bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Simulation of Wellbore Pressure and Temperature During Gas-Well Testing
Authors: Liu Tong , Zhong Hai-quan , Li Ying-chuan
Published: January 2014

An abnormal phenomenon may occur during gas-well testing: the wellhead pressure initially rises and then drops when shutting-in a well; the wellhead pressure initially drops and then rises when opening a well. To determine why and how this phenomenon occurs, a transient nonisothermal wellbore flow model for gas-well testing is developed. Governing equations are based on depth- and time-dependent mass, momentum equations, and the gas state equation. Temperature is predicted using the unsteady-state heat transfer model of Hasan. Boundary conditions include the restriction of formation inflow and wellhead throttling to the flow. The difference equations are established based on the implicit central finite difference method. The model can simulate the influences of temperature and flux (mass velocity). The model also considers the effects of formation inflow and surface throttling on the system. The results indicate wellhead pressure under flowing temperature is higher than that under static temperature, thus causing the abnormal phenomenon. A larger pressure difference makes the abnormal phenomenon more significant. Without considering temperature variation, simulated wellhead pressure would not exhibit the abnormity. Without considering flux variation, simulated pressure curve is not smooth. A new model has thus been validated using a gas field example.
Recommendations for Energy Water Nexus Problems
Authors: Vincent Wong Kaufui
Published: January 2014

The chronic water problems in parts of India are probably due mainly to mismanagement. The rolling blackout and brownout problems in the larger Indian cities are due to lack of generation capacity. Since about ninety percent of the world's electricity is generated based on the steam Rankine cycle, environmental water is necessary for cooling, and freshwater is used as the working fluid. Furthermore, electricity is tied to water as part of the bigger water energy nexus phenomena occurring worldwide. China has started and continued with many initiatives to correct problems with water management. Projects do exist where the climatically dry north is being fed water from the wet south. China has water energy nexus conditions occurring too. The review of the scientific literature on studies about the sources of the Ganges, the Yangtze, the Yellow river, the Indus and the Mekong (the drinking water source of about forty percent of the World's population), the glaciers that feed these sources and how they are shrinking with global warming, has yielded a simple policy decision. Mass balance considerations provide the answer that the logical solution of the recent accelerated water changing from solid to liquid on mountain tops, requires dams and storage areas (lakes) to prevent all that freshwater from escaping to the lowlands, and ultimately being discharged into the oceans. One of the other major contributions in this work is to suggest conversion of (old) Rankine cycle generation of electricity to (new) combined gas cycle generation and/or simple gas cycle generation. The combined gas cycle generation can achieve efficiencies of 55–60%, while that of the Rankine cycle power generation languishes around 30%. Less water is required per MW electric power generated for condenser cooling in the combined cycle. The simple gas cycle generation can achieve 40% thermal efficiency on the average and use no water for cooling. There is also the suggestion to upgrade to supercritical power plants due to the advances in power plant technologies. The improved thermal efficiencies gained from this upgrade generate other benefits as well. Another contribution is the suggestion to use seawater for closed system condenser cooling in power plants that are not near the sea or ocean or any large body of freshwater. The open system seawater condenser cooling has been practiced for years throughout the world. This will definitely reduce the demand for freshwater, which could otherwise be used for human consumption or agriculture. Additionally, the rising seas problem locally may be reduced somewhat if enough of the seawater is used.
Leveraging Virtual Reality Experiences With Mixed-Integer Nonlinear Programming Visualization of Disassembly Sequence Planning Under Uncertainty
Authors: Behdad Sara , Berg Leif P. , Thurston Deborah , Vance Judy
Published: January 2014

Disassembly sequence planning at the early conceptual stage of design leads to enormous benefits including simplification of products, lower assembly and disassembly costs, and design modifications which result in increased potential profitability of end-of-life salvaging operations. However, in the early design stage, determining the best disassembly sequence is challenging. First, the required information is not readily available and very time-consuming to gather. In addition, the best solution is sometimes counterintuitive, even to those with experience and expertise in disassembly procedures. Integrating analytical models with immersive computing technology (ICT) can help designers overcome these issues. A two-stage procedure for doing so is introduced in this paper. In the first stage, a stochastic programming model together with the information obtained through immersive simulation is applied to determine the optimal disassembly sequence, while considering uncertain outcomes, such as time, cost, and the probability of causing damage. In the second stage, ICT is applied as a tool to explore alternative disassembly sequence solutions in an intuitive way. The benefit of using this procedure is to determine the best disassembly sequence, not only by solving the analytic model but also by capturing human expertise. The designer can apply the obtained results from these two stages to analyze and modify the product design. An example of a Burr puzzle is used to illustrate the application of the method.
Water Cooling Method to Improve the Performance of Field-Mounted, Insulated, and Concentrating Photovoltaic Modules
Authors: Smith Matthew K. , Selbak Hanny , Wamser Carl C. , Day Nicholas U. , Krieske Mathew , Sailor David J. , Rosenstiel Todd N.
Published: January 2014

