Excellence in Research and Innovation for Humanity

International Science Index

Commenced in January 1999 Frequency: Monthly Edition: International Abstract Count: 39602

Aerospace and Mechanical Engineering

Development of a Multi-Resonance Force Generator for Vibration Reduction
Passive absorbers offer a simple solution to reduce structure-borne vibrations using the effect of a narrow band notch filter near the tuned frequency. If the excitation frequency is varying, even just a little bit or the installation at the crucial locations cannot be achieved this methodology will quickly become less ineffective. Therefore active vibration control systems (AVCS) are deployed to actively reduce the induced vibrations by means of a destructive interference with a secondary vibration field at freely selectable sensor positions. The AVCS typically comprises several force generators, accelerometers power amplifiers, and a controller. The signals from the accelerometers and the sensing signals of the actuator, like voltage or current, can be synergistically used namely for controlling the actuator as well as for monitoring the structural integrity. A standard inertial force generator is similar in structure to a passive absorber, consisting of spring and inertial mass. However, in addition, an actuator device is arranged in parallel to the spring which generates forces, acting on the inertial mass and attachment point. The amplification of the inertial mass near the resonance frequency helps to generate high dynamic forces by using low electrical power consumption. If the suppression of vibrations within a single frequency range is not sufficient because of the existence of higher harmonics or other conspicuous resonances, it is common practice to integrate separate AVCSs tuned for their particular frequency ranges. Consequently, not only the number of force generators but also the number of electronic equipment has to be multiplied. In the special case that two vibration modes have to be extinguished simultaneously a new solution was found to minimize the system weight and complexity. The novel concept utilizes a two degree of freedom spring-mass system with a single force generator acting between both inertial masses. Therefore the amount of electronic equipment is minimized, as only a single amplifier respectively a single controller is required. This methodology is of great interest, as existing AVCSs could easily be retrofitted for another frequency range. The present paper describes the approach, how an existing AVCS can be modified in order to control the second harmonic frequency by utilizing the original force generator. Taking advantage of the mechanical-electrical analogy of transducers a design tool is introduced to optimize a multi-resonance force generator with consideration of its mechanical and electrical functionality. The results of the experimental tests are briefly presented which verify the design concept and validate the simulation model. A recommendation can be derived to correctly adjust the Eigen-frequencies of the AVCS with respect to minimizing the electrical power consumption.
Design and Fabrication of ZSO Nanocomposite Thin Film Based NO2 Gas Sensor
In the present study, ZnO doped SnO2 thin films of various compositions were deposited on the surface of a corning substrate by dropping the two sols containing the precursors for composite (ZSO) with subsequent heat treatment. The sensor materials used for selective detection of nitrogen dioxide (NO2) were designed from the correlation between the sensor composition and gas response. The available NO2 sensors are operative at very high temperature (150-800 °C) with low sensing response (2-100) even in higher concentrations. Efforts are continuing towards the development of NO2 gas sensor aiming with an enhanced response along with a reduction in operating temperature by incorporating some catalysts or dopants. Thus in this work, a novel sensor structure based on ZSO nanocomposite has been fabricated using chemical route for the detection of NO2 gas. The structural, surface morphological and optical properties of prepared films have been studied by using X-ray diffraction (XRD), Atomic force microscopy (AFM), Transmission electron microscope (TEM) and UV-visible spectroscopy respectively. The effect of thickness variation from 230 nm to 644 nm of ZSO composite thin film has been studied and the ZSO thin film of thickness ~ 460 nm was found to exhibit the maximum gas sensing response ~ 2.1×103 towards 20 ppm NO2 gas at an operating temperature of 90 °C. The average response and recovery times of the sensor were observed to be 3.51 and 6.91 min respectively. Selectivity of the sensor was checked with the cross-exposure of vapour CO, acetone, IPA, CH4, NH3 and CO2 gases. It was found that besides the higher sensing response towards NO2 gas, the prepared ZSO thin film was also highly selective towards NO2 gas.
Predictive Factors of Prognosis in Acute Stroke Patients Receiving Traditional Chinese Medicine Therapy: A Retrospective Study
Background: Traditional Chinese medicine has been used to treat stroke, which is a major cause of morbidity and mortality. There is, however, no clear agreement about the optimal timing, population, efficacy, and predictive prognosis factors of traditional Chinese medicine supplemental therapy. Method: In this study, we used a retrospective analysis with data collection from stroke patients in Stroke Registry In Chang Gung Healthcare System (SRICHS). Stroke patients who received traditional Chinese medicine consultation in neurology ward of Keelung Chang Gung Memorial Hospital from Jan 2010 to Dec 2014 were enrolled. Clinical profiles including the neurologic deficit, activities of daily living and other basic characteristics were analyzed. Through propensity score matching, we compared the NIHSS and Barthel index before and after the hospitalization, and applied with subgroup analysis, and adjusted by multivariate regression method. Results: Totally 115 stroke patients were enrolled with experiment group in 23 and control group in 92. The most important factor for prognosis prediction were the scores of National Institutes of Health Stroke Scale and Barthel index right before the hospitalization. Traditional Chinese medicine intervention had no statistically significant influence on the neurological deficit of acute stroke patients, and mild negative influence on daily activity performance of acute hemorrhagic stroke patient. Conclusion: Efficacy of traditional Chinese medicine as a supplemental therapy for acute stroke patients was controversial. The reason for this phenomenon might be complex and require more research to comprehend. Key words: traditional Chinese medicine, acupuncture, Stroke, NIH stroke scale, Barthel index, predictive factor. Method: In this study, we used a retrospective analysis with data collection from stroke patients in Stroke Registry In Chang Gung Healthcare System (SRICHS). Stroke patients who received traditional Chinese medicine consultation in neurology ward of Keelung Chang Gung Memorial Hospital from Jan 2010 to Dec 2014 were enrolled. Clinical profiles including the neurologic deficit, activities of daily living and other basic characteristics were analyzed. Through propensity score matching, we compared the NIHSS and Barthel index before and after the hospitalization, and applied with subgroup analysis, and adjusted by multivariate regression method. Results: Totally 115 stroke patients were enrolled with experiment group in 23 and control group in 92. The most important factor for prognosis prediction were the scores of National Institutes of Health Stroke Scale and Barthel index right before the hospitalization. Traditional Chinese medicine intervention had no statistically significant influence on the neurological deficit of acute stroke patients, and mild negative influence on daily activity performance of acute hemorrhagic stroke patient. Conclusion: Efficacy of traditional Chinese medicine as a supplemental therapy for acute stroke patients was controversial. The reason for this phenomenon might be complex and require more research to comprehend.
Study and Solving Partial Differential Equation of Danel Equation in the Vibration Shells
This paper we deal with an analysis of the free vibrations of the governing partial differential equation that it is Danel equation in the shells. The problem considered represents the governing equation of the nonlinear, large amplitude free vibrations of the hinged shell. A new implementation of the new method is presented to obtain natural frequency and corresponding displacement on the shell. Our purpose is to enhance the ability to solve the mentioned complicated partial differential equation (PDE) with a simple and innovative approach. The results reveal that this new method to solve Danel equation is very effective and simple, and can be applied to other nonlinear partial differential equations. It is necessary to mention that there are some valuable advantages in this way of solving nonlinear differential equations and also most of the sets of partial differential equations can be answered in this manner which in the other methods they have not had acceptable solutions up to now. We can solve equation(s), and consequently, there is no need to utilize similarity solutions which make the solution procedure a time-consuming task.
Influence of Vibration Amplitude on Reaction Time and Drowsiness Level
It is well established that exposure to vibration has an adverse effect on human health, comfort, and performance. However, there is little quantitative knowledge on performance combined with drowsiness level during vibration exposure. This paper reports a study investigating the influence of vibration amplitude on seated occupant reaction time and drowsiness level. Eighteen male volunteers were recruited for this experiment. Before commencing the experiment, total transmitted acceleration measured at interfaces between the seat pan and seatback to human body was adjusted to become 0.2 ms-2 r.m.s and 0.4 ms-2 r.m.s for each volunteer. Seated volunteers were exposed to Gaussian random vibration with frequency band 1-15 Hz at two level of amplitude (low vibration amplitude and medium vibration amplitude) for 20-minutes in separate days. For the purpose of drowsiness measurement, volunteers were asked to complete 10-minutes PVT test before and after vibration exposure and rate their subjective drowsiness by giving score using Karolinska Sleepiness Scale (KSS) before vibration, every 5-minutes interval and following 20-minutes of vibration exposure. Strong evidence of drowsiness was found as there was a significant increase in reaction time and number of lapse following exposure to vibration in both conditions. However, the effect is more apparent in medium vibration amplitude. A steady increase of drowsiness level can also be observed in KSS in all volunteers. However, no significant differences were found in KSS between low vibration amplitude and medium vibration amplitude. It is concluded that exposure to vibration has an adverse effect on human alertness level and more pronounced at higher vibration amplitude. Taken together, these findings suggest a role of vibration in promoting drowsiness, especially at higher vibration amplitude.
Computational Fluid Dynamics and Experimental Evaluation of Two Batch Type Electrocoagulation Stirred Tank Reactors Used in the Removal of Cr (VI) from Waste Water
In this study, hydrodynamics analysis of two batch type electrocoagulation stirred tank reactors, used for the electrocoagulation treatment of Cr(VI) wastewater, was carried using computational fluid dynamics (CFD). The aim of the study was to evaluate the impact of mixing characteristics on overall performance of electrocoagulation reactor. The CFD simulations were performed using ANSYS FLUENT 14.4 software. The mixing performance of each reactor was evaluated by numerically modelling tracer dispersion in each reactor configuration. The uniformity in tracer dispersion was assumed when 90% of the ratio of the maximum to minimum concentration of the tracer was realized. In parallel, experimental evaluation of both the electrocoagulation reactors for removal of Cr(VI) from wastewater was also carried out. The results of CFD and experimental analysis clearly show that the reactor which can give higher uniformity in lesser time, will perform better as an electrocoagulation reactor for removal of Cr(VI) from wastewater.
An Experimental (Wind Tunnel) and Numerical (CFD) Study on the Flow over Hills
The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 68° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data; this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used.
Computational Fluid Dynamics Modeling of Air Stream Pressure Drop inside Combustion Air Duct of Coal-Fired Power Plant with and without Airfoil
The flow pattern inside rectangular intake air duct of 300 MW lignite coal-fired power plant is investigated, in order to analyze and reduce overall inlet system pressure drop. Before entering the fan, airstream through the 45 degree inlet elbow, the flow instrument and 90 degree mitered elbow respectively. The loss in each section can find the proximate calculation from Bernoulli’s equation and ASHRAE’s standard table except the flow instrument hence computational fluid dynamics (CFD) is used in this study base on Navier-Stroke equation and the standard k-epsilon turbulence modelling. Input boundary condition is 175 kg/s mass flow rate inside the 11 m2 cross sectional duct. According to the inlet air flow rate, the Reynold number of airstream is 2.7x106 based on the hydraulic duct diameter thus the flow behavior is turbulence. The numerical results are verified with the operation data in case of original design. It is found that the numerical result is agreed well with the operating data and dominant loss is from the flow instrument. Normally, the air flow rate is measured by the airfoil, and it brings to get high pressure drop inside the duct. To overcome this problem, the airfoil is planned to be replaced with the other measuring instrument, such as the average pitot tube which, generates low pressure drop of airstream. The numerical result in the case of average pitot tube shows that the pressure drop inside the inlet airstream duct is decreased significantly. It should be noted that the energy consumption of inlet air system is reduced too.
Influence of Maximum Fatigue Load on Probabilistic Aspect of Fatigue Crack Propagation Life at Specified Grown Crack in Magnesium Alloys
Magnesium alloys is a lightest material in all metals used in structural parts. Magnesium alloys are increasingly adopted in automotive industry owing to the requirement of a weight reduction for an emission regulation. The uncertainty is essential in the behavior of the structure. It is required to consider the probabilistic aspect of the fatigue crack propagation life at a specified grown crack for an estimation of structural integrity. The primary purpose of this paper is to find the influence of a maximum fatigue load on the probabilistic aspect of fatigue crack propagation life at a specified grown crack in magnesium alloys. The experiments of fatigue crack propagation are carried out in laboratory air under different maximum fatigue loads to obtain the fatigue data for the statistical analysis. The goodness-of fit test for probability distribution of the fatigue crack propagation life at a specified grown crack is performed through Anderson-Darling test. The good probability distribution of the fatigue crack propagation life is also confirmed under maximum fatigue loads.
Effect of Scarp Topography on Seismic Ground Motion under Inclined SV Wave
Local irregular topography has a great impact on earthquake ground motion. For scarp topography, using numerical simulation method, the influence extent and scope of the scarp terrain on scarp's upside and downside ground motion are discussed in case of different vertical incident SV waves. The results show that: (1) The amplification factor of scarp's upside region is greater than that of the free surface, while the amplification factor of scarp's downside part is less than that of the free surface; (2) when the slope angle increases, for x component, amplification factors of the scarp upside also increase, while the downside part decrease with it. For z component, both of the upside and downside amplification factors will increase; (3) when the slope angle changes, the influence scope of scarp's downside part is almost unchanged, but for the upside part, it slightly becomes greater with the increase of slope angle; (4) due to the existence of the scarp, the z component ground motion appears at the surface. Its amplification factor increases for larger slope angle, and the peaks of the surface responses are related with incident waves. However, the input wave has little effects on the x component amplification factors.
Effect of Fault Depth on Near-Fault Peak Ground Velocity
Fault depth is an important parameter to be determined in ground motion simulation, and peak ground velocity (PGV) demonstrates good application prospect. Using numerical simulation method, the variations of distribution and peak value of near-fault PGV with different fault depth were studied in detail, and the reason of some phenomena were discussed. The results show that the distribution characteristics of PGV fault-parallel (FP) component and fault-normal (FN) component are distinctly different, the value of PGV FN component is much larger than that of FP component. With the increase of fault depth, the region of strong FN component PGVs move forward along the rupture direction, while the strong FP component PGVs become gradually far away from the fault trace along the direction perpendicular to the strike. However, no matter for FN component or FP component, the strong PGV area and its values are both quickly reduced with increasing fault depth. The results above suggest that the fault depth have significant effect on both FN and FP component of near-fault peak ground velocity.
Vibration Analysis of Power Lines with Moving Dampers
In order to reduce the Aeolian vibration of overhead transmission lines, the Stockbridge damper is usually attached. The efficiency of Stockbridge damper depends on its location on the conductor and its resonant frequencies. When the Stockbridge damper is located on a vibration node, it becomes inefficient. Hence, the static damper should be subrogated by a dynamic one. In the present study, a proposed dynamic absorber for transmission lines is studied. Hamilton’s principle is used to derive the governing equations, then the system of ordinary differential equations is solved numerically. Parametric studies are conducted to determine how certain parameters affect the performance of the absorber. The results demonstrate that replacing the static absorber by a dynamic one enhance the absorber performance for wider range of frequencies. The results also indicate that the maximum displacement decreases as the absorber speed and the forcing frequency increase. However, this reduction in maximum displacement is accompanying with increasing in the steady state vibration displacement. It is also indicated that the energy dissipation in moving absorber covers higher range of frequencies.
Design of a Nozzle to Produce Continuously Varying Mach Number
Unsteady phenomena in high-speed flow like flow around bodies and high-speed intakes require a variable Mach number tunnel which can simulate the practical flow conditions like upper atmosphere conditions in the test section. The high and varying stagnation pressures and temperatures required cannot be achieved in the current day tunnels with flexible nozzle walls. In order to have a nozzle with variable area with provision for wall cooling, method of characteristics was used to demonstrate two simple techniques, viz., nozzle wall rotation and translation which changes the area ratio of the nozzle. It was found through MOC simulations of nozzle profiles, that rotation and translation can both give a variation in Mach number at the exit of the nozzle. The variations in exit Mach number, flow distortion, and range of Mach numbers achievable for various nozzles was characterized. It was found that translation of the walls was better in all aspects compared to the rotation of the nozzle walls. The nozzle profiles generated were then corrected for boundary layer growth and simulated numerically using k-ε model for a few nozzle profiles. The results were similar to the inviscid MOC based predictions, with small deviations due to viscosity.
Modeling Electrical Discharge Machining Process Using Artificial Neural Network for the Machining of Inconel 825
Inconel 825 (titanium stabilized fully austenitic), a Ni-Fe-Cr alloy has alluring applications in aerospace, nuclear and chemical processing industries. Electrical Discharge Machining (EDM) is a complex process and to establish the correlation between input and output Artificial Neural Network (ANN) is used to model the process. In EDM no single combination of the input parameter can offer the maximum metal removal rate (MRR) and better surface finish (SR), due to conflicting nature of the process. The input parameters considered are dielectric fluid, pulse-on-time, discharge current, duty cycle, gap voltage, tool electrode lift time and tool electrode material. From the reported results the proposed model can satisfactorily predict the MRR and SR in EDM process. Moreover, they can be considered as the viable tool for the planning of the process in EDM.
Experimental Research and Numerical Analysis on Sloshing Dynamics of Irregular Annular Cylindrical Water Tank
Passive containment cooling system (PCS) is the significant characteristic of the third-generation nuclear power plants, which is different from the traditional nuclear power plants, and the water tank is one important component of passive containment cooling system. The seismic response of structure and nuclear equipment may be changed due to the water tank. Therefore, the dynamic characteristics of water tank should be studied. This study focuses on the irregular annular cylindrical water tank of nuclear island building. An experimental model was designed with a geometrical scale of 1/16, in which the height of free water surface is 550 mm. In order to measure the wave height, the roof of water tank was replaced by toughened glass and connected to the water tank with fixed parts. For obtaining the testing data of the sloshing characteristic of liquid, the laser displacement sensor was used, and a colored substance dissolved by organic solvent was used to increase laser reflection. In the experiment, the three-direction acceleration time histories with the PGAs of 1.20g, 0.80g and 0.60g were used as the input motion of shaking table, and to recognize the sloshing frequencies, single-direction sine waves with the PGAs of 0.05g and 0.10g were used. Hydrodynamic pressure and attenuation data of wave height were recorded. The sloshing frequencies are recognized by FFT of hydrodynamic pressure time histories, and the sloshing damping ratio are calculated using logarithmic decrement method. A numerical model was established based on ADINA, in which the model base and the tank walls are modeled using 3D solid finite elements, the toughened glass was modeled using shell finite element and the water was modeled using 3D PBFE. The material parameters are the same with experiment. Modal analysis and time history analysis were done, and the simulated frequencies were compared with the experimental results. It can be seen that the water is rotating along the walls of tank under the three-direction seismic loadings, and the maximum vertical displacement appears at the junction of water and inner tank wall. Moreover, the maximum vertical displacement not only appears in X axis or Y axis but also in other direction. After the seismic loadings, the water is sloshing continuously and the attention is small. It shows that the errors of 1st, 2nd and 4th sloshing frequencies are all less than 1%. Although the error of 3rd sloshing frequency is larger than other three, 6.15% error is acceptable. The conclusions are reached, as follows: (1) The measuring methods of the water responses mentioned in this paper can be used to recognize sloshing frequency and damping ratio. (2) The sloshing damping ratio of irregular annular cylindrical water is 0.5138% and it has a good agreement with the suggestion of regular tanks. It implies that the sloshing damping ratio could not be influenced obviously by the shape of water tank. (3) The formulation of PBFE is suitable for modal analysis and time history analysis. The accuracy of numerical results is acceptable.
The Effects of Displacer-Cylinder-Wall Conditions on the Performance of a Medium-Temperature-Differential γ-Type Stirling Engine
In this study, we conducted CFD simulation to study the gas cycle of a medium-temperature-differential (MTD) γ-type Stirling engine. Mesh compression and expansion as well as overset mesh techniques are employed to simulate the moving parts of the engine. Shear-Stress Transport (SST) k-ω turbulence model has been adopted because the model is not prone to generate excessive turbulence upon impingement regions. Hence, wall heat transfer rates at the hot and cold ends will not be overestimated. The effects of several different displacer-cylinder-wall temperature setups, including smooth and finned walls, on engine performance are investigated. The results include temperature contours, pressure versus volume diagrams, and variations of heat transfer rates, indicated power, and efficiency. It is found that displacer-wall heat transfer is one of the most important factors on engine performance, and some wall-temperature setups produce better results than others.
Experimental Set-Up for Investigation of Fault Diagnosis of a Centrifugal Pump
Centrifugal pumps are complex machines which can experience different types of fault. Condition monitoring can be used in centrifugal pump fault detection through vibration analysis for the mechanical and hydraulic forces. Vibration analysis methods have the potential to be combined with artificial intelligence systems where an automatic diagnostic method can be approached. An automatic fault diagnosis approach could be a good option to minimize human error and to provide a precise machine fault classification. This work aims to introduce an approach to centrifugal pump fault diagnosis based on artificial intelligence and genetic algorithm systems. An overview of the future works, research methodology and proposed experimental setup is presented and discussed. The expected results and outcomes based on the experimental work are illustrated.
Effect of Transverse Eccentric Ballistic Damage on Static Torsional Strength of Tail Drive Shaft of Helicopter
Military helicopters have high probability of acquiring ballistic damage during their operations. One such damage concerned with the drive train of tail rotors of helicopter is due to ballistic effects that may be introduced as a consequence of passage of bullets or other ballistic objects. The ballistic damage may jeopardize the structural integrity of the shaft. The focus of the work exhibited here is to analyze the effect of transversely varying ballistic impact location on the static torsional strength of tail rotor drive shaft. The holes generated as a consequence of ballistic impact turned out to be the areas of stress concentration which is rational. The maximum torsional shear stress was calculated for each case, and comparison was drawn with yield strength and ultimate strength using failure theories assorting the drive shaft as safe or unsafe. Moreover, the effect of varying ballistic location on the magnitude of maximum torsional stress is also discussed.
Stability Characteristics of Angle Ply Bi-Stable Laminates by Considering the Effect of Resin Layers
In this study, the stability characteristics of a bi-stable composite plate with different asymmetric composition are considered. The interest in bi-stable structures comes from their ability that these structures can have two different stable equilibrium configurations to define a discrete set of stable shapes. The structures can easily change the first stable shape to the second one by a simple snap action. The main purpose of the current research is to consider the effect of including resin layers on the stability characteristics of bi-stable laminates. To this end and In order to determine the magnitude of the loads that are responsible for snap through and snap back phenomena between two stable shapes of the laminate, a non-linear finite element method (FEM) is utilized. An experimental investigation was also carried out to study the critical loads that caused snapping between two different stable shapes. Several specimens were manufactured from T300/5208 graphite-epoxy with [0/90]T, [-30/60]T, [-20/70]T asymmetric stacking sequence. In order to create an accurate finite element model, different thickness of resin layers created during the manufacturing process of the laminate was measured and taken into account. The geometry of each lamina and the resin layers was characterized by optical microscopy from different locations of the laminates thickness. The exact thickness of each lamina and the resin layer in all specimens with [0/90]T,[-30/60]T, [-20/70]T stacking sequence were determined by using image processing technique.
Whole Body Cooling Hypothermia Treatment Modelling Using a Finite Element Thermoregulation Model
This paper presents a thermoregulation model using the finite element method to perform numerical analyses of brain cooling procedures as a contribution to the investigation on the use of therapeutic hypothermia after ischemia in adults. The use of computational methods can aid clinicians to observe body temperature using different cooling methods without the need of invasive techniques, and can thus be a valuable tool to assist clinical trials simulating different cooling options that can be used for treatment. In this work, we developed a FEM package applied to the solution of the continuum bioheat Pennes equation. Blood temperature changes were considered using a blood pool approach and a lumped analysis for intravascular catheter method of blood cooling. Some analyses are performed using a three-dimensional mesh based on a complex geometry obtained from computed tomography medical images, considering a cooling blanket and a intravascular catheter. A comparison is made between the results obtained and the effects of each case in brain temperature reduction in a required time, maintenance of body temperature at moderate hypothermia levels and gradual rewarming.
High-Speed Particle Image Velocimetry of the Flow around a Moving Train Model with Boundary Layer Control Elements
Trackside induced airflow velocities, also known as slipstream velocities, are an important criterion for the design of high-speed trains. The maximum permitted values are given by the Technical Specifications for Interoperability (TSI) and have to be checked in the approval process. For train manufactures it is of great interest to know in advance, how new train geometries would perform in TSI tests. The Reynolds number in moving model experiments is lower compared to full-scale. Especially the limited model length leads to a thinner boundary layer at the rear end. The hypothesis is, that the boundary layer rolls up to characteristic flow structures in the train wake, in which the maximum flow velocities can be observed. The idea is to enlarge the boundary layer using roughness elements at the train model head so that the ratio between the boundary layer thickness and the car width at the rear end is comparable to a full-scale train. This may lead to similar flow structures in the wake and better prediction accuracy for TSI tests. In this case, the design of the roughness elements is limited by the moving model rig. Small rectangular roughness shapes are used to get a sufficient effect on the boundary layer, while the elements are robust enough to withstand the high accelerating and decelerating forces during the test runs. For this investigation, High-Speed Particle Image Velocimetry (HS-PIV) measurements on an ICE3 train model have been realized in the moving model rig of the DLR in Göttingen, the so called tunnel simulation facility Göttingen (TSG). The flow velocities within the boundary layer are analysed in a plain parallel to the ground. The height of the plane corresponds to a test position in the EN standard (TSI). Three different shapes of roughness elements are tested. The boundary layer thickness and displacement thickness as well as the momentum thickness and the form factor are calculated along the train model. Conditional sampling is used to analyse the size and dynamics of the flow structures at the time of maximum velocity in the train wake behind the train. As expected, larger roughness elements increase the boundary layer thickness and lead to larger flow velocities in the boundary layer and in the wake flow structures. The boundary layer thickness, displacement thickness and momentum thickness are increased by using larger roughness especially when applied in the height close to the measuring plane. The roughness elements also cause high fluctuations in the form factors of the boundary layer. Behind the roughness elements, the form factors rapidly are approaching toward constant values. This indicates that the boundary layer, while growing slowly along the second half of the train model, has reached a state of equilibrium.
A Parallel Poromechanics Finite Element Method (FEM) Model for Reservoir Analyses
The present paper aims at developing a parallel computational model for numerical simulation of poromechanics analyses of heterogeneous reservoirs. In the context of macroscopic poroelastoplasticity, the hydromechanical coupling between the skeleton deformation and the fluid pressure is addressed by means of two constitutive equations. The first state equation relates the stress to skeleton strain and pore pressure, while the second state equation relates the Lagrangian porosity change to skeleton volume strain and pore pressure. A specific algorithm for local plastic integration using a tangent operator is devised. A modified Cam-clay type yield surface with associated plastic flow rule is adopted to account for both contractive and dilative behavior.
Nuclear Fuel Safety Threshold Determine by Logistic Regression plus Uncertainty
Analysis of the uncertainty quantification related to nuclear safety margins applied to the nuclear reactor is an important concept to prevent future radioactive accidents. The nuclear fuel performance code may involve the tolerance level determined by traditional deterministic models producing acceptable results at burn cycles under 62 GWd/MTU. The behavior of nuclear fuel can simulate applying a series of material properties under irradiation and physics models to calculate the safety limits. In this study, theoretical predictions of nuclear fuel failure under transient conditions investigate extended radiation cycles at 75 GWd/MTU, considering the behavior of fuel rods in light-water reactors under reactivity accident conditions. The transient can melt the core reactor partially due to the quick increase of reactivity based on the adiabatic Fuchs-Hansen model using state equations. The kinetic equations show characteristics of complex non-linear applying the adiabatic Fuchs-Hansen model to calculate the dynamic state equations. In this investigation, employs the multivariate logistic regression to a probabilistic forecast of fuel failure. A comparison of computational simulation and experimental results were acceptable. The experiments carried out use the pre-irradiated fuels rods subjected to a rapid energy pulse exhibit the same behavior during a nuclear accident. The propagation of uncertainty utilizes the Wilk's formulation. The variables chosen as essentials to failure prediction were the fuel burn-up, the applied peak power, the pulse width, the oxidation layer thickness, and the cladding type.
Realization of Wearable Inertial Measurement Units-Sensor-Fusion Harness to Control Therapeutic Smartphone Applications
This paper presents the end-to-end development of a wearable motion sensing harness consisting of computational unit and four inertial measurement units to control three smartphone therapeutic games for children. The inertial data is processed in real time to obtain lower body motion information like knee raises, feet taps and squads. By providing a Wi-Fi connection interface the sensor harness acts wireless remote control for smartphone applications. By performing various lower body movements the users provoke corresponding game state changes. In contrary to the current similar offers, like Nintendo Wii Remote, Xbox Kinect and Playstation Move, this product, consisting of the sensor harness and the applications on top of it, are fully wearable, which means they do not rely on the user to be bound to concrete soft- or hardwareequipped space.
Three Dimensional Finite Element Analysis of Functionally Graded Radiation Shielding Nanoengineered Sandwich Composites
In recent years, nanotechnology has played an important role in design of efficient radiation shielding polymeric composites. It has been known that high loading of nanomaterials with radiation absorption properties can enhance the radiation attenuation efficiency of shielding structures. However, due to difficulties in dispersion of nanomaterials into polymer matrices, there has been a limitation in loading of these materials. Therefore, the objective of the present work is, to provide a new insight to fabricate and characterize the functionally graded radiation shielding structures, which can provide efficient radiation absorption properties along with good mechanical integrity. Sandwich structures composed of Ultra High Molecular Weight Polyethylene (UHMWPE) fabric as face sheets and functionally graded epoxy nanocomposite as core material were fabricated. A new method to fabricate a functionally graded core panel with controllable gradient dispersion of nanoparticles has been described. In order to optimize the design of functionally graded sandwich composites and to analyze the stress distribution throughout the composite thickness, a finite element method was used. To predict the stress distribution, a method of superposition principles is described using iso-strain boundary conditions. The sandwich panels were discretized using 3-D 8 nodded brick elements. Also, laminate analysis was used to obtain the properties for the face sheets. The proposed finite element model would provide insight into deformation/damage mechanics of the functionally graded sandwich composites from structural point of view.
Experimental Study of Unconfined and Confined Isothermal Swirling Jets
A 3C-2D PIV technique was applied to investigate the swirling flow generated by an axial plus tangential type swirl generator. This work is focused on the near-exit region of an isothermal swirling jet to characterize the effect of swirl on the flow field and to identify the large coherent structures both in unconfined and confined conditions for geometrical swirl number, Sg = 4.6. Effects of the Reynolds number on the flow structure were also studied. The experimental results show significant effects of the confinement on the mean velocity fields and its fluctuations. The size of the recirculation zone was significantly enlarged upon confinement compared to the free swirling jet. Increasing in the Reynolds number further enhanced the recirculation zone. The frequency characteristics have been measured with a capacitive microphone which indicates the presence of periodic oscillation related to the existence of PVC. Proper orthogonal decomposition of the jet velocity field was carried out, enabling the identification of coherent structures. A three-component POD applied to the instantaneous velocity fields allow to identify the dominant flow structures associated to the PVC. The time coefficients of the first two most energetic POD modes were used to reconstruct the phase-averaged velocity field of the oscillatory motion in the swirling flow. The instantaneous minima of negative swirl strength values calculated from the instantaneous velocity field revealed the presence of two helical structures located in the inner and outer shear layers and this structure fade out at an axial location of approximately z/D = 1.5 for unconfined case and z/D = 1.2 for confined case. By phase averaging the instantaneous swirling strength maps, the 3D helical vortex structure was reconstructed.
Mechanical Properties of Spark Plasma Sintered 2024 AA Reinforced with TiB₂ and Nano Yttrium
The main advantages of 'Metal Matrix Nano Composites (MMNCs)' include excellent mechanical performance, good wear resistance, low creep rate, etc. The method of fabrication of MMNCs is quite a challenge, which includes processing techniques like Spark Plasma Sintering (SPS), etc. The objective of the present work is to fabricate aluminum based MMNCs with the addition of small amounts of yttrium using Spark Plasma Sintering and to evaluate their mechanical and microstructure properties. Samples of 2024 AA with yttrium ranging from 0.1% to 0.5 wt% keeping 1 wt% TiB2 constant are fabricated by Spark Plasma Sintering (SPS). The mechanical property like hardness is determined using Vickers hardness testing machine. The metallurgical characterization of the samples is evaluated by Optical Microscopy (OM), Field Emission Scanning Electron Microscopy (FE-SEM) and X-Ray Diffraction (XRD). Unreinforced 2024 AA sample is also fabricated as a benchmark to compare its properties with that of the composite developed. It is found that the yttrium addition increases the above-mentioned properties to some extent and then decreases gradually when yttrium wt% increases beyond a point between 0.3 and 0.4 wt%. High density is achieved in the samples fabricated by spark plasma sintering when compared to any other fabrication route, and uniform distribution of yttrium is observed.
Prediction of Trailing-Edge Noise under Adverse-Pressure Gradient Effect
For an aerofoil or hydrofoil in high Reynolds number flows, broadband noise is generated efficiently as the result of the turbulence convecting over the trailing edge. This noise can be related to the surface pressure fluctuations, which can be predicted by either CFD or empirical models. However, in reality, the aerofoil or hydrofoil often operates at an angle of attack. Under this situation, the flow is subjected to an Adverse-Pressure-Gradient (APG), and as a result, a flow separation may occur. This study is to assess trailing-edge noise models for such flows. In the present work, the trailing-edge noise from a 2D airfoil at 6 degree of angle of attach is investigated. Under this condition, the flow is experiencing a strong APG, and the flow separation occurs. The flow over the airfoil with a chord of 300 mm, equivalent to a Reynold Number 4x10⁵, is simulated using RANS with the SST k-ɛ turbulent model. The predicted surface pressure fluctuations are compared with the published experimental data and empirical models, and show a good agreement with the experimental data. The effect of the APG on the trailing edge noise is discussed, and the associated trailing edge noise is calculated.
Prediction of Bubbly Plume Characteristics Using the Self-Similarity Model
Gas releasing into water can be found in for many industrial situations. This process results in the formation of bubbles and acoustic emission which depends upon the bubble characteristics. If the bubble creation rates (bubble volume flow rate) are of interest, an inverse method has to be used based on the measurement of acoustic emission. However, there will be sound attenuation through the bubbly plume which will influence the measurement and should be taken into consideration in the model. The sound transmission through the bubbly plume depends on the characteristics of the bubbly plume, such as the shape and the bubble distributions. In this study, the bubbly plume shape is modelled using a self-similarity model, which has been normally applied for a single phase buoyant plume. The prediction is compared with the experimental data. It has been found the model can be applied to a buoyant plume of gas-liquid mixture. The influence of the gas flow rate and discharge nozzle size is studied.
On the Influence of the End Cap Vibration of a Hollow Transmission Bar on the Hollow Split Hopkinson Pressure Bar Test Results
The vibration of an end cap was found when analyzing a hollow transmission bar with an end cap. The vibration may cause errors in the hollow Split Hopkinson Pressure Bar (SHPB) test results. Therefore, the influence of the end cap vibration of a hollow transmission bar on the hollow SHPB test results was analyzed. It is known that the hollow split Hopkinson pressure bar technique which uses a hollow transmission bar with an end cap is a material dynamic properties testing technology which is used to increase the amplitude of the transmitted signal by reducing the transmission bar cross-sectional area. Several simulations and hollow SHPB experiments on the hollow transmission bars with end caps in different thickness were undertaken to analyze the influence of the end cap vibration on Hopkinson bar test results. And the end cap vibration was also analyzed with mechanical liberation theory, and the analysis results were compared with simulation and experiment results. A high-frequency interference could be found in a transmitted wave when the end cap was vibrating. The frequency of the interference in a transmitted wave was similar to the frequency of the end cap vibration which was also similar to the natural frequency of the end cap. The amplitude of the interference in the transmitted wave was related to the amplitude of end cap vibration. The wavelength of the interference could be similar to the transmitted wave if the end cap was in a specific thickness in which condition the interference was difficult to be identified in the transmitted wave. The vibration and the interference became weak and the interference frequency became high when the thickness of an end cap got large. While the thickness of an end cap was larger than the radius of a hollow transmission bar, both the vibration and the interference disappeared, however the transmitted wave invited other distortion, of which the cause is in need of further study.