Characterization of the field-effect conductivity distribution in pentacene thin-film transistors by a near-field scanning microwave microscope

Direct probing of the conductivity distribution in organic materials is motivated by the need to obtain a deeper understanding of carrier behavior in organic thin-film transistors (OTFT), organic electro-luminescent devices, organic photoconductors, and organic biosensors. Here we used a near-field scanning microwave microscope to visualize conductivity profiles in OTFT channel. Applying this technique to pentacene field-effect transistors has revealed changes of the conductivity distribution in the channel arising from the development and exhaustion of an accumulated charge region. The electric field profiles, the complementary image of conductivity profiles, which are visualized by using an optical second harmonic generation method, support the results. We anticipate that direct observation by this microwave method will find wide application in measurement of carrier conductivity in organic and nonorganic materials.     

A study on the flow characteristics of butterfly valve with baffles

Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically...     

Fatigue life analysis of wheels on guideway vehicle using multibody dynamics

A guideway vehicle is used in automobile, semiconductor and LCD manufacturing industries to transport products efficiently. Since the operating speed of the guideway vehicle should be increased for maximum productivity, the weight of the vehicle has to be reduced, and this weight reduction may cause a failure of a part in the system. Therefore, the estimation of the fatigue life of the parts becomes an important problem. In this study, the fatigue life of the wheels in the guideway vehicle is estimated using an S-N curve. To obtain the fatigue life of a part, the S-N curve, the dynamic stress time history applied to the part, and the material property of the part are required. The S-N curve of the driving wheel is obtained from the fatigue experiment on wheels. To obtain the material properties of the driving wheel, which is composed of aluminum with urethane coating, the result of a compression hardware test and static analysis of the wheel’s FE model are used. The dynamic stress time history influencing the driving wheel can be obtained from linear superposition of the dynamic load time history and the static stress. The dynamic load time history is estimated by multibody dynamic analysis, and the static stress is obtained by finite element analysis.     

Recent advances in finite element modeling of the human cervical spine

The human cervical spine is a complex structure that is the most frequently injured site among all spinal injuries. Therefore, understanding of the cervical spine injury and dysfunction, and also biomechanical response to external stimuli is important. Finite element (FE) modeling can help researchers to access the internal stresses and strains in the bones, ligaments and soft tissues more realistically, and it has been widely adopted for spine biomechanics research. Although in recent years numerous techniques have been developed, there are no recent literature reviews on FE models of the cervical spine. Our objective was to present recent advances in FE modeling of the human cervical spine in terms of component modeling, material properties, and validation procedures. Model applications and further development are also discussed. The integration of new technologies will allow us to generate more accurate and comprehensive model of the cervical spine, which can increase efficiency and model applicability. Finally, the FE modeling can help to facilitate diagnosis, treatment, and prevention technologies for cervical spine injuries.     

Determination of Johnson-Cook constitutive equation for Inconel 601

Due to their superior thermal and mechanical properties, super alloys widely used in the aerospace industry have been well-documented in terms of AdvantEdge-based analysis of cutting characteristics rather than experimental methods. However, the well-known super alloy Inconel 601 does not have any database of its material properties in AdvantEdge, which underscores the urgency to build such a database. Hence, the current study uses the Johnson-Cook equation to build a database of Inconel 601’s material properties in AdvantEdge. To that end, drawing on a room temperature tensile test, elevated temperature tensile test and orthogonal cutting test, the current study determines the Johnson-Cook constitutive equation for Inconel 601, and verifies the reliability of the determined Johnson-Cook constitutive equation by comparing the experimental values with the analytical values.     

Research on characteristics and effects of combustion performance by amplified ignition energy in CVCC system

Journal of Mechanical Science and Technology - This study was conducted to analyze the flame characteristics, which is generated through the combustion process according to air/propane mixture...     

Numerical study on design for wave energy generation of a floater for energy absorption

In order to design a wave energy generating system of a floater type, a 6-DOF motion technique was applied to the three-Dimensional CFD analysis on a floating body and the behavior was interpreted according to the nature of the incoming waves. Waves in a tank model were generated using a single floater comparing with that of a Pelamis wave energy converter. In this paper, we focus on four variables, namely the wave height, angular velocity, diameter and length of the floater. The process was carried out in three stages and it was found that there are energy absorption differences in different parameters of wave height, length and the diameter of a floater during simulation, thus leading for the necessity of an optimal design for wave energy generation.     

Numerical study on the range enhancement of a centrifugal compressor with a ring groove system

A numerical study of casing treatments on a centrifugal compressor to improve stability and stall margin is presented. High efficiency, high pressure ratio, and a wide operating range are required for a high-performance centrifugal compressor. A ring groove casing treatment is effective for flow range enhancement in centrifugal compressors. Compressor performance was analyzed according to the ring groove location, and the results were compared with the case without a ring groove. The effect of guide vanes in the ring groove was also investigated. Four variants of grooves were modeled and simulated using computational fluid dynamics to optimize the groove location. Numerical analysis was performed using a commercial code ANSYS-CFX program. The simulation results showed that the ring groove increased the operating range of the compressor. The ring groove with guide vanes improved both performance of the compressor at low flow rates and the stall margin of the compressor.     

Fatigue life analysis of shot-peened bearing steel

Shot-peening effects on the fatigue life behavior of bearing steel (JIS SUJ2) have been investigated. Hourglass-shaped test specimens were heat-treated and then surface-treated using a shot-peening machine. Results of a rotary bending fatigue test showed that shotpeening suppressed not only much of the surface-originated fracture but also the scattering error of the probabilistic stress-life data, and improved the fatigue life by about 6 times through the load levels of the cyclic tests. Such large increase in fatigue life was driven by the following reasons: The increase of hardness in the skin caused the predicted fatigue limit stress to increase by 15%; fracture-initiating inclusions were distributed at deeper locations, experiencing low nominal stresses; and the increase in the fish-eye fracture size by an average of 180%.     

A study on the thermal characteristics of hydrogen storage vessel related to condition of charging

Recently, study on renewable energy has been carried out due to environmental pollution and depletion of fossil fuels. In particular, hydrogen, a clean energy, is environmentally friendly because it produces only pure water as a by-product of the reaction process. In the case of liquified hydrogen, the energy density is about 848 times higher than that of gas hydrogen, but it is not currently widely used due to technical constraints and other problems because it has to maintain a cryogenic state. Therefore, in this work, numerical method was verified by comparing results of precedent study and this study. And relationship between Reynolds number and Nusselt number was confirmed. Based on this results, code was made by using programming language (Fortran 77) with relationship between Reynolds number and Nusselt number to analyze the state of charge (SOC). Variables were set as mass flow rate, temperature of hydrogen gas, and initial tank temperature. As a result, the effect of hydrogen gas temperature is dominant as a factor that affects the temperature of the fully charged state. Therefore, it is determined that the temperature control of the hydrogen storage will be possible through the hydrogen gas temperature setting.