The installation rate of crystalline silicon photovoltaic (PV) modules worldwide is at an all-time high and is projected to continue to grow as the cost of PV technology is reduced. It is important to note that PV power generation is heavily influenced by the local climate. In particular, for crystalline silicon-based PV devices, as the operating temperature of the panel increases, the efficiency decreases. Higher operating temperatures also lead to accelerated material and mechanical degradation, potentially compromising system effectiveness over the lifetime of the panels. In addition, atmospheric pollution can cause particle deposition on the surface of PV modules (soiling), reducing the amount of solar irradiance that reaches the PV material and reducing panel efficiency. Various cooling and cleaning methods have been proposed in the literature to mitigate these problems. In this study, a uniform film of water was continuously recirculated by pumping over the surface of a solar panel using an emitter head attached to the top of the panel. The water cooling technique was able to maintain panel temperature below 40 °C while adjacent untreated panels were operating near 55 °C. Besides the efficiency improvements due to cooling, the film of water also kept the panels clean, avoiding any reduced power output caused by panel soiling. Additional studies were carried out with artificially chilled cooling fluid, insulating materials, and side mirrors to examine the cooling system performance under different installation scenarios. Water cooling is concluded to be an effective means of increasing the efficiency of monocrystalline silicon photovoltaic panels. Under normal operating conditions, the increased energy output from the panels is more than sufficient to compensate for the energy required to pump the water.
Assessment of the Effectiveness of a Polar Fuzzy Approach for the Control of Centrifugal Compressors
Authors: Defoy Benjamin , Alban Thomas , Mahfoud Jarir
Published: January 2014

The aim of this study is to assess the possibility to apply a new control approach dedicated to turbomachinery. The controller is fuzzy based using inputs expressed in polar coordinates. The advantage is that it manages two significant physical quantities, namely tangential and radial velocities that are related to steady state and transient behaviors, respectively. A synchronous filter is associated to the controller in order to enhance the ratio command force/bearing dynamic capacity. The approach was previously applied experimentally with success for the control of an academic test rig. It is adapted here for the control of an industrial compressor whose flexible rotor is supported by active magnetic bearings (AMB). At this stage, only numerical investigations are performed. The controller has to satisfy the standards and the end users requirements. In addition, it should be easy to implement. The behavior of the machine studied is assessed for several configurations of unbalances. A test that corresponds to usual industrial excitations (subsynchronous excitations at nominal speed) is also carried out. Results obtained are satisfactory and give insight into the potential of the approach. In addition, and as the fuzzy controller parameters are independent from the rotor design, the approach is a first step for the standardization of magnetic bearing controller synthesis.
Mechanics of Solar Module on Structured Substrates
Authors: Liu Zhuangjian , Cheng Huanyu , Wu Jian
Published: January 2014

In the island-interconnect design, the device islands connected by interconnects are mounted on a soft elastomeric substrate. The out-of-plane motion of interconnects accommodates the deformation applied to the system, enabling stretchable feather in electronics. The areal coverage, however, decreases due to the presence of interconnects. This problem is difficult to address for many important applications where high areal coverage is desired. By minimizing the interfacial stress between the device islands and substrate, a structured substrate introduces surface relief in the substrate and this design offers a desired level of stretchability with a relatively large areal coverage. Theoretical and numerical investigations give the strain levels in both the substrate and interconnect, providing design guidance on the optimization of the geometric and material parameters in the experiment.
Real-Time Estimation of Endogenous and Exogenous Inputs
Authors: Kirchner William , Southward Steve
Published: January 2014

Nearly all dynamic systems have input excitations that are either unmeasurable or unknown due to practical constraints such as feasibility or cost. Estimation of these excitations can be useful both in control applications as well as system modeling applications. The objective of this work is to expand upon an observer based approach to estimate unmeasurable or unknown inputs to a dynamic system using linear systems theory in an efficient manner that is suitable for real-time implementation. In this work, we explicitly explore two fundamental questions. How should the structure, dimensionality, and parameterization of an internal model or waveform generator model be selected for a given dynamic system? How do we determine, based on the structure of the dynamic system, whether estimation of exogenous and endogenous inputs is possible? A series of numerical simulations is performed, providing insight into these issues.
Study of Erosive Cavitation Detection in Pump Mode of Pump–Storage Hydropower Plant Prototype
Authors: Cencîc Tine , Hoĉevar Marko , Ŝirok Brane
Published: January 2014

