bluuebunny/crossref_metadata_2025 huggingface dataset:
Aero-Thermodynamic Modelling and Gas Path Simulation for a Twin Spool Turbo Jet Engine
Authors: Sankar Balaji , Subramanian Thennavarajan , Shah Brijeshkumar , Vanam Vijayendranath , Jana Soumendu , Ramamurthy Srinivisan , Satpathy Radhakant , Sahoo Benudhar , Yadav Satish
Published: July 2018

The user community of civil and military aircraft powered by gas turbine engines has a significant interest on simulation models for design, development and maintenance activities. These play a crucial role in understanding the aircraft mission performance. The simulation models can be used to understand the behavior of gas turbine engine running at various operating conditions, which are used for studying the aircraft performance and also vital for engine diagnostics. Other significant advantage of simulation model is that it can generate required data at intermediate stages in gas turbine engine, which sometimes cannot be obtained by measurement. Thus engine simulation model / virtual engine building is one of the important aspects towards development of Engine Health Management (EHM) system. This paper describes in detail the engine simulation model development for a typical twin spool turbo jet engine using commercially available Gas turbine Simulation Program (GSP). The engine simulation model has been used for typical aero-engine to get aero-thermodynamic gas path performance analysis related to engine run at Design point, Off Design points and the engine Acceleration-Deceleration Cycles (ADC). Simulations at different operating conditions have been carried out using scaled up characteristic maps of engine components. Design point data as well as engine gas path data obtained from test bed has been used to develop scaled up characteristic maps of the engine components. The simulation results have been compared with various test bed data sets for the purpose of validation. Predicted results of engine parameters like engine mass flow rate and thrust are in good agreement with the test bed data. This validated model can be used to simulate faulty engine components and to develop the fault identification modules and subsequently an EHM system.
Development of Foil Bearings for Small Rotors
Authors: Kulkarni Sadanand , Naik Soniya D. , Kumar K. Sarosh , Radhakrishna M. , Jana Soumendu
Published: July 2018

Lubricant free high speed turbo-machineries are one of the emerging fields in the gas turbine technology. Foil bearings are the major contenders in the lubricant free bearings due to their ability to support significant loads at very high speeds. The paper deals with the various stages in the development of discrete and continuous bump foil bearings and testing of the same for designed speeds and loads. Development of bumps involves determination of bump geometry for the desired load capacity, design of special purpose dies for the fabrication of corrugated sheets, identification of suitable bump material and evolution of heat treatment process. Here Beryllium–Copper (Be-Cu) is used as a bump material because of its self-lubricating property and good mechanical strength. The clearance between the shaft and top foil can be adjusted by providing the back-up foils between the encircling foil and bump foil. The rotor system simulating the weight of a typical micro gas turbine is designed and fabricated. The foil bearings developed are tested under this simulated load conditions at speeds above 50,000 rpm. The results obtained show that the rotor is completely airborne at speed slightly above 9000 rpm and at higher speeds the rotor is stable.
Parametric Study of Moss-Brookes (MB) and Moss-Brookes-Hall (MBH) Model Constants for Prediction of Soot Formation in a Turbulent Hydrocarbon Flames
Authors: Rajeshirke Pravin , Nakod Pravin , Yadav Rakesh , Orsino Stefano
Published: July 2018

In the present work, two equation soot models proposed by Moss-Brookes (MB) and Moss-Brookes-Hall (MBH), available in ANSYS FLUENT14.5, are used to study the soot formation in a turbulent kerosene-air flame. The model constants in the original works of MB and MBH model were primarily tuned for the methane-air or other lower hydrocarbon flames. In this work, the emphasis has been given on the applicability of these models in modeling the soot formation in heavy hydrocarbon fuels. The current work is primarily focused on the parametric study of the various modeling constants for calculating the soot inception and oxidation rates. A parametric study is performed to calculate the soot inception rates by considering different soot precursors like C2H2, C2H4, C6H6 and C6H5. Steady laminar flamelet approach with a detailed chemical reaction mechanism (Jet_SurF_2.0), is used for modeling gas phase combustion. The current numerical predictions are compared with experimental results of Young et al. [1] and earlier published numerical results of Wen et al. [2]. The study is further extended to understand the role of chemical reaction mechanism on soot predictions considering detailed versus reduced (JP10revC) chemical mechanisms.
Free Vibration Responses of Functionally Graded Spherical Shell Panels Using Finite Element Method
Authors: Kar Vishesh Ranjan , Panda Subrata Kumar
Published: July 2018

Free vibration responses of functionally graded spherical shell panels are investigated in the present article. A general mathematical model is developed based on higher order shear deformation theory mid-plane kinematics. The effective material properties are graded in the thickness direction according to a power-law distribution and it varies continuously from metal (bottom surface) to ceramic (top surface). The model is discretized using a nine noded quadrilateral Lagrangian element. A convergence test has been done with different mesh refinement and compared with the available published results. In addition to that the present study includes an ANSYS model check with the developed mathematical model to show the efficacy. New results are computed for different parameters such as volume fraction, thickness ratio, curvature ratio and support conditions which indicates the effect of parametric study on non-dimensional frequency parameters.
Drop Size Characteristics of Forward Angled Injectors in Subsonic Cross Flows
Authors: Iyengar Venkat S. , Kumarasamy Sathiyamoorthy , Jangam Srinivas , Pulumathi Manjunath
Published: July 2018

