The pulsatile pressure in an artery is accompanied by the radial motion of the arterial wall. In this paper, the governing equation of the radial wall motion is first derived, indicating that longitudinal stretching of the arterial wall plays a critical role in the radial wall motion. Based on the derived equation and time-harmonic nature of its radial motion, the arterial wall is modeled as a second-order dynamic system. A microfluidic-based tactile sensor is used to acquire the arterial pulsatile pressure waveform, which is used to represent the radial displacement of the arterial wall. Consequently, the 1 st -order and 2 nd -order derivatives of the radial displacement are the wall velocity and wall acceleration. In the context of time-harmonic vibration, the key features in the radial displacement and its two derivatives are interpreted to obtain the elasticity and viscosity of the arterial wall: spring stiffness and damping coefficient in the circumferential direction. Pulse signals at radial artery (RA) and superficial temporal artery (STA) on seven healthy human subjects are measured and processed to estimate the two physical properties of the arterial wall. The measured difference in the physical properties between the two arteries and among the seven subjects validates the feasibility of the proposed dynamic modeling of the radial wall motion to capture the physical properties of the arterial wall, and at the same time demonstrates the necessity of subject-specific and artery-site-specific measurements.

The paper proposes a numerical approach for the analysis of the blood flow in human aorta under real operating conditions. An ad-hoc procedure is developed for importing the aorta geometry from magnetic resonance imaging in order to have a patient based analysis. The aortic flow is simulated accounting for the dynamic behavior of the flow resulting from the heart pulse and for the non-Newtonian properties of blood. Fluid – structure analysis is carried out to address the mutual influence of the flow transient nature and the aorta walls’ deformation on the pressure flow field and tissue’s stresses. Finite element method approach is used for the structural analysis of the aorta walls which are assumed as a linear elastic isotropic material; nevertheless, different regions are introduced to account for the Young modulus variation from the ascending aorta to the common iliac arteries. Mesh morphing techniques are adopted to simulate the wall deformation and a two equation turbulence model is adopted to include the turbulence effects. The proposed numerical approach is validated against the measurements carried out on magnetic resonance imaging scanner and a good agreement is found in terms of aorta wall maximum and minimum deformation during the cardiac cycle. Therefore, the fluid-structure analysis can provide an important tool to extend the insight of the aortic system from magnetic resonance imaging techniques and improve the understanding of arteriosclerosis and the related phenomena as well as their dependence on flow structure and tissue stresses.

Current understanding of blast wave transmission and mechanism of primary traumatic brain injury (TBI) and the role of helmet is incomplete thus limiting the development of protection and therapeutic measures. Combat helmets are usually designed based on costly and time consuming laboratory tests, firing range, and forensic data. Until now advanced medical imaging and computational modeling tools have not been adequately utilized in the design and optimization of combat helmets. The goal of this work is to develop high fidelity computational tools, representative virtual human head and combat helmet models that could help in the design of next generation helmets with improved blast and ballistic protection. We explore different helmet configurations to investigate blast induced brain biomechanics and understand the protection role of helmet by utilizing an integrated experimental and computational method. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we solved the dynamic problem of helmet and head under the blast exposure. Experimental shock tube tests of the head surrogate provide benchmark quality data and were used for the validation of computational models. The full-scale computational NRL head-neck model with a combat helmet provides physical quantities such as acceleration, pressure, strain, and energy to blast loads thus provides a more complete understanding of the conditions that may contribute to TBI. This paper discusses possible pathways of blast energy transmission to the brain and the effectiveness of helmet systems at blast loads. The existing high-fidelity image-based finite element (FE) head model was applied to investigate the influence of helmet configuration, suspension pads, and shell material stiffness. The two-phase flow model was developed to simulate the helium-air shock wave interaction with the helmeted head in the shock tube. The main contribution was the elucidation of blast wave brain injury pathways, including wave focusing in ocular cavities and the back of head under the helmet, the effect of neck, and the frequency spectrum entering the brain through the helmet and head. The suspension material was seen to significantly affect the ICP results and energy transmission. These findings can be used to design next generation helmets including helmet shape, suspension system, and eye protection.