An experimental investigation has been made to detect cavitation in a pump–storage hydropower plant prototype suffering from leading edge cavitation in pump mode. Vibrations and acoustic emission on the housing of the turbine bearing and pressure fluctuations in the draft tube were measured and the corresponding signals were recorded and analyzed. The analysis was based on the analysis of high-frequency content of measured variables. The pump–storage hydropower plant prototype has been operated at various input loads and Thoma numbers. Several estimators of cavitation were evaluated according to a coefficient of determination between the Thoma number and cavitation estimators. The best results were achieved with a compound discharge coefficient cavitation estimator that is based on the discharge coefficient and several rms estimators: vibrations, acoustic emission, and pressure fluctuations. The compound discharge estimator was set as a product of the rms estimator and the squared discharge coefficient. Cavitation estimators were evaluated in several intervals of frequencies; the best frequency interval for the vibration sensor on the turbine cover was from 24 to 26 kHz, for the vibration sensor on the guide vane 36–40 kHz, for the acoustic emission sensor on the turbine cover 140–145 kHz, and for the pressure fluctuation sensor in the draft tube wall 130–150 kHz.
Numerical and Experimental Study of Unsteady Flow in a Large Centrifugal Pump With Stay Vanes
Authors: Gao Zhongxin , Zhu Wenruo , Lu Li , Deng Jie , Zhang Jianguang , Wuang Fujun
Published: January 2014

The unsteady flow inside a large centrifugal pump with stay vanes was analyzed in this study. The static performance and pressure fluctuations in the pump were numerically predicted and were compared with experimental data. Considering the relative positions of the impeller to the volute tongue and stay vanes, the static performance which was obtained using a full unsteady calculation was compared with traditional steady calculation results. A comparison of the results with the experimental data showed that the operation condition farther from the design condition resulted in larger differences between the steady simulation and experimental results, with errors beyond reasonable limits, while the performance curves obtained by the unsteady calculations were closer to the experimental data. A comparison of the pressure fluctuations at four monitoring points with the experimental data showed that the amplitudes at HVS1 and HVS2 are much larger than at HD1 and HD2. The main frequency for these four monitoring points, which agreed well with the experimental data, was the blade passing frequency. The relative obvious errors in pressure fluctuations for HD1and HD2 were due to the inlet flow rate variation of the simulation. Thus, unsteady numerical simulations can be used to predict the pressure fluctuations when designing a pump.
Lagrangian Formulation and Numerical Solutions to Dump Truck Vibrations Under HISLO Conditions
Authors: Aouad Nassib , Frimpong Samuel
Published: January 2014

Heavy mining machinery has exposed the human body to extreme vibrations that may limit the performance of operators and further impact the overall system performance. Large capacity shovels and dump trucks have been deployed in surface mines to achieve economic, bulk production operations. The high-impact shovel loading operation (HISLO) causes severe truck vibrations that expose operators to whole-body vibrations (WBV) levels that may exceed ISO standards. The effects of these shockwaves on the human body are severe resulting in long-term lower-back disorders and other health problems. There is a need for fundamental and applied research to determine HISLO vibration levels, their comparisons to ISO 2631 limits, and the safety of operators under these conditions. A fundamental research has been carried to model these HISLO shockwave generation and propagation through the truck body and attenuated via the suspension mechanism and within the rollover protective structures (ROPS) cabin. The Lagrangian mechanics technique has been used to formulate the equations of motions governing the HISLO problem. The Fehberg fourth–fifth order Runge–Kutta (RKF45) numerical method in maple environment (maple classic Version 10.00, 2006, Maplesoft, a division of Waterloo Maple Inc., Waterloo, ON, Canada) is used to solve the equations of motions symbolically. The Lagrangian formulation and the RKF45 solutions provide efficient solutions to complex functions with stability, convergence, and minimum errors. The results of this analysis show that the vertical root mean square (rms) accelerations are equal to 3.56, 1.12, and 0.87 m/s2 for the operator's seat, lower-back, and cervical regions, respectively. These vibration levels also fall within the extremely uncomfortable zone compared to the ISO 2631-1 comfort zone (less than 0.315 m/s2), which pose severe health threats to truck operators over long-term exposure to these vibrations.
Discussion: “Optimization of a Two Degree of Freedom System Acting as a Dynamic Vibration Absorber” (Febbo, M., and Vera, S. A., 2008, ASME J. Vib. Acoust., 130, p. 011013)
Authors: Chun Semin , Baek Hyunwook , Kim Tae-Hyoung
Published: January 2014

