bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Reversal Structure of Photoelectrode in DSSCs
Authors: Chao Wei-Shi , Ting Chen-Ching
Published: May 2012

This article presents significant experimental data about the dye-sensitized nano solar cells (DSSCs) using new developed photoelectrode with the reversal structure in our CCT laboratory. The common structure of a photoelectrode from the incident light is the transparent conduction glass, the nano TiO2 semiconduction porous film, and the dye. In working process of DSSC, the photons energy of the incident light is mainly absorbed by the dye. This causes excited electrons in the dye to jump into conduction band of the TiO2 and further to transfer into the outer circuit through the conduction glass. The common structure causes the light hindrance of the dye by the TiO2 semiconduction layer. To reduce the light hindrance of the dye, experimental study in this work used metal mesh to connect the TiO2 layer with the outer circuit. In other words, the new developed photoelectrode used the metal mesh as the conduction substrate to coat the nano TiO2 semiconduction layer and the dye. In this way, the new structure of the photoelectrode from the incident light is the dye, the nano TiO2 semiconduction film, and the conduction metal mesh. The new structure increases amounts of the absorbed light in the dye and further receives the improved results of larger short-circuit current and photoelectric conversion efficiency in DSSCs.
Visual Investigation of an Ejector Motive Nozzle
Authors: Tischendorf Christian , Lucas Christian , Koehler Juergen , Tegethoff Wilhelm
Published: May 2012

Previous investigations by other authors, e.g. Lorentzen [1], have shown that in a conventional refrigeration cycle significant throttling losses occurs. With the help of an ejector, these losses can be reduced. As a result, the energetic efficiency (COP) of the refrigerant system will be improved. Investigations show that CO2 ejector cycles are feasible and that some systems have already been commercialized successfully. The key issues in the optimization of the ejector used in a refrigeration cycle are the geometries of the different ejector parts. To optimize the geometry, a deeper understanding of the physical effects and the flow conditions within the ejector are essential. So far there are only a few investigations published on this issue, e.g. Elbel [2], investigated the flow in the mixing section of the ejector. This paper presents experimental results for different ejector nozzle geometries and operational condiditons. The motive nozzle was investigated separately from the other ejector parts. Investigated were multi-hole nozzles and the effect of the jet shape. Parameters were chosen according to the typical conditions in ejector refrigeration systems. Based on these conditions, the free jet exiting the motive nozzle was observed. To investigate the jet shape, an new experimental setup was designed. The motive jet was visually observed in a glass cylinder. The combination of both the contraction and compressibility effect on mass flow rate was also investigated.
An Experimental Study for Clarifying the Mechanism of a Microjet in an Electro-Conjugate Fluid by the 2D PIV Analysis
Authors: Satoh Akira , Katoh Kiyohiro
Published: May 2012

If a high voltage is applied to a pair of electrodes immersed in a certain dielectric fluid, a strong microjet occurs between the electrodes. This is called the ECF (electro-conjugate fluid) effect. However, the mechanism of the occurrence of such a microjet has not been clarified yet. As a first step, we here attempt to clarify this mechanism by means of a laser visualization technique with a PIV analysis tool. From this analysis tool, we have obtained flow field solutions and also evaluated the maximum velocity of a microjet as functions of the magnitude of an applied voltage, the separation of a pair of electrodes, etc. Some important results obtained here are summarized as follows. The average maximum velocity decreases linearly with decreasing values of the gap between the electrodes and also with increasing values of the magnitude of an applied voltage in a surface liquid area. Moreover, the average maximum velocity has a tendency to decrease gradually with increasing values of the depth of the electrodes immersed in an electro-conjugate fluid.
Analytical-Numerical Study of Coupled Hyperbolic Heat and Moisture Diffusion in Porous Bodies
Authors: Basirat Tabrizi H. , Andarwa S.
Published: May 2012

Non-Fourier heat conduction and non-Fickian diffusion equations are applied on Luikov’s system for considering finite speeds of thermal and mass propagation. This can be detected in fast transient process. The obtained equation is called Hyperbolic Luikov’s Equation (HLE). It is solved by hybrid analytical-numerical method. By considering non-classical equations for both heat and mass diffusion, there will be two wavefront speeds. They are found via asymptotic analysis based on partial expansion technique. The results show that HLE makes different trends in comparison with Luikov’s system. This difference is significant and more reliable for intense heat and mass process.
Numerical Simulation of Hydrogen-Air Reacting Flows in Rectangular Channels With Catalytic Surface Reactions
Authors: Abou-Ellail Mohsen M. , Amano Ryoichi S. , Elhaw Samer , Saeed Mohamed
Published: May 2012