Cross flow fuel injection is a widely used approach for injecting liquid fuel in gas turbine combustors and afterburners due to the higher penetration and rapid mixing of fuel and the cross flowing airstream. Because of the very limited residence time available in these combustors it is essential to ensure that smaller drop sizes are generated within a short axial distance from the injector in order to promote effective mixing. This requirement calls for detailed investigations into spray characteristics of different injector configurations in a cross-flow environment for identifying promising configurations. The drop size characteristics of a liquid jet issuing from a forward angled injector into a cross-flow of air were investigated experimentally at conditions relevant to gas turbine afterburners. A rig was designed and fabricated to investigate the injection of liquid jet in subsonic cross-flow with a rectangular test section of cross section measuring 50 mm by 70 mm. Experiments were done with a 10 degree forward angled 0.8 mm diameter plain orifice nozzle which was flush mounted on the bottom plate of test section. Laser diffraction using Malvern Spraytec particle analyzer was used to measure drops size and distributions in the near field of the spray. Measurements were performed at a distance of 70 mm from the injector at various locations along the height of the spray plume for a reasonable range of liquid flow rates as in practical devices.

The sprays were characterized using the non dimensional parameters such as the Weber number and the momentum flux ratio and drop sizes were measured at three locations along the height of the spray from the bottom wall. The momentum flux ratio was varied from 5 to 25. Results indicate that with increase in momentum flux ratio the SMD reduced at the specific locations and an higher overall SMD was observed as one goes from the bottom to the top of the spray plume. This was accompanied by a narrowing of the drop size distribution.
Investigations on the Effect of Aspect Ratio Into the Performance of Savonius Rotors
Authors: Roy Sukanta , Saha Ujjwal K.
Published: July 2018

With the rapid execution in the renewable energy field, vertical axis wind turbines are finding its application in the small-scale distributed wind energy generation, particularly in rural areas. The Savonius rotor is a drag based vertical axis wind turbine and is used as a small-scale wind energy converter with low installation and maintenance cost. These rotors are simple in design, easy to assemble and can be operated at low-speed wind from any direction. However, these rotors are not gaining popularity because of its low efficiency and improper design. The aspect ratio (height to diameter of the rotor) is one of the very important factors for designing a suitable small-scale wind turbine. The other important factors include overlap ratio, gap ratio and blade profile of the rotor. In the present investigation, a number of rotor models with different aspect ratios are tested in a low speed wind tunnel with open test section facility. The effects of overlap ratio and gap ratio are also studied keeping the rotor height to be the same. The wind speed is varied from 5–10 m/s. To estimate the performance of these rotors, electrical loads are given with respect to different wind speeds and the power output is calculated in terms of voltage and current. The results depicted an optimum aspect ratio of 0.80, which can be used to improve the performance of Savonius rotors.
An Assessment of Turbulence Models for Predicting the Fluid Flow in Spiral Casing of a Hydraulic Turbomachine Using SUPG-Finite Element Method
Authors: Rao N. Parameswara , Prakash K. Arul
Published: July 2018

Numerical simulation of complex three-dimensional flow through the spiral casing has been studied using a finite element method. An explicit Eulerian velocity correction scheme has been employed to solve the Reynolds averaged Navier-stokes equations. The simulation has been performed to describe the flow in high Reynolds number (106) regime and two k-ε turbulence models (standard k-ε and RNG k-ε) have been used for computing the turbulent flow. A streamline upwind Petrov Galerkin technique has been used for spatial discretisation. The velocity field and the pressure distribution inside the spiral casing has been studied. It has been observed that very strong secondary flow is evolved on the cross-stream planes.
Effect of Trailing Edge Crenulation on the Performance and Stall Margin of a Transonic Axial Compressor
Authors: Subbaramu S. , Nagpurwala Quamber H. , Sriram A. T.
Published: July 2018

This paper deals with the numerical investigations on the effect of trailing edge crenulation on the performance of a transonic axial compressor rotor. Crenulation is broadly considered as a series of small notches or slots at the edge of a thin object, like a plate. Incorporating such notches at the trailing edge of a compressor cascade has shown beneficial effect in terms of reduction in total pressure loss due to enhanced mixing in the wake region. These notches act as vortex generators to produce counter rotating vortices, which increase intermixing between the free stream flow and the low momentum wake fluid. Considering the positive effects of crenulation in a cascade, it was hypothesized that the same technique would work in a rotating compressor to enhance its performance and stall margin. However, the present CFD simulations on a transonic compressor rotor have given mixed results. Whereas the peak total pressure ratio in the presence of trailing edge crenulation reduced, the stall margin improved by 2.97% compared to the rotor with straight edge blades. The vortex generation at the crenulated trailing edge was not as strong as reported in case of linear compressor cascade, but it was able to influence the flow field in the rotor tip region so as to energize the low momentum end-wall flow in the aft part of the blade passage. This beneficial effect delayed flow separation and allowed the mass flow rate to be reduced to still lower levels resulting in improved stall margin. The reduction in pressure ratio with crenulation was surprising and might be due to increased mixing losses downstream of the blade.
Experimental Investigation of Flow Characteristics in a Square Duct With Delta-Wing Vortex Generators
Authors: Katti Vadiraj V. , Malipatil Anandkumar S. , Ingalagi Mahesh R.
Published: July 2018