Sleeping is one of the most important factors that influence the quality of human life, and this state of existence should be thoroughly investigated to improve the quality of the life. The mechanical design of bedding has great influence on the comfort of a mattress. Thus, objective and conventional techniques to evaluate the mechanics of mattress comfort could help improve the quality of sleep. In this report, an analysis technique for the assessment of the sleeping posture of humans is presented to facilitate the development of mattress design technology. Herein, an analytical model which imitates the human body has been formulated to determine the design parameters of a mass-spring-joint system on a soft underlay. The physical model is composed of five components that represent the head, chest, hip, femur, and calf, with each body part being represented by a simple ball model. The spring joint connecting the five parts reflects the neck, lumbar, hip, and knee joints. The specifications of the body model are determined by actual measurements and previous studies. In order to determine the physical properties of the mattress, two types of mattress urethane foam material are tested using the ball indenter method. The parameters include Young’s modulus, plateau stress, and other physical parameters. Variation due to the type of mattress has been observed in the laying test using a pressure distribution sensor sheet. In the analysis performed using the physical model, the variation in the lying posture and the extent of body sinking are observed to be the same during experiments. Both variations are compared using the change in force distribution in each body part. In conclusion, it was found that the observed changes in distribution are the same in the experimental and physical models. Therefore, the proposed model reliably reflects the design characteristics of the mattress.

Recently, compression wear has become the preferred performance material for many athletes, where it has the effect of reducing the burden on the body by suppressing muscle vibrations and improves athletic performance by providing the body with suitable moderate pressure. This study concerns thigh sleeves formed of compression wear. The optimal level of compression is studied in order to improve athletic performance and reduce muscular strain. Subsequently, the mechanics of the thigh compression sleeve are discussed. Here, the optimal tensile rigidity of the sleeve, which is calculated using the Young’s modulus of the sleeve in the circumferential direction, is discussed with the aim of reducing muscular strain. The finite element method model is adopted to represent the thigh, which commonly experiences muscle strain during running. The model is constructed using a semi-circular shape, which represents the thigh cut in the transverse plane. The model consists of two solid components, which reflect the muscle (outer) and femur (inner), as well as a shell that covers the thigh. The model generates sinusoidal vibrations, which reflect human behavior when running in a uniaxial direction. The maximum shear strain is approximately half of the tensile rigidity of the sleeve. Indeed, the muscle is sufficiently soft that the tensile rigidity of the sleeve is generally smaller when there is little shear strain on the muscle. From these results, it is concluded that the maximum shear strain of the muscle decreases by almost half when covered by the thigh compression sleeve compared to when no thigh compression sleeve is worn. Furthermore, the shear strain of the muscle can be reduced by varying the tensile rigidity of the sleeve when the human is running. Finally, the tensile rigidity of the sleeve can be decreased to reduce the shear strain of the muscle as it softens.

