Constant Velocity Conditions Research Articles

Comparative investigation of heat extraction performance in 3D self-affine rough single fractures using CO2,N2O and H2O as heat transfer fluid

The type and thermophysical properties of heat transfer fluids significantly impact the heat extraction rate of Enhanced Geothermal Systems (EGS). Studies based on field-scale stochastic discrete fracture network geometric models have certain limitations and uncertainties. To compare the heat extraction performance of heat transfer fluids H2O, CO2, and N2O in a core-scale (φ50 × 100 mm) rough single fracture in hot dry rock, we first constructed the fracture geometry with rock surface roughness characteristics using a fractal self-affine function, with a joint roughness coefficient (JRC) of 12.38. Then, at temperatures ranging from 37 to 300°C and a pressure of 30 MPa, we established a thermo-hydraulic (TH) coupling model based on the thermophysical parameter equations of the three heat transfer fluids. Finally, we conducted a comparative study of the changes in the outlet mean temperature and heat extraction rate after flowing through the fracture, as well as the temperature distribution on the fracture surface, under conditions of constant inlet flow velocity with varying inlet temperature and constant inlet temperature with varying inlet flow velocity. The results indicate that (1) with the increase in inlet flow velocity and temperature, the outlet mean temperature and heat extraction rate of CO2 and N2O at the fracture outlet are essentially the same and lower than those of H2O. (2) When the inlet flow velocity increases from 0.005 m/s to 0.025 m/s, the thermal convection effect from the rock matrix to the fluid in the fracture predominates, and flow velocity is the main factor affecting the heat transfer process between the fluid and the rock matrix. When the inlet temperature increases from 37°C to 57°C, the thermal conduction effect from the rock matrix to the fluid in the fracture predominates, and temperature is the main factor affecting the heat transfer process between the fluid and the rock matrix.(3)When maintaining constant inlet temperature, increasing inlet flow velocity from 0.005 m/s to 0.025 m/s results in CO2 experiencing a maximum heat extraction rate increase of 118.85 W. In contrast, N2O experiences 117.05 W, and H2O experiences 266.4 W.(4) When the inlet flow rate is constant, the maximum increase in heat extraction rate for CO2 is 15.34 W as the inlet temperature increases from 37 °C to 57 °C; for N2O, it is 13.9 W; and for H2O, it is 45.45 W.

Persons with Unilateral Transtibial Amputations Modulate Ipsilateral Hip and Contralateral Ankle Joint Work to Accelerate and Decelerate Walking

ABSTRACT Introduction Loss of power production at the ankle joint contributes to many problems people with unilateral transtibial (UTT) amputation experience during walking. Little is known about walking acceleration and deceleration, which is common in daily living and may require substantial compensatory behaviors from the residual lower-limb joints. Objective The aim of this study was to quantify individual lower-limb joint contributions to walking acceleration and deceleration in people with UTT amputations. We hypothesized that joint work on the prosthetic limb would be primarily modulated at the hip, and joint work on the sound limb would be primarily modulated at the ankle. Study Design The study is a repeated-measures design. Methods Six K3 level ambulators with UTT amputations participated. Participants performed a total of 40 walking trials while wearing their own nonarticulated dynamic prosthetic foot and socket. Each trial consisted of walking along a straight walkway. After walking approximately 2 m, participants received a cue instructing them to perform one of three walking conditions: continue walking at a constant average velocity, rapidly accelerate, or rapidly decelerate. We used ground reaction forces and motion capture data to derive joint kinematics and kinetics during the three walking conditions. We used one-way repeated-measures analyses of variance (ANOVAs) to identify significant differences between conditions. Results For the sound limb, positive hip and ankle work was significantly greater during acceleration compared with constant average velocity or deceleration conditions, and negative knee work was significantly greater during acceleration compared with deceleration. For the prosthetic limb, negative ankle work was significantly greater during acceleration compared with deceleration. Conclusions People with UTT amputation who use nonarticulated prostheses primarily modulated joint work on their sound limb to accelerate or decelerate walking speed. Clinical Relevance Characterizing compensatory behaviors of people with a UTT amputation is important for understanding injury mechanisms, informing clinical guidelines, and improving future ankle-foot prosthesis designs.