The influence of delta wing vortex generators on the wall of square duct and the pressure loss penalty has been experimentally investigated in this study. The combined effects of geometrical parameters of delta wing vortex generators on friction factor ratios are reported for the Reynolds number based on the duct hydraulic diameter in the range of 8000–24000. The geometrical parameters of vortex generators systematically varied in this study are the pitch to vortex generator height ratio (p/e), vortex generator height to duct hydraulic diameter ratio (e/Dh), aspect ratio of vortex generator (ar). Results are reported for 0.1 ≤ e/Dh ≤ 0.5, 1.6 ≤ p/e ≤ 16, 1.6 ≤ ar ≤ 14.9, in duct having aspect ratio AR = 1. The experimental results of the present study for friction factor in smooth square duct agree well with values estimated from correlations proposed by Blasius.
Reduced Order Modeling of Deflection of a Membrane Covered Airfoil in a Fluid Flow
Authors: Narayana Murthy Srinath , Loganathan Jaikumar , Gopinath Ashok
Published: July 2018

Flow over a flexible membrane is different to that over a rigid object. Fluid stresses developed over a membrane create a deflection, which in turn affects the flow field and generates a new stress distribution, thereby altering the original deflection. The behavior of the membrane can be modeled using the Young-Laplace equation which links the pressure difference across the membrane and the surface tension force with the radius of curvature of the membrane surface. In this work a computational approach is developed to solve the Young-Laplace equation. The approach is validated with a simple case of simply supported membrane subjected to a pressure load and a pretension. The performance of a S825 airfoil whose upper surface is replaced with a membrane is studied for various angles of attack. It is noted that the deformed airfoils perform better than the S825 till α = 6°. Beyond this angle of attack it is observed that the drop in performance is small.
Validity of Molecular Dynamics by Quantum Mechanics
Authors: Prevenslik Thomas
Published: July 2018

MD is commonly used in computational physics to determine the atomic response of nanostructures. MD stands for molecular dynamics. With theoretical basis in statistical mechanics, MD relates the thermal energy of the atom to its momentum by the equipartition theorem. Momenta of atoms in an ensemble are determined by solving Newton’s equations with inter-atomic forces derived from Lennard-Jones potentials. MD therefore assumes the atom always has heat capacity as otherwise the momenta of the atoms cannot be related to their temperature. In bulk materials, the continuum is simulated in MD by imposing PBC on an ensemble of atoms, the atoms always having heat capacity. PBC stands for periodic boundary conditions. MD simulations of the bulk are valid because atoms in the bulk do indeed have heat capacity.

Nanostructures differ from the bulk. Unlike the continuum, the atom confined in discrete submicron geometries is precluded by QM from having the heat capacity necessary to conserve absorbed EM energy by an increase in temperature. QM stands for quantum mechanics and EM for electromagnetic. Quantum corrections of MD solutions that would show the heat capacity of nanostructures vanishes are not performed. What this means is the MD simulations of discrete nanostructures in the literature not only have no physical meaning, but are knowingly invalid by QM. In the alternative, conservation of absorbed EM energy is proposed to proceed by the creation of QED induced non-thermal EM radiation at the TIR frequency of the nanostructure. QED stands for quantum electrodynamics and TIR for total internal reflection. The QED radiation creates excitons (holon and electron pairs) that upon recombination produce EM radiation that charges the nanostructure or is emitted to the surroundings — a consequence only possible by QM as charge is not created in statistical mechanics. Invalid discrete MD simulations are illustrated with nanofluids, nanocars, linear motors, and sputtering. Finally, a valid MD simulation by QM is presented for the stiffening of NWs in tensile tests. NW stands for nanowire.
Rheological Characteristics of Viscoelastic Surfactant Fluid Mixed With Silica Nanoparticles
Authors: Wu Yueqiong , Luo Zhongyang , Yin Hong , Wang Tao
Published: July 2018

Since the surfactant can form rod-like micelles or even cross-link structures, viscoelastic surfactant (VES) fluid has unique rheological characteristics. The demerits of VES fluids have been proven after being applied as the fracturing fluid for several years. However, the fluid has high fluid loss and a low viscosity at high temperature, which limits the application to hydraulic fracturing. This paper focuses on the VES fluid mixed with nanoparticles which should be an effective way to maintain the viscosity at high temperature and high shear rate. The experiments were based on preparation of uniform and stable nanocolloids, which utilize Microfluidizer high shear fluid processor. Dynamic light scattering and microscopic methods are employed to investigate the stability and micro-structure of the VES fluid. The effects of temperature, shear rate and volume fraction of the nanoparticles on rheology of VES were studied. The SiO2 nanoparticles could significantly improve the rheological performance of VES fluid, although the rheological performance at the temperature over 90 °C needs to be enhanced. The mechanisms of interactions between nanoparticles and micelles are also discussed later in the paper. At the end, the potential of VES fluid mixed with nanoparticles during application in fracturing process was discussed.
Investigation of Boiling Heat Transfer and Critical Heat Flux Enhancement for SiC and Graphene Layers on ITO Surfaces
Authors: Seo Han , Seo Seok Bin , Moon Sung Bo , Kwon Soon-Yong , Kim Ji Hyun , Bang In Cheol
Published: July 2018

