tests. Another test series was conducted on graphite/epoxy box beams simulating a wing cover to spar cap joint configuration of a pressurized fuel tank. These tests evaluated the effectiveness of sealing methods with various fastener types and spacings under fatigue loading and with pressurized fuel. Another test series evaluated the ability of the selected coatings, film, and materials to prevent fuel leakage through 32-ply AS4/2220-1 laminates at various impact energy levels. To verify the structural integrity of the technology demonstration article structural details, tests were conducted on blade stiffened panels and sections. Compression tests were performed on undamaged and impacted stiffened AS4/2220-1 panels and smaller element tests to evaluate stiffener pull-off, side load and failsafe properties. Compression tests were also performed on panels subjected to Zone 2 lightning strikes. All of these data were integrated into a demonstration article representing a moderately loaded area of a transport wing. This test combined lightning strike, pressurized fuel, impact, impact repair, fatigue and residual strength.

Wear resistance and compression strength of ceramics tested in fluoride environments.

PubMed

Theodoro, Guilherme Teixeira; Fiorin, Lívia; Moris, Izabela Cristina Maurício; Rodrigues, Renata Cristina Silveira; Ribeiro, Ricardo Faria; Faria, Adriana Cláudia Lapria

2017-01-01

Dental ceramics have been widely used because of aesthetic, but wear is still questioned. There are relates that ceramic surface is prone to degradation by acidulated fluoride, that can increase wear rates. The aim of this study was to evaluate the effect of neutral and acidulated fluoride gel, used as preventive agents for professional use, at wear and compression strength of dental ceramics IPS e.max ZirPress (ZIR), IPS Empress Esthetic (EMP) e IPS Inline POM (POM). For this, 30 crowns and 30 disks were obtained by heat-pressing. Crowns and disks were submitted to two-body wear test at machine of mechanical loading, simulating occlusion, lateral movement and disocclusion. It was performed 300,000 cycles at 1Hz frequency under 20N load, to simulate 1 year of mastication. Samples were totally immersed during the test and were divided into three groups according to the gel used for immersion (n=10): control, neutral (sodium fluoride 2%) and acidulated (acidulated phosphate fluoride 1.23%). Samples (crowns and disks) were analyzed for vertical height loss after the test using, respectively, profile projector and stereomicroscope. Roughness of worn surface of crowns and disks was evaluated by laser confocal microscopy. Data of height loss and roughness were evaluated by two-way ANOVA and Bonferroni's test. A crown/disk of each group was analyzed by scanning electronic microscopy. After wear resistance tests, crowns were cemented to their abutments and submitted to compressive load at 30° angulation and 1mm/min speed. Type of failures was compared by qui-square test. Ceramic EMP worn less while ZIR worn more. Control gel worn more at crowns while acidulated gel worn more at disks. Surface roughness of samples tested at acidulated gel was significantly lower. Type of failures found at compression resistance tests was affected by ceramic type, but not by gel used. The results suggest that ceramic and fluoride gel affect wear and roughness of worn surface while type of failure is only affected by ceramic. Copyright © 2016 Elsevier Ltd. All rights reserved.

Introduction to study and simulation of low rate video coding schemes

NASA Technical Reports Server (NTRS)

1992-01-01

During this period, the development of simulators for the various HDTV systems proposed to the FCC were developed. These simulators will be tested using test sequences from the MPEG committee. The results will be extrapolated to HDTV video sequences. Currently, the simulator for the compression aspects of the Advanced Digital Television (ADTV) was completed. Other HDTV proposals are at various stages of development. A brief overview of the ADTV system is given. Some coding results obtained using the simulator are discussed. These results are compared to those obtained using the CCITT H.261 standard. These results in the context of the CCSDS specifications are evaluated and some suggestions as to how the ADTV system could be implemented in the NASA network are made.

Further Investigations of Control Surface Seals for the X-38 Re-Entry Vehicle

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H., Jr.; Steinetz, Bruce M.; Curry, Donald M.; Newquist, Charles W.; Verzemnieks, Juris

2001-01-01

NASA is currently developing the X-38 vehicle that will be used to demonstrate the technologies required for a potential crew return vehicle (CRV) for the International Space Station. This vehicle would serve both as an ambulance for medical emergencies and as an evacuation vehicle for the Space Station. Control surfaces on the X-38 (body flaps and rudder/fin assemblies) require high temperature seals to limit hot gas ingestion and transfer of heat to underlying low-temperature structures to prevent over-temperature of these structures and possible loss of the vehicle. NASAs Johnson Space Center (JSC) and Glenn Research Center (GRC) are working together to develop and evaluate seals for these control surfaces. This paper presents results for compression. flow, scrub, and arc jet tests conducted on the baseline X-38 rudder/fin seal design. Room temperature seal compression tests were performed at low compression levels to determine load versus linear compression, preload. contact area, stiffness. and resiliency characteristics under low load conditions. For all compression levels that were tested, unit loads and contact pressures for the seals were below the 5 lb/in. and 10 psi limits required to limit the loads on the adjoining Shuttle thermal tiles that the seals will contact. Flow rates through an unloaded (i.e. 0% compression) double arrangement were twice those of a double seal compressed to the 20% design compression level. The seals survived an ambient temperature 1000 cycle scrub test over relatively rough Shuttle tile surfaces. The seals were able to disengage and re-engage the edges of the rub surface tiles while being scrubbed over them. Arc jet tests were performed to experimentally determine anticipated seal temperatures for representative flow boundary conditions (pressures and temperatures) under simulated vehicle re-entry conditions. Installation of a single seat in the gap of the test fixture caused a large temperature drop (1710 F) across the seal location as compared to an open gap condition (140 F) confirming the need for seals in the rudder/fin gap location. The seal acted as an effective thermal barrier limiting heat convection through the seal gap and minimizing temperature increases downstream of the seal during maximum heating conditions.

Artificial Neural Network-Based Three-dimensional Continuous Response Relationship Construction of 3Cr20Ni10W2 Heat-Resisting Alloy and Its Application in Finite Element Simulation

NASA Astrophysics Data System (ADS)

Li, Le; Wang, Li-yong

2018-04-01

The application of accurate constitutive relationship in finite element simulation would significantly contribute to accurate simulation results, which plays a critical role in process design and optimization. In this investigation, the true stress-strain data of 3Cr20Ni10W2 heat-resisting alloy were obtained from a series of isothermal compression tests conducted in a wide temperature range of 1203-1403 K and strain rate range of 0.01-10 s-1 on a Gleeble 1500 testing machine. Then the constitutive relationship was modeled by an optimally constructed and well-trained back-propagation artificial neural network (BP-ANN). The evaluation of the BP-ANN model revealed that it has admirable performance in characterizing and predicting the flow behaviors of 3Cr20Ni10W2 heat-resisting alloy. Meanwhile, a comparison between improved Arrhenius-type constitutive equation and BP-ANN model shows that the latter has higher accuracy. Consequently, the developed BP-ANN model was used to predict abundant stress-strain data beyond the limited experimental conditions and construct the three-dimensional continuous response relationship for temperature, strain rate, strain, and stress. Finally, the three-dimensional continuous response relationship was applied to the numerical simulation of isothermal compression tests. The results show that such constitutive relationship can significantly promote the accuracy improvement of numerical simulation for hot forming processes.

Mechanical properties of metal-ceramic nanolaminates: Effect of constraint and temperature

DOE PAGES

Yang, Ling Wei; Mayer, Carl; Li, Nan; ...

2017-09-21

Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanicalmore » response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). Here, these mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.« less

Microgravity

NASA Image and Video Library

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Finite Element Modeling of Multilayer Orthogonal Auxetic Composites under Low-Velocity Impact

PubMed Central

Jiang, Lili; Hu, Hong

2017-01-01

The multilayer orthogonal auxetic composites have been previously developed and tested to prove that they own excellent energy absorption and impact protection characteristics in a specific strain range under low-velocity impact. In this study, a three dimensional finite element (FE) model in ANSYS LS-DYNA was established to simulate the mechanical behavior of auxetic composites under low-velocity drop-weight impact. The simulation results including the Poisson’s ratio versus compressive strain curves and the contact stress versus compressive strain curves were compared with those in the experiments. The clear deformation pictures of the FE models have provided a simple and effective way for investigating the damage mechanism and optimizing the material, as well as structure design. PMID:28783054

LES of Supersonic Turbulent Channel Flow at Mach Numbers 1.5 and 3

NASA Astrophysics Data System (ADS)

Raghunath, Sriram; Brereton, Giles

2009-11-01

LES of compressible, turbulent, body-force driven, isothermal-wall channel flows at Reτ of 190 and 395 at moderate supersonic speeds (Mach 1.5 and 3) are presented. Simulations are fully resolved in the wall-normal direction without the need for wall-layer models. SGS models for incompressible flows, with appropriate extensions for compressibility, are tested a priori/ with DNS results and used in LES. Convergence of the simulations is found to be sensitive to the initial conditions and to the choice of model (wall-normal damping) in the laminar sublayer. The Nicoud--Ducros wall adapting SGS model, coupled with a standard SGS heat flux model, is found to yield results in good agreement with DNS.

Matrerials Characterization of Craninal Simulants for Blast Induced Traumatic Brain Injury

DTIC Science & Technology

2017-08-28

34.....,,. Witt.. Cranial Simulants Under Tensile, Compressive, and Shear Stresses Tensile Testing i 2 !’u ~ t . .. · Bovine Skin Derived Gel• tin 0𔄀...1 : • •• ..... 50 100 l,50 ~VM/1) ""’ 2°" tone Gel• tin Stress Comparhon u 14 l2 7 10 6. •• I .. , ... " .... -2 0 so 100 uo r

Low-speed performance of an axisymmetric, mixed-compression, supersonic inlet with auxiliary inlets

NASA Technical Reports Server (NTRS)

Trefny, C. J.; Wasserbauer, J. W.

1986-01-01

A test program was conducted to determine the aerodynamic performance and acoustic characteristics associated with the low-speed operation of a supersonic, axisymmetric, mixed-compression inlet with auxiliary inlets. Blow-in-auxiliary doors were installed on the NASA Ames P inlet. One door per quadrant was located on the cowl in the subsonic diffuser selection of the inlet. Auxiliary inlets with areas of 20 and 40 percent of the inlet capture area were tested statically and at free-stream Mach numbers of 0.1 and 0.2. The effects of boundary layer bleed inflow were investigated. A JT8D fan simulator driven by compressed air was used to pump inlet flow and to provide a characteristic noise signature. Baseline data were obtained at static free-stream conditions with the sharp P-inlet cowl lip replaced by a blunt lip. Auxiliary inlets increased overall total pressure recovery of the order of 10 percent.

High-Gain High-Field Fusion Plasma

PubMed Central

Li, Ge

2015-01-01

A Faraday wheel (FW)—an electric generator of constant electrical polarity that produces huge currents—could be implemented in an existing tokamak to study high-gain high-field (HGHF) fusion plasma, such as the Experimental Advanced Superconducting Tokamak (EAST). HGHF plasma can be realized in EAST by updating its pulsed-power system to compress plasma in two steps by induction fields; high gains of the Lawson trinity parameter and fusion power are both predicted by formulating the HGHF plasma. Both gain rates are faster than the decrease rate of the plasma volume. The formulation is checked by earlier ATC tests. Good agreement between theory and tests indicates that scaling to over 10 T at EAST may be possible by two-step compressions with a compression ratio of the minor radius of up to 3. These results point to a quick new path of fusion plasma study, i.e., simulating the Sun by EAST. PMID:26507314

Enhancement of a dynamic porous model considering compression-release hysteresis behavior: application to graphite

NASA Astrophysics Data System (ADS)

Jodar, B.; Seisson, G.; Hébert, D.; Bertron, I.; Boustie, M.; Berthe, L.

2016-08-01

Because of their shock wave attenuation properties, porous materials and foams are increasingly used for various applications such as graphite in the aerospace industry and polyurethane (PU) foams in biomedical engineering. For these two materials, the absence of residual compaction after compression and release cycles limits the efficiency of the usual numerical dynamic porous models such as P-α and POREQST. In this paper, we suggest a simple enhancement of the latter in order to take into account the compression-release hysteresis behavior experimentally observed for the considered materials. The new model, named H-POREQST, was implemented into a Lagrangian hydrocode and tested for simulating plate impact experiments at moderate pressure onto a commercial grade of porous graphite (EDM3). It proved to be in far better agreement with experimental data than the original model which encourages us to pursue numerical tests and developments.

Isentropic Compression up to 200 KBars for LX 04, Numerical Simulations and Comparison with Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lefrancois, A.; Hare, D.; L'Eplattenier, P.

2006-02-13

Isentropic compression experiments and numerical simulations on LX-04 (HMX / Viton 85/15) were performed respectively at Z accelerator facility from Sandia National Laboratory and at Lawrence Livermore National Laboratory in order to study the isentrope and associated Hugoniot of this HE. 2D and 3D configurations have been calculated here to test the new beta version of the electromagnetism package coupled with the dynamics in Ls-Dyna and compared with the ICE Z shot 1067 on LX 04. The electromagnetism module is being developed in the general-purpose explicit and implicit finite element program LS-DYNA{reg_sign} in order to perform coupled mechanical/thermal/electromagnetism simulations. Themore » Maxwell equations are solved using a Finite Element Method (FEM) for the solid conductors coupled with a Boundary Element Method (BEM) for the surrounding air (or vacuum). More details can be read in the references.« less

Simulated Hail Ice Mechanical Properties and Failure Mechanism at Quasi-Static Strain Rates

NASA Astrophysics Data System (ADS)

Swift, Jonathan M.

Hail is a significant threat to aircraft both on the ground and in the air. Aeronautical engineers are interested in better understanding the properties of hail to improve the safety of new aircraft. However, the failure mechanism and mechanical properties of hail, as opposed to clear ice, are not well understood. A literature review identifies basic mechanical properties of ice and a failure mechanism based upon the state of stress within an ice sphere is proposed. To better understand the properties of Simulated Hail Ice (SHI), several tests were conducted using both clear and cotton fiber reinforced ice. Pictures were taken to show the internal crystal structure of SHI. SHI crush tests were conducted to identify the overall force-displacement trends at various quasi-static strain rates. High speed photography was also used to visually track the failure mechanism of spherical SHI. Compression tests were done to measure the compression strength of SHI and results were compared to literature data. Fracture toughness tests were conducted to identify the crack resistance of SHI. Results from testing clear ice samples were successfully compared to previously published literature data to instill confidence in the testing methods. The methods were subsequently used to test and characterize the cotton fiber reinforced ice.

Evaluating lossy data compression on climate simulation data within a large ensemble

DOE PAGES

Baker, Allison H.; Hammerling, Dorit M.; Mickelson, Sheri A.; ...

2016-12-07

High-resolution Earth system model simulations generate enormous data volumes, and retaining the data from these simulations often strains institutional storage resources. Further, these exceedingly large storage requirements negatively impact science objectives, for example, by forcing reductions in data output frequency, simulation length, or ensemble size. To lessen data volumes from the Community Earth System Model (CESM), we advocate the use of lossy data compression techniques. While lossy data compression does not exactly preserve the original data (as lossless compression does), lossy techniques have an advantage in terms of smaller storage requirements. To preserve the integrity of the scientific simulation data,more » the effects of lossy data compression on the original data should, at a minimum, not be statistically distinguishable from the natural variability of the climate system, and previous preliminary work with data from CESM has shown this goal to be attainable. However, to ultimately convince climate scientists that it is acceptable to use lossy data compression, we provide climate scientists with access to publicly available climate data that have undergone lossy data compression. In particular, we report on the results of a lossy data compression experiment with output from the CESM Large Ensemble (CESM-LE) Community Project, in which we challenge climate scientists to examine features of the data relevant to their interests, and attempt to identify which of the ensemble members have been compressed and reconstructed. We find that while detecting distinguishing features is certainly possible, the compression effects noticeable in these features are often unimportant or disappear in post-processing analyses. In addition, we perform several analyses that directly compare the original data to the reconstructed data to investigate the preservation, or lack thereof, of specific features critical to climate science. Overall, we conclude that applying lossy data compression to climate simulation data is both advantageous in terms of data reduction and generally acceptable in terms of effects on scientific results.« less

Evaluating lossy data compression on climate simulation data within a large ensemble

NASA Astrophysics Data System (ADS)

Baker, Allison H.; Hammerling, Dorit M.; Mickelson, Sheri A.; Xu, Haiying; Stolpe, Martin B.; Naveau, Phillipe; Sanderson, Ben; Ebert-Uphoff, Imme; Samarasinghe, Savini; De Simone, Francesco; Carbone, Francesco; Gencarelli, Christian N.; Dennis, John M.; Kay, Jennifer E.; Lindstrom, Peter

2016-12-01

High-resolution Earth system model simulations generate enormous data volumes, and retaining the data from these simulations often strains institutional storage resources. Further, these exceedingly large storage requirements negatively impact science objectives, for example, by forcing reductions in data output frequency, simulation length, or ensemble size. To lessen data volumes from the Community Earth System Model (CESM), we advocate the use of lossy data compression techniques. While lossy data compression does not exactly preserve the original data (as lossless compression does), lossy techniques have an advantage in terms of smaller storage requirements. To preserve the integrity of the scientific simulation data, the effects of lossy data compression on the original data should, at a minimum, not be statistically distinguishable from the natural variability of the climate system, and previous preliminary work with data from CESM has shown this goal to be attainable. However, to ultimately convince climate scientists that it is acceptable to use lossy data compression, we provide climate scientists with access to publicly available climate data that have undergone lossy data compression. In particular, we report on the results of a lossy data compression experiment with output from the CESM Large Ensemble (CESM-LE) Community Project, in which we challenge climate scientists to examine features of the data relevant to their interests, and attempt to identify which of the ensemble members have been compressed and reconstructed. We find that while detecting distinguishing features is certainly possible, the compression effects noticeable in these features are often unimportant or disappear in post-processing analyses. In addition, we perform several analyses that directly compare the original data to the reconstructed data to investigate the preservation, or lack thereof, of specific features critical to climate science. Overall, we conclude that applying lossy data compression to climate simulation data is both advantageous in terms of data reduction and generally acceptable in terms of effects on scientific results.

Evaluating lossy data compression on climate simulation data within a large ensemble

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Allison H.; Hammerling, Dorit M.; Mickelson, Sheri A.

High-resolution Earth system model simulations generate enormous data volumes, and retaining the data from these simulations often strains institutional storage resources. Further, these exceedingly large storage requirements negatively impact science objectives, for example, by forcing reductions in data output frequency, simulation length, or ensemble size. To lessen data volumes from the Community Earth System Model (CESM), we advocate the use of lossy data compression techniques. While lossy data compression does not exactly preserve the original data (as lossless compression does), lossy techniques have an advantage in terms of smaller storage requirements. To preserve the integrity of the scientific simulation data,more » the effects of lossy data compression on the original data should, at a minimum, not be statistically distinguishable from the natural variability of the climate system, and previous preliminary work with data from CESM has shown this goal to be attainable. However, to ultimately convince climate scientists that it is acceptable to use lossy data compression, we provide climate scientists with access to publicly available climate data that have undergone lossy data compression. In particular, we report on the results of a lossy data compression experiment with output from the CESM Large Ensemble (CESM-LE) Community Project, in which we challenge climate scientists to examine features of the data relevant to their interests, and attempt to identify which of the ensemble members have been compressed and reconstructed. We find that while detecting distinguishing features is certainly possible, the compression effects noticeable in these features are often unimportant or disappear in post-processing analyses. In addition, we perform several analyses that directly compare the original data to the reconstructed data to investigate the preservation, or lack thereof, of specific features critical to climate science. Overall, we conclude that applying lossy data compression to climate simulation data is both advantageous in terms of data reduction and generally acceptable in terms of effects on scientific results.« less

[Effects of a voice metronome on compression rate and depth in telephone assisted, bystander cardiopulmonary resuscitation: an investigator-blinded, 3-armed, randomized, simulation trial].

PubMed

van Tulder, Raphael; Roth, Dominik; Krammel, Mario; Laggner, Roberta; Schriefl, Christoph; Kienbacher, Calvin; Lorenzo Hartmann, Alexander; Novosad, Heinz; Constantin Chwojka, Christof; Havel, Christoph; Schreiber, Wolfgang; Herkner, Harald

2015-01-01

We investigated the effect on compression rate and depth of a conventional metronome and a voice metronome in simulated telephone-assisted, protocol-driven bystander Cardiopulmonary resucitation (CPR) compared to standard instruction. Thirty-six lay volunteers performed 10 minutes of compression-only CPR in a prospective, investigator-blinded, 3-arm study on a manikin. Participants were randomized either to standard instruction ("push down firmly, 5 cm"), a regular metronome pacing 110 beats per minute (bpm), or a voice metronome continuously prompting "deep-deepdeep- deeper" at 110 bpm. The primary outcome was deviation from the ideal chest compression target range (50 mm compression depth x 100 compressions per minute x 10 minutes = 50 m). Secondary outcomes were CPR quality measures (compression and leaning depth, rate, no-flow times) and participants' related physiological response (heart rate, blood pressure and nine hole peg test and borg scales score). We used a linear regression model to calculate effects. The mean (SD) deviation from the ideal target range (50 m) was -11 (9) m in the standard group, -20 (11) m in the conventional metronome group (adjusted difference [95%, CI], 9.0 [1.2-17.5 m], P=.03), and -18 (9) m in the voice metronome group (adjusted difference, 7.2 [-0.9-15.3] m, P=.08). Secondary outcomes (CPR quality measures and physiological response of participants to CPR performance) showed no significant differences. Compared to standard instruction, the conventional metronome showed a significant negative effect on the chest compression target range. The voice metronome showed a non-significant negative effect and therefore cannot be recommended for regular use in telephone-assisted CPR.

Extracting material response from simple mechanical tests on hardening-softening-hardening viscoplastic solids

NASA Astrophysics Data System (ADS)

Mohan, Nisha

Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches. A fundamental question that motivates the modeling of foams is `how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?' A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,"Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes," J. Mech.Phys. Solids, 59, pp. 2227--2237, Erratum 60, 1753-1756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like 1) The initial linear elastic response. 2) One or more nonlinear instabilities, yielding, and hardening. The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.

Rapid distortion analysis and direct simulation of compressible homogeneous turbulence at finite Mach number

NASA Technical Reports Server (NTRS)

Cambon, C.; Coleman, G. N.; Mansour, N. N.

1992-01-01

The effect of rapid mean compression on compressible turbulence at a range of turbulent Mach numbers is investigated. Rapid distortion theory (RDT) and direct numerical simulation results for the case of axial (one-dimensional) compression are used to illustrate the existence of two distinct rapid compression regimes. These regimes are set by the relationships between the timescales of the mean distortion, the turbulence, and the speed of sound. A general RDT formulation is developed and is proposed as a means of improving turbulence models for compressible flows.

Numerical simulation of the change characteristics of power dissipation coefficient of Ti-24Al-15Nb alloy in hot deformation

NASA Astrophysics Data System (ADS)

Wang, Kelu; Li, Xin; Zhang, Xiaobo

2018-03-01

The power dissipation maps of Ti-25Al-15Nb alloy were constructed by using the compression test data. A method is proposed to predict the distribution and variation of power dissipation coefficient in hot forging process using both the dynamic material model and finite element simulation. Using the proposed method, the change characteristics of the power dissipation coefficient are simulated and predicted. The effectiveness of the proposed method was verified by comparing the simulation results with the physical experimental results.

Hydromechanics in dentine: role of dentinal tubules and hydrostatic pressure on mechanical stress-strain distribution.

PubMed

Kishen, A; Vedantam, S

2007-10-01

This investigation is to understand the role of free water in the dentinal tubules on the mechanical integrity of bulk dentine. Three different experiments were conducted in this study. In experiment 1, three-dimensional models of dentine with gradient elastic modulus, homogenous elastic modulus, and with and without hydrostatic pressure were simulated using the finite element method. Static compressive loads of 15, 50 and 100 N were applied and the distribution of the principal stresses, von Mises stresses, and strains in loading direction were determined. In experiment 2, experimental compression testing of fully hydrated and partially dehydrated dentine (21 degrees C for 72 h) was conducted using a Universal testing machine. In experiment 3, Fourier transform infrared spectroscopic analysis of hydrated and partially dehydrated dentine was carried out. The finite element analysis revealed that the dentine model with simulated hydrostatic pressure displayed residual tensile stresses and strains in the inner region adjacent to the root canal. When external compressive loads were applied to the model, the residual stresses and strains counteracted the applied loads. Similarly the hydrated specimens subjected to experimental compression loads showed greater toughness when compared to the partially dehydrated specimens. The stress at fracture was significantly higher in partially dehydrated specimens (p=0.014), while the strain at fracture was significantly higher in hydrated dentine specimens (p=0.037). These experiments highlighted the distinct role of free water in the dentinal tubules and hydrostatic pressure on the stress-strain distribution within the bulk dentine.

The simulation of a propulsive jet and force measurement using a magnetically suspended wind tunnel model

NASA Technical Reports Server (NTRS)

Garbutt, K. S.; Goodyer, M. J.

1994-01-01

Models featuring the simulation of exhaust jets were developed for magnetic levitation in a wind tunnel. The exhaust gas was stored internally producing a discharge of sufficient duration to allow nominal steady state to be reached. The gas was stored in the form of compressed gas or a solid rocket propellant. Testing was performed with the levitated models although deficiencies prevented the detection of jet-induced aerodynamic effects. Difficulties with data reduction led to the development of a new force calibration technique, used in conjunction with an exhaust simulator and also in separate high incidence aerodynamic tests.

Finite element simulation of location- and time-dependent mechanical behavior of chondrocytes in unconfined compression tests.

PubMed

Wu, J Z; Herzog, W

2000-03-01

Experimental evidence suggests that cells are extremely sensitive to their mechanical environment and react directly to mechanical stimuli. At present, it is technically difficult to measure fluid pressure, stress, and strain in cells, and to determine the time-dependent deformation of chondrocytes. For this reason, there are no data in the published literature that show the dynamic behavior of chondrocytes in articular cartilage. Similarly, the dynamic chondrocyte mechanics have not been calculated using theoretical models that account for the influence of cell volumetric fraction on cartilage mechanical properties. In the present investigation, the location- and time-dependent stress-strain state and fluid pressure distribution in chondrocytes in unconfined compression tests were simulated numerically using a finite element method. The technique involved two basic steps: first, cartilage was approximated as a macroscopically homogenized material and the mechanical behavior of cartilage was obtained using the homogenized model; second, the solution of the time-dependent displacements and fluid pressure fields of the homogenized model was used as the time-dependent boundary conditions for a microscopic submodel to obtain average location- and time-dependent mechanical behavior of cells. Cells and extracellular matrix were assumed to be biphasic materials composed of a fluid phase and a hyperelastic solid phase. The hydraulic permeability was assumed to be deformation dependent and the analysis was performed using a finite deformation approach. Numerical tests were made using configurations similar to those of experiments described in the literature. Our simulations show that the mechanical response of chondrocytes to cartilage loading depends on time, fluid boundary conditions, and the locations of the cells within the specimen. The present results are the first to suggest that chondrocyte deformation in a stress-relaxation type test may exceed the imposed system deformation by a factor of 3-4, that chondrocyte deformations are highly dynamic and do not reach a steady state within about 20 min of steady compression (in an unconfined test), and that cell deformations are very much location dependent.

Effect of the rate of chest compression familiarised in previous training on the depth of chest compression during metronome-guided cardiopulmonary resuscitation: a randomised crossover trial

PubMed Central

Bae, Jinkun; Chung, Tae Nyoung; Je, Sang Mo

2016-01-01

Objectives To assess how the quality of metronome-guided cardiopulmonary resuscitation (CPR) was affected by the chest compression rate familiarised by training before the performance and to determine a possible mechanism for any effect shown. Design Prospective crossover trial of a simulated, one-person, chest-compression-only CPR. Setting Participants were recruited from a medical school and two paramedic schools of South Korea. Participants 42 senior students of a medical school and two paramedic schools were enrolled but five dropped out due to physical restraints. Intervention Senior medical and paramedic students performed 1 min of metronome-guided CPR with chest compressions only at a speed of 120 compressions/min after training for chest compression with three different rates (100, 120 and 140 compressions/min). Friedman's test was used to compare average compression depths based on the different rates used during training. Results Average compression depths were significantly different according to the rate used in training (p<0.001). A post hoc analysis showed that average compression depths were significantly different between trials after training at a speed of 100 compressions/min and those at speeds of 120 and 140 compressions/min (both p<0.001). Conclusions The depth of chest compression during metronome-guided CPR is affected by the relative difference between the rate of metronome guidance and the chest compression rate practised in previous training. PMID:26873050

Simulated pain and cervical motion in patients with chronic disorders of the cervical spine.

PubMed

Dvir, Zeevi; Gal-Eshel, Noga; Shamir, Boaz; Pevzner, Evgeny; Peretz, Chava; Knoller, Nachshon

2004-01-01

The primary objective of the present study was to determine how simulated severe cervical pain affects cervical motion in patients suffering from two distinct chronic cervical disorders: whiplash (n=25) and degenerative changes (n=25). The second objective was to derive an index that would allow the differentiation of maximal from submaximal performances of cervical range of motion. Patients first performed maximal movement of the head (maximal effort) in each of the six primary directions and then repeated the test as if they were suffering from a much more intense level of pain (submaximal effort). All measurements were repeated within four to seven days. In both groups, there was significant compression of cervical motion during the submaximal effort. This compression was also highly stable on a test-retest basis. In both groups, a significantly higher average coefficient of variation was associated with the imagined pain and it was significantly different between the two clinical groups. In the whiplash group, a logistic regression model allowed the derivation of coefficient of variation-based cutoff scores that might, at selected levels of probability and an individual level, identify chronic whiplash patients who intentionally magnify their motion restriction using pain as a cue. However, the relatively small and very stable compression of cervical motion under pain simulation supports the view that the likelihood that chronic whiplash patients are magnifying their restriction of cervical range of motion using pain as a cue is very low.

Magnetized Target Fusion At General Fusion: An Overview

NASA Astrophysics Data System (ADS)

Laberge, Michel; O'Shea, Peter; Donaldson, Mike; Delage, Michael; Fusion Team, General

2017-10-01

Magnetized Target Fusion (MTF) involves compressing an initial magnetically confined plasma on a timescale faster than the thermal confinement time of the plasma. If near adiabatic compression is achieved, volumetric compression of 350X or more of a 500 eV target plasma would achieve a final plasma temperature exceeding 10 keV. Interesting fusion gains could be achieved provided the compressed plasma has sufficient density and dwell time. General Fusion (GF) is developing a compression system using pneumatic pistons to collapse a cavity formed in liquid metal containing a magnetized plasma target. Low cost driver, straightforward heat extraction, good tritium breeding ratio and excellent neutron protection could lead to a practical power plant. GF (65 employees) has an active plasma R&D program including both full scale and reduced scale plasma experiments and simulation of both. Although pneumatic driven compression of full scale plasmas is the end goal, present compression studies use reduced scale plasmas and chemically accelerated aluminum liners. We will review results from our plasma target development, motivate and review the results of dynamic compression field tests and briefly describe the work to date on the pneumatic driver front.

Development and mechanical properties of construction materials from lunar simulants

NASA Technical Reports Server (NTRS)

Desai, Chandra S.

1990-01-01

The development of construction materials such as concrete from lunar soils without the use of water requires a different methodology than that used for conventional terrestrial concrete. Currently, this research involves two aspects: (1) liquefaction of lunar simulants with various additives in a furnace so as to produce a construction material like an intermediate ceramic; and (2) cyclic loading of simulant with different initial vacuums and densities with respect to the theoretical maximum densities (TMD). In both cases, bending, triaxial compression, extension, and hydrostatic tests will be performed to define the stress-strain strength response of the resulting materials. In the case of the intermediate ceramic, bending and available multiaxial test devices will be used, while for the compacted case, tests will be performed directly in the new device. The tests will be performed by simulating in situ confining conditions. A preliminary review of high-purity metal is also conducted.

Seat cushion to provide realistic acceleration cues to aircraft simulator pilot

NASA Technical Reports Server (NTRS)

Ashworth, B. R. (Inventor)

1979-01-01

Seat cushions, each including an air cell with a non-compressible surface, are disclosed. The apparatus are provided for initially controlling the air pressure in the air cells to allow the two main support areas of the simulator pilot to touch the non-compressible surface and thus begin to compress the flesh near these areas. During a simulated flight the apparatus control the air pressure in the cells to simulate the events that occur in a seat cushion during actual flight.

A Comparison of Compressed Sensing and Sparse Recovery Algorithms Applied to Simulation Data

DOE PAGES

Fan, Ya Ju; Kamath, Chandrika

2016-09-01

The move toward exascale computing for scientific simulations is placing new demands on compression techniques. It is expected that the I/O system will not be able to support the volume of data that is expected to be written out. To enable quantitative analysis and scientific discovery, we are interested in techniques that compress high-dimensional simulation data and can provide perfect or near-perfect reconstruction. In this paper, we explore the use of compressed sensing (CS) techniques to reduce the size of the data before they are written out. Using large-scale simulation data, we investigate how the sufficient sparsity condition and themore » contrast in the data affect the quality of reconstruction and the degree of compression. Also, we provide suggestions for the practical implementation of CS techniques and compare them with other sparse recovery methods. Finally, our results show that despite longer times for reconstruction, compressed sensing techniques can provide near perfect reconstruction over a range of data with varying sparsity.« less

A Comparison of Compressed Sensing and Sparse Recovery Algorithms Applied to Simulation Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Ya Ju; Kamath, Chandrika

The move toward exascale computing for scientific simulations is placing new demands on compression techniques. It is expected that the I/O system will not be able to support the volume of data that is expected to be written out. To enable quantitative analysis and scientific discovery, we are interested in techniques that compress high-dimensional simulation data and can provide perfect or near-perfect reconstruction. In this paper, we explore the use of compressed sensing (CS) techniques to reduce the size of the data before they are written out. Using large-scale simulation data, we investigate how the sufficient sparsity condition and themore » contrast in the data affect the quality of reconstruction and the degree of compression. Also, we provide suggestions for the practical implementation of CS techniques and compare them with other sparse recovery methods. Finally, our results show that despite longer times for reconstruction, compressed sensing techniques can provide near perfect reconstruction over a range of data with varying sparsity.« less

Analysis of visual quality improvements provided by known tools for HDR content

NASA Astrophysics Data System (ADS)

Kim, Jaehwan; Alshina, Elena; Lee, JongSeok; Park, Youngo; Choi, Kwang Pyo

2016-09-01

In this paper, the visual quality of different solutions for high dynamic range (HDR) compression using MPEG test contents is analyzed. We also simulate the method for an efficient HDR compression which is based on statistical property of the signal. The method is compliant with HEVC specification and also easily compatible with other alternative methods which might require HEVC specification changes. It was subjectively tested on commercial TVs and compared with alternative solutions for HDR coding. Subjective visual quality tests were performed using SUHD TVs model which is SAMSUNG JS9500 with maximum luminance up to 1000nit in test. The solution that is based on statistical property shows not only improvement of objective performance but improvement of visual quality compared to other HDR solutions, while it is compatible with HEVC specification.

Investigation of the Constitutive Model Used in Nonlinear, Incremental Structural Analyses.

DTIC Science & Technology

1998-06-01

package, ABAQUS , was chosen for performing NISA studies in part because user supplied subroutines could be used for constitutive relationships. After a...loading and the shrinkage and thermally induced strains determined from control specimens. The majority of creep tests are uniaxial compressive tests...Kennedy, and Perry (1970). Description of FE Model The tests were simulated using the finite element (FE) program ABAQUS and the aging viscoelastic

A workstation based simulator for teaching compressible aerodynamics

NASA Technical Reports Server (NTRS)

Benson, Thomas J.

1994-01-01

A workstation-based interactive flow simulator has been developed to aid in the teaching of undergraduate compressible aerodynamics. By solving the equations found in NACA 1135, the simulator models three basic fluids problems encountered in supersonic flow: flow past a compression corner, flow past two wedges in series, and flow past two opposed wedges. The study can vary the geometry or flow conditions through a graphical user interface and the new conditions are calculated immediately. Various graphical formats present the results of the flow calculations to the student. The simulator includes interactive questions and answers to aid in both the use of the tool and to develop an understanding of some of the complexities of compressible aerodynamics. A series of help screens make the simulator easy to learn and use.

Adequate performance of cardiopulmonary resuscitation techniques during simulated cardiac arrest over and under protective equipment in football.

PubMed

Waninger, Kevin N; Goodbred, Andrew; Vanic, Keith; Hauth, John; Onia, Joshua; Stoltzfus, Jill; Melanson, Scott

2014-07-01

To investigate (1) cardiopulmonary resuscitation (CPR) adequacy during simulated cardiac arrest of equipped football players and (2) whether protective football equipment impedes CPR performance measures. Exploratory crossover study performed on Laerdal SimMan 3 G interactive manikin simulator. Temple University/St Luke's University Health Network Regional Medical School Simulation Laboratory. Thirty BCLS-certified ATCs and 6 ACLS-certified emergency department technicians. Subjects were given standardized rescuer scenarios to perform three 2-minute sequences of compression-only CPR. Baseline CPR sequences were captured on each subject. Experimental conditions included 2-minute sequences of CPR either over protective football shoulder pads or under unlaced pads. Subjects were instructed to adhere to 2010 American Heart Association guidelines (initiation of compressions alone at 100/min to 51 mm). Dependent variables included average compression depth, average compression rate, percentage of time chest wall recoiled, and percentage of hands-on contact during compressions. Differences between subject groups were not found to be statistically significant, so groups were combined (n = 36) for analysis of CPR compression adequacy. Compression depth was deeper under shoulder pads than over (P = 0.02), with mean depths of 36.50 and 31.50 mm, respectively. No significant difference was found with compression rate or chest wall recoil. Chest compression depth is significantly decreased when performed over shoulder pads, while there is no apparent effect on rate or chest wall recoil. Although the clinical outcomes from our observed 15% difference in compression depth are uncertain, chest compression under the pads significantly increases the depth of compressions and more closely approaches American Heart Association guidelines for chest compression depth in cardiac arrest.

Finite-element modeling of compression and gravity on a population of breast phantoms for multimodality imaging simulation.

PubMed

Sturgeon, Gregory M; Kiarashi, Nooshin; Lo, Joseph Y; Samei, E; Segars, W P

2016-05-01

The authors are developing a series of computational breast phantoms based on breast CT data for imaging research. In this work, the authors develop a program that will allow a user to alter the phantoms to simulate the effect of gravity and compression of the breast (craniocaudal or mediolateral oblique) making the phantoms applicable to multimodality imaging. This application utilizes a template finite-element (FE) breast model that can be applied to their presegmented voxelized breast phantoms. The FE model is automatically fit to the geometry of a given breast phantom, and the material properties of each element are set based on the segmented voxels contained within the element. The loading and boundary conditions, which include gravity, are then assigned based on a user-defined position and compression. The effect of applying these loads to the breast is computed using a multistage contact analysis in FEBio, a freely available and well-validated FE software package specifically designed for biomedical applications. The resulting deformation of the breast is then applied to a boundary mesh representation of the phantom that can be used for simulating medical images. An efficient script performs the above actions seamlessly. The user only needs to specify which voxelized breast phantom to use, the compressed thickness, and orientation of the breast. The authors utilized their FE application to simulate compressed states of the breast indicative of mammography and tomosynthesis. Gravity and compression were simulated on example phantoms and used to generate mammograms in the craniocaudal or mediolateral oblique views. The simulated mammograms show a high degree of realism illustrating the utility of the FE method in simulating imaging data of repositioned and compressed breasts. The breast phantoms and the compression software can become a useful resource to the breast imaging research community. These phantoms can then be used to evaluate and compare imaging modalities that involve different positioning and compression of the breast.

Efficient compression of molecular dynamics trajectory files.

PubMed

Marais, Patrick; Kenwood, Julian; Smith, Keegan Carruthers; Kuttel, Michelle M; Gain, James

2012-10-15

We investigate whether specific properties of molecular dynamics trajectory files can be exploited to achieve effective file compression. We explore two classes of lossy, quantized compression scheme: "interframe" predictors, which exploit temporal coherence between successive frames in a simulation, and more complex "intraframe" schemes, which compress each frame independently. Our interframe predictors are fast, memory-efficient and well suited to on-the-fly compression of massive simulation data sets, and significantly outperform the benchmark BZip2 application. Our schemes are configurable: atomic positional accuracy can be sacrificed to achieve greater compression. For high fidelity compression, our linear interframe predictor gives the best results at very little computational cost: at moderate levels of approximation (12-bit quantization, maximum error ≈ 10(-2) Å), we can compress a 1-2 fs trajectory file to 5-8% of its original size. For 200 fs time steps-typically used in fine grained water diffusion experiments-we can compress files to ~25% of their input size, still substantially better than BZip2. While compression performance degrades with high levels of quantization, the simulation error is typically much greater than the associated approximation error in such cases. Copyright © 2012 Wiley Periodicals, Inc.

Lattice and beam optics design for suppression of CSR-induced emittance growth at the KEK-ERL test facility

NASA Astrophysics Data System (ADS)

Shimada, M.; Yokoya, K.; Suwada, T.; Enomoto, A.

2007-06-01

The lattice and beam optics of the arc section of the KEK-ERL test facility, having an energy of 200 MeV, were optimized to efficiently suppress emittance growth based on a simulation using a particle-tracking method taking coherent synchrotron radiation effects into account. The lattice optimization in the arc section was performed under two conditions: a high-current mode with a bunch charge of 76.9 pC without bunch compression, and a short-bunch mode with bunch compression, producing a final bunch length of around 0.1 ps. The simulation results showed that, in the high-current mode, emittance growth was efficiently suppressed by keeping a root-mean-square (rms) bunch length of 1 ps at a bunch charge of 76.9 pC, and in the short-bunch mode, emittance growth was kept within permissible limits with a maximum allowable bunch charge of 23.1 pC at an rms bunch length of 0.1 ps.

One-dimensional magnetohydrodynamics of a cylindrical liner imploded by an azimuthal magnetic field and compressing an axial field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamann, F., E-mail: franck.hamann@cea.fr; Combis, P.; Videau, L.

The one-dimensional magnetohydrodynamics of a plasma cylindrical liner is addressed in the case of a two components magnetic field. The azimuthal component is responsible for the implosion of the liner and the axial field is compressed inside the liner. A complete set of analytical profiles for the magnetic field components, the density, and the local velocity are proposed at the scale of the liner thickness. Numerical simulations are also presented to test the validity of the analytical formulas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Wei-Yang

Foam materials are used to protect sensitive components from impact loading. In order to predict and simulate the foam performance under various loading conditions, a validated foam model is needed and the mechanical properties of foams need to be characterized. Uniaxial compression and tension tests were conducted for different densities of foams under various temperatures and loading rates. Crush stress, tensile strength, and elastic modulus were obtained. A newly developed confined compression experiment provided data for investigating the foam flow direction. A biaxial tension experiment was also developed to explore the damage surface of a rigid polyurethane foam.

A Preliminary Study on the Toxic Combustion Products Testing of Polymers Used in High-Pressure Oxygen Systems

NASA Technical Reports Server (NTRS)

Hshieh, Fu-Yu; Beeson, Harold D.

2004-01-01

One likely cause of polymer ignition in a high-pressure oxygen system is adiabatic-compression heating of polymers caused by pneumatic impact. Oxidative _ pyrolysis or combustion of polymers in a high-pressure oxygen system could generate toxic gases. This paper reports the preliminary results of toxic combustion product testing of selected polymers in a pneumatic-impact test system. Five polymers commonly used in high-pressure oxygen systems, Nylon 6/6, polychlorotrifluoroethylene (CTFE), polytetrafluoroethylene (PTFE), fluoroelastomer (Viton(TradeMark) A), and nitrile rubber (Buna N), were tested in a pneumatic-impact test system at 2500- or 3500-psia oxygen pressure. The polymers were ignited and burned, then combustion products were collected in a stainless-steel sample bottle and analyzed by GC/MS/IRD, GC/FID, and GC/Methanizer/FID. The results of adiabatic-compression tests show that combustion of hydrocarbon polymers, nitrogen-containing polymers, and halogenated polymers in high-pressure oxygen systems are relatively complete. Toxicity of the combustion product gas is presumably much lower than the combustion product gas generated from ambient-pressure oxygen (or air) environments. The NASA-Lewis equilibrium code was used to determine the composition of combustion product gas generated from a simulated, adiabatic-compression test of nine polymers. The results are presented and discussed.

Novel Method to Characterize and Model the Multiaxial Constitutive and Damage Response of Energetic Materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaneshige, Michael J.; Rabbi, Md Fazle; Kaneshige, Michael J.

2017-12-01

Simulant polymer bonded explosives are widely used to simulate the mechanical response of real energetic materials. In this paper, the fracture resistance of a simulant polymer bo nded explosive (PBX) is experimentally investigated. The simulant is composed of 80 wt.% soda lime glass beads (SLGB) and 20 wt.% high impact Polystyrene 825 (HIPS). Brazilian disk tests are performed to characterize the tensile and compressive properties. Fracture toughness and energy tests are performed in the semi - circular bending (SCB) configuration on 80, 81, 82, and 83 wt % SLGB compositions. Digital image correlation is performed to record the surface displacementsmore » and calculate surface strains during testing. The m icromechanical behavior of ductile and brittle fracture are evaluated using digital microscopy and scanning electron microscopy of the fracture surface. It is determined that (i) the manufacturing process produces a credible simulant of PBX properties, and (ii) the SCB test measures fracture resistance with a reasonable coefficient of variation.« less

Compressible homogeneous shear: Simulation and modeling

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

1992-01-01

Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

Compressible homogeneous shear - Simulation and modeling

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

1991-01-01

Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

Closed-loop controller for chest compressions based on coronary perfusion pressure: a computer simulation study.

PubMed

Wang, Chunfei; Zhang, Guang; Wu, Taihu; Zhan, Ningbo; Wang, Yaling

2016-03-01

High-quality cardiopulmonary resuscitation contributes to cardiac arrest survival. The traditional chest compression (CC) standard, which neglects individual differences, uses unified standards for compression depth and compression rate in practice. In this study, an effective and personalized CC method for automatic mechanical compression devices is provided. We rebuild Charles F. Babbs' human circulation model with a coronary perfusion pressure (CPP) simulation module and propose a closed-loop controller based on a fuzzy control algorithm for CCs, which adjusts the CC depth according to the CPP. Compared with a traditional proportion-integration-differentiation (PID) controller, the performance of the fuzzy controller is evaluated in computer simulation studies. The simulation results demonstrate that the fuzzy closed-loop controller results in shorter regulation time, fewer oscillations and smaller overshoot than traditional PID controllers and outperforms the traditional PID controller for CPP regulation and maintenance.

Characterization of compression behaviors of fully covered biodegradable polydioxanone biliary stent for human body: A numerical approach by finite element model.

PubMed

Liu, Yanhui; Zhang, Peihua

2016-09-01

This paper presents a study of the compression behaviors of fully covered biodegradable polydioxanone biliary stents (FCBPBs) developed for human body by finite element method. To investigate the relationship between the compression force and structure parameter (monofilament diameter and braid-pin number), nine numerical models based on actual biliary stent were established, the simulation and experimental results are in good agreement with each other when calculating the compression force derived from both experiment and simulation results, indicating that the simulation results can be provided a useful reference to the investigation of biliary stents. The stress distribution on FCBPBSs was studied to optimize the structure of FCBPBSs. In addition, the plastic dissipation analysis and plastic strain of FCBPBSs were obtained via the compression simulation, revealing the structure parameter effect on the tolerance. Copyright © 2016 Elsevier Ltd. All rights reserved.

Investigation of GDL compression effects on the performance of a PEM fuel cell cathode by lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Molaeimanesh, G. R.; Nazemian, M.

2017-08-01

Proton exchange membrane (PEM) fuel cells with a great potential for application in vehicle propulsion systems will have a promising future. However, to overcome the exiting challenges against their wider commercialization further fundamental research is inevitable. The effects of gas diffusion layer (GDL) compression on the performance of a PEM fuel cell is not well-recognized; especially, via pore-scale simulation technique capturing the fibrous microstructure of the GDL. In the current investigation, a stochastic microstructure reconstruction method is proposed which can capture GDL microstructure changes by compression. Afterwards, lattice Boltzmann pore-scale simulation technique is adopted to simulate the reactive gas flow through 10 different cathode electrodes with dissimilar carbon paper GDLs produced from five different compression levels and two different carbon fiber diameters. The distributions of oxygen mole fraction, water vapor mole fraction and current density for the simulated cases are presented and analyzed. The results of simulations demonstrate that when the fiber diameter is 9 μm adding compression leads to lower average current density while when the fiber diameter is 7 μm the compression effect is not monotonic.

Evaluation of upper body muscle activity during cardiopulmonary resuscitation performance in simulated microgravity

NASA Astrophysics Data System (ADS)

Waye, A. B.; Krygiel, R. G.; Susin, T. B.; Baptista, R.; Rehnberg, L.; Heidner, G. S.; de Campos, F.; Falcão, F. P.; Russomano, T.

2013-09-01

Performance of efficient single-person cardiopulmonary resuscitation (CPR) is vital to maintain cardiac and cerebral perfusion during the 2-4 min it takes for deployment of advanced life support during a space mission. The aim of the present study was to investigate potential differences in upper body muscle activity during CPR performance at terrestrial gravity (+1Gz) and in simulated microgravity (μG). Muscle activity of the triceps brachii, erector spinae, rectus abdominis and pectoralis major was measured via superficial electromyography in 20 healthy male volunteers. Four sets of 30 external chest compressions (ECCs) were performed on a mannequin. Microgravity was simulated using a body suspension device and harness; the Evetts-Russomano (ER) method was adopted for CPR performance in simulated microgravity. Heart rate and perceived exertion via Borg scores were also measured. While a significantly lower depth of ECCs was observed in simulated microgravity, compared with +1Gz, it was still within the target range of 40-50 mm. There was a 7.7% decrease of the mean (±SEM) ECC depth from 48 ± 0.3 mm at +1Gz, to 44.3 ± 0.5 mm during microgravity simulation (p < 0.001). No significant difference in number or rate of compressions was found between the two conditions. Heart rate displayed a significantly larger increase during CPR in simulated microgravity than at +1Gz, the former presenting a mean (±SEM) of 23.6 ± 2.91 bpm and the latter, 76.6 ± 3.8 bpm (p < 0.001). Borg scores were 70% higher post-microgravity compressions (17 ± 1) than post +1Gz compressions (10 ± 1) (p < 0.001). Intermuscular comparisons showed the triceps brachii to have significantly lower muscle activity than each of the other three tested muscles, in both +1Gz and microgravity. As shown by greater Borg scores and heart rate increases, CPR performance in simulated microgravity is more fatiguing than at +1Gz. Nevertheless, no significant difference in muscle activity between conditions was found, a result that is favourable for astronauts, given the inevitable muscular and cardiovascular deconditioning that occurs during space travel.

Geotechnical properties of core sample from methane hydrate deposits in Eastern Nankai Trough

NASA Astrophysics Data System (ADS)

Yoneda, J.; Masui, A.; Egawa, K.; Konno, Y.; Ito, T.; Kida, M.; Jin, Y.; Suzuki, K.; Nakatsuka, Y.; Tenma, N.; Nagao, J.

2013-12-01

To date, MH extraction has been simulated in several ways to help ensure the safe and efficient production of gas, with a particular focus on the investigation of landsliding, uneven settlement, and production well integrity. The mechanical properties of deep sea sediments and gas-hydrate-bearing sediments, typically obtained through material tests, are essential for the geomechanical response simulation to hydrate extraction. We conducted triaxial compression tests and the geotechnical properties of the sediments was investigated. Consolidated undrained compression tests were performed for silty sediments. And consolidated drained tests were performed for sandy samples. In addition, permeability was investigated from isotropic consolidation results. These core samples recovered from methane hydrate deposits of Daini Atsumi Knoll in Eastern Nankai Trough during the 2012 JOGMEC/JAPEX Pressure coring operation. The pressure core samples were rapidly depressurized on the ship and it were frozen using liquid nitrogen to prevent MH dissociation. Undrained shear strength of the core samples increase linearly with depth from sea floor. These core samples should be normally consolidated sample in-situ. Drained shear strength increases dramatically with hydrate saturation increases. Peak stress ratio q/p' of the core sample which has 73% of hydrate saturation was approximately 2.0 and it decrease down to 1.3 at the critical state. Dilatancy also changed from compressive tendency to dilative tendency with hydrate saturation increase. This study was financially supported by the Research Consortium for Methane Hydrate Resources in Japan (MH21 Research Consortium) that carries out Japan's Methane Hydrate R&D Program conducted by the Ministry of Economy, Trade and Industry (METI).

Experimental Characterization and Material Modelling of an AZ31 Magnesium Sheet Alloy at Elevated Temperatures under Consideration of the Tension-Compression Asymmetry

NASA Astrophysics Data System (ADS)

Behrens, B.-A.; Bouguecha, A.; Bonk, C.; Dykiert, M.

2017-09-01

Magnesium sheet alloys have a great potential as a construction material in the aerospace and automotive industry. However, the current state of research regarding temperature dependent material parameters for the description of the plastic behaviour of magnesium sheet alloys is scarce in literature and accurate statements concerning yield criteria and appropriate characterization tests to describe the plastic behaviour of a magnesium sheet alloy at elevated temperatures in deep drawing processes are to define. Hence, in this paper the plastic behaviour of the well-established magnesium sheet alloy AZ31 has been characterized by means of convenient mechanical tests (e. g. tension, compression and biaxial tests) at temperatures between 180 and 230 °C. In this manner, anisotropic and hardening behaviour as well as differences between the tension-compression asymmetry of the yield locus have been estimated. Furthermore, using the evaluated data from the above mentioned tests, two different yield criteria have been parametrized; the commonly used Hill’48 and an orthotropic yield criterion, CPB2006, which was developed especially for materials with hexagonal close packed lattice structure and is able to describe an asymmetrical yielding behaviour regarding tensile and compressive stress states. Numerical simulations have been finally carried out with both yield functions in order to assess the accuracy of the material models.

A Correction to the Stress-Strain Curve During Multistage Hot Deformation of 7150 Aluminum Alloy Using Instantaneous Friction Factors

NASA Astrophysics Data System (ADS)

Jiang, Fulin; Tang, Jie; Fu, Dinfa; Huang, Jianping; Zhang, Hui

2018-04-01

Multistage stress-strain curve correction based on an instantaneous friction factor was studied for axisymmetric uniaxial hot compression of 7150 aluminum alloy. Experimental friction factors were calculated based on continuous isothermal axisymmetric uniaxial compression tests at various deformation parameters. Then, an instantaneous friction factor equation was fitted by mathematic analysis. After verification by comparing single-pass flow stress correction with traditional average friction factor correction, the instantaneous friction factor equation was applied to correct multistage stress-strain curves. The corrected results were reasonable and validated by multistage relative softening calculations. This research provides a broad potential for implementing axisymmetric uniaxial compression in multistage physical simulations and friction optimization in finite element analysis.

Effect of the rate of chest compression familiarised in previous training on the depth of chest compression during metronome-guided cardiopulmonary resuscitation: a randomised crossover trial.

PubMed

Bae, Jinkun; Chung, Tae Nyoung; Je, Sang Mo

2016-02-12

To assess how the quality of metronome-guided cardiopulmonary resuscitation (CPR) was affected by the chest compression rate familiarised by training before the performance and to determine a possible mechanism for any effect shown. Prospective crossover trial of a simulated, one-person, chest-compression-only CPR. Participants were recruited from a medical school and two paramedic schools of South Korea. 42 senior students of a medical school and two paramedic schools were enrolled but five dropped out due to physical restraints. Senior medical and paramedic students performed 1 min of metronome-guided CPR with chest compressions only at a speed of 120 compressions/min after training for chest compression with three different rates (100, 120 and 140 compressions/min). Friedman's test was used to compare average compression depths based on the different rates used during training. Average compression depths were significantly different according to the rate used in training (p<0.001). A post hoc analysis showed that average compression depths were significantly different between trials after training at a speed of 100 compressions/min and those at speeds of 120 and 140 compressions/min (both p<0.001). The depth of chest compression during metronome-guided CPR is affected by the relative difference between the rate of metronome guidance and the chest compression rate practised in previous training. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

The impact of manual defibrillation technique on no-flow time during simulated cardiopulmonary resuscitation.

PubMed

Perkins, Gavin D; Davies, Robin P; Soar, Jasmeet; Thickett, David R

2007-04-01

Rapid defibrillation is the most effective strategy for establishing return of spontaneous circulation following cardiac arrest due to ventricular fibrillation. The aim of this study is to measure the delay due to of charging the defibrillator during chest compression in an attempt to reduce the duration of the pre-shock pause in between cessation of chest compressions and shock delivery as advocated by the American Heart Association (AHA) guidelines compared to charging the defibrillator immediately following rhythm analysis without resuming chest compressions as recommended by the European Resuscitation Council (ERC). This was a randomised controlled cross over trial comparing pre-shock pause times when defibrillation was performed on a manikin according to the AHA and ERC guidelines using paddles and hands free defibrillation systems. The pre-shock pause between cessation of chest compression and shock delivery was significantly different between techniques (Friedman test, P<0.0001). ERC paddles technique had the greatest pre-shock pause (7.4 s [6.7-11.2]) followed by ERC hands free (7.0 s [6.5-8.5]) and AHA paddles (1.6 s [1.1-2.3]). AHA hands free took the least amount of time (1.5 s [0.8-1.5]). Extrapolating these data to older defibrillators with longer charge times saw pre-shock pause intervals of 9 s (Codemaster XL) and 12 s (Lifepak 20) with the ERC approach. This study demonstrated clinically significant delays to defibrillation by analysing and charging the defibrillator without performing concurrent chest compressions. In a simulated scenario, charging the defibrillator whilst performing chest compressions was perceived as safe and significantly reduced the pre-shock pause between cessation of chest compression and shock delivery.

Analysis of the microstructure and mechanical performance of composite resins after accelerated artificial aging.

PubMed

De Oliveira Daltoé, M; Lepri, C Penazzo; Wiezel, J Guilherme G; Tornavoi, D Cremonezzi; Agnelli, J A Marcondes; Reis, A Cândido Dos

2013-03-01

Researches that assess the behavior of dental materials are important for scientific and industrial development especially when they are tested under conditions that simulate the oral environment, so this work analyzed the compressive strength and microstructure of three composite resins subjected to accelerated artificial aging (AAA). Three composites resins of 3M (P90, P60 and Z100) were analyzed and were obtained 16 specimens for each type (N.=48). Half of each type were subjected to UV-C system AAA and then were analyzed the surfaces of three aged specimens and three not aged of each type through the scanning electron microscope (SEM). After, eight specimens of each resin, aged and not aged, were subjected to compression test. After statistical analysis of compressive strength values, it was found that there was difference between groups (α <0.05). The resin specimens aged P60 presented lower values of compressive strength statistically significant when compared to the not subject to the AAA. For the other composite resins, there was no difference, regardless of aging, a fact confirmed by SEM. The results showed that the AAA influenced the compressive strength of the resin aged P60; confirmed by surface analysis by SEM, which showed greater structural disarrangement on surface material.

Three-dimensional numerical simulation for plastic injection-compression molding

NASA Astrophysics Data System (ADS)

Zhang, Yun; Yu, Wenjie; Liang, Junjie; Lang, Jianlin; Li, Dequn

2018-03-01

Compared with conventional injection molding, injection-compression molding can mold optical parts with higher precision and lower flow residual stress. However, the melt flow process in a closed cavity becomes more complex because of the moving cavity boundary during compression and the nonlinear problems caused by non-Newtonian polymer melt. In this study, a 3D simulation method was developed for injection-compression molding. In this method, arbitrary Lagrangian- Eulerian was introduced to model the moving-boundary flow problem in the compression stage. The non-Newtonian characteristics and compressibility of the polymer melt were considered. The melt flow and pressure distribution in the cavity were investigated by using the proposed simulation method and compared with those of injection molding. Results reveal that the fountain flow effect becomes significant when the cavity thickness increases during compression. The back flow also plays an important role in the flow pattern and redistribution of cavity pressure. The discrepancy in pressures at different points along the flow path is complicated rather than monotonically decreased in injection molding.

Some Results Relevant to Statistical Closures for Compressible Turbulence

NASA Technical Reports Server (NTRS)

Ristorcelli, J. R.

1998-01-01

For weakly compressible turbulent fluctuations there exists a small parameter, the square of the fluctuating Mach number, that allows an investigation using a perturbative treatment. The consequences of such a perturbative analysis in three different subject areas are described: 1) initial conditions in direct numerical simulations, 2) an explanation for the oscillations seen in the compressible pressure in the direct numerical simulations of homogeneous shear, and 3) for turbulence closures accounting for the compressibility of velocity fluctuations. Initial conditions consistent with small turbulent Mach number asymptotics are constructed. The importance of consistent initial conditions in the direct numerical simulation of compressible turbulence is dramatically illustrated: spurious oscillations associated with inconsistent initial conditions are avoided, and the fluctuating dilatational field is some two orders of magnitude smaller for a compressible isotropic turbulence. For the isotropic decay it is shown that the choice of initial conditions can change the scaling law for the compressible dissipation. A two-time expansion of the Navier-Stokes equations is used to distinguish compressible acoustic and compressible advective modes. A simple conceptual model for weakly compressible turbulence - a forced linear oscillator is described. It is shown that the evolution equations for the compressible portions of turbulence can be understood as a forced wave equation with refraction. Acoustic modes of the flow can be amplified by refraction and are able to manifest themselves in large fluctuations of the compressible pressure.

Prospects for Nonlinear Laser Diagnostics in the Jet Noise Laboratory

NASA Technical Reports Server (NTRS)

Herring, Gregory C.; Hart, Roger C.; Fletcher, mark T.; Balla, R. Jeffrey; Henderson, Brenda S.

2007-01-01

Two experiments were conducted to test whether optical methods, which rely on laser beam coherence, would be viable for off-body flow measurement in high-density, compressible-flow wind tunnels. These tests measured the effects of large, unsteady density gradients on laser diagnostics like laser-induced thermal acoustics (LITA). The first test was performed in the Low Speed Aeroacoustics Wind Tunnel (LSAWT) of NASA Langley Research Center's Jet Noise Laboratory (JNL). This flow facility consists of a dual-stream jet engine simulator (with electric heat and propane burners) exhausting into a simulated flight stream, reaching Mach numbers up to 0.32. A laser beam transited the LSAWT flow field and was imaged with a high-speed gated camera to measure beam steering and transverse mode distortion. A second, independent test was performed on a smaller laboratory jet (Mach number < 1.2 and mass flow rate < 0.1 kg/sec). In this test, time-averaged LITA velocimetry and thermometry were performed at the jet exit plane, where the effect of unsteady density gradients is observed on the LITA signal. Both experiments show that LITA (and other diagnostics relying on beam overlap or coherence) faces significant hurdles in the high-density, compressible, and turbulent flow environments similar to those of the JNL.

Modeling Micro-cracking Behavior of Bukit Timah Granite Using Grain-Based Model

NASA Astrophysics Data System (ADS)

Peng, Jun; Wong, Louis Ngai Yuen; Teh, Cee Ing; Li, Zhihuan

2018-01-01

Rock strength and deformation behavior has long been recognized to be closely related to the microstructure and the associated micro-cracking process. A good understanding of crack initiation and coalescence mechanisms will thus allow us to account for the variation of rock strength and deformation properties from a microscopic view. This paper numerically investigates the micro-cracking behavior of Bukit Timah granite by using a grain-based modeling approach. First, the principles of grain-based model adopted in the two-dimensional Particle Flow Code and the numerical model generation procedure are reviewed. The micro-parameters of the numerical model are then calibrated to match the macro-properties of the rock obtained from tension and compression tests in the laboratory. The simulated rock properties are in good agreement with the laboratory test results with the errors less than ±6%. Finally, the calibrated model is used to study the micro-cracking behavior and the failure modes of the rock under direct tension and under compression with different confining pressures. The results reveal that when the numerical model is loaded in direct tension, only grain boundary tensile cracks are generated, and the simulated macroscopic fracture agrees well with the results obtained in laboratory tests. When the model is loaded in compression, the ratio of grain boundary tensile cracks to grain boundary shear cracks decreases with the increase in confining pressure. In other words, the results show that as the confining pressure increases, the failure mechanism changes from tension to shear. The simulated failure mode of the model changes from splitting to shear as the applied confining pressure gradually increases, which is comparable with that observed in laboratory tests. The grain-based model used in this study thus appears promising for further investigation of microscopic and macroscopic behavior of crystalline rocks under different loading conditions.

Comparison of intubation modalities in a simulated cardiac arrest with uninterrupted chest compressions.

PubMed

Tandon, Navin; McCarthy, Matthew; Forehand, Brett; Carlson, Jestin N

2014-10-01

Interruptions in chest compressions during cardiopulmonary resuscitation can negatively impact survival. Several new endotracheal intubation (ETI) techniques including video laryngoscopy may allow for ETI with minimal or no interruptions in chest compressions. We sought to determine the impact of three different ETI techniques upon time to intubation (TTI) in a simulated cardiac arrest during uninterrupted chest compression. We performed a randomised crossover study with a convenience sample of emergency physicians using three different ETI techniques: direct laryngoscopy (DL), GlideScope video laryngoscopy (GVL) and GlideScope video laryngoscopy with bougie (GVL-B). Providers performed ETI on a manikin on a hospital bed with concurrent chest compressions. Our primary outcome, TTI, was defined as the time from insertion of the laryngoscope blade until first breath. Given the correlated nature of the data, we used the paired t test to assess the differences in mean TTIs between GVL minus DL and GVL-B minus DL. We also ran the analysis stratified by provider experience. We enrolled 20 providers with a median TTI (IQR) by device of: DL 27 s (20.3, 35.4), GVL 20.6 s (17.7, 27.1) and GVL-B 60.1 s (39.1, 99). The mean GVL-DL difference was -10.1 s (-17.9-2.3) while the mean GVL-B-DL difference was 45.6 s (19.8-71.4) (p<0.001). The GVL-B required the greatest TTI across providers of varying experience levels. In this simulated model of cardiac arrest with uninterrupted chest compressions, TTI was shorter for GVL than DL while use of the GVL with bougie resulted in longer TTI. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Novel biofuel formulations for enhanced vehicle performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Dennis; Narayan, Ramani; Berglund, Kris

2013-08-30

This interdisciplinary research program at Michigan State University, in collaboration with Ford Motor Company, has explored the application of tailored or designed biofuels for enhanced vehicle performance and reduced emissions. The project has included a broad range of experimental research, from chemical and biological formation of advanced biofuel components to multicylinder engine testing of blended biofuels to determine engine performance parameters. In addition, the project included computation modeling of biofuel physical and combustion properties, and simulation of advanced combustion modes in model engines and in single cylinder engines. Formation of advanced biofuel components included the fermentation of five-carbon and six-carbonmore » sugars to n-butanol and to butyric acid, two four-carbon building blocks. Chemical transformations include the esterification of the butyric acid produced to make butyrate esters, and the esterification of succinic acid with n-butanol to make dibutyl succinate (DBS) as attractive biofuel components. The conversion of standard biodiesel, made from canola or soy oil, from the methyl ester to the butyl ester (which has better fuel properties), and the ozonolysis of biodiesel and the raw oil to produce nonanoate fuel components were also examined in detail. Physical and combustion properties of these advanced biofuel components were determined during the project. Physical properties such as vapor pressure, heat of evaporation, density, and surface tension, and low temperature properties of cloud point and cold filter plugging point were examined for pure components and for blends of components with biodiesel and standard petroleum diesel. Combustion properties, particularly emission delay that is the key parameter in compression ignition engines, was measured in the MSU Rapid Compression Machine (RCM), an apparatus that was designed and constructed during the project simulating the compression stroke of an internal combustion engine under highly instrumented conditions. Simulation of and experimentation on combustion in single and multicylinder engines was carried out in detail throughout the project. The combustion behavior of biofuel blends neat and in petroleum were characterized in the MSU optical engine, in part to validate results obtained in the RCM and to provide data for comparison with simulations. Simulation of in- cylinder, low-temperature combustion included development of an extensive fuel injection model that included fuel spray breakup, evaporation, and ignition, along with prediction of cylinder temperature, pressure, and work produced. Single cylinder and multicylinder engine tests under advanced low-temperature combustion conditions conducted at Ford Motor Company validated experimental and simulation results obtained in the MSU engine and in MSU simulations. Single cylinder engine tests of an advanced biofuel containing biodiesel and dibutyl succinate, carried out under low-temperature combustion conditions, showed similar power generation and gas-phase emissions (CO, HC, NOx), but a reduction in particulates of as much as 60% relative to neat biodiesel and 95% relative to petroleum diesel at the same operating conditions. This remarkable finding suggests that biofuels may be able to play a role in eliminating the need for particulate removal systems in diesel vehicles. The multicylinder engine tests at Ford, carried out using butyl nonanoate as an advanced biofuel, also gave promising results, showing a strong decline in particulate emissions and simultaneously a modest decrease in NOx emissions relative to standard petroleum diesel at the same conditions. In summary, this project has shown that advanced biofuels and their blends are capable of maintaining performance while reducing emissions, particularly particulates (soot), in 3 compression ignition engines. The interdisciplinary nature of biofuel production and testing has identified fuel properties that are capable of producing such performance, thus providing direction for the implementation of renewable fuels for U.S. transportation. The testing and simulation studies have deepened our understanding of combustion 1) by advancing the rigor with which simulations can be carried out and 2) by illustrating that differences in biofuel and petroleum fuel properties can be used to predict differences in combustion behavior in engines. The future viability of biofuels for compression ignition (diesel) engines is now subject to economic (cost) uncertainty more so than to technical barriers, as the advanced biofuel blends developed here can improve cold-weather fuel properties, provide similar engine performance, and reduce emissions.« less

Numerical and Experimental Studies on Crash Characteristics of Closed Form Thin—Walled Steel Sections

NASA Astrophysics Data System (ADS)

Veerasamy, M.; Srinivasan, K.; Prakash, Raghu V.

2010-10-01

The crash behavior of Cold Rolled Mild Steel (CRMS) closed form thin section was studied by conducting compressive tests at loading velocities of 5 mm/min and 1000 mm/min. The numerical simulations were conducted for the same experimental conditions to understand the deformation shape, peak forces and energy absorption capacity of sections at different impact velocities. The simulation results correlated well with the experimental results.

Mechanical Properties of Polymers Used for Anatomical Components in the Warrior Injury Assessment Manikin (WIAMan) Technology Demonstrator

DTIC Science & Technology

2016-07-01

14. ABSTRACT The Warrior Injury Assessment Manikin was developed to provide an instrumented anthropomorphic test device (ATD) specifically...underbody blasts . To achieve that goal, the ATD used numerous polymeric materials for component parts that simulate human tissue and enable compliance in...strain rate, underbody blast , mechanical testing, tension, compression 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT

Suggested techniques, equipment, and standards for the testing of hand insecticide-spraying equipment

PubMed Central

Hall, Lawrence B.

1955-01-01

The new demands placed upon application equipment by the introduction of modern insecticides have revealed the deficiencies of this equipment when required for continuous use on a large scale. If adequate equipment is to be produced, specifications must be based not only on basic materials tests but also on “use” tests, in which the conditions of field use are simulated. The author outlines suggested techniques to be followed and standards to be adopted in testing the performance of compression sprayers and allied equipment, with reference to the following features: compression-sprayer tank fatigue; tank impact; pump resistance to bursting; pump resistance to collapse; pump friction; cut-off valve durability; constant-pressure valves; cut-off valve actuation; hose flexure; hose tension and bursting-pressure; hose friction; gaskets, valve faces, and similar non-metallic parts; nozzle-orifice erosion; and nozzle pattern. ImagesFIG. 1FIG. 14FIG. 20 PMID:14364189

Compact and portable digitally controlled device for testing footwear materials: technical note.

PubMed

Foto, James G

2008-01-01

Little or no practical decision-making data are available to the foot-care provider regarding the selection of orthotic materials used in therapeutic footwear. A device for simulating in-shoe forefoot conditions for the testing of orthosis materials is described. Materials are tested for their effectiveness by evaluating and comparing stress-strain and dynamic compression fatigue characteristics. The device, called the Cyclical Compression Tester (CCT), has been optimized for size, simplicity of construction, and cost. Application of the device ranges from the clinician deciding the useful life of single- and multidensity orthosis materials to the researcher characterizing materials for finite-element analysis modeling. This real-time CCT device and custom user interface combine to make an evaluation tool useful for testing how the pressure distribution of in-shoe materials changes over time in therapeutic footwear for those with peripheral neuropathy at risk for foot injury.

Geopolymers from lunar and Martian soil simulants

NASA Astrophysics Data System (ADS)

Alexiadis, Alessio; Alberini, Federico; Meyer, Marit E.

2017-01-01

This work discusses the geopolymerization of lunar dust simulant JSC LUNAR-1A and Martian dust simulant JSC MARS-1A. The geopolymerization of JSC LUNAR-1A occurs easily and produces a hard, rock-like, material. The geopolymerization of JSC MARS-1A requires milling to reduce the particle size. Tests were carried out to measure, for both JSC LUNAR-1A and JSC MARS-1A geopolymers, the maximum compressive and flexural strengths. In the case of the lunar simulant, these are higher than those of conventional cements. In the case of the Martian simulant, they are close to those of common building bricks.

Distributed Relaxation Multigrid and Defect Correction Applied to the Compressible Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Thomas, J. L.; Diskin, B.; Brandt, A.

1999-01-01

The distributed-relaxation multigrid and defect- correction methods are applied to the two- dimensional compressible Navier-Stokes equations. The formulation is intended for high Reynolds number applications and several applications are made at a laminar Reynolds number of 10,000. A staggered- grid arrangement of variables is used; the coupled pressure and internal energy equations are solved together with multigrid, requiring a block 2x2 matrix solution. Textbook multigrid efficiencies are attained for incompressible and slightly compressible simulations of the boundary layer on a flat plate. Textbook efficiencies are obtained for compressible simulations up to Mach numbers of 0.7 for a viscous wake simulation.

Gradient Compression Stockings may Prevent Recovery after Bed Rest Deconditioning

NASA Technical Reports Server (NTRS)

Stenger, Michael B.; Lee, Stuart M.; Westby, Christian M.; Willig, Michael C.; Platts, Steven H.

2011-01-01

Introduction: Astronauts continue to wear a compression garment during and immediately after landing to prevent orthostatic intolerance (OI). We recently developed a custom-fitted, 3-piece garment that consists of thigh-high stockings with biker-style shorts that provides continuous, gradient compression: 55 mmHg at the ankle that decreases to approximately 20 mmHg at the top of the leg and 15 mmHg over the abdomen. This garment has been shown to be effective in preventing symptoms of OI during a short stand test after Space Shuttle missions, but symptoms may persist for several days after a long-duration mission in some astronauts. The purpose of this study was to confirm the effectiveness of wearing these elastic, gradient compression garments during orthostatic testing after 2 weeks of 6 degree head-down tilt bed rest as a model of spaceflight and to determine whether they would impact recovery after bed rest. Methods: Eight (5 treatment, 3 control) of 16 subjects have completed this study to-date. All subjects wore the 3-piece garment from waking until tilt testing (3 h) as a simulation of the timeline for astronauts on landing day (BR+0). Control subjects removed the garment after the tilt test. Treatment subjects wore the garment for the remainder of the day and wore lower compression thigh-high only garments on the day after bed rest (BR+1). Blood pressure, heart rate, and stroke volume responses to a 15-min 80 degree head-up tilt test were determined before 2 weeks of 6 degree head-down tilt, and on BR+0 and BR+1. Plasma volume (PV) was measured before each of these test sessions. Data are mean SE. Results: Compression garments prevented signs of OI on BR+0; all subjects in both groups completed the full 15-min test. Heart rate responses to tilt were lower on BR+0 than all other test days. Control subjects demonstrated a marginal PV decrease after bed rest, but showed typical recovery the day after bed rest (BR+0: 2.32 plus or minus 0.15 L to BR+1: 2.79 plus or minus 0.15 L). Treatment subjects did not recover PV the day after bed rest (BR+0: 2.61 plus or minus 0.23 L to BR+1: 2.61 plus or minus 0.23 L). Conclusion: Abdomen-high compression garments, which are effective in preventing post-bed rest orthostatic intolerance, may slow recovery of PV. Modified garments with reduced compression may be necessary to prevent prolonging recovery.

Study of a Compression-Molding Process for Ultraviolet Light-Emitting Diode Exposure Systems via Finite-Element Analysis

PubMed Central

Wu, Kuo-Tsai; Hwang, Sheng-Jye; Lee, Huei-Huang

2017-01-01

Although wafer-level camera lenses are a very promising technology, problems such as warpage with time and non-uniform thickness of products still exist. In this study, finite element simulation was performed to simulate the compression molding process for acquiring the pressure distribution on the product on completion of the process and predicting the deformation with respect to the pressure distribution. Results show that the single-gate compression molding process significantly increases the pressure at the center of the product, whereas the multi-gate compressing molding process can effectively distribute the pressure. This study evaluated the non-uniform thickness of product and changes in the process parameters through computer simulations, which could help to improve the compression molding process. PMID:28617315

Artificial acoustic stiffness reduction in fully compressible, direct numerical simulation of combustion

NASA Astrophysics Data System (ADS)

Wang, Yi; Trouvé, Arnaud

2004-09-01

A pseudo-compressibility method is proposed to modify the acoustic time step restriction found in fully compressible, explicit flow solvers. The method manipulates terms in the governing equations of order Ma2, where Ma is a characteristic flow Mach number. A decrease in the speed of acoustic waves is obtained by adding an extra term in the balance equation for total energy. This term is proportional to flow dilatation and uses a decomposition of the dilatational field into an acoustic component and a component due to heat transfer. The present method is a variation of the pressure gradient scaling (PGS) method proposed in Ramshaw et al (1985 Pressure gradient scaling method for fluid flow with nearly uniform pressure J. Comput. Phys. 58 361-76). It achieves gains in computational efficiencies similar to PGS: at the cost of a slightly more involved right-hand-side computation, the numerical time step increases by a full order of magnitude. It also features the added benefit of preserving the hydrodynamic pressure field. The original and modified PGS methods are implemented into a parallel direct numerical simulation solver developed for applications to turbulent reacting flows with detailed chemical kinetics. The performance of the pseudo-compressibility methods is illustrated in a series of test problems ranging from isothermal sound propagation to laminar premixed flame problems.

Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting.

PubMed

Contuzzi, Nicola; Campanelli, Sabina L; Casavola, Caterina; Lamberti, Luciano

2013-08-13

The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456-0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading.

High-Speed Photography of Detonation Propagation in Dynamically Precompressed Liquid Explosives

NASA Astrophysics Data System (ADS)

Petel, Oren; Higgins, Andrew; Yoshinaka, Akio; Zhang, Fan

2007-06-01

The propagation of detonation in shock compressed nitromethane was observed with a high speed framing camera. The test explosive, nitromethane, was compressed by a reverberating shock wave to pressures on the order of 10 GPa prior to being detonated by a secondary detonation event. The pressure and density in the test explosive prior to detonation was determined using two methods: manganin strain gauge measurements and LS-DYNA simulations. The velocity of the detonation front was determined from consecutive frames and correlated to the density of the explosive post-reverberating shock wave and prior to being detonated. Observing detonation propagation under these non-ambient conditions provides data which can be useful in the validation of equation of state models.

Investigation on Flexure Test of Composite Beam of Repair Materials and Substrate Concrete for Durable Repair

NASA Astrophysics Data System (ADS)

Pattnaik, Rashmi R.; Rangaraju, Prasada Rao

2014-12-01

An experimental study was conducted on composite beam of repair materials and substrate concrete to investigate the failures of concrete repair due to differences in strength of repair materials and substrate concrete. In this investigation the flexural strength, load-deflection curves and failure patterns of the composite beam specimens are studied for the durability of the concrete repair. Flexure test was conducted to simulate tensile stress in the concrete repair material. Compressive strength and split tensile strength of the repair materials and substrate concrete are investigated to aid in the analysis of the concrete repair. It was observed that the repair materials of higher compressive strength than the substrate concrete are causing an incompatible failure in the concrete repair.

On the design of a DEA-based device to pot entially assist lower leg disorders: an analytical and FEM investigation accounting for nonlinearities of the leg and device deformations.

PubMed

Pourazadi, Shahram; Ahmadi, Sadegh; Menon, Carlo

2015-11-05

One of the recommended treatments for disorders associated with the lower extremity venous insufficiency is the application of external mechanical compression. Compression stockings and elastic bandages are widely used for the purpose of compression therapy and are usually designed to exert a specified value or range of compression on the leg. However, the leg deforms under external compression, which can lead to undesirable variations in the amount of compression applied by the compression bandages. In this paper, the use of an active compression bandage (ACB), whose compression can be regulated through an electrical signal, is investigated. The ACB is based on the use of dielectric elastomer actuators. This paper specifically investigates, via both analytical and non-linear numerical simulations, the potential pressure the ACB can apply when the compliancy of the human leg is taken into account. The work underpins the need to account for the compressibility of the leg when designing compression garments for lower extremity venous insufficiency. A mathematical model is used to simulate the volumetric change of a calf when compressed. Suitable parameters for this calf model are selected from the literature where the calf, from ankle to knee, is divided into six different regions. An analytical electromechanical model of the ACB, which considers its compliancy as a function of its pre-stretch and electricity applied, is used to predict the ACB's behavior. Based on these calf and ACB analytical models, a simulation is performed to investigate the interaction between the ACB and the human calf with and without an electrical stimulus applied to the ACB. This simulation is validated by non-linear analysis performed using a software based on the finite element method (FEM). In all simulations, the ACB's elastomer is stretched to a value in the range between 140 and 220 % of its initial length. Using data from the literature, the human calf model, which is examined in this work, has different compliancy in its different regions. For example, when a 28.5 mmHg (3.8 kPa) of external compression is applied to the entire calf, the ankle shows a 3.7 % of volume change whereas the knee region undergoes a 2.7 % of volume change. The paper presents the actual pressure in the different regions of the calf for different values of the ACB's stretch ratio when it is either electrically activated or not activated, and when compliancy of the leg is either considered or not considered. For example, results of the performed simulation show that about 10 % variation in compression in the ankle region is expected when the ACB initially applies 6 kPa and the compressibility of the calf is first considered and then not considered. Such a variation reduces to 5 % when the initial pressure applied by the ACB reduced by half. Comparison with non-linear FEM simulations show that the analytical models used in this work can closely estimate interaction between an active compression bandage and a human calf. In addition, compliancy of the leg should not be neglected when either designing a compression band or predicting the compressive force it can exert. The methodology proposed in this work can be extended to other types of elastic compression bandages and garments for biomedical applications.

Finite Element Simulation of Compression Molding of Woven Fabric Carbon Fiber/Epoxy Composites: Part I Material Model Development

DOE PAGES

Li, Yang; Zhao, Qiangsheng; Mirdamadi, Mansour; ...

2016-01-06

Woven fabric carbon fiber/epoxy composites made through compression molding are one of the promising choices of material for the vehicle light-weighting strategy. Previous studies have shown that the processing conditions can have substantial influence on the performance of this type of the material. Therefore the optimization of the compression molding process is of great importance to the manufacturing practice. An efficient way to achieve the optimized design of this process would be through conducting finite element (FE) simulations of compression molding for woven fabric carbon fiber/epoxy composites. However, performing such simulation remains a challenging task for FE as multiple typesmore » of physics are involved during the compression molding process, including the epoxy resin curing and the complex mechanical behavior of woven fabric structure. In the present study, the FE simulation of the compression molding process of resin based woven fabric composites at continuum level is conducted, which is enabled by the implementation of an integrated material modeling methodology in LS-Dyna. Specifically, the chemo-thermo-mechanical problem of compression molding is solved through the coupling of three material models, i.e., one thermal model for temperature history in the resin, one mechanical model to update the curing-dependent properties of the resin and another mechanical model to simulate the behavior of the woven fabric composites. Preliminary simulations of the carbon fiber/epoxy woven fabric composites in LS-Dyna are presented as a demonstration, while validations and models with real part geometry are planned in the future work.« less

Mesoscale Phase Field Modeling of Glass Strengthening Under Triaxial Compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yulan; Sun, Xin

2015-09-28

Recent hydraulic bomb and confined sleeve tests on transparent armor glass materials such as borosilicate glass and soda-lime glass showed that the glass strength was a function of confinement pressure. The measured stress-strain relation is not a straight line as most brittle materials behave under little or no confinement. Moreover, borosilicate glass exhibited a stronger compressive strength when compared to soda-lime glass, even though soda-lime has higher bulk and shear moduli as well as apparent yield strength. To better understand these experimental findings, a mesoscale phase field model is developed to simulate the nonlinear stress versus strain behaviors under confinementmore » by considering heterogeneity formation under triaxial compression and the energy barrier of a micro shear banding event (referred to as pseudo-slip hereafter) in the amorphous glass. With calibrated modeling parameters, the simulation results demonstrate that the developed phase field model can quantitatively predict the pressure-dependent strength, and it can also explain the difference between the two types of glasses from the perspective of energy barrier associated with a pseudo-slip event.« less

Characterization of synthetic foam structures used to manufacture artificial vertebral trabecular bone.

PubMed

Fürst, David; Senck, Sascha; Hollensteiner, Marianne; Esterer, Benjamin; Augat, Peter; Eckstein, Felix; Schrempf, Andreas

2017-07-01

Artificial materials reflecting the mechanical properties of human bone are essential for valid and reliable implant testing and design. They also are of great benefit for realistic simulation of surgical procedures. The objective of this study was therefore to characterize two groups of self-developed synthetic foam structures by static compressive testing and by microcomputed tomography. Two mineral fillers and varying amounts of a blowing agent were used to create different expansion behavior of the synthetic open-cell foams. The resulting compressive and morphometric properties thus differed within and also slightly between both groups. Apart from the structural anisotropy, the compressive and morphometric properties of the synthetic foam materials were shown to mirror the respective characteristics of human vertebral trabecular bone in good approximation. In conclusion, the artificial materials created can be used to manufacture valid synthetic bones for surgical training. Further, they provide novel possibilities for studying the relationship between trabecular bone microstructure and biomechanical properties. Copyright © 2017 Elsevier B.V. All rights reserved.

SUPG Finite Element Simulations of Compressible Flows

NASA Technical Reports Server (NTRS)

Kirk, Brnjamin, S.

2006-01-01

The Streamline-Upwind Petrov-Galerkin (SUPG) finite element simulations of compressible flows is presented. The topics include: 1) Introduction; 2) SUPG Galerkin Finite Element Methods; 3) Applications; and 4) Bibliography.

Simulation of Inviscid Compressible Multi-Phase Flow with Condensation

NASA Technical Reports Server (NTRS)

Kelleners, Philip

2003-01-01

Condensation of vapours in rapid expansions of compressible gases is investigated. In the case of high temperature gradients the condensation will start at conditions well away from thermodynamic equilibrium of the fluid. In those cases homogeneous condensation is dominant over heterogeneous condensation. The present work is concerned with development of a simulation tool for computation of high speed compressible flows with homogeneous condensation. The resulting ow solver should preferably be accurate and robust to be used for simulation of industrial flows in general geometries.

Progress with lossy compression of data from the Community Earth System Model

NASA Astrophysics Data System (ADS)

Xu, H.; Baker, A.; Hammerling, D.; Li, S.; Clyne, J.

2017-12-01

Climate models, such as the Community Earth System Model (CESM), generate massive quantities of data, particularly when run at high spatial and temporal resolutions. The burden of storage is further exacerbated by creating large ensembles, generating large numbers of variables, outputting at high frequencies, and duplicating data archives (to protect against disk failures). Applying lossy compression methods to CESM datasets is an attractive means of reducing data storage requirements, but ensuring that the loss of information does not negatively impact science objectives is critical. In particular, test methods are needed to evaluate whether critical features (e.g., extreme values and spatial and temporal gradients) have been preserved and to boost scientists' confidence in the lossy compression process. We will provide an overview on our progress in applying lossy compression to CESM output and describe our unique suite of metric tests that evaluate the impact of information loss. Further, we will describe our processes how to choose an appropriate compression algorithm (and its associated parameters) given the diversity of CESM data (e.g., variables may be constant, smooth, change abruptly, contain missing values, or have large ranges). Traditional compression algorithms, such as those used for images, are not necessarily ideally suited for floating-point climate simulation data, and different methods may have different strengths and be more effective for certain types of variables than others. We will discuss our progress towards our ultimate goal of developing an automated multi-method parallel approach for compression of climate data that both maximizes data reduction and minimizes the impact of data loss on science results.

3D Compressed Sensing for Highly Accelerated Hyperpolarized 13C MRSI With In Vivo Applications to Transgenic Mouse Models of Cancer

PubMed Central

Hu, Simon; Lustig, Michael; Balakrishnan, Asha; Larson, Peder E. Z.; Bok, Robert; Kurhanewicz, John; Nelson, Sarah J.; Goga, Andrei; Pauly, John M.; Vigneron, Daniel B.

2010-01-01

High polarization of nuclear spins in liquid state through hyperpolarized technology utilizing dynamic nuclear polarization has enabled the direct monitoring of 13C metabolites in vivo at a high signal-to-noise ratio. Acquisition time limitations due to T1 decay of the hyperpolarized signal require accelerated imaging methods, such as compressed sensing, for optimal speed and spatial coverage. In this paper, the design and testing of a new echo-planar 13C three-dimensional magnetic resonance spectroscopic imaging (MRSI) compressed sensing sequence is presented. The sequence provides up to a factor of 7.53 in acceleration with minimal reconstruction artifacts. The key to the design is employing x and y gradient blips during a fly-back readout to pseudorandomly undersample kf-kx-ky space. The design was validated in simulations and phantom experiments where the limits of undersampling and the effects of noise on the compressed sensing nonlinear reconstruction were tested. Finally, this new pulse sequence was applied in vivo in preclinical studies involving transgenic prostate cancer and transgenic liver cancer murine models to obtain much higher spatial and temporal resolution than possible with conventional echo-planar spectroscopic imaging methods. PMID:20017160

Temperature Evolution During Plane Strain Compression Of Tertiary Oxide Scale On Steel

NASA Astrophysics Data System (ADS)

Suarez, L.; Vanden Eynde, X.; Lamberigts, M.; Houbaert, Y.

2007-04-01

An oxide scale layer always forms at the steel surface during hot rolling. This scale layer separates the work roll from the metal substrate. Understanding the deformation behaviour and mechanical properties of the scale is of great interest because it affects the frictional conditions during hot rolling and the heat-transfer behaviour at the strip-roll interface. A thin wustite scale layer (<20 μm) was created under controlled conditions in an original laboratory device adequately positioned in a compression testing machine to investigate plane strain compression. Oxidation tests were performed on an ULC steel grade. After the oxide growth at 1050°C, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. PSC experiments were performed at a deformation temperature of 1050°C, with reduction ratios from 5 to 70%, and strain rates of 10s-1 under controlled gas atmospheres. Results show that for wustite, ductility is obvious at 1050°C. Even after deformation oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness. The tool/sample temperature difference seems to be the reason for the unexpected ductile behaviour of the scale layer.

The effects of simulated bone loss on the implant-abutment assembly and likelihood of fracture: an in vitro study.

PubMed

Manzoor, Behzad; Suleiman, Mahmood; Palmer, Richard M

2013-01-01

The crestal bone level around a dental implant may influence its strength characteristics by offering protection against mechanical failures. Therefore, the present study investigated the effect of simulated bone loss on modes, loads, and cycles to failure in an in vitro model. Different amounts of bone loss were simulated: 0, 1.5, 3.0, and 4.5 mm from the implant head. Forty narrow-diameter (3.0-mm) implant-abutment assemblies were tested using compressive bending and cyclic fatigue testing. Weibull and accelerated life testing analysis were used to assess reliability and functional life. Statistical analyses were performed using the Fisher-Exact test and the Spearman ranked correlation. Compressive bending tests showed that the level of bone loss influenced the load-bearing capacity of implant-abutment assemblies. Fatigue testing showed that the modes, loads, and cycles to failure had a statistically significant relationship with the level of bone loss. All 16 samples with bone loss of 3.0 mm or more experienced horizontal implant body fractures. In contrast, 14 of 16 samples with 0 and 1.5 mm of bone loss showed abutment and screw fractures. Weibull and accelerated life testing analysis indicated a two-group distribution: the 0- and 1.5-mm bone loss samples had better functional life and reliability than the 3.0- and 4.5-mm samples. Progressive bone loss had a significant effect on modes, loads, and cycles to failure. In addition, bone loss influenced the functional life and reliability of the implant-abutment assemblies. Maintaining crestal bone levels is important in ensuring biomechanical sustainability and predictable long-term function of dental implant assemblies.

Development of a stress-mode sensitive viscoelastic constitutive relationship for asphalt concrete: experimental and numerical modeling

NASA Astrophysics Data System (ADS)

Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam

2017-08-01

Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.

Microstructure based simulations for prediction of flow curves and selection of process parameters for inter-critical annealing in DP steel

NASA Astrophysics Data System (ADS)

Deepu, M. J.; Farivar, H.; Prahl, U.; Phanikumar, G.

2017-04-01

Dual phase steels are versatile advanced high strength steels that are being used for sheet metal applications in automotive industry. It also has the potential for application in bulk components like gear. The inter-critical annealing in dual phase steels is one of the crucial steps that determine the mechanical properties of the material. Selection of the process parameters for inter-critical annealing, in particular, the inter-critical annealing temperature and time is important as it plays a major role in determining the volume fractions of ferrite and martensite, which in turn determines the mechanical properties. Selection of these process parameters to obtain a particular required mechanical property requires large number of experimental trials. Simulation of microstructure evolution and virtual compression/tensile testing can help in reducing the number of such experimental trials. In the present work, phase field modeling implemented in the commercial software Micress® is used to predict the microstructure evolution during inter-critical annealing. Virtual compression tests are performed on the simulated microstructure using finite element method implemented in the commercial software, to obtain the effective flow curve of the macroscopic material. The flow curves obtained by simulation are experimentally validated with physical simulation in Gleeble® and compared with that obtained using linear rule of mixture. The methodology could be used in determining the inter-critical annealing process parameters required for achieving a particular flow curve.

Three-dimensional multigrid Navier-Stokes computations for turbomachinery applications

NASA Astrophysics Data System (ADS)

Subramanian, S. V.

1989-07-01

The fully three-dimensional, time-dependent compressible Navier-Stokes equations in cylindrical coordinates are presently used, in conjunction with the multistage Runge-Kutta numerical integration scheme for solution of the governing flow equations, to simulate complex flowfields within turbomechanical components whose pertinent effects encompass those of viscosity, compressibility, blade rotation, and tip clearance. Computed results are presented for selected cascades, emphasizing the code's capabilities in the accurate prediction of such features as airfoil loadings, exit flow angles, shocks, and secondary flows. Computations for several test cases have been performed on a Cray-YMP, using nearly 90,000 grid points.

Brief compression-only cardiopulmonary resuscitation training video and simulation with homemade mannequin improves CPR skills.

PubMed

Wanner, Gregory K; Osborne, Arayel; Greene, Charlotte H

2016-11-29

Cardiopulmonary resuscitation (CPR) training has traditionally involved classroom-based courses or, more recently, home-based video self-instruction. These methods typically require preparation and purchase fee; which can dissuade many potential bystanders from receiving training. This study aimed to evaluate the effectiveness of teaching compression-only CPR to previously untrained individuals using our 6-min online CPR training video and skills practice on a homemade mannequin, reproduced by viewers with commonly available items (towel, toilet paper roll, t-shirt). Participants viewed the training video and practiced with the homemade mannequin. This was a parallel-design study with pre and post training evaluations of CPR skills (compression rate, depth, hand position, release), and hands-off time (time without compressions). CPR skills were evaluated using a sensor-equipped mannequin and two blinded CPR experts observed testing of participants. Twenty-four participants were included: 12 never-trained and 12 currently certified in CPR. Comparing pre and post training, the never-trained group had improvements in average compression rate per minute (64.3 to 103.9, p = 0.006), compressions with correct hand position in 1 min (8.3 to 54.3, p = 0.002), and correct compression release in 1 min (21.2 to 76.3, p < 0.001). The CPR-certified group had adequate pre and post-test compression rates (>100/min), but an improved number of compressions with correct release (53.5 to 94.7, p < 0.001). Both groups had significantly reduced hands-off time after training. Achieving adequate compression depths (>50 mm) remained problematic in both groups. Comparisons made between groups indicated significant improvements in compression depth, hand position, and hands-off time in never-trained compared to CPR-certified participants. Inter-rater agreement values were also calculated between the CPR experts and sensor-equipped mannequin. A brief internet-based video coupled with skill practice on a homemade mannequin improved compression-only CPR skills, especially in the previously untrained participants. This training method allows for widespread compression-only CPR training with a tactile learning component, without fees or advance preparation.

Effects of repetitive or intensified instructions in telephone assisted, bystander cardiopulmonary resuscitation: an investigator-blinded, 4-armed, randomized, factorial simulation trial.

PubMed

van Tulder, R; Roth, D; Krammel, M; Laggner, R; Heidinger, B; Kienbacher, C; Novosad, H; Chwojka, C; Havel, C; Sterz, F; Schreiber, W; Herkner, H

2014-01-01

Compression depth is frequently suboptimal in cardiopulmonary resuscitation (CPR). We investigated effects of intensified wording and/or repetitive target depth instructions on compression depth in telephone-assisted, protocol driven, bystander CPR on a simulation manikin. Thirty-two volunteers performed 10 min of compression only-CPR in a prospective, investigator-blinded, 4-armed, factorial setting. Participants were randomized either to standard wording ("push down firmly 5 cm"), intensified wording ("it is very important to push down 5 cm every time") or standard or intensified wording repeated every 20s. Three dispatchers were randomized to give these instructions. Primary outcome was relative compression depth (absolute compression depth minus leaning depth). Secondary outcomes were absolute distance, hands-off times as well as BORG-scale and nine-hole peg test (NHPT), pulse rate and blood pressure to reflect physical exertion. We applied a random effects linear regression model. Relative compression depth was 35 ± 10 mm (standard) versus 31 ± 11 mm (intensified wording) versus 25 ± 8 mm (repeated standard) and 31 ± 14 mm (repeated intensified wording). Adjusted for design, body mass index and female sex, intensified wording and repetition led to decreased compression depth of 13 (95%CI -25 to -1) mm (p=0.04) and 9 (95%CI -21 to 3) mm (p=0.13), respectively. Secondary outcomes regarding intensified wording showed significant differences for absolute distance (43 ± 2 versus 20 (95%CI 3-37) mm; p=0.01) and hands-off times (60 ± 40 versus 157 (95%CI 63-251) s; p=0.04). In protocol driven, telephone-assisted, bystander CPR, intensified wording and/or repetitive target depth instruction will not improve compression depth compared to the standard instruction. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, Cyrus K.; Steinberger, Craig J.

1990-01-01

This research is involved with the implementation of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program to extend the present capabilities of this method was initiated for the treatment of chemically reacting flows. In the DNS efforts, the focus is on detailed investigations of the effects of compressibility, heat release, and non-equilibrium kinetics modelings in high speed reacting flows. Emphasis was on the simulations of simple flows, namely homogeneous compressible flows, and temporally developing high speed mixing layers.

The analysis and modelling of dilatational terms in compressible turbulence

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.; Kreiss, H. O.

1991-01-01

It is shown that the dilatational terms that need to be modeled in compressible turbulence include not only the pressure-dilatation term but also another term - the compressible dissipation. The nature of these dilatational terms in homogeneous turbulence is explored by asymptotic analysis of the compressible Navier-Stokes equations. A non-dimensional parameter which characterizes some compressible effects in moderate Mach number, homogeneous turbulence is identified. Direct numerical simulations (DNS) of isotropic, compressible turbulence are performed, and their results are found to be in agreement with the theoretical analysis. A model for the compressible dissipation is proposed; the model is based on the asymptotic analysis and the direct numerical simulations. This model is calibrated with reference to the DNS results regarding the influence of compressibility on the decay rate of isotropic turbulence. An application of the proposed model to the compressible mixing layer has shown that the model is able to predict the dramatically reduced growth rate of the compressible mixing layer.

The analysis and modeling of dilatational terms in compressible turbulence

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.; Kreiss, H. O.

1989-01-01

It is shown that the dilatational terms that need to be modeled in compressible turbulence include not only the pressure-dilatation term but also another term - the compressible dissipation. The nature of these dilatational terms in homogeneous turbulence is explored by asymptotic analysis of the compressible Navier-Stokes equations. A non-dimensional parameter which characterizes some compressible effects in moderate Mach number, homogeneous turbulence is identified. Direct numerical simulations (DNS) of isotropic, compressible turbulence are performed, and their results are found to be in agreement with the theoretical analysis. A model for the compressible dissipation is proposed; the model is based on the asymptotic analysis and the direct numerical simulations. This model is calibrated with reference to the DNS results regarding the influence of compressibility on the decay rate of isotropic turbulence. An application of the proposed model to the compressible mixing layer has shown that the model is able to predict the dramatically reduced growth rate of the compressible mixing layer.

An open-loop controlled active lung simulator for preterm infants.

PubMed

Cecchini, Stefano; Schena, Emiliano; Silvestri, Sergio

2011-01-01

We describe the underlying theory, design and experimental evaluation of an electromechanical analogue infant lung to simulate spontaneous breathing patterns of preterm infants. The aim of this work is to test the possibility to obtain breathing patterns of preterm infants by taking into consideration the air compressibility. Respiratory volume function represents the actuation pattern, and pulmonary pressure and flow-rate waveforms are mathematically obtained through the application of the perfect gas and adiabatic laws. The mathematical model reduces the simulation interval into a step shorter than 1 ms, allowing to consider an entire respiratory act as composed of a large number of almost instantaneous adiabatic transformations. The device consists of a spherical chamber where the air is compressed by four cylinder-pistons, moved by stepper motors, and flows through a fluid-dynamic resistance, which also works as flow-rate sensor. Specifically designed software generates the actuators motion, based on the desired ventilation parameters, without controlling the gas pneumatic parameters with a closed-loop. The system is able to simulate tidal volumes from 3 to 8 ml, breathing frequencies from 60 to 120 bpm and functional residual capacities from 25 to 80 ml. The simulated waveforms appear very close to the measured ones. Percentage differences on the tidal volume waveform vary from 7% for the tidal volume of 3 ml, down to 2.2-3.5% for tidal volumes in the range of 4-7 ml, and 1.3% for the tidal volume equal to 8 ml in the whole breathing frequency and functional residual capacity ranges. The open-loop electromechanical simulator shows that gas compressibility can be theoretically assessed in the typical pneumatic variable range of preterm infant respiratory mechanics. Copyright © 2010 IPEM. Published by Elsevier Ltd. All rights reserved.

Data compression/error correction digital test system. Appendix 2: Theory of operation

NASA Technical Reports Server (NTRS)

1972-01-01

An overall block diagram of the DC/EC digital system test is shown. The system is divided into two major units: the transmitter and the receiver. In operation, the transmitter and receiver are connected only by a real or simulated transmission link. The system inputs consist of: (1) standard format TV video, (2) two channels of analog voice, and (3) one serial PCM bit stream.

Low-Power Baseline Test Results for the GPU 3 Stirling Engine

NASA Technical Reports Server (NTRS)

Thieme, L. G.

1979-01-01

A 7.5 kW (10 hp) Stirling engine was converted to a research configuration in order to obtain data for validating Stirling-cycle computer simulations. Test results for a range of heater-tube gas temperatures, mean compression-space pressures, and engine speeds with both helium and hydrogen as the working fluid are summarized. An instrumentation system to determine indicated work is described and preliminary results are presented.

Reactivity-controlled compression ignition drive cycle emissions and fuel economy estimations using vehicle system simulations

DOE PAGES

Curran, Scott J.; Gao, Zhiming; Wagner, Robert M.

2014-12-22

In-cylinder blending of gasoline and diesel to achieve reactivity-controlled compression ignition has been shown to reduce NO X and soot emissions while maintaining or improving brake thermal efficiency as compared with conventional diesel combustion. The reactivity-controlled compression ignition concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load, allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. In this paper, a multi-mode reactivity-controlled compression ignition strategy is employed where the engine switches from reactivity-controlled compression ignition to conventional diesel combustionmore » when speed and load demand are outside of the experimentally determined reactivity-controlled compression ignition range. The potential for reactivity-controlled compression ignition to reduce drive cycle fuel economy and emissions is not clearly understood and is explored here by simulating the fuel economy and emissions for a multi-mode reactivity-controlled compression ignition–enabled vehicle operating over a variety of US drive cycles using experimental engine maps for multi-mode reactivity-controlled compression ignition, conventional diesel combustion, and a 2009 port-fuel injected gasoline engine. Drive cycle simulations are completed assuming a conventional mid-size passenger vehicle with an automatic transmission. Multi-mode reactivity-controlled compression ignition fuel economy simulation results are compared with the same vehicle powered by a representative 2009 port-fuel injected gasoline engine over multiple drive cycles. Finally, engine-out drive cycle emissions are compared with conventional diesel combustion, and observations regarding relative gasoline and diesel tank sizes needed for the various drive cycles are also summarized.« less

Limit analysis, rammed earth material and Casagrande test

NASA Astrophysics Data System (ADS)

El-Nabouch, Ranime; Pastor, Joseph; Bui, Quoc-Bao; Plé, Olivier

2018-02-01

The present paper is concerned with the simulation of the Casagrande test carried out on a rammed earth material for wall-type structures in the framework of Limit Analysis (LA). In a preliminary study, the material is considered as a homogeneous Coulomb material, and existing LA static and kinematic codes are used for the simulation of the test. In each loading case, static and kinematic bounds coincide; the corresponding exact solution is a two-rigid-block mechanism together with a quasi-constant stress vector and a velocity jump also constant along the interface, for the three loading cases. In a second study, to take into account the influence of compressive loadings related to the porosity of the material, an elliptic criterion (denoted Cohesive Cam-Clay, CCC) is defined based on recent homogenization results about the hollow sphere model for porous Coulomb materials. Finally, original finite element formulations of the static and mixed kinematic methods for the CCC material are developed and applied to the Casagrande test. The results are the same than above, except that this time the velocity jump depends on the compressive loading, which is more realistic but not satisfying fully the experimental observations. Therefore, the possible extensions of this work towards non-standard direct methods are analyzed in the conclusion section.

Elastic behavior of brain simulants in comparison to porcine brain at different loading velocities.

PubMed

Falland-Cheung, Lisa; Scholze, Mario; Hammer, Niels; Waddell, J Neil; Tong, Darryl C; Brunton, Paul A

2018-01-01

Blunt force impacts to the head and the resulting internal force transmission to the brain and other cranial tissue are difficult to measure. To model blunt force impact scenarios, the compressive properties resembling tissue elasticity are of importance. Therefore, this study investigated and compared the elastic behavior of gelatin, alginate, agar/glycerol and agar/glycerol/water simulant materials to that of porcine brain in a fresh and unfixed condition. Specimens, 10 × 10 × 10mm 3 , were fabricated and tested at 22°C, apart from gelatin which was conditioned to 4°C prior to testing. For comparison, fresh porcine brains were sourced and prepared to the same dimensions as the simulants. Specimens underwent compression tests at crosshead displacement rates of 2.5, 10 and 16mms -1 (equivalent to strain rates of 0.25, 1 and 1.6s -1 ), obtaining apparent elastic moduli values at different strain rate intervals (0-0.2, 0.2-0.4 and 0.4-0.5). The results of this study indicate that overall all simulant materials had an apparent elastic moduli similar in magnitude across all strain ranges compared to brain, even though comparatively higher, especially the apparent elastic moduli values of alginate. In conclusion, while agar/glycerol/water and agar/glycerol had similar apparent elastic moduli in magnitude and the closest apparent elastic moduli in the initial strain range (E 1 ), gelatin showed the most similar values to fresh porcine brain at the transitional (E 2 ) and higher strain range (E 3 ). The simulant materials and the fresh porcine brain exhibited strain rate dependent behavior, with increasing elastic moduli upon increasing loading velocities. Copyright © 2017 Elsevier Ltd. All rights reserved.

Developments in the simulation of compressible inviscid and viscous flow on supercomputers

NASA Technical Reports Server (NTRS)

Steger, J. L.; Buning, P. G.

1985-01-01

In anticipation of future supercomputers, finite difference codes are rapidly being extended to simulate three-dimensional compressible flow about complex configurations. Some of these developments are reviewed. The importance of computational flow visualization and diagnostic methods to three-dimensional flow simulation is also briefly discussed.

How oral environment simulation affects ceramic failure behavior.

PubMed

Lodi, Ediléia; Weber, Kátia R; Benetti, Paula; Corazza, Pedro H; Della Bona, Álvaro; Borba, Márcia

2018-05-01

Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear. The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions. Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37ºC water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37ºC water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×10 6 and 2×10 6 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data. A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (P f ) for 1×10 6 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×10 6 cycles, the P f increased approximately 20% in comparison with the values predicted for 1×10 6 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping). Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic. Copyright © 2017 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Simulation of diesel engine emissions on the example of Fiat Panda in the NEDC test

NASA Astrophysics Data System (ADS)

Botwinska, Katarzyna; Mruk, Remigiusz; Słoma, Jacek; Tucki, Karol; Zaleski, Mateusz

2017-10-01

Road transport may be deemed a strategic branch of modern economy. Unfortunately, a rapid increase in the number of on-road motor vehicles entails some negative consequences as well, for instance, excessive concentration of exhausts produced by engines which results in deterioration of air quality. EURO emission standards which define acceptable limits for exhaust emissions of power units is an example of an activity performed in attempt to improve air quality. The EURO standard defines permissible amount of exhausts produced by a vehicle. Presently new units are examined through NEDC test. For the purpose of this thesis, a virtual test stand in a form of a computer simulation of a chassis dynamometer was used to simulate emission of a diesel engine (compression-ignition engine) in the NEDC test. Actual parameters of the 1.3 MultiJet engine of the Fiat Panda passenger car of 2014 were applied in the model. The simulation was carried out in the Matlab Simulink environment. The simulation model of the Fiat Panda passenger car enables the designation of the emission waveform for all test stages which corresponds to the values received during an approval test in real-life conditions.

Influence of Tension-Compression Asymmetry on the Mechanical Behavior of AZ31B Magnesium Alloy Sheets in Bending

NASA Astrophysics Data System (ADS)

Zhou, Ping; Beeh, Elmar; Friedrich, Horst E.

2016-03-01

Magnesium alloys are promising materials for lightweight design in the automotive industry due to their high strength-to-mass ratio. This study aims to study the influence of tension-compression asymmetry on the radius of curvature and energy absorption capacity of AZ31B-O magnesium alloy sheets in bending. The mechanical properties were characterized using tension, compression, and three-point bending tests. The material exhibits significant tension-compression asymmetry in terms of strength and strain hardening rate due to extension twinning in compression. The compressive yield strength is much lower than the tensile yield strength, while the strain hardening rate is much higher in compression. Furthermore, the tension-compression asymmetry in terms of r value (Lankford value) was also observed. The r value in tension is much higher than that in compression. The bending results indicate that the AZ31B-O sheet can outperform steel and aluminum sheets in terms of specific energy absorption in bending mainly due to its low density. In addition, the AZ31B-O sheet was deformed with a larger radius of curvature than the steel and aluminum sheets, which brings a benefit to energy absorption capacity. Finally, finite element simulation for three-point bending was performed using LS-DYNA and the results confirmed that the larger radius of curvature of a magnesium specimen is mainly attributed to the high strain hardening rate in compression.

A biomechanical evaluation of a cannulated compressive screw for use in fractures of the scaphoid.

PubMed

Rankin, G; Kuschner, S H; Orlando, C; McKellop, H; Brien, W W; Sherman, R

1991-11-01

The compressive force generated by a 3.5 mm ASIF cannulated cancellous screw with a 5 mm head was compared with that generated by a standard 3.5 mm ASIF screw (6 mm head), a 2.7 mm ASIF screw (5 mm head), and a Herbert screw. The screws were evaluated in the laboratory with the use of a custom-designed load washer (transducer) to the maximum compressive force generated by each screw until failure, either by thread stripping or by head migration into the specimen. Testing was done on paired cadaver scaphoids. To minimize the variability that occurs with human bone, and because of the cost and difficulty of obtaining human tissue specimens, a study was also done on polyurethane foam simulated bones. The 3.5 cannulated screw generated greater compressive forces than the Herbert screw but less compression than the 2.7 mm and 3.5 mm ASIF cortical screws. The 3.5 mm cannulated screw offers more rigid internal fixation for scaphoid fractures than the Herbert screw and gives the added advantage of placement over a guide wire.

A method for data handling numerical results in parallel OpenFOAM simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anton, Alin; Muntean, Sebastian

Parallel computational fluid dynamics simulations produce vast amount of numerical result data. This paper introduces a method for reducing the size of the data by replaying the interprocessor traffic. The results are recovered only in certain regions of interest configured by the user. A known test case is used for several mesh partitioning scenarios using the OpenFOAM toolkit{sup ®}[1]. The space savings obtained with classic algorithms remain constant for more than 60 Gb of floating point data. Our method is most efficient on large simulation meshes and is much better suited for compressing large scale simulation results than the regular algorithms.

Dynamic biomechanical examination of the lumbar spine with implanted total disc replacement using a pendulum testing system.

PubMed

Daniels, Alan H; Paller, David J; Koruprolu, Sarath; McDonnell, Matthew; Palumbo, Mark A; Crisco, Joseph J

2012-11-01

Biomechanical cadaver investigation. To examine dynamic bending stiffness and energy absorption of the lumbar spine with and without implanted total disc replacement (TDR) under simulated physiological motion. The pendulum testing system is capable of applying physiological compressive loads without constraining motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. Five unembalmed, frozen human lumbar FSUs were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Synthes ProDisc-L TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5º resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N·m/º) was calculated and compared for each testing mode. In flexion/extension, the TDR constructs reached equilibrium with significantly (P < 0.05) fewer cycles than the intact FSU with compressive loads of 282 N, 385 N, and 488 N. Mean dynamic bending stiffness in flexion, extension, and lateral bending increased significantly with increasing load for both the intact FSU and TDR constructs (P < 0.001). In flexion, with increasing compressive loading from 181 N to 488 N, the bending stiffness of the intact FSUs increased from 4.0 N·m/º to 5.5 N·m/º, compared with 2.1 N·m/º to 3.6 N·m/º after TDR implantation. At each compressive load, the intact FSU was significantly stiffer than the TDR (P < 0.05). Lumbar FSUs with implanted TDR were found to be less stiff, but absorbed more energy during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion-preserving devices are not fully known, these results provide further insight into the biomechanical behavior of these devices under approximated physiological loading conditions.

Acoustically Driven Magnetized Target Fusion At General Fusion: An Overview

NASA Astrophysics Data System (ADS)

O'Shea, Peter; Laberge, M.; Donaldson, M.; Delage, M.; the Fusion Team, General

2016-10-01

Magnetized Target Fusion (MTF) involves compressing an initial magnetically confined plasma of about 1e23 m-3, 100eV, 7 Tesla, 20 cm radius, >100 μsec life with a 1000x volume compression in 100 microseconds. If near adiabatic compression is achieved, the final plasma of 1e26 m-3, 10keV, 700 Tesla, 2 cm radius, confined for 10 μsec would produce interesting fusion energy gain. General Fusion (GF) is developing an acoustic compression system using pneumatic pistons focusing a shock wave on the CT plasma in the center of a 3 m diameter sphere filled with liquid lead-lithium. Low cost driver, straightforward heat extraction, good tritium breeding ratio and excellent neutron protection could lead to a practical power plant. GF (65 employees) has an active plasma R&D program including both full scale and reduced scale plasma experiments and simulation of both. Although acoustic driven compression of full scale plasmas is the end goal, present compression studies use reduced scale plasmas and chemically accelerated Aluminum liners. We will review results from our plasma target development, motivate and review the results of dynamic compression field tests and briefly describe the work to date on the acoustic driver front.

Observational Signatures of Parametric Instability at 1AU

NASA Astrophysics Data System (ADS)

Bowen, T. A.; Bale, S. D.; Badman, S.

2017-12-01

Observations and simulations of inertial compressive turbulence in the solar wind are characterized by density structures anti-correlated with magnetic fluctuations parallel to the mean field. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures (PBS), kinetic ion acoustic waves, as well as the MHD slow mode. Recent work, specifically Verscharen et al. (2017), has highlighted the unexpected fluid like nature of the solar wind. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising and suggests the presence of a driving process. One possible candidate for the generation of compressive fluctuations in the solar wind is the parametric instability, in which large amplitude Alfvenic fluctuations decay into parallel propagating compressive waves. This work employs 10 years of WIND observations in order to test the parametric decay process as a source of compressive waves in the solar wind through comparing collisionless damping rates of compressive fluctuations with growth rates of the parametric instability. Preliminary results suggest that generation of compressive waves through parametric decay is overdamped at 1 AU. However, the higher parametric decay rates expected in the inner heliosphere likely allow for growth of the slow mode-the remnants of which could explain density fluctuations observed at 1AU.

Fitted hyperelastic parameters for Human brain tissue from reported tension, compression, and shear tests.

PubMed

Moran, Richard; Smith, Joshua H; García, José J

2014-11-28

The mechanical properties of human brain tissue are the subject of interest because of their use in understanding brain trauma and in developing therapeutic treatments and procedures. To represent the behavior of the tissue, we have developed hyperelastic mechanical models whose parameters are fitted in accordance with experimental test results. However, most studies available in the literature have fitted parameters with data of a single type of loading, such as tension, compression, or shear. Recently, Jin et al. (Journal of Biomechanics 46:2795-2801, 2013) reported data from ex vivo tests of human brain tissue under tension, compression, and shear loading using four strain rates and four different brain regions. However, they do not report parameters of energy functions that can be readily used in finite element simulations. To represent the tissue behavior for the quasi-static loading conditions, we aimed to determine the best fit of the hyperelastic parameters of the hyperfoam, Ogden, and polynomial strain energy functions available in ABAQUS for the low strain rate data, while simultaneously considering all three loading modes. We used an optimization process conducted in MATLAB, calling iteratively three finite element models developed in ABAQUS that represent the three loadings. Results showed a relatively good fit to experimental data in all loading modes using two terms in the energy functions. Values for the shear modulus obtained in this analysis (897-1653Pa) are in the range of those presented in other studies. These energy-function parameters can be used in brain tissue simulations using finite element models. Copyright © 2014 Elsevier Ltd. All rights reserved.

Instructions to "put the phone down" do not improve the quality of bystander initiated dispatcher-assisted cardiopulmonary resuscitation.

PubMed

Brown, Todd B; Saini, Devashish; Pepper, Tracy; Mirza, Muzna; Nandigam, Hari Krishna; Kaza, Niroop; Cofield, Stacey S

2008-02-01

The quality of early bystander CPR appears important in maximizing survival. This trial tests whether explicit instructions to "put the phone down" improve the quality of bystander initiated dispatch-assisted CPR. In a randomized, double-blinded, controlled trial, subjects were randomized to a modified version of the Medical Priority Dispatch System (MPDS) version 11.2 protocol or a simplified protocol, each with or without instruction to "put the phone down" during CPR. Data were recorded from a Laerdal Resusci Anne Skillreporter manikin. A simulated emergency medical dispatcher, contacted by cell phone, delivered standardized instructions. Primary outcome measures included chest compression rate, depth, and the proportion of compressions without error, with correct hand position, adequate depth, and total release. Time was measured in two distinct ways: time required for initiation of CPR and total amount of time hands were off the chest during CPR. Proportions were analyzed by Wilcoxon rank sum tests and time variables with ANOVA. All tests used a two-sided alpha-level of 0.05. Two hundred and fifteen subjects were randomized-107 in the "put the phone down" instruction group and 108 in the group without "put the phone down" instructions. The groups were comparable across demographic and experiential variables. The additional instruction to "put the phone down" had no effect on the proportion of compressions administered without error, with the correct depth, and with the correct hand position. Likewise, "put the phone down" did not affect the average compression depth, the average compression rate, the total hands-off-chest time, or the time to initiate chest compressions. A statistically significant, yet trivial, effect was found in the proportion of compressions with total release of the chest wall. Instructions to "put the phone down" had no effect on the quality of bystander initiated dispatcher-assisted CPR in this trial.

Study on the CO2 electric driven fixed swash plate type compressor for eco-friendly vehicles

NASA Astrophysics Data System (ADS)

Nam, Donglim; Kim, Kitae; Lee, Jehie; Kwon, Yunki; Lee, Geonho

2017-08-01

The purpose of this study is to experiment and to performance analysis about the electric-driven fixed swash plate compressor using alternate refrigerant(R744). Comprehensive simulation model for an electric driven compressor using CO2 for eco-friendly vehicle is presented. This model consists of compression model and dynamic model. The compression model included valve dynamics, leakage, and heat transfer models. And the dynamic model included frictional loss between piston ring and cylinder wall, frictional loss between shoe and swash plate, frictional loss of bearings, and electric efficiency. Especially, because the efficiency of an electric parts(motor and inverter) in the compressor affects the loss of the compressor, the dynamo test was performed. We made the designed compressor, and tested the performance of the compressor about the variety pressure conditions. Also we compared the performance analysis result and performance test result.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, C. K.; Steinberger, C. J.; Tsai, A.

1991-01-01

This research is involved with the implementations of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program was initiated to extend the present capabilities of this method for the treatment of chemically reacting flows, whereas in the DNS efforts, focus was on detailed investigations of the effects of compressibility, heat release, and nonequilibrium kinetics modeling in high speed reacting flows. The efforts to date were primarily focussed on simulations of simple flows, namely, homogeneous compressible flows and temporally developing hign speed mixing layers. A summary of the accomplishments is provided.

Hydro-mechanical properties of pressure core sediments recovered from the Krishna-Godavari Basin during India's National Gas Hydrate Program Expedition NGHP-02

NASA Astrophysics Data System (ADS)

Yoneda, J.; Oshima, M.; Kida, M.; Kato, A.; Konno, Y.; Jin, Y.; Waite, W. F.; Jang, J.; Kumar, P.; Tenma, N.

2017-12-01

Pressure coring and analysis technology allows for gas hydrate to be recovered from the deep seabed, transferred to the laboratory and characterized while continuously maintaining gas hydrate stability. For this study, dozens of hydrate-bearing pressure core sediment subsections recovered from the Krishna-Godavari Basin during India's National Gas Hydrate Program Expedition NGHP-02 were tested with Pressure Core Non-destructive Analysis Tools (PNATs) through a collaboration between Japan and India. PNATs, originally developed by AIST as a part of the Japanese National hydrate research program (MH21, funded by METI) conducted permeability, compression and consolidation tests under various effective stress conditions, including the in situ stress state estimated from downhole bulk density measurements. At the in situ effective stress, gas hydrate-bearing sediments had an effective permeability range of 0.01-10mD even at pore-space hydrate saturations above 60%. Permeability increased by 10 to 100 times after hydrate dissociation at the same effective stress, but these post-dissociation gains were erased when effective stress was increased from in situ values ( 1 MPa) to 10MPa in a simulation of the depressurization method for methane extraction from hydrate. Vertical-to-horizontal permeability anisotropy was also investigated. First-ever multi-stage loading tests and strain-rate alternation compression tests were successfully conducted for evaluating sediment strengthening dependence on the rate and magnitude of effective confining stress changes. In addition, oedometer tests were performed up to 40MPa of consolidation stress to simulate the depressurization method in ultra-deep sea environments. Consolidation curves measured with and without gas hydrate were investigated over a wide range of effective confining stresses. Compression curves for gas hydrate-bearing sediments were convex downward due to high hydrate saturations. Consolidation tests show that, regardless of the consolidation history with hydrate in place, the consolidation behavior after dissociation will first return to, then follow, the original normal consolidation curve for the hydrate-free host sediment.

Numerical Simulation of Earth Pressure on Head Chamber of Shield Machine with FEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Shouju; Kang Chengang; Sun, Wei

2010-05-21

Model parameters of conditioned soils in head chamber of shield machine are determined based on tree-axial compression tests in laboratory. The loads acting on tunneling face are estimated according to static earth pressure principle. Based on Duncan-Chang nonlinear elastic constitutive model, the earth pressures on head chamber of shield machine are simulated in different aperture ratio cases for rotating cutterhead of shield machine. Relationship between pressure transportation factor and aperture ratio of shield machine is proposed by using aggression analysis.

Entropy Splitting for High Order Numerical Simulation of Compressible Turbulence

NASA Technical Reports Server (NTRS)

Sandham, N. D.; Yee, H. C.; Kwak, Dochan (Technical Monitor)

2000-01-01

A stable high order numerical scheme for direct numerical simulation (DNS) of shock-free compressible turbulence is presented. The method is applicable to general geometries. It contains no upwinding, artificial dissipation, or filtering. Instead the method relies on the stabilizing mechanisms of an appropriate conditioning of the governing equations and the use of compatible spatial difference operators for the interior points (interior scheme) as well as the boundary points (boundary scheme). An entropy splitting approach splits the inviscid flux derivatives into conservative and non-conservative portions. The spatial difference operators satisfy a summation by parts condition leading to a stable scheme (combined interior and boundary schemes) for the initial boundary value problem using a generalized energy estimate. A Laplacian formulation of the viscous and heat conduction terms on the right hand side of the Navier-Stokes equations is used to ensure that any tendency to odd-even decoupling associated with central schemes can be countered by the fluid viscosity. A special formulation of the continuity equation is used, based on similar arguments. The resulting methods are able to minimize spurious high frequency oscillation producing nonlinear instability associated with pure central schemes, especially for long time integration simulation such as DNS. For validation purposes, the methods are tested in a DNS of compressible turbulent plane channel flow at a friction Mach number of 0.1 where a very accurate turbulence data base exists. It is demonstrated that the methods are robust in terms of grid resolution, and in good agreement with incompressible channel data, as expected at this Mach number. Accurate turbulence statistics can be obtained with moderate grid sizes. Stability limits on the range of the splitting parameter are determined from numerical tests.

Nonlinear closures for scale separation in supersonic magnetohydrodynamic turbulence

NASA Astrophysics Data System (ADS)

Grete, Philipp; Vlaykov, Dimitar G.; Schmidt, Wolfram; Schleicher, Dominik R. G.; Federrath, Christoph

2015-02-01

Turbulence in compressible plasma plays a key role in many areas of astrophysics and engineering. The extreme plasma parameters in these environments, e.g. high Reynolds numbers, supersonic and super-Alfvenic flows, however, make direct numerical simulations computationally intractable even for the simplest treatment—magnetohydrodynamics (MHD). To overcome this problem one can use subgrid-scale (SGS) closures—models for the influence of unresolved, subgrid-scales on the resolved ones. In this work we propose and validate a set of constant coefficient closures for the resolved, compressible, ideal MHD equations. The SGS energies are modeled by Smagorinsky-like equilibrium closures. The turbulent stresses and the electromotive force (EMF) are described by expressions that are nonlinear in terms of large scale velocity and magnetic field gradients. To verify the closures we conduct a priori tests over 137 simulation snapshots from two different codes with varying ratios of thermal to magnetic pressure ({{β }p}=0.25,1,2.5,5,25) and sonic Mach numbers ({{M}s}=2,2.5,4). Furthermore, we make a comparison to traditional, phenomenological eddy-viscosity and α -β -γ closures. We find only mediocre performance of the kinetic eddy-viscosity and α -β -γ closures, and that the magnetic eddy-viscosity closure is poorly correlated with the simulation data. Moreover, three of five coefficients of the traditional closures exhibit a significant spread in values. In contrast, our new closures demonstrate consistently high correlations and constant coefficient values over time and over the wide range of parameters tested. Important aspects in compressible MHD turbulence such as the bi-directional energy cascade, turbulent magnetic pressure and proper alignment of the EMF are well described by our new closures.

[Randomised study of the relationship between the use of CPRmeter® device and the quality of chest compressions in a simulated cardiopulmonary resuscitation].

PubMed

Calvo-Buey, J A; Calvo-Marcos, D; Marcos-Camina, R M

2016-01-01

To determine whether the use of CPRmeter(®) during the resuscitation manoeuvres, is related to a higher quality of external cardiac massage, as recommended by the International Liaison Committee on Resuscitation (ILCOR). To compare the quality obtained without the use or this, and whether there are differences related to anthropometric, demographic, professional and/or occupational factors. Experimental, open trial performed with life support simulators in a stratified random sample of 88 health workers randomly distributed between groups A (without indications of the device) and B (with them). The homogeneity of their confounding variables was compared, as well as the compressions depth and compressions rate, the proportion of completed release, and distribution of the quality massage variable (according to criteria ILCOR) between the groups. The qualitative variables were analysed with the chi-square test, and quantitative variables with the Student t-test or Mann-Whitney U-test and the association between the variable quality massage variable, and use of the device with the odds ratio. Group A: mean depth 42.1mm (standard deviation 10.1), mean rate 121.3/min (21.6), percentage of complete release 71.2% (36.9). Group B: 51.2mm (5.9) 111.9/min (6.4), 92.9% (10.1) respectively. Odds ratio for quality massage regarding the use of the device was 5.170 (95% CI; 2.060-12.977). The use of CPRmeter(®) device in simulated resuscitations is related to a higher quality of cardiac massage, improving the approach to the ILCOR recommendations, regardless of the characteristics of the participants. They were 83.8% more likely to achieve a quality massage using the device than without it. Copyright © 2015 Elsevier España, S.L.U. y SEEIUC. All rights reserved.

Compact, compression-free, displaceable, and resealable vacuum feedthrough with built-in strain relief for sensitive components such as optical fibers.

PubMed

Buchholz, B; Ebert, V

2014-05-01

For the direct fiber coupling of small optical measurement cells, we developed a new compact vacuum feedthrough for glass fibers and other similarly shaped objects that are compact and that offer the possibility of adjusting the fiber in longitudinal and in circular direction. The feedthrough assembly avoids compression or torsion on the fiber and thus protects, e.g., highly frangible fiber materials. In the following, we will present a brief simulation of the tightness requirements for low-pressure and low-concentration water vapor measurements and we will explain an integrated concept for a displaceable and self-adjustable, compression-free, compact, ultra-high vacuum, resealable feedthrough with good strain relief. The feedthrough has been successfully tested in a laboratory test facility and in several extractive airborne tunable diode laser absorption spectroscopy hygrometers. The leakage rate of the feedthrough presented here was tested via a helium leak searcher and was quantified further in an 8-week vacuum measurement campaign. The leakage rate is determined to be 0.41 ± 0.04 × 10(-9) hPa l/s, which--to our knowledge--is the first time a leakage rate for such a feedthrough has been quantified.

Numerical Investigation of Magnetically Driven Isentropic Compression of Solid Aluminum Cylinders with a Semi-Analytical Code

NASA Astrophysics Data System (ADS)

Largent, Billy T.

The state of matter at extremely high pressures and densities is of fundamental interest to many branches of research, including planetary science, material science, condensed matter physics, and plasma physics. Matter with pressures, or energy densities, above 1 megabar (100 gigapascal) are defined as High Energy Density (HED) plasmas. They are directly relevant to the interiors of planets such as Earth and Jupiter and to the dense fuels in Inertial Confinement Fusion (ICF) experiments. To create HEDP conditions in laboratories, a sample may be compressed by a smoothly varying pressure ramp with minimal temperature increase, following the isentropic thermodynamic process. Isentropic compression of aluminum targets has been done using magnetic pressure produced by megaampere, pulsed power currents having 100 ns rise times. In this research project, magnetically driven, cylindrical isentropic compression has been numerically studied. In cylindrical geometry, material compression and pressure become higher than in planar geometry due to geometrical effects. Based on a semi-analytical model for the Magnetized Liner Inertial Fusion (MagLIF) concept, a code called "SA" was written to design cylindrical compression experiments on the 1.0 MA Zebra pulsed power generator at the Nevada Terawatt Facility (NTF). To test the physics models in the code, temporal progresses of rod compression and pressure were calculated with SA and compared with 1-D magnetohydrodynamic (MHD) codes. The MHD codes incorporated SESAME tables, for equation of state and resistivity, or the classical Spitzer model. A series of simulations were also run to find optimum rod diameters for 1.0 MA and 1.8 MA Zebra current pulses. For a 1.0 MA current peak and 95 ns rise time, a maximum compression of 2.35 ( 6.3 g/cm3) and a pressure of 900 GPa within a 100 mum radius were found for an initial diameter of 1.05 mm. For 1.8 MA peak simulations with the same rise time, the initial diameter of 1.3 mm was optimal with 3.32 ( 9.0 g/cm 3) compression.

Using Simulation as an Investigational Methodology to Explore the Impact of Technology on Team Communication and Patient Management: A Pilot Evaluation of the Effect of an Automated Compression Device.

PubMed

Gittinger, Matthew; Brolliar, Sarah M; Grand, James A; Nichol, Graham; Fernandez, Rosemarie

2017-06-01

This pilot study used a simulation-based platform to evaluate the effect of an automated mechanical chest compression device on team communication and patient management. Four-member emergency department interprofessional teams were randomly assigned to perform manual chest compressions (control, n = 6) or automated chest compressions (intervention, n = 6) during a simulated cardiac arrest with 2 phases: phase 1 baseline (ventricular tachycardia), followed by phase 2 (ventricular fibrillation). Patient management was coded using an Advanced Cardiovascular Life Support-based checklist. Team communication was categorized in the following 4 areas: (1) teamwork focus; (2) huddle events, defined as statements focused on re-establishing situation awareness, reinforcing existing plans, and assessing the need to adjust the plan; (3) clinical focus; and (4) profession of team member. Statements were aggregated for each team. At baseline, groups were similar with respect to total communication statements and patient management. During cardiac arrest, the total number of communication statements was greater in teams performing manual compressions (median, 152.3; interquartile range [IQR], 127.6-181.0) as compared with teams using an automated compression device (median, 105; IQR, 99.5-123.9). Huddle events were more frequent in teams performing automated chest compressions (median, 4.0; IQR, 3.1-4.3 vs. 2.0; IQR, 1.4-2.6). Teams randomized to the automated compression intervention had a delay to initial defibrillation (median, 208.3 seconds; IQR, 153.3-222.1 seconds) as compared with control teams (median, 63.2 seconds; IQR, 30.1-397.2 seconds). Use of an automated compression device may impact both team communication and patient management. Simulation-based assessments offer important insights into the effect of technology on healthcare teams.

Development and Analysis of Desiccant Enhanced Evaporative Air Conditioner Prototype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozubal, E.; Woods, J.; Judkoff, R.

2012-04-01

This report documents the design of a desiccant enhanced evaporative air conditioner (DEVAP AC) prototype and the testing to prove its performance. Previous numerical modeling and building energy simulations indicate a DEVAP AC can save significant energy compared to a conventional vapor compression AC (Kozubal et al. 2011). The purposes of this research were to build DEVAP prototypes, test them to validate the numerical model, and identify potential commercialization barriers.

Turbulence modeling for hypersonic flight

NASA Technical Reports Server (NTRS)

Bardina, Jorge E.

1992-01-01

The objective of the present work is to develop, verify, and incorporate two equation turbulence models which account for the effect of compressibility at high speeds into a three dimensional Reynolds averaged Navier-Stokes code and to provide documented model descriptions and numerical procedures so that they can be implemented into the National Aerospace Plane (NASP) codes. A summary of accomplishments is listed: (1) Four codes have been tested and evaluated against a flat plate boundary layer flow and an external supersonic flow; (2) a code named RANS was chosen because of its speed, accuracy, and versatility; (3) the code was extended from thin boundary layer to full Navier-Stokes; (4) the K-omega two equation turbulence model has been implemented into the base code; (5) a 24 degree laminar compression corner flow has been simulated and compared to other numerical simulations; and (6) work is in progress in writing the numerical method of the base code including the turbulence model.

Numerical analysis of bubble-cluster formation in an ultrasonic field

NASA Astrophysics Data System (ADS)

Kim, Donghyun; Son, Gihun

2016-11-01

Bubble-cluster formation in an ultrasonic field is investigated numerically solving the conservation equations of mass, momentum and energy. The liquid-gas interface is calculated using the volume-of-fluid method with variable gas density to consider the bubble compressibility. The effect of liquid-gas phase change is also included as the interface source terms of the mass and energy equations. The numerical approach is tested through the simulation of the expansion and contraction motion of a compressed bubble adjacent to a wall. When the bubble is placed in an ultrasonic field, it oscillates radially and then collapses violently. Numerical simulation is also performed for bubble-cluster formation induced by an ultrasonic generator, where the generated bubbles are merged into a macrostructure along the acoustic flow field. The effects of ultrasonic power and frequency, liquid properties and pool temperature on the bubble-cluster formation are investigated. This work was supported by the Korea Institute of Energy Research.

Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting

PubMed Central

Contuzzi, Nicola; Campanelli, Sabina L.; Casavola, Caterina; Lamberti, Luciano

2013-01-01

The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456–0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading. PMID:28811445

Numerical simulation of the compressible Orszag-Tang vortex. Interim report, June 1988-February 1989

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahlburg, R.B.; Picone, J.M.

Results of fully compressible, Fourier collocation, numerical simulations of the Orszag-Tang vortex system are presented. Initial conditions consist of a nonrandom, periodic field in which the magnetic and velocity fields contain X-points but differ in modal structure along one spatial direction. The velocity field is initially solenoidal, with the total initial pressure-field consisting of the superposition of the appropriate incompressible pressure distribution upon a flat pressure field corresponding to the initial, average flow Mach number of the flow. In the numerical simulations, this initial Mach number is varied from 0.2 to 0.6. These values correspond to average plasma beta valuesmore » ranging from 30.0 to 3.3, respectively. Compressible effects develop within one or two Alfven transit times, as manifested in the spectra of compressible quantities such as mass density and nonsolenoidal flow field. These effects include (1) retardation of growth of correlation between the magnetic field and the velocity field, (2) emergence of compressible small-scale structure such as massive jets, and (3) bifurcation of eddies in the compressible-flow field. Differences between the incompressible and compressible results tend to increase with increasing initial average Mach number.« less

Turbulence in Compressible Flows

NASA Technical Reports Server (NTRS)

1997-01-01

Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.

Automatic physical inference with information maximizing neural networks

NASA Astrophysics Data System (ADS)

Charnock, Tom; Lavaux, Guilhem; Wandelt, Benjamin D.

2018-04-01

Compressing large data sets to a manageable number of summaries that are informative about the underlying parameters vastly simplifies both frequentist and Bayesian inference. When only simulations are available, these summaries are typically chosen heuristically, so they may inadvertently miss important information. We introduce a simulation-based machine learning technique that trains artificial neural networks to find nonlinear functionals of data that maximize Fisher information: information maximizing neural networks (IMNNs). In test cases where the posterior can be derived exactly, likelihood-free inference based on automatically derived IMNN summaries produces nearly exact posteriors, showing that these summaries are good approximations to sufficient statistics. In a series of numerical examples of increasing complexity and astrophysical relevance we show that IMNNs are robustly capable of automatically finding optimal, nonlinear summaries of the data even in cases where linear compression fails: inferring the variance of Gaussian signal in the presence of noise, inferring cosmological parameters from mock simulations of the Lyman-α forest in quasar spectra, and inferring frequency-domain parameters from LISA-like detections of gravitational waveforms. In this final case, the IMNN summary outperforms linear data compression by avoiding the introduction of spurious likelihood maxima. We anticipate that the automatic physical inference method described in this paper will be essential to obtain both accurate and precise cosmological parameter estimates from complex and large astronomical data sets, including those from LSST and Euclid.

MD modeling of screw dislocation influence upon initiation and mechanism of BCC-HCP polymorphous transition in iron

NASA Astrophysics Data System (ADS)

Dremov, V. V.; Ionov, G. V.; Sapozhnikov, F. A.; Smirnov, N. A.; Karavaev, A. V.; Vorobyova, M. A.; Ryzhkov, M. V.

2015-09-01

The present work is devoted to classical molecular dynamics investigation into microscopic mechanisms of the bcc-hcp transition in iron. The interatomic potential of EAM type used in the calculations was tested for the capability to reproduce ab initio data on energy evolution along the bcc-hcp transformation path (Burgers deformation + shuffe) and then used in the large-scale MD simulations. The large-scale simulations included constant volume deformation along the Burgers path to study the origin and nature of the plasticity, hydrostatic volume compression of defect free samples above the bcc to hcp transition threshold to observe the formation of new phase embryos, and the volume compression of samples containing screw dislocations to study the effect of the dislocations on the probability of the new phase critical embryo formation. The volume compression demonstrated high level of metastability. The transition starts at pressure much higher than the equilibrium one. Dislocations strongly affect the probability of the critical embryo formation and significantly reduce the onset pressure of transition. The dislocations affect also the resulting structure of the samples upon the transition. The formation of layered structure is typical for the samples containing the dislocations. The results of the simulations were compared with the in-situ experimental data on the mechanism of the bcc-hcp transition in iron.

Compression-ignition Engine Performance at Altitudes and at Various Air Pressures and Temperatures

NASA Technical Reports Server (NTRS)

Moore, Charles S; Collins, John H

1937-01-01

Engine test results are presented for simulated altitude conditions. A displaced-piston combustion chamber on a 5- by 7-inch single cylinder compression-ignition engine operating at 2,000 r.p.m. was used. Inlet air temperature equivalent to standard altitudes up to 14,000 feet were obtained. Comparison between performance at altitude of the unsupercharged compression-ignition engine compared favorably with the carburetor engine. Analysis of the results for which the inlet air temperature, inlet air pressure, and inlet and exhaust pressure were varied indicates that engine performance cannot be reliably corrected on the basis of inlet air density or weight of air charge. Engine power increases with inlet air pressure and decreases with inlet air temperatures very nearly as straight line relations over a wide range of air-fuel ratios. Correction factors are given.

Toward Sodium X-Ray Diffraction in the High-Pressure Regime

NASA Astrophysics Data System (ADS)

Gong, X.; Polsin, D. N.; Rygg, J. R.; Boehly, T. R.; Crandall, L.; Henderson, B. J.; Hu, S. X.; Huff, M.; Saha, R.; Collins, G. W.; Smith, R.; Eggert, J.; Lazicki, A. E.; McMahon, M.

2017-10-01

We are working to quasi-isentropically compress sodium into the terapascal regime to test theoretical predictions that sodium transforms to an electride. A series of hydrodynamic simulations have been performed to design experiments to investigate the structure and optical properties of sodium at pressures up to 500 GPa. We show preliminary results where sodium samples, sandwiched between diamond plates and lithium-fluoride windows, are ramp compressed by a gradual increase in the drive-laser intensity. The low sound speed in sodium makes it particularly susceptible to forming a shock; therefore, it is difficult to compress without melting the sample. Powder x-ray diffraction is used to provide information on the structure of sodium at these high pressures. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Reversible dilatancy in entangled single-wire materials.

PubMed

Rodney, David; Gadot, Benjamin; Martinez, Oriol Riu; du Roscoat, Sabine Rolland; Orgéas, Laurent

2016-01-01

Designing structures that dilate rapidly in both tension and compression would benefit devices such as smart filters, actuators or fasteners. This property however requires an unusual Poisson ratio, or Poisson function at finite strains, which has to vary with applied strain and exceed the familiar bounds: less than 0 in tension and above 1/2 in compression. Here, by combining mechanical tests and discrete element simulations, we show that a simple three-dimensional architected material, made of a self-entangled single long coiled wire, behaves in between discrete and continuum media, with a large and reversible dilatancy in both tension and compression. This unusual behaviour arises from an interplay between the elongation of the coiled wire and rearrangements due to steric effects, which, unlike in traditional discrete media, are hysteretically reversible when the architecture is made of an elastic fibre.

The effects of an online basic life support course on undergraduate nursing students' learning.

PubMed

Tobase, Lucia; Peres, Heloisa H C; Gianotto-Oliveira, Renan; Smith, Nicole; Polastri, Thatiane F; Timerman, Sergio

2017-08-25

To describe learning outcomes of undergraduate nursing students following an online basic life support course (BLS). An online BLS course was developed and administered to 94 nursing students. Pre- and post-tests were used to assess theoretical learning. Checklist simulations and feedback devices were used to assess the cardiopulmonary resuscitation (CPR) skills of the 62 students who completed the course. A paired t-test revealed a significant increase in learning [pre-test (6.4 ± 1.61), post-test (9.3 ± 0.82), p < 0.001]. The increase in the average grade after taking the online course was significant (p<0.001). No learning differences (p=0.475) had been observed between 1st and 2nd year (9.20 ± 1.60), and between 3rd and 4th year (9.67 ± 0.61) students. A CPR simulation was performed after completing the course: students checked for a response (90%), exposed the chest (98%), checked for breathing (97%), called emergency services (76%), requested for a defibrillator (92%), checked for a pulse (77%), positioned their hands properly (87%), performed 30 compressions/cycle (95%), performed compressions of at least 5 cm depth (89%), released the chest (90%), applied two breaths (97%), used the automated external defibrillator (97%), and positioned the pads (100%). The online course was an effective method for teaching and learning key BLS skills wherein students were able to accurately apply BLS procedures during the CPR simulation. This short-term online training, which likely improves learning and self-efficacy in BLS providers, can be used for the continuing education of health professionals.

The role of fluid compression in energy conversion and particle energization during magnetic reconnection

NASA Astrophysics Data System (ADS)

Li, X.; Guo, F.; Li, G.; Li, H.

2016-12-01

Theories of particle transport and acceleration have shown that fluid compression is the leading mechanism for particle acceleration and plasma energization. However, the role of compression in particle acceleration during magnetic reconnection is unclear. We use two approaches to study this issue. First, using fully kinetic simulations, we quantitatively calculate the effect of compression in energy conversion and particle energization during magnetic reconnection for a range of plasma beta and guide field. We show that compression has an important contribution for the energy conversion between the bulk kinetic energy and the internal energy when the guide field is smaller than the reconnecting component. Based on this result, we then study the large-scale reconnection acceleration by solving the Parker's transport equation in a background reconnecting flow provided by MHD simulations. Due to the compression effect, the simulations suggest fast particle acceleration to high energies in the reconnection layer. This study clarifies the nature of particle acceleration in reconnection layer, and may be important to understand particle acceleration and plasma energization during solar flares.

Compressible Turbulent Channel Flows: DNS Results and Modeling

NASA Technical Reports Server (NTRS)

Huang, P. G.; Coleman, G. N.; Bradshaw, P.; Rai, Man Mohan (Technical Monitor)

1994-01-01

The present paper addresses some topical issues in modeling compressible turbulent shear flows. The work is based on direct numerical simulation of two supersonic fully developed channel flows between very cold isothermal walls. Detailed decomposition and analysis of terms appearing in the momentum and energy equations are presented. The simulation results are used to provide insights into differences between conventional time-and Favre-averaging of the mean-flow and turbulent quantities. Study of the turbulence energy budget for the two cases shows that the compressibility effects due to turbulent density and pressure fluctuations are insignificant. In particular, the dilatational dissipation and the mean product of the pressure and dilatation fluctuations are very small, contrary to the results of simulations for sheared homogeneous compressible turbulence and to recent proposals for models for general compressible turbulent flows. This provides a possible explanation of why the Van Driest density-weighted transformation is so successful in correlating compressible boundary layer data. Finally, it is found that the DNS data do not support the strong Reynolds analogy. A more general representation of the analogy is analysed and shown to match the DNS data very well.

Experimental analysis and constitutive modelling of steel of A-IIIN strength class

NASA Astrophysics Data System (ADS)

Kruszka, Leopold; Janiszewski, Jacek

2015-09-01

Fundamentally important is the better understanding of behaviour of new building steels under impact loadings, including plastic deformations. Results of the experimental analysis in wide range of strain rates in compression at room temperature, as well as constitutive modelling for and B500SP structural steels of new A-IIIN Polish strength class, examined dynamically by split Hopkinson pressure bar technique at high strain rates, are presented in table and graphic forms. Dynamic mechanical characteristics of compressive strength for tested building structural steel are determined as well as dynamic mechanical properties of this material are compared with 18G2-b steel of A-II strength class, including effects of the shape of tested specimens, i.e. their slenderness. The paper focuses the attention on those experimental tests, their interpretation, and constitutive semi-empirical modelling of the behaviour of tested steels based on Johnson-Cook's model. Obtained results of analyses presented here are used for designing and numerical simulations of reinforced concrete protective structures.

Studies Of Coherent Synchrotron Radiation And Longitudinal Space Charge In The Jefferson Lab FEL Driver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tennant, Christopher D.; Douglas, David R.; Li, Rui

2014-12-01

The Jefferson Laboratory IR FEL Driver provides an ideal test bed for studying a variety of beam dynamical effects. Recent studies focused on characterizing the impact of coherent synchrotron radiation (CSR) with the goal of benchmarking measurements with simulation. Following measurements to characterize the beam, we quantitatively characterized energy extraction via CSR by measuring beam position at a dispersed location as a function of bunch compression. In addition to operating with the beam on the rising part of the linac RF waveform, measurements were also made while accelerating on the falling part. For each, the full compression point was movedmore » along the backleg of the machine and the response of the beam (distribution, extracted energy) measured. Initial results of start-to-end simulations using a 1D CSR algorithm show remarkably good agreement with measurements. A subsequent experiment established lasing with the beam accelerated on the falling side of the RF waveform in conjunction with positive momentum compaction (R56) to compress the bunch. The success of this experiment motivated the design of a modified CEBAF-style arc with control of CSR and microbunching effects.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yang; Zhao, Qiangsheng; Mirdamadi, Mansour

Woven fabric carbon fiber/epoxy composites made through compression molding are one of the promising choices of material for the vehicle light-weighting strategy. Previous studies have shown that the processing conditions can have substantial influence on the performance of this type of the material. Therefore the optimization of the compression molding process is of great importance to the manufacturing practice. An efficient way to achieve the optimized design of this process would be through conducting finite element (FE) simulations of compression molding for woven fabric carbon fiber/epoxy composites. However, performing such simulation remains a challenging task for FE as multiple typesmore » of physics are involved during the compression molding process, including the epoxy resin curing and the complex mechanical behavior of woven fabric structure. In the present study, the FE simulation of the compression molding process of resin based woven fabric composites at continuum level is conducted, which is enabled by the implementation of an integrated material modeling methodology in LS-Dyna. Specifically, the chemo-thermo-mechanical problem of compression molding is solved through the coupling of three material models, i.e., one thermal model for temperature history in the resin, one mechanical model to update the curing-dependent properties of the resin and another mechanical model to simulate the behavior of the woven fabric composites. Preliminary simulations of the carbon fiber/epoxy woven fabric composites in LS-Dyna are presented as a demonstration, while validations and models with real part geometry are planned in the future work.« less

An iterative forward analysis technique to determine the equation of state of dynamically compressed materials

DOE PAGES

Ali, S. J.; Kraus, R. G.; Fratanduono, D. E.; ...

2017-05-18

Here, we developed an iterative forward analysis (IFA) technique with the ability to use hydrocode simulations as a fitting function for analysis of dynamic compression experiments. The IFA method optimizes over parameterized quantities in the hydrocode simulations, breaking the degeneracy of contributions to the measured material response. Velocity profiles from synthetic data generated using a hydrocode simulation are analyzed as a first-order validation of the technique. We also analyze multiple magnetically driven ramp compression experiments on copper and compare with more conventional techniques. Excellent agreement is obtained in both cases.

Application of Compressible Volume of Fluid Model in Simulating the Impact and Solidification of Hollow Spherical ZrO2 Droplet on a Surface

NASA Astrophysics Data System (ADS)

Safaei, Hadi; Emami, Mohsen Davazdah; Jazi, Hamidreza Salimi; Mostaghimi, Javad

2017-12-01

Applications of hollow spherical particles in thermal spraying process have been developed in recent years, accompanied by attempts in the form of experimental and numerical studies to better understand the process of impact of a hollow droplet on a surface. During such process, volume and density of the trapped gas inside droplet change. The numerical models should be able to simulate such changes and their consequent effects. The aim of this study is to numerically simulate the impact of a hollow ZrO2 droplet on a flat surface using the volume of fluid technique for compressible flows. An open-source, finite-volume-based CFD code was used to perform the simulations, where appropriate subprograms were added to handle the studied cases. Simulation results were compared with the available experimental data. Results showed that at high impact velocities ( U 0 > 100 m/s), the compression of trapped gas inside droplet played a significant role in the impact dynamics. In such velocities, the droplet splashed explosively. Compressibility effects result in a more porous splat, compared to the corresponding incompressible model. Moreover, the compressible model predicted a higher spread factor than the incompressible model, due to planetary structure of the splat.

Numerical simulation of transient hypervelocity flow in an expansion tube

NASA Technical Reports Server (NTRS)

Jacobs, P. A.

1992-01-01

Several numerical simulations of the transient flow of helium in an expansion tube are presented in an effort to identify some of the basic mechanisms which cause the noisy test flows seen in experiments. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in experiments. In particular, the discontinuity in tube diameter of the primary diaphragm station introduced a transverse perturbation to the expanding driver gas and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either small amplitude, low frequency noise possibly introduced during shock compression or large amplitude, high frequency noise associated with the passage of the reflected head of the unsteady expansion.

The use of ZFP lossy floating point data compression in tornado-resolving thunderstorm simulations

NASA Astrophysics Data System (ADS)

Orf, L.

2017-12-01

In the field of atmospheric science, numerical models are used to produce forecasts of weather and climate and serve as virtual laboratories for scientists studying atmospheric phenomena. In both operational and research arenas, atmospheric simulations exploiting modern supercomputing hardware can produce a tremendous amount of data. During model execution, the transfer of floating point data from memory to the file system is often a significant bottleneck where I/O can dominate wallclock time. One way to reduce the I/O footprint is to compress the floating point data, which reduces amount of data saved to the file system. In this presentation we introduce LOFS, a file system developed specifically for use in three-dimensional numerical weather models that are run on massively parallel supercomputers. LOFS utilizes the core (in-memory buffered) HDF5 driver and includes compression options including ZFP, a lossy floating point data compression algorithm. ZFP offers several mechanisms for specifying the amount of lossy compression to be applied to floating point data, including the ability to specify the maximum absolute error allowed in each compressed 3D array. We explore different maximum error tolerances in a tornado-resolving supercell thunderstorm simulation for model variables including cloud and precipitation, temperature, wind velocity and vorticity magnitude. We find that average compression ratios exceeding 20:1 in scientifically interesting regions of the simulation domain produce visually identical results to uncompressed data in visualizations and plots. Since LOFS splits the model domain across many files, compression ratios for a given error tolerance can be compared across different locations within the model domain. We find that regions of high spatial variability (which tend to be where scientifically interesting things are occurring) show the lowest compression ratios, whereas regions of the domain with little spatial variability compress extremely well. We observe that the overhead for compressing data with ZFP is low, and that compressing data in memory reduces the amount of memory overhead needed to store the virtual files before they are flushed to disk.

Development and mechanical properties of structural materials from lunar simulants

NASA Technical Reports Server (NTRS)

Desai, Chandra S.; Girdner, K.; Saadatmanesh, H.; Allen, T.

1991-01-01

Development of the technologies for manufacture of structural and construction materials on the Moon, utilizing local lunar soil (regolith), without the use of water, is an important element for habitats and explorations in space. Here, it is vital that the mechanical behavior such as strength and flexural properties, fracture toughness, ductility and deformation characteristics be defined toward establishment of the ranges of engineering applications of the materials developed. The objective is to describe the research results in two areas for the above goal: (1) liquefaction of lunar simulant (at about 100 C) with different additives (fibers, powders, etc.); and (2) development and use of a new triaxial test device in which lunar simulants are first compressed under cycles of loading, and then tested with different vacuums and initial confining or in situ stress.

An object-oriented simulator for 3D digital breast tomosynthesis imaging system.

PubMed

Seyyedi, Saeed; Cengiz, Kubra; Kamasak, Mustafa; Yildirim, Isa

2013-01-01

Digital breast tomosynthesis (DBT) is an innovative imaging modality that provides 3D reconstructed images of breast to detect the breast cancer. Projections obtained with an X-ray source moving in a limited angle interval are used to reconstruct 3D image of breast. Several reconstruction algorithms are available for DBT imaging. Filtered back projection algorithm has traditionally been used to reconstruct images from projections. Iterative reconstruction algorithms such as algebraic reconstruction technique (ART) were later developed. Recently, compressed sensing based methods have been proposed in tomosynthesis imaging problem. We have developed an object-oriented simulator for 3D digital breast tomosynthesis (DBT) imaging system using C++ programming language. The simulator is capable of implementing different iterative and compressed sensing based reconstruction methods on 3D digital tomosynthesis data sets and phantom models. A user friendly graphical user interface (GUI) helps users to select and run the desired methods on the designed phantom models or real data sets. The simulator has been tested on a phantom study that simulates breast tomosynthesis imaging problem. Results obtained with various methods including algebraic reconstruction technique (ART) and total variation regularized reconstruction techniques (ART+TV) are presented. Reconstruction results of the methods are compared both visually and quantitatively by evaluating performances of the methods using mean structural similarity (MSSIM) values.

An Object-Oriented Simulator for 3D Digital Breast Tomosynthesis Imaging System

PubMed Central

Cengiz, Kubra

2013-01-01

Digital breast tomosynthesis (DBT) is an innovative imaging modality that provides 3D reconstructed images of breast to detect the breast cancer. Projections obtained with an X-ray source moving in a limited angle interval are used to reconstruct 3D image of breast. Several reconstruction algorithms are available for DBT imaging. Filtered back projection algorithm has traditionally been used to reconstruct images from projections. Iterative reconstruction algorithms such as algebraic reconstruction technique (ART) were later developed. Recently, compressed sensing based methods have been proposed in tomosynthesis imaging problem. We have developed an object-oriented simulator for 3D digital breast tomosynthesis (DBT) imaging system using C++ programming language. The simulator is capable of implementing different iterative and compressed sensing based reconstruction methods on 3D digital tomosynthesis data sets and phantom models. A user friendly graphical user interface (GUI) helps users to select and run the desired methods on the designed phantom models or real data sets. The simulator has been tested on a phantom study that simulates breast tomosynthesis imaging problem. Results obtained with various methods including algebraic reconstruction technique (ART) and total variation regularized reconstruction techniques (ART+TV) are presented. Reconstruction results of the methods are compared both visually and quantitatively by evaluating performances of the methods using mean structural similarity (MSSIM) values. PMID:24371468

Comprehensive numerical methodology for direct numerical simulations of compressible Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reckinger, Scott James; Livescu, Daniel; Vasilyev, Oleg V.

A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.

Heating and Acceleration of Charged Particles by Weakly Compressible Magnetohydrodynamic Turbulence

NASA Astrophysics Data System (ADS)

Lynn, Jacob William

We investigate the interaction between low-frequency magnetohydrodynamic (MHD) turbulence and a distribution of charged particles. Understanding this physics is central to understanding the heating of the solar wind, as well as the heating and acceleration of other collisionless plasmas. Our central method is to simulate weakly compressible MHD turbulence using the Athena code, along with a distribution of test particles which feel the electromagnetic fields of the turbulence. We also construct analytic models of transit-time damping (TTD), which results from the mirror force caused by compressible (fast or slow) MHD waves. Standard linear-theory models in the literature require an exact resonance between particle and wave velocities to accelerate particles. The models developed in this thesis go beyond standard linear theory to account for the fact that wave-particle interactions decorrelate over a short time, which allows particles with velocities off resonance to undergo acceleration and velocity diffusion. We use the test particle simulation results to calibrate and distinguish between different models for this velocity diffusion. Test particle heating is larger than the linear theory prediction, due to continued acceleration of particles with velocities off-resonance. We also include an artificial pitch-angle scattering to the test particle motion, representing the effect of high-frequency waves or velocity-space instabilities. For low scattering rates, we find that the scattering enforces isotropy and enhances heating by a modest factor. For much higher scattering rates, the acceleration is instead due to a non-resonant effect, as particles "frozen" into the fluid adiabatically gain and lose energy as eddies expand and contract. Lastly, we generalize our calculations to allow for relativistic test particles. Linear theory predicts that relativistic particles with velocities much higher than the speed of waves comprising the turbulence would undergo no acceleration; resonance-broadening modifies this conclusion and allows for a continued Fermi-like acceleration process. This may affect the observed spectra of black hole accretion disks by accelerating relativistic particles into a quasi-powerlaw tail.

Lagrangian transported MDF methods for compressible high speed flows

NASA Astrophysics Data System (ADS)

Gerlinger, Peter

2017-06-01

This paper deals with the application of thermochemical Lagrangian MDF (mass density function) methods for compressible sub- and supersonic RANS (Reynolds Averaged Navier-Stokes) simulations. A new approach to treat molecular transport is presented. This technique on the one hand ensures numerical stability of the particle solver in laminar regions of the flow field (e.g. in the viscous sublayer) and on the other hand takes differential diffusion into account. It is shown in a detailed analysis, that the new method correctly predicts first and second-order moments on the basis of conventional modeling approaches. Moreover, a number of challenges for MDF particle methods in high speed flows is discussed, e.g. high cell aspect ratio grids close to solid walls, wall heat transfer, shock resolution, and problems from statistical noise which may cause artificial shock systems in supersonic flows. A Mach 2 supersonic mixing channel with multiple shock reflection and a model rocket combustor simulation demonstrate the eligibility of this technique to practical applications. Both test cases are simulated successfully for the first time with a hybrid finite-volume (FV)/Lagrangian particle solver (PS).

Low sidelobe level and high time resolution for metallic ultrasonic testing with linear-chirp-Golay coded excitation

NASA Astrophysics Data System (ADS)

Zhang, Jiaying; Gang, Tie; Ye, Chaofeng; Cong, Sen

2018-04-01

Linear-chirp-Golay (LCG)-coded excitation combined with pulse compression is proposed in this paper to improve the time resolution and suppress sidelobe in ultrasonic testing. The LCG-coded excitation is binary complementary pair Golay signal with linear-chirp signal applied on every sub pulse. Compared with conventional excitation which is a common ultrasonic testing method using a brief narrow pulse as exciting signal, the performances of LCG-coded excitation, in terms of time resolution improvement and sidelobe suppression, are studied via numerical and experimental investigations. The numerical simulations are implemented using Matlab K-wave toolbox. It is seen from the simulation results that time resolution of LCG excitation is 35.5% higher and peak sidelobe level (PSL) is 57.6 dB lower than linear-chirp excitation with 2.4 MHz chirp bandwidth and 3 μs time duration. In the B-scan experiment, time resolution of LCG excitation is higher and PSL is lower than conventional brief pulse excitation and chirp excitation. In terms of time resolution, LCG-coded signal has better performance than chirp signal. Moreover, the impact of chirp bandwidth on LCG-coded signal is less than that on chirp signal. In addition, the sidelobe of LCG-coded signal is lower than that of chirp signal with pulse compression.

Evaluation of a metal fuselage panel selectively reinforced with filamentary composites for space shuttle application

NASA Technical Reports Server (NTRS)

Wennhold, W. F.

1974-01-01

The use of high strength and modulus of advanced filamentary composites to reduce the structural weight of aerospace vehicles was investigated. Application of the technology to space shuttle components was the primary consideration. The mechanical properties for the boron/epoxy, graphite/epoxy, and polyimide data are presented. Structural testing of two compression panel components was conducted in a simulated space shuttle thermal environment. Results of the tests are analyzed.

Kinematic response of the spine during simulated aircraft ejections.

PubMed

Damon, Andrew M; Lessley, David J; Salzar, Robert S; Bass, Cameron R; Shen, Francis H; Paskoff, Glenn R; Shender, Barry S

2010-05-01

Military aviators are susceptible to spinal injuries during high-speed ejection scenarios. These injuries commonly arise as a result of strains induced by extreme flexion or compression of the spinal column. This study characterizes the vertebral motion of two postmortem human surrogates (PMHS) during a simulated catapult phase of ejection on a horizontal decelerator sled. During testing, the PMHS were restrained supinely to a mock ejection seat and subjected to a horizontal deceleration profile directed along the local z-axis. Two midsized males (175.3 cm, 77.1 kg; 185.4 cm, 72.6 kg) were tested. High-rate motion capture equipment was used to measure the three-dimensional displacement of the head, vertebrae, and pelvis during the ejection event. The two PMHS showed generally similar kinematic motion. Head injury criterion (HIC) results were well below injury threshold levels for both specimens. The specimens both showed compression of the spine, with a reduction in length of 23.9 mm and 45.7 mm. Post-test autopsies revealed fractures in the C5, T1, and L1 vertebrae. This paper provides an analysis of spinal motion during an aircraft ejection.The injuries observed in the test subjects were consistent with those seen in epidemiological studies. Future studies should examine the effects of gender, muscle tensing, out-of-position (of head from neutral position) occupants, and external forces (e.g., windblast) on spinal kinematics during aircraft ejection.

Simulated life-threatening emergency during robot-assisted surgery.

PubMed

Huser, Anna-Sophia; Müller, Dirk; Brunkhorst, Violeta; Kannisto, Päivi; Musch, Michael; Kröpfl, Darko; Groeben, Harald

2014-06-01

With the increasing use of robot-assisted techniques for urologic and gynecologic surgery in patients with severe comorbidities, the risk of a critical incidence during surgery increases. Due to limited access to the patient the start of effective measures to treat a life-threatening emergency could be delayed. Therefore, we tested the management of an acute emergency in an operating room setting with a full-size simulator in six complete teams. A full-size simulator (ISTAN, Meti, CA), modified to hold five trocars, was placed in a regular operating room and connected to a robotic system. Six teams (each with three nurses, one anesthesiologist, two urologists or gynecologists) were introduced to the scenario. Subsequently, myocardial fibrillation occurred. Time to first chest compression, removal of the robot, first defibrillation, and stabilization of circulation were obtained. After 7 weeks the simulation was repeated. The time to the start of chest compressions, removal of the robotic system, and first defibrillation were significantly improved at the second simulation. Time for restoration of stable circulation was improved from 417 ± 125 seconds to 224 ± 37 seconds (P=0.0054). Unexpected delays occurred during the first simulation because trocars had been removed from the patient but not from the robot, thus preventing the robot to be moved. Following proper training, resuscitation can be started within seconds. A repetition of the simulation significantly improved time for all steps of resuscitation. An emergency simulation of a multidisciplinary team in a real operating room setting can be strongly recommended.

LES of Temporally Evolving Mixing Layers by an Eighth-Order Filter Scheme

NASA Technical Reports Server (NTRS)

Hadjadj, A; Yee, H. C.; Sjogreen, B.

2011-01-01

An eighth-order filter method for a wide range of compressible flow speeds (H.C. Yee and B. Sjogreen, Proceedings of ICOSAHOM09, June 22-26, 2009, Trondheim, Norway) are employed for large eddy simulations (LES) of temporally evolving mixing layers (TML) for different convective Mach numbers (Mc) and Reynolds numbers. The high order filter method is designed for accurate and efficient simulations of shock-free compressible turbulence, turbulence with shocklets and turbulence with strong shocks with minimum tuning of scheme parameters. The value of Mc considered is for the TML range from the quasi-incompressible regime to the highly compressible supersonic regime. The three main characteristics of compressible TML (the self similarity property, compressibility effects and the presence of large-scale structure with shocklets for high Mc) are considered for the LES study. The LES results using the same scheme parameters for all studied cases agree well with experimental results of Barone et al. (2006), and published direct numerical simulations (DNS) work of Rogers & Moser (1994) and Pantano & Sarkar (2002).

Proposal of a critical test of the Navier-Stokes-Fourier paradigm for compressible fluid continua.

PubMed

Brenner, Howard

2013-01-01

A critical, albeit simple experimental and/or molecular-dynamic (MD) simulation test is proposed whose outcome would, in principle, establish the viability of the Navier-Stokes-Fourier (NSF) equations for compressible fluid continua. The latter equation set, despite its longevity as constituting the fundamental paradigm of continuum fluid mechanics, has recently been criticized on the basis of its failure to properly incorporate volume transport phenomena-as embodied in the proposed bivelocity paradigm [H. Brenner, Int. J. Eng. Sci. 54, 67 (2012)]-into its formulation. Were the experimental or simulation results found to accord, even only qualitatively, with bivelocity predictions, the temperature distribution in a gas-filled, thermodynamically and mechanically isolated circular cylinder undergoing steady rigid-body rotation in an inertial reference frame would not be uniform; rather, the temperature would be higher at the cylinder wall than along the axis of rotation. This radial temperature nonuniformity contrasts with the uniformity of the temperature predicted by the NSF paradigm for these same circumstances. Easily attainable rates of rotation in centrifuges and readily available tools for measuring the expected temperature differences render experimental execution of the proposed scheme straightforward in principle. As such, measurement-via experiment or MD simulation-of, say, the temperature difference ΔT between the gas at the wall and along the axis of rotation would provide quantitative tests of both the NSF and bivelocity hydrodynamic models, whose respective solutions for the stated set of circumstances are derived in this paper. Independently of the correctness of the bivelocity model, any temperature difference observed during the proposed experiment or simulation, irrespective of magnitude, would preclude the possibility of the NSF paradigm being correct for fluid continua, except for incompressible flows.

Wavelet-based Encoding Scheme for Controlling Size of Compressed ECG Segments in Telecardiology Systems.

PubMed

Al-Busaidi, Asiya M; Khriji, Lazhar; Touati, Farid; Rasid, Mohd Fadlee; Mnaouer, Adel Ben

2017-09-12

One of the major issues in time-critical medical applications using wireless technology is the size of the payload packet, which is generally designed to be very small to improve the transmission process. Using small packets to transmit continuous ECG data is still costly. Thus, data compression is commonly used to reduce the huge amount of ECG data transmitted through telecardiology devices. In this paper, a new ECG compression scheme is introduced to ensure that the compressed ECG segments fit into the available limited payload packets, while maintaining a fixed CR to preserve the diagnostic information. The scheme automatically divides the ECG block into segments, while maintaining other compression parameters fixed. This scheme adopts discrete wavelet transform (DWT) method to decompose the ECG data, bit-field preserving (BFP) method to preserve the quality of the DWT coefficients, and a modified running-length encoding (RLE) scheme to encode the coefficients. The proposed dynamic compression scheme showed promising results with a percentage packet reduction (PR) of about 85.39% at low percentage root-mean square difference (PRD) values, less than 1%. ECG records from MIT-BIH Arrhythmia Database were used to test the proposed method. The simulation results showed promising performance that satisfies the needs of portable telecardiology systems, like the limited payload size and low power consumption.

Improved recognition of ineffective chest compressions after a brief Crew Resource Management (CRM) training: a prospective, randomised simulation study.

PubMed

Haffner, Leopold; Mahling, Moritz; Muench, Alexander; Castan, Christoph; Schubert, Paul; Naumann, Aline; Reddersen, Silke; Herrmann-Werner, Anne; Reutershan, Jörg; Riessen, Reimer; Celebi, Nora

2017-03-03

Chest compressions are a core element of cardio-pulmonary resuscitation. Despite periodic training, real-life chest compressions have been reported to be overly shallow and/or fast, very likely affecting patient outcomes. We investigated the effect of a brief Crew Resource Management (CRM) training program on the correction rate of improperly executed chest compressions in a simulated cardiac arrest scenario. Final-year medical students (n = 57) were randomised to receive a 10-min computer-based CRM or a control training on ethics. Acting as team leaders, subjects performed resuscitation in a simulated cardiac arrest scenario before and after the training. Team members performed standardised overly shallow and fast chest compressions. We analysed how often the team leader recognised and corrected improper chest compressions, as well as communication and resuscitation quality. After the CRM training, team leaders corrected improper chest compressions (35.5%) significantly more often compared with those undergoing control training (7.7%, p = 0.03*). Consequently, four students have to be trained (number needed to treat = 3.6) for one improved chest compression scenario. Communication quality assessed by the Leader Behavior Description Questionnaire significantly increased in the intervention group by a mean of 4.5 compared with 2.0 (p = 0.01*) in the control group. A computer-based, 10-min CRM training improved the recognition of ineffective of chest compressions. Furthermore, communication quality increased. As guideline-adherent chest compressions have been linked to improved patient outcomes, our CRM training might represent a brief and affordable approach to increase chest compression quality and potentially improve patient outcomes.

Output MSE and PSNR prediction in DCT-based lossy compression of remote sensing images

NASA Astrophysics Data System (ADS)

Kozhemiakin, Ruslan A.; Abramov, Sergey K.; Lukin, Vladimir V.; Vozel, Benoit; Chehdi, Kacem

2017-10-01

Amount and size of remote sensing (RS) images acquired by modern systems are so large that data have to be compressed in order to transfer, save and disseminate them. Lossy compression becomes more popular for aforementioned situations. But lossy compression has to be applied carefully with providing acceptable level of introduced distortions not to lose valuable information contained in data. Then introduced losses have to be controlled and predicted and this is problematic for many coders. In this paper, we analyze possibilities of predicting mean square error or, equivalently, PSNR for coders based on discrete cosine transform (DCT) applied either for compressing singlechannel RS images or multichannel data in component-wise manner. The proposed approach is based on direct dependence between distortions introduced due to DCT coefficient quantization and losses in compressed data. One more innovation deals with possibility to employ a limited number (percentage) of blocks for which DCT-coefficients have to be calculated. This accelerates prediction and makes it considerably faster than compression itself. There are two other advantages of the proposed approach. First, it is applicable for both uniform and non-uniform quantization of DCT coefficients. Second, the approach is quite general since it works for several analyzed DCT-based coders. The simulation results are obtained for standard test images and then verified for real-life RS data.

Simulations of X-ray diffraction of shock-compressed single-crystal tantalum with synchrotron undulator sources.

PubMed

Tang, M X; Zhang, Y Y; E, J C; Luo, S N

2018-05-01

Polychromatic synchrotron undulator X-ray sources are useful for ultrafast single-crystal diffraction under shock compression. Here, simulations of X-ray diffraction of shock-compressed single-crystal tantalum with realistic undulator sources are reported, based on large-scale molecular dynamics simulations. Purely elastic deformation, elastic-plastic two-wave structure, and severe plastic deformation under different impact velocities are explored, as well as an edge release case. Transmission-mode diffraction simulations consider crystallographic orientation, loading direction, incident beam direction, X-ray spectrum bandwidth and realistic detector size. Diffraction patterns and reciprocal space nodes are obtained from atomic configurations for different loading (elastic and plastic) and detection conditions, and interpretation of the diffraction patterns is discussed.

Simulations of X-ray diffraction of shock-compressed single-crystal tantalum with synchrotron undulator sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, M. X.; Zhang, Y. Y.; E, J. C.

Polychromatic synchrotron undulator X-ray sources are useful for ultrafast single-crystal diffraction under shock compression. Here, simulations of X-ray diffraction of shock-compressed single-crystal tantalum with realistic undulator sources are reported, based on large-scale molecular dynamics simulations. Purely elastic deformation, elastic–plastic two-wave structure, and severe plastic deformation under different impact velocities are explored, as well as an edge release case. Transmission-mode diffraction simulations consider crystallographic orientation, loading direction, incident beam direction, X-ray spectrum bandwidth and realistic detector size. Diffraction patterns and reciprocal space nodes are obtained from atomic configurations for different loading (elastic and plastic) and detection conditions, and interpretation of themore » diffraction patterns is discussed.« less

A new method for aerodynamic test of high altitude propellers

NASA Astrophysics Data System (ADS)

Gong, Xiying; Zhang, Lin

A ground test system is designed for aerodynamic performance tests of high altitude propellers. The system is consisted of stable power supply, servo motors, two-component balance constructed by tension-compression sensors, ultrasonic anemometer, data acquisition module. It is loaded on a truck to simulate propellers' wind-tunnel test for different wind velocities at low density circumstance. The graphical programming language LABVIEW for developing virtual instrument is used to realize the test system control and data acquisition. Aerodynamic performance test of a propeller with 6.8 m diameter was completed by using this system. The results verify the feasibility of the ground test method.

An equivalent-time-lines model for municipal solid waste based on its compression characteristics.

PubMed

Gao, Wu; Bian, Xuecheng; Xu, Wenjie; Chen, Yunmin

2017-10-01

Municipal solid waste (MSW) demonstrates a noticeable time-dependent stress-strain behavior, which contributes greatly to the settlement of landfills and therefore influences both the storage capacity of landfills and the integrity of internal structures. The long-term compression tests for MSW under different biodegradation conditions were analyzed. It showed that the primary compression can affect the secondary compression due to the biodegradation and mechanical creep. Based on the time-lines model for clays and the compression characteristics of MSW, relationships between MSW's viscous strain rate and equivalent time were established, and then the viscous strain functions of MSW under different biodegradation conditions were deduced, and an equivalent-time-lines model for MSW settlement for two biodegradation conditions was developed, including the Type I model for the enhanced biodegradation condition and the Type II model for the normal biodegradation condition. The simulated compression results of laboratory and field compression tests under different biodegradation conditions were consistent with the measured data, which showed the reliability of both types of the equivalent-time-lines model for MSW. In addition, investigations of the long-term settlement of landfills from the literature indicated that the Type I model is suitable for predicting settlement in MSW landfills with a distinct biodegradation progress of MSW, a high content of organics in MSW, a short fill age or under an enhanced biodegradation environment; while the Type II model is good at predicting settlement in MSW landfills with a distinct progress of mechanical creep compression, a low content of organics in MSW, a long fill age or under a normal biodegradation condition. Furthermore, relationships between model parameters and the fill age of landfills were summarized. Finally, the similarities and differences between the equivalent-time-lines model for MSW and the stress-biodegradation model for MSW were discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Simulated effect on the compressive and shear mechanical properties of bionic integrated honeycomb plates.

PubMed

He, Chenglin; Chen, Jinxiang; Wu, Zhishen; Xie, Juan; Zu, Qiao; Lu, Yun

2015-05-01

Honeycomb plates can be applied in many fields, including furniture manufacturing, mechanical engineering, civil engineering, transportation and aerospace. In the present study, we discuss the simulated effect on the mechanical properties of bionic integrated honeycomb plates by investigating the compressive and shear failure modes and the mechanical properties of trabeculae reinforced by long or short fibers. The results indicate that the simulated effect represents approximately 80% and 70% of the compressive and shear strengths, respectively. Compared with existing bionic samples, the mass-specific strength was significantly improved. Therefore, this integrated honeycomb technology remains the most effective method for the trial manufacturing of bionic integrated honeycomb plates. The simulated effect of the compressive rigidity is approximately 85%. The short-fiber trabeculae have an advantage over the long-fiber trabeculae in terms of shear rigidity, which provides new evidence for the application of integrated bionic honeycomb plates. Copyright © 2015 Elsevier B.V. All rights reserved.

Large eddy simulations of time-dependent and buoyancy-driven channel flows

NASA Technical Reports Server (NTRS)

Cabot, William H.

1993-01-01

The primary goal of this work has been to assess the performance of the dynamic SGS model in the large eddy simulation (LES) of channel flows in a variety of situations, viz., in temporal development of channel flow turned by a transverse pressure gradient and especially in buoyancy-driven turbulent flows such as Rayleigh-Benard and internally heated channel convection. For buoyancy-driven flows, there are additional buoyant terms that are possible in the base models, and one objective has been to determine if the dynamic SGS model results are sensitive to such terms. The ultimate goal is to determine the minimal base model needed in the dynamic SGS model to provide accurate results in flows with more complicated physical features. In addition, a program of direct numerical simulation (DNS) of fully compressible channel convection has been undertaken to determine stratification and compressibility effects. These simulations are intended to provide a comparative base for performing the LES of compressible (or highly stratified, pseudo-compressible) convection at high Reynolds number in the future.

Biomechanical Comparison of Inter-fragmentary Compression Pressures: Lag Screw versus Herbert Screw for Anterior Odontoid Screw Fixation.

PubMed

Park, Jin-Woo; Kim, Kyoung-Tae; Sung, Joo-Kyung; Park, Seong-Hyun; Seong, Ki-Woong; Cho, Dae-Chul

2017-09-01

The purpose of the present study was to compare inter-fragmentary compression pressures after fixation of a simulated type II odontoid fracture with the headless compression Herbert screw and a half threaded cannulated lag screw. We compared inter-fragmentary compression pressures between 40- and 45-mm long 4.5-mm Herbert screws (n=8 and n=9, respectively) and 40- and 45-mm long 4.0-mm cannulated lag screws (n=7 and n=10, respectively) after insertion into rigid polyurethane foam test blocks (Sawbones, Vashon, WA, USA). A washer load cell was placed between the two segments of test blocks to measure the compression force. Because the total length of each foam block was 42 mm, the 40-mm screws were embedded in the cancellous foam, while the 45-mm screws penetrated the denser cortical foam at the bottom. This enabled us to compare inter-fragmentary compression pressures as they are affected by the penetration of the apical dens tip by the screws. The mean compression pressures of the 40- and 45-mm long cannulated lag screws were 50.48±1.20 N and 53.88±1.02 N, respectively, which was not statistically significant (p=0.0551). The mean compression pressures of the 40-mm long Herbert screw was 52.82±2.17 N, and was not statistically significant compared with the 40-mm long cannulated lag screw (p=0.3679). However, 45-mm Herbert screw had significantly higher mean compression pressure (60.68±2.03 N) than both the 45-mm cannulated lag screw and the 40-mm Herbert screw (p=0.0049 and p=0.0246, respectively). Our results showed that inter-fragmentary compression pressures of the Herbert screw were significantly increased when the screw tip penetrated the opposite dens cortical foam. This can support the generally recommended surgical technique that, in order to facilitate maximal reduction of the fracture gap using anterior odontoid screws, it is essential to penetrate the apical dens tip with the screw.

Fully-coupled aeroelastic simulation with fluid compressibility — For application to vocal fold vibration

PubMed Central

Yang, Jubiao; Wang, Xingshi; Krane, Michael; Zhang, Lucy T.

2017-01-01

In this study, a fully-coupled fluid–structure interaction model is developed for studying dynamic interactions between compressible fluid and aeroelastic structures. The technique is built based on the modified Immersed Finite Element Method (mIFEM), a robust numerical technique to simulate fluid–structure interactions that has capabilities to simulate high Reynolds number flows and handles large density disparities between the fluid and the solid. For accurate assessment of this intricate dynamic process between compressible fluid, such as air and aeroelastic structures, we included in the model the fluid compressibility in an isentropic process and a solid contact model. The accuracy of the compressible fluid solver is verified by examining acoustic wave propagations in a closed and an open duct, respectively. The fully-coupled fluid–structure interaction model is then used to simulate and analyze vocal folds vibrations using compressible air interacting with vocal folds that are represented as layered viscoelastic structures. Using physiological geometric and parametric setup, we are able to obtain a self-sustained vocal fold vibration with a constant inflow pressure. Parametric studies are also performed to study the effects of lung pressure and vocal fold tissue stiffness in vocal folds vibrations. All the case studies produce expected airflow behavior and a sustained vibration, which provide verification and confidence in our future studies of realistic acoustical studies of the phonation process. PMID:29527067

Impact tests on fibrous composite sandwich structures

NASA Technical Reports Server (NTRS)

Rhodes, M. D.

1978-01-01

The effect of low velocity impact on the strength of laminates fabricated from graphite/epoxy and Kevlar 49/epoxy composite materials was studied. The test laminates were loaded statically either in uniaxial tension or compression when impact occurred to evaluate the effect of loading on the initiation of damage and/or failure. Typical aircraft service conditions such as runway debris encountered during landing were simulated by impacting 1.27-cm-diameter projectiles normal to the plane of the test laminates at velocities between 5.2 and 48.8 m/s.

Computer simulation of plasma and N-body problems

NASA Technical Reports Server (NTRS)

Harries, W. L.; Miller, J. B.

1975-01-01

The following FORTRAN language computer codes are presented: (1) efficient two- and three-dimensional central force potential solvers; (2) a three-dimensional simulator of an isolated galaxy which incorporates the potential solver; (3) a two-dimensional particle-in-cell simulator of the Jeans instability in an infinite self-gravitating compressible gas; and (4) a two-dimensional particle-in-cell simulator of a rotating self-gravitating compressible gaseous system of which rectangular coordinate and superior polar coordinate versions were written.

Modelling deformation and fracture in confectionery wafers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohammed, Idris K.; Charalambides, Maria N.; Williams, J. Gordon

2015-01-22

The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which wasmore » then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.« less

Modelling deformation and fracture in confectionery wafers

NASA Astrophysics Data System (ADS)

Mohammed, Idris K.; Charalambides, Maria N.; Williams, J. Gordon; Rasburn, John

2015-01-01

The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.

Application of PDF methods to compressible turbulent flows

NASA Astrophysics Data System (ADS)

Delarue, B. J.; Pope, S. B.

1997-09-01

A particle method applying the probability density function (PDF) approach to turbulent compressible flows is presented. The method is applied to several turbulent flows, including the compressible mixing layer, and good agreement is obtained with experimental data. The PDF equation is solved using a Lagrangian/Monte Carlo method. To accurately account for the effects of compressibility on the flow, the velocity PDF formulation is extended to include thermodynamic variables such as the pressure and the internal energy. The mean pressure, the determination of which has been the object of active research over the last few years, is obtained directly from the particle properties. It is therefore not necessary to link the PDF solver with a finite-volume type solver. The stochastic differential equations (SDE) which model the evolution of particle properties are based on existing second-order closures for compressible turbulence, limited in application to low turbulent Mach number flows. Tests are conducted in decaying isotropic turbulence to compare the performances of the PDF method with the Reynolds-stress closures from which it is derived, and in homogeneous shear flows, at which stage comparison with direct numerical simulation (DNS) data is conducted. The model is then applied to the plane compressible mixing layer, reproducing the well-known decrease in the spreading rate with increasing compressibility. It must be emphasized that the goal of this paper is not as much to assess the performance of models of compressibility effects, as it is to present an innovative and consistent PDF formulation designed for turbulent inhomogeneous compressible flows, with the aim of extending it further to deal with supersonic reacting flows.

A finite difference model for free surface gravity drainage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couri, F.R.; Ramey, H.J. Jr.

1993-09-01

The unconfined gravity flow of liquid with a free surface into a well is a classical well test problem which has not been well understood by either hydrologists or petroleum engineers. Paradigms have led many authors to treat an incompressible flow as compressible flow to justify the delayed yield behavior of a time-drawdown test. A finite-difference model has been developed to simulate the free surface gravity flow of an unconfined single phase, infinitely large reservoir into a well. The model was verified with experimental results in sandbox models in the literature and with classical methods applied to observation wells inmore » the Groundwater literature. The simulator response was also compared with analytical Theis (1935) and Ramey et al. (1989) approaches for wellbore pressure at late producing times. The seepage face in the sandface and the delayed yield behavior were reproduced by the model considering a small liquid compressibility and incompressible porous medium. The potential buildup (recovery) simulated by the model evidenced a different- phenomenon from the drawdown, contrary to statements found in the Groundwater literature. Graphs of buildup potential vs time, buildup seepage face length vs time, and free surface head and sand bottom head radial profiles evidenced that the liquid refills the desaturating cone as a flat moving surface. The late time pseudo radial behavior was only approached after exaggerated long times.« less

Compressive self-interference Fresnel digital holography with faithful reconstruction

NASA Astrophysics Data System (ADS)

Wan, Yuhong; Man, Tianlong; Han, Ying; Zhou, Hongqiang; Wang, Dayong

2017-05-01

We developed compressive self-interference digital holographic approach that allows retrieving three-dimensional information of the spatially incoherent objects from single-shot captured hologram. The Fresnel incoherent correlation holography is combined with parallel phase-shifting technique to instantaneously obtain spatial-multiplexed phase-shifting holograms. The recording scheme is regarded as compressive forward sensing model, thus the compressive-sensing-based reconstruction algorithm is implemented to reconstruct the original object from the under sampled demultiplexed sub-holograms. The concept was verified by simulations and experiments with simulating use of the polarizer array. The proposed technique has great potential to be applied in 3D tracking of spatially incoherent samples.

Working Characteristics of Variable Intake Valve in Compressed Air Engine

PubMed Central

Yu, Qihui; Shi, Yan; Cai, Maolin

2014-01-01

A new camless compressed air engine is proposed, which can make the compressed air energy reasonably distributed. Through analysis of the camless compressed air engine, a mathematical model of the working processes was set up. Using the software MATLAB/Simulink for simulation, the pressure, temperature, and air mass of the cylinder were obtained. In order to verify the accuracy of the mathematical model, the experiments were conducted. Moreover, performance analysis was introduced to design compressed air engine. Results show that, firstly, the simulation results have good consistency with the experimental results. Secondly, under different intake pressures, the highest output power is obtained when the crank speed reaches 500 rpm, which also provides the maximum output torque. Finally, higher energy utilization efficiency can be obtained at the lower speed, intake pressure, and valve duration angle. This research can refer to the design of the camless valve of compressed air engine. PMID:25379536

Working characteristics of variable intake valve in compressed air engine.

PubMed

Yu, Qihui; Shi, Yan; Cai, Maolin

2014-01-01

A new camless compressed air engine is proposed, which can make the compressed air energy reasonably distributed. Through analysis of the camless compressed air engine, a mathematical model of the working processes was set up. Using the software MATLAB/Simulink for simulation, the pressure, temperature, and air mass of the cylinder were obtained. In order to verify the accuracy of the mathematical model, the experiments were conducted. Moreover, performance analysis was introduced to design compressed air engine. Results show that, firstly, the simulation results have good consistency with the experimental results. Secondly, under different intake pressures, the highest output power is obtained when the crank speed reaches 500 rpm, which also provides the maximum output torque. Finally, higher energy utilization efficiency can be obtained at the lower speed, intake pressure, and valve duration angle. This research can refer to the design of the camless valve of compressed air engine.

Intelligent bandwith compression

NASA Astrophysics Data System (ADS)

Tseng, D. Y.; Bullock, B. L.; Olin, K. E.; Kandt, R. K.; Olsen, J. D.

1980-02-01

The feasibility of a 1000:1 bandwidth compression ratio for image transmission has been demonstrated using image-analysis algorithms and a rule-based controller. Such a high compression ratio was achieved by first analyzing scene content using auto-cueing and feature-extraction algorithms, and then transmitting only the pertinent information consistent with mission requirements. A rule-based controller directs the flow of analysis and performs priority allocations on the extracted scene content. The reconstructed bandwidth-compressed image consists of an edge map of the scene background, with primary and secondary target windows embedded in the edge map. The bandwidth-compressed images are updated at a basic rate of 1 frame per second, with the high-priority target window updated at 7.5 frames per second. The scene-analysis algorithms used in this system together with the adaptive priority controller are described. Results of simulated 1000:1 band width-compressed images are presented. A video tape simulation of the Intelligent Bandwidth Compression system has been produced using a sequence of video input from the data base.

KSC-2010-5310

NASA Image and Video Library

2010-10-27

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, the 600-Ton Test Fixture outside the Launch Equipment Test Facility conducts a 500,000-pound pull test of a bridge crane lifting element, which is used to lift space shuttles in the Vehicle Assembly Building. The fixture proofload tests, in tension and compression, a variety of ground support equipment, including slings, lifting beams and other critical lifting hardware that require periodic proofloading. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a 6,000-square-foot high bay, cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, launch simulation towers and a cryogenic system. Photo credit: NASA/Jim Grossmann

KSC-2010-5308

NASA Image and Video Library

2010-10-27

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, the 600-Ton Test Fixture outside the Launch Equipment Test Facility is prepared to conduct a 500,000-pound pull test of a bridge crane lifting element, which is used to lift space shuttles in the Vehicle Assembly Building. The fixture proofload tests, in tension and compression, a variety of ground support equipment, including slings, lifting beams and other critical lifting hardware that require periodic proofloading. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a 6,000-square-foot high bay, cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, launch simulation towers and a cryogenic system. Photo credit: NASA/Jim Grossmann

KSC-2010-5311

NASA Image and Video Library

2010-10-27

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, the 600-Ton Test Fixture outside the Launch Equipment Test Facility conducts a 500,000-pound pull test of a bridge crane lifting element, which is used to lift space shuttles in the Vehicle Assembly Building. The fixture proofload tests, in tension and compression, a variety of ground support equipment, including slings, lifting beams and other critical lifting hardware that require periodic proofloading. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a 6,000-square-foot high bay, cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, launch simulation towers and a cryogenic system. Photo credit: NASA/Jim Grossmann

KSC-2010-5309

NASA Image and Video Library

2010-10-27

CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, the 600-Ton Test Fixture outside the Launch Equipment Test Facility conducts a 500,000-pound pull test of a bridge crane lifting element, which is used to lift space shuttles in the Vehicle Assembly Building. The fixture proofload tests, in tension and compression, a variety of ground support equipment, including slings, lifting beams and other critical lifting hardware that require periodic proofloading. Since 1977, the facility has supported NASA’s Launch Services, shuttle, International Space Station, and Constellation programs, as well as commercial providers. The facility recently underwent a major upgrade to support even more programs, projects and customers. It houses a 6,000-square-foot high bay, cable fabrication and molding shop, pneumatics shop, machine and weld shop and full-scale control room. Outside, the facility features a water flow test loop, vehicle motion simulator, launch simulation towers and a cryogenic system. Photo credit: NASA/Jim Grossmann

Mechanical response of common millet (Panicum miliaceum) seeds under quasi-static compression: Experiments and modeling.

PubMed

Hasseldine, Benjamin P J; Gao, Chao; Collins, Joseph M; Jung, Hyun-Do; Jang, Tae-Sik; Song, Juha; Li, Yaning

2017-09-01

The common millet (Panicum miliaceum) seedcoat has a fascinating complex microstructure, with jigsaw puzzle-like epidermis cells articulated via wavy intercellular sutures to form a compact layer to protect the kernel inside. However, little research has been conducted on linking the microstructure details with the overall mechanical response of this interesting biological composite. To this end, an integrated experimental-numerical-analytical investigation was conducted to both characterize the microstructure and ascertain the microscale mechanical properties and to test the overall response of kernels and full seeds under macroscale quasi-static compression. Scanning electron microscopy (SEM) was utilized to examine the microstructure of the outer seedcoat and nanoindentation was performed to obtain the material properties of the seedcoat hard phase material. A multiscale computational strategy was applied to link the microstructure to the macroscale response of the seed. First, the effective anisotropic mechanical properties of the seedcoat were obtained from finite element (FE) simulations of a microscale representative volume element (RVE), which were further verified from sophisticated analytical models. Then, macroscale FE models of the individual kernel and full seed were developed. Good agreement between the compression experiments and FE simulations were obtained for both the kernel and the full seed. The results revealed the anisotropic property and the protective function of the seedcoat, and showed that the sutures of the seedcoat play an important role in transmitting and distributing loads in responding to external compression. Copyright © 2017 Elsevier Ltd. All rights reserved.

Evaluation of a Text Compression Algorithm Against Computer-Aided Instruction (CAI) Material.

ERIC Educational Resources Information Center

Knight, Joseph M., Jr.

This report describes the initial evaluation of a text compression algorithm against computer assisted instruction (CAI) material. A review of some concepts related to statistical text compression is followed by a detailed description of a practical text compression algorithm. A simulation of the algorithm was programed and used to obtain…

Effect of shock waves on the statistics and scaling in compressible isotropic turbulence

NASA Astrophysics Data System (ADS)

Wang, Jianchun; Wan, Minping; Chen, Song; Xie, Chenyue; Chen, Shiyi

2018-04-01

The statistics and scaling of compressible isotropic turbulence in the presence of large-scale shock waves are investigated by using numerical simulations at turbulent Mach number Mt ranging from 0.30 to 0.65. The spectra of the compressible velocity component, density, pressure, and temperature exhibit a k-2 scaling at different turbulent Mach numbers. The scaling exponents for structure functions of the compressible velocity component and thermodynamic variables are close to 1 at high orders n ≥3 . The probability density functions of increments of the compressible velocity component and thermodynamic variables exhibit a power-law region with the exponent -2 . Models for the conditional average of increments of the compressible velocity component and thermodynamic variables are developed based on the ideal shock relations and are verified by numerical simulations. The overall statistics of the compressible velocity component and thermodynamic variables are similar to one another at different turbulent Mach numbers. It is shown that the effect of shock waves on the compressible velocity spectrum and kinetic energy transfer is different from that of acoustic waves.

Quasi 1D Modeling of Mixed Compression Supersonic Inlets

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Woolwine, Kyle J.

2012-01-01

The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of the 2-dimensional bifurcated mixed compression supersonic inlet is being developed. The model utilizes computational fluid dynamics for both the supersonic and subsonic diffusers. The oblique shocks are modeled utilizing compressible flow equations. This model also implements variable geometry required to control the normal shock position. The model is flexible and can also be utilized to simulate other mixed compression supersonic inlet designs. The model was validated both in time and in the frequency domain against the legacy LArge Perturbation INlet code, which has been previously verified using test data. This legacy code written in FORTRAN is quite extensive and complex in terms of the amount of software and number of subroutines. Further, the legacy code is not suitable for closed loop feedback controls design, and the simulation environment is not amenable to systems integration. Therefore, a solution is to develop an innovative, more simplified, mixed compression inlet model with the same steady state and dynamic performance as the legacy code that also can be used for controls design. The new nonlinear dynamic model is implemented in MATLAB Simulink. This environment allows easier development of linear models for controls design for shock positioning. The new model is also well suited for integration with a propulsion system model to study inlet/propulsion system performance, and integration with an aero-servo-elastic system model to study integrated vehicle ride quality, vehicle stability, and efficiency.

Shock Response of Lightweight Adobe Masonry

NASA Astrophysics Data System (ADS)

Sauer, C.; Bagusat, F.; Heine, A.; Riedel, W.

2018-06-01

The behavior of a low density and low-strength building material under shock loading is investigated. The considered material is lightweight adobe masonry characterized by a density of 1.2 g/cm3 and a quasi-static uniaxial compressive strength of 2.8 MPa. Planar-plate-impact (PPI) tests with velocities in between 295 and 950 m/s are performed in order to obtain Hugoniot data and to derive parameters for an equation of state (EOS) that captures the occurring phenomenology of porous compaction and subsequent unloading. The resulting EOS description is validated by comparing the experimental free surface velocity time curves with those obtained by numerical simulations of the performed PPI tests. The non-linear compression behavior, including the pore compaction mechanism, constitutes a main ingredient for modelling the response of adobe to blast and high-velocity impact loading. We hence present a modeling approach for lightweight adobe which can be applied to such high rate loading scenarios in future studies. In general, this work shows that PPI tests on lightweight and low-strength geological materials can be used to extract Hugoniot data despite significant material inhomogeneity. Furthermore, we demonstrate that a homogenous material model is able to numerically describe such a material under shock compression and release with a reasonable accuracy.

Shock Response of Lightweight Adobe Masonry

NASA Astrophysics Data System (ADS)

Sauer, C.; Bagusat, F.; Heine, A.; Riedel, W.

2018-04-01

The behavior of a low density and low-strength building material under shock loading is investigated. The considered material is lightweight adobe masonry characterized by a density of 1.2 g/cm3 and a quasi-static uniaxial compressive strength of 2.8 MPa. Planar-plate-impact (PPI) tests with velocities in between 295 and 950 m/s are performed in order to obtain Hugoniot data and to derive parameters for an equation of state (EOS) that captures the occurring phenomenology of porous compaction and subsequent unloading. The resulting EOS description is validated by comparing the experimental free surface velocity time curves with those obtained by numerical simulations of the performed PPI tests. The non-linear compression behavior, including the pore compaction mechanism, constitutes a main ingredient for modelling the response of adobe to blast and high-velocity impact loading. We hence present a modeling approach for lightweight adobe which can be applied to such high rate loading scenarios in future studies. In general, this work shows that PPI tests on lightweight and low-strength geological materials can be used to extract Hugoniot data despite significant material inhomogeneity. Furthermore, we demonstrate that a homogenous material model is able to numerically describe such a material under shock compression and release with a reasonable accuracy.

U. S. Army Engineer Research and Development Center: Rapid Repair of Levee Breaches

DTIC Science & Technology

2011-06-01

tensile loads while allowing rigid (nonfabric) structural elements to bear the compressive loads, as shown in Figure 2.2. In Figure 2.2(a), the...Report 81000-01 2.7.3 Small-Scale Modeling Flume Tests An 80 ft long tilting flume was used to provide a simulated levee breach and flow for...somewhat peripheral to the main thrust of the DHS-SERRI funding in this project, only a cursory description of the technology and testing results will

The effects of an online basic life support course on undergraduate nursing students’ learning

PubMed Central

Tobase, Lucia; Peres, Heloisa H.C.; Smith, Nicole; Polastri, Thatiane F.; Timerman, Sergio

2017-01-01

Objectives To describe learning outcomes of undergraduate nursing students following an online basic life support course (BLS). Methods An online BLS course was developed and administered to 94 nursing students. Pre- and post-tests were used to assess theoretical learning. Checklist simulations and feedback devices were used to assess the cardiopulmonary resuscitation (CPR) skills of the 62 students who completed the course. Results A paired t-test revealed a significant increase in learning [pre-test (6.4 ± 1.61), post-test (9.3 ± 0.82), p < 0.001]. The increase in the average grade after taking the online course was significant (p<0.001). No learning differences (p=0.475) had been observed between 1st and 2nd year (9.20 ± 1.60), and between 3rd and 4th year (9.67 ± 0.61) students. A CPR simulation was performed after completing the course: students checked for a response (90%), exposed the chest (98%), checked for breathing (97%), called emergency services (76%), requested for a defibrillator (92%), checked for a pulse (77%), positioned their hands properly (87%), performed 30 compressions/cycle (95%), performed compressions of at least 5 cm depth (89%), released the chest (90%), applied two breaths (97%), used the automated external defibrillator (97%), and positioned the pads (100%). Conclusions The online course was an effective method for teaching and learning key BLS skills wherein students were able to accurately apply BLS procedures during the CPR simulation. This short-term online training, which likely improves learning and self-efficacy in BLS providers, can be used for the continuing education of health professionals. PMID:28850944

Dynamic Biomechanical Examination of the Lumbar Spine with Implanted Total Disc Replacement (TDR) Utilizing a Pendulum Testing System

PubMed Central

Daniels, Alan H; Paller, David J; Koruprolu, Sarath; McDonnell, Matthew; Palumbo, Mark A; Crisco, Joseph J

2013-01-01

Study Design Biomechanical cadaver investigation Objective To examine dynamic bending stiffness and energy absorption of the lumbar spine with and without implanted Total Disc Replacement (TDR) under simulated physiologic motion. Summary of background data The pendulum testing system is capable of applying physiologic compressive loads without constraining motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. Methods Five unembalmed, frozen human lumbar FSUs were tested on the pendulum system with axial compressive loads of 181N, 282N, 385N, and 488N before and after Synthes ProDisc-L TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5° resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode. Results In flexion/extension, the TDR constructs reached equilibrium with significantly (p<0.05) fewer cycles than the intact FSU with compressive loads of 282N, 385N and 488N. Mean dynamic bending stiffness in flexion, extension, and lateral bending increased significantly with increasing load for both the intact FSU and TDR constructs (p<0.001). In flexion, with increasing compressive loading from 181N to 488N, the bending stiffness of the intact FSUs increased from 4.0N-m/° to 5.5N-m/°, compared to 2.1N-m/° to 3.6N-m/° after TDR implantation. At each compressive load, the intact FSU was significantly more stiff than the TDR (p<0.05). Conclusion Lumbar FSUs with implanted TDR were found to be less stiff, but also absorbed more energy during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion preserving devices are not fully known, these results provide further insight into the biomechanical behavior of this device under approximated physiologic loading conditions. PMID:22869057

Cervical total disc replacement exhibits similar stiffness to intact cervical functional spinal units tested on a dynamic pendulum testing system.

PubMed

Esmende, Sean M; Daniels, Alan H; Paller, David J; Koruprolu, Sarath; Palumbo, Mark A; Crisco, Joseph J

2015-01-01

The pendulum testing system is capable of applying physiologic compressive loads without constraining the motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. To examine the dynamic bending stiffness and energy absorption of the cervical spine, with and without implanted cervical total disc replacement (TDR) under simulated physiologic motion. A biomechanical cadaver investigation. Nine unembalmed, frozen human cervical FSUs from levels C3-C4 and C5-C6 were tested on the pendulum system with axial compressive loads of 25, 50, and 100 N before and after TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°, resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and the bending stiffness (Newton-meter/°) was calculated and compared for each testing mode. In flexion/extension, with increasing compressive loading from 25 to 100 N, the average number of cycles to equilibrium for the intact FSUs increased from 6.6 to 19.1, compared with 4.1 to 12.7 after TDR implantation (p<.05 for loads of 50 and 100 N). In flexion, with increasing compressive loading from 25 to 100 N, the bending stiffness of the intact FSUs increased from 0.27 to 0.59 Nm/°, compared with 0.21 to 0.57 Nm/° after TDR implantation. No significant differences were found in stiffness between the intact FSU and the TDR in flexion/extension and lateral bending at any load (p<.05). Cervical FSUs with implanted TDR were found to have similar stiffness, but had greater energy absorption than intact FSUs during cyclic loading with an unconstrained pendulum system. These results provide further insight into the biomechanical behavior of cervical TDR under approximated physiologic loading conditions. Copyright © 2015 Elsevier Inc. All rights reserved.

Post-Buckling and Ultimate Strength Analysis of Stiffened Composite Panel Base on Progressive Damage

NASA Astrophysics Data System (ADS)

Zhang, Guofan; Sun, Xiasheng; Sun, Zhonglei

Stiffened composite panel is the typical thin wall structure applied in aerospace industry, and its main failure mode is buckling subjected to compressive loading. In this paper, the development of an analysis approach using Finite Element Method on post-buckling behavior of stiffened composite structures under compression was presented. Then, the numerical results of stiffened panel are obtained by FE simulations. A thorough comparison were accomplished by comparing the load carrying capacity and key position strains of the specimen with test. The comparison indicates that the FEM results which adopted developed methodology could meet the demand of engineering application in predicting the post-buckling behavior of intact stiffened structures in aircraft design stage.

Digital-computer normal shock position and restart control of a Mach 2.5 axisymmetric mixed-compression inlet

NASA Technical Reports Server (NTRS)

Neiner, G. H.; Cole, G. L.; Arpasi, D. J.

1972-01-01

Digital computer control of a mixed-compression inlet is discussed. The inlet was terminated with a choked orifice at the compressor face station to dynamically simulate a turbojet engine. Inlet diffuser exit airflow disturbances were used. A digital version of a previously tested analog control system was used for both normal shock and restart control. Digital computer algorithms were derived using z-transform and finite difference methods. Using a sample rate of 1000 samples per second, the digital normal shock and restart controls essentially duplicated the inlet analog computer control results. At a sample rate of 100 samples per second, the control system performed adequately but was less stable.

Strength and compressibility of returned lunar soil.

NASA Technical Reports Server (NTRS)

Carrier, W. D., III; Bromwell, L. G.; Martin, R. T.

1972-01-01

Two oedometer and three direct shear tests have been performed in vacuum on a 200 g sample of lunar soil from Apollo 12 (12001, 119). The compressibility data have been used to calculate bulk density and shear wave velocity versus depth on the lunar surface. The shear wave velocity was found to increase approximately with the one-fourth power of the depth, and the results suggest that the Apollo 14 Active Seismic Experiment may not have detected the Fra Mauro formation at a depth of 8.5 m, but only naturally consolidated lunar soil. The shear data indicate that the strength of the lunar soil sample is about 65% that of a ground basalt simulant at the same void ratio.

Implementation of Hydrodynamic Simulation Code in Shock Experiment Design for Alkali Metals

NASA Astrophysics Data System (ADS)

Coleman, A. L.; Briggs, R.; Gorman, M. G.; Ali, S.; Lazicki, A.; Swift, D. C.; Stubley, P. G.; McBride, E. E.; Collins, G.; Wark, J. S.; McMahon, M. I.

2017-10-01

Shock compression techniques enable the investigation of extreme P-T states. In order to probe off-Hugoniot regions of P-T space, target makeup and laser pulse parameters must be carefully designed. HYADES is a hydrodynamic simulation code which has been successfully utilised to simulate shock compression events and refine the experimental parameters required in order to explore new P-T states in alkali metals. Here we describe simulations and experiments on potassium, along with the techniques required to access off-Hugoniot states.

Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique

NASA Technical Reports Server (NTRS)

Li, Lihua; Coon, Michael; McLinden, Matthew

2013-01-01

Pulse compression has been widely used in radars so that low-power, long RF pulses can be transmitted, rather than a highpower short pulse. Pulse compression radars offer a number of advantages over high-power short pulsed radars, such as no need of high-power RF circuitry, no need of high-voltage electronics, compact size and light weight, better range resolution, and better reliability. However, range sidelobe associated with pulse compression has prevented the use of this technique on spaceborne radars since surface returns detected by range sidelobes may mask the returns from a nearby weak cloud or precipitation particles. Research on adaptive pulse compression was carried out utilizing a field-programmable gate array (FPGA) waveform generation board and a radar transceiver simulator. The results have shown significant improvements in pulse compression sidelobe performance. Microwave and millimeter-wave radars present many technological challenges for Earth and planetary science applications. The traditional tube-based radars use high-voltage power supply/modulators and high-power RF transmitters; therefore, these radars usually have large size, heavy weight, and reliability issues for space and airborne platforms. Pulse compression technology has provided a path toward meeting many of these radar challenges. Recent advances in digital waveform generation, digital receivers, and solid-state power amplifiers have opened a new era for applying pulse compression to the development of compact and high-performance airborne and spaceborne remote sensing radars. The primary objective of this innovative effort is to develop and test a new pulse compression technique to achieve ultrarange sidelobes so that this technique can be applied to spaceborne, airborne, and ground-based remote sensing radars to meet future science requirements. By using digital waveform generation, digital receiver, and solid-state power amplifier technologies, this improved pulse compression technique could bring significant impact on future radar development. The novel feature of this innovation is the non-linear FM (NLFM) waveform design. The traditional linear FM has the limit (-20 log BT -3 dB) for achieving ultra-low-range sidelobe in pulse compression. For this study, a different combination of 20- or 40-microsecond chirp pulse width and 2- or 4-MHz chirp bandwidth was used. These are typical operational parameters for airborne or spaceborne weather radars. The NLFM waveform design was then implemented on a FPGA board to generate a real chirp signal, which was then sent to the radar transceiver simulator. The final results have shown significant improvement on sidelobe performance compared to that obtained using a traditional linear FM chirp.

Factors affecting team leadership skills and their relationship with quality of cardiopulmonary resuscitation.

PubMed

Yeung, Joyce H Y; Ong, G J; Davies, Robin P; Gao, Fang; Perkins, Gavin D

2012-09-01

This study aims to explore the relationship between team-leadership skills and quality of cardiopulmonary resuscitation in an adult cardiac-arrest simulation. Factors affecting team-leadership skills were also assessed. Forty advanced life-support providers leading a cardiac arrest team in a standardized cardiac-arrest simulation were videotaped. Background data were collected, including age (in yrs), sex, whether they had received any leadership training in the past, whether they were part of a professional group, the most recent advanced life-support course (in months) they had undergone, advanced life-support instructor/provider status, and whether they had led in any cardiac arrest situation in the preceding 6 months. Participants were scored using the Cardiac Arrest Simulation test score and Leadership Behavior Description Questionnaire for leadership skills. Process-focused quality of cardiopulmonary resuscitation data were collected directly from manikin and video recordings. Primary outcomes were complex technical skills (measured as Cardiac Arrest Simulation test score, preshock pause, and hands-off ratio). Secondary outcomes were simple technical skills (chest-compression rate, depth, and ventilation rate). Univariate linear regressions were performed to examine how leadership skills affect quality of cardiopulmonary resuscitation and bivariate correlations elicited factors affecting team-leadership skills.Teams led by leaders with the best leadership skills performed higher quality cardiopulmonary resuscitation with better technical performance (R = 0.75, p < .001), shorter preshock pauses (R = 0.18, p < .001), with lower total hands-off ratio (R = 0.24, p = .01), and shorter time to first shock (R = 0.14, p = .02). Leadership skills were not significantly associated with more simple technical skills such as chest-compression rate, depth, and ventilation rate. Prior training in team leader skills was independently associated with better leadership behavior. There is an association between team leadership skills and cardiac arrest simulation test score, preshock pause, and hands off ratio. Developing leadership skills should be considered an integral part of resuscitation training.

Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging

NASA Technical Reports Server (NTRS)

Kimura, S.; Steinbach, G. C.; Watenpaugh, D. E.; Hargens, A. R.

2001-01-01

STUDY DESIGN: Axial load-dependent changes in the lumbar spine of supine healthy volunteers were examined using a compression device compatible with magnetic resonance imaging. OBJECTIVE: To test two hypotheses: Axial loading of 50% body weight from shoulder to feet in supine posture 1) simulates the upright lumbar spine alignment and 2) decreases disc height significantly. SUMMARY OF BACKGROUND DATA: Axial compression on the lumbar spine has significantly narrowed the lumbar dural sac in patients with sciatica, neurogenic claudication or both. METHODS: Using a device compatible with magnetic resonance imaging, the lumbar spine of eight young volunteers, ages 22 to 36 years, was axially compressed with a force equivalent to 50% of body weight, approximating the normal load on the lumbar spine in upright posture. Sagittal lumbar magnetic resonance imaging was performed to measure intervertebral angle and disc height before and during compression. RESULTS: Each intervertebral angle before and during compression was as follows: T12-L1 (-0.8 degrees +/- 2.5 degrees and -1.5 degrees +/- 2.6 degrees ), L1-L2 (0.7 degrees +/- 1.4 degrees and 3.3 degrees +/- 2.9 degrees ), L2-L3 (4.7 degrees +/- 3.5 degrees and 7.3 degrees +/- 6 degrees ), L3-L4 (7.9 degrees +/- 2.4 degrees and 11.1 degrees +/- 4.6 degrees ), L4-L5 (14.3 degrees +/- 3.3 degrees and 14.9 degrees +/- 1.7 degrees ), L5-S1 (25.8 degrees +/- 5.2 degrees and 20.8 degrees +/- 6 degrees ), and L1-S1 (53.4 degrees +/- 11.9 degrees and 57.3 degrees +/- 16.7 degrees ). Negative values reflect kyphosis, and positive values reflect lordosis. A significant difference between values before and during compression was obtained at L3-L4 and L5-S1. There was a significant decrease in disc height only at L4-L5 during compression. CONCLUSIONS: The axial force of 50% body weight in supine posture simulates the upright lumbar spine morphologically. No change in intervertebral angle occurred at L4-L5. However, disc height at L4-L5 decreased significantly during compression.

Combustor Operability and Performance Verification for HIFiRE Flight 2

NASA Technical Reports Server (NTRS)

Storch, Andrea M.; Bynum, Michael; Liu, Jiwen; Gruber, Mark

2011-01-01

As part of the Hypersonic International Flight Research Experimentation (HIFiRE) Direct-Connect Rig (HDCR) test and analysis activity, three-dimensional computational fluid dynamics (CFD) simulations were performed using two Reynolds-Averaged Navier Stokes solvers. Measurements obtained from ground testing in the NASA Langley Arc-Heated Scramjet Test Facility (AHSTF) were used to specify inflow conditions for the simulations and combustor data from four representative tests were used as benchmarks. Test cases at simulated flight enthalpies of Mach 5.84, 6.5, 7.5, and 8.0 were analyzed. Modeling parameters (e.g., turbulent Schmidt number and compressibility treatment) were tuned such that the CFD results closely matched the experimental results. The tuned modeling parameters were used to establish a standard practice in HIFiRE combustor analysis. Combustor performance and operating mode were examined and were found to meet or exceed the objectives of the HIFiRE Flight 2 experiment. In addition, the calibrated CFD tools were then applied to make predictions of combustor operation and performance for the flight configuration and to aid in understanding the impacts of ground and flight uncertainties on combustor operation.

Molecular-dynamic simulations of the thermophysical properties of hexanitrohexaazaisowurtzitane single crystal at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Kozlova, S. A.; Gubin, S. A.; Maklashova, I. V.; Selezenev, A. A.

2017-11-01

Molecular dynamic simulations of isothermal compression parameters are performed for a hexanitrohexaazaisowurtzitane single crystal (C6H6O12N12) using a modified ReaxFF-log reactive force field. It is shown that the pressure-compression ratio curve for a single C6H6O12N12 crystal at constant temperature T = 300 K in pressure range P = 0.05-40 GPa is in satisfactory agreement with experimental compression isotherms obtained for a single C6H6O12N12 crystal. Hugoniot molecular-dynamic simulations of the shock-wave hydrostatic compression of a single C6H6O12N12 crystal are performed. Along with Hugoniot temperature-pressure curves, calculated shock-wave pressure-compression ratios for a single C6H6O12N12 crystal are obtained for a wide pressure range of P = 1-40 GPa. It is established that the percussive adiabat obtained for a single C6H6O12N12 crystal is in a good agreement with the experimental data. All calculations are performed using a LAMMPS molecular dynamics simulation software package that provides a ReaxFF-lg reactive force field to support the approach.

Calculation of dose distribution in compressible breast tissues using finite element modeling, Monte Carlo simulation and thermoluminescence dosimeters

NASA Astrophysics Data System (ADS)

Mohammadyari, Parvin; Faghihi, Reza; Mosleh-Shirazi, Mohammad Amin; Lotfi, Mehrzad; Rahim Hematiyan, Mohammad; Koontz, Craig; Meigooni, Ali S.

2015-12-01

Compression is a technique to immobilize the target or improve the dose distribution within the treatment volume during different irradiation techniques such as AccuBoost® brachytherapy. However, there is no systematic method for determination of dose distribution for uncompressed tissue after irradiation under compression. In this study, the mechanical behavior of breast tissue between compressed and uncompressed states was investigated. With that, a novel method was developed to determine the dose distribution in uncompressed tissue after irradiation of compressed breast tissue. Dosimetry was performed using two different methods, namely, Monte Carlo simulations using the MCNP5 code and measurements using thermoluminescent dosimeters (TLD). The displacement of the breast elements was simulated using a finite element model and calculated using ABAQUS software. From these results, the 3D dose distribution in uncompressed tissue was determined. The geometry of the model was constructed from magnetic resonance images of six different women volunteers. The mechanical properties were modeled by using the Mooney-Rivlin hyperelastic material model. Experimental dosimetry was performed by placing the TLD chips into the polyvinyl alcohol breast equivalent phantom. The results determined that the nodal displacements, due to the gravitational force and the 60 Newton compression forces (with 43% contraction in the loading direction and 37% expansion in the orthogonal direction) were determined. Finally, a comparison of the experimental data and the simulated data showed agreement within 11.5%  ±  5.9%.

Calculation of dose distribution in compressible breast tissues using finite element modeling, Monte Carlo simulation and thermoluminescence dosimeters.

PubMed

Mohammadyari, Parvin; Faghihi, Reza; Mosleh-Shirazi, Mohammad Amin; Lotfi, Mehrzad; Hematiyan, Mohammad Rahim; Koontz, Craig; Meigooni, Ali S

2015-12-07

Compression is a technique to immobilize the target or improve the dose distribution within the treatment volume during different irradiation techniques such as AccuBoost(®) brachytherapy. However, there is no systematic method for determination of dose distribution for uncompressed tissue after irradiation under compression. In this study, the mechanical behavior of breast tissue between compressed and uncompressed states was investigated. With that, a novel method was developed to determine the dose distribution in uncompressed tissue after irradiation of compressed breast tissue. Dosimetry was performed using two different methods, namely, Monte Carlo simulations using the MCNP5 code and measurements using thermoluminescent dosimeters (TLD). The displacement of the breast elements was simulated using a finite element model and calculated using ABAQUS software. From these results, the 3D dose distribution in uncompressed tissue was determined. The geometry of the model was constructed from magnetic resonance images of six different women volunteers. The mechanical properties were modeled by using the Mooney-Rivlin hyperelastic material model. Experimental dosimetry was performed by placing the TLD chips into the polyvinyl alcohol breast equivalent phantom. The results determined that the nodal displacements, due to the gravitational force and the 60 Newton compression forces (with 43% contraction in the loading direction and 37% expansion in the orthogonal direction) were determined. Finally, a comparison of the experimental data and the simulated data showed agreement within 11.5%  ±  5.9%.

Development of a biaxial compression device for biological samples: preliminary experimental results for a closed cell foam.

PubMed

Little, J P; Tevelen, G; Adam, C J; Evans, J H; Pearcy, M J

2009-07-01

Biological tissues are subjected to complex loading states in vivo and in order to define constitutive equations that effectively simulate their mechanical behaviour under these loads, it is necessary to obtain data on the tissue's response to multiaxial loading. Single axis and shear testing of biological tissues is often carried out, but biaxial testing is less common. We sought to design and commission a biaxial compression testing device, capable of obtaining repeatable data for biological samples. The apparatus comprised a sealed stainless steel pressure vessel specifically designed such that a state of hydrostatic compression could be created on the test specimen while simultaneously unloading the sample along one axis with an equilibrating tensile pressure. Thus a state of equibiaxial compression was created perpendicular to the long axis of a rectangular sample. For the purpose of calibration and commissioning of the vessel, rectangular samples of closed cell ethylene vinyl acetate (EVA) foam were tested. Each sample was subjected to repeated loading, and nine separate biaxial experiments were carried out to a maximum pressure of 204 kPa (30 psi), with a relaxation time of two hours between them. Calibration testing demonstrated the force applied to the samples had a maximum error of 0.026 N (0.423% of maximum applied force). Under repeated loading, the foam sample demonstrated lower stiffness during the first load cycle. Following this cycle, an increased stiffness, repeatable response was observed with successive loading. While the experimental protocol was developed for EVA foam, preliminary results on this material suggest that this device may be capable of providing test data for biological tissue samples. The load response of the foam was characteristic of closed cell foams, with consolidation during the early loading cycles, then a repeatable load-displacement response upon repeated loading. The repeatability of the test results demonstrated the ability of the test device to provide reproducible test data and the low experimental error in the force demonstrated the reliability of the test data.

Pulse compression at 1.06 μm in dispersion-decreasing holey fibers

NASA Astrophysics Data System (ADS)

Tse, M. L. V.; Horak, P.; Price, J. H. V.; Poletti, F.; He, F.; Richardson, D. J.

2006-12-01

We report compression of low-power femtosecond pulses at 1.06 μm in a dispersion-decreasing holey fiber. Near-adiabatic compression of 130 fs pulses down to 60 fs has been observed. Measured spectra and pulse shapes agree well with numerical simulations. Compression factors of ten are possible in optimized fibers.

Microstructure based hygromechanical modelling of deformation of fruit tissue

NASA Astrophysics Data System (ADS)

Abera, M. K.; Wang, Z.; Verboven, P.; Nicolai, B.

2017-10-01

Quality parameters such as firmness and susceptibility to mechanical damage are affected by the mechanical properties of fruit tissue. Fruit tissue is composed of turgid cells that keep cell walls under tension, and intercellular gas spaces where cell walls of neighboring cells have separated. How the structure and properties of these complex microstructures are affecting tissue mechanics is difficult to unravel experimentally. In this contribution, a modelling methodology is presented to calculate the deformation of apple fruit tissue affected by differences in structure and properties of cells and cell walls. The model can be used to perform compression experiments in silico using a hygromechanical model that computes the stress development and water loss during tissue deformation, much like in an actual compression test. The advantage of the model is that properties and structure can be changed to test the influence on the mechanical deformation process. The effect of microstructure, turgor pressure, cell membrane permeability, wall thickness and damping) on the compressibility of the tissue was simulated. Increasing the turgor pressure and thickness of the cell walls results in increased compression resistance of apple tissue increases, as do decreasing cell size and porosity. Geometric variability of the microstructure of tissues plays a major role, affecting results more than other model parameters. Different fruit cultivars were compared, and it was demonstrated, that microstructure variations within a cultivar are so large that interpretation of cultivar-specific effects is difficult.

The effects of polymers' visco-elastoplastic properties on the micro cavities filling step of hot embossing process

NASA Astrophysics Data System (ADS)

Cheng, Gang; Barrière, Thierry

2018-05-01

The hot embossing process has been widely used in the manufacturing of polymer components, especially for the fabrication of micro or nano components. The significant advantage of the hot embossing process compared to the traditional injection moulding process is the excellent effective filling ratio for the high aspect ratio components and large surface structural components. The lack of material behavior modeling and numerical simulation limits the further development the hot embossing process, especially at the micro and nano scales. In this paper, a visco-elastoplastic behavior law has been proposed to describe the amorphous thermoplastic polymer mechanical properties in the hot embossing processing temperature range, which is lightly above their glass transition temperature. Uniaxial compression tests have been carried out in order to investigate the amorphous thermoplastic polymers properties. The material parameters in the visco-elastoplastic model have been identified according to the experimental results. A 3D numerical model has been created in the simulation software, which is based on the finite element method. The numerical simulation of the filling step of the hot embossing process has been effectuated by taking into account the viscous, elastic and plastic behaviors of thermoplastic polymers. The micro hot embossing process has been carried out using horizontal injection compression moulding equipment. A complete compression mould tool, equipped with the heating system, the cooling system, the ejection system and the vacuum system, has been designed and elaborated for this research work. The microfluidic devices based on the amorphous thermoplastic polymers have been successfully elaborated by hot embossing process. Proper agreement between the numerical simulation and the experimental elaboration has been obtained.

Hypersonic separated flows about "tick" configurations with sensitivity to model design

NASA Astrophysics Data System (ADS)

Moss, J. N.; O'Byrne, S.; Gai, S. L.

2014-12-01

This paper presents computational results obtained by applying the direct simulation Monte Carlo (DSMC) method for hypersonic nonequilibrium flow about "tick-shaped" model configurations. These test models produces a complex flow where the nonequilibrium and rarefied aspects of the flow are initially enhanced as the flow passes over an expansion surface, and then the flow encounters a compression surface that can induce flow separation. The resulting flow is such that meaningful numerical simulations must have the capability to account for a significant range of rarefaction effects; hence the application of the DSMC method in the current study as the flow spans several flow regimes, including transitional, slip, and continuum. The current focus is to examine the sensitivity of both the model surface response (heating, friction and pressure) and flowfield structure to assumptions regarding surface boundary conditions and more extensively the impact of model design as influenced by leading edge configuration as well as the geometrical features of the expansion and compression surfaces. Numerical results indicate a strong sensitivity to both the extent of the leading edge sharpness and the magnitude of the leading edge bevel angle. Also, the length of the expansion surface for a fixed compression surface has a significant impact on the extent of separated flow.

Hypersonic Separated Flows About "Tick" Configurations With Sensitivity to Model Design

NASA Technical Reports Server (NTRS)

Moss, J. N.; O'Byrne, S.; Gai, S. L.

2014-01-01

This paper presents computational results obtained by applying the direct simulation Monte Carlo (DSMC) method for hypersonic nonequilibrium flow about "tick-shaped" model configurations. These test models produces a complex flow where the nonequilibrium and rarefied aspects of the flow are initially enhanced as the flow passes over an expansion surface, and then the flow encounters a compression surface that can induce flow separation. The resulting flow is such that meaningful numerical simulations must have the capability to account for a significant range of rarefaction effects; hence the application of the DSMC method in the current study as the flow spans several flow regimes, including transitional, slip, and continuum. The current focus is to examine the sensitivity of both the model surface response (heating, friction and pressure) and flowfield structure to assumptions regarding surface boundary conditions and more extensively the impact of model design as influenced by leading edge configuration as well as the geometrical features of the expansion and compression surfaces. Numerical results indicate a strong sensitivity to both the extent of the leading edge sharpness and the magnitude of the leading edge bevel angle. Also, the length of the expansion surface for a fixed compression surface has a significant impact on the extent of separated flow.

The Investigation of Ghost Fluid Method for Simulating the Compressible Two-Medium Flow

NASA Astrophysics Data System (ADS)

Lu, Hai Tian; Zhao, Ning; Wang, Donghong

2016-06-01

In this paper, we investigate the conservation error of the two-dimensional compressible two-medium flow simulated by the front tracking method. As the improved versions of the original ghost fluid method, the modified ghost fluid method and the real ghost fluid method are selected to define the interface boundary conditions, respectively, to show different effects on the conservation error. A Riemann problem is constructed along the normal direction of the interface in the front tracking method, with the goal of obtaining an efficient procedure to track the explicit sharp interface precisely. The corresponding Riemann solutions are also used directly in these improved ghost fluid methods. Extensive numerical examples including the sod tube and the shock-bubble interaction are tested to calculate the conservation error. It is found that these two ghost fluid methods have distinctive performances for different initial conditions of the flow field, and the related conclusions are made to suggest the best choice for the combination.

Lubrication mechanisms of hollow-core inorganic fullerene-like nanoparticles: coupling experimental and computational works

NASA Astrophysics Data System (ADS)

Lahouij, I.; Bucholz, E. W.; Vacher, B.; Sinnott, S. B.; Martin, J. M.; Dassenoy, F.

2012-09-01

Inorganic fullerene-like (IF) nanoparticles made of metal dichalcogenides have previously been recognized to be good friction modifiers and anti-wear additives under boundary lubrication conditions. The tribological performance of these particles appears to be a result of their size, structure and morphology, along with the test conditions. However, the very small scale of the IF nanoparticles makes distinguishing the properties which affect the lubrication mechanism exceedingly difficult. In this work, a high resolution transmission electron microscope equipped with a nanoindentation holder is used to manipulate individual hollow IF-WS2 nanoparticles and to investigate their responses to compression. Additional atomistic molecular dynamics (MD) simulations of similarly structured, individual hollow IF-MoS2 nanoparticles are performed for compression studies between molybdenum surfaces on their major and minor axis diameters. MD simulations of these structures allows for characterization of the influence of structural orientation on the mechanical behavior and nano-sheet exfoliation of hollow-core IF nanoparticles. The experimental and theoretical results for these similar nanoparticles are qualitatively compared.

Lubrication mechanisms of hollow-core inorganic fullerene-like nanoparticles: coupling experimental and computational works.

PubMed

Lahouij, I; Bucholz, E W; Vacher, B; Sinnott, S B; Martin, J M; Dassenoy, F

2012-09-21

Inorganic fullerene-like (IF) nanoparticles made of metal dichalcogenides have previously been recognized to be good friction modifiers and anti-wear additives under boundary lubrication conditions. The tribological performance of these particles appears to be a result of their size, structure and morphology, along with the test conditions. However, the very small scale of the IF nanoparticles makes distinguishing the properties which affect the lubrication mechanism exceedingly difficult. In this work, a high resolution transmission electron microscope equipped with a nanoindentation holder is used to manipulate individual hollow IF-WS(2) nanoparticles and to investigate their responses to compression. Additional atomistic molecular dynamics (MD) simulations of similarly structured, individual hollow IF-MoS(2) nanoparticles are performed for compression studies between molybdenum surfaces on their major and minor axis diameters. MD simulations of these structures allows for characterization of the influence of structural orientation on the mechanical behavior and nano-sheet exfoliation of hollow-core IF nanoparticles. The experimental and theoretical results for these similar nanoparticles are qualitatively compared.

Three-Dimensional Numerical Simulation on Triaxial Failure Mechanical Behavior of Rock-Like Specimen Containing Two Unparallel Fissures

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Zhao, Jian

2016-12-01

A three-dimensional particle flow code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of rock-like material specimens containing two unparallel fissures under conventional triaxial compression. The micro-parameters of the parallel bond model were first calibrated using the laboratory results of intact specimens and then validated from the experimental results of pre-fissured specimens under triaxial compression. Numerically simulated stress-strain curves, strength and deformation parameters and macro-failure modes of pre-fissured specimens were all in good agreement with the experimental results. The relationship between stress and the micro-crack numbers was summarized. Crack initiation, propagation and coalescence process of pre-fissured specimens were analyzed in detail. Finally, horizontal and vertical cross sections of numerical specimens were derived from PFC3D. A detailed analysis to reveal the internal damage behavior of rock under triaxial compression was carried out. The experimental and simulated results are expected to improve the understanding of the strength failure and cracking behavior of fractured rock under triaxial compression.

A Feasibility Study for Measuring Accurate Chest Compression Depth and Rate on Soft Surfaces Using Two Accelerometers and Spectral Analysis

PubMed Central

Gutiérrez, J. J.; Russell, James K.

2016-01-01

Background. Cardiopulmonary resuscitation (CPR) feedback devices are being increasingly used. However, current accelerometer-based devices overestimate chest displacement when CPR is performed on soft surfaces, which may lead to insufficient compression depth. Aim. To assess the performance of a new algorithm for measuring compression depth and rate based on two accelerometers in a simulated resuscitation scenario. Materials and Methods. Compressions were provided to a manikin on two mattresses, foam and sprung, with and without a backboard. One accelerometer was placed on the chest and the second at the manikin's back. Chest displacement and mattress displacement were calculated from the spectral analysis of the corresponding acceleration every 2 seconds and subtracted to compute the actual sternal-spinal displacement. Compression rate was obtained from the chest acceleration. Results. Median unsigned error in depth was 2.1 mm (4.4%). Error was 2.4 mm in the foam and 1.7 mm in the sprung mattress (p < 0.001). Error was 3.1/2.0 mm and 1.8/1.6 mm with/without backboard for foam and sprung, respectively (p < 0.001). Median error in rate was 0.9 cpm (1.0%), with no significant differences between test conditions. Conclusion. The system provided accurate feedback on chest compression depth and rate on soft surfaces. Our solution compensated mattress displacement, avoiding overestimation of compression depth when CPR is performed on soft surfaces. PMID:27999808

Characterization of hot bonding of bi-metal C45/25CrMo4 by plane strain compression test

NASA Astrophysics Data System (ADS)

Enaim, Mohammed; Langlois, Laurent; Zimmer-Chevret, Sandra; Bigot, Régis; Krumpipe, Pierre

2018-05-01

The need to produce multifunctional parts in order to conform to complex specifications becomes crucial in today's industrial context. This is why new processes are under study to develop multi-material parts which can satisfy this kind of requirements. This paper investigates the possibility of producing hot bonding of bi-metal C45/25CrMo4 parts by forging. This manufacturing process is a solid state joining process that involves, simultaneously, the welding and shaping of multi-material part. In this study, the C45/25CrMo4 bimetal was investigated. The forging is conducted at 1100°C and the influence of reduction rate on microstructure and bonding was investigated. The bonding model is inspired from Bay's model. Following this model, two parameters govern the solid-state bonding at the interface between materials: normal contact pressure and surface expansion. The objective is to check the bonding quality under different pressure and surface expansion. To achieve this goal, the plane strain compression test is chosen as the characterization test. Finally, simulations and experiments of this test are compared.

Modeling the mechanical response of PBX 9501

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ragaswamy, Partha; Lewis, Matthew W; Liu, Cheng

2010-01-01

An engineering overview of the mechanical response of Plastic-Bonded eXplosives (PBXs), specifically PBX 9501, will be provided with emphasis on observed mechanisms associated with different types of mechanical testing. Mechanical tests in the form of uniaxial tension, compression, cyclic loading, creep (compression and tension), and Hopkinson bar show strain rate and temperature dependence. A range of mechanical behavior is observed which includes small strain recoverable response in the form of viscoelasticity; change in stiffness and softening beyond peak strength due to damage in the form microcracks, debonding, void formation and the growth of existing voids; inelastic response in the formmore » of irrecoverable strain as shown in cyclic tests, and viscoelastic creep combined with plastic response as demonstrated in creep and recovery tests. The main focus of this paper is to elucidate the challenges and issues involved in modeling the mechanical behavior of PBXs for simulating thermo-mechanical responses in engineering components. Examples of validation of a constitutive material model based on a few of the observed mechanisms will be demonstrated against three point bending, split Hopkinson pressure bar and Brazilian disk geometry.« less

Real-Time SCADA Cyber Protection Using Compression Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyle G. Roybal; Gordon H Rueff

2013-11-01

The Department of Energy’s Office of Electricity Delivery and Energy Reliability (DOE-OE) has a critical mission to secure the energy infrastructure from cyber attack. Through DOE-OE’s Cybersecurity for Energy Delivery Systems (CEDS) program, the Idaho National Laboratory (INL) has developed a method to detect malicious traffic on Supervisory, Control, and Data Acquisition (SCADA) network using a data compression technique. SCADA network traffic is often repetitive with only minor differences between packets. Research performed at the INL showed that SCADA network traffic has traits desirable for using compression analysis to identify abnormal network traffic. An open source implementation of a Lempel-Ziv-Welchmore » (LZW) lossless data compression algorithm was used to compress and analyze surrogate SCADA traffic. Infected SCADA traffic was found to have statistically significant differences in compression when compared against normal SCADA traffic at the packet level. The initial analyses and results are clearly able to identify malicious network traffic from normal traffic at the packet level with a very high confidence level across multiple ports and traffic streams. Statistical differentiation between infected and normal traffic level was possible using a modified data compression technique at the 99% probability level for all data analyzed. However, the conditions tested were rather limited in scope and need to be expanded into more realistic simulations of hacking events using techniques and approaches that are better representative of a real-world attack on a SCADA system. Nonetheless, the use of compression techniques to identify malicious traffic on SCADA networks in real time appears to have significant merit for infrastructure protection.« less

Crack cause analysis of a graphite nozzle throat insert

NASA Astrophysics Data System (ADS)

Sun, Lin; Bao, Futing; Zhao, Yu; Hou, Lian; Hui, Weihua; Zhang, Ning; Shi, Wei

2017-08-01

With an objective to determine the failure cause of a throughout crack at an angle of 45° and a breach during a firing test, a simplified analysis procedure with consideration of the structure gap was established to simulate the thermo-structural response of a nozzle. By neglecting erosion and pyrolysis of the insulating materials and establishing temperature-dependent or anisotropic material models, ANSYS Parameter Design Language codes were written to perform the fully coupled thermal-structural simulation. A Quasi-1D flow was calculated for supplying boundary conditions. Study on mesh independence and time step independence was also conducted to evaluate simulated results. It was found that shortly after ignition, compressive stress in the x direction and tensile stress in the y direction contributed to anomalies. And through contact status analysis, inappropriate gap design was regarded as the origin of the too large stress, which was the primary cause of these anomalies during firing test. Simulation results were in good agreement with firing test results. In addition, the simplified analysis procedure was proven effective. Gap size should be seriously dealt with in the future design.

Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser

NASA Astrophysics Data System (ADS)

Sano, Yuji; Kimura, Motohiko; Mukai, Naruhiko; Yoda, Masaki; Obata, Minoru; Ogisu, Tatsuki

2000-02-01

The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training for operational personnel, the system was applied to the core shroud of an existing nuclear power plant.

Near-wall modelling of compressible turbulent flows

NASA Technical Reports Server (NTRS)

So, Ronald M. C.

1990-01-01

Work was carried out to extend the near-wall models formulated for the incompressible Reynolds stress equations to compressible flows. The idea of splitting the compressible dissipation function into a solenoidal part that is not sensitive to changes of compressibility indicators and a compressible part that is directly affected by these changes is adopted. This means that all models involving the dissipation rate could be expressed in terms of the solenoidal dissipation rate and an equation governing its transport could be formulated to close the set of compressible Reynolds stress equations. The near-wall modelling of the dissipation rate equation is investigated and its behavior near a wall is studied in detail using k-epsilon closure. It is found that all existing modelled equations give the wrong behavior for the dissipation rate near a wall. Improvements are suggested and the resultant behavior is found to be in good agreement with near-wall data. Furthermore, the present modified k-epsilon closure is used too calculate a flat plate boundary layer and the results are compared with four existing k-epsilon closures. These comparisons show that all closures tested give essentially the same flow properties, except in a region very close to the wall. In this region, the present k-epsilon closure calculations are in better agreement with measurements and direct simulation data; in particular, the behavior of the dissipation rate.

Simulation-based Randomized Comparative Assessment of Out-of-Hospital Cardiac Arrest Resuscitation Bundle Completion by Emergency Medical Service Teams Using Standard Life Support or an Experimental Automation-assisted Approach.

PubMed

Choi, Bryan; Asselin, Nicholas; Pettit, Catherine C; Dannecker, Max; Machan, Jason T; Merck, Derek L; Merck, Lisa H; Suner, Selim; Williams, Kenneth A; Jay, Gregory D; Kobayashi, Leo

2016-12-01

Effective resuscitation of out-of-hospital cardiac arrest (OHCA) patients is challenging. Alternative resuscitative approaches using electromechanical adjuncts may improve provider performance. Investigators applied simulation to study the effect of an experimental automation-assisted, goal-directed OHCA management protocol on EMS providers' resuscitation performance relative to standard protocols and equipment. Two-provider (emergency medical technicians (EMT)-B and EMT-I/C/P) teams were randomized to control or experimental group. Each team engaged in 3 simulations: baseline simulation (standard roles); repeat simulation (standard roles); and abbreviated repeat simulation (reversed roles, i.e., basic life support provider performing ALS tasks). Control teams used standard OHCA protocols and equipment (with high-performance cardiopulmonary resuscitation training intervention); for second and third simulations, experimental teams performed chest compression, defibrillation, airway, pulmonary ventilation, vascular access, medication, and transport tasks with goal-directed protocol and resuscitation-automating devices. Videorecorders and simulator logs collected resuscitation data. Ten control and 10 experimental teams comprised 20 EMT-B's; 1 EMT-I, 8 EMT-C's, and 11 EMT-P's; study groups were not fully matched. Both groups suboptimally performed chest compressions and ventilations at baseline. For their second simulations, control teams performed similarly except for reduced on-scene time, and experimental teams improved their chest compressions (P=0.03), pulmonary ventilations (P<0.01), and medication administration (P=0.02); changes in their performance of chest compression, defibrillation, airway, and transport tasks did not attain significance against control teams' changes. Experimental teams maintained performance improvements during reversed-role simulations. Simulation-based investigation into OHCA resuscitation revealed considerable variability and improvable deficiencies in small EMS teams. Goal-directed, automation-assisted OHCA management augmented select resuscitation bundle element performance without comprehensive improvement.

Hybrid thermal link-wise artificial compressibility method

NASA Astrophysics Data System (ADS)

Obrecht, Christian; Kuznik, Frédéric

2015-10-01

Thermal flow prediction is a subject of interest from a scientific and engineering points of view. Our motivation is to develop an accurate, easy to implement and highly scalable method for convective flows simulation. To this end, we present an extension to the link-wise artificial compressibility method (LW-ACM) for thermal simulation of weakly compressible flows. The novel hybrid formulation uses second-order finite difference operators of the energy equation based on the same stencils as the LW-ACM. For validation purposes, the differentially heated cubic cavity was simulated. The simulations remained stable for Rayleigh numbers up to Ra =108. The Nusselt numbers at isothermal walls and dynamics quantities are in good agreement with reference values from the literature. Our results show that the hybrid thermal LW-ACM is an effective and easy-to-use solution to solve convective flows.

Auto-adaptive finite element meshes

NASA Technical Reports Server (NTRS)

Richter, Roland; Leyland, Penelope

1995-01-01

Accurate capturing of discontinuities within compressible flow computations is achieved by coupling a suitable solver with an automatic adaptive mesh algorithm for unstructured triangular meshes. The mesh adaptation procedures developed rely on non-hierarchical dynamical local refinement/derefinement techniques, which hence enable structural optimization as well as geometrical optimization. The methods described are applied for a number of the ICASE test cases are particularly interesting for unsteady flow simulations.

Simulation of Prestressed Concrete Sandwich Panels Subjected to Blast Loads (Preprint)

DTIC Science & Technology

2010-02-01

configuration. Conventionally reinforced panels had configurations of 3-2-3 a nd 6-2-3. Insulating foams included expanded polystyrene , extruded expanded ...Properties of Extruded Expanded Polystyrene Foam Building Materials. M.S.C.E. report, University of Alabama at Birmingham. Livermore Software... polystyrene , and polyisocyanurate. Compressive testing of insulating f oams used as construction materials was used to define the stress/strain

Characterization of Triaxial Braided Composite Material Properties for Impact Simulation

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Goldberg, Robert K.; Biniendak, Wieslaw K.; Arnold, William A.; Littell, Justin D.; Kohlman, Lee W.

2009-01-01

The reliability of impact simulations for aircraft components made with triaxial braided carbon fiber composites is currently limited by inadequate material property data and lack of validated material models for analysis. Improvements to standard quasi-static test methods are needed to account for the large unit cell size and localized damage within the unit cell. The deformation and damage of a triaxial braided composite material was examined using standard quasi-static in-plane tension, compression, and shear tests. Some modifications to standard test specimen geometries are suggested, and methods for measuring the local strain at the onset of failure within the braid unit cell are presented. Deformation and damage at higher strain rates is examined using ballistic impact tests on 61- by 61- by 3.2-mm (24- by 24- by 0.125-in.) composite panels. Digital image correlation techniques were used to examine full-field deformation and damage during both quasi-static and impact tests. An impact analysis method is presented that utilizes both local and global deformation and failure information from the quasi-static tests as input for impact simulations. Improvements that are needed in test and analysis methods for better predictive capability are examined.

A testing program to evaluate the effects of simulant mixed wastes on plastic transportation packaging components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigrey, P.J.; Dickens, T.G.; Dickman, P.T.

1997-08-01

Based on regulatory requirements for Type A and B radioactive material packaging, a Testing Program was developed to evaluate the effects of mixed wastes on plastic materials which could be used as liners and seals in transportation containers. The plastics evaluated in this program were butadiene-acrylonitrile copolymer (Nitrile rubber), cross-linked polyethylene, epichlorohydrin, ethylene-propylene rubber (EPDM), fluorocarbons, high-density polyethylene (HDPE), butyl rubber, polypropylene, polytetrafluoroethylene, and styrene-butadiene rubber (SBR). These plastics were first screened in four simulant mixed wastes. The liner materials were screened using specific gravity measurements and seal materials by vapor transport rate (VTR) measurements. For the screening of linermore » materials, Kel-F, HDPE, and XLPE were found to offer the greatest resistance to the combination of radiation and chemicals. The tests also indicated that while all seal materials passed exposure to the aqueous simulant mixed waste, EPDM and SBR had the lowest VTRs. In the chlorinated hydrocarbon simulant mixed waste, only Viton passed the screening tests. In both the simulant scintillation fluid mixed waste and the ketone mixture waste, none of the seal materials met the screening criteria. Those materials which passed the screening tests were subjected to further comprehensive testing in each of the simulant wastes. The materials were exposed to four different radiation doses followed by exposure to a simulant mixed waste at three temperatures and four different exposure times (7, 14, 28, 180 days). Materials were tested by measuring specific gravity, dimensional, hardness, stress cracking, VTR, compression set, and tensile properties. The second phase of this Testing Program involving the comprehensive testing of plastic liner has been completed and for seal materials is currently in progress.« less

Development of iterative techniques for the solution of unsteady compressible viscous flows

NASA Technical Reports Server (NTRS)

Hixon, Duane; Sankar, L. N.

1993-01-01

During the past two decades, there has been significant progress in the field of numerical simulation of unsteady compressible viscous flows. At present, a variety of solution techniques exist such as the transonic small disturbance analyses (TSD), transonic full potential equation-based methods, unsteady Euler solvers, and unsteady Navier-Stokes solvers. These advances have been made possible by developments in three areas: (1) improved numerical algorithms; (2) automation of body-fitted grid generation schemes; and (3) advanced computer architectures with vector processing and massively parallel processing features. In this work, the GMRES scheme has been considered as a candidate for acceleration of a Newton iteration time marching scheme for unsteady 2-D and 3-D compressible viscous flow calculation; from preliminary calculations, this will provide up to a 65 percent reduction in the computer time requirements over the existing class of explicit and implicit time marching schemes. The proposed method has ben tested on structured grids, but is flexible enough for extension to unstructured grids. The described scheme has been tested only on the current generation of vector processor architecture of the Cray Y/MP class, but should be suitable for adaptation to massively parallel machines.

Supernova Driving. II. Compressive Ratio in Molecular-cloud Turbulence

NASA Astrophysics Data System (ADS)

Pan, Liubin; Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke

2016-07-01

The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been previously studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence (250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence with a broad lognormal distribution of the compressive ratio, with a mean value ≈0.3, lower than the equilibrium value of ≈0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor are the mean cloud radial (expansion or contraction) and solid-body rotation velocities. Furthermore, the clouds follow a general relation between the rms density and the rms Mach number similar to that of supersonic isothermal turbulence, though with a large scatter, and their average gas density probability density function is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included.

Pre-recorded instructional audio vs. dispatchers' conversational assistance in telephone cardiopulmonary resuscitation: A randomized controlled simulation study.

PubMed

Birkun, Alexei; Glotov, Maksim; Ndjamen, Herman Franklin; Alaiye, Esther; Adeleke, Temidara; Samarin, Sergey

2018-01-01

To assess the effectiveness of the telephone chest-compression-only cardiopulmonary resuscitation (CPR) guided by a pre-recorded instructional audio when compared with dispatcher-assisted resuscitation. It was a prospective, blind, randomised controlled study involving 109 medical students without previous CPR training. In a standardized mannequin scenario, after the step of dispatcher-assisted cardiac arrest recognition, the participants performed compression-only resuscitation guided over the telephone by either: (1) the pre-recorded instructional audio ( n =57); or (2) verbal dispatcher assistance ( n =52). The simulation video records were reviewed to assess the CPR performance using a 13-item checklist. The interval from call reception to the first compression, total number and rate of compressions, total number and duration of pauses after the first compression were also recorded. There were no significant differences between the recording-assisted and dispatcher-assisted groups based on the overall performance score (5.6±2.2 vs. 5.1±1.9, P >0.05) or individual criteria of the CPR performance checklist. The recording-assisted group demonstrated significantly shorter time interval from call receipt to the first compression (86.0±14.3 vs. 91.2±14.2 s, P <0.05), higher compression rate (94.9±26.4 vs. 89.1±32.8 min -1 ) and number of compressions provided (170.2±48.0 vs. 156.2±60.7). When provided by untrained persons in the simulated settings, the compression-only resuscitation guided by the pre-recorded instructional audio is no less efficient than dispatcher-assisted CPR. Future studies are warranted to further assess feasibility of using instructional audio aid as a potential alternative to dispatcher assistance.

Pre-recorded instructional audio vs. dispatchers’ conversational assistance in telephone cardiopulmonary resuscitation: A randomized controlled simulation study

PubMed Central

Birkun, Alexei; Glotov, Maksim; Ndjamen, Herman Franklin; Alaiye, Esther; Adeleke, Temidara; Samarin, Sergey

2018-01-01

BACKGROUND: To assess the effectiveness of the telephone chest-compression-only cardiopulmonary resuscitation (CPR) guided by a pre-recorded instructional audio when compared with dispatcher-assisted resuscitation. METHODS: It was a prospective, blind, randomised controlled study involving 109 medical students without previous CPR training. In a standardized mannequin scenario, after the step of dispatcher-assisted cardiac arrest recognition, the participants performed compression-only resuscitation guided over the telephone by either: (1) the pre-recorded instructional audio (n=57); or (2) verbal dispatcher assistance (n=52). The simulation video records were reviewed to assess the CPR performance using a 13-item checklist. The interval from call reception to the first compression, total number and rate of compressions, total number and duration of pauses after the first compression were also recorded. RESULTS: There were no significant differences between the recording-assisted and dispatcher-assisted groups based on the overall performance score (5.6±2.2 vs. 5.1±1.9, P>0.05) or individual criteria of the CPR performance checklist. The recording-assisted group demonstrated significantly shorter time interval from call receipt to the first compression (86.0±14.3 vs. 91.2±14.2 s, P<0.05), higher compression rate (94.9±26.4 vs. 89.1±32.8 min-1) and number of compressions provided (170.2±48.0 vs. 156.2±60.7). CONCLUSION: When provided by untrained persons in the simulated settings, the compression-only resuscitation guided by the pre-recorded instructional audio is no less efficient than dispatcher-assisted CPR. Future studies are warranted to further assess feasibility of using instructional audio aid as a potential alternative to dispatcher assistance.

Exploring the Relationship Between Working Memory, Compressor Speed, and Background Noise Characteristics.

PubMed

Ohlenforst, Barbara; Souza, Pamela E; MacDonald, Ewen N

2016-01-01

Previous work has shown that individuals with lower working memory demonstrate reduced intelligibility for speech processed with fast-acting compression amplification. This relationship has been noted in fluctuating noise, but the extent of noise modulation that must be present to elicit such an effect is unknown. This study expanded on previous study by exploring the effect of background noise modulations in relation to compression speed and working memory ability, using a range of signal to noise ratios. Twenty-six older participants between ages 61 and 90 years were grouped by high or low working memory according to their performance on a reading span test. Speech intelligibility was measured for low-context sentences presented in background noise, where the noise varied in the extent of amplitude modulation. Simulated fast- or slow-acting compression amplification combined with individual frequency-gain shaping was applied to compensate for the individual's hearing loss. Better speech intelligibility scores were observed for participants with high working memory when fast compression was applied than when slow compression was applied. The low working memory group behaved in the opposite way and performed better under slow compression compared with fast compression. There was also a significant effect of the extent of amplitude modulation in the background noise, such that the magnitude of the score difference (fast versus slow compression) depended on the number of talkers in the background noise. The presented signal to noise ratios were not a significant factor on the measured intelligibility performance. In agreement with earlier research, high working memory allowed better speech intelligibility when fast compression was applied in modulated background noise. In the present experiment, that effect was present regardless of the extent of background noise modulation.

Fully compressible solutions for early stage Richtmyer–Meshkov instability

DOE PAGES

Margolin, Len G.; Reisner, Jon Michael

2016-10-27

Here, we will consider the effects of compressibility and viscosity on the early dynamics of the Richtmyer–Meshkov instability (RMI). In particular, we will combine theory, scaling, and high resolution simulation of RMI to probe the details of the initial compression and the subsequent viscous damping as a shock interacts with a density discontinuity. We will propose a refinement of the classic 1D model for the linear regime of RMI that, for small initial perturbation wavelengths, more accurately reproduces the 2D dynamics of a fully resolved numerical simulation.

Summer Work Experience: Determining Methane Combustion Mechanisms and Sub-Scale Diffuser Properties for Space Transporation System Engine Testing

NASA Technical Reports Server (NTRS)

Williams, Powtawche N.

1998-01-01

To assess engine performance during the testing of Space Shuttle Main Engines (SSMEs), the design of an optimal altitude diffuser is studied for future Space Transportation Systems (STS). For other Space Transportation Systems, rocket propellant using kerosene is also studied. Methane and dodecane have similar reaction schemes as kerosene, and are used to simulate kerosene combustion processes at various temperatures. The equations for the methane combustion mechanism at high temperature are given, and engine combustion is simulated on the General Aerodynamic Simulation Program (GASP). The successful design of an altitude diffuser depends on the study of a sub-scaled diffuser model tested through two-dimensional (2-D) flow-techniques. Subroutines given calculate the static temperature and pressure at each Mach number within the diffuser flow. Implementing these subroutines into program code for the properties of 2-D compressible fluid flow determines all fluid characteristics, and will be used in the development of an optimal diffuser design.

Characteristic-based and interface-sharpening algorithm for high-order simulations of immiscible compressible multi-material flows

NASA Astrophysics Data System (ADS)

He, Zhiwei; Tian, Baolin; Zhang, Yousheng; Gao, Fujie

2017-03-01

The present work focuses on the simulation of immiscible compressible multi-material flows with the Mie-Grüneisen-type equation of state governed by the non-conservative five-equation model [1]. Although low-order single fluid schemes have already been adopted to provide some feasible results, the application of high-order schemes (introducing relatively small numerical dissipation) to these flows may lead to results with severe numerical oscillations. Consequently, attempts to apply any interface-sharpening techniques to stop the progressively more severe smearing interfaces for a longer simulation time may result in an overshoot increase and in some cases convergence to a non-physical solution occurs. This study proposes a characteristic-based interface-sharpening algorithm for performing high-order simulations of such flows by deriving a pressure-equilibrium-consistent intermediate state (augmented with approximations of pressure derivatives) for local characteristic variable reconstruction and constructing a general framework for interface sharpening. First, by imposing a weak form of the jump condition for the non-conservative five-equation model, we analytically derive an intermediate state with pressure derivatives treated as additional parameters of the linearization procedure. Based on this intermediate state, any well-established high-order reconstruction technique can be employed to provide the state at each cell edge. Second, by designing another state with only different reconstructed values of the interface function at each cell edge, the advection term in the equation of the interface function is discretized twice using any common algorithm. The difference between the two discretizations is employed consistently for interface compression, yielding a general framework for interface sharpening. Coupled with the fifth-order improved accurate monotonicity-preserving scheme [2] for local characteristic variable reconstruction and the tangent of hyperbola for the interface capturing scheme [3] for designing other reconstructed values of the interface function, the present algorithm is examined using some typical tests, with the Mie-Grüneisen-type equation of state used for characterizing the materials of interest in both one- and two-dimensional spaces. The results of these tests verify the effectiveness of the present algorithm: essentially non-oscillatory and interface-sharpened results are obtained.

Large eddy simulations of compressible magnetohydrodynamic turbulence

NASA Astrophysics Data System (ADS)

Grete, Philipp

2017-02-01

Supersonic, magnetohydrodynamic (MHD) turbulence is thought to play an important role in many processes - especially in astrophysics, where detailed three-dimensional observations are scarce. Simulations can partially fill this gap and help to understand these processes. However, direct simulations with realistic parameters are often not feasible. Consequently, large eddy simulations (LES) have emerged as a viable alternative. In LES the overall complexity is reduced by simulating only large and intermediate scales directly. The smallest scales, usually referred to as subgrid-scales (SGS), are introduced to the simulation by means of an SGS model. Thus, the overall quality of an LES with respect to properly accounting for small-scale physics crucially depends on the quality of the SGS model. While there has been a lot of successful research on SGS models in the hydrodynamic regime for decades, SGS modeling in MHD is a rather recent topic, in particular, in the compressible regime. In this thesis, we derive and validate a new nonlinear MHD SGS model that explicitly takes compressibility effects into account. A filter is used to separate the large and intermediate scales, and it is thought to mimic finite resolution effects. In the derivation, we use a deconvolution approach on the filter kernel. With this approach, we are able to derive nonlinear closures for all SGS terms in MHD: the turbulent Reynolds and Maxwell stresses, and the turbulent electromotive force (EMF). We validate the new closures both a priori and a posteriori. In the a priori tests, we use high-resolution reference data of stationary, homogeneous, isotropic MHD turbulence to compare exact SGS quantities against predictions by the closures. The comparison includes, for example, correlations of turbulent fluxes, the average dissipative behavior, and alignment of SGS vectors such as the EMF. In order to quantify the performance of the new nonlinear closure, this comparison is conducted from the subsonic (sonic Mach number M s ≈ 0.2) to the highly supersonic (M s ≈ 20) regime, and against other SGS closures. The latter include established closures of eddy-viscosity and scale-similarity type. In all tests and over the entire parameter space, we find that the proposed closures are (significantly) closer to the reference data than the other closures. In the a posteriori tests, we perform large eddy simulations of decaying, supersonic MHD turbulence with initial M s ≈ 3. We implemented closures of all types, i.e. of eddy-viscosity, scale-similarity and nonlinear type, as an SGS model and evaluated their performance in comparison to simulations without a model (and at higher resolution). We find that the models need to be calculated on a scale larger than the grid scale, e.g. by an explicit filter, to have an influence on the dynamics at all. Furthermore, we show that only the proposed nonlinear closure improves higher-order statistics.

Simulation of Texture Evolution during Uniaxial Deformation of Commercially Pure Titanium

NASA Astrophysics Data System (ADS)

Bishoyi, B.; Debta, M. K.; Yadav, S. K.; Sabat, R. K.; Sahoo, S. K.

2018-03-01

The evolution of texture in commercially pure (CP) titanium during uniaxial tension and compression through VPSC (Visco-plastic self-consistent) simulation is reported in the present study. CP-titanium was subjected to both uniaxial tension and compression upto 35% deformation. During uniaxial tension, tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of \\{11\\bar{2}2\\}\\unicode{x003C;}11\\bar{2}\\bar{3}\\unicode{x003E;} type were observed in the samples. However, only tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of type was observed in the samples during uniaxial compression. Volume fractions of the twins were increased linearly as a function of percentage deformation during uniaxial tension. Whereas, during uniaxial compression the twinning volume fraction was increased up to 20% deformation and then decreased rapidly on further increasing the percentage deformation. During uniaxial tension, the general t-type textures were observed in the samples irrespective of the percentage deformation. The initial non-basal texture was oriented to split basal texture during uniaxial compression of the sample. VPSC formulation was used for simulating the texture development in the material. Different hardening parameters were estimated through correlating the simulated stress-strain curve with the experimental stress-strain data. It was observed that, prismatic slip \\{10\\bar{1}0\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} operated as the primary deformation mode during uniaxial tension whereas basal slip \\{0001\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} acquired the leading role during deformation through uniaxial compression. It was also revealed that active deformation modes were fully depending on percentage deformation, loading direction, and orientation of grains.

Numerical Modelling of the Compressive and Tensile Response of Glass and Ceramic under High Pressure Dynamic Loading

NASA Astrophysics Data System (ADS)

Clegg, Richard A.; Hayhurst, Colin J.

1999-06-01

Ceramic materials, including glass, are commonly used as ballistic protection materials. The response of a ceramic to impact, perforation and penetration is complex and difficult and/or expensive to instrument for obtaining detailed physical data. This paper demonstrates how a hydrocode, such as AUTODYN, can be used to aid in the understanding of the response of brittle materials to high pressure impact loading and thus promote an efficient and cost effective design process. Hydrocode simulations cannot be made without appropriate characterisation of the material. Because of the complexitiy of the response of ceramic materials this often requires a number of complex material tests. Here we present a methodology for using the results of flyer plate tests, in conjunction with numerical simulations, to derive input to the Johnson-Holmquist material model for ceramics. Most of the research effort in relation to the development of hydrocode material models for ceramics has concentrated on the material behaviour under compression and shear. While the penetration process is dominated by these aspects of the material response, the final damaged state of the material can be significantly influenced by the tensile behaviour. Modelling of the final damage state is important since this is often the only physical information which is available. In this paper we present a unique implementation, in a hydrocode, for improved modelling of brittle materials in the tensile regime. Tensile failure initiation is based on any combination of principal stress or strain while the post-failure tensile response of the material is controlled through a Rankine plasticity damaging failure surface. The tensile failure surface can be combined with any of the traditional plasticity and/or compressive damage models. Finally, the models and data are applied in both traditional grid based Lagrangian and Eulerian solution techniques and the relativley new SPH (Smooth Particle Hydrodynamics) meshless technique. Simulations of long rod impacts onto ceramic faced armour and hypervelocity impacts on glass solar array space structures are presented and compared with experiments.

Multi-Scale Impact and Compression-After-Impact Modeling of Reinforced Benzoxazine/Epoxy Composites using Micromechanics Approach

NASA Astrophysics Data System (ADS)

Montero, Marc Villa; Barjasteh, Ehsan; Baid, Harsh K.; Godines, Cody; Abdi, Frank; Nikbin, Kamran

A multi-scale micromechanics approach along with finite element (FE) model predictive tool is developed to analyze low-energy-impact damage footprint and compression-after-impact (CAI) of composite laminates which is also tested and verified with experimental data. Effective fiber and matrix properties were reverse-engineered from lamina properties using an optimization algorithm and used to assess damage at the micro-level during impact and post-impact FE simulations. Progressive failure dynamic analysis (PFDA) was performed for a two step-process simulation. Damage mechanisms at the micro-level were continuously evaluated during the analyses. Contribution of each failure mode was tracked during the simulations and damage and delamination footprint size and shape were predicted to understand when, where and why failure occurred during both impact and CAI events. The composite laminate was manufactured by the vacuum infusion of the aero-grade toughened Benzoxazine system into the fabric preform. Delamination footprint was measured using C-scan data from the impacted panels and compared with the predicated values obtained from proposed multi-scale micromechanics coupled with FE analysis. Furthermore, the residual strength was predicted from the load-displacement curve and compared with the experimental values as well.

High accuracy mantle convection simulation through modern numerical methods - II: realistic models and problems

NASA Astrophysics Data System (ADS)

Heister, Timo; Dannberg, Juliane; Gassmöller, Rene; Bangerth, Wolfgang

2017-08-01

Computations have helped elucidate the dynamics of Earth's mantle for several decades already. The numerical methods that underlie these simulations have greatly evolved within this time span, and today include dynamically changing and adaptively refined meshes, sophisticated and efficient solvers, and parallelization to large clusters of computers. At the same time, many of the methods - discussed in detail in a previous paper in this series - were developed and tested primarily using model problems that lack many of the complexities that are common to the realistic models our community wants to solve today. With several years of experience solving complex and realistic models, we here revisit some of the algorithm designs of the earlier paper and discuss the incorporation of more complex physics. In particular, we re-consider time stepping and mesh refinement algorithms, evaluate approaches to incorporate compressibility, and discuss dealing with strongly varying material coefficients, latent heat, and how to track chemical compositions and heterogeneities. Taken together and implemented in a high-performance, massively parallel code, the techniques discussed in this paper then allow for high resolution, 3-D, compressible, global mantle convection simulations with phase transitions, strongly temperature dependent viscosity and realistic material properties based on mineral physics data.

A unified approach for numerical simulation of viscous compressible and incompressible flows over adiabatic and isothermal walls

NASA Technical Reports Server (NTRS)

Hafez, M.; Soliman, M.; White, S.

1992-01-01

A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.

Rapid Prototyping of an Aircraft Model in an Object-Oriented Simulation

NASA Technical Reports Server (NTRS)

Kenney, P. Sean

2003-01-01

A team was created to participate in the Mars Scout Opportunity. Trade studies determined that an aircraft provided the best opportunity to complete the science objectives of the team. A high fidelity six degree of freedom flight simulation was required to provide credible evidence that the aircraft design fulfilled mission objectives and to support the aircraft design process by providing performance evaluations. The team created the simulation using the Langley Standard Real-Time Simulation in C++ (LaSRS++) application framework. A rapid prototyping approach was necessary because the team had only three months to both develop the aircraft simulation model and evaluate aircraft performance as the design and mission parameters matured. The design of LaSRS++ enabled rapid-prototyping in several ways. First, the framework allowed component models to be designed, implemented, unit-tested, and integrated quickly. Next, the framework provides a highly reusable infrastructure that allowed developers to maximize code reuse while concentrating on aircraft and mission specific features. Finally, the framework reduces risk by providing reusable components that allow developers to build a quality product with a compressed testing cycle that relies heavily on unit testing of new components.

Comprehensive testing to measure the response of butyl rubber to Hanford tank waste simulant

DOE Office of Scientific and Technical Information (OSTI.GOV)

NIGREY,PAUL J.

This report presents the findings of the Chemical Compatibility Program developed to evaluate plastic packaging components that may be incorporated in packaging mixed-waste forms for transportation. Consistent with the methodology outlined in this report, the authors performed the second phase of this experimental program to determine the effects of simulant Hanford tank mixed wastes on packaging seal materials. That effort involved the comprehensive testing of five plastic liner materials in an aqueous mixed-waste simulant. The testing protocol involved exposing the materials to {approximately}143, 286, 571, and 3,670 krad of gamma radiation and was followed by 7-, 14-, 28-, 180-day exposuresmore » to the waste simulant at 18, 50, and 60 C. Butyl rubber samples subjected to the same protocol were then evaluated by measuring seven material properties: specific gravity, dimensional changes, mass changes, hardness, compression set, vapor transport rates, and tensile properties. From the analyses, they determined that butyl rubber has relatively good resistance to radiation, this simulant, and a combination of these factors. These results suggest that butyl rubber is a relatively good seal material to withstand aqueous mixed wastes having similar composition to the one used in this study.« less

Modeling of Compressible Flow with Friction and Heat Transfer Using the Generalized Fluid System Simulation Program (GFSSP)

NASA Technical Reports Server (NTRS)

Bandyopadhyay, Alak; Majumdar, Alok

2007-01-01

The present paper describes the verification and validation of a quasi one-dimensional pressure based finite volume algorithm, implemented in Generalized Fluid System Simulation Program (GFSSP), for predicting compressible flow with friction, heat transfer and area change. The numerical predictions were compared with two classical solutions of compressible flow, i.e. Fanno and Rayleigh flow. Fanno flow provides an analytical solution of compressible flow in a long slender pipe where incoming subsonic flow can be choked due to friction. On the other hand, Raleigh flow provides analytical solution of frictionless compressible flow with heat transfer where incoming subsonic flow can be choked at the outlet boundary with heat addition to the control volume. Nonuniform grid distribution improves the accuracy of numerical prediction. A benchmark numerical solution of compressible flow in a converging-diverging nozzle with friction and heat transfer has been developed to verify GFSSP's numerical predictions. The numerical predictions compare favorably in all cases.

Fracture simulation of restored teeth using a continuum damage mechanics failure model.

PubMed

Li, Haiyan; Li, Jianying; Zou, Zhenmin; Fok, Alex Siu-Lun

2011-07-01

The aim of this paper is to validate the use of a finite-element (FE) based continuum damage mechanics (CDM) failure model to simulate the debonding and fracture of restored teeth. Fracture testing of plastic model teeth, with or without a standard Class-II MOD (mesial-occusal-distal) restoration, was carried out to investigate their fracture behavior. In parallel, 2D FE models of the teeth are constructed and analyzed using the commercial FE software ABAQUS. A CDM failure model, implemented into ABAQUS via the user element subroutine (UEL), is used to simulate the debonding and/or final fracture of the model teeth under a compressive load. The material parameters needed for the CDM model to simulate fracture are obtained through separate mechanical tests. The predicted results are then compared with the experimental data of the fracture tests to validate the failure model. The failure processes of the intact and restored model teeth are successfully reproduced by the simulation. However, the fracture parameters obtained from testing small specimens need to be adjusted to account for the size effect. The results indicate that the CDM model is a viable model for the prediction of debonding and fracture in dental restorations. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

The Most Cut-Resistant Neck Guard for Preventing Lacerations to the Neck

PubMed Central

Loyd, Andre M.; Berglund, Lawrence; Twardowski, Casey P.; Stuart, Michael B.; Smith, Aynsley M.; Gaz, Daniel V.; Krause, David A.; An, Kai-Nan; Stuart, Michael J.

2017-01-01

Objective To evaluate the effectiveness of a variety of neck guard brands when contacted by a sharpened hockey skate blade. Design Analytic experimental. Setting Laboratory. Participants Neck surrogate. Interventions Forty-six samples of 14 different types of neck guards were tested on a custom-made laceration machine using a neck surrogate. Closed-cell polyethylene foam was placed between the neck surrogate and the protective device. Main Outcome Measures The effectiveness of the neck guard was evaluated by observation of the foam after the simulated slicing action of the skate blade. Two sets of tests were performed on each device sample including low and high force. For low-force tests, initial compression loads of 100, 200, and 300 N were applied between the neck surrogate for each of 2 orientations of the blade at 45 and 90 degrees. For high-force tests, representing a more severe simulation, the applied load was increased to 600 N and a blade angle fixed at 45 degrees. All tests were performed at a blade speed of 5 m/s. Results Only 1 product, the Bauer N7 Nectech, failed during the 300-N compression tests. All of the neck guards failed during 600-N test condition except for the Skate Armor device and 1 of the 3 Reebok 11K devices. Conclusions A skate blade angle of 45 degrees increased the likelihood of a neck laceration compared with a skate blade angle of 90 degrees due to decreased contact area. Damage to the neck guard is not an indicator of the cut resistance of a neck guard. Neck protectors with Spectra fibers were the most cut resistant. Clinical Relevance The study provides data for the selection of neck guards and neck guard materials that can reduce lacerations to the neck. PMID:24949830

Fuel Areal-Density Measurements in Laser-Driven Magnetized Inertial Fusion from Secondary Neutrons

NASA Astrophysics Data System (ADS)

Davies, J. R.; Barnak, D. H.; Betti, R.; Glebov, V. Yu.; Knauer, J. P.; Peebles, J. L.

2017-10-01

Laser-driven magnetized liner inertial fusion is being developed on the OMEGA laser to provide the first data at a significantly smaller scale than the Z pulsed-power machine in order to test scaling and to provide more shots with better diagnostic access than Z. In OMEGA experiments, a 0.6-mm-outer-diam plastic cylinder filled with 11 atm of D2 is placed in an axial magnetic field of 10 T, the D2 is preheated by a single beam along the axis, and then the cylinder is compressed by 40 beams. Secondary DT neutron yields provide a measurement of the areal density of the compressed D2 because the compressed fuel is much smaller than the mean free path and the Larmor radius of the T produced in D-D fusion. Measured secondary yields confirm theoretical predictions that preheating and magnetization reduce fuel compression. Higher fuel compression is found to consistently lead to lower neutron yields, which is not predicted by simulations. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000568 and the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Detailed Modeling of Distillation Technologies for Closed-Loop Water Recovery Systems

NASA Technical Reports Server (NTRS)

Allada, Rama Kumar; Lange, Kevin E.; Anderson, Molly S.

2011-01-01

Detailed chemical process simulations are a useful tool in designing and optimizing complex systems and architectures for human life support. Dynamic and steady-state models of these systems help contrast the interactions of various operating parameters and hardware designs, which become extremely useful in trade-study analyses. NASA?s Exploration Life Support technology development project recently made use of such models to compliment a series of tests on different waste water distillation systems. This paper presents efforts to develop chemical process simulations for three technologies: the Cascade Distillation System (CDS), the Vapor Compression Distillation (VCD) system and the Wiped-Film Rotating Disk (WFRD) using the Aspen Custom Modeler and Aspen Plus process simulation tools. The paper discusses system design, modeling details, and modeling results for each technology and presents some comparisons between the model results and recent test data. Following these initial comparisons, some general conclusions and forward work are discussed.

Numerical simulation of transient hypervelocity flow in an expansion tube

NASA Technical Reports Server (NTRS)

Jacobs, P. A.

1992-01-01

Several numerical simulations of the transient flow of helium in an expansion tube are presented. The aim of the exercise is to provide further information on the operational problems of the NASA Langley expansion tube. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite-volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in the experiments. In particular, the discontinuity in the tube diameter at the primary diaphragm station introduced a transverse perturbation to the expanding driver gas, and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either 'small-amplitude' noise possibly introduced during shock compression or 'large-amplitude' noise associated with the passage of the reflected head of the unsteady expansion.

Compressive Properties and Anti-Erosion Characteristics of Foam Concrete in Road Engineering

NASA Astrophysics Data System (ADS)

Li, Jinzhu; Huang, Hongxiang; Wang, Wenjun; Ding, Yifan

2018-01-01

To analyse the compression properties and anti-erosion characteristics of foam concrete, one dimensional compression tests were carried out using ring specimens of foam concrete, and unconfined compression tests were carried out using foam concrete specimens cured in different conditions. The results of one dimensional compression tests show that the compression curve of foam concrete has two critical points and three stages, which has significant difference with ordinary geotechnical materials such as soil. Based on the compression curve the compression modulus of each stage were determined. The results of erosion tests show that sea water has a slight influence on the long-term strength of foam concrete, while the sulphate solution has a significant influence on the long-term strength of foam concrete, which needs to pay more attention.

Morphological changes in polycrystalline Fe after compression and release

NASA Astrophysics Data System (ADS)

Gunkelmann, Nina; Tramontina, Diego R.; Bringa, Eduardo M.; Urbassek, Herbert M.

2015-02-01

Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3, 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.

A Static Burst Test for Composite Flywheel Rotors

NASA Astrophysics Data System (ADS)

Hartl, Stefan; Schulz, Alexander; Sima, Harald; Koch, Thomas; Kaltenbacher, Manfred

2016-06-01

High efficient and safe flywheels are an interesting technology for decentralized energy storage. To ensure all safety aspects, a static test method for a controlled initiation of a burst event for composite flywheel rotors is presented with nearly the same stress distribution as in the dynamic case, rotating with maximum speed. In addition to failure prediction using different maximum stress criteria and a safety factor, a set of tensile and compressive tests is carried out to identify the parameters of the used carbon fiber reinforced plastics (CFRP) material. The static finite element (FE) simulation results of the flywheel static burst test (FSBT) compare well to the quasistatic FE-simulation results of the flywheel rotor using inertia loads. Furthermore, it is demonstrated that the presented method is a very good controllable and observable possibility to test a high speed flywheel energy storage system (FESS) rotor in a static way. Thereby, a much more expensive and dangerous dynamic spin up test with possible uncertainties can be substituted.

A numerical code for the simulation of non-equilibrium chemically reacting flows on hybrid CPU-GPU clusters

NASA Astrophysics Data System (ADS)

Kudryavtsev, Alexey N.; Kashkovsky, Alexander V.; Borisov, Semyon P.; Shershnev, Anton A.

2017-10-01

In the present work a computer code RCFS for numerical simulation of chemically reacting compressible flows on hybrid CPU/GPU supercomputers is developed. It solves 3D unsteady Euler equations for multispecies chemically reacting flows in general curvilinear coordinates using shock-capturing TVD schemes. Time advancement is carried out using the explicit Runge-Kutta TVD schemes. Program implementation uses CUDA application programming interface to perform GPU computations. Data between GPUs is distributed via domain decomposition technique. The developed code is verified on the number of test cases including supersonic flow over a cylinder.

Baseline performance of the GPU 3 Stirling engine

NASA Technical Reports Server (NTRS)

Thieme, L. G.; Tew, R. C., Jr.

1978-01-01

A 10 horsepower single-cylinder rhombic-drive Stirling engine was converted to a research configuration to obtain data for validation of Stirling computer simulations. The engine was originally built by General Motors Research Laboratories for the U.S. Army in 1965 as part of a 3 kW engine-generator set, designated the GHU 3 (Ground Power Unit). This report presents test results for a range of heater gas temperatures, mean compression-space pressures, and engine speeds with both helium and hydrogen as the working fluids. Also shown are initial data comparisons with computer simulation predictions.

Lightweight, low compression aircraft diesel engine. [converting a spark ignition engine to the diesel cycle

NASA Technical Reports Server (NTRS)

Gaynor, T. L.; Bottrell, M. S.; Eagle, C. D.; Bachle, C. F.

1977-01-01

The feasibility of converting a spark ignition aircraft engine to the diesel cycle was investigated. Procedures necessary for converting a single cylinder GTS10-520 are described as well as a single cylinder diesel engine test program. The modification of the engine for the hot port cooling concept is discussed. A digital computer graphics simulation of a twin engine aircraft incorporating the diesel engine and Hot Fort concept is presented showing some potential gains in aircraft performance. Sample results of the computer program used in the simulation are included.

Consolidation modelling for thermoplastic composites forming simulation

NASA Astrophysics Data System (ADS)

Xiong, H.; Rusanov, A.; Hamila, N.; Boisse, P.

2016-10-01

Pre-impregnated thermoplastic composites are widely used in the aerospace industry for their excellent mechanical properties, Thermoforming thermoplastic prepregs is a fast manufacturing process, the automotive industry has shown increasing interest in this manufacturing processes, in which the reconsolidation is an essential stage. The model of intimate contact is investigated as the consolidation model, compression experiments have been launched to identify the material parameters, several numerical tests show the influents of the temperature and pressure applied during processing. Finally, a new solid-shell prismatic element has been presented for the simulation of consolidation step in the thermoplastic composites forming process.

Simplified dispatch-assisted CPR instructions outperform standard protocol.

PubMed

Dias, J A; Brown, T B; Saini, D; Shah, R C; Cofield, S S; Waterbor, J W; Funkhouser, E; Terndrup, T E

2007-01-01

Dispatch-assisted chest compressions only CPR (CC-CPR) has gained widespread acceptance, and recent research suggests that increasing the proportion of compression time during CPR may increase survival from out-of-hospital cardiac arrest. We created a simplified CC-CPR protocol to reduce time to start chest compressions and to increase the proportion of time spent delivering chest compressions. This simplified protocol was compared to a published protocol, Medical Priority Dispatch System (MPDS) Version 11.2, recommended by the National Academies of Emergency Dispatch. Subjects were randomized to the MPDS v11.2 protocol or a simplified protocol. Data was recorded from a Laerdal Resusci Anne Skillreporter manikin. A simulated emergency medical dispatcher, contacted by cell phone, delivered standardized instructions for both protocols. Outcomes included chest compression rate, depth, hand position, full release, overall proportion of compressions without error, time to start of CPR and total hands-off chest time. Proportions were analyzed by Wilcoxon's Rank Sum tests and time variables with Welch ANOVA and Wilcoxon's Rank Sum test. All tests used a two-sided alpha-level of 0.05. One hundred and seventeen subjects were randomized prospectively, 58 to the standard protocol and 59 to the simplified protocol. The average age of subjects in both groups was 25 years old. For both groups, the compression rate was equivalent (104 simplified versus 94 MPDS, p = 0.13), as was the proportion with total release (1.0 simplified versus 1.0 MPDS, p = 0.09). The proportion to the correct depth was greater in the simplified protocol (0.31 versus 0.03, p < 0.01), as was the proportion of compressions done without error (0.05 versus 0.0, p = 0.16). Time to start of chest compressions and total hands-off chest time were better in the simplified protocol (start time 60.9s versus 78.6s, p < 0.0001; hands-off chest time 69 s versus 95 s, p < 0.0001). The proportion with correct hand position, however, was worse in the simplified protocol (0.35 versus 0.84, p < 0.01). The simplified protocol was as good as, or better than the MPDS v11.2 protocol in every aspect studied except hand position, and the simplified protocol resulted in significant time savings. The protocol may need modification to ensure correct hand position. Time savings and improved quality of CPR achieved by the new set of instructions could be important in strengthening critical links in the cardiac chain of survival.

Residual stresses in shape memory alloy fiber reinforced aluminium matrix composite

NASA Astrophysics Data System (ADS)

Tsz Loong, Tang; Jamian, Saifulnizan; Ismail, Al Emran; Nur, Nik Hisyammudin Muhd; Watanabe, Yoshimi

2017-01-01

Process-induced residual stress in shape memory alloy (SMA) fiber reinforced aluminum (Al) matrix composite was simulated by ANSYS APDL. The manufacturing process of the composite named as NiTi/Al is start with loading and unloading process of nickel titanium (NiTi) wire as SMA to generate a residual plastic strain. Then, this plastic deformed NiTi wire would be embedded into Al to become a composite. Lastly, the composite is heated form 289 K to 363 K and then cooled back to 300 K. Residual stress is generated in composite because of shape memory effect of NiTi and mismatch of thermal coefficient between NiTi wire and Al matrix of composite. ANSYS APDL has been used to simulate the distribution of residual stress and strain in this process. A sensitivity test has been done to determine the optimum number of nodes and elements used. Hence, the number of nodes and elements used are 15680 and 13680, respectively. Furthermore, the distribution of residual stress and strain of nickel fiber reinforced aluminium matrix composite (Ni/Al) and titanium fiber reinforced aluminium matrix composite (Ti/Al) under same simulation process also has been simulated by ANSYS APDL as comparison to NiTi/Al. The simulation results show that compressive residual stress is generated on Al matrix of Ni/Al, Ti/Al and NiTi/Al during heating and cooling process. Besides that, they also have similar trend of residual stress distribution but difference in term of value. For Ni/Al and Ti/Al, they are 0.4% difference on their maximum compressive residual stress at 363K. At same circumstance, NiTi/Al has higher residual stress value which is about 425% higher than Ni/Al and Ti/Al composite. This implies that shape memory effect of NiTi fiber reinforced in composite able to generated higher compressive residual stress in Al matrix, hence able to enhance tensile property of the composite.

[New Insights into Maternal Cardiopulmonary Resuscitation--Significance of Simulation Research and Training].

PubMed

Komasawa, Nobuyasu; Fujiwara, Shunsuke; Majima, Nozomi; Minami, Toshiaki

2015-08-01

Pregnancy-related mortality, estimated to occur in approximately 1: 50,000 deliveries, is rare in developed countries. The 2010 American Heart Association (AHA) Guidelines for Resuscitation emphasize the importance of high-quality chest compression as a key determinant of successful cardiopulmonary resuscitation. During pregnancy, the uterus can compress the inferior vena cava, impeding venous return and thereby reducing stroke volume and cardiac output. To maximize the effectiveness of chest compressions in pregnancy, the AHA guidelines recommend the 27-30 degrees left-lateral tilt (LLT) position. When CPR is performed on parturients in the LLT position, chest compressions will probably be more effective if performed with the operator standing on the left side of the patient. The videolaryngoscope Pentax-AWS Airwayscope (AWS) was found to be an effective tool for airway management during chest compressions in 27 LLT simulations, suggesting that the AWS may be a useful device for airway management during maternal resuscitation.

Ultrasound Shear Wave Simulation of Breast Tumor Using Nonlinear Tissue Elasticity

PubMed Central

Park, Dae Woo

2016-01-01

Shear wave elasticity imaging (SWEI) can assess the elasticity of tissues, but the shear modulus estimated in SWEI is often less sensitive to a subtle change of the stiffness that produces only small mechanical contrast to the background tissues. Because most soft tissues exhibit mechanical nonlinearity that differs in tissue types, mechanical contrast can be enhanced if the tissues are compressed. In this study, a finite element- (FE-) based simulation was performed for a breast tissue model, which consists of a circular (D: 10 mm, hard) tumor and surrounding tissue (soft). The SWEI was performed with 0% to 30% compression of the breast tissue model. The shear modulus of the tumor exhibited noticeably high nonlinearity compared to soft background tissue above 10% overall applied compression. As a result, the elastic modulus contrast of the tumor to the surrounding tissue was increased from 0.46 at 0% compression to 1.45 at 30% compression. PMID:27293476

A Numerical/Experimental Study on the Impact and CAI Behaviour of Glass Reinforced Compsite Plates

NASA Astrophysics Data System (ADS)

Perillo, Giovanni; Jørgensen, Jens K.; Cristiano, Roberta; Riccio, Aniello

2018-04-01

This paper focuses on the development of an advance numerical model specifically for simulating low velocity impact events and related stiffness reduction on composite structures. The model is suitable for low cost thick composite structures like wind turbine blade and maritime vessels. The model consist of a combination of inter and intra laminar models. The intra-laminar model present a combination of Puck and Hashin failure theories for the evaluation of the fibre and matrix failure. The inter-laminar damage is instead simulated by Cohesive Zone Method based on energy approach. Basic material properties, easily measurable according to standardized tests, are required. The model has been used to simulate impact and compression after impact tests. Experimental tests have been carried out on thick E-Glass/Epoxy composite commonly used in the wind turbine industry. The clustering effect as well as the consequence of the impact energy have been experimentally tested. The accuracy of numerical model has been verified against experimental data showing a very good accuracy of the model.

Time dependent variation of carrying capacity of prestressed precast beam

NASA Astrophysics Data System (ADS)

Le, Tuan D.; Konečný, Petr; Matečková, Pavlína

2018-04-01

The article deals with the evaluation of the precast concrete element time dependent carrying capacity. The variation of the resistance is inherited property of laboratory as well as in-situ members. Thus the specification of highest, yet possible, laboratory sample resistance is important with respect to evaluation of laboratory experiments based on the test machine loading capabilities. The ultimate capacity is evaluated through the bending moment resistance of a simply supported prestressed concrete beam. The probabilistic assessment is applied. Scatter of random variables of compressive strength of concrete and effective height of the cross section is considered. Monte Carlo simulation technique is used to investigate the performance of the cross section of the beam with changes of tendons’ positions and compressive strength of concrete.

The design and development of a vapor compression refrigerator/freezer for spacelab

NASA Technical Reports Server (NTRS)

Hye, A.

1983-01-01

A computer simulation was performed to determine the design criteria for a spacelab refrigerator/freezer using the test results of a vapor compression refrigerator/freezer which flew on STS-4 without problem. It has been established to have a vapor Reynolds number over 3000 at a vapor quality of 0.2 to maintain annular boiling in the evaporator and for the condenser to have a vapor Reynolds number over 15000 at its inlet to maintain annular condensation. These two constraints will virtually eliminate the effect of gravity on the performance of the refrigerator/freezer. These results are being used to build a refrigerator/freezer which will fly in Spacelab-4 scheduled for launch in December 1985.

Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code

NASA Technical Reports Server (NTRS)

Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.

2006-01-01

The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.

An effective simplified model of composite compression struts for partially-restrained steel frame with reinforced concrete infill walls

NASA Astrophysics Data System (ADS)

Sun, Guohua; Chuang-Sheng, Walter Yang; Gu, Qiang; DesRoches, Reginald

2018-04-01

To resolve the issue regarding inaccurate prediction of the hysteretic behavior by micro-based numerical analysis for partially-restrained (PR) steel frames with solid reinforced concrete (RC) infill walls, an innovative simplified model of composite compression struts is proposed on the basis of experimental observation on the cracking distribution, load transferring mechanism, and failure modes of RC infill walls filled in PR steel frame. The proposed composite compression struts model for the solid RC infill walls is composed of α inclined struts and main diagonal struts. The α inclined struts are used to reflect the part of the lateral force resisted by shear connectors along the frame-wall interface, while the main diagonal struts are introduced to take into account the rest of the lateral force transferred along the diagonal direction due to the complicated interaction between the steel frame and RC infill walls. This study derives appropriate formulas for the effective widths of the α inclined strut and main diagonal strut, respectively. An example of PR steel frame with RC infill walls simulating simulated by the composite inclined compression struts model is illustrated. The maximum lateral strength and the hysteresis curve shape obtained from the proposed composite strut model are in good agreement with those from the test results, and the backbone curve of a PR steel frame with RC infill walls can be predicted precisely when the inter-story drift is within 1%. This simplified model can also predict the structural stiffness and the equivalent viscous damping ratio well when the inter-story drift ratio exceeds 0.5%.

Turbulence statistics with quantified uncertainty in cold-wall supersonic channel flow

NASA Astrophysics Data System (ADS)

Ulerich, Rhys; Moser, Robert D.

2012-11-01

To investigate compressibility effects in wall-bounded turbulence, a series of direct numerical simulations of compressible channel flow with isothermal (cold) walls have been conducted. All combinations of Re = { 3000 , 5000 } and Ma = { 0 . 1 , 0 . 5 , 1 . 5 , 3 . 0 } have been simulated where the Reynolds and Mach numbers are based on bulk velocity and sound speed at the wall temperature. Turbulence statistics with precisely quantified uncertainties computed from these simulations will be presented and are being made available in a public data base at http://turbulence.ices.utexas.edu/. The simulations were performed using a new pseudo-spectral code called Suzerain, which was designed to efficiently produce high quality data on compressible, wall-bounded turbulent flows using a semi-implicit Fourier/B-spline numerical formulation. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615].

The pressure-dilatation correlation in compressible flows

NASA Technical Reports Server (NTRS)

Sarkar, S.

1992-01-01

Simulations of simple compressible flows have been performed to enable the direct estimation of the pressure-dilatation correlation. The generally accepted belief that this correlation may be important in high-speed flows has been verified by the simulations. The pressure-dilatation correlation is theoretically investigated by considering the equation for fluctuating pressure in an arbitrary compressible flow. This leads to the isolation of a component of the pressure-dilatation that exhibits temporal oscillations on a fast time scale. Direct numerical simulations of homogeneous shear turbulence and isotropic turbulence show that this fast component has a negligible contribution to the evolution of turbulent kinetic energy. Then, an analysis for the case of homogeneous turbulence is performed to obtain a formal solution for the nonoscillatory pressure-dilatation. Simplifications lead to a model that algebraically relates the pressure-dilatation to quantities traditionally obtained in incompressible turbulence closures. The model is validated by direct comparison with the simulations.

A Randomized Control Trial of Cardiopulmonary Feedback Devices and Their Impact on Infant Chest Compression Quality: A Simulation Study.

PubMed

Austin, Andrea L; Spalding, Carmen N; Landa, Katrina N; Myer, Brian R; Donald, Cure; Smith, Jason E; Platt, Gerald; King, Heather C

2017-10-27

In effort to improve chest compression quality among health care providers, numerous feedback devices have been developed. Few studies, however, have focused on the use of cardiopulmonary resuscitation feedback devices for infants and children. This study evaluated the quality of chest compressions with standard team-leader coaching, a metronome (MetroTimer by ONYX Apps), and visual feedback (SkillGuide Cardiopulmonary Feedback Device) during simulated infant cardiopulmonary resuscitation. Seventy voluntary health care providers who had recently completed Pediatric Advanced Life Support or Basic Life Support courses were randomized to perform simulated infant cardiopulmonary resuscitation into 1 of 3 groups: team-leader coaching alone (control), coaching plus metronome, or coaching plus SkillGuide for 2 minutes continuously. Rate, depth, and frequency of complete recoil during cardiopulmonary resuscitation were recorded by the Laerdal SimPad device for each participant. American Heart Association-approved compression techniques were randomized to either 2-finger or encircling thumbs. The metronome was associated with more ideal compression rate than visual feedback or coaching alone (104/min vs 112/min and 113/min; P = 0.003, 0.019). Visual feedback was associated with more ideal depth than auditory (41 mm vs 38.9; P = 0.03). There were no significant differences in complete recoil between groups. Secondary outcomes of compression technique revealed a difference of 1 mm. Subgroup analysis of male versus female showed no difference in mean number of compressions (221.76 vs 219.79; P = 0.72), mean compression depth (40.47 vs 39.25; P = 0.09), or rate of complete release (70.27% vs 64.96%; P = 0.54). In the adult literature, feedback devices often show an increase in quality of chest compressions. Although more studies are needed, this study did not demonstrate a clinically significant improvement in chest compressions with the addition of a metronome or visual feedback device, no clinically significant difference in Pediatric Advanced Life Support-approved compression technique, and no difference between compression quality between genders.

Measurement and simulation of the impact of coherent synchrotron radiation on the Jefferson Laboratory energy recovery linac electron beam

NASA Astrophysics Data System (ADS)

Hall, C. C.; Biedron, S. G.; Edelen, A. L.; Milton, S. V.; Benson, S.; Douglas, D.; Li, R.; Tennant, C. D.; Carlsten, B. E.

2015-03-01

In an experiment conducted on the Jefferson Laboratory IR free-electron laser driver, the effects of coherent synchrotron radiation (CSR) on beam quality were studied. The primary goal of this work was to explore CSR output and effect on the beam with variation of the bunch compression in the IR recirculator. Here we examine the impact of CSR on the average energy loss as a function of bunch compression as well as the impact of CSR on the energy spectrum of the bunch. Simulation of beam dynamics in the machine, including the one-dimensional CSR model, shows very good agreement with the measured effect of CSR on the average energy loss as a function of compression. Finally, a well-defined structure is observed in the energy spectrum with a feature in the spectrum that varies as a function of the compression. This effect is examined in simulations, as well, and a simple explanation for the variation is proposed.

NIMROD simulations of the IPA FRC experiment

NASA Astrophysics Data System (ADS)

Milroy, Richard

2015-11-01

The IPA experiment created a high temperature plasma by merging and compressing supersonic θ-pinch formed FRCs. The NIMROD code has been used to simulate this process. These calculations include the θ-pinch formation and acceleration of two FRC's using the dynamic formation methodology, and their translation to a central compression chamber where they merge and are magnetically compressed. Transport coefficients have been tuned so simulation results agree well with experimental observation. The inclusion of the Hall term is essential for the FRCs merge quickly, as observed experimentally through the excluded flux profiles. The inclusion of a significant anisotropic viscosity is required for the excluded flux profiles to agree well with the experiment. We plan to extend this validation work using the new ARPA-E funded Venti experiment at Helion Energy in Redmond WA. This will be a very well diagnosed experiment where two FRCs merge (like the IPA experiment) and are then compressed to near-fusion conditions. Preliminary calculations with parameters relevant to this experiment have been made, and some numerical issues identified.

Measurement and simulation of the impact of coherent synchrotron radiation on the Jefferson Laboratory energy recovery linac electron beam

DOE PAGES

Hall, C C.; Biedron, S G.; Edelen, A L.; ...

2015-03-09

In an experiment conducted on the Jefferson Laboratory IR free-electron laser driver, the effects of coherent synchrotron radiation (CSR) on beam quality were studied. The primary goal of this work was to explore CSR output and effect on the beam with variation of the bunch compression in the IR recirculator. Here we examine the impact of CSR on the average energy loss as a function of bunch compression as well as the impact of CSR on the energy spectrum of the bunch. Simulation of beam dynamics in the machine, including the one-dimensional CSR model, shows very good agreement with themore » measured effect of CSR on the average energy loss as a function of compression. Finally, a well-defined structure is observed in the energy spectrum with a feature in the spectrum that varies as a function of the compression. This effect is examined in simulations, as well, and a simple explanation for the variation is proposed.« less

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

PubMed Central

Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-01-01

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process. PMID:29027925

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

PubMed

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Test of simple fluid theories for the Lennard-Jones system

NASA Astrophysics Data System (ADS)

Malijevský, A.; Labik, S.

1988-03-01

A test is made of a new version of the reference-hypernetted chain approximation (RHNC) with minimized free energy proposed by Lado, Foiles and Ashcroft. An accurate relationship is used for the bridge function of the reference hard spheres. The calculated values of the compressibility factor and the internal energy are compared with simulation data, with results of the exponential approximation of Andersen et al., and with results of the Madden-Fitts approximation. The RHNC provides the most reliable results over wide ranges of reduced temperatures and densities.

NASA Marshall Impact Testing Facility Capabilities Applicable to Lunar Dust Work

NASA Technical Reports Server (NTRS)

Evans, Steven W.; Finchum, Andy; Hubbs, Whitney; Eskridge, Richard; Martin, Jim

2008-01-01

The Impact Testing Facility at Marshall Space Flight Center has several guns that would be of use in studying impact phenomena with respect to lunar dust. These include both ballistic guns, using compressed gas and powder charges, and hypervelocity guns, either light gas guns or an exploding wire gun. In addition, a plasma drag accelerator expected to reach 20 km/s for small particles is under development. Velocity determination and impact event recording are done using ultra-high-speed cameras. Simulation analysis is also available using the SPHC hydrocode.

Low-cost endoscopic third ventriculostomy simulator with mimetic endoscope.

PubMed

Garling, Richard Justin; Jin, Xin; Yang, Jianzhong; Khasawneh, Ahmad H; Harris, Carolyn Anne

2018-05-11

OBJECTIVE Hydrocephalus affects approximately 1 in 500 people in the US, yet ventricular shunting, the gold standard of treatment, has a nearly 85% failure rate. Endoscopic third ventriculostomy (ETV) is an alternative surgical approach for a specific subset of hydrocephalic patients, but can be limited by the inability of neurosurgical residents to practice prior to patient contact. The goal of this study was to create an affordable ETV model and endoscope for resident training. METHODS Open-source software was used to isolate the skull and brain from the CT and MR images of a 2-year-old boy with hydrocephalus. A 3D printer created the skull and a 3D mold of the brain. A mixture of silicone and silicone tactile mutator was used to cast the brain mold prior to subsequent compression and shearing modulus testing. A mimetic endoscope was then created from basic supplies and a 3D printed frame. A small cohort of neurosurgical residents and attending physicians evaluated the ETV simulator with mimetic endoscope. RESULTS The authors successfully created a mimetic endoscope and ETV simulator. After compression and shearing modulus testing, a silicone/Slacker ratio between 10:6 and 10:7 was found to be similar to that of human brain parenchyma. Eighty-seven percent of participants strongly agreed that the simulator was useful for resident training, and 93% strongly agreed that the simulator helped them understand how to orient themselves with the endoscope. CONCLUSIONS The authors created an affordable (US$123, excluding 3D printer), easy-to-use ETV simulator with endoscope. Previous models have required expensive software and costly operative endoscopes that may not be available to most residents. Instead, this attempt takes advantage of open-source software for the manipulation and fabrication of a patient-specific mold. This model can assist with resident development, allowing them to safely practice use of the endoscope in ETV.

Simulation of moving boundaries interacting with compressible reacting flows using a second-order adaptive Cartesian cut-cell method

NASA Astrophysics Data System (ADS)

Muralidharan, Balaji; Menon, Suresh

2018-03-01

A high-order adaptive Cartesian cut-cell method, developed in the past by the authors [1] for simulation of compressible viscous flow over static embedded boundaries, is now extended for reacting flow simulations over moving interfaces. The main difficulty related to simulation of moving boundary problems using immersed boundary techniques is the loss of conservation of mass, momentum and energy during the transition of numerical grid cells from solid to fluid and vice versa. Gas phase reactions near solid boundaries can produce huge source terms to the governing equations, which if not properly treated for moving boundaries, can result in inaccuracies in numerical predictions. The small cell clustering algorithm proposed in our previous work is now extended to handle moving boundaries enforcing strict conservation. In addition, the cell clustering algorithm also preserves the smoothness of solution near moving surfaces. A second order Runge-Kutta scheme where the boundaries are allowed to change during the sub-time steps is employed. This scheme improves the time accuracy of the calculations when the body motion is driven by hydrodynamic forces. Simple one dimensional reacting and non-reacting studies of moving piston are first performed in order to demonstrate the accuracy of the proposed method. Results are then reported for flow past moving cylinders at subsonic and supersonic velocities in a viscous compressible flow and are compared with theoretical and previously available experimental data. The ability of the scheme to handle deforming boundaries and interaction of hydrodynamic forces with rigid body motion is demonstrated using different test cases. Finally, the method is applied to investigate the detonation initiation and stabilization mechanisms on a cylinder and a sphere, when they are launched into a detonable mixture. The effect of the filling pressure on the detonation stabilization mechanisms over a hyper-velocity sphere launched into a hydrogen-oxygen-argon mixture is studied and a qualitative comparison of the results with the experimental data are made. Results indicate that the current method is able to correctly reproduce the different regimes of combustion observed in the experiments. Through the various examples it is demonstrated that our method is robust and accurate for simulation of compressible viscous reacting flow problems with moving/deforming boundaries.

Compression of magnetized target in the magneto-inertial fusion

NASA Astrophysics Data System (ADS)

Kuzenov, V. V.

2017-12-01

This paper presents a mathematical model, numerical method and results of the computer analysis of the compression process and the energy transfer in the target plasma, used in magneto-inertial fusion. The computer simulation of the compression process of magnetized cylindrical target by high-power laser pulse is presented.

Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGonegle, David, E-mail: d.mcgonegle1@physics.ox.ac.uk; Wark, Justin S.; Higginbotham, Andrew

2015-08-14

A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as maymore » occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. The simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.« less

Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

DOE PAGES

McGonegle, David; Milathianaki, Despina; Remington, Bruce A.; ...

2015-08-11

A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as maymore » occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. In conclusion, the simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.« less

The effects of tibiofibularis anterior ligaments on ankle joint biomechanics.

PubMed

Karakaşlı, Ahmet; Erduran, Mehmet; Baktıroğlu, Lütfü; Büdeyri, Aydın; Yıldız, Didem Venüs; Havıtçıoğlu, Hasan

2015-03-01

The aim of this study was to evaluate the biomechanical behavior of anterior inferior tibiofibularis ligament (AITFL) deficient human ankle under axial loading of ankle at stance phase of gait. In order to investigate the contribution of AITFL to ankle stability, an in vitro sequential experimental setup was simulated. The measurement of posterior displacement of distal tibia and anterior displacement of the foot, in neutral position, secondary to axial compression, was performed by two non-contact video extensometers. Eight freshly frozen, anatomically intact, cadaveric human ankle specimens were included and tested. An axial compression test machine was utilized from 0 to 800 Newtonswith a loading speed of 5 mm/min in order to simulate the axial weight-bearing sequence of the ankle at stance phase of human gait. There was a statistically significant difference between anteroposterior displacement values for AITFL-Intact and AITFL-Dissected specimens (p≤0.05). Mean AITFL-Intact and mean AITFL-Dissected ankle anteroposterior displacement was 1.28±0.47 mm and 2.06±0.7 mm, respectively. This study determined some numerical and quantitative data about the biomechanical properties of AITFL in neutral foot position. In the emergency department, diagnosis and treatment of AITFL injury, due to ankle distortion, is important. In AITFL injuries, ankle biomechanics is affected, and ankle instability occurs.

A comparison of the lattice discrete particle method to the finite-element method and the K&C material model for simulating the static and dynamic response of concrete.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Jovanca J.; Bishop, Joseph E.

2013-11-01

This report summarizes the work performed by the graduate student Jovanca Smith during a summer internship in the summer of 2012 with the aid of mentor Joe Bishop. The projects were a two-part endeavor that focused on the use of the numerical model called the Lattice Discrete Particle Model (LDPM). The LDPM is a discrete meso-scale model currently used at Northwestern University and the ERDC to model the heterogeneous quasi-brittle material, concrete. In the first part of the project, LDPM was compared to the Karagozian and Case Concrete Model (K&C) used in Presto, an explicit dynamics finite-element code, developed atmore » Sandia National Laboratories. In order to make this comparison, a series of quasi-static numerical experiments were performed, namely unconfined uniaxial compression tests on four varied cube specimen sizes, three-point bending notched experiments on three proportional specimen sizes, and six triaxial compression tests on a cylindrical specimen. The second part of this project focused on the application of LDPM to simulate projectile perforation on an ultra high performance concrete called CORTUF. This application illustrates the strengths of LDPM over traditional continuum models.« less

Analysis of the Effect of Injection Pressure on Ignition Delay and Combustion Process of Biodiesel from Palm Oil, Algae and Waste Cooking Oil

NASA Astrophysics Data System (ADS)

Irham Anas, Mohd; Khalid, Amir; Hakim Zulkifli, Fathul; Jaat, Norrizam; Faisal Hushim, Mohd; Manshoor, Bukhari; Zaman, Izzuddin

2017-10-01

Biodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant grease for use in diesel engines. The objective of this research is investigation the effects of the variant injection pressure on ignition delay and emission for different biodiesel using rapid compression machine. Rapid Compression Machine (RCM) is used to simulate a single compression stroke of an internal combustion engine as a real engine. Four types of biodiesel which are waste cooking oil, crude palm oil, algae and jatropha were tested at injection pressure of 80 MPa, 90 MPa and 130 MPa under constant ambient temperature at 950 K. Increased in injection pressure resulted shorter ignition delay proven by WCO5 which decreased from 1.3 ms at 80 MPa to 0.7 ms at 130 MPa. Meanwhile, emission for CO2 increased due to better fuel atomization for fuel-air mixture formation lead to completed combustion.

Mechanical Properties of Recycled Concrete in Marine Environment

PubMed Central

Wang, Jianxiu; Huang, Tianrong; Liu, Xiaotian; Wu, Pengcheng; Guo, Zhiying

2013-01-01

Experimental work was carried out to develop information about mechanical properties of recycled concrete (RC) in marine environment. By using the seawater and dry-wet circulation to simulate the marine environment, specimens of RC were tested with different replacement percentages of 0%, 30%, and 60% after immersing in seawater for 4, 8, 12, and 16 months, respectively. Based on the analysis of the stress-strain curves (SSCs) and compressive strength, it is revealed that RC' peak value and elastic modulus decreased with the increase of replacement percentage and corroding time in marine environment. And the failure of recycled concrete was speeded up with more obvious cracks and larger angles of 65° to 85° in the surface when compared with normal concrete. Finally, the grey model (GM) with equal time intervals was constructed to investigate the law of compressive strength of recycled concrete in marine environment, and it is found that the GM is accurate and feasible for the prediction of RC compressive strength in marine environment. PMID:23766707

Mid-IR soliton compression in silicon optical fibers and fiber tapers.

PubMed

Peacock, Anna C

2012-03-01

Numerical simulations are used to investigate soliton compression in silicon core optical fibers at 2.3 μm in the mid-infrared waveguide regime. Compression in both standard silicon fibers and fiber tapers is compared to establish the relative compression ratios for a range of input pulse conditions. The results show that tapered fibers can be used to obtain higher levels of compression for moderate soliton orders and thus lower input powers. © 2012 Optical Society of America

Tight swimming trunks to prevent post scrotal surgery: an experimental justification.

PubMed

Al-Abed, Yahya A; Carr, Thomas W

2013-01-01

To conduct a study to measure the pressure effects of the different scrotal supports applied on a simulated expanding scrotal hematoma. We created a model of an expanding hematoma with simultaneous pressure recording using a urodynamics system. Pressures were recorded independently first without application of any support. Then, three types of scrotal supports were tested, including Euron Net Knickers, scrotal suspensory bandage, and tight swimming trunks brand Speedo® brief and shorts. Subsequent pressures were recorded using the model created, which was applied inside the supports worn by two male volunteers A and B. Without any external compression, the pressure inside the simulated expanding hematoma "balloon" reached a maximum of 15 cmH2O. The pressures measured whilst wearing "Netelast knickers" in both subjects A and B reached a maximum of 15 cmH2O suggesting that this garment exerted no measurable compression. The suspensory scrotal support was then tested in both subjects. As the balloon started to fill with saline, the simulated hematoma pushed the scrotal support forward resulting in falling of the balloon outside the scrotal support. Subsequently, Speedo® briefs and shorts were tested. With Speedo® briefs, maximum filling pressures of 49 cmH2O and 40 cmH2O were reached in subjects A and B, respectively. When using Speedo® shorts, however, maximum pressures of 55 cmH2O in subject A and 54 cmH2O in subject B were reached at the end of the balloon filling to 300 mL of saline. The use of tight swimming trunks (Speedo®) has led to satisfactory results in the prevention of hematoma post scrotal surgery.

Molecular dynamics simulations indicate that deoxyhemoglobin, oxyhemoglobin, carboxyhemoglobin, and glycated hemoglobin under compression and shear exhibit an anisotropic mechanical behavior.

PubMed

Yesudasan, Sumith; Wang, Xianqiao; Averett, Rodney D

2018-05-01

We developed a new mechanical model for determining the compression and shear mechanical behavior of four different hemoglobin structures. Previous studies on hemoglobin structures have focused primarily on overall mechanical behavior; however, this study investigates the mechanical behavior of hemoglobin, a major constituent of red blood cells, using steered molecular dynamics (SMD) simulations to obtain anisotropic mechanical behavior under compression and shear loading conditions. Four different configurations of hemoglobin molecules were considered: deoxyhemoglobin (deoxyHb), oxyhemoglobin (HbO 2 ), carboxyhemoglobin (HbCO), and glycated hemoglobin (HbA 1C ). The SMD simulations were performed on the hemoglobin variants to estimate their unidirectional stiffness and shear stiffness. Although hemoglobin is structurally denoted as a globular protein due to its spherical shape and secondary structure, our simulation results show a significant variation in the mechanical strength in different directions (anisotropy) and also a strength variation among the four different hemoglobin configurations studied. The glycated hemoglobin molecule possesses an overall higher compressive mechanical stiffness and shear stiffness when compared to deoxyhemoglobin, oxyhemoglobin, and carboxyhemoglobin molecules. Further results from the models indicate that the hemoglobin structures studied possess a soft outer shell and a stiff core based on stiffness.

Entropic lattice Boltzmann model for compressible flows.

PubMed

Frapolli, N; Chikatamarla, S S; Karlin, I V

2015-12-01

We present a lattice Boltzmann model (LBM) that covers the entire range of fluid flows, from low Mach weakly compressible to transonic and supersonic flows. One of the most restrictive limitations of the lattice Boltzmann method, the low Mach number limit, is overcome here by three fundamental changes to the LBM scheme: use of an appropriately chosen multispeed lattice, accurate evaluation of the equilibrium, and the entropic relaxation for the collision. The range of applications is demonstrated through the simulation of a bow shock in front of an airfoil and the simulation of decaying compressible turbulence with shocklets.

SUPERNOVA DRIVING. II. COMPRESSIVE RATIO IN MOLECULAR-CLOUD TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Liubin; Padoan, Paolo; Haugbølle, Troels

2016-07-01

The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been previously studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence (250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence with a broad lognormal distribution of themore » compressive ratio, with a mean value ≈0.3, lower than the equilibrium value of ≈0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor are the mean cloud radial (expansion or contraction) and solid-body rotation velocities. Furthermore, the clouds follow a general relation between the rms density and the rms Mach number similar to that of supersonic isothermal turbulence, though with a large scatter, and their average gas density probability density function is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included.« less

Fast and efficient compression of floating-point data.

PubMed

Lindstrom, Peter; Isenburg, Martin

2006-01-01

Large scale scientific simulation codes typically run on a cluster of CPUs that write/read time steps to/from a single file system. As data sets are constantly growing in size, this increasingly leads to I/O bottlenecks. When the rate at which data is produced exceeds the available I/O bandwidth, the simulation stalls and the CPUs are idle. Data compression can alleviate this problem by using some CPU cycles to reduce the amount of data needed to be transfered. Most compression schemes, however, are designed to operate offline and seek to maximize compression, not throughput. Furthermore, they often require quantizing floating-point values onto a uniform integer grid, which disqualifies their use in applications where exact values must be retained. We propose a simple scheme for lossless, online compression of floating-point data that transparently integrates into the I/O of many applications. A plug-in scheme for data-dependent prediction makes our scheme applicable to a wide variety of data used in visualization, such as unstructured meshes, point sets, images, and voxel grids. We achieve state-of-the-art compression rates and speeds, the latter in part due to an improved entropy coder. We demonstrate that this significantly accelerates I/O throughput in real simulation runs. Unlike previous schemes, our method also adapts well to variable-precision floating-point and integer data.

Force characteristics of a modular squeeze mode magneto-rheological element

NASA Astrophysics Data System (ADS)

Craft, Michael J.; Ahmadian, Mehdi; Farjoud, Alireza; Burke, William C. T.; Nagode, Clement

2010-04-01

While few publications exist on the behavior of Magneto-Rheological (MR) fluid in squeeze mode, devices using squeeze mode may take advantage of the very large range of adjustment that squeeze mode offers. Based on results obtained through modeling and testing MR fluid in a squeeze mode rheometer, a novel compression-adjustable element has been fabricated and tested, which utilizes MR fluid in squeeze mode. While shear and valve modes have been used exclusively for MR fluid damping applications, recent modeling and testing with MR fluid has revealed that much larger adjustment ranges are achievable in squeeze mode. Utilizing squeeze mode, a compression element, or MR Pouch, was developed consisting of a flexible cylindrical membrane with each end fastened to a steel endplate (pole plates). The silicone rubber pouch material was molded in the required shape for use in the squeeze mode rheometer. This flexible membrane allows for the complete self-containment of MR fluid and because the pouch compensates for volume changes, there is no need for dynamic seals and associated surface finish treatments on the steel components. An electromagnet incorporated in the rheometer passes an adjustable magnetic field axially through the pole plates and MR fluid. Test results show the device was capable of varying the compression force from less than 8lbs to greater than 1000lbs when the pole plates were 0.050" apart. Simulations were compared against test data with good correlation. Possible applications of this technology include primary suspension components, auxiliary suspension bump stops, and other vibration isolation components, as MR Pouches are scalable depending on the application and force requirements.

Fabrication and investigation on field-dependent properties of natural rubber based magneto-rheological elastomer isolator

NASA Astrophysics Data System (ADS)

Ain Abd Wahab, Nurul; Amri Mazlan, Saiful; Ubaidillah; Kamaruddin, Shamsul; Intan Nik Ismail, Nik; Choi, Seung-Bok; Haziq Rostam Sharif, Amirul

2016-10-01

This study presents a laminated magnetorheological elastomer (MRE) isolator which applies to vibration control in practice. The proposed isolator is fabricated with multilayer MRE sheets associated with the natural rubber (NR) as a matrix, and steel plates. The fabricated MRE isolator is then magnetically analysed to achieve high magnetic field intensity which can produce high damping force required for effective vibration control. Subsequently, the NR-based MRE specimen is tested to identify the field-dependent rheological properties such as storage modulus with 60 weight percentage of carbonyl iron particles. It is shown from this test that the MR effect of MRE specimen is quantified to reach up to 120% at 0.8 T. Following the design stage, the electromagnetic simulation using the finite element method magnetic (FEMM) software is carried out for analysing the magnetic flux distribution in the laminated MRE isolator. The laminated MRE isolator is then examined to a series of compression for static and dynamic test under various applied currents using the dynamic fatigue machine and biaxial dynamic testing machine. It is shown that the static compression force is increased by 14.5% under strong magnetic field compared to its off-state. Meanwhile, the dynamic compression test results show that the force increase of the laminated MRE isolator is up to 16% and 7% for low and high frequency respectively. From the results presented in this work, it is demonstrated that the full-scale concept of the MRE isolator can be one of the potential candidates for vibration control applications by tunability of the dynamic stiffness.

Gradient Compression Garments as a Countermeasure to Post-Space Flight Orthostatic Intolerance: Potential Interactions with the Maximum Absorbency Garment

NASA Technical Reports Server (NTRS)

Lee, S. M. C.; Laurie, S. S.; Macias, B. R.; Willig, M.; Johnson, K.; Stenger, M. B.

2017-01-01

Astronauts and cosmonauts may experience symptoms of orthostatic intolerance during re-entry, landing, and for several days post-landing following short- and long-duration spaceflight. Presyncopal symptoms have been documented in approximately 20% of short-duration and greater than 60% of long-duration flyers on landing day specifically during 5-10 min of controlled (no countermeasures employed at the time of testing) stand tests or 80 deg head-up tilt tests. Current operational countermeasures to orthostatic intolerance include fluid loading prior to and whole body cooling during re-entry as well as compression garments that are worn during and for up to several days after landing. While both NASA and the Russian space program have utilized compression garments to protect astronauts and cosmonauts traveling on their respective vehicles, a "next-generation" gradient compression garment (GCG) has been developed and tested in collaboration with a commercial partner to support future space flight missions. Unlike previous compression garments used operationally by NASA that provide a single level of compression across only the calves, thighs, and lower abdomen, the GCG provides continuous coverage from the feet to below the pectoral muscles in a gradient fashion (from approximately 55 mm Hg at the feet to approximately 16 mmHg across the abdomen). The efficacy of the GCG has been demonstrated previously after a 14-d bed rest study without other countermeasures and after short-duration Space Shuttle missions. Currently the GCG is being tested during a stand test following long-duration missions (6 months) to the International Space Station. While results to date have been promising, interactions of the GCG with other space suit components have not been examined. Specifically, it is unknown whether wearing the GCG over NASA's Maximum Absorbency Garment (MAG; absorbent briefs worn for the collection of urine and feces while suited during re-entry and landing) will interfere with the effectiveness of the GCG or conversely whether the GCG will reduce the fluid absorption capabilities of the MAG. Methods: This operational, directed study, will (1) determine whether the effectiveness of the GCG is affected by the MAG with regard to cardiovascular responses to head-up tilt, the standard orthostatic intolerance test employed for astronauts and bed rest subjects; (2) determine whether the effectiveness of the MAG is compromised by the GCG tested by injecting a standard fluid volume (950 ml in 3 separate simulated "urine voids") at a standardized rate (30 ml/sec); and (3) determine whether comfort is affected by wearing the MAG under the GCG using a standardized questionnaire. Results from this study will guide future development and operational use of the GCG and MAG to maximize crew health, safety, and comfort.

Impacts to the chest of PMHSs - Influence of impact location and load distribution on chest response.

PubMed

Holmqvist, Kristian; Svensson, Mats Y; Davidsson, Johan; Gutsche, Andreas; Tomasch, Ernst; Darok, Mario; Ravnik, Dean

2016-02-01

The chest response of the human body has been studied for several load conditions, but is not well known in the case of steering wheel rim-to-chest impact in heavy goods vehicle frontal collisions. The aim of this study was to determine the response of the human chest in a set of simulated steering wheel impacts. PMHS tests were carried out and analysed. The steering wheel load pattern was represented by a rigid pendulum with a straight bar-shaped front. A crash test dummy chest calibration pendulum was utilised for comparison. In this study, a set of rigid bar impacts were directed at various heights of the chest, spanning approximately 120mm around the fourth intercostal space. The impact energy was set below a level estimated to cause rib fracture. The analysed results consist of responses, evaluated with respect to differences in the impacting shape and impact heights on compression and viscous criteria chest injury responses. The results showed that the bar impacts consistently produced lesser scaled chest compressions than the hub; the Middle bar responses were around 90% of the hub responses. A superior bar impact provided lesser chest compression; the average response was 86% of the Middle bar response. For inferior bar impacts, the chest compression response was 116% of the chest compression in the middle. The damping properties of the chest caused the compression to decrease in the high speed bar impacts to 88% of that in low speed impacts. From the analysis it could be concluded that the bar impact shape provides lower chest criteria responses compared to the hub. Further, the bar responses are dependent on the impact location of the chest. Inertial and viscous effects of the upper body affect the responses. The results can be used to assess the responses of human substitutes such as anthropomorphic test devices and finite element human body models, which will benefit the development process of heavy goods vehicle safety systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

Easy-to-learn cardiopulmonary resuscitation training programme: a randomised controlled trial on laypeople’s resuscitation performance

PubMed Central

Ko, Rachel Jia Min; Lim, Swee Han; Wu, Vivien Xi; Leong, Tak Yam; Liaw, Sok Ying

2018-01-01

INTRODUCTION Simplifying the learning of cardiopulmonary resuscitation (CPR) is advocated to improve skill acquisition and retention. A simplified CPR training programme focusing on continuous chest compression, with a simple landmark tracing technique, was introduced to laypeople. The study aimed to examine the effectiveness of the simplified CPR training in improving lay rescuers’ CPR performance as compared to standard CPR. METHODS A total of 85 laypeople (aged 21–60 years) were recruited and randomly assigned to undertake either a two-hour simplified or standard CPR training session. They were tested two months after the training on a simulated cardiac arrest scenario. Participants’ performance on the sequence of CPR steps was observed and evaluated using a validated CPR algorithm checklist. The quality of chest compression and ventilation was assessed from the recording manikins. RESULTS The simplified CPR group performed significantly better on the CPR algorithm when compared to the standard CPR group (p < 0.01). No significant difference was found between the groups in time taken to initiate CPR. However, a significantly higher number of compressions and proportion of adequate compressions was demonstrated by the simplified group than the standard group (p < 0.01). Hands-off time was significantly shorter in the simplified CPR group than in the standard CPR group (p < 0.001). CONCLUSION Simplifying the learning of CPR by focusing on continuous chest compressions, with simple hand placement for chest compression, could lead to better acquisition and retention of CPR algorithms, and better quality of chest compressions than standard CPR. PMID:29167910

Easy-to-learn cardiopulmonary resuscitation training programme: a randomised controlled trial on laypeople's resuscitation performance.

PubMed

Ko, Rachel Jia Min; Lim, Swee Han; Wu, Vivien Xi; Leong, Tak Yam; Liaw, Sok Ying

2018-04-01

Simplifying the learning of cardiopulmonary resuscitation (CPR) is advocated to improve skill acquisition and retention. A simplified CPR training programme focusing on continuous chest compression, with a simple landmark tracing technique, was introduced to laypeople. The study aimed to examine the effectiveness of the simplified CPR training in improving lay rescuers' CPR performance as compared to standard CPR. A total of 85 laypeople (aged 21-60 years) were recruited and randomly assigned to undertake either a two-hour simplified or standard CPR training session. They were tested two months after the training on a simulated cardiac arrest scenario. Participants' performance on the sequence of CPR steps was observed and evaluated using a validated CPR algorithm checklist. The quality of chest compression and ventilation was assessed from the recording manikins. The simplified CPR group performed significantly better on the CPR algorithm when compared to the standard CPR group (p < 0.01). No significant difference was found between the groups in time taken to initiate CPR. However, a significantly higher number of compressions and proportion of adequate compressions was demonstrated by the simplified group than the standard group (p < 0.01). Hands-off time was significantly shorter in the simplified CPR group than in the standard CPR group (p < 0.001). Simplifying the learning of CPR by focusing on continuous chest compressions, with simple hand placement for chest compression, could lead to better acquisition and retention of CPR algorithms, and better quality of chest compressions than standard CPR. Copyright: © Singapore Medical Association.

Ultrafast transformation of graphite to diamond: an ab initio study of graphite under shock compression.

PubMed

Mundy, Christopher J; Curioni, Alessandro; Goldman, Nir; Will Kuo, I-F; Reed, Evan J; Fried, Laurence E; Ianuzzi, Marcella

2008-05-14

We report herein ab initio molecular dynamics simulations of graphite under shock compression in conjunction with the multiscale shock technique. Our simulations reveal that a novel short-lived layered diamond intermediate is formed within a few hundred of femtoseconds upon shock loading at a shock velocity of 12 kms (longitudinal stress>130 GPa), followed by formation of cubic diamond. The layered diamond state differs from the experimentally observed hexagonal diamond intermediate found at lower pressures and previous hydrostatic calculations in that a rapid buckling of the graphitic planes produces a mixture of hexagonal and cubic diamond (layered diamond). Direct calculation of the x-ray absorption spectra in our simulations reveals that the electronic structure of the final state closely resembles that of compressed cubic diamond.

Evaluating the effect of online data compression on the disk cache of a mass storage system

NASA Technical Reports Server (NTRS)

Pentakalos, Odysseas I.; Yesha, Yelena

1994-01-01

A trace driven simulation of the disk cache of a mass storage system was used to evaluate the effect of an online compression algorithm on various performance measures. Traces from the system at NASA's Center for Computational Sciences were used to run the simulation and disk cache hit ratios, number of files and bytes migrating to tertiary storage were measured. The measurements were performed for both an LRU and a size based migration algorithm. In addition to seeing the effect of online data compression on the disk cache performance measure, the simulation provided insight into the characteristics of the interactive references, suggesting that hint based prefetching algorithms are the only alternative for any future improvements to the disk cache hit ratio.

Characterization of short-pulse laser-produced x-rays for diagnosing magnetically driven cylindrical isentropic compression

NASA Astrophysics Data System (ADS)

Sawada, Hiroshi; Daykin, Tyler; Bauer, Bruno; Beg, Farhat

2017-10-01

We have developed an experimental platform to study material properties of magnetically compressed cylinder using a 1 MA pulsed power generator Zebra and a 50 TW subpicosecond short-pulse laser Leopard at the UNR's Nevada Terawatt Facility. According to a MHD simulation, strong magnetic fields generated by 100 ns rise time Zebra current can quasi-isentropically compress a material to the strongly coupled plasma regime. Taking advantage of the cylindrical geometry, a metal rod can be brought to higher pressures than that in the planar geometry. To diagnose the compressed rod with high precision x-ray measurements, an initial laser-only experiment was carried out to characterize laser-produced x-rays. Interaction of a high-intensity, short-pulse laser with solids produces broadband and monochromatic x-rays with photon energies high enough to probe dense metal rods. Bremsstrahlung was measured with Imaging plate-based filter stack spectrometers and monochromatic 8.0 keV Cu K-alpha was recorded with an absolutely calibrated Bragg crystal spectrometer. The broadband x-ray source was applied to radiography of thick metal objects and different filter materials were tested. The experimental results and a design of a coupled experiment will be presented.

Towards the development of active compression bandages using dielectric elastomer actuators

NASA Astrophysics Data System (ADS)

Pourazadi, S.; Ahmadi, S.; Menon, C.

2014-06-01

Disorders associated with the lower extremity venous system are common and significantly affect the quality of life of a large number of individuals. These disorders include orthostatic hypotension, oedema, deep vein thrombosis and a number of other conditions related to insufficient venous blood return. The common recommended treatment for these disorders is the use of hosiery compression stockings. In this research, an active compression bandage (ACB) based on the technology of dielectric elastomeric actuators (DEA) was designed, prototyped and tested. A customized calf prototype (CP) was developed to measure the pressure applied by the ACB. Experimental results performed with the CP showed that the pressure applied by the ACB could be electrically controlled to be either below or above the pressure exerted by commercially available compression stockings. An analytical model was used to provide the design criteria. A finite element model (FEM) was also developed to simulate the electromechanical behaviour of the DEA. Comparison of the experimental results with the FEM and analytical models showed that the modelling could accurately predict the behaviour of the ACB. The FEM was subsequently used to study how to improve the ACB performance by varying geometrical parameters such as the ACB thickness.

Finite element comparison of human and Hybrid III responses in a frontal impact.

PubMed

Danelson, Kerry A; Golman, Adam J; Kemper, Andrew R; Gayzik, F Scott; Clay Gabler, H; Duma, Stefan M; Stitzel, Joel D

2015-12-01

The improvement of finite element (FE) Human Body Models (HBMs) has made them valuable tools for investigating restraint interactions compared to anthropomorphic test devices (ATDs). The objective of this study was to evaluate the effect of various combinations of safety restraint systems on the sensitivity of thoracic injury criteria using matched ATD and Human Body Model (HBM) simulations at two crash severities. A total of seven (7) variables were investigated: 3-point belt with two (2) load limits, frontal airbag, knee bolster airbag, a buckle pretensioner, and two (2) delta-v's - 40kph and 50kph. Twenty four (24) simulations were conducted for the Hybrid III ATD FE model and repeated with a validated HBM for 48 total simulations. Metrics tested in these conditions included sternum deflection, chest acceleration, chest excursion, Viscous Criteria (V*C) criteria, pelvis acceleration, pelvis excursion, and femur forces. Additionally, chest band deflection and rib strain distribution were measured in the HBM for additional restraint condition discrimination. The addition of a frontal airbag had the largest effect on the occupant chest metrics with an increase in chest compression and acceleration but a decrease in excursion. While the THUMS and Hybrid III occupants demonstrated the same trend in the chest compression measurements, there were conflicting results in the V*C, acceleration, and displacement metrics. Similarly, the knee bolster airbag had the largest effect on the pelvis with a decrease in acceleration and excursion. With a knee bolster airbag the simulated occupants gave conflicting results, the THUMS had a decrease in femur force and the ATD had an increase. Preferential use of dummies or HBM's is not debated; however, this study highlights the ability of HBM metrics to capture additional chest response metrics. Copyright © 2015 Elsevier Ltd. All rights reserved.

Cosmological Particle Data Compression in Practice

NASA Astrophysics Data System (ADS)

Zeyen, M.; Ahrens, J.; Hagen, H.; Heitmann, K.; Habib, S.

2017-12-01

In cosmological simulations trillions of particles are handled and several terabytes of unstructured particle data are generated in each time step. Transferring this data directly from memory to disk in an uncompressed way results in a massive load on I/O and storage systems. Hence, one goal of domain scientists is to compress the data before storing it to disk while minimizing the loss of information. To prevent reading back uncompressed data from disk, this can be done in an in-situ process. Since the simulation continuously generates data, the available time for the compression of one time step is limited. Therefore, the evaluation of compression techniques has shifted from only focusing on compression rates to include run-times and scalability.In recent years several compression techniques for cosmological data have become available. These techniques can be either lossy or lossless, depending on the technique. For both cases, this study aims to evaluate and compare the state of the art compression techniques for unstructured particle data. This study focuses on the techniques available in the Blosc framework with its multi-threading support, the XZ Utils toolkit with the LZMA algorithm that achieves high compression rates, and the widespread FPZIP and ZFP methods for lossy compressions.For the investigated compression techniques, quantitative performance indicators such as compression rates, run-time/throughput, and reconstruction errors are measured. Based on these factors, this study offers a comprehensive analysis of the individual techniques and discusses their applicability for in-situ compression. In addition, domain specific measures are evaluated on the reconstructed data sets, and the relative error rates and statistical properties are analyzed and compared. Based on this study future challenges and directions in the compression of unstructured cosmological particle data were identified.

Random lattice structures. Modelling, manufacture and FEA of their mechanical response

NASA Astrophysics Data System (ADS)

Maliaris, G.; Sarafis, I. T.; Lazaridis, T.; Varoutoglou, A.; Tsakataras, G.

2016-11-01

The implementation of lightweight structures in various applications, especially in Aerospace/ Automotive industries and Orthopaedics, has become a necessity due to their exceptional mechanical properties with respect to reduced weight. In this work we present a Voronoi tessellation based algorithm, which has been developed for modelling stochastic lattice structures. With the proposed algorithm, is possible to generate CAD geometry with controllable structural parameters, such as porosity, cell number and strut thickness. The digital structures were transformed into physical objects through the combination of 3D printing technics and investment casting. This process was applied to check the mechanical behaviour of generated digital models. Until now, the only way to materialize such structures into physical objects, was feasible through 3D printing methods such as Selective Laser Sintering/ Melting (SLS/ SLM). Investment casting possesses numerous advantages against SLS or SLA, with the major one being the material variety. On the other hand, several trials are required in order to calibrate the process parameters to have successful castings, which is the major drawback of investment casting. The manufactured specimens were subjected to compression tests, where their mechanical response was registered in the form of compressive load - displacement curves. Also, a finite element model was developed, using the specimens’ CAD data and compression test parameters. The FE assisted calculation of specimen plastic deformation is identical with the one of the physical object, which validates the conclusions drawn from the simulation results. As it was observed, strut contact is initiated when specimen deformation is approximately 5mm. Although FE calculated compressive force follows the same trend for the first 3mm of compression, then diverges because of the elasto-plastic FE model type definition and the occurred remeshing steps.

Effect of shoulder abduction angle on biomechanical properties of the repaired rotator cuff tendons with 3 types of double-row technique.

PubMed

Mihata, Teruhisa; Fukuhara, Tetsutaro; Jun, Bong Jae; Watanabe, Chisato; Kinoshita, Mitsuo

2011-03-01

After rotator cuff repair, the shoulder is immobilized in various abduction positions. However, there is no consensus on the proper abduction angle. To assess the effect of shoulder abduction angle on the biomechanical properties of the repaired rotator cuff tendons among 3 types of double-row techniques. Controlled laboratory study. Thirty-two fresh-frozen porcine shoulders were used. A simulated rotator cuff tear was repaired by 1 of 3 double-row techniques: conventional double-row repair, transosseous-equivalent repair, and a combination of conventional double-row and bridging sutures (compression double-row repair). Each specimen underwent cyclic testing followed by tensile testing to failure at a simulated shoulder abduction angle of 0° or 40° on a material testing machine. Gap formation and failure loads were measured. Gap formation in conventional double-row repair at 0° (1.2 ± 0.5 mm) was significantly greater than that at 40° (0.5 ± 0.3mm, P = .01). The yield and ultimate failure loads for conventional double-row repair at 40° were significantly larger than those at 0° (P < .01), whereas those for transosseous-equivalent repair (P < .01) and compression double-row repair (P < .0001) at 0° were significantly larger than those at 40°. The failure load for compression double-row repair was the greatest among the 3 double-row techniques at both 0° and 40° of abduction. Bridging sutures have a greater effect on the biomechanical properties of the repaired rotator cuff tendon at a low abduction angle, and the conventional double-row technique has a greater effect at a high abduction angle. Proper abduction position after rotator cuff repair differs between conventional double-row repair and transosseous-equivalent repair. The authors recommend the use of the combined technique of conventional double-row and bridging sutures to obtain better biomechanical properties at both low and high abduction angles.

The effect of artificial bulk viscosity in simulations of forced compressible turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campos, A.; Morgan, B.

The use of an artificial bulk viscosity for shock stabilization is a common approach employed in turbulence simulations with high-order numerics. The effect of the artificial bulk viscosity is analyzed in the context of large eddy simulations by using as a test case simulations of linearly-forced compressible homogeneous turbulence (Petersen and Livescu, 2010 [12]). This case is unique in that it allows for the specification of a priori target values for total dissipation and ratio of solenoidal to dilatational dissipation. A comparison between these target values and the true predicted levels of dissipation is thus used to investigate the performancemore » of the artificial bulk viscosity. Results show that the artificial bulk viscosity is effective at achieving stable solutions, but also leads to large values of artificial dissipation that outweigh the physical dissipation caused by fluid viscosity. An alternate approach, which employs the artificial thermal conductivity only, shows that the dissipation of dilatational modes is entirely due to the fluid viscosity. However, this method leads to unwanted Gibbs oscillations around the shocklets. The use of shock sensors that further localize the artificial bulk viscosity did not reduce the amount of artificial dissipation introduced by the artificial bulk viscosity. Finally, an improved forcing function that explicitly accounts for the role of the artificial bulk viscosity in the budget of turbulent kinetic energy was explored.« less

The effect of artificial bulk viscosity in simulations of forced compressible turbulence

DOE PAGES

Campos, A.; Morgan, B.

2018-05-17

The use of an artificial bulk viscosity for shock stabilization is a common approach employed in turbulence simulations with high-order numerics. The effect of the artificial bulk viscosity is analyzed in the context of large eddy simulations by using as a test case simulations of linearly-forced compressible homogeneous turbulence (Petersen and Livescu, 2010 [12]). This case is unique in that it allows for the specification of a priori target values for total dissipation and ratio of solenoidal to dilatational dissipation. A comparison between these target values and the true predicted levels of dissipation is thus used to investigate the performancemore » of the artificial bulk viscosity. Results show that the artificial bulk viscosity is effective at achieving stable solutions, but also leads to large values of artificial dissipation that outweigh the physical dissipation caused by fluid viscosity. An alternate approach, which employs the artificial thermal conductivity only, shows that the dissipation of dilatational modes is entirely due to the fluid viscosity. However, this method leads to unwanted Gibbs oscillations around the shocklets. The use of shock sensors that further localize the artificial bulk viscosity did not reduce the amount of artificial dissipation introduced by the artificial bulk viscosity. Finally, an improved forcing function that explicitly accounts for the role of the artificial bulk viscosity in the budget of turbulent kinetic energy was explored.« less

Analysis of hardening behavior of sheet metals by a new simple shear test method taking into account the Bauschinger effect

NASA Astrophysics Data System (ADS)

Bang, Sungsik; Rickhey, Felix; Kim, Minsoo; Lee, Hyungyil; Kim, Naksoo

2013-12-01

In this study we establish a process to predict hardening behavior considering the Bauschinger effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Bauschinger effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with FEA. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments.

CFD Modeling of Helium Pressurant Effects on Cryogenic Tank Pressure Rise Rates in Normal Gravity

NASA Technical Reports Server (NTRS)

Grayson, Gary; Lopez, Alfredo; Chandler, Frank; Hastings, Leon; Hedayat, Ali; Brethour, James

2007-01-01

A recently developed computational fluid dynamics modeling capability for cryogenic tanks is used to simulate both self-pressurization from external heating and also depressurization from thermodynamic vent operation. Axisymmetric models using a modified version of the commercially available FLOW-3D software are used to simulate actual physical tests. The models assume an incompressible liquid phase with density that is a function of temperature only. A fully compressible formulation is used for the ullage gas mixture that contains both condensable vapor and a noncondensable gas component. The tests, conducted at the NASA Marshall Space Flight Center, include both liquid hydrogen and nitrogen in tanks with ullage gas mixtures of each liquid's vapor and helium. Pressure and temperature predictions from the model are compared to sensor measurements from the tests and a good agreement is achieved. This further establishes the accuracy of the developed FLOW-3D based modeling approach for cryogenic systems.

Simulated Prompt Acceleration of Multi-MeV Electrons by the 17 March 2015 Interplanetary Shock

NASA Astrophysics Data System (ADS)

Hudson, Mary; Jaynes, Allison; Kress, Brian; Li, Zhao; Patel, Maulik; Shen, Xiao-Chen; Thaller, Scott; Wiltberger, Michael; Wygant, John

2017-10-01

Prompt enhancement of relativistic electron flux at L = 3-5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by ˜1 MeV is inferred on less than a drift timescale as seen in prior shock compression events, which launch a magnetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at >1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L = 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression.

Micro-Ramps for External Compression Low-Boom Inlets

NASA Technical Reports Server (NTRS)

Rybalko, Michael; Loth, Eric; Chima, Rodrick V.; Hirt, Stefanie M.; DeBonis, James R.

2010-01-01

The application of vortex generators for flow control in an external compression, axisymmetric, low-boom concept inlet was investigated using RANS simulations with three-dimensional (3-D), structured, chimera (overset) grids and the WIND-US code. The low-boom inlet design is based on previous scale model 1- by 1-ft wind tunnel tests and features a zero-angle cowl and relaxed isentropic compression centerbody spike, resulting in defocused oblique shocks and a weak terminating normal shock. Validation of the methodology was first performed for micro-ramps in supersonic flow on a flat plate with and without oblique shocks. For the inlet configuration, simulations with several types of vortex generators were conducted for positions both upstream and downstream of the terminating normal shock. The performance parameters included incompressible axisymmetric shape factor, separation area, inlet pressure recovery, and massflow ratio. The design of experiments (DOE) methodology was used to select device size and location, analyze the resulting data, and determine the optimal choice of device geometry. The optimum upstream configuration was found to substantially reduce the post-shock separation area but did not significantly impact recovery at the aerodynamic interface plane (AIP). Downstream device placement allowed for fuller boundary layer velocity profiles and reduced distortion. This resulted in an improved pressure recovery and massflow ratio at the AIP compared to the baseline solid-wall configuration.

Applied axial magnetic field effects on laboratory plasma jets: Density hollowing, field compression, and azimuthal rotation

DOE PAGES

Byvank, T.; Banasek, J. T.; Potter, W. M.; ...

2017-12-07

We experimentally measure the effects of an applied axial magnetic field (B z) on laboratory plasma jets and compare experimental results with numerical simulations using an extended magnetohydrodynamics code. A 1 MA peak current, 100 ns rise time pulse power machine is used to generate the plasma jet. On application of the axial field, we observe on-axis density hollowing and a conical formation of the jet using interferometry, compression of the applied B z using magnetic B-dot probes, and azimuthal rotation of the jet using Thomson scattering. Experimentally, we find densities ≤ 5×10 17 cm -3 on-axis relative to jetmore » densities of ≥ 3×10 18 cm -3. For aluminum jets, 6.5 ± 0.5 mm above the foil, we find on-axis compression of the applied 1.0 ± 0.1 T B z to a total 2.4 ± 0.3 T, while simulations predict a peak compression to a total 3.4 T at the same location. On the aluminum jet boundary, we find ion azimuthal rotation velocities of 15-20 km/s, while simulations predict 14 km/s at the density peak. We discuss possible sources of discrepancy between the experiments and simulations, including: surface plasma on B-dot probes, optical fiber spatial resolution, simulation density floors, and 2D vs. 3D simulation effects. Lastly, this quantitative comparison between experiments and numerical simulations helps elucidate the underlying physics that determine the plasma dynamics of magnetized plasma jets.« less

Applied axial magnetic field effects on laboratory plasma jets: Density hollowing, field compression, and azimuthal rotation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byvank, T.; Banasek, J. T.; Potter, W. M.

We experimentally measure the effects of an applied axial magnetic field (B z) on laboratory plasma jets and compare experimental results with numerical simulations using an extended magnetohydrodynamics code. A 1 MA peak current, 100 ns rise time pulse power machine is used to generate the plasma jet. On application of the axial field, we observe on-axis density hollowing and a conical formation of the jet using interferometry, compression of the applied B z using magnetic B-dot probes, and azimuthal rotation of the jet using Thomson scattering. Experimentally, we find densities ≤ 5×10 17 cm -3 on-axis relative to jetmore » densities of ≥ 3×10 18 cm -3. For aluminum jets, 6.5 ± 0.5 mm above the foil, we find on-axis compression of the applied 1.0 ± 0.1 T B z to a total 2.4 ± 0.3 T, while simulations predict a peak compression to a total 3.4 T at the same location. On the aluminum jet boundary, we find ion azimuthal rotation velocities of 15-20 km/s, while simulations predict 14 km/s at the density peak. We discuss possible sources of discrepancy between the experiments and simulations, including: surface plasma on B-dot probes, optical fiber spatial resolution, simulation density floors, and 2D vs. 3D simulation effects. Lastly, this quantitative comparison between experiments and numerical simulations helps elucidate the underlying physics that determine the plasma dynamics of magnetized plasma jets.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Chao; Xu, Jun; Cao, Lei

The electrodes of lithium-ion batteries (LIB) are known to be brittle and to fail earlier than the separators during an external crush event. Thus, the understanding of mechanical failure mechanism for LIB electrodes (anode and cathode) is critical for the safety design of LIB cells. In this paper, we present experimental and numerical studies on the constitutive behavior and progression of failure in LIB electrodes. Mechanical tests were designed and conducted to evaluate the constitutive properties of porous electrodes. Constitutive models were developed to describe the stress-strain response of electrodes under uniaxial tensile and compressive loads. The failure criterion andmore » a damage model were introduced to model their unique tensile and compressive failure behavior. The failure mechanism of LIB electrodes was studied using the blunt rod test on dry electrodes, and numerical models were built to simulate progressive failure. The different failure processes were examined and analyzed in detail numerically, and correlated with experimentally observed failure phenomena. Finally, the test results and models improve our understanding of failure behavior in LIB electrodes, and provide constructive insights on future development of physics-based safety design tools for battery structures under mechanical abuse.« less

Vapor Compression Cycle Design Program (CYCLE_D)

National Institute of Standards and Technology Data Gateway

SRD 49 NIST Vapor Compression Cycle Design Program (CYCLE_D) (PC database for purchase)   The CYCLE_D database package simulates the vapor compression refrigeration cycles. It is fully compatible with REFPROP 9.0 and covers the 62 single-compound refrigerants . Fluids can be used in mixtures comprising up to five components.

Volume and tissue composition preserving deformation of breast CT images to simulate breast compression in mammographic imaging

NASA Astrophysics Data System (ADS)

Han, Tao; Chen, Lingyun; Lai, Chao-Jen; Liu, Xinming; Shen, Youtao; Zhong, Yuncheng; Ge, Shuaiping; Yi, Ying; Wang, Tianpeng; Shaw, Chris C.

2009-02-01

Images of mastectomy breast specimens have been acquired with a bench top experimental Cone beam CT (CBCT) system. The resulting images have been segmented to model an uncompressed breast for simulation of various CBCT techniques. To further simulate conventional or tomosynthesis mammographic imaging for comparison with the CBCT technique, a deformation technique was developed to convert the CT data for an uncompressed breast to a compressed breast without altering the breast volume or regional breast density. With this technique, 3D breast deformation is separated into two 2D deformations in coronal and axial views. To preserve the total breast volume and regional tissue composition, each 2D deformation step was achieved by altering the square pixels into rectangular ones with the pixel areas unchanged and resampling with the original square pixels using bilinear interpolation. The compression was modeled by first stretching the breast in the superior-inferior direction in the coronal view. The image data were first deformed by distorting the voxels with a uniform distortion ratio. These deformed data were then deformed again using distortion ratios varying with the breast thickness and re-sampled. The deformation procedures were applied in the axial view to stretch the breast in the chest wall to nipple direction while shrinking it in the mediolateral to lateral direction re-sampled and converted into data for uniform cubic voxels. Threshold segmentation was applied to the final deformed image data to obtain the 3D compressed breast model. Our results show that the original segmented CBCT image data were successfully converted into those for a compressed breast with the same volume and regional density preserved. Using this compressed breast model, conventional and tomosynthesis mammograms were simulated for comparison with CBCT.

Mechanical characterization of diesel soot nanoparticles: in situ compression in a transmission electron microscope and simulations

NASA Astrophysics Data System (ADS)

Jenei, Istvan Zoltan; Dassenoy, Fabrice; Epicier, Thierry; Khajeh, Arash; Martini, Ashlie; Uy, Dairene; Ghaednia, Hamed; Gangopadhyay, Arup

2018-02-01

Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Young’s modulus and hardness of the SNPs were calculated. The Young’s modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp2/sp3 ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp2/sp3 ratio.

Mechanical characterization of diesel soot nanoparticles: in situ compression in a transmission electron microscope and simulations.

PubMed

Jenei, Istvan Zoltan; Dassenoy, Fabrice; Epicier, Thierry; Khajeh, Arash; Martini, Ashlie; Uy, Dairene; Ghaednia, Hamed; Gangopadhyay, Arup

2018-02-23

Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Young's modulus and hardness of the SNPs were calculated. The Young's modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp 2 /sp 3 ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp 2 /sp 3 ratio.

The effect of compressor-administered defibrillation on peri-shock pauses in a simulated cardiac arrest scenario.

PubMed

Glick, Joshua; Lehman, Erik; Terndrup, Thomas

2014-03-01

Coordination of the tasks of performing chest compressions and defibrillation can lead to communication challenges that may prolong time spent off the chest. The purpose of this study was to determine whether defibrillation provided by the provider performing chest compressions led to a decrease in peri-shock pauses as compared to defibrillation administered by a second provider, in a simulated cardiac arrest scenario. This was a randomized, controlled study measuring pauses in chest compressions for defibrillation in a simulated cardiac arrest model. We approached hospital providers with current CPR certification for participation between July, 2011 and October, 2011. Volunteers were randomized to control (facilitator-administered defibrillation) or experimental (compressor-administered defibrillation) groups. All participants completed one minute of chest compressions on a mannequin in a shockable rhythm prior to administration of defibrillation. We measured and compared pauses for defibrillation in both groups. Out of 200 total participants, we analyzed data from 197 defibrillations. Compressor-initiated defibrillation resulted in a significantly lower pre-shock hands-off time (0.57 s; 95% CI: 0.47-0.67) compared to facilitator-initiated defibrillation (1.49 s; 95% CI: 1.35-1.64). Furthermore, compressor-initiated defibrillation resulted in a significantly lower peri-shock hands-off time (2.77 s; 95% CI: 2.58-2.95) compared to facilitator-initiated defibrillation (4.25 s; 95% CI: 4.08-4.43). Assigning the responsibility for shock delivery to the provider performing compressions encourages continuous compressions throughout the charging period and decreases total time spent off the chest. However, as this was a simulation-based study, clinical implementation is necessary to further evaluate these potential benefits.

Modeling Two-Stage Bunch Compression With Wakefields: Macroscopic Properties And Microbunching Instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bosch, R.A.; Kleman, K.J.; /Wisconsin U., SRC

2011-09-08

In a two-stage compression and acceleration system, where each stage compresses a chirped bunch in a magnetic chicane, wakefields affect high-current bunches. The longitudinal wakes affect the macroscopic energy and current profiles of the compressed bunch and cause microbunching at short wavelengths. For macroscopic wavelengths, impedance formulas and tracking simulations show that the wakefields can be dominated by the resistive impedance of coherent edge radiation. For this case, we calculate the minimum initial bunch length that can be compressed without producing an upright tail in phase space and associated current spike. Formulas are also obtained for the jitter in themore » bunch arrival time downstream of the compressors that results from the bunch-to-bunch variation of current, energy, and chirp. Microbunching may occur at short wavelengths where the longitudinal space-charge wakes dominate or at longer wavelengths dominated by edge radiation. We model this range of wavelengths with frequency-dependent impedance before and after each stage of compression. The growth of current and energy modulations is described by analytic gain formulas that agree with simulations.« less

Hollow microgels squeezed in overcrowded environments

NASA Astrophysics Data System (ADS)

Scotti, A.; Brugnoni, M.; Rudov, A. A.; Houston, J. E.; Potemkin, I. I.; Richtering, W.

2018-05-01

We study how a cavity changes the response of hollow microgels with respect to regular ones in overcrowded environments. The structural changes of hollow poly(N-isopropylacrylamide) microgels embedded within a matrix of regular ones are probed by small-angle neutron scattering with contrast variation. The form factors of the microgels at increasing compressions are directly measured. The decrease of the cavity size with increasing concentration shows that the hollow microgels have an alternative way with respect to regular cross-linked ones to respond to the squeezing due to their neighbors. The structural changes under compression are supported by the radial density profiles obtained with computer simulations. The presence of the cavity offers to the polymer network the possibility to expand toward the center of the microgels in response to the overcrowded environment. Furthermore, upon increasing compression, a two step transition occurs: First the microgels are compressed but the internal structure is unchanged; then, further compression causes the fuzzy shell to collapse completely and reduce the size of the cavity. Computer simulations also allow studying higher compression degrees than in the experiments leading to the microgel's faceting.

GENASIS: General Astrophysical Simulation System. I. Refinable Mesh and Nonrelativistic Hydrodynamics

NASA Astrophysics Data System (ADS)

Cardall, Christian Y.; Budiardja, Reuben D.; Endeve, Eirik; Mezzacappa, Anthony

2014-02-01

GenASiS (General Astrophysical Simulation System) is a new code being developed initially and primarily, though by no means exclusively, for the simulation of core-collapse supernovae on the world's leading capability supercomputers. This paper—the first in a series—demonstrates a centrally refined coordinate patch suitable for gravitational collapse and documents methods for compressible nonrelativistic hydrodynamics. We benchmark the hydrodynamics capabilities of GenASiS against many standard test problems; the results illustrate the basic competence of our implementation, demonstrate the strengths and limitations of the HLLC relative to the HLL Riemann solver in a number of interesting cases, and provide preliminary indications of the code's ability to scale and to function with cell-by-cell fixed-mesh refinement.

Simulation of car collision with an impact block

NASA Astrophysics Data System (ADS)

Kostek, R.; Aleksandrowicz, P.

2017-10-01

This article presents the experimental results of crash test of Fiat Cinquecento performed by Allgemeiner Deutscher Automobil-Club (ADAC) and the simulation results obtained with program called V-SIM for default settings. At the next stage a wheel was blocked and the parameters of contact between the vehicle and the barrier were changed for better results matching. The following contact parameters were identified: stiffness at compression phase, stiffness at restitution phase, the coefficients of restitution and friction. The changes lead to various post-impact positions, which shows sensitivity of the results to contact parameters. V-SIM is commonly used by expert witnesses who tend to use default settings, therefore the companies offering simulation programs should identify those parameters with due diligence.

Effects of flashlight guidance on chest compression performance in cardiopulmonary resuscitation in a noisy environment.

PubMed

You, Je Sung; Chung, Sung Phil; Chang, Chul Ho; Park, Incheol; Lee, Hye Sun; Kim, SeungHo; Lee, Hahn Shick

2013-08-01

In real cardiopulmonary resuscitation (CPR), noise can arise from instructional voices and environmental sounds in places such as a battlefield and industrial and high-traffic areas. A feedback device using a flashing light was designed to overcome noise-induced stimulus saturation during CPR. This study was conducted to determine whether 'flashlight' guidance influences CPR performance in a simulated noisy setting. We recruited 30 senior medical students with no previous experience of using flashlight-guided CPR to participate in this prospective, simulation-based, crossover study. The experiment was conducted in a simulated noisy situation using a cardiac arrest model without ventilation. Noise such as patrol car and fire engine sirens was artificially generated. The flashlight guidance device emitted light pulses at the rate of 100 flashes/min. Participants also received instructions to achieve the desired rate of 100 compressions/min. CPR performances were recorded with a Resusci Anne mannequin with a computer skill-reporting system. There were significant differences between the control and flashlight groups in mean compression rate (MCR), MCR/min and visual analogue scale. However, there were no significant differences in correct compression depth, mean compression depth, correct hand position, and correctly released compression. The flashlight group constantly maintained the pace at the desired 100 compressions/min. Furthermore, the flashlight group had a tendency to keep the MCR constant, whereas the control group had a tendency to decrease it after 60 s. Flashlight-guided CPR is particularly advantageous for maintaining a desired MCR during hands-only CPR in noisy environments, where metronome pacing might not be clearly heard.

Effective Size Analysis of the Diametral Compression (Brazil) Test Specimen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadaan, Osama M.; Wereszczak, Andrew A

2009-04-01

This study considers the finite element analysis (FEA) simulation and Weibull effective size analysis for the diametral compression (DC) or Brazil specimen loaded with three different push-rod geometries. Those geometries are a flat push-rod, a push-rod whose radius of curvature is larger than that for the DC specimen, and a push-rod whose radius of curvature matches that of the DC specimen. Such established effective size analysis recognizes that the tensile strength of structural ceramics is typically one to two orders of magnitude less than its compressive strength. Therefore, because fracture is much more apt to result from a tensile stressmore » than a compressive one, this traditional analysis only considers the first principal tensile stress field in the mechanically loaded ceramic component for the effective size analysis. The effective areas and effective volumes were computed as function of Weibull modulus using the CARES/Life code. Particular attention was devoted to the effect of mesh sensitivity and localized stress concentration. The effect of specimen width on the stress state was also investigated. The effects of push-rod geometry, the use of steel versus WC push-rods, and considering a frictionless versus no-slip interface between push-rod and specimen on the maximum stresses, where those stresses are located, and the effective area and effective volume results are described. Of the three push-rod geometries, it is concluded that the push-rod (made from WC rather than steel) whose radius of curvature matches that of the DC specimen is the most apt to cause fracture initiation within the specimen's bulk rather than at the loading interface. Therefore, its geometry is the most likely to produce a valid diametral compression strength test. However, the DC specimen remains inefficient in terms of its area and volume efficiencies; namely, the tensile strength of only a few percent of the specimen's entire area or volume is sampled. Given the high probability that a valid (or invalid) test can be proven by ceramic fractographic practices suggests that this test method and specimen is questionable for use with relatively strong structural ceramics.« less

Effects of radial compression on a novel simulated intervertebral disc-like assembly using bone marrow-derived mesenchymal stem cell cell-sheets for annulus fibrosus regeneration.

PubMed

See, Eugene Yong-Shun; Toh, Siew Lok; Goh, James Cho-Hong

2011-10-01

The aim of this study was to develop a tissue engineering approach in regenerating the annulus fibrosus (AF) as part of an overall strategy to produce a tissue-engineered intervertebral disc (IVD) replacement. To determine whether a rehabilitative simulation regime on bone marrow–derived mesenchymal stem cell cell-sheet is able to aid the regeneration of the AF. No previous study has used bone marrow–derived mesenchymal stem cell cell-sheets simulated by a rehabilitative regime to regenerate the AF. The approach was to use bone marrow–derived stem cells to form cell-sheets and incorporating them onto silk scaffolds to simulate the native lamellae of the AF. The in vitro experimental model used to study the efficacy of such a system was made up of the tissue engineering AF construct wrapped around a silicone disc to form a simulated IVD-like assembly. The assembly was cultured within a custom-designed bioreactor that provided a compressive mechanical stimulation onto the silicone disc. The silicone nucleus pulposus would bulge radially and compress the simulated AF to mimic the physiological conditions. The simulated IVD-like assembly was compressed using a rehabilitative regime that lasted for 4 weeks at 0.25 Hz, for 15 minutes each day. With the rehabilitative regime, the cell-sheets remained viable but showed a decrease in cell numbers and viability. Gene expression analysis showed significant upregulation of IVD-related genes and there was an increased ratio of collagen type II to collagen type I found within the extracellular matrix. The results suggested that a rehabilitative regime caused extensive remodeling to take place within the simulated IVD-like assembly, producing extracellular matrix similar to that found in the inner AF.

Biomechanical behavior of bone scaffolds made of additive manufactured tricalciumphosphate and titanium alloy under different loading conditions.

PubMed

Wieding, Jan; Fritsche, Andreas; Heinl, Peter; Körner, Carolin; Cornelsen, Matthias; Seitz, Hermann; Mittelmeier, Wolfram; Bader, Rainer

2013-12-16

The repair of large segmental bone defects caused by fracture, tumor or infection remains challenging in orthopedic surgery. The capability of two different bone scaffold materials, sintered tricalciumphosphate and a titanium alloy (Ti6Al4V), were determined by mechanical and biomechanical testing. All scaffolds were fabricated by means of additive manufacturing techniques with identical design and controlled pore geometry. Small-sized sintered TCP scaffolds (10 mm diameter, 21 mm length) were fabricated as dense and open-porous samples and tested in an axial loading procedure. Material properties for titanium alloy were determined by using both tensile (dense) and compressive test samples (open-porous). Furthermore, large-sized open-porous TCP and titanium alloy scaffolds (30 mm in height and diameter, 700 µm pore size) were tested in a biomechanical setup simulating a large segmental bone defect using a composite femur stabilized with an osteosynthesis plate. Static physiologic loads (1.9 kN) were applied within these tests. Ultimate compressive strength of the TCP samples was 11.2 ± 0.7 MPa and 2.2 ± 0.3 MPa, respectively, for the dense and the open-porous samples. Tensile strength and ultimate compressive strength was 909.8 ± 4.9 MPa and 183.3 ± 3.7 MPa, respectively, for the dense and the open-porous titanium alloy samples. Furthermore, the biomechanical results showed good mechanical stability for the titanium alloy scaffolds. TCP scaffolds failed at 30% of the maximum load. Based on recent data, the 3D printed TCP scaffolds tested cannot currently be recommended for high load-bearing situations. Scaffolds made of titanium could be optimized by adapting the biomechanical requirements.

Micromechanics of composite laminate compression failure

NASA Technical Reports Server (NTRS)

Guynn, E. Gail; Bradley, Walter L.

1986-01-01

The Dugdale analysis for metals loaded in tension was adapted to model the failure of notched composite laminates loaded in compression. Compression testing details, MTS alignment verification, and equipment needs were resolved. Thus far, only 2 ductile material systems, HST7 and F155, were selected for study. A Wild M8 Zoom Stereomicroscope and necessary attachments for video taping and 35 mm pictures were purchased. Currently, this compression test system is fully operational. A specimen is loaded in compression, and load vs shear-crippling zone size is monitored and recorded. Data from initial compression tests indicate that the Dugdale model does not accurately predict the load vs damage zone size relationship of notched composite specimens loaded in compression.

Simulation of Mechanical Behavior of Agglutinates

NASA Technical Reports Server (NTRS)

Nakagawa, Masami; Moon, Tae-Hyun

2005-01-01

Due to lack of "real" lunar soil or even lunar simulant, it is difficult to characterize the interaction between lunar soil (or simulant) with different surfaces that are involved in excavation and processing machinery. One unique feature possessed by lunar soil is the agglutinates produced by repeated high-speed micrometeoroid impacts and subsequent pulverization[l and 2]. The large particles are impacted by micrometeoroids [Fig.l] and pulverized to produce finer particles. This process continues until there are no more "large" particles left on the surface of the moon. Due to high impact speed, the impact melting process fuses fines to make agglutinates such as shown in Fig. 2. We will present a series of simulation results and movies will be shown to indicate brittle behavior of each individual agglutinate and also similar compressibility charts shown by Carrier et al. [3]. Fig. 3 shows our preliminary result of the simulated oedometer tests.

Collapsible Cryogenic Storage Vessel Project

NASA Technical Reports Server (NTRS)

Fleming, David C.

2002-01-01

Collapsible cryogenic storage vessels may be useful for future space exploration missions by providing long-term storage capability using a lightweight system that can be compactly packaged for launch. Previous development efforts have identified an 'inflatable' concept as most promising. In the inflatable tank concept, the cryogen is contained within a flexible pressure wall comprised of a flexible bladder to contain the cryogen and a fabric reinforcement layer for structural strength. A flexible, high-performance insulation jacket surrounds the vessel. The weight of the tank and the cryogen is supported by rigid support structures. This design concept is developed through physical testing of a scaled pressure wall, and through development of tests for a flexible Layered Composite Insulation (LCI) insulation jacket. A demonstration pressure wall is fabricated using Spectra fabric for reinforcement, and burst tested under noncryogenic conditions. An insulation test specimens is prepared to demonstrate the effectiveness of the insulation when subject to folding effects, and to examine the effect of compression of the insulation under compressive loading to simulate the pressure effect in a nonrigid insulation blanket under the action atmospheric pressure, such as would be seen in application on the surface of Mars. Although pressure testing did not meet the design goals, the concept shows promise for the design. The testing program provides direction for future development of the collapsible cryogenic vessel concept.

Reduced order modeling of fluid/structure interaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barone, Matthew Franklin; Kalashnikova, Irina; Segalman, Daniel Joseph

2009-11-01

This report describes work performed from October 2007 through September 2009 under the Sandia Laboratory Directed Research and Development project titled 'Reduced Order Modeling of Fluid/Structure Interaction.' This project addresses fundamental aspects of techniques for construction of predictive Reduced Order Models (ROMs). A ROM is defined as a model, derived from a sequence of high-fidelity simulations, that preserves the essential physics and predictive capability of the original simulations but at a much lower computational cost. Techniques are developed for construction of provably stable linear Galerkin projection ROMs for compressible fluid flow, including a method for enforcing boundary conditions that preservesmore » numerical stability. A convergence proof and error estimates are given for this class of ROM, and the method is demonstrated on a series of model problems. A reduced order method, based on the method of quadratic components, for solving the von Karman nonlinear plate equations is developed and tested. This method is applied to the problem of nonlinear limit cycle oscillations encountered when the plate interacts with an adjacent supersonic flow. A stability-preserving method for coupling the linear fluid ROM with the structural dynamics model for the elastic plate is constructed and tested. Methods for constructing efficient ROMs for nonlinear fluid equations are developed and tested on a one-dimensional convection-diffusion-reaction equation. These methods are combined with a symmetrization approach to construct a ROM technique for application to the compressible Navier-Stokes equations.« less

Technologies for Propelled Hypersonic Flight Volume 2 - Subgroup 2: Scram Propulsion

DTIC Science & Technology

2006-01-01

effort is focused on the MSD code, initially developed by ONERA to simulate internal aerodynamic flows, which has been upgraded in cooperation...inlets were studied: a mixed, external/ internal , compression inlet studied at DLR with testing in the H2K and TMK wind-tunnels, and an internal ...movable panels during operation along the trajectory, modification of the internal geometry by a control-command computer connected with sensors on the

Blind Compressed Image Watermarking for Noisy Communication Channels

DTIC Science & Technology

2015-10-26

Lenna test image [11] for our simulations, and gradient projection for sparse recon- struction (GPSR) [12] to solve the convex optimization prob- lem...E. Candes, J. Romberg , and T. Tao, “Robust uncertainty prin- ciples: exact signal reconstruction from highly incomplete fre- quency information,” IEEE...Images - Requirements and Guidelines,” ITU-T Recommen- dation T.81, 1992. [6] M. Gkizeli, D. Pados, and M. Medley, “Optimal signature de - sign for

Microstructure and hot compression deformation of the as-cast Mg-5.0Sn-1.5Y-0.1Zr alloy

NASA Astrophysics Data System (ADS)

Luo, Xiaoping; Kang, Li; Li, Qiushu; Chai, Yuesheng

2015-08-01

The hot compression deformation behavior and microstructure of as-cast Mg-5.0Sn-1.5Y-0.1Zr alloy were investigated by performing isothermal hot compression tests. The tests were conducted using a thermal mechanical simulator at 250-450 °C and strain rates ranging from 0.002 to 2 s-1, with a maximum deformation strain of 50 %. The effects of the deformation parameters on the microstructure evolution of the Mg-5.0Sn-1.5Y-0.1Zr alloy were discussed. The study revealed the flow behavior and the deformation mechanism of the Mg-5.0Sn-1.5Y-0.1Zr alloy. The dependence of flow stress on temperature and strain rate was described by a hyperbolic sine constitutive equation. Through regression analysis, the activation energy of 223.26 kJ mol-1 for plastic deformation was determined by considering flow stress at a strain rate of 0.2. Microstructure observation showed that dynamic recrystallization occurred extensively along grain boundaries at temperatures higher than 300 °C and strain rates lower than 0.02 s-1. This observation provides a theoretical basis for the manufacture and application of the Mg-5.0Sn-1.5Y-0.1Zr alloy.

A metabolic simulator for unmanned testing of breathing apparatuses in hyperbaric conditions.

PubMed

Frånberg, Oskar; Loncar, Mario; Larsson, Åke; Ornhagen, Hans; Gennser, Mikael

2014-11-01

A major part of testing of rebreather apparatuses for underwater diving focuses on the oxygen dosage system. A metabolic simulator for testing breathing apparatuses was built and evaluated. Oxygen consumption was achieved through catalytic combustion of propene. With an admixture of carbon dioxide in the propene fuel, the system allowed the respiratory exchange ratio to be set freely within human variability and also made it possible to increase test pressures above the condensation pressure of propene. The system was tested by breathing ambient air in a pressure chamber with oxygen uptake (Vo₂) ranging from 1-4 L · min(-1), tidal volume (VT) from 1-3 L, breathing frequency (f) of 20 and 25 breaths/min, and chamber pressures from 100 to 670 kPa. The measured end-tidal oxygen concentration (Fo₂) was compared to calculated end-tidal Fo₂. The largest average difference in end-tidal Fo₂during atmospheric pressure conditions was 0.63%-points with a 0.28%-point average difference during the whole test. During hyperbaric conditions with pressures ranging from 100 to 670 kPa, the largest average difference in Fo₂was 1.68%-points seen during compression from 100 kPa to 400 kPa and the average difference in Fo₂during the whole test was 0.29%-points. In combination with a breathing simulator simulating tidal breathing, the system can be used for dynamic continuous testing of breathing equipment with changes in VT, f, Vo2, and pressure.

Factors affecting the sticking of insects on modified aircraft wings

NASA Technical Reports Server (NTRS)

Yi, O.; Chitsaz-Z, M. R.; Eiss, N. S.; Wightman, J. P.

1988-01-01

Previous work showed that the total number of insects sticking to an aluminum surface was reduced by coating the aluminum surface with elastomers. Due to a large number of possible experimental errors, no correlation between the modulus of elasticity, the elastomer, and the total number of insects sticking to a given elastomer was obtained. One of the errors assumed to be introduced during the road test is a variable insect flux so the number of insects striking one surface might be different from that striking another sample. To eliminate this source of error, the road test used to collect insects was simulated in a laboratory by development of an insect impacting technique using a pipe and high pressure compressed air. The insects are accelerated by a compressed air gun to high velocities and are then impacted with a stationary target on which the sample is mounted. The velocity of an object exiting from the pipe was determined and further improvement of the technique was achieved to obtain a uniform air velocity distribution.

Resistance Curves in the Tensile and Compressive Longitudinal Failure of Composites

NASA Technical Reports Server (NTRS)

Camanho, Pedro P.; Catalanotti, Giuseppe; Davila, Carlos G.; Lopes, Claudio S.; Bessa, Miguel A.; Xavier, Jose C.

2010-01-01

This paper presents a new methodology to measure the crack resistance curves associated with fiber-dominated failure modes in polymer-matrix composites. These crack resistance curves not only characterize the fracture toughness of the material, but are also the basis for the identification of the parameters of the softening laws used in the analytical and numerical simulation of fracture in composite materials. The method proposed is based on the identification of the crack tip location by the use of Digital Image Correlation and the calculation of the J-integral directly from the test data using a simple expression derived for cross-ply composite laminates. It is shown that the results obtained using the proposed methodology yield crack resistance curves similar to those obtained using FEM-based methods in compact tension carbon-epoxy specimens. However, it is also shown that the Digital Image Correlation based technique can be used to extract crack resistance curves in compact compression tests for which FEM-based techniques are inadequate.

Experimental study of a DMD based compressive line sensing imaging system in the turbulence environment

NASA Astrophysics Data System (ADS)

Ouyang, Bing; Hou, Weilin; Gong, Cuiling; Caimi, Frank M.; Dalgleish, Fraser R.; Vuorenkoski, Anni K.

2016-05-01

The Compressive Line Sensing (CLS) active imaging system has been demonstrated to be effective in scattering mediums, such as turbid coastal water through simulations and test tank experiments. Since turbulence is encountered in many atmospheric and underwater surveillance applications, a new CLS imaging prototype was developed to investigate the effectiveness of the CLS concept in a turbulence environment. Compared with earlier optical bench top prototype, the new system is significantly more robust and compact. A series of experiments were conducted at the Naval Research Lab's optical turbulence test facility with the imaging path subjected to various turbulence intensities. In addition to validating the system design, we obtained some unexpected exciting results - in the strong turbulence environment, the time-averaged measurements using the new CLS imaging prototype improved both SNR and resolution of the reconstructed images. We will discuss the implications of the new findings, the challenges of acquiring data through strong turbulence environment, and future enhancements.

Performance of Subscale Docking Seals Under Simulated Temperature Conditions

NASA Technical Reports Server (NTRS)

Smith, Ian M.; Daniels, Christopher C.

2008-01-01

A universal docking system is being developed by the National Aeronautics and Space Administration (NASA) to support future space exploration missions to low Earth orbit (LEO), to the moon, and to Mars. The candidate docking seals for the system are a composite design consisting of elastomer seal bulbs molded into the front and rear sides of a metal ring. The test specimens were subscale seals with two different elastomer cross-sections and a 12-in. outside diameter. The seal assemblies were mated in elastomer seal-on-metal plate and elastomer seal-on-elastomer seal configurations. The seals were manufactured from S0383-70 silicone elastomer compound. Nominal and off-nominal joint configurations were examined. Both the compression load required to mate the seals and the leak rate observed were recorded while the assemblies were subjected to representative docking system operating temperatures of -58, 73, and 122 F (-50, 23, and 50 C). Both the loads required to fully compress the seals and their leak rates were directly proportional to the test temperature.

Measurements of spatially resolved velocity variations in shock compressed heterogeneous materials using a line-imaging velocity interferometer

NASA Astrophysics Data System (ADS)

Trott, Wayne M.; Knudson, Marcus D.; Chhabildas, Lalit C.; Asay, James R.

2000-04-01

Relatively straightforward changes in the design of a conventional optically recording velocity interferometer system (ORVIS) can be used to produce a line-imaging instrument that allows adjustment of spatial resolution over a wide range. As a result, line-imaging ORVIS can be tailored to various specific applications involving dynamic deformation of heterogeneous materials as required by their characteristic length scales (ranging from a few μm for ferroelectric ceramics to a few mm for concrete). A line-imaging system has been successfully interfaced to a compressed gas gun driver and fielded on numerous tests in combination with simultaneous dual delay-leg, "push-pull" VISAR measurements. These tests include shock loading of glass-reinforced polyester composites, foam reverberation experiments (measurements at the free surface of a thin aluminum plate impacted by foam), and measurements of dispersive velocity in a shock-loaded explosive simulant (sugar). Results are presented that illustrate the capability for recording detailed spatially resolved material response.

Visual information processing II; Proceedings of the Meeting, Orlando, FL, Apr. 14-16, 1993

NASA Technical Reports Server (NTRS)

Huck, Friedrich O. (Editor); Juday, Richard D. (Editor)

1993-01-01

Various papers on visual information processing are presented. Individual topics addressed include: aliasing as noise, satellite image processing using a hammering neural network, edge-detetion method using visual perception, adaptive vector median filters, design of a reading test for low-vision image warping, spatial transformation architectures, automatic image-enhancement method, redundancy reduction in image coding, lossless gray-scale image compression by predictive GDF, information efficiency in visual communication, optimizing JPEG quantization matrices for different applications, use of forward error correction to maintain image fidelity, effect of peanoscanning on image compression. Also discussed are: computer vision for autonomous robotics in space, optical processor for zero-crossing edge detection, fractal-based image edge detection, simulation of the neon spreading effect by bandpass filtering, wavelet transform (WT) on parallel SIMD architectures, nonseparable 2D wavelet image representation, adaptive image halftoning based on WT, wavelet analysis of global warming, use of the WT for signal detection, perfect reconstruction two-channel rational filter banks, N-wavelet coding for pattern classification, simulation of image of natural objects, number-theoretic coding for iconic systems.

Discrete modelling of front propagation in backward piping erosion

NASA Astrophysics Data System (ADS)

Tran, Duc-Kien; Prime, Noémie; Froiio, Francesco; Callari, Carlo; Vincens, Eric

2017-06-01

A preliminary discrete numerical model of a REV at the front region of an erosion pipe in a cohesive granular soil is briefly presented. The results reported herein refer to a simulation carried out by coupling the Discrete Element Method (DEM) with the Lattice Boltzmann Method (LBM) for the representation of the granular and fluid phases, respectively. The numerical specimen, consisiting of bonded grains, is tested under fully-saturated conditions and increasing pressure difference between the inlet (confined) and the outlet (unconfined) flow regions. The key role of compression arches of force chains that transversely cross the sample and carry most part of the hydrodynamic actions is pointed out. These arches partition the REV into an upstream region that remains almost intact and a downstream region that gradually degrades and is subsequently eroded in the form of a cluster. Eventually, the collapse of the compression arches causes the upstream region to be also eroded, abruptly, as a whole. A complete presentation of the numerical model and of the results of the simulation can be found in [12].

Survey and analysis of multiresolution methods for turbulence data

DOE PAGES

Pulido, Jesus; Livescu, Daniel; Woodring, Jonathan; ...

2015-11-10

This paper compares the effectiveness of various multi-resolution geometric representation methods, such as B-spline, Daubechies, Coiflet and Dual-tree wavelets, curvelets and surfacelets, to capture the structure of fully developed turbulence using a truncated set of coefficients. The turbulence dataset is obtained from a Direct Numerical Simulation of buoyancy driven turbulence on a 512 3 mesh size, with an Atwood number, A = 0.05, and turbulent Reynolds number, Re t = 1800, and the methods are tested against quantities pertaining to both velocities and active scalar (density) fields and their derivatives, spectra, and the properties of constant density surfaces. The comparisonsmore » between the algorithms are given in terms of performance, accuracy, and compression properties. The results should provide useful information for multi-resolution analysis of turbulence, coherent feature extraction, compression for large datasets handling, as well as simulations algorithms based on multi-resolution methods. In conclusion, the final section provides recommendations for best decomposition algorithms based on several metrics related to computational efficiency and preservation of turbulence properties using a reduced set of coefficients.« less

Optimization of plasma amplifiers

DOE PAGES

Sadler, James D.; Trines, Raoul M. G. M.; Tabak, Max; ...

2017-05-24

Here, plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities. We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found tomore » maintain good transverse coherence and high-energy efficiency. Effective compression of a 10kJ, nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier.« less

Relevance of postmortem radiology to the diagnosis of fatal cerebral gas embolism from compressed air diving.

PubMed

Cole, A J; Griffiths, D; Lavender, S; Summers, P; Rich, K

2006-05-01

To test the hypothesis that artefact caused by postmortem off-gassing is at least partly responsible for the presence of gas within the vascular system and tissues of the cadaver following death associated with compressed air diving. Controlled experiment sacrificing sheep after a period of simulated diving in a hyperbaric chamber and carrying out sequential postmortem computed tomography (CT) on the cadavers. All the subject sheep developed significant quantities of gas in the vascular system within 24 hours, as demonstrated by CT and necropsy, while the control animals did not. The presence of gas in the vascular system of human cadavers following diving associated fatalities is to be expected, and is not necessarily connected with gas embolism following pulmonary barotrauma, as has previously been claimed.

Optimization of plasma amplifiers

NASA Astrophysics Data System (ADS)

Sadler, James D.; Trines, Raoul M. Â. G. Â. M.; Tabak, Max; Haberberger, Dan; Froula, Dustin H.; Davies, Andrew S.; Bucht, Sara; Silva, Luís O.; Alves, E. Paulo; Fiúza, Frederico; Ceurvorst, Luke; Ratan, Naren; Kasim, Muhammad F.; Bingham, Robert; Norreys, Peter A.

2017-05-01

Plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities. We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found to maintain good transverse coherence and high-energy efficiency. Effective compression of a 10 kJ , nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier.

A Novel Range Compression Algorithm for Resolution Enhancement in GNSS-SARs.

PubMed

Zheng, Yu; Yang, Yang; Chen, Wu

2017-06-25

In this paper, a novel range compression algorithm for enhancing range resolutions of a passive Global Navigation Satellite System-based Synthetic Aperture Radar (GNSS-SAR) is proposed. In the proposed algorithm, within each azimuth bin, firstly range compression is carried out by correlating a reflected GNSS intermediate frequency (IF) signal with a synchronized direct GNSS base-band signal in the range domain. Thereafter, spectrum equalization is applied to the compressed results for suppressing side lobes to obtain a final range-compressed signal. Both theoretical analysis and simulation results have demonstrated that significant range resolution improvement in GNSS-SAR images can be achieved by the proposed range compression algorithm, compared to the conventional range compression algorithm.

Trajectory NG: portable, compressed, general molecular dynamics trajectories.

PubMed

Spångberg, Daniel; Larsson, Daniel S D; van der Spoel, David

2011-10-01

We present general algorithms for the compression of molecular dynamics trajectories. The standard ways to store MD trajectories as text or as raw binary floating point numbers result in very large files when efficient simulation programs are used on supercomputers. Our algorithms are based on the observation that differences in atomic coordinates/velocities, in either time or space, are generally smaller than the absolute values of the coordinates/velocities. Also, it is often possible to store values at a lower precision. We apply several compression schemes to compress the resulting differences further. The most efficient algorithms developed here use a block sorting algorithm in combination with Huffman coding. Depending on the frequency of storage of frames in the trajectory, either space, time, or combinations of space and time differences are usually the most efficient. We compare the efficiency of our algorithms with each other and with other algorithms present in the literature for various systems: liquid argon, water, a virus capsid solvated in 15 mM aqueous NaCl, and solid magnesium oxide. We perform tests to determine how much precision is necessary to obtain accurate structural and dynamic properties, as well as benchmark a parallelized implementation of the algorithms. We obtain compression ratios (compared to single precision floating point) of 1:3.3-1:35 depending on the frequency of storage of frames and the system studied.

Choice of word length in the design of a specialized hardware for lossless wavelet compression of medical images

NASA Astrophysics Data System (ADS)

Urriza, Isidro; Barragan, Luis A.; Artigas, Jose I.; Garcia, Jose I.; Navarro, Denis

1997-11-01

Image compression plays an important role in the archiving and transmission of medical images. Discrete cosine transform (DCT)-based compression methods are not suitable for medical images because of block-like image artifacts that could mask or be mistaken for pathology. Wavelet transforms (WTs) are used to overcome this problem. When implementing WTs in hardware, finite precision arithmetic introduces quantization errors. However, lossless compression is usually required in the medical image field. Thus, the hardware designer must look for the optimum register length that, while ensuring the lossless accuracy criteria, will also lead to a high-speed implementation with small chip area. In addition, wavelet choice is a critical issue that affects image quality as well as system design. We analyze the filters best suited to image compression that appear in the literature. For them, we obtain the maximum quantization errors produced in the calculation of the WT components. Thus, we deduce the minimum word length required for the reconstructed image to be numerically identical to the original image. The theoretical results are compared with experimental results obtained from algorithm simulations on random test images. These results enable us to compare the hardware implementation cost of the different filter banks. Moreover, to reduce the word length, we have analyzed the case of increasing the integer part of the numbers while maintaining constant the word length when the scale increases.

Research on the response characteristics of solenoid valve of the air-jet loom by simulation

NASA Astrophysics Data System (ADS)

Jin, Yuzhen; Deng, Ruoyu; Jin, Yingzi; Hu, Xudong

2013-12-01

Solenoid valve is one of the executive parts of weft insertion control system. According to the response characteristics of the solenoid valve, an improved design becomes a necessity. Firstly, the numerical model was established after analyzing the solenoid valve during its start-up and shut-down. Comparing the simulation data with the practical data, it is verified that the numerical simulation model has a high feasibility. Secondly, excitation voltage and spring pre-compression were adjusted respectively, and the response rules after adjusting were investigated. The research of the study shows: the response time tends to be inverse proportional to the excitation voltage during start-up, and it becomes a constant value with the increase of the excitation voltage; the response time is proportional to the spring pre-compression when the solenoid valve starts up, it is inverse proportional to spring pre-compression when the solenoid valve shuts down. And the total response time is a constant value with the increase of the spring pre-compression. Therefore, the value of the excitation voltage and the spring pre-compression should be selected when the curve is becoming flatten. The results of the research can provide the reference to the further development of the solenoid valve.

The Role of Fluid Compression in Particle Energization during Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Li, X.; Guo, F.; Li, H.; Li, S.

2017-12-01

Theories of particle transport and acceleration have shown that fluid compression is the leading mechanism for particle energization. However, the role of compression in particle energization during magnetic reconnection is unclear. We present a cluster of studies to clarify and show the effect of fluid compression in accelerating particles to high energies during magnetic reconnection. Using fully kinetic reconnection simulations, we show that fluid compression is the leading mechanism for high-energy particle energization. We find that the compressional energization is more important in a low-beta plasma or in a reconnection layer with a weak guide field (the magnetic field component perpendicular to the reconnecting magnetic field), which are relevant to solar flares. Our analysis on 3D kinetic simulations shows that the self-generated turbulence scatters particles and enhances the particle diffusion processes in the acceleration regions. Based on these results, we then study large-scale reconnection acceleration by solving the particle transport equation in a large-scale reconnection layer evolved with MHD simulations. Due to the compressional effect, particles are accelerated to high energies and develop power-law energy distributions. This study clarifies the nature of particle acceleration in reconnection layer and is important to understand particle energization during large-scale acceleration such as solar flares.

Improvement of shallow landslide prediction accuracy using soil parameterisation for a granite area in South Korea

NASA Astrophysics Data System (ADS)

Kim, M. S.; Onda, Y.; Kim, J. K.

2015-01-01

SHALSTAB model applied to shallow landslides induced by rainfall to evaluate soil properties related with the effect of soil depth for a granite area in Jinbu region, Republic of Korea. Soil depth measured by a knocking pole test and two soil parameters from direct shear test (a and b) as well as one soil parameters from a triaxial compression test (c) were collected to determine the input parameters for the model. Experimental soil data were used for the first simulation (Case I) and, soil data represented the effect of measured soil depth and average soil depth from soil data of Case I were used in the second (Case II) and third simulations (Case III), respectively. All simulations were analysed using receiver operating characteristic (ROC) analysis to determine the accuracy of prediction. ROC analysis results for first simulation showed the low ROC values under 0.75 may be due to the internal friction angle and particularly the cohesion value. Soil parameters calculated from a stochastic hydro-geomorphological model were applied to the SHALSTAB model. The accuracy of Case II and Case III using ROC analysis showed higher accuracy values rather than first simulation. Our results clearly demonstrate that the accuracy of shallow landslide prediction can be improved when soil parameters represented the effect of soil thickness.

Modeling of turbulent separated flows for aerodynamic applications

NASA Technical Reports Server (NTRS)

Marvin, J. G.

1983-01-01

Steady, high speed, compressible separated flows modeled through numerical simulations resulting from solutions of the mass-averaged Navier-Stokes equations are reviewed. Emphasis is placed on benchmark flows that represent simplified (but realistic) aerodynamic phenomena. These include impinging shock waves, compression corners, glancing shock waves, trailing edge regions, and supersonic high angle of attack flows. A critical assessment of modeling capabilities is provided by comparing the numerical simulations with experiment. The importance of combining experiment, numerical algorithm, grid, and turbulence model to effectively develop this potentially powerful simulation technique is stressed.

Numerical simulation of air hypersonic flows with equilibrium chemical reactions

NASA Astrophysics Data System (ADS)

Emelyanov, Vladislav; Karpenko, Anton; Volkov, Konstantin

2018-05-01

The finite volume method is applied to solve unsteady three-dimensional compressible Navier-Stokes equations on unstructured meshes. High-temperature gas effects altering the aerodynamics of vehicles are taken into account. Possibilities of the use of graphics processor units (GPUs) for the simulation of hypersonic flows are demonstrated. Solutions of some test cases on GPUs are reported, and a comparison between computational results of equilibrium chemically reacting and perfect air flowfields is performed. Speedup of solution on GPUs with respect to the solution on central processor units (CPUs) is compared. The results obtained provide promising perspective for designing a GPU-based software framework for practical applications.

Propulsion simulator for magnetically-suspended wind tunnel models

NASA Technical Reports Server (NTRS)

Joshi, Prakash B.; Goldey, C. L.; Sacco, G. P.; Lawing, Pierce L.

1991-01-01

The objective of phase two of a current investigation sponsored by NASA Langley Research Center is to demonstrate the measurement of aerodynamic forces/moments, including the effects of exhaust gases, in magnetic suspension and balance system (MSBS) wind tunnels. Two propulsion simulator models are being developed: a small-scale and a large-scale unit, both employing compressed, liquified carbon dioxide as propellant. The small-scale unit was designed, fabricated, and statically-tested at Physical Sciences Inc. (PSI). The large-scale simulator is currently in the preliminary design stage. The small-scale simulator design/development is presented, and the data from its static firing on a thrust stand are discussed. The analysis of this data provides important information for the design of the large-scale unit. A description of the preliminary design of the device is also presented.

Simulations of Bubble Motion in an Oscillating Liquid

NASA Astrophysics Data System (ADS)

Kraynik, A. M.; Romero, L. A.; Torczynski, J. R.

2010-11-01

Finite-element simulations are used to investigate the motion of a gas bubble in a liquid undergoing vertical vibration. The effect of bubble compressibility is studied by comparing "compressible" bubbles that obey the ideal gas law with "incompressible" bubbles that are taken to have constant volume. Compressible bubbles exhibit a net downward motion away from the free surface that does not exist for incompressible bubbles. Net (rectified) velocities are extracted from the simulations and compared with theoretical predictions. The dependence of the rectified velocity on ambient gas pressure, bubble diameter, and bubble depth are in agreement with the theory. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

pyPcazip: A PCA-based toolkit for compression and analysis of molecular simulation data

NASA Astrophysics Data System (ADS)

Shkurti, Ardita; Goni, Ramon; Andrio, Pau; Breitmoser, Elena; Bethune, Iain; Orozco, Modesto; Laughton, Charles A.

The biomolecular simulation community is currently in need of novel and optimised software tools that can analyse and process, in reasonable timescales, the large generated amounts of molecular simulation data. In light of this, we have developed and present here pyPcazip: a suite of software tools for compression and analysis of molecular dynamics (MD) simulation data. The software is compatible with trajectory file formats generated by most contemporary MD engines such as AMBER, CHARMM, GROMACS and NAMD, and is MPI parallelised to permit the efficient processing of very large datasets. pyPcazip is a Unix based open-source software (BSD licenced) written in Python.

Simulating the Impact of Premixed Charge Compression Ignition on Light-Duty Diesel Fuel Economy and Emissions of Particulates and NOx

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Zhiming; Daw, C Stuart; Wagner, Robert M

2013-01-01

We utilize the Powertrain Systems Analysis Toolkit (PSAT) combined with transient engine and aftertreatment component models implemented in Matlab/Simulink to simulate the effect of premixed charge compression ignition (PCCI) on the fuel economy and emissions of light-duty diesel-powered conventional and hybrid electric vehicles (HEVs). Our simulated engine is capable of both conventional diesel combustion (CDC) and premixed charge compression ignition (PCCI) over real transient driving cycles. Our simulated aftertreatment train consists of a diesel oxidation catalyst (DOC), lean NOx trap (LNT), and catalyzed diesel particulate filter (DPF). The results demonstrate that, in the simulated conventional vehicle, PCCI can significantly reducemore » fuel consumption and emissions by reducing the need for LNT and DPF regeneration. However, the opportunity for PCCI operation in the simulated HEV is limited because the engine typically experiences higher loads and multiple stop-start transients that are outside the allowable PCCI operating range. Thus developing ways of extending the PCCI operating range combined with improved control strategies for engine and emissions control management will be especially important for realizing the potential benefits of PCCI in HEVs.« less

Compression After Impact Testing of Sandwich Structures Using the Four Point Bend Test

NASA Technical Reports Server (NTRS)

Nettles, Alan T.; Gregory, Elizabeth; Jackson, Justin; Kenworthy, Devon

2008-01-01

For many composite laminated structures, the design is driven by data obtained from Compression after Impact (CAI) testing. There currently is no standard for CAI testing of sandwich structures although there is one for solid laminates of a certain thickness and lay-up configuration. Most sandwich CAI testing has followed the basic technique of this standard where the loaded ends are precision machined and placed between two platens and compressed until failure. If little or no damage is present during the compression tests, the loaded ends may need to be potted to prevent end brooming. By putting a sandwich beam in a four point bend configuration, the region between the inner supports is put under a compressive load and a sandwich laminate with damage can be tested in this manner without the need for precision machining. Also, specimens with no damage can be taken to failure so direct comparisons between damaged and undamaged strength can be made. Data is presented that demonstrates the four point bend CAI test and is compared with end loaded compression tests of the same sandwich structure.

Self-similar regimes of turbulence in weakly coupled plasmas under compression

NASA Astrophysics Data System (ADS)

Viciconte, Giovanni; Gréa, Benoît-Joseph; Godeferd, Fabien S.

2018-02-01

Turbulence in weakly coupled plasmas under compression can experience a sudden dissipation of kinetic energy due to the abrupt growth of the viscosity coefficient governed by the temperature increase. We investigate in detail this phenomenon by considering a turbulent velocity field obeying the incompressible Navier-Stokes equations with a source term resulting from the mean velocity. The system can be simplified by a nonlinear change of variable, and then solved using both highly resolved direct numerical simulations and a spectral model based on the eddy-damped quasinormal Markovian closure. The model allows us to explore a wide range of initial Reynolds and compression numbers, beyond the reach of simulations, and thus permits us to evidence the presence of a nonlinear cascade phase. We find self-similarity of intermediate regimes as well as of the final decay of turbulence, and we demonstrate the importance of initial distribution of energy at large scales. This effect can explain the global sensitivity of the flow dynamics to initial conditions, which we also illustrate with simulations of compressed homogeneous isotropic turbulence and of imploding spherical turbulent layers relevant to inertial confinement fusion.

Ethane-xenon mixtures under shock conditions

NASA Astrophysics Data System (ADS)

Flicker, Dawn; Magyar, Rudolph; Root, Seth; Cochrane, Kyle; Mattsson, Thomas

2015-06-01

Mixtures of light and heavy elements arise in inertial confinement fusion and planetary science. We present results on the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT/QMD) at elevated-temperature and pressure is used to obtain the properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. To validate the QMD simulations, we performed high-precision shock compression experiments using Sandia's Z-Machine. A bond tracking analysis of the simulations correlates the sharp rise in the Hugoniot curve with completion of dissociation in ethane. DFT-based simulation results compare well with experimental data and are used to provide insight into the dissociation as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for ethane, Xe-ethane, polymethyl-pentene, and polystyrene, suggesting that a limiting compression exists for C-C bonded systems. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, Security Administration under contract DE-AC04-94AL85000.