We present this discussion on “Optimization of a Two Degree of Freedom System Acting as a Dynamic Vibration Absorber,” by M. Febbo and S. A. Vera, published in the Feb. 2008 issue of the ASME Journal of Vibration and Acoustics, Vol. 130, No. 1, p. 010013, and then derive the corrections in detail.
Application of Womersley Model to Reconstruct Pulsatile Flow From Doppler Ultrasound Measurements
Authors: Daidzic Nihad E.
Published: January 2014

A Womersley model-based assessment of pulsatile rigid-tube flow is presented. Multigate Doppler ultrasound was used to measure axial velocities at many radial locations along a single interrogation beam going through the center of a stiff tube. However, a large impediment to Doppler ultrasound diagnostics and resolution close to the wall is considerable noise due to the presence of the wall-fluid interface as well as many other effects, such as spectral broadening, coherent scattering, time resolution, and Doppler angle uncertainty. Thus, our confidence in measured signals is questionable, especially in the wall vicinity where the important oscillatory shear stresses occur. In order to alleviate known biases and shortcomings of the pulsed Doppler ultrasound measurements we have applied Womersley's laminar axisymmetric rigid-tube approximation to reconstruct velocity profiles over the entire flow domain and specifically close to wall, enabling unambiguous determination of the shear stresses. We employ harmonic analysis of the measured velocity profiles at all or selected trusted tube radial locations over one or more periods. Each of estimated Fourier coefficients has a unique counterpart in the respective pressure gradient component. From ensemble-averaged cross-sectional pressure gradient components we compute velocity profiles, volume flow rate, wall shear stress, and other flow parameters. Estimation of the pressure gradients from spatially resolved pulsed Doppler ultrasound velocity measurements is an added benefit of our reconstruction method. Multigate pulsed Doppler ultrasound scanners offer powerful capabilities to noninvasively and nonintrusively measure velocity profiles for hemodynamic and other fluid flow applications. This flow reconstruction method can also be tailored for use with other flow diagnostic modalities, such as magnetic resonance imaging (MRI) and a wide class of optical methods.
Computationally Efficient Magnetic Resonance Imaging Based Surface Contact Modeling as a Tool to Evaluate Joint Injuries and Outcomes of Surgical Interventions Compared to Finite Element Modeling
Authors: Johnson Joshua E. , Lee Phil , McIff Terence E. , Bruce Toby E. , Fischer Kenneth J.
Published: January 2014

Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.
The Effects of Piston Skirt Profiles on Secondary Motion and Friction
Authors: Gunelsu Ozgur , Akalin Ozgen
Published: January 2014

Piston skirt form deviating from a perfect cylinder is investigated numerically for an improved frictional performance. Three features defining the barrel and oval form of the skirt are compared in the search for lower friction power loss. Radius of curvature around the bulge of the barrel is changed to obtain a flatter or more-rounded lubricated area with respect to a hot-piston profile as well as the axial location of this bulge. On the other hand, the circumferential variation in the separation between the skirt and cylinder wall is represented by an elliptical piston and the aspect ratio is varied for comparison. These different skirt profiles are used in a developed piston secondary dynamics model solving for the lateral movement of the piston by calculating the hydrodynamic and boundary normal forces acting on the piston together with friction. Finally, an improved skirt profile is suggested to obtain better frictional efficiency.
Numerical Investigation of the Transient Hydrothermal Behavior of a Ferrofluid Flowing Through a Helical Duct in the Presence of Nonuniform Magnetic Field
Authors: Aminfar Habib , Mohammadpourfard Mousa , Ahangar Zonouzi Sajjad
Published: January 2014

This paper investigates numerically the time dependent hydrothermal behavior of a ferrofluid (water and 4 vol. % Fe3O4) flowing in a helical channel, which is exposed to a nonuniform transverse magnetic field and its walls are subjected to uniform heat flux. The two phase mixture model and control volume technique have been used to study the flow. The results show that applying the nonuniform transverse magnetic field considerably increases the velocity and flow rate in the vicinity of the channel walls while it significantly decreases the velocity at the center of the channel. Applying magnetic field also decreases considerably the temperature of the inner wall of the helical channel. Furthermore, the average Nusselt number is increased by applying the nonuniform transverse magnetic field and it is more enhanced by increasing the magnetic field intensity.
Thermal Conductivity and Interface Thermal Conductance in Composites of Titanium With Graphene Platelets
Authors: Zheng H. , Jaganandham K.
Published: January 2014

Composite films of graphene platelets (GPs) in titanium matrix were prepared on silicon (001) substrates by physical vapor deposition of titanium using magnetron sputtering and dispersion of graphene platelets. The graphene platelets were dispersed six times after each deposition of titanium film to form the composite film. Samples of titanium film and titanium film with a single layer of dispersed graphene platelets were also prepared by the same procedure. The distribution of the graphene platelets in the film was analyzed by scanning electron microscopy. Energy dispersive spectrometry was used to infer the absence of interstitial elements. The thermal conductivity of the composite and the interface thermal conductance between titanium and silicon or titanium and graphene platelets was determined by three-omega and transient thermo reflectance (TTR) techniques, respectively. The results indicate that the thermal conductivity of the composite is isotropic and improved to 40 Wm−1K−1 from 21 Wm−1 K−1 for Ti. The interface thermal conductance between titanium and silicon is found to be 200 MWm−2K−1 and that between titanium and graphene platelets in the C-direction to be 22 MWm−2K−1. Modeling using acoustic and diffuse mismatch models was carried out to infer the magnitude of interface thermal conductance. The results indicate that the higher value of interface thermal conductance between graphene platelets in the ab plane and titanium matrix is responsible for the isotropic and improved thermal conductivity of the composite. Effective mean field analysis showed that the interface thermal conductance in the ab plane is high at 440 MWm−2K−1 when GPs consist of 8 atomic layers of graphene so that it is not a limitation to improve the thermal conductivity of the composites.
A Look on Fang Number
Authors: Awad M. M.
Published: January 2014

In this study, a look on Fang number (Fa) is presented. The Fa was introduced recently in 2013 by Professor Xiande Fang to provide great facilitation in describing flow boiling heat transfer coefficients. It is defined as the product of two terms. The first term is the ratio of buoyancy force to gravitational force, which has effects on bubble departure. The second term is the ratio of surface tension force to inertial force, which affects bubble formation. As a result, Fa is associated with the formation and departure of bubbles. The Fa will be expressed by using a combination of the Eötvös number (Eo), Froude number (Fr), and Weber number (We). Based on this study, it is clear that existing dimensionless numbers in literature, i.e., Eötvös number, Froude number, Weber number, and their combinations can be used to describe flow boiling heat transfer coefficients. This combination of existing non-dimensional groups (Eo, Fr, and We) leads to good correlation with flow boiling data of different working fluids such as CO2, R134a, and R22.
Experimental Study on Convective Heat Transfer Performance of Iron Oxide Based Ferrofluids in Microtubes
Authors: Kurtoğlu Evrim , Kaya Alihan , Gözüaçık Devrim , Yağcı Acar Havva Funda , Koşar Ali
Published: January 2014

Ferrofluids are colloidal suspensions, in which the solid phase material is composed of magnetic nanoparticles, while the base fluid can potentially be any fluid. The solid particles are held in suspension by weak intermolecular forces and may be made of materials with different magnetic properties. Magnetite is one of the materials used for its natural ferromagnetic properties. Heat transfer performance of ferrofluids should be carefully analyzed and considered for their potential of their use in wide range of applications. In this study, convective heat transfer experiments were conducted in order to characterize convective heat transfer enhancements with lauric acid coated ironoxide (Fe3O4) nanoparticle based ferrofluids, which have volumetric fractions varying from 0% to ∼5% and average particle diameter of 25 nm, in a hypodermic stainless steel microtube with an inner diameter of 514 μm, an outer diameter of 819 μm, and a heated length of 2.5 cm. Heat fluxes up to 184 W/cm2 were applied to the system at three different flow rates (1 ml/s, 0.62 ml/s, and 0.36 ml/s). A decrease of around 100% in the maximum surface temperature (measured at the exit of the microtube) with the ferrofluid compared to the pure base fluid at significant heat fluxes (>100 W/cm2) was observed. Moreover, the enhancement in heat transfer increased with nanoparticle concentration, and there was no clue for saturation in heat transfer coefficient profiles with increasing volume fraction over the volume fraction range in this study (0–5%). The promising results obtained from the experiments suggest that the use of ferrofluids for heat transfer, drug delivery, and biological applications can be advantageous and a viable alternative as new generation coolants and futuristic drug carriers.
Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in SUS304-Circular Tubes With Various Twisted-Tape Inserts (Influence of Twist Ratio)
Authors: Hata Koichi , Fukuda Katsuya , Masuzaki Suguru
Published: January 2014

The transient critical heat fluxes (transient CHFs) in SUS304-circular tubes with various twisted-tape inserts are systematically measured for mass velocities (G = 3988–13,620 kg/m2s), inlet liquid temperatures (Tin = 287.55–313.14 K), outlet pressures (Pout = 805.11–870.23 kPa) and exponentially increasing heat inputs (Q = Q0 exp(t/τ), exponential periods, τ, of 28.39 ms to 8.43 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304-circular tube of inner diameter (d = 6 mm), heated length (L = 59.4 mm), effective length (Leff = 49.4 mm), L/d (=9.9), Leff/d (=8.23), and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.89 μm) is used in this work. The SUS304 twisted-tapes with twist ratios, y [H/d = (pitch of 180 deg rotation)/d], of 2.40 and 4.45 are used. The transient critical heat fluxes for SUS304-circular tubes with the twisted-tapes of y = 2.40 and 4.45 are compared with authors' transient CHF data for the empty SUS304-circular tube and a SUS304-circular tube with the twisted-tape of y = 3.37, and the values calculated by authors' transient CHF correlations for the empty circular tube and the circular tube with twisted-tape insert. The influences of heating rate, twist ratio and swirl velocity on the transient CHF are investigated into details and the widely and precisely predictable correlations of the transient CHF against inlet and outlet subcoolings for the circular tubes with various twisted-tape inserts are given based on the experimental data. The correlations can describe the transient CHFs for SUS304-circular tubes with various twisted-tapes of twist ratios (y = 2.40, 3.37, and 4.45) in the wide experimental ranges of exponential periods (τ = 28.39 ms to 8.43 s) and swirl velocities (usw = 5.04–20.72 m/s) obtained in this work within −26.19% to 14.03% difference. The mechanism of the subcooled flow boiling critical heat flux in a circular tube with twisted-tape insert is discussed.
Model Predictive Control of Fractional Order Systems
Authors: Rhouma Aymen , Bouani Faouzi , Bouzouita Badreddine , Ksouri Mekki
Published: January 2014

This paper provides the model predictive control (MPC) of fractional order systems. The direct method will be used as internal model to predict the future dynamic behavior of the process, which is used to achieve the control law. This method is based on the Grünwald–Letnikov's definition that consists of replacing the noninteger derivation operator of the adopted system representation by a discrete approximation. The performances and the efficiency of this approach are illustrated with practical results on a thermal system and compared to the MPC based on the integer ARX model.
Development of Sketch-Based 3-D Modeling System for Rapid Generation and Evaluation of Automotive Seat Shape Using Reference Models
Authors: Song Inho , Yang Jeongsam , Shimada Kenji
Published: January 2014

Seat style designers transform their ideas into 3-D forms using creative, iterative modeling processes to quickly evolve their designs from concept to reality, while refining the design details of the seat shape. Although the recent introduction of computer-aided styling systems to the design process has greatly enhanced designers' productivity, they still prefer to ideate using “pen and paper.” Here, we propose a sketch-based 3-D modeling system that enables designers to rapidly and intuitively create a seat shape by applying a 2-D sketch to a normalized seat reference model and then evaluating the newly designed model. For this purpose, we describe three modeling techniques that support interactive shape editing: curve manipulation using pen strokes, vertex point manipulation, and tangent vector manipulation. In addition, we propose three methods for the design and functional evaluation of an automotive seat, checking for interference between a seat skin and its frame, checking for foldability among seat components with regard to their positioning, and checking for coupling between a seat model and a digital human body.
Development of Creep-Fatigue Evaluation Method for Modified 9Cr-1Mo Steel
Authors: Takaya Shigeru , Nagae Yuji , Asayama Tai
Published: January 2014

This paper describes a creep–fatigue evaluation method for modified 9Cr-1Mo steel, which has been newly included in the 2012 edition of the Japan Society of Mechanical Engineers code for design and construction of fast reactors (JSME FRs code). In this method, creep and fatigue damages are evaluated on the basis of Miner's rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. The conservativeness of this method without design factors was investigated using material test results, and it was shown that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data are hardly obtained. These results confirm that the creep–fatigue evaluation method in the JSME FRs code has implicit conservatism in addition to explicit margins in the design procedures such as design factor.
Temperature Jump Coefficient for Superhydrophobic Surfaces
Authors: Ng Chiu-On , Wang C. Y.
Published: January 2014

Mathematical models are developed for heat conduction in creeping flow of a liquid over a microstructured superhydrophobic surface, where because of hydrophobicity, a gas is trapped in the cavities of the microstructure. As gas is much lower in thermal conductivity than liquid, an interfacial temperature slip between the liquid and the surface will develop on the macroscale. In this note, the temperature jump coefficient is numerically determined for several types of superhydrophobic surfaces: a surface with parallel grooves, and surfaces with two-dimensionally distributed patches corresponding to the top of circular or square posts, and circular or square holes. These temperature jump coefficients are found to have a nearly constant ratio with the corresponding velocity slip lengths.
A Nonisothermal Fluid-Structure Interaction Analysis on the Piston/Cylinder Interface Leakage of High-Pressure Fuel Pump
Authors: Qian Dexing , Liao Ridong
Published: January 2014

In this paper, a nonisothermal fluid-structure interaction mathematical model for the piston/cylinder interface leakage is presented. Full account is taken of the piston eccentricity, elastic deformations of the piston pair, the nonisothermal flow in the interface, and the physical properties of the fluid such as the pressure-viscosity and temperature-viscosity effects. The numerical method for the solution of the model is given, which can simultaneously solve for the fluid pressure distribution and leakage rate in the interface. The model is validated by comparing the calculated leakage rates with the measurements. Results show the good accuracy of the model. The impacts of parameters such as the piston diameter, the initial clearance between the piston pair, and the piston velocity on the leakage rate are discussed. Some of the conclusions provide good guidance for the design of high-pressure fuel pumps.
A Helical Gear Pair Pocketing Power Loss Model
Authors: Talbot David , Kahraman Ahmet , Seetharaman Satya
Published: January 2014

A new fluid dynamics model is proposed to predict the power losses due to pocketing of air, oil, or an air-oil mixture in the helical gear meshes. The proposed computational procedure treats a helical gear pair as a combination of a number of narrow face width spur gear segments staggered according to the helix angle and forms a discrete fluid dynamics model of the medium being pocketed in the gear mesh. Continuity and conservation of momentum equations are applied to each coupled control volume filled with a compressible fluid mixture to predict fluid pressure and velocity distributions from which the instantaneous pocketing power loss is calculated. The proposed model is exercised in order to investigate the fluid pressure and velocity distributions in time along with the pocketing power loss as a function of the speed, helix angle, and oil-to-air ratio.
Influence of Carbon Nanotubes on Wear of Carbide/Cobalt Micropunch
Authors: Wei Guo Kelvii
Published: January 2014

Carbon nanotubes (CNTs) coated on a tungsten carbide/cobalt (WC/Co) micropunch (150 μm in diameter) and their effect on the wear of micropunches were investigated. CNTs were synthesized by homemade method. After the punching test with Ti as the substrate, the effect of CNTs on the wear loss and the surface morphology of the micropunch had been studied by confocal laser, scanning electron microscopy (SEM), and digital balance. Results show the wear of a CNTs coated micropunch obviously decreases. Even in the severe wear period, the wear loss is less than that of a non-CNTs coated micropunch. Compared with the micropunch without CNTs coating, the promising results are due to the formation of a lubrication film at the contact region by rubbing of the CNT forest; CNTs produced adhere to the micropunch surface avoiding direct contact during the punching period and providing lubricant properties to the interface by virtue of their graphitic nature.
Reheat-Air Brayton Combined Cycle Power Conversion Design and Performance Under Nominal Ambient Conditions
Authors: Andreades Charalampos , Scarlat Raluca O. , Dempsey Lindsay , Peterson Per
Published: January 2014

Modern large air Brayton gas turbines have compression ratios ranging from 15 to 40 resulting in compressor outlet temperatures ranging from 350 °C to 580 °C. Fluoride-salt-cooled, high-temperature reactors, molten salt reactors, and concentrating solar power can deliver heat at temperatures above these outlet temperatures. This article presents an approach to use these low-carbon energy sources with a reheat-air Brayton combined cycle (RACC) power conversion system that would use existing gas turbine technology modified to introduce external air heating and one or more stages of reheat, coupled to a heat recovery steam generator to produce bottoming power or process heat. Injection of fuel downstream of the last reheat stage is shown to enable the flexible production of additional peaking power. This article presents basic configuration options for RACC power conversion, two reference designs based upon existing Alstom and GE gas turbine compressors and performance of the reference designs under nominal ambient conditions. A companion article studies RACC start up, transients, and operation under off-nominal ambient conditions.
Unsteady Half-Annulus Computational Fluid Dynamics Calculations of Thermal Migration Through a Cooled 2.5 Stage High-Pressure Turbine
Authors: Tallman James A.
Published: January 2014

This paper presents an industrial perspective on the potential use of multiple-airfoil row unsteady computational fluid dynamics (CFD) calculations in high-pressure turbine design cycles. A sliding-mesh unsteady CFD simulation is performed for a high-pressure turbine section of a modern aviation engine at conditions representative of engine take-off. The turbine consists of two stages plus a center-frame strut upstream of the low-pressure turbine. The airfoil counts per row are such that a half-annulus model domain must be simulated for periodicity. The total model domain size is 170 MM computational grid points and the solution requires approximately nine days of clock time on 6288 processing cores of a Cray XE6 supercomputer. Airfoil and endwall cooling flows are modeled via source term additions to the flow. The endwall flowpath cavities and their purge/leakage flows are resolved in the computational meshes to an extent. The time-averaged temperature profile solution is compared with static rake data taken in engine tests. The unsteady solution shows a considerable improvement in agreement with the rake data, compared with a steady-state solution using circumferential mixing planes. Passage-to-passage variations in the gas temperature prediction are present in the 2nd stage, due to nonperiodic alignment between the nozzle vanes and rotor blades. These passage-to-passage differences are quantified and contrasted.
Silicone-Based Tissue-Mimicking Phantom for Needle Insertion Simulation
Authors: Wang Yancheng , Tai Bruce L. , Yu Hongwei , Shih Albert J.
Published: January 2014

Silicone-based tissue-mimicking phantom is widely used as a surrogate of tissue for clinical simulators, allowing clinicians to practice medical procedures and researchers to study the performance of medical devices. This study investigates using the mineral oil in room-temperature vulcanizing silicone to create the desired mechanical properties and needle insertion characteristics of a tissue-mimicking phantom. Silicone samples mixed with 0, 20, 30, and 40 wt. % mineral oil were fabricated for indentation and needle insertion tests and compared to four types of porcine tissues (liver, muscle with the fiber perpendicular or parallel to the needle, and fat). The results demonstrated that the elastic modulus and needle insertion force of the phantom both decrease with an increasing concentration of mineral oil. Use of the mineral oil in silicone could effectively tailor the elastic modulus and needle insertion force to mimic the soft tissue. The silicone mixed with 40 wt. % mineral oil was found to be the best tissue-mimicking phantom and can be utilized for needle-based medical procedures.
Analysis of Collaborative Design Networks: A Case Study of OpenIDEO
Authors: Fuge Mark , Tee Kevin , Agogino Alice , Maton Nathan
Published: January 2014

This paper presents a large-scale empirical study of OpenIDEO, an online collaborative design community. Using network analysis techniques, we describe the properties of this collaborative design network and discuss how it differs from common models of network formation seen in other social or technological networks. One major finding is that in OpenIDEO's social network the highly connected members talk more to less connected members than each other—a behavior not commonly found in other social and collaborative networks. We discuss how some of the interventions and incentives inherent in OpenIDEO's platform might cause this unique structure, and what advantages and disadvantages this structure has for coordinating distributed design teams. Specifically, its core-periphery structure is robust to network changes, but is at risk of decreasing design exploration ability if the core becomes too heavily clustered or loses efficiency. We discuss possible interventions that can prevent this outcome: encouraging core members to collaborate with periphery nodes, and increasing the diversity of the user population.
Tracking Error Analysis for Feedback Systems With Hysteresis Inversion and Fast Linear Dynamics1
Authors: Edardar Mohamed , Tan Xiaobo , Khalil Hassan K.
Published: January 2014

Analysis of closed-loop systems involving hysteresis is important to both the understanding of these systems and the synthesis of control schemes. However, such analysis is challenging due to the nonsmooth nature of hysteresis nonlinearities. In this paper, singular perturbation techniques are employed to derive an analytical approximation to the tracking error for a system consisting of fast linear dynamics preceded by a piecewise linear hysteresis nonlinearity, which is motivated by applications such as piezo-actuated nanopositioning. The control architecture considered combines hysteresis inversion and proportional-integral feedback, with and without a constant feedforward control. The analysis incorporates the effect of uncertainty in the hysteresis model, and offers insight into how the tracking performance depends on the system parameters and the references, thereby offering guidance in the controller design. Simulation and experimental results on a piezo-actuated nanopositioning system are presented to support the analysis. In particular, the control scheme incorporating the feedforward element consistently outperforms the classical PI controller in tracking a variety of references.
The Application of Wall Similarity Techniques to Determine Wall Shear Velocity in Smooth and Rough Wall Turbulent Boundary Layers
Authors: Walker Jessica M.
Published: January 2014

Smooth and rough wall turbulent boundary layer profiles are frequently scaled using the wall shear velocity u*, thus it is important that u* is accurately known. This paper reviews and assesses several wall similarity techniques to determine u* and compares results with data from the total stress, Preston tube, and direct force methods. The performance of each method was investigated using experimental repeatability data of smooth and rough wall turbulent boundary layer profiles at Reθ of 3330 and 4840, respectively, obtained using laser Doppler velocimetry (LDV) in a recirculating water tunnel. To validate the results, an analysis was also performed on the direct numerical simulation (DNS) data of Jimenez et al. (2010, “Turbulent Boundary Layers and Channels at Moderate Reynolds Numbers,” J. Fluid Mech., 657, pp. 335–360) at Reθ = 1968. The inner layer similarity methods of Bradshaw had low experimental uncertainty and accurately determined u* and ε for the DNS data and are the recommended wall similarity methods for turbulent boundary layer profile analysis. The outer layer similarity methods did not perform well, due to the need to simultaneously solve for three parameters: u*, ε, and Π. It is strongly recommended that the u* values determined using wall similarity techniques are independently verified using another method such as the total stress or direct force methods.