Structures of Laminar Lean Premixed H2/CH4/Air Polyhedral Flames: Effects of Flow Velocity, H2 Content and Equivalence Ratio

AbstractPolyhedral Bunsen flames, induced by hydrodynamic and thermo-diffusive instabilities, are characterized by periodic trough and cusp cellular structures along the conical flame front. In this study, the effects of flow velocity, hydrogen content, and equivalence ratio on the internal cellular structure of premixed fuel-lean hydrogen/methane/air polyhedral flames are experimentally investigated. A high-spatial-resolution one-dimensional Raman/Rayleigh scattering system is employed to measure the internal scalar structures of polyhedral flames in troughs and cusps. Planar laser-induced fluorescence of hydroxyl radicals and chemiluminescence imaging measurements are used to quantify the flame front morphology. In the experiments, stationary polyhedral flames with varying flow velocities from 1.65 to 2.50 m/s, hydrogen contents from 50 to 83%, and equivalence ratios from 0.53 to 0.64 are selected and measured. The results indicate that the positively curved troughs exhibit significantly higher hydrogen mole fractions and local equivalence ratios compared to the negatively curved cusps, due to the respective focusing/defocusing effect of trough/cusp structure on highly diffusive hydrogen. The hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are first increased and then decreased with increasing measurement height from 5 to 13 mm, due to the three-dimensional effect of the flame front. With increasing flow velocity from 1.65 to 2.50 m/s, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps decrease, which is attributed to the overall decreasing curvatures in troughs and cusps due to the decreased residence time and increased velocity-induced strain. With increasing hydrogen content from 50 to 83%, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are amplified, due to the enhanced effects of the flame front curvature and the differential diffusion of hydrogen. With increasing equivalence ratio from 0.53 to 0.64, a clear increasing trend in hydrogen mole fraction and equivalence ratio differences between troughs and cusps is observed at constant flow velocity condition, which is a trade-off result between increasing effective Lewis number and increasing curvatures in troughs and cusps.

Study on the stability of oil-water annular flow under different amplitude

Compared with the traditional transportation of high-viscosity crude oil, water annular transportation has the advantages of low energy consumption and no change in crude oil composition. With the continuous development of marine heavy oil transportation, submarine oil pipelines are inevitably subjected to vibration and impact, affecting the annular flow in the pipeline. In this paper, the VOF model in Fluent software is used to simulate the stability of oil-water annular flow in a horizontal pipeline under different amplitudes and the interface characteristic parameters of annular flow. In addition, the influence of vibration on oil-water annular flow in the horizontal pipeline under different marine environments is studied. The results showed that the vibration parameters have an influence on the flow of oil-water annular flow in the horizontal pipeline. Under the condition of constant inlet velocity, the eccentricity degree of oil core is analyzed to reveal the law that the stability of annular flow decreases with the increase of amplitude. The relationship between the eccentricity of oil core and the vibrational parameters of pipes are explored in this paper. At the same time, the unit pressure drop under the condition of pipe vibration and its mechanism are studied. These results could provide references for parameters optimization of heavy oil-water annular flow transportation under vibration conditions.

A coupled model for phase mixing, grain damage and shear localization in the lithosphere: comparison to lab experiments

SUMMARYThe occurrence of plate tectonics on Earth is rooted in the physics of lithospheric ductile weakening and shear-localization. The pervasiveness of mylonites at lithospheric shear zones is a key piece of evidence that localization correlates with reduction in mineral grain size. Most lithospheric mylonites are polymineralic and the interaction between mineral phases, such as olivine and pyroxene, especially through Zener pinning, impedes normal grain growth while possibly enhancing grain damage, both of which facilitate grain size reduction and weakening, as evident in lab experiments and field observations. The efficacy of pinning, however, relies on the mineral phases being mixed and dispersed at the grain scale, where well-mixed states lead to greater mylonitization. To model grain mixing between different phases at the continuum scale, we previously developed a theory treating grain-scale processes as diffusion between phases, but driven by imposed compressive stresses acting on the boundary between phases. Here we present a new model for shearing rock that combines our theory for diffusive grain mixing, 2-D non-Newtonian flow and two-phase grain damage. The model geometry is designed specifically for comparison to torsional shear-deformation experiments. Deformation is either forced by constant velocity or constant stress boundary conditions. As the layer is deformed, mixing zones between different mineralogical units undergo enhanced grain size reduction and weakening, especially at high strains. For constant velocity boundary experiments, stress drops towards an initial piezometric plateau by a strain of around 4; this is also typical of monophase experiments for which this initial plateau is the final steady state stress. However, polyphase experiments can undergo a second large stress drop at strains of 10–20, and which is associated with enhanced phase mixing and resultant grain size reduction and weakening. Model calculations for polyphase media with grain mixing and damage capture the experimental behaviour when damage to the interface between phases is moderately slower or less efficient than damage to the grain boundaries. Other factors such as distribution and bulk fraction of the secondary phase, as well as grain-mixing diffusivity also influence the timing of the second stress drop. For constant stress boundary conditions, the strain rate increases during weakening and localization. For a monophase medium, there is theoretically one increase in strain rate to a piezometric steady state. But for the polyphase model, the strain rate undergoes a second abrupt increase, the timing for which is again controlled by interface damage and grain mixing. The evolution of heterogeneity through mixing and deformation, and that of grain size distributions also compare well to experimental observations. In total, the comparison of theory to deformation experiments provides a framework for guiding future experiments, scaling microstructural physics to geodynamic applications and demonstrates the importance of grain mixing and damage for the formation of plate tectonic boundaries.