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computations of momentum transfer, heat transfer and chemical reactions in rectangular channel flows of hydrogen-air mixtures. Chemical reactions are included in the gas phase as well as on the solid platinum surfaces. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surfaces, additional surface species are included that are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is pre-specified, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a rectangular channel burner. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations of the reacting gas flow properties are solved by a combined iterative-marching algorithm. On the platinum surfaces, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surfaces. The channel flow computational results are compared with recent detailed experimental data for similar geometry. In this case, the catalytic surface temperature profile along the x-axis was measured accurately and is used in the present work as the boundary condition for the gas phase energy equation. The present numerical results for the gas temperature, water vapor mole fraction and hydrogen mole fraction are compared with the corresponding experimental data. In general, the agreement is very good especially in the first 105 millimeters. However, some differences are observed in the vicinity of the exit section of the rectangular channel. The numerical results show that the production of water vapor is very fast near the entrance section followed by a much slower reaction rate. Gas phase ignition is noticed near the catalytic surface at a streamwise distance of about 120 mm. This gas-phase ignition manifests itself as a sudden increase in the mole fractions of OH.
Configuration Consideration in Improving the Power Output of the PZT Energy Harvester
Authors: Hussein Wael S. , Salleh Hanim
Published: May 2012

The current trend of producing small autonomous electronic devices and the disadvantages of using batteries encourage the researchers to find new power resources with a long lifetime and suitable size to use them with these devices. In this paper different configurations and mounting methods for a vibration based piezoelectric power generator array consists of triangular shaped PZT cantilevers with a proof mass at the end have been investigated to find the optimum design to maximize the power output and minimize the volume of the device. At the same time many vertical and horizontal arrangements are tested and for a variable number of cantilevers within a range of low frequencies and a fixed acceleration to confirm the principle function of the generator which is the ability to produce a maximum power in a wide range of low frequencies which is laid around the resonant frequency of the cantilevers. Four cantilevers have been used in this experiment with a 10mm width and 25mm length, these cantilevers composed of two layers of PZT ceramic and a brass centre shim, the range of input frequency is (50–150)Hz with a 10 m/s2 acceleration. The horizontal cross arrangement showed a very good performance in terms of output voltage but it takes a large space, other configuration which is a combination of the horizontal and the vertical mountings can give better results in terms of power output and space consumption.
Normalized Cross-Correlation of Subsequent Strides for Evaluation of Walking Stability
Authors: Wang Xue , Lu Wen Feng , Loh Han Tong , Wong Yoke San , Ong Fook Rhu
Published: May 2012

Evaluation of walking stability is essential for the elderly population to prevent possible falls due to degradation of their walking stability caused by aging. Previous studies mainly focused on center of pressure (COP) and center of body mass (COM) and their relationship during walking. However COM can not be directly measured and existing COP parameters are mainly investigated within one stride and their effectiveness is not conclusive. In this study, new parameters are proposed based on normalized cross-correlation of subsequent strides (NCSS), derived from comparison of subsequent strides of foot plantar pressure. The mean and standard deviation of NCSS are calculated for three walking conditions that are progressively less stable (1 - normal walking, 2 - walking with eyes closed, and 3 - walking with eyes closed after being spun around) for six healthy subjects. Results show that the NCSS can effectively distinguish normal walking (1) and the less stable walking with eyes closed after being spun around (3). The mean of NCSS decreases from stable to less stable walking conditions, whereas the corresponding standard deviation of NCSS increases. For each subject the value of NCSS of walking with eyes closed (2) is between those of the other two walking conditions (1 and 3), although the value varies somewhat, depending on the controllability and adaptability of the subject.
Dynamic Analysis of an A-Shaped Piezo-Actuated Walking Microrobot
Authors: Kamali Eigoli Ali , Vossoughi GholamReza
Published: May 2012

In this paper, a novel, A-shaped microrobot with nanometric resolution for precision positioning applications is addressed. The locomotion concept of the mechanism is founded on the “friction drive principle”. To achieve the translational motion, a stack piezoelectric actuates the microrobot near its natural frequency. The dynamic modeling of the mechanism is based on the assumptions of linear behavior of piezo stack actuator and Coulomb friction model at contact points. The suitability of three simple, friction-based locomotion modes for implementation on the proposed device is presented. Influences of different friction coefficients on the behavior of the microrobot, with respect to defined criteria, are invoked. Simulations show a velocity of 1 mm/s, a motion resolution of 180 nm, and a power consumption of 1.5 mW. Comparisons made with other microrobots of the same locomotion principle indicate good improvements in all criteria.
Chromium-Free Surface Pre-Treatment of Aluminum for Adhesive Bonding
Authors: Ngoh S. L. , Tan S. C. , Goh C. S. , Wei J.
Published: May 2012