Endovascular treatment has become the standard for intracranial aneurysm management. In vitro systems including an artery model are required for devices evaluation and clinician training. Although silicone is usually use for such model, its compliance is known to be lower than blood vessels. The purpose of this study was to analyze the influence of model material compliance on flow properties. Silicone and 12 [wt%] poly (vinyl alcohol) hydrogel (PVA-H) were used to create two box-shaped models of significantly different compliance. The inner lumen geometry was a 4 [mm] diameter straight tube (parent vessel) and a 10 [mm] diameter sphere representing the aneurysm. A blood-mimicking fluid made of a mixture of glycerin, water and sodium iodide was used to reproduce the viscosity and density of blood and fit models refractive index. The circulation system consisted of a pulsatile blood pump and resistance valve. A flow rate of 250±50 [ml/min] and pressure from 75 to 115 [mmHg] were set inside the model. Pressure and flow rate sensors were used to monitor flow conditions before and after the model. Particle image velocimetry (PIV) was performed to record the difference of flow patterns inside the aneurysm of both model using a Nd:YAG solid laser system and fluorescent particles. Results revealed a significant change of flow conditions due to model compliance. Attenuation of the flow rate pulse was recorded between the inlet and the outlet of the both model. This attenuation was 51% for PVA-H model. Moreover, a time lag between outlet pressure and outlet flow rate curves was recorded in both model. This time lag was longer with the PVA-H model, as this model exhibit a greater compliance. PIV experiments revealed significant changes of flow patterns and velocity inside the aneurysm. Because of its high compliance, PVA-H model walls moved under the pulsatile conditions. A change of flow direction and decrease of its velocity were observed near the proximal wall of the aneurysm, compared to the silicone model. Such differences might modify the stress on the wall of the aneurysm. To conclude, our experiments revealed that compliance has significant impacts on flow properties and should be taken into account for in vitro vascular model manufacturing.

Breastfeeding provides both nutrients and immunities necessary for infant growth. Understanding the biomechanics of breastfeeding requires capturing both positive and negative pressures exerted by infants on the breast. This clinical experimental work utilizes thin, flexible pressure sensors to capture the positive oral pressures of 7 mother-infant dyads during breastfeeding while simultaneously measuring vacuum pressures and imaging of the infants oral cavity movement via ultrasound. Methods for denoising signals and evaluating ultrasound images are discussed. Changes and deformations on the nipple are evaluated. The results reveal that pressure from the infant’s maxilla and mandible are evenly distributed in an oscillatory pattern corresponding to the vacuum pressure patterns. Variations in nipple dimensions are considerably smaller than variations in either pressure but the ultrasound shows positive pressure dominates structural changes during breastfeeding. Clinical implications for infant-led milk expression and data processing are discussed.

The continuous demand for oil and gas forces the petroleum industry to develop new and cost-effective technologies to increase recovery from new fields and enhance extraction from existing fields. Subsea wet gas compression stands out as a promising solution for increasing production capacity, utilizing remote regions and reducing costs. A prerequisite for successful oil and gas production utilizing subsea wet gas compressors is operability. This includes the system’s ability to cope with operational changes, without having to shut down. One of the fundamental operational changes is the liquid content in the inlet pipe, which may fluctuate considerably at certain time intervals. The current study investigates how changes in liquid content impacts compressor performance. An experimental test campaign has been performed at the Norwegian University of Science and Technology (NTNU). The test facility is an open loop configuration consisting of a single shrouded centrifugal impeller, a vaneless diffuser and a symmetrical circular volute. The main objectives were to document how the presence of liquid impacts the compressor characteristics and further, how the operating point moves within the characteristics when solely subjected to an increase of liquid content. The compressor was exposed to liquid contents ranging from gas mass fraction 1.0 to 0.60. The test reveals that the compressor pressure ratio at wet conditions is higher in comparison to dry conditions. Care should be taken when analysing stability and surge margins at variations in fluid liquid content. Further, the compressor behaves in a predictable manner, revealing several linear trends, when subjected to stepwise changes in liquid content from a fixed operating point.

We consider modeling of single phase fluid flow in heterogeneous porous media governed by elliptic partial differential equations (PDEs) with random field coefficients. Our target application is biotransport in tumors with uncertain heterogeneous material properties. We numerically explore dimension reduction of the input parameter and model output. In the present work, the permeability field is modeled as a log-Gaussian random field, and its covariance function is specified. Uncertainties in permeability are then propagated into the pressure field through the elliptic PDE governing porous media flow. The covariance matrix of pressure is constructed via Monte Carlo sampling. The truncated Karhunen–Loève (KL) expansion technique is used to decompose the log-permeability field, as well as the random pressure field resulting from random permeability. We find that although very high-dimensional representation is needed to recover the permeability field when the correlation length is small, the pressure field is not sensitive to high-oder KL terms of input parameter, and itself can be modeled using a low-dimensional model. Thus a low-rank representation of the pressure field in a low-dimensional parameter space is constructed using the truncated KL expansion technique.