Four-Objective Optimization of an Irreversible Magnetohydrodynamic Cycle

Based on the existing model of an irreversible magnetohydrodynamic cycle, this paper uses finite time thermodynamic theory and multi-objective genetic algorithm (NSGA-II), introduces heat exchanger thermal conductance distribution and isentropic temperature ratio of working fluid as optimization variables, and takes power output, efficiency, ecological function, and power density as objective functions to carry out multi-objective optimization with different objective function combinations, and contrast optimization results with three decision-making approaches of LINMAP, TOPSIS, and Shannon Entropy. The results indicate that in the condition of constant gas velocity, deviation indexes are 0.1764 acquired by LINMAP and TOPSIS approaches when four-objective optimization is performed, which is less than that (0.1940) of the Shannon Entropy approach and those (0.3560, 0.7693, 0.2599, 0.1940) for four single-objective optimizations of maximum power output, efficiency, ecological function, and power density, respectively. In the condition of constant Mach number, deviation indexes are 0.1767 acquired by LINMAP and TOPSIS when four-objective optimization is performed, which is less than that (0.1950) of the Shannon Entropy approach and those (0.3600, 0.7630, 0.2637, 0.1949) for four single-objective optimizations, respectively. This indicates that the multi-objective optimization result is preferable to any single-objective optimization result.

Study on erosion-wear characteristics of bidirectional metal seal floating ball valve in liquid-solid two-phase flow environment

In the residual ebullated-bed hydrocracking process, the transportation mediums of catalyst addition/withdrawal drum are heavy distillate oil and catalysts. The bidirectional metal seal floating ball valve used in the outlet pipeline of this drum occurs internal leakage after a period of operation. Aiming at this phenomenon, the computational fluid dynamics and discrete phase model (CFD-DPM) is employed to calculate the erosion-wear of the valve in liquid-solid two-phase flow, and study the erosion-wear characteristics of the ball valve during the closing process. In order to better explain the influence of different openings of the ball valve for the erosion-wear characteristics, the relationship between the erosion-wear rate and the resistance coefficient is established. The results show that the erosion-wear of the valve is more serious when it has a greater resistance coefficient under the condition of constant inlet velocity. When the valve is closed from 60% to 20% relative opening, the erosion-wear rate increases slowly with the change of opening. When the valve is closed from 20% to 10% relative opening, the erosion-wear rate increases sharply with the change of opening. In order to reduce the erosion-wear rate of the valve, different structural optimization schemes are proposed to reduce the resistance coefficient of the valve at a small opening. These schemes include changing the flow channel in the valve ball from a circular cross section to a polygonal cross section and changing the seat structure to change the flow direction of the fluid entering the ball. The results show that the scheme of changing the flow direction of the fluid entering the valve ball by changing the valve seat structure works best, and the erosion-wear rate is reduced by 79.7%.