Adhesive bonding offers many advantages, such as light weight, ease of manufacturing, corrosion resistance and more uniform stress distribution at joint. In order to achieve good initial adhesion and durability of adhesive bonded aluminum joint, pre-treatment of the aluminum substrate is essential. Some of the surface pre-treatment procedures commonly used are chromium-based chemical and electro-chemical methods. However, due to the environmental and health concerns, and legislation to ban the use of hexavalent chromium, there is a need to omit the use of chromium-based pre-treatment methods in the surface preparation process. Therefore, this work aims to study the effect of the developed hybrid chromium-free surface pre-treatment method on the bonding strength of adhesive bonded aluminum joint. The study on the effects of solution concentration level and processing time of the hybrid treatment on the bonding strength suggests that bonding strength can be improved through enhancement of mechanical interlocking and increase of bonding area between the adhesive and adherend. Even though comparable or rougher surface morphologies were obtained from hybrid treatments as compared to the chromium-based treatment, lower bonding strengths were observed. This further suggests that the nano-scale level interaction between the adhesive and adherend has vital effect on the bonding performance.
A Novel Approach to Process Modeling for Ultrasonic Plastics Welding
Authors: Ying M. , Cheng C. K. , Wei J.
Published: May 2012

Ultrasonic plastics welding is a widely employed joining technique for thermoplastic polymer assembly nowadays. As one fusion joining method, the ultrasonic welding quality is mainly dependent on the interfacial temperature which is affected by many process factors, such as welding time, welding pressure, and vibration amplitude, as well as material properties. Many attempts have been made to understand the mechanism of creation of an ultrasonic weld but limited by the complexity of the welding process. The current study developed a novel approach to process modeling for ultrasonic plastics welding. The thermoplastic materials were characterized with time domain viscoelastic model. The energy dissipation by the viscoelasticity was converted into the heating source which caused the temperature rose. The temperature change affected the material and structure responses and eventually the dissipated energy. As such, a fully coupled thermal-stress finite element (FE) model was established to simulate the performances of the ultrasonic welding. With the fully coupled model, the temperature distribution and displacement could be solved accurately and simultaneously. Meanwhile, the interfacial temperature was experimentally measured under the different process parameters. The simulation model was further validated by the measured temperature. With this novel approach, the ultrasonic plastics welding process can be completely simulated and the process parameters can be optimized numerically.
Marine Energy Devices for Colombian Seas
Authors: Correa Julio C. , Flo´rez Diego A. , Posada Norha L. , Valencia Rau´l A. , Zuluaga Carlos A.
Published: May 2012

There are several alternatives to obtain marine energy: waves, tides, currents, gradients of temperature and gradients of salinity. All of them have been studied extensively, however their implementation is closely related to the particular conditions of the local sea. This paper presents preliminary results related with the kind of the instrumentation required to monitor the behavior of the variables associated with marine energy and the best available technologies to take advantage of the marine power in the Colombian seas.
The Influence of Nanofillers and Additives on the Adhesion Strength of Aluminum
Authors: Goh C. S. , Tan S. C. , Ngoh S. L. , Wei J.
Published: May 2012

In this study, adhesives with Al2O3 nanofillers or silane additives incorporated have been developed. Functionalization of the Al2O3 nanofillers has been carried out to improve the bonding of the fillers to both the adhesive and Al substrate. The silane coupling agents on the nanofillers can react with the Al2O3, Al substrate and adhesive through their functional end groups and form strong covalent and hydrogen bonds which can improve the lap shear strength of the adhesive substantially. An improvement in lap shear strength has also been achieved when glycidoxypropyltrimethoxysilane is added directly into Epon 160 adhesive. There is also an obvious change in fracture mode from adhesive to cohesive due to the effect of silane addition which facilitates bond formation between the adhesive and Al substrate.
Advanced Exergoenvironmental Analysis of a Steam Methane Reforming System for Hydrogen Production
Authors: Tsatsaronis G. , Boyano A. , Morosuk T. , Blanco-Marigorta A. M.
Published: May 2012

In this paper, an advanced exergoenvironmental analysis is conducted for a steam methane reforming process for the production of hydrogen. The approach for calculating pollutant formation is generalized and the assumptions required for applying the analysis are discussed in detail. These are the main contributions of this work to the development of exergy-based methods for the analysis of energy-intensive chemical processes. In an advanced exergoenvironmental analysis, the environmental impact associated with the exergy destruction within a component as well as the component-related environmental impact and a component-related pollutant formation are split into unavoidable/avoidable and endogenous/exogenous parts. This splitting improves our understanding of the sources of thermodynamic inefficiencies and their effect to the formation of environmental impacts and pollutants, and facilitates a subsequent improvement of the overall process. Finally, some improvement options developed on the basis of the results of the advanced exergoenvironmental analysis are discussed.
An Experimental and Analytical Investigation Into Friction-Induced Vibrations and Parameters Affecting Its Occurrence
Authors: Bahzad A. , Mokhtar M. O. A. , El-Butch A. M. A. , Fahim A. F.
Published: May 2012

The condition for the occurrence of friction-induced vibrations is examined numerically and experimentally based on a single degree of freedom system with different friction models that relates the friction force with the relative interface speed. In this study the dimensionless parameters which control the occurrence of stick-slip motion are investigated, it is found that some of these parameters results in the occurrence of stick-slip motion while others are acting to avoid it. The equations governing the occurrence of friction-induced vibrations are derived in dimensionless form and solved numerically in order to have both high accuracy and reducing the number of the system parameters. The attained numerical results are validated by the comparison with the experimental results. Results also showed that damping ratio, speed, load factor, the used friction models and excitation frequency greatly affecting the occurrence of stick-slip motion.
Exergetic Analysis of Systems Generating Electricity Through Expansion of Natural Gas
Authors: Tsatsaronis G. , Griepentrog H. , Morosuk T.
Published: May 2012

This paper discusses the thermodynamic performance of three different system configurations used to expand natural gas: (1) A system in which all natural gas passes through a throttling valve, (2) a system that uses only an expander as the expansion device, and (3) a system using in parallel both an expander and a throttling valve as expansion devices. The overall energetic efficiencies for the second system are between 89.2 and 89.4% while for the third system they are between 89.4 and 89.9% depending on mass throughput. The corresponding exergetic efficiencies are between 25% and 32% for the second system and 10% and 25% for the third one. The sensitivity analysis demonstrated that the mass flow rate of natural gas affects the thermodynamic efficiency of the systems generating electricity through expansion of natural gas. The differences in efficiencies between the second and third system, particularly at higher mass flow rates could justify the higher investment costs required for the second system and make it the most attractive system also from the cost viewpoint among the three systems studied here.
Copper to Copper Direct Bonding Assisted by Self-Assembled Monolayer
Authors: Lim D. F. , Ang X. F. , Wei J. , Ng C. M. , Tan C. S.
Published: May 2012

In this article, a self-assembled monolayer (SAM) is applied onto the copper surface in an attempt to lower the required bonding temperature. Alkane-thiol with 6-carbon chain length is used and tested for bonding experiment. The adsorption of SAM is confirmed by the sharp rise of the water contact angle measurement and the reduced in the surface roughness. Next, the desorption of SAM is done at a high temperature anneal (<300°C) in an inert ambient and its properties are characterized by the water contact angle measurement and XPS. It is found that the water contact angle measurement decreases sharply close back to the contact angle of the pure blanket copper surface after annealing of SAM. The XPS results also show the ability of SAM in protecting Copper surface from oxidation. Finally, shear test is performed on Cu-Cu structures bonded at low temperature (250°C) in order to verify the SAM behavior in protecting the copper surface from oxidation and enhancement for bonding. The wafer pairs with and without SAM are intentionally exposed in clean room environment for few days. The bonded pieces are diced and subject to shear stress and results show that with SAM protection, shear strength is improved due to the enhancement in grain growth as a result of cleaner surface.
The Influence of Ambient Pressure on the Dynamic Response of RF MEMS Switches
Authors: Ohana Avihay , Aharon Oren , Maimon Ronen , Nepomnyashchy Boris , Kogut Lior
Published: May 2012

A study of the dynamic behavior of an RF MEMS switch is presented at different operating conditions. Experimental results for the actuation and release time and Q-factor as a function of the ambient pressure and actuation voltage are compared to theoretical predictions based on existing model. Optimal operating conditions (ambient pressure and actuation voltage) are determined based on two criterions: minimal actuation and release time and minimal oscillations upon switch release. In light of the experimental results optimal operating conditions determined to be 1.4Vpi at a pressure of a few torrs where actuation and release time are equal and short enough with no release oscillations. Three pressure regimes are identified with characteristic behavior of the Q-factor and actuation and release time in each regime. These behaviors have significant implications in many MEMS devices, especially RF MEMS switches.
Study of Chatter Stability in Boring Process Using Operating Deflection Shape
Authors: Mohammadi Zohreh , Movahhedy Mohammad R.
Published: May 2012

Chatter is a limiting factor in machining systems with adverse effects for workpiece surface, tool and machine life and material removal rate. Proper modelling of this phenomenon requires that the dynamic characteristics of the machining system is known. It is common to obtain the dynamic of the system by modal tests in stationary condition. However, the vibration characteristics of a machine change between its operating and resting mode. The goal of this work is to study vibrations in boring using the vibrational characteristic in operational conditions using the operating deflection shape method. In this paper, vibration characteristics of the in the boring bar is obtained by both modal analysis and operating deflection shape methods and the results are compared. The results show that differences exist between the two conditions that can be small or large in different machining conditions.
Effects of Miniaturisation on Electromagnetic Motors for Micro Mechatronic Systems
Authors: Mekid Samir
Published: May 2012

This paper explores the possibilities and the limitations of scaling down DC motors needed for micro mechatronic systems. It is observed that power and torque decrease with the volume of the motor i.e. diameter and length. Hence producing powerful micro-motors with high torque is currently not possible with direct miniaturisation. Alternative ways of improving the performance are crucial. Background discussion is suggested in this paper. Yet, rotational speed increases when the motors become smaller. They can reach very high speed ranges (in the order of 100,000 rpm) due to the reduction in inertia and friction but with lower torques though. A general behaviour trend between the motor size and its characteristics are discussed. It is expected in order to reach the full potential of micro motors that innovative principles should be considered to generate rotational motion suitable for miniaturisation.
Dynamic Modeling and Fluid-Structure Interactive Analysis of an Innovative Self-Tuning Shock Absorber for the Prosthesis Knee Joint
Authors: Mao Yen-Chieh , Chang Wei-Chih
Published: May 2012

The above-knee prosthesis, as a supplement of the lost biological leg, is supposed to provide equivalent or enhanced shock absorption capability and reduce the shock waves on the amputee body when walking and running. Prosthesis knee joint with a shock absorber is a feasible solution that efficiently absorbs the impact loads during each heel-strike. Conventional shock absorbers consist of springs and dampers with constant coefficients produce excessive rigid reactions when encountering impact forces, while unreasonable weak responses for gentle loads. This study proposes an innovative viscous damper design for the prosthesis knee joint which automatically and smoothly tunes the damping coefficient without any electronic components according to the input force velocities. High order differential system of the shock absorber is constructed and simulates the system dynamics during cyclic loads. The fluid-structure interactive finite element model for key components in the absorber is established in this study. Design parameters of the damper system under certain absorbing performance requirements are determined in this paper.
The Elastic Limits of Colon Tissues for Different Radii of a Tool Tip End Using a Simple Modeling
Authors: Choi Junghun
Published: May 2012

Mechanical properties of colon tissues are very important to prevent trauma and perforation during colonoscopy procedure. Most of forces are generated by the shaft of a colonoscope and a distal tip. A shaft of a colonoscope causes mechanical trauma at various locations. A distal tip of a colonoscope can cause not only for mechanical trauma but also serious perforation. In this study, elastic limits of forces were predicted for different sizes of a simplified shape of a tool tip end with a simple characteristic modeling. Published data on the various parts of a colon were used for the reference and a simple way of modeling was applied to estimate the quantity of forces with assumptions. Stress on Descending colon was used and a true stress-strain curve was generated. Descending colon has a wide range of a force limit for two different directions (longitudinal and lateral). A simple characteristic modeling was applied for a spherical shape of tool tip. Even though different parts of a colon and directions will generate diverse results, the model should be insensitive within a limited length and boundary conditions of a colon. The different radii of a tool tip end represent various tool ends from dull to sharp needle-type tool ends in several grades. The results show the elastic limit of force for different radii of tool tip end. The range of tool tip radius is between 0.1 and 10 mm. For the smallest radius of a tool tip, a colon wall will be perforated for a small force (less than 0.05N) and big forces were needed to damage the colon tissue when a tool tip diameter is more than 20 mm with the assumption that the boundary condition of a tool tip test should match up with the simple modeling statement. As the radius of a tool tip end is larger, the contact area between the interface area between a tool tip and a colon wall is wide enough to sustain applied forces. The structure of a human colon was briefly reviewed and determined the elastic limits of forces for different radii of tool ends.
Single Screw vs. Double Screw Device for Use in Treating Femoral Bone Fractures
Authors: Ondrake J. E. , Lifer K. C. , Haman S. P. , Marquart J. E. , Shen Hui
Published: May 2012

Proximal femur fractures commonly occur between the head of the femur and the femoral shaft. As the third most common injury encountered in orthopedic clinics, these fractures are typically treated with medical implants creating internal stabilization of the bone. Over 100 different implants are available for this application. Although the optimal choice for the implants is still controversial, traditional devices which include a single cylindrical screw, such as SHS (Sliding Hip Screw) and IMHS – CP (Intramedullary Hip Screw, Clinically Proven), are widely used to repair the bone fracture. However, the application of the single screw device still suffers technical problems. The head of the femur has the potential to rotate about the screw and the fracture surfaces have potential to slide over each other. In addition, force relaxation can occur, leading to inadequate contact between the fracture surfaces. To attack these problems and prevent possible complications, a new device has been developed. The new device consists of one long screw interlocked with one short screw, creating a cross-sectional figure-eight pattern and offering an integrated, interlocking screw option. The objective of the current study is to compare biomechanical characteristics within the bone caused by the new double screw device verses the traditional single screw device. Experiments were preformed to compare the torsional stiffness of the two devices. 2D and 3D finite element analysis methods were carried out to obtain macroscopic and microscopic responses of each device’s interaction with the fractured bone. The modeled results show a significant difference between the two geometries. The single screw geometry has higher maximum total deformation, equivalent strain, equivalent von Mises stress, and maximum principle stress. The improved rotational stability of the new double screw device may reduce the complication rate of instability of the fracture fragments.
Molecular Dynamics of Crack Propagation in Nickel and Nickel-Aluminum Bimetal Interface
Authors: Purohit Yojna , Mohan Ram
Published: May 2012

Molecular dynamics simulations were used to study crack propagation in a Nickel single crystal and a Nickel-Aluminum bimetal interface. The embedded atom method interatomic potential was used to investigate the behavior of (001) [100] crack system under mode I loading in the two systems. The propagation mechanisms and fracture behavior and properties of a propagating crack in Ni were compared with propagation, behavior and properties of a surface crack in Ni-Al that initiates and propagates from Ni towards the Ni-Al bimetal interface. Our results for Ni show an initial brittle crack propagation followed by a roughening of the crack surfaces at one-third of the Rayleigh wave speed and are in agreement with previous investigations. In Ni-Al the crack surfaces initially grow brittle. However, two regimes of crack propagation velocities were observed in this case with crack getting decelerated as it nears the interface. Further dynamic analysis of the crack propagation indicated a cease in the crack propagation in Ni due to a brittle to ductile transition. In Ni-Al bimetal interface system, as the crack approaches the interface, a process zone representing local disorder at the crack tip was observed to start growing and interacting with interfacial defects that eventually results in a blunting of the crack tip.
Finite Element Study of Collapse of Pediatric Spine Due to Tuberculosis of Spine
Authors: Jebaraj C. , Jebaseelan D. Davidson , Rajasekaran S. , Yoganandan Narayan
Published: May 2012

The study of pediatric spine has been limited due to few experimental and numerical studies. The geometry and the material properties for the pediatric spine are age-specific. The current study develops an anatomially accurate finite element model (FEM) of a (T2/S1 thoracolumbar spine from an 8-year-old’s CT scan. The FEM model has to be validated to study the collapse pattern of a juvenile spine due to discitis. Hence the present model was scaled up to 141% to represent an adult model and adult moment loads were applied. Buckling studies and flexion bending moment were applied on the intact 8-year-old’s spine and for the two stages of discitis. The flexion-extension and lateral bending on the 141% model was found comparable at various levels with the literature. The buckling analysis found the 8-year-old’s model to behave as a straight slender column as curvatures are less defined. The buckling load for the pediatric model was 13.45N and 5N for the extreme discitis model. The flexion study found minimum disruptions in the initial infection but when the disc becomes puss like, the bending stiffness at the infected level reduces drastically leading to high angulations, and a significant degree of disruptions are observed at other locations.
Parametric Analysis of a Bayonet Tube With a Special Type of Extended Surface
Authors: Almanza-Huerta L. , Hernandez-Guerrero A. , Krarti M. , Luna J. M.
Published: May 2012

The present paper provides a numerical study of a parametric analysis of a bayonet tube with a special type of extended surface during the laminar-turbulent transition. The working internal fluid is air. Attention is focused on the heat transfer characteristics of the tube. The results constitute a systematic investigation of the effect of the extended surface located along the annulus of the bayonet on the overall heat transfer rate. The effects of the variation of some parameters related to the extended surface aiming to attain the maximum heat transfer with the minimum pressure drop are discussed. Comparisons between designs with and without extended surface are also made.
Frequency Division Multiplexing of a Multi-Channel Resistive Pulse Sensor
Authors: Jagtiani Ashish , Zhe Jiang , Carletta Joan
Published: May 2012

We present the design, fabrication and testing of a microfluidic multichannel resistive pulse sensor for high throughput counting of microparticles. The high throughput counting results from using multiple parallel microfluidic channels to analyze the sample. Detection is achieved by using frequency division multiplexing where a known and unique frequency is applied to modulate each microchannel and a combined measurement is made across a single pair of electrodes. Testing results using 30μm polystyrene particles demonstrate that the throughput of the multiplexed device is improved 300% over a single channel device. In addition, the AC modulation method reduces the polarization effect on the microelectrodes, and thereby allows for measurement of the actual particle sizes. The multiplexed detection principle can be extended to a larger number of channels to further improve the throughput, without increasing the external detection electronics.
The Effect of Static Roof Crush Tests Relative to Real World Rollover Injury Potential
Authors: Friedman Donald , Mattos Garrett
Published: May 2012

Rollover crashworthiness for passenger vehicles is currently evaluated by the Federal Motor Vehicle Safety Standard (FMVSS) 216 static roof strength compliance test. However, research clearly shows that the static test is inadequate in evaluating a vehicle’s injury potential performance in a real-world rollover event. Studies previously conducted by the Insurance Institute for Highway Safety (IIHS) show a general relationship between a vehicle’s Strength-to-Weight-Ratio (SWR) and its real world injury potential. Although this general relationship is fairly accurate for most vehicles, there are many individual vehicle anomalies. The real world injury performance of the vehicles which make up these anomalies depends much less on the static roof strength (as measured in a FMVSS 216 test) and more on the dynamic performance of the roof and occupant protection systems during a real world rollover (as simulated on the Jordan Rollover System [JRS]). Repeatable dynamic crash tests are used by IIHS, National Highway Traffic Safety Administration (NHTSA), and the New Car Assessment Program (NCAP) to evaluate the performance of a vehicle in every major crash mode except rollovers. Dynamic tests represent the real world effect of vehicle dynamics, orientation, geometry, roof strength, occupant position and kinematics, restraint and other safety system effectiveness while directly measuring comparative dummy injury criteria. Because National Accident Sampling System (NASS) investigations can only measure the cumulative effect of post crash roof crush, NHTSA has established an empirical relationship that a vehicle with post crash negative headroom (PCNH) is five times more likely to injure the occupant. However, data indicates that the anomalies in head, neck, and spinal cord injury are related to the momentum exchange of dynamic head impact speed and the duration of neck loading in each roll, not the cumulative amount of residual roof crush. This paper suggests a means of comparatively evaluating a vehicle’s dynamic rollover occupant injury potential performance.
Multi-Objective Crashworthiness Optimization of Composite Hat-Shape Energy Absorber Using GMDH-Type Neural Networks and Genetic Algorithms
Authors: Tavassoli Naser , Notghi Bahram , Darvizeh Abolfazl , Darvizeh Mansour
Published: May 2012

Reducing the weight of car body and increasing the crashworthiness capability of car body are two important objectives of car design. In this paper, a multi-objective optimization for optimal composite hat-shape energy absorption system is presented At the first, the behaviors of the hat shape under impact, as simplified model of side member of a vehicle body, are studied by the finite element method using commercial software ABAQUS. Two meta-models based on the evolved group method of data handling (GMDH) type neural networks are then achieved for modeling of both the absorbed energy (E) and the Tsai-Hill Failure Criterion (TS) with respect to geometrical design variables using those training and testing data obtained models. The obtained polynomial neural meta-models are finally used in a multi-objective optimum design procedure using NSGA-II with a new diversity preserving mechanism for Pareto based optimization of hat-shape. Two conflicting objectives such as maximizing the energy absorption capability (E), minimizing the Tsai-Hill Failure Criterion are considered in this work.
Investigation of the 3D Velocity Field of a Segmented Flow Utilizing a Novel 3C3D Micro-PIV Approach
Authors: Abdolrazaghi Mona , Nobes David S.
Published: May 2012

Segmented flow occurs in several microfluidic systems such as monolith reactors, cellular systems, and human airways. Liquid-gas bubbles can cause different issues in the micro-channel by disturbing the flow and even blocking the channel. Investigating this kind of flow phenomenon provides useful information for improving the efficiency of both industrial and biomedical devices. Predicting the velocity of bubbles, velocity within the liquid slug and the thickness of the thin liquid film in the slug flow is one of the challenges in this field. In this paper, a novel measurement technique capable of measuring three components of the velocity is described and used to investigate the flow in the region of the gas-fluid interface of a segmented flow.
Design of an Embedded Sensor Network for Manufacturing Process Monitoring, Quality Control Management and Structural Health Assessment of Advanced Composite Structures
Authors: Keulen Casey , Rocha Bruno , Suleman Afzal , Yildiz Mehmet
Published: May 2012

This paper proposes the use of an embedded network of fiber optic sensors for process and Structural Health Monitoring (SHM) of Resin Transfer Molded (RTM) composite structures. A single sensor network is used at each stage of life of a RTM composite panel: flow monitoring, cure monitoring and health monitoring. A laboratory scale RTM apparatus was designed and built with the capability of visually monitoring the resin filling process. A technique for embedding fiber optic sensors into the mold has also been developed. Both Fiber Bragg Gratings (FBG) and Etched Fiber Sensors (EFS) have been embedded in composite panels using the apparatus. Etched Fiber Sensors have the capability of detecting the presence of resin. The sensors have proven to be capable of detecting the presence of resin at various locations as it is injected into the mold and have the capability of being multiplexed with FBGs thus reducing the number of ingress/egress locations required per sensor. Two FBGs and three EFSs were embedded on a single optical fiber. Tensile test specimens that contain embedded FBG sensors have also been produced with this apparatus. These specimen and embedded sensors have been characterized using a strain gage and a material testing machine. FBG sensors have been embedded into composite panels also in a manner that is conducive to detecting Lamb waves generated with a centrally located PZT. To detect Lamb waves a high speed, high precision sensing technique is required for embedded FBGs, since these guided waves travel through the material at very high velocities, presenting relatively small strain amplitudes. A technique based in a filter consisting of a second FBG was developed. Since this filter is not dependant on moving parts, it does not limit the velocity or frequency at which the tests can be performed. Preliminary tests performed using this filter showed that it is possible to detect Lamb waves with amplitudes smaller than 1 microstrain. A damage detection algorithm has been developed and is applied to this system in an attempt to detect and localize damages (cracks and delaminations) in the composite structure.
Reduced-Order Models of Mistuned Cracked Bladed Disks
Authors: Marinescu Olguta , Epureanu Bogdan I. , Banu Mihaela
Published: May 2012

Predicting the influence of cracks on the dynamics of bladed disks is a very important challenge. Cracks change the structural response, which in turn changes the crack propagation characteristics. Hence, accurate and computationally effective means to model the dynamics of cracked bladed disks and blisks is particularly crucial in applications such as prognosis, guidance for repairs, characterization after repairs, design, and structural health monitoring. Most current models of bladed disks exploit cyclic symmetry to gain computational efficiency. However, the presence of cracks and mistuning destroys that symmetry and makes computational predictions much more expensive. In this work, we propose a new reduced order modeling methodology which can speed up computations by several orders of magnitude. There are two key components of the new methodology. First, the displacements and deformations of the crack surfaces are not modeled in absolute coordinates but relative coordinates. That allows for an effective model reduction based on (fixed-interface Craig-Bampton) component mode synthesis (CMS). The use of relative coordinates allows one to define one of the components in CMS as the pristine/uncracked structure (with mistuning). This approach is used in combination with a set of accurate approximations for the constraint modes used in CMS. Second, the effects of mistuning are captured by component mode mistuning (CMM) which allows the construction of extremely efficient reduced order models for the pristine/uncracked component with mistuning. The novel proposed method is applied to a finite element model of an industrial blisk. The combined presence of mistuning and cracks is shown to have important effects. Also, the proposed approach is shown to provide accurate predictions for the overall blisk while requiring computations using single-sector models only. The influence of various parameters on the accuracy of the reduced order models is investigated. Overall, the results show a very good agreement between full finite element analyses and the proposed reduced order modeling approach.
Flow Characteristics in a Channel With Corona Wind Generator
Authors: Zhang J. , Lai F. C.
Published: May 2012

Electrohydrodynamically induced flows have shown great potential for many engineering applications. Previous studies have revealed that a corona wind generator can be used to enhance flow transport in a channel. In this study, a corona wind generator with emitting wire electrodes flush mounted on the channel walls is considered for a wide range of operating conditions. Specifically, three configurations of the generator (with 4, 12, and 28 pins of emitting electrodes) are evaluated for their effectiveness in delivering the air flow. To investigate the flow characteristics inside a square channel, three-dimensional governing equations for electric and flow fields are numerically solved. The corona current is first measured experimentally and used in the numerical calculations. Numerical predictions on the velocity profile of corona-induced air flows as well as the volume flow rate delivered have been successfully verified by experimental results.
Multiscale Thermal Transport Across Solid-Solid Interfaces
Authors: Balasubramanian Ganesh , Kappiyoor Ravi , Puri Ishwar K.
Published: May 2012

We propose a novel multiscale model in order to better understand thermal transport across solid-solid interfaces in a mesoscale system. While Molecular Dynamics (MD) simulations tend to be very accurate, they are also computationally rather expensive. Continuum simulations such as Symmetric Smoothed Particle Hydrodynamics (SSPH), cannot take temperature discontinuities that may occur across interfaces into account, which can cause erroneous results. As such, we develop a multiscale model in which we run MD simulations over the region containing the interface, while running SSPH simulations over the remainder of the domain. This drastically reduces the number of molecules simulated by MD, reducing computational time, while hopefully still maintaining the accuracy provided by a “pure” MD run. Results from the simulation indicate that when boundary temperatures are specified, the data from the multiscale model is highly similar to the data from the pure MD run. However, when boundary fluxes are specified, the multiscale model tends to predict higher temperatures than does MD. We believe that this may be due to continuum SSPH simulations being unable to take into account phonon scattering with non-periodic boundary conditions.
An Improved Algorithm of Evaporator Steady-State Simulation
Authors: Jiang Baoshi , Cui Wenzhi , Xiang Yong , Jen Tien-Chien
Published: May 2012

The characteristics of heat pump evaporator are simulated using steady-state lumped parameter model. Considering the difference between the heat transfer of vapor and liquid refrigerant, the calculating method of the weighted average temperature in evaporator is revised, and the scope of the calculation is expanded to superheat section. The assumption of the chilled water outlet temperature is generally used in conventional simulation program and iteration of the temperature is necessary, which is a time-consuming process. In this paper, the outlet temperature of chilled water is determined by energy conservation and only the outlet enthalpy of refrigerant needs to be iterated, making the calculating process much fast. The effects of inlet parameters of chilled water on overall heat transfer and outlet chilled water temperature are examined using the new program. The prediction of simulation is compared with experimental results and good agreement obtained.