A membrane humidifier is a device to provide water vapor into the proton exchange membrane fuel cell stack that is used for transportation application due to global warming. Since inadequate humidification severely affects the performance and durability of a fuel cell stack, it is necessary to equip the humidifier for delivery humidification into the fuel cell vehicle. In this study, the performance of humidification in hollow fiber membrane is investigated. While the test section is exposed to external humidity condition, dry air is provided through hollow fiber membrane so that the water transport is facilitated. Since various parameters can change the performance, the performance investigation has to be carried out with parameters. In this study the water transport of hollow fiber membrane is investigated in terms of principle operating conditions such as temperature, pressure, and flow rate.

The thickening of the aortic wall is a mechanical adaptation to the prolonged increase in intravascular pressure resulting from hypertension, which is regulated by the smooth muscle cell layer (SML) and the elastic lamina (EL). Herein, we built a simplified computational model of the aortic media composed of SML and EL and simulated the phenomenon of EL undulation or EL buckling at no-load condition ( in vitro ) by releasing compressive prestress assigned to the EL. Using the design of experiments approach, we found that the prestress assigned to the EL, the thickness of the EL, and a coupled or interspace connecting length between the SML and the EL are significantly influential factors in representing EL buckling at the unloaded state. We also found that the degree of EL waviness and the change in residual stresses within the SML and the EL are inversely correlated. Furthermore, by increasing the stiffness of the SML, we successfully reconstructed the disappearance of EL undulation at 25% stretch, replicating the dilation of a normal aorta under physiological loading conditions. It can be expected that these findings will help unveil the roles of the SML and the EL in maintaining the mechanical homeostasis of the arterial wall.

Background: Pressure distribution for transtibial amputees (TTA) patients varies at the limb socket interface according to several factors. Although socket technology is getting more advanced, the majority of researchers are still facing problems with relief areas. Objectives: This study focused on the theoretical and experimental aspects of the design to figure out patients’ sensitivity to pain when wearing sockets. Relief areas were analyzed using data collected from patients’ centers and optimized under different static and dynamic conditions. Methods: Finite element trials and DOE optimization using Design Expert 8 software and analysis of variance (ANOVA) revealed that holes with relief areas are appropriates for lower extremities patients where scanning electron images (SEM) of the worn areas show direct relations between relieved sockets with holes at fibula head (FH) and patient lifestyle and activity. Clinical Relevance: A patient that moves rather slowly, as a result of old age or sedentary level of activity would greatly benefit from the FH socket hole implementation, and thus reduces the wear of socket materials after longer period of time and increases the level of comfort of patient skins. the interviews conducted were evident that patients endured pain at the PT and FH. Moreover, further studies were performed on the FH, and results revealed that lateral forces play a major role and is influenced by the lifestyle of the patient.

Liquid water management is critical for Proton Exchange Membrane (PEM) fuel cell operation, as excessive humidity can lead to flooding and cell performance degradation. Water is produced in the cathode catalyst layer during the electrochemical reaction. If reactant gas streams become saturated, liquid water forms and must travel through anode and cathode Gas Diffusion Layers (GDLs) to reach flow channels for removal. Understanding the dynamic behavior of the droplet is critical to improve water removal strategies for PEM fuel cells. In this study a 3D, transient, two-phase model based on the Volume of Fluid (VOF) method was developed to study a single droplet in the gas channel. The formation, growth, and breakup of the droplet is tracked numerically and analyzed. The pressure drop across the droplet is monitored over time and compared with theoretical analysis. The droplet size and shape change over time for two different pore sizes are compared. The impact of various gases including air, helium, and hydrogen on droplet dynamics is presented. The viscous force and pressure force on the droplet and the drag coefficient are calculated.

To support the broader development of isothermal compressor technology for natural gas systems, an experimental system has been designed and constructed to determine void fraction of a gas over time. The goal of this project was to determine how much time it takes for a gas, already statured in a working fluid, to separate from the working fluid. The result is a pressure vessel paired with a data acquisition system that could operate at a maximum of 3600 psi. A medium and high pressure system were designed, and the medium pressure system has been tested using visual methods.

The unconventional gas reservoir has attracted more and more attention as the shale gas greatly expands worldwide energy supply, for which the gaseous fluid transport in complex porous domain is one important process as the shale gas is extracted. The apparent permeability of porous media is one important parameter in the related numerical model, however, its determination is still challenging. The apparent permeability varies with gas pressure, the porous media properties and gas–solid interactions based on the previous studies. For the slip gas flows, the velocity slip at the gas-solid interface in confined porous space is one significant difference compared with that on macro scale, which is caused by the gas rarefaction effect. In this work, a pore-scale LB model is established to simulate the gaseous fluid flow in the confined porous media. An effective curved boundary treatment is adopted for the porous surface and the validation test shows that the present model has superiority in capturing the slip phenomenon on the curved surfaces. Based on the numerical predictions, the different influential factors on the permeability of confined porous media are thoroughly studied, for which the gas rarefaction effect is considered.

In order to investigate the performance and emissions behavior of a high compression ratio Compression Ignition (CI) engine operating in Partially Premixed Charge Compression Ignition (PPCI) mode, a series of experiments were conducted using a single cylinder naturally aspirated engine with a high-pressure rail fuel injection system. This included a moderately advanced direct injection strategy to attempt PPCI combustion under low load conditions by varying the injection timing between 25° and 35° Before Top Dead Center (BTDC) in steps of 2.5°. Furthermore, during experimentation the fuel injection pressure, engine speed, and engine torque (through variance of the fuel injection quantity) were kept constant. In-cylinder pressure, emissions, and performance parameters were measured and analyzed using a zero-dimensional heat release model. Compared to the baseline conventional 12.5° BTDC injection, in-cylinder pressure and temperature was higher at advanced timings for all load conditions considered. Additionally, NO x , PM, CO, and THC were higher than conventional results at the 0.5 N-m load condition. While PM emissions were lower, and CO and THC emissions were comparable to conventional injection results at the 1.5 N-m load condition between 25° and 30° BTDC, NO x emissions were relatively high. Hence, there was limited success in beating the NO x -PM tradeoff. In addition, since Start of Combustion (SOC) occurred BTDC, the resulting higher peak combustion pressures restricted the operating condition to lower loads to ensure engine safety. As a result, further investigation including Exhaust Gas Recirculation (EGR) and/or variance in fuel Cetane Number (CN) is required to achieve PPCI in a high compression ratio CI engine.

A general correlation is presented for predicting maximum heat transfer coefficient for surfaces submerged in gas-fluidized beds. It has been verified with data for horizontal and vertical cylinders and spheres in beds of a wide variety of particles and gases. The gases include air, cryogens, methane, CO 2 , ammonia, and R-12. The range of parameters includes: heat transfer surface diameter 0.05 to 220 mm, particle diameter 31 to 15000 μm, pressure 0.026 to 0.95 MPa, and temperature 13 to 1028 °C. The 363 data points from 53 sources are predicted with a mean absolute deviation of 16.2 %. Several other correlations were also compared to the same data but had much larger deviations.

Deep surge is a violent fluid instability that occurs within turbomachinery compression systems and limits the low-flow operating range. It is characterized by large amplitude pressure and flow rate fluctuations, where the cross-sectional averaged flow direction alternates between forward and reverse. When a compressor transitions into deep surge, the time-averaged compressor outlet pressure and temperature decrease and increase, respectively, along with a drastic rise in narrowband, low-frequency noise. The present study includes both measurements and predictions from a turbocharger centrifugal compressor installed on a gas stand. The compressor breathes air from ambient through an inlet duct with a bellmouth opening. The downstream compression system consists of a compressor outlet duct attached to a plenum with increased cross-sectional area, and an additional duct that connects the plenum outlet to a control valve. A detailed three-dimensional (3D) computational fluid dynamics (CFD) model of this compression system was constructed to carry out unsteady surge predictions. The results included here capture the transition from mild to deep surge, as the flow rate at the outlet boundary (valve) is reduced. During this transition, the amplitude of pressure and flow rate fluctuations greatly increase until they reach a repeating cyclic structure characteristic of deep surge. During the deep surge portion of the prediction, pressure fluctuations are compared with measurements at the corresponding compressor inlet and outlet transducer locations, where the amplitudes and frequency exhibit excellent agreement. The predicted flow-field throughout the compression system is studied in detail during operation in deep surge, in order to characterize the unsteady and highly 3D structures present within the impeller, diffuser, and compressor inlet duct. Key observations include a core flow region near the center of the inlet duct, where the flow remains in the forward direction throughout the deep surge cycle. The dominant noise generation occurs at the fundamental surge frequency, which is near the Helmholtz resonance of the compression system, along with harmonics at integer multiples of this fundamental frequency.

When vapor bubbles are subjected to suddenly reduced pressure or immediate subcooling, it may rapidly condense, rupture, and generate cavitation corrosions. This phenomenon often occurs behind the blade of a rapidly rotating propeller or on any surface vibrating in liquid with sufficient amplitude and acceleration. In this article, we reported cavitation and its corrosive collapse occurring in capillary tubes, called pulsating heat pipes. Visualization images of cut and opened tubes show that internal copper surface was seriously etched after a certain period of operation. Sub-millimeter etching pits are observed on the tube internal surface. Copper particles in size of a few hundred micrometers are also found in the reclaimed operating fluid. Starting from this finding, the temperature effect of performance is analyzed to understand the cavitation occurrence and collapse. Pulsating heat pipe requires a certain temperature difference between the evaporator and condenser sections, typically > 10°C, to generate continuous two-phase oscillating movements. However, during the transient startup period, this temperature difference could reach as high as 50°C. Large saturation temperature difference, associated with highly turbulent two-phase flow, drives the saturated vapor bubbles from the hot evaporation region to the subcooled environment in less than 100ms. During the rapid condensation, the accelerated shrinking vapor bubbles create interface instability, followed by forming a strong impingement jet to etch the solid pipe wall. The collapse of cavitation is associated with the generation of acoustically tinkling signals that are often heard during most of the operating pulsating heat pipe.

The involute spur gear system has been widely utilized in the mechanical transmission domain, and the control of the acceleration noise of the involute spur gear system has become the key technology to solve the NVH performance of the power transmission system, especially in the automobile industry. In the process of the gear meshing, the unavoidable acceleration noise of the involute spur gear system is mainly caused by the meshing stiffness and error excitation due to the structural parameters. Therefore, the investigation on the effects of structure parameters on acceleration noise of the involute spur gear system is necessary. In this paper, the numerical model for predicting the acceleration noise of the involute spur gear system has been established. The simulation results of the acceleration noise were compared with the experimental results, and the errors between these two results were only 2.9%, within permission. The effects of structure parameters including base pitch error and pressure angle on the acceleration noise of the involute spur gear system have been discussed. Results showed that increasing the base pitch error, the acceleration noise level of the involute spur gear increased, and the gap of the noise level between different base pitch errors narrowed according to the increase of gear load and rotation speed. Increasing the pressure angle also increased the acceleration noise level, however, the gap between different pressure angles remained the same regardless the variations of gear load and rotation speed, which was different than the variations of base pitch error.