Unsteady aerodynamic force modelling for 3-DoF-galloping of four-bundled conductors

Galloping of overhead transmission lines is characterised by large-amplitude, low-frequency, vertical–horizontal–torsional three degree-of-freedom (DoF) oscillations, which can potentially induce interphase short circuits and fatigue in the conductors and support structures. Numerical analyses are useful for estimating the galloping response of transmission lines, and unsteady aerodynamic forces should be evaluated for accurate simulation. In this study, the unsteady aerodynamic force modelling of four-bundled conductors is investigated based on aerodynamic force measurement test results. Three types of unsteady aerodynamic force measurement tests were performed: under constant torsional angular velocity and under torsional and vertical 1-DoF sinusoidal oscillations. Evaluating the dependence of the aerodynamic forces on the various motions enabled an improved unsteady aerodynamic force model to be developed, considering the effect of angular velocity. First, two-variable aerodynamic coefficients were proposed as a function of the angle of attack and non-dimensional angular velocity. These coefficients were determined via tests performed at constant torsional angular velocities; results with different combinations of wind speed and angular velocity confirmed that the non-dimensional angular velocity can be used to define the unsteady aerodynamic forces. Then, the validity of the two-variable aerodynamic force formulation was confirmed for predicting torsional or vertical 1-DoF oscillations, by comparing the unsteady aerodynamic force obtained via the sinusoidal forced-vibration tests and via the constant angular-velocity tests. Finally, results of the time-history​ analyses using the two-variable aerodynamic coefficients were compared with those of previous wind-response measurement tests to obtain the best unsteady aerodynamic force model for simulating large-amplitude 3-DoF galloping. These results indicate that the unsteady aerodynamic forces for 3-DoF-galloping of four-bundled conductors can be evaluated using the relative angle of attack, the rate of change of the relative angle of attack, and the relative wind speed, using two-variable aerodynamic coefficients measured under constant angular velocity conditions.

Determination of the Minimum Safe Distance between a USV and a Hydro-Engineering Structure in a Restricted Water Region Sounding

Bathymetric surveys performed using small, unmanned vessels are increasingly used in coastal areas and regions difficult to access by hydrographic motorboats. Their geometric dimensions, manoeuvring parameters, low labour intensity, and costs of survey execution have allowed the unmanned survey vessel (USV) to be a commonly recognised surveying platform. It is equipped with a navigation system for positioning, maintaining a course or survey line, determining spatial orientation, and measuring depths. The operation zone of the global navigation satellite system (GNSS) in coastal water regions enables geodetic positioning in land-based surveys and of moving objects, also including, for example, a sounding vessel. Under difficult observational conditions, the positioning is limited by the obscuration of the upper hemisphere, i.e., the visibility of satellites and the reflection from high field buildings. This poses a threat to a small vessel operating at a very short distance from a hydro-engineering structure. Based on a study performed in a marina, the article presents the determination of the minimum safe distance of the planned survey line to the quay in terms of the USV’s dimensions under good sounding conditions. These include low and constant velocity and good observational conditions for a GNSS receiver. The analysis was conducted on survey lines perpendicular to the quay, which was approached twice at distances of 1–5 m, with a 0.5 m interval. A 1 m distance between the end of the survey line and the quay has been determined for the safety of USV’s navigation and continuity of geospatial data collection during bathymetric surveys.

Mitigation of groundwater iron-induced clogging by low-cost bioadsorbent in open loop geothermal heat pump systems

Green energy production from natural resources can reduce emissions of greenhouse gases and pollutants from burning of fossil fuels in power plants. Recently, groundwater geothermal energy (GGE) is harnessed by deploying closed- and open-loop heat systems. In open-loop geothermal heat pump systems (OLGHPS), groundwater is reinjected into aquifer after harnessing GGE. Nevertheless, OLGHPS face noxious clogging issue because of elusive chemistry (corrosion or precipitation) of chemical species, principally of iron (Fe), in pipes and aquifers during reinjection process via oxidation reactions. Plethora of filtering materials are available for removal of ions, but these are quite expensive and environmentally unsafe. More recently, low-cost, eco-friendly, green filtering materials gain much interest. These materials can remove ions from groundwater that can minimize clogging in heat exchange systems, injection wells, and aquifer. In the present study, three filtering materials, i.e., wooden charcoal (biomaterial), yamazuna fine sand, and volcanic ash, were tested to estimate their Fe removal capacity. In upward flow mode with minimum oxygen-water contact, serial column (each with 6 ports) experiments were conducted under constant pressure head and constant velocity conditions. Columns were connected to well water having dissolved Fe concentration of 10.85 mg L−1. Sampling was done at the well, column inlets, column’s six sampling ports and column outlets, and samples were analyzed for Fe by atomic absorption spectroscopy. Related tested parameters include pH, EC, temperature, turbidity, porosity, particle diameter, and dissolved oxygen. Volcanic ash showed less Fe removal, while sand filter showed substantial reduction in velocity. Biomaterial (wooden charcoal) displayed higher Fe adsorption capacity compared to other materials that can be ascribed to its surface chemistry and functional groups. Under different flow rates, maximum Fe content of 3.5 g Fe kg−1 dry charcoal was obtained. By considering a safety factor and influence of groundwater composition, it is possible to design a biomaterial-based iron filter system to minimize Fe-induced chemical clogging in OLGHPS which is an eco-friendly, green energy source.

Freeform surface topography model for ultraprecision turning under the influence of various errors

This work establishes an accurate freeform surface topography model considering geometric errors, tracking errors, and cutting forces. Regarding geometric errors, based on the theory of multibody systems and homogeneous coordinate transformation, the transfer relationship between various geometric errors and the tool error in the workpiece coordinate system is described. Using the continuous acceleration Position-Velocity-Time (PVT) interpolation method, the offset discrete points caused by geometric errors are interpolated and rediscretized, and the accurate mathematical model between the tool errors (position and posture) in the workpiece coordinate system and the topography of the freeform surface is established. Based on the model, the influence of geometric errors on the contour errors of freeform surfaces is accurately calculated, and the contribution and similarity of the effects of various geometric errors on the contour errors of freeform surfaces are analyzed. For dynamic-dependent factors, a second-order system with two degrees of freedom on the X or Z axis is established. According to the simplified result of the equivalent system, the contour error of the freeform surface caused by the tracking error and cutting force is analyzed. For the tracking error, under the condition of constant rotation velocity of the spindle, the change of the slope of the freeform surface along the circumferential direction causes the change in the velocity and acceleration of the motion axis; thus, the corresponding area of the surface has a larger contour error. For cutting force, the change of the slope of the freeform surface along the circumferential direction changes the tool working rake angle, the tool working clearance angle, and the shearing angle, resulting in a change in the cutting force. Moreover, the change of cutting speed is accompanied by the change of cutting force. An experiment verifies the effectiveness of the proposed modeling method. In addition, the modeling method provides an effective solution for the calculation of the contribution rate of different error sources to the contour error of the freeform surface.

Path Tracking Control of Autonomous Vehicle Based on Nonlinear Tire Model

The tire forces of vehicles will fall into the non-linear region under extreme handling conditions, which cause poor path tracking performance. In this paper, a model predictive controller based on a nonlinear tire model is designed. The tire forces are characterized with nonlinear composite functions of the magic formula instead of a simple linear relation model. Taylor expansion is used to linearize the controller, the first-order difference quotient method is used for discretization, and the partial derivative of the composite function is used for matrix transformation. Constant velocity and variable velocity conditions are selected to compare the designed controller with the conventional controller in Carsim/Simulink. The results show that when the tire forces fall in the nonlinear region, two controllers have good stability, and the tracking accuracy of the controller designed in this paper is slightly better. However, after the tire forces become nonlinear, the controller with linear tire force becomes worse, the tracking accuracy is far worse than the controller with the nonlinear tire model, and the vehicle stability is also degraded. In addition, an active steering test platform based on LabVIEW-RT is established, and hardware-in-the-loop tests are carried out. The effectiveness of the designed controller is verified.

Numerical investigation to evaluate the energy effect on the impact resistance of an aircraft carbon fiber-reinforced polymer composite

By analyzing the impact energy effects, impact resistance of CFRP composite plate is investigated using LS DYNA. For accurate simulations, a finite element model is developed and validated through comparison of time-force curves and damage profiles from simulations and experiments. Numerical simulations are performed to find the safe, critically safe, and failure energies for four different conditions: constant velocity, constant mass, constant energy, and different energies. Results show that for constant velocity, constant mass, and different energy conditions, the composite plates fail at 77.492 J, 74.649 J, and 75.990 J, respectively, and no failure was observed for constant energy conditions.

Nanoparticles shape effects on thermal performance of Brinkman-type ferrofluid under heat injection/consumption and thermal radiation: A fractional model with non-singular kernel and non-uniform temperature and velocity conditions

The prime aim of this article is the construction of a fractional model to enhance the heat transfer rate for magnetohydrodynamic (MHD) convectional transport of ferrofluid by applying the time-fractional concept of Caputo-Fabrizio derivative on Brinkman-type fluid model. Kerosene oil and water are considered to serve as carrier fluids for iron oxide (Fe3O4) nanoparticles of various non-spherical shapes (brick, cylinder, platelet, and blade). The non-uniform time-dependent motion of an unbounded upward plate causes to generate the flow of ferrofluid. The supplementary physical phenomena such as ramped heating, thermal radiation, and heat injection/consumption are also analyzed. In addition, the effectiveness of using differently shaped Fe3O4 nanoparticles for heat transfer and ferrofluid flow is evaluated. The exact solutions for non-integer order modeled differential equations are computed by employing the Laplace transform method. The comparative graphical illustrations for ramped and constant (isothermal) velocity and temperature conditions are prepared to scrutinize the impacts of several associated thermal and physical quantities. Besides, the outcomes of numerical simulations of Nusselt number and shear stress are communicated through multiple tables for an in-depth analysis. It is perceived that blade and platelet shaped Fe3O4 nanoparticles are more effective to enhance the thermal efficiency of Brinkman-type ferrofluid in contrast to cylinder and brick shaped nanoparticles. It is interesting to report that an improvement of 13.80% in Nusselt number is observed for water based ferrofluid that significantly advances its thermal properties. The fractional parameter γ produces inverse variations in momentum boundary layer thickness for isothermal and ramped plate cases. Additionally, velocity and temperature curves for ramped plate case are always lower than those of isothermal plate case. This fact highlights the importance of plate ramping in heat and flow control problems.

Modeling and simulation based investigation of unsteady MHD radiative flow of rate type fluid; a comparative fractional analysis

In this work, a generalized unsteady magnetohydrodynamic transport of a rate type fluid near an unbounded upright plate is analyzed under Newtonian heating and non-uniform velocity conditions. The vertical plate is suspended in a porous medium and is encountering the radiation effects. Three different fractional models for Maxwell fluid are established by using the modern definitions of Atangana–Baleanu, Caputo–Fabrizio, and Caputo fractional operators. Triple fractional analysis is conducted to reach out to the solutions of consequent flow and energy equations. Laplace transform and Stehfest’s numerical algorithm are jointly applied to solve each fractional model. Shear stress and heat transfer rate are measured at the solid–fluid interface in the form of skin friction coefficient and Nusselt number respectively. The physical significance of associated parameters in velocity and energy boundary layers is investigated and graphs are provided to discuss the relevant physical arguments. A tabular analysis is performed to demonstrate the influence of physical parameters on shear stress and heat transfer rate. An empirical comparison between fractional and classical solutions indicates that fractional operators provide a better explanation of the physical features of the model. It is also analyzed that for Newtonian heating and non-uniform velocity conditions, the Atangana–Baleanu fractional operator is the finest fractional model to describe the memory effect of velocity and energy distribution. The velocity of a Maxwell fluid is always higher for constant velocity condition as compared to the ramped velocity condition. Furthermore, the heat transfer rate declines for increasing values of the fractional parameter α and a minimum value is witnessed for the classical model but, it follows an inverse trend when the radiation parameter Rd increases.

Estimation of watershed width function: a statistical approach using LiDAR data

Terrain variability and channel network characteristics critically influence the hydrologic response of watersheds. Width function represents this response under idealized flow conditions of constant velocity and absence of losses, and can be estimated solely using the terrain data. However, the width function, in its graphical form, is less tractable for further analytical applications such as in the derivation of link-based geomorphological instantaneous unit hydrograph. In this study, we systematically redress these issues in the following manner: (a) develop a framework for the functional estimation of width functions using a mixture of truncated skew-normal distributions that captures a wide variety of distribution shapes, (b) provide a basis for model selection based on the Bayesian Information Criterion, (c) demonstrate the utility of a functional estimation approach by identifying hydrologically similar watersheds based on divergence measures applied to the width function estimates, and (d) illustrate the utility of efficient statistical estimation of geomorphic functions and metrics, which affords data reduction and can be scaled to very-large terrain datasets.

Effect of Friction Velocity on Tribological Behavior of Coumarin as Mineral Oil Additive

Abstract The tribological behavior of lubricants, prepared with a mineral base oil, lauryl alcohol, and different concentrations of coumarin, was examined using a four-ball tester under constant and variable friction velocity conditions. At constant friction velocity, the maximum non-seizure load (PB) increased from 304 N to 392 N at a coumarin concentration of 0.5 wt%. Lubricants with 0.7 wt% coumarin exhibited optimum lubricating properties, and the maximum reductions in friction coefficient (FC) and wear scar diameter (WSD) were 20.0% and 11.88%, respectively. Further investigation of the tribological mechanism implied that the ester group in the coumarin molecule established a connection with the surface atom, resulting in the formation of a tribofilm, which further restricted the adhesion wear regime. Additionally, under variable friction velocity conditions, increasing the coumarin concentration had an obvious effect on the mixed lubrication (ML) and elasto-hydrodynamic lubrication (EHL) regions but not on other lubrication regions. Moreover, a mathematical model was proposed to show the relationship between FC and friction velocity. Importantly, the present work clarifies the effect of friction velocity on the tribological behavior of coumarin and also supports the use of coumarin as a novel additive in mineral oils.

Numerical Study on the Characteristics of Boger Type Viscoelastic Fluid Flow in a Micro Cross-Slot under Sinusoidal Stimulation.

The cross-slot geometry plays an important role in the study of nonlinear effects of viscoelastic fluids. The flow of viscoelastic fluid in a micro cross-slot with a high channel aspect ratio (AR, the ratio of channel depth to width) can be divided into three types, which are symmetric flow, steady-state asymmetric flow and time-dependent flow under the inlet condition with a constant velocity. However, the flow pattern of a viscoelastic fluid in the cross-slot when a stimulation is applied at inlets has been rarely reported. In this paper, the response of cross-slot flow under an external sinusoidal stimulation is studied by numerical simulations of a two-dimensional model representing the geometry with a maximum limit of AR. For the cases under constant inlet velocity conditions, three different flow patterns occur successively with the increase of Weissenberg number (Wi). For the cases under sinusoidal varying inlet velocity conditions, when the stimulation frequency is far away from the natural frequency of a viscoelastic fluid, the frequency spectrum of velocity fluctuation field shows the characteristics of a fundamental frequency and several harmonics. However, the harmonic frequency disappears when the stimulation frequency is close to the natural frequency of the viscoelastic fluid. Besides, the flow pattern shows spatial symmetry and changes with time. In conclusion, the external stimulation has an effect on the flow pattern of viscoelastic fluid in the 2D micro cross-slot channel, and a resonance occurs when the stimulation frequency is close to the natural frequency of the fluid.

Model analysis, design and experiment of a fan-wing underwater vehicle

Abstract In order to achieve 5 degrees of freedom (DOFs) movement in an underwater space with only two moving parts, a new kind of unmanned underwater vehicle, Fan-wing Underwater Vehicle (FUV), is proposed. The FUV is driven by two fan-wings which are adapted from the fan-wings for aircraft. The features of the underwater fan-wing are analyzed by 2D computational fluid dynamic (CFD) simulations. In order to analyze the movement of the FUV, a 6-DOF hydrodynamics mathematical model is built. The model is simplified for analyzing two kinds of common conditions movements. According to the simplified model of the ideal straight-line depth-keeping cruise with constant velocity condition, a general procedure to design the FUV is put forward. Some 3D CFD simulations are added to solve the mathematical model in the procedure of the FUV design. Then, according to the design procedure, a control system and a mechanical structure of the FUV are designed. Finally, a real FUV is manufactured, and an underwater test is completed. The experiment shows that the real FUV can achieve 5 DOFs movement in an underwater space, and the results match the design proposes.

Standard penetration testing in a virtual calibration chamber

The virtual calibration chamber technique, based on the discrete element method, is here applied to study the standard penetration test (SPT). A macro-element approach is used to represent a rod driven with an impact like those applied to perform SPT. The rod is driven into a chamber filled with a scaled discrete analogue of a quartz sand. The contact properties of the discrete analogue are calibrated simulating two low-pressure triaxial tests. The rod is driven changing input energy and controlling initial density and confinement stress. Energy-based blowcount normalization is shown to be effective. Results obtained are in good quantitative agreement with well-accepted experimentally-based relations between blowcount, density and overburden. It is also shown that the tip resistance measured under impact dynamic penetration conditions is close to that under constant velocity conditions, hence supporting recent proposals to relate CPT and SPT results.