This paper presents a study on the enhancement in the boiling heat transfer (BHT) and critical heat flux (CHF) with a bare indium tin oxide (ITO) surface, few-graphene layer deposited on an ITO surface, and silicon carbide (SiC) particles deposited on an ITO surface. The experiment was conducted in atmospheric pressure using FC-72 refrigerant at saturation. Infrared (IR) thermometry was used to determine the temperature fields of the heater surfaces and CHF. The values of CHF for the graphene layer on the ITO surface and SiC deposited on the ITO heater were increased by 9% and 42%, compared to the bare ITO heater, respectively. All the heater surfaces showed hydrophilic condition with the working fluid (FC-72 refrigerant). The enhancement in the BHT coefficient and CHF was attributed to surface modifications such as the formation of microporous structures and the material properties.
Experimental and Simulation Study on Motion of an Isolated Liquid Plug Inside a Dry Circular Capillary
Authors: Srinivasan Vyas , Sikarwar Basant Singh , Khandekar Sameer
Published: July 2018

Classical study of motion of a single liquid plug (water) inside a micro/mini capillary tube is revisited to understand the contribution of meniscus friction and effect of contact angle hysteresis on the pressure required to initiate the motion of liquid plug of different L/D ratio. Experiments are carried out by injecting a known mass flow rate of air to push the liquid plug from rest. While the plug is at rest, as the air pressure increases linearly, the menisci deform till a limiting value, at which the plug starts moving. The initial phase of plug motion is dominated by its acceleration, which is then opposed by wall shear, and eventually leads to a steady motion of liquid plug at constant pressure and dynamic contact angle hysteresis.

Experimental results show that, the pressure required to initiate the motion of the liquid is independent of its length, indicating the dominance of static menisci friction at initial stages. Also, steady state pressure drop is observed to be much greater than that predicted by fully developed tube flow.

The flow is simulated in COMSOL using level set method. Simulation results agree well with the experimental result. Contribution of menisci towards static and dynamic friction and velocity development near menisci are obtained from simulations to model the friction factor for the flow.
Nanobubbles on a Very Flat Hydrophobic Surface Prepared by Self-Assembled Monolayers
Authors: Nishiyama Takashi , Takahashi Koji , Takata Yasuyuki
Published: July 2018

Boiling is one of the most effective heat transfer methods due to its high heat transfer coefficient. Therefore, boiling heat transfer plays a very important role for various applications in many technological and industrial areas. However, a very complex mechanism of boiling, especially bubble nucleation, is still not sufficiently understood. On the other hand, numerous experiments have revealed the existence of soft domains that called nanobubbles at the solid-liquid interface. In this study, to investigate the influence of the solid-liquid interface nanobubbles on the bubble nucleation, an atomic force microscope (AFM) is used to characterize the morphology of nanobubbles. In order to separate the effect of wettability of a solid surface from that of surface structure, a very flat hydrophobic surface was prepared. 1H,1H,2H,2H-Perfluoro-n-octylphosphonic acid (FOPA) formed the interface of hydrophobic self-assembled monolayers (SAMs). As the result of AFM measurement, many nanobubbles about 100 nm in diameter and 30 nm thick are observed at the interface of the FOPA surface and the pure water. In addition, to prove the existence of gaseous phase, the heat conductance measurement by time-domain thermoreflectance method (TDTR) was introduced. TDTR is an ultrafast optical pump probe technique well suited for thermal measurement of thin films. It enables to resolve the thermal conductivity of the thin film and the thermal conductance of the interface. If nanobubbles are the gaseous phase, the big change of interface heat thermal resistance will be seen and the TDTR signal should also change. The effectiveness of a TDTR to confirm the existence of nanobubbles is shown by the model simulation of TDTR. A clear difference is seen in TDTR signal by the existence of only 1 nm gaseous phase. After confirming the existence of nanobubbles by AFM measurement, it can be proved that the nanobubbles are truly gaseous phase of the TDTR measurement.
Bubble Growth at Nucleation Cavity in Microchannels
Authors: Kadam Sambhaji T. , Kumar Ritunesh , Baghel Kuldeep
Published: July 2018

Bubble dynamics i.e. bubble nucleation, growth and departure plays an important role in heat transfer and pressure drop characteristics during two phase flow of microchannels. A simplified mathematical model has been developed to predict the bubble growth rate in microchannels at nucleation cavity after its inception. It is assumed that heat supplied at nucleation site is divided between liquid phase and vapor phase as per instantaneous void fraction value. The energy consumed by vapor phase is utilized in overcoming evaporation, surface tension, inertia, shear and gravity effects. Proposed model shows good agreement (∼14 % error) with available experimental work. In addition, the physical phenomena of the bubble waiting time for flow boiling is also addressed utilizing proposed model. The waiting time predicted by the model is close to that obtained from experimental data.
Effects of Free Surface Evaporation on Water Nano-Droplet Wetting Kinetics: A Molecular Dynamics Study
Authors: Lu Gui , Duan Yuan-Yuan , Wang Xiao-Dong
Published: July 2018

The dynamic wetting of water nano-droplet with evaporation on the heated gold substrate was examined using molecular dynamics simulation. Various substrate and droplet pre-heated temperatures were calculated to obtained different evaporating rates. Water molecules attachment-detachment details were traced near the contact line region to show the microscopic details and evidences for the spreading-evaporating droplet. The increasing substrate temperature greatly affected the dynamic wetting process, while the initial temperature of water droplet had very limited effects. The effects of free surface evaporation on wetting kinetics for both hydrophobic and hydrophilic substrates were examined. The radius versus time curves agree well with the Molecular kinetic theory (MKT) for spreading without evaporation and deviate from the MKT for the spreading with evaporation. The enhancement on wetting kinetics due to evaporation can be attributed to the reducing of liquid-vapor surface tension and the strengthening in water molecules transport in contact line region and bulk droplet.
Heating Effects of the Magnetic-Nanoparticle Enhanced Hyperthermia Targeting Tumors Underneath the Ribs
Authors: Jin Chao , He Zhi Zhu , Liu Jing
Published: July 2018

Aiming at providing a detailed disclosure on the thermal effects of EM (electromagnetic) hyperthermia on the liver tumor underneath the ribs, this paper has numerically provided comprehensive interpretations on the heating effects of magnetic nano-particles induced hyperthermia for target tumor treatment. The results revealed the following factors: (1) The existing of bone structure, i.e. ribs has an inevitable effect on the distribution of EM field; specifically, due to its lower dielectric property, the bone structure seemingly acts as a barrier to attenuate the access of EM energy into the tissue, especially the tumor in the deep body. (2) Using higher dosage or bigger size magnetic nano-particles have greatly enhanced the temperature elevation of targeted tumor tissue and thereby obtain good performance of hyperthermia. (3) Further parametric studies indicated that a worse heating effect would be obtained when utilizing external EM field with a higher frequency of 10MHz; while higher strength of EM field would evidently enhance the heating effects of such EM hyperthermia. The present study would promote the understandings of thermal effects on the specific organs in EM hyperthermia, and the findings are expected to provide valuable guidance for planning an accurate dosage in clinical liver tumor thermal ablation.
Experimental Investigation of Spray Cooling on Nano- and Hybrid-Structured Surfaces
Authors: Zhang Zhen , Jiang Pei-Xue , Ouyang Xiao-Long , Chen Jian-Nan , Christopher David M. , Jiang Kai-Li
Published: July 2018

The heat transfer during spray cooling was studied experimentally using deionized water to investigate the spray characteristics and the differences between spray cooling on a smooth silicon surface and nano- and hybrid micro/nano-structured surfaces. The spray cooling experiments show that the heat transfer rates were best for the nano-structured surface, followed by the smooth surface coated with the SiO2 film and the pure silicon surface since the contact angle was smallest on the nano-structured surface and increased on the other two surfaces. The Critical Heat Flux (CHF) was largest for the 25G×25S surface coated with four Carbon Nano Tube (CNT) films with a 75.3% increase over the smooth surface.
Measurement of Air Flow Velocities in Microsized Ionic Wind Pumps Using Particle Image Velocimetry
Authors: Henning James C. , Abramson Alexis R. , Kadambi Jaikrishnan R.
Published: July 2018

The knowledge of the flow fields inside of microsized ionic wind pumps has become more important as the need for smaller and more efficient heat removal devices has increased. Understanding these flow fields will help optimize the ionic wind pump performance. Non-intrusive microscale particle image velocemity (PIV) utilizing a microscopic objective lens is used to obtain the flow field inside of the ionic wind pump. Atomized olive oil droplets are used as seed particles with air as the flow medium. Voltages ranging from 1700 to 2000 V are used, as well as seeded flow rates of 1.5 and 2.0 L/min. Computational models, developed using COMSOL Multiphysics, are used to qualitatively verify the flow fields. The effects of voltage and seed flow rate are also compared. The computational and PIV flow fields are shown to be very similar. It is shown that as the voltage applied to the ionic wind pump increases the maximum velocity inside of the ionic wind pump, ranging from 1.71 m/s to 3.19 m/s. The average mass flow rate inside of the device also increases as the voltage is increased, ranging from .0009 g/s to .0019 g/s. It is also shown that the seed flow rate has little effect on the PIV flow field obtained.
Thermal Performance of Microchannels With Dimples for Electronics Cooling
Authors: Lu Hui , Gong Liang , Xu Minghai
Published: July 2018

The thermal management of integrated circuits becomes more and more serious since the density of transistors grows gradually. Recently, a new cooling method is dedicated to develop microchannel heat sink with high integrated and high cooling efficiency. In view of above purpose, the heat transfer enhancement and pressure drop reduction in microchannel with dimples are investigated in this paper. A single module of 1mm×1mm×20mm with a microchannel was employed, which hydraulic diameter and aspect ratio are 500 μm and 2:1 respectively. For replacing the running integrated circuits, a constant heat flux of 1W/mm2 was arranged on the bottom of the heat sink. Six different types of microchannels with dimples were designed and numerically studied under the condition of laminar flow. The results show that dimple could enhance heat transfer and decrease flow resistance under the condition of laminar flow. Compared with traditional microchannel heat sink, dimple-microchannel heat sink has stronger cooling capacity, could be an attractive choice for cooling of future microelectronics.
Solvent Soaking and Drying of Carbon Nanotube Forests for Enhanced Contact Area and Thermal Interface Conductance
Authors: Taphouse John H. , Cola Baratunde A.
Published: July 2018

Forests comprised of nominally vertically aligned carbon nanotubes (CNTs), having outstanding thermal and mechanical properties, are excellent candidates for thermal interface materials (TIMs). However, the thermal performance of CNT forest TIMs has been limited by the presence of high thermal contact resistances at the CNT tip interface. The high thermal contact resistance at the CNT tip interface stems from two sources: (1) the relatively weak van der Waals type bonding, which impedes phonon transport, and (2) low contact area. In this work we will show that common solvents, such as water, can be applied to the CNT forest to increase the contact area and reduce the contact resistance by an average of 75%. Specifically, there are two likely mechanisms that can increase the contact area when a CNT forest is wet with a fluid and compressed in an interface. The first is relaxing the van der Waals interactions between contacting CNTs within the forest, consequently decreasing the stiffness of the forest and allowing it to better conform to the opposing surface. The second is the pulling of CNT tips through capillary interactions into contact with the opposing surface as the solvent evaporates. By measuring the thermal resistance of CNT TIMs before and after soaking in variety of solvents the capacity of each mechanism for reducing the contact resistance is explored.
Numerical Analysis of Dual-Phase-Lag Heat Transfer in a Micro-Scale Thermal Barrier Coating With an Interfacial Resistance
Authors: Akwaboa Stephen , Mensah Patrick
Published: July 2018

Microstructural effects on heat transfer in a thermal barrier coatings system subjected to a pulsed surface heating is presented in this paper within the framework of dual phase lag heat conduction model. The effects of thermo-physical properties on the energy transport for the simplified two-layered thermal barrier coating and substrate system (TBC-substrate system) are presented. Interfacial thermal resistance is specified as a function of temperature differential on both sides of the imperfect thermal contact. Due to the difference in properties between the two dissimilar materials on both sides of the interface, a strong nonlinear interfacial boundary condition is introduced into the problem. A robust numerical scheme, named Mean Value Finite Volume Method (MVFVM), which is capable of solving conservation equations, is used to analyze the present problem. Results show that the lagging thermal behavior is affected by the thermal properties of the padding material (substrate) and the thermal resistance at the interface. Furthermore, for low values of thermal interfacial resistance (h ≥ 1000), and a given TBC material, the interfacial temperature difference approaches the perfect thermal contact condition when the thermal pulse propagates towards a substrate material with low thermal conductivity value. The results also indicate that the thermo-physical properties of substrate material have more pronounced effects on the temperature distributions than heat flux and temperature gradient lagging parameters.
Numerical Methods for Modeling the Rock Cutting Process in Deep Sea Mining
Authors: Chen Xiuhan , Miedema Sape A. , van Rhee Cees
Published: July 2018

The increasing demand on precious metals has motivated the development of a promising industry, deep sea mining. Currently major technical challenges exist in the development of this new industry, such as the vertical transportation, the seabed excavation process and the stability of the riser system. This paper will focus on the excavation process on the seabed.

Considering the fact that the deep sea mining excavation process may occur at 3000∼6000 meters water depth, the hyperbaric pressure applied by the sea water will greatly influence the cutting process. Especially when the cutting speed of the cutter is very high, the so called “dilatancy hardening effect” (Brace and Martin, 1968) may make the seabed rock very difficult to excavate. These factors will make the rock excavation in deep sea much different from shallow water, which is the case in a normal dredging project. In this paper, the physics of the hyperbaric excavation process will first be described into detail.

Because the hyperbaric rock cutting experiments are expensive, it is more feasible to make a numerical model to simulate the process, which eventually can replace the experiments. The main difficulties are to model the failure of rock and the interaction between the rock and the pore water. Considering the scale of the problem and the characteristics of the material, it is concluded that the discrete element method (DEM) will be the best tool to simulate the rock behavior. On the other hand, to describe the influence from the hyperbaric pressure which is induced by the sea water, governing equations for the fluid phase are derived and the finite volume method (FVM) is chosen to solve the equations. This paper will give a detailed description about the numerical methods and their interactions regarding this specific problem and show some preliminary tests on clay-like material cutting process.
Mechanical Response of Two Carbonate Sediments From Australia’s North West Shelf
Authors: Lehane Barry M. , H. Carraro J. Antonio , Boukpeti Nathalie , Elkhatib Sarah
Published: July 2018

The carbonate sediments found offshore on the North West Shelf of Australia can generally be described as silts with varying proportions of clay-sized and sand-sized carbonate particles. This paper investigates the undrained shearing response (as measured under simple shear and triaxial conditions) of two sediments with different grading curves. The importance of the fines content in controlling the density and hence dilatancy and undrained strength of the materials is demonstrated. The paper discusses the importance of fabric to the behavior of these soils and provides guidance on how undrained strengths of soils of this nature may be assessed with a knowledge of a material’s in-situ water content (or void ratio) and composition.
Large Deformation Finite Element Analysis of Gravity Installed Anchors in Clay
Authors: Liu Jun , Lu Lihui , Yu Long
Published: July 2018

The OMNI-Max anchor is a multi-directional, self-inserting, gravity-installed anchor and used as foundation for mooring deep water offshore facilities, including risers and floating structures. The OMNI-Max anchor offers a cost effective anchoring solution with improved reliability in the mooring system. Pullout capacity and keying behavior are two important issues in the design of the OMNI-Max anchor. In this paper, the pullout capacity and the keying process of a vertically installed OMNI-Max anchor embedded in normally consolidated clay were simulated using three dimensional large deformation finite element analysis. In these numerical analyses, 10-node tetrahedral elements were used to predict the collapse loads of undrained geotechnical problems involving material incompressibility. Nodal joint elements were used to simulate the interaction between the anchor and soil. The effect of the loading angle on the keying behavior of the OMNI-Max anchor was considered. The analyses clearly show the two important processes (1) “keying”: the anchor rotates rapidly until reaching the best bearing capacity position; (2) “diving”: the anchor mainly translates with tiny rotation. It agrees well with the keying and diving phenomenon in published model test results.
Feasibility of a Dynamically Stable Rock Armour Layer Scour Protection for Offshore Wind Farms
Authors: de Schoesitter Philippe , Audenaert Sarah , Baelus Leen , Bolle Annelies , Brown Andrew , Das Neves Luciana , Ferradosa Tiago , Haerens Piet , Pinto Francisco T. , Troch Peter , Whitehouse Richard
Published: July 2018

Armour layer scour protections around offshore wind turbine foundations are commonly designed to provide a static protection in storm conditions, which means no or limited movement of rock is allowed (Den Boon et al., 2004, De Vos et al., 2011). This approach often results in large stone sizes and high scour protection costs. Therefore, a dynamic approach can be an interesting alternative. Such a dynamic design can be achieved by decreasing the armour stone size allowing movement of the stones and increasing the armour layer thickness to prevent filter layer exposure. A physical test program was conducted to investigate the feasibility and behaviour of such a dynamically stable scour protection. In this model, a monopile foundation exposed to typical North Sea combinations of unidirectional currents and waves was reproduced in a wave flume. The program included a number of test series each with different water depths. In each test series, the armour layer stone size and the armour layer thickness were varied, in order to obtain a reshaping scour protection, without filter material exposure. Damage and failure were assessed both visually and using a 3D-laser profiler. Because previous works on damage numbers of rock armour layer scour protections mainly focus on static design, a new damage number was introduced and compared to the visual observation. This allowed the definition of a ‘dynamic area’ between static design and failure. Scour pit development in time and equilibrium profiling were also analyzed. The results of the tests showed that the concept of a dynamically stable scour protection is feasible.
Analyzing transient-evoked otoacoustic emissions by concentration of frequency and time
Authors: Wu Hau-Tieng , Liu Yi-Wen
Published: July 2018

The linear part of transient evoked otoacoustic emission (TEOAE) is thought to be generated via coherent reflection near the characteristic place of constituent wave components. Because of the tonotopic organization of the cochlea, high frequency emissions return earlier than low frequencies; however, due to the random nature of coherent reflection, the instantaneous frequency (IF) and amplitude envelope of TEOAEs both fluctuate. Multiple reflection components and synchronized spontaneous emissions can further make it difficult to extract the IF by linear transforms. This paper proposes to model TEOAEs as a sum of intrinsic mode-type functions and analyze it by a nonlinear-type time-frequency (T-F) analysis technique called concentration of frequency and time (ConceFT). When tested with synthetic otoacoustic emission signals with possibly multiple oscillatory components, the present method is able to produce clearly visualized traces of individual components on the T-F plane. Further, when the signal is noisy, the proposed method is compared with existing linear and bilinear methods in its accuracy for estimating the fluctuating IF. Results suggest that ConceFT outperforms the best of these methods in terms of optimal transport distance, reducing the error by 10% to 21% when the signal to noise ratio is 10 dB or below.
In Situ
Structures of the Polymerase Complex and RNA Genome Show How Aquareovirus Transcription Machineries Respond to Uncoating
Authors: Ding Ke , Nguyen Lisa , Zhou Z. Hong
Published: July 2018

Viruses in the family
Reoviridae
are characterized by the ability to endogenously synthesize nascent RNA within the virus. However, the mechanisms for assembling their RNA genomes with transcriptional enzymes into a multilayered virion and for priming such a virion for transcription are poorly understood. By cryo-EM and novel asymmetric reconstruction, we determined the atomic structure of the transcription complex inside aquareoviruses (ARV) that are primed for infection. The transcription complex is anchored by the N-terminal segments of enclosing capsid proteins and contains an NTPase and a polymerase. The NTPase has a newly discovered domain that translocates the 5′ end of plus-sense RNA in segmented dsRNA genomes from the NTPase to polymerase VP2 when the virus changes from the inactive (quiescent) to the primed state. Conformation changes in capsid proteins and transcriptional complexes suggest a mechanism for relaying information from the outside to the inside of the virus during priming.
Fungal Light-Oxygen-Voltage Domains for Optogenetic Control of Gene Expression and Flocculation in Yeast
Authors: Salinas Francisco , Rojas Vicente , Delgado Verónica , López Javiera , Agosin Eduardo , Larrondo Luis F.
Published: July 2018

Optogenetic switches permit accurate control of gene expression upon light stimulation. These synthetic switches have become a powerful tool for gene regulation, allowing modulation of customized phenotypes, overcoming the obstacles of chemical inducers, and replacing their use by an inexpensive resource: light. In this work, we implemented FUN-LOV, an optogenetic switch based on the photon-regulated interaction of WC-1 and VVD, two LOV (light-oxygen-voltage) blue-light photoreceptors from the fungus
Neurospora crassa
. When tested in yeast, FUN-LOV yields light-controlled gene expression with exquisite temporal resolution and a broad dynamic range of over 1,300-fold, as measured by a luciferase reporter. We also tested the FUN-LOV switch for heterologous protein expression in
Saccharomyces cerevisiae
, where Western blot analysis confirmed strong induction upon light stimulation, surpassing by 2.5 times the levels achieved with a classic
GAL4
/galactose chemical-inducible system. Additionally, we utilized FUN-LOV to control the ability of yeast cells to flocculate. Light-controlled expression of the flocculin-encoding gene
FLO1
, by the FUN-LOV switch, yielded flocculation in light (FIL), whereas the light-controlled expression of the corepressor
TUP1
provided flocculation in darkness (FID). Altogether, the results reveal the potential of the FUN-LOV optogenetic switch to control two biotechnologically relevant phenotypes such as heterologous protein expression and flocculation, paving the road for the engineering of new yeast strains for industrial applications. Importantly, FUN-LOV’s ability to accurately manipulate gene expression, with a high temporal dynamic range, can be exploited in the analysis of diverse biological processes in various organisms.

IMPORTANCE
Optogenetic switches are molecular devices which allow the control of different cellular processes by light, such as gene expression, providing a versatile alternative to chemical inducers. Here, we report a novel optogenetic switch (FUN-LOV) based on the LOV domain interaction of two blue-light photoreceptors (WC-1 and VVD) from the fungus
N. crassa
. In yeast cells, FUN-LOV allowed tight regulation of gene expression, with low background in darkness and a highly dynamic and potent control by light. We used FUN-LOV to optogenetically manipulate, in yeast, two biotechnologically relevant phenotypes, heterologous protein expression and flocculation, resulting in strains with potential industrial applications. Importantly, FUN-LOV can be implemented in diverse biological platforms to orthogonally control a multitude of cellular processes.
An Aspartate-Specific Solute-Binding Protein Regulates Protein Kinase G Activity To Control Glutamate Metabolism in Mycobacteria
Authors: Bhattacharyya Nabanita , Nkumama Irene Nailain , Newland-Smith Zaccheus , Lin Li-Ying , Yin Wen , Cullen Rebecca E. , Griffiths Jack S. , Jarvis Alexander R. , Price Michael J. , Chong Pei Ying , Wallis Russell , O’Hare Helen M.
Published: July 2018

Signaling by serine/threonine phosphorylation controls diverse processes in bacteria, and identification of the stimuli that activate protein kinases is an outstanding question in the field. Recently, we showed that nutrients stimulate phosphorylation of the protein kinase G substrate GarA in
Mycobacterium smegmatis
and
Mycobacterium tuberculosis
and that the action of GarA in regulating central metabolism depends upon whether it is phosphorylated. Here we present an investigation into the mechanism by which nutrients activate PknG. Two unknown genes were identified as co-conserved and co-expressed with PknG: their products were a putative lipoprotein, GlnH, and putative transmembrane protein, GlnX. Using a genetic approach, we showed that the membrane protein GlnX is functionally linked to PknG. Furthermore, we determined that the ligand specificity of GlnH matches the amino acids that stimulate GarA phosphorylation. We determined the structure of GlnH in complex with different amino acid ligands (aspartate, glutamate, and asparagine), revealing the structural basis of ligand specificity. We propose that the amino acid concentration in the periplasm is sensed by GlnH and that protein-protein interaction allows transmission of this information across the membrane via GlnX to activate PknG. This sensory system would allow regulation of nutrient utilization in response to changes in nutrient availability. The sensor, signaling, and effector proteins are conserved throughout the
Actinobacteria
, including the important human pathogen
Mycobacterium tuberculosis
, industrial amino acid producer
Corynebacterium glutamicum
, and antibiotic-producing
Streptomyces
species.

IMPORTANCE
Tuberculosis (TB) kills 5,000 people every day, and the prevalence of multidrug-resistant TB is increasing in every country. The processes by which the pathogen
Mycobacterium tuberculosis
senses and responds to changes in its environment are attractive targets for drug development. Bacterial metabolism differs dramatically between growing and dormant cells, and these changes are known to be important in pathogenesis of TB. Here, we used genetic and biochemical approaches to identify proteins that allow
M. tuberculosis
to detect amino acids in its surroundings so that it can regulate its metabolism. We have also shown how individual amino acids are recognized. The findings have broader significance for other actinobacterial pathogens, such as nontuberculous mycobacteria, as well as
Actinobacteria
used to produce billions of dollars of amino acids and antibiotics every year.