Surface Quantities Research Articles

Computational analysis of the flow field structure of a non-reacting hypersonic flow over forward-facing steps

AbstractThis work is a computational study of a rarefied non-reacting hypersonic flow past a forward-facing step at zero-degree angle of attack in thermal non-equilibrium. Effects on the flow field structure and on the aerodynamic surface quantities due to changes in step frontal-face height are investigated by employing the direct simulation Monte Carlo method. The work focuses the attention of designers of hypersonic configurations on the fundamental parameter of surface discontinuity, which can have an important impact on even initial design. The results presented highlight the sensitivity of the primary flow field properties, velocity, density, pressure and temperature, to changes in the step frontal-face height. In addition, the behaviour of heat transfer, pressure and skin friction coefficients with variation of the step frontal-face height is detailed. The analysis shows that hypersonic flow past a forward-facing step in the transition flow regime is characterized by a strong compression ahead of the frontal face, which influences the aerodynamic surface properties upstream and adjacent to the frontal face. The analysis also shows that the extension of the upstream disturbance depends on the step frontal-face height. It was found that the recirculation region ahead of the step is also a function of the frontal-face height. A sequence of Moffatt eddies of decreasing size and intensity is observed in the concave step corner. Locally high heating and pressure loads were observed at three locations along the surface, i.e. on the lower surface, on the frontal face and on the upper surface. The results showed that both loads rely on the frontal-face height. The peak values for the heat transfer coefficient on the frontal-face surface were at least one order of magnitude larger than the maximum value observed for a smooth surface, i.e. a flat plate without a step. A comparison of the present simulation results with numerical and experimental data showed close agreement concerning the wall pressure acting on the step surface.

Looking at the earth as a planet: Passive microwave remote sensing of land surfaces

Multi-frequency microwave radiometry from satellites is an excellent tool for providing continuous monitoring of land surfaces, which is crucial in making long-term decisions about land management in terms of water resources, agriculture, forestry, energy, tourism, transportation, etc., as well as in rapid detection of natural and man-made disasters. Microwave radiometers are highly sensitive, stable receivers that measure the thermal emission from observed surfaces. One of the greatest challenges of remote sensing involves inverting the measurements and retrieving the quantities of interest from the observed data. After a short description of the principles of microwave radiometry, the observation instruments, and the techniques, this paper addresses the issue of retrieving the significant quantities of land surfaces, which affect the water cycle and are important indicators of climate change.

Control of flow around a circular cylinder for minimizing energy dissipation.

Control of flow around a circular cylinder is studied numerically aiming at minimization of the energy dissipation. First, we derive a mathematical relationship (i.e., identity) between the energy dissipation in an infinitely large volume and the surface quantities, so that the cost function can be expressed by the surface quantities only. Subsequently a control law to minimize the energy dissipation is derived by using the suboptimal control procedure [J. Fluid Mech. 401, 123 (1999)JFLSA70022-112010.1017/S002211209900659X]. The performance of the present suboptimal control law is evaluated by a parametric study by varying the value of the arbitrary parameter contained. Two Reynolds numbers, Re=100 and 1000, are investigated by two-dimensional simulations. Although no improvement is obtained at Re=100, the present suboptimal control shows better results at Re=1000 than the suboptimal controls previously proposed. With the present suboptimal control, the dissipation and the drag are reduced by 58% and 44% as compared to the uncontrolled case, respectively. The suction around the front stagnation point and the blowing in the rear half are found to be weakened as compared to those in the previous suboptimal control targeting at pressure drag reduction. A predetermined control based on the control input profile obtained by the suboptimal control is also performed. The energy dissipation and the drag are found to be reduced as much as those in the present suboptimal control. It is also found that the present suboptimal and predetermined controls have better energy efficiencies than the suboptimal control previously proposed. Investigation at different control amplitudes reveals an advantage of the present control at higher amplitude. Toward its practical implementