Jae Pahk - Academia.edu (original) (raw)

Papers by Jae Pahk

Research paper thumbnail of Biomechanical Assessment of the Bridging Vein Rupture of Blast-Induced Traumatic Brain Injury Using the Finite Element Human Head Model

ABSTRACT The incidence of the blast-induced traumatic brain injury (bTBI) among American troops i... more ABSTRACT The incidence of the blast-induced traumatic brain injury (bTBI) among American troops in battle environments is dramatically high in recent years. Shock wave, a production of detonation, is a brief and acute overpressure wave that travels supersonically with a magnitude which can be several times higher than atmospheric pressure. Primary bTBI means that human exposure to shock wave itself without any other impact of solid objects can still result in the impairment of cerebral tissues. The mechanism of this type of brain injury is different from that of the conventional TBI, and has not been fully understood. So far, it is believed that the shock wave transmitted through skull and into cerebral tissues may induce specific injury patterns. This study is trying to develop a methodology to numerically investigate the mechanism of the blast-induced subdural hematoma (bSDH), which is caused by bridging vein rupture. The effort of this study can be divided to three major parts: first, a finite element (FE) model of human head is developed from the magnetic resonance imaging (MRI) of a real human head to contain skull, CSF and brain. Numerically simulated shock waves transmits through the human head model whose mechanical responses are recorded; second, in order to obtain the mechanical properties of human bridging vein, an standard inflation test of blood vessels is conducted on a real human bridging vein sample gained from autopsy. Material parameters are found by fitting the experimental data to an anisotropic hyperelastic constitutive model for blood vessel (Gerhard A. Holzapfel 2000); third, The bridging vein rupture in bTBI is evaluated by the finite element analysis of a separate human bridging vein model under the external loadings in terms of the internal pressure and relative skull-brain motion which are extracted from the mechanical response of the subarachnoid space of the head in the blast-head simulation of the first part.

Research paper thumbnail of Computational Study of Human Head Response to Primary Blast Waves of Five Levels from Three Directions

PLoS ONE, 2014

Human exposure to blast waves without any fragment impacts can still result in primary blast-indu... more Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts.

Research paper thumbnail of Experimental study of pneumatic conveying by various methods of analysis

Pneumatic transport of solids is widely used due to many of its advantages. Many studies have bee... more Pneumatic transport of solids is widely used due to many of its advantages. Many studies have been carried out to explore the details of the transport of solids with pneumatic conveying with the aim to develop enhanced operations. The flow pattern seen in pneumatic conveying can vary widely depending on the gas velocity, the solid feed rate and the characteristics of the solid. In this study a deeper understanding of the interactions of the parameters has been explored using classical signal analysis of pressure fluctuations.Experiments on dilute phase pneumatic transport were performed using polyester, polystyrene, and polyolefin pellets. Material properties such as mean diameter of polymer pellets and density of each polymer have been determined. The parameters of gas velocity and the solid loading ratio were varied producing the distinct pressure gradients which were measured at three different locations: vertical, lower and upper horizontal sections of the piping arrangement. Using these data, a phase space analysis, a power spectral density (PSD) analysis, a fractal dimension analysis, and a rescaled range analysis with Hursti¯s exponents were carried out to try to develop means to identify the flow conditions using simple pressure transducers. By taking a high speed video of the flow process through the transparent section in the pipe, the flow pattern was visually observed and unique dynamics were seen for the polyolefin particles. Furthermore, by using a wavelet analysis to decompose the original signal, noting the contributions due to the blower and feeder, the flow - pressure fluctuation yielded information about details of the particle-gas interaction.

Research paper thumbnail of Local Friction Forces Between Plug and Pipe Wall in Dense Phase Pneumatic Conveying

Dense phase pneumatic conveying is widely used to transport granular materials or powder due to i... more Dense phase pneumatic conveying is widely used to transport granular materials or powder due to its efficiencies gained on cost and abrasion and erosion. To date these systems have been designed and analyzed using average frictional representation for the conveyed plug. This study explorer the effect of this friction force at a single point by measuring strains on the pipe wall when the plug is moving passed the strain rosette installed directly in the inner pipe wall. Strains on axial and circumferential direction of plug flow measured from four different locations, top, bottom, front side, and back side of inner pipe wall. Dynamics strains with the sampling frequency of 10 KHz were measured by using data acquisition card with related software. In this study, comparison the magnitude of the strain under different plug velocity, plug length, and different material transported will be presented. It was found that the magnitude of the axial direction of strain was higher than the one ...

Research paper thumbnail of Computational Study on the Bridging Vein Rupture of Blast-Induced Traumatic Brain Injury Using a Numerical Human Head Model

ABSTRACT The occurrence of blast-induced traumatic brain injury (bTBI) in people serving in battl... more ABSTRACT The occurrence of blast-induced traumatic brain injury (bTBI) in people serving in battle environments is dramatically high. The blast front, or leading edge of the shock wave is a brief, acute overpressure wave that travels supersonically with a magnitude that is several times higher than that of ambient. The shock wave propagates through the human head and injures intracranial tissues. Classical neuropathologic signs of bTBI include cerebral contusion, diffuse axonal injury, subdural hematoma (SDH) and subarachnoid hematoma, of which subdural hematoma is the most dominating sign of bTBI. Here, computational finite element (FE) modeling is used to investigate the mechanical process of bTBI. The overall goal of the present study is to find the injury threshold of the SDH injury due to bTBI, by investigating the biomechanical response of the bridging veins in the human brain under shock wave loading that originates from detonation. This research mainly develops a basic FE human head model which consists of skull and parts of the brain. The geometric models of skull and brain are developed from segmentations of magnetic resonance imaging (MRI) files of a real human head. The boundary conditions on the neck and head are modeled as a displacement-fixed condition. The numerically simulated blast waves are applied on the human head model as external loading conditions. The internal response in the subarachnoid space is used as loadings on the bridging vein submodel. The maximum principal stress of the bridging vein is used to determine the whether there is failure of the bridging vein, thus estimating the “injury threshold” of SDH in bTBI. Results show that 150g TNT blast of 1 meter away from the head can result in a high possibility of SDH occurrence.

Research paper thumbnail of Frictional force measurement between a single plug and the pipe wall in dense phase pneumatic conveying

Powder Technology, 2012

A new measurement technique to determine the frictional force between a plug and the pipe wall in... more A new measurement technique to determine the frictional force between a plug and the pipe wall in dense phase pneumatic conveying was developed. Four strain gauges were installed on the outer surface of the pipe wall and strains were measured at different locations (top, back, bottom, and front) of the pipe wall, where the strain signals were obtained. The frictional forces were determined for different experimental conditions such as the superficial air velocity and the amount of material being transported. Polyester and polystyrenes with different size and shape, and polyolefin materials were tested in this study. It was found that the frictional force is related to the plug length as well as material properties such as size, shape of the polymer particles and contact area with the wall. In addition, it was found that the frictional force was the highest at the top or sides of the pipe and was smallest at the bottom of the pipe depending on the particle characteristics. The ratio of shear stress to the overall driving pressure for the plug decreased when the plug length is increased.

Research paper thumbnail of Assessing Flow Regimes from Pressure Fluctuations in Pneumatic Conveying of Polymer Pellets

Particulate Science and Technology, 2008

Relating pressure fluctuations to the various flow regimes in dilute phase pneumatic conveying sy... more Relating pressure fluctuations to the various flow regimes in dilute phase pneumatic conveying systems and exploring the effects of the variations of a number of intrinsic flow parameters through the analysis of complex pressure signals are of importance. To explore the pressure fluctuations, a series of experiments were conducted by monitoring the pressure drop and its fluctuations in horizontal and vertical pipe sections of an experimental conveying rig of industrial relevance. Observed pressure signals contained not only the effects of flow rates of conveyed polymeric solid particles and the conveying air, but also the effects of the pipe orientation, solids feeder, and the air blower employed. Time series of the observed pressure signals were analyzed in order to obtain information about the relations based on four different analysis techniques: power spectral density (PSD) analysis, phase space diagram, rescaled range analysis, and wavelet analysis. The sampling frequency of the study was determined through the application of the PSD analysis. Variations in gas and particle flow rates were found that could be traced by the locations of the dominant peaks on the frequency axis of spectrum plots generated from the PSD analysis. Additionally, the level of multiplicity of such dominant PSD peaks pointed to the differences in the flow behavior between the interconnected vertical and horizontal pipe sections. Variations in the Hurst's exponent of the rescaled range analysis technique with the solids loading ratios were found relatable to the observed flow regimes prevailing in the pneumatic conveying system studied. Eccentricity ratios and the number of attractors of the phase space diagrams provided further information about the effects of the changes in solids loading ratios on the flow behavior and the flow mode, respectively. The wavelet analysis, through its detailed signals at different scale levels, helped to give information from the pressure fluctuations. Unique frequencies were determined that corresponded to certain flow behaviors and devices, gas-particle interactions, the mechanical blower, and feeder units. This finding enabled the investigation of the intrinsic flow behavior by filtering out the signals caused by such mechanical devices.

Research paper thumbnail of Voidage Measurement for a Moving Plug in Dense Phase Pneumatic Conveying Using Two Different Methods

Particulate Science and Technology, 2010

ABSTRACT Two simple ways to measure voidage in a moving plug in dense phase pneumatic conveying h... more ABSTRACT Two simple ways to measure voidage in a moving plug in dense phase pneumatic conveying have been explored, along with voidage behavior and other parameters. The first method (bulk solid method) determines the average voidage for a single plug, by measuring the length and the weight of the plug, while the second method (Ergun's method) determines the voidage along the plug length from plug head to tail by using the Ergun equation. The experiments were performed under different experimental conditions of plug lengths, gas velocities, and materials. The results from both methods showed varying degrees of agreement, depending on the material transported. The measurements also found that the voidage varied only slightly with the plug velocity. However, it did vary more within the plug (e.g., plug head, middle of plug, and plug tail).

Research paper thumbnail of Comparison of flow characteristics for dilute phase pneumatic conveying for two different plastic pellets

Journal of the Chinese Institute of Chemical Engineers, 2008

A series of dilute phase pneumatic conveying experiments using two different types of plastic pel... more A series of dilute phase pneumatic conveying experiments using two different types of plastic pellets has led to the determination and development of distinguishing flow characteristics. Separate experiments on polystyrene and polyolefin pellets captured pressure-drop fluctuations and values at two different measuring points—one at the lower horizontal section of the transporting pipe and another at the upper section and at two different solid-loading ratios for each material.Also, comparison and analysis of the pressure-drop fluctuations and values obtained from the experiments were carried out under the same solid-loading ratio and blower rotational speed for both materials. Basic pressure drop calculations were made to find pressure drop due to pure gas, and that due to the presence of solids using a solid friction factor. In addition, the power spectral density analysis, and the wavelet analysis were conducted for both materials to evaluate the flow characteristics.

Research paper thumbnail of Experimental Study of Pressure Fluctuation in Pneumatic Conveying by Various Methods of Analysis

Pneumatic transport of solids is widely used due to many of its advantages. Many studies have bee... more Pneumatic transport of solids is widely used due to many of its advantages. Many studies have been carried out to explore the details of the transport of solids with pneumatic conveying with the aim to develop enhanced operations. The flow pattern seen in pneumatic conveying can vary widely depending on the gas velocity, the solid feed rate and the characteristics of the solid. In this study a deeper understanding of the interactions of the parameters has been explored using classical signal analysis of pressure fluctuations. Experiments on dilute phase pneumatic transport were performed using polyester, polystyrene, and polyolefin pellets. Material properties such as mean diameter of polymer pellets and density of each polymer have been determined. The parameters of gas velocity and the solid loading ratio were varied producing the distinct pressure gradients which were measured at three different locations: vertical, lower and upper horizontal sections of the piping arrangement. Using these data, a phase space analysis, a power spectral density (PSD) analysis, a fractal dimension analysis, and a rescaled range analysis with Hurst's exponents were carried out to try to develop means to identify the flow conditions using simple pressure transducers. By taking a high speed video of the flow process through the transparent section in the pipe, the flow pattern was visually observed and unique dynamics were seen for the polyolefin particles.

Research paper thumbnail of Frictional Force Measurement for Multiple Plugs in Dense Phase Pneumatic Conveying of Polymer Particles: An Industry Application

Industrial & Engineering Chemistry Research, 2012

ABSTRACT Frictional forces between particles and the pipe wall in dense phase pneumatic conveying... more ABSTRACT Frictional forces between particles and the pipe wall in dense phase pneumatic conveying were determined using strain gauges attached to the outside of the pipe wall. To perform the frictional force measurement, a special strain measurement section was designed and inserted in the industrial scale pneumatic conveying system. Three different polymer particles, polyolefin elastomer, polyethylene, and SARAN were transported under the different flow conditions of the superficial air velocity and the mass flow rate of solids. The frictional forces were determined from three different locations of the pipe wall, top, bottom, and sides of the pipe. The plug velocity and plug length were also determined by analyzing pressure signals measured at two different locations. The magnitude of frictional force was found to be proportional to the plug length. In general, the largest frictional forces were measured at the top of the pipe. In addition, the frictional forces were related to the particle’s interaction with the pipe (i.e., the area of contact of individual particle and number of particles that interact with the pipe wall) as well as the material properties. It was also found that the minimum fluidization of the particles could be related to the strain signal fluctuations. Materials with a smaller minimum fluidization velocity showed more fluctuations and thus have less stable operation. The results obtained were compared to the smaller scale laboratory pneumatic conveying system previously performed.(1)

Research paper thumbnail of Computational Study of Human Head Response to Primary Blast Waves of Five Levels from Three Directions

PLoS ONE, 2014

Human exposure to blast waves without any fragment impacts can still result in primary blast-indu... more Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts.

Research paper thumbnail of Biomechanical Assessment of the Bridging Vein Rupture of Blast-Induced Traumatic Brain Injury Using the Finite Element Human Head Model

ABSTRACT The incidence of the blast-induced traumatic brain injury (bTBI) among American troops i... more ABSTRACT The incidence of the blast-induced traumatic brain injury (bTBI) among American troops in battle environments is dramatically high in recent years. Shock wave, a production of detonation, is a brief and acute overpressure wave that travels supersonically with a magnitude which can be several times higher than atmospheric pressure. Primary bTBI means that human exposure to shock wave itself without any other impact of solid objects can still result in the impairment of cerebral tissues. The mechanism of this type of brain injury is different from that of the conventional TBI, and has not been fully understood. So far, it is believed that the shock wave transmitted through skull and into cerebral tissues may induce specific injury patterns. This study is trying to develop a methodology to numerically investigate the mechanism of the blast-induced subdural hematoma (bSDH), which is caused by bridging vein rupture. The effort of this study can be divided to three major parts: first, a finite element (FE) model of human head is developed from the magnetic resonance imaging (MRI) of a real human head to contain skull, CSF and brain. Numerically simulated shock waves transmits through the human head model whose mechanical responses are recorded; second, in order to obtain the mechanical properties of human bridging vein, an standard inflation test of blood vessels is conducted on a real human bridging vein sample gained from autopsy. Material parameters are found by fitting the experimental data to an anisotropic hyperelastic constitutive model for blood vessel (Gerhard A. Holzapfel 2000); third, The bridging vein rupture in bTBI is evaluated by the finite element analysis of a separate human bridging vein model under the external loadings in terms of the internal pressure and relative skull-brain motion which are extracted from the mechanical response of the subarachnoid space of the head in the blast-head simulation of the first part.

Research paper thumbnail of Computational Study of Human Head Response to Primary Blast Waves of Five Levels from Three Directions

PLoS ONE, 2014

Human exposure to blast waves without any fragment impacts can still result in primary blast-indu... more Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts.

Research paper thumbnail of Experimental study of pneumatic conveying by various methods of analysis

Pneumatic transport of solids is widely used due to many of its advantages. Many studies have bee... more Pneumatic transport of solids is widely used due to many of its advantages. Many studies have been carried out to explore the details of the transport of solids with pneumatic conveying with the aim to develop enhanced operations. The flow pattern seen in pneumatic conveying can vary widely depending on the gas velocity, the solid feed rate and the characteristics of the solid. In this study a deeper understanding of the interactions of the parameters has been explored using classical signal analysis of pressure fluctuations.Experiments on dilute phase pneumatic transport were performed using polyester, polystyrene, and polyolefin pellets. Material properties such as mean diameter of polymer pellets and density of each polymer have been determined. The parameters of gas velocity and the solid loading ratio were varied producing the distinct pressure gradients which were measured at three different locations: vertical, lower and upper horizontal sections of the piping arrangement. Using these data, a phase space analysis, a power spectral density (PSD) analysis, a fractal dimension analysis, and a rescaled range analysis with Hursti¯s exponents were carried out to try to develop means to identify the flow conditions using simple pressure transducers. By taking a high speed video of the flow process through the transparent section in the pipe, the flow pattern was visually observed and unique dynamics were seen for the polyolefin particles. Furthermore, by using a wavelet analysis to decompose the original signal, noting the contributions due to the blower and feeder, the flow - pressure fluctuation yielded information about details of the particle-gas interaction.

Research paper thumbnail of Local Friction Forces Between Plug and Pipe Wall in Dense Phase Pneumatic Conveying

Dense phase pneumatic conveying is widely used to transport granular materials or powder due to i... more Dense phase pneumatic conveying is widely used to transport granular materials or powder due to its efficiencies gained on cost and abrasion and erosion. To date these systems have been designed and analyzed using average frictional representation for the conveyed plug. This study explorer the effect of this friction force at a single point by measuring strains on the pipe wall when the plug is moving passed the strain rosette installed directly in the inner pipe wall. Strains on axial and circumferential direction of plug flow measured from four different locations, top, bottom, front side, and back side of inner pipe wall. Dynamics strains with the sampling frequency of 10 KHz were measured by using data acquisition card with related software. In this study, comparison the magnitude of the strain under different plug velocity, plug length, and different material transported will be presented. It was found that the magnitude of the axial direction of strain was higher than the one ...

Research paper thumbnail of Computational Study on the Bridging Vein Rupture of Blast-Induced Traumatic Brain Injury Using a Numerical Human Head Model

ABSTRACT The occurrence of blast-induced traumatic brain injury (bTBI) in people serving in battl... more ABSTRACT The occurrence of blast-induced traumatic brain injury (bTBI) in people serving in battle environments is dramatically high. The blast front, or leading edge of the shock wave is a brief, acute overpressure wave that travels supersonically with a magnitude that is several times higher than that of ambient. The shock wave propagates through the human head and injures intracranial tissues. Classical neuropathologic signs of bTBI include cerebral contusion, diffuse axonal injury, subdural hematoma (SDH) and subarachnoid hematoma, of which subdural hematoma is the most dominating sign of bTBI. Here, computational finite element (FE) modeling is used to investigate the mechanical process of bTBI. The overall goal of the present study is to find the injury threshold of the SDH injury due to bTBI, by investigating the biomechanical response of the bridging veins in the human brain under shock wave loading that originates from detonation. This research mainly develops a basic FE human head model which consists of skull and parts of the brain. The geometric models of skull and brain are developed from segmentations of magnetic resonance imaging (MRI) files of a real human head. The boundary conditions on the neck and head are modeled as a displacement-fixed condition. The numerically simulated blast waves are applied on the human head model as external loading conditions. The internal response in the subarachnoid space is used as loadings on the bridging vein submodel. The maximum principal stress of the bridging vein is used to determine the whether there is failure of the bridging vein, thus estimating the “injury threshold” of SDH in bTBI. Results show that 150g TNT blast of 1 meter away from the head can result in a high possibility of SDH occurrence.

Research paper thumbnail of Frictional force measurement between a single plug and the pipe wall in dense phase pneumatic conveying

Powder Technology, 2012

A new measurement technique to determine the frictional force between a plug and the pipe wall in... more A new measurement technique to determine the frictional force between a plug and the pipe wall in dense phase pneumatic conveying was developed. Four strain gauges were installed on the outer surface of the pipe wall and strains were measured at different locations (top, back, bottom, and front) of the pipe wall, where the strain signals were obtained. The frictional forces were determined for different experimental conditions such as the superficial air velocity and the amount of material being transported. Polyester and polystyrenes with different size and shape, and polyolefin materials were tested in this study. It was found that the frictional force is related to the plug length as well as material properties such as size, shape of the polymer particles and contact area with the wall. In addition, it was found that the frictional force was the highest at the top or sides of the pipe and was smallest at the bottom of the pipe depending on the particle characteristics. The ratio of shear stress to the overall driving pressure for the plug decreased when the plug length is increased.

Research paper thumbnail of Assessing Flow Regimes from Pressure Fluctuations in Pneumatic Conveying of Polymer Pellets

Particulate Science and Technology, 2008

Relating pressure fluctuations to the various flow regimes in dilute phase pneumatic conveying sy... more Relating pressure fluctuations to the various flow regimes in dilute phase pneumatic conveying systems and exploring the effects of the variations of a number of intrinsic flow parameters through the analysis of complex pressure signals are of importance. To explore the pressure fluctuations, a series of experiments were conducted by monitoring the pressure drop and its fluctuations in horizontal and vertical pipe sections of an experimental conveying rig of industrial relevance. Observed pressure signals contained not only the effects of flow rates of conveyed polymeric solid particles and the conveying air, but also the effects of the pipe orientation, solids feeder, and the air blower employed. Time series of the observed pressure signals were analyzed in order to obtain information about the relations based on four different analysis techniques: power spectral density (PSD) analysis, phase space diagram, rescaled range analysis, and wavelet analysis. The sampling frequency of the study was determined through the application of the PSD analysis. Variations in gas and particle flow rates were found that could be traced by the locations of the dominant peaks on the frequency axis of spectrum plots generated from the PSD analysis. Additionally, the level of multiplicity of such dominant PSD peaks pointed to the differences in the flow behavior between the interconnected vertical and horizontal pipe sections. Variations in the Hurst's exponent of the rescaled range analysis technique with the solids loading ratios were found relatable to the observed flow regimes prevailing in the pneumatic conveying system studied. Eccentricity ratios and the number of attractors of the phase space diagrams provided further information about the effects of the changes in solids loading ratios on the flow behavior and the flow mode, respectively. The wavelet analysis, through its detailed signals at different scale levels, helped to give information from the pressure fluctuations. Unique frequencies were determined that corresponded to certain flow behaviors and devices, gas-particle interactions, the mechanical blower, and feeder units. This finding enabled the investigation of the intrinsic flow behavior by filtering out the signals caused by such mechanical devices.

Research paper thumbnail of Voidage Measurement for a Moving Plug in Dense Phase Pneumatic Conveying Using Two Different Methods

Particulate Science and Technology, 2010

ABSTRACT Two simple ways to measure voidage in a moving plug in dense phase pneumatic conveying h... more ABSTRACT Two simple ways to measure voidage in a moving plug in dense phase pneumatic conveying have been explored, along with voidage behavior and other parameters. The first method (bulk solid method) determines the average voidage for a single plug, by measuring the length and the weight of the plug, while the second method (Ergun's method) determines the voidage along the plug length from plug head to tail by using the Ergun equation. The experiments were performed under different experimental conditions of plug lengths, gas velocities, and materials. The results from both methods showed varying degrees of agreement, depending on the material transported. The measurements also found that the voidage varied only slightly with the plug velocity. However, it did vary more within the plug (e.g., plug head, middle of plug, and plug tail).

Research paper thumbnail of Comparison of flow characteristics for dilute phase pneumatic conveying for two different plastic pellets

Journal of the Chinese Institute of Chemical Engineers, 2008

A series of dilute phase pneumatic conveying experiments using two different types of plastic pel... more A series of dilute phase pneumatic conveying experiments using two different types of plastic pellets has led to the determination and development of distinguishing flow characteristics. Separate experiments on polystyrene and polyolefin pellets captured pressure-drop fluctuations and values at two different measuring points—one at the lower horizontal section of the transporting pipe and another at the upper section and at two different solid-loading ratios for each material.Also, comparison and analysis of the pressure-drop fluctuations and values obtained from the experiments were carried out under the same solid-loading ratio and blower rotational speed for both materials. Basic pressure drop calculations were made to find pressure drop due to pure gas, and that due to the presence of solids using a solid friction factor. In addition, the power spectral density analysis, and the wavelet analysis were conducted for both materials to evaluate the flow characteristics.

Research paper thumbnail of Experimental Study of Pressure Fluctuation in Pneumatic Conveying by Various Methods of Analysis

Pneumatic transport of solids is widely used due to many of its advantages. Many studies have bee... more Pneumatic transport of solids is widely used due to many of its advantages. Many studies have been carried out to explore the details of the transport of solids with pneumatic conveying with the aim to develop enhanced operations. The flow pattern seen in pneumatic conveying can vary widely depending on the gas velocity, the solid feed rate and the characteristics of the solid. In this study a deeper understanding of the interactions of the parameters has been explored using classical signal analysis of pressure fluctuations. Experiments on dilute phase pneumatic transport were performed using polyester, polystyrene, and polyolefin pellets. Material properties such as mean diameter of polymer pellets and density of each polymer have been determined. The parameters of gas velocity and the solid loading ratio were varied producing the distinct pressure gradients which were measured at three different locations: vertical, lower and upper horizontal sections of the piping arrangement. Using these data, a phase space analysis, a power spectral density (PSD) analysis, a fractal dimension analysis, and a rescaled range analysis with Hurst's exponents were carried out to try to develop means to identify the flow conditions using simple pressure transducers. By taking a high speed video of the flow process through the transparent section in the pipe, the flow pattern was visually observed and unique dynamics were seen for the polyolefin particles.

Research paper thumbnail of Frictional Force Measurement for Multiple Plugs in Dense Phase Pneumatic Conveying of Polymer Particles: An Industry Application

Industrial & Engineering Chemistry Research, 2012

ABSTRACT Frictional forces between particles and the pipe wall in dense phase pneumatic conveying... more ABSTRACT Frictional forces between particles and the pipe wall in dense phase pneumatic conveying were determined using strain gauges attached to the outside of the pipe wall. To perform the frictional force measurement, a special strain measurement section was designed and inserted in the industrial scale pneumatic conveying system. Three different polymer particles, polyolefin elastomer, polyethylene, and SARAN were transported under the different flow conditions of the superficial air velocity and the mass flow rate of solids. The frictional forces were determined from three different locations of the pipe wall, top, bottom, and sides of the pipe. The plug velocity and plug length were also determined by analyzing pressure signals measured at two different locations. The magnitude of frictional force was found to be proportional to the plug length. In general, the largest frictional forces were measured at the top of the pipe. In addition, the frictional forces were related to the particle’s interaction with the pipe (i.e., the area of contact of individual particle and number of particles that interact with the pipe wall) as well as the material properties. It was also found that the minimum fluidization of the particles could be related to the strain signal fluctuations. Materials with a smaller minimum fluidization velocity showed more fluctuations and thus have less stable operation. The results obtained were compared to the smaller scale laboratory pneumatic conveying system previously performed.(1)

Research paper thumbnail of Computational Study of Human Head Response to Primary Blast Waves of Five Levels from Three Directions

PLoS ONE, 2014

Human exposure to blast waves without any fragment impacts can still result in primary blast-indu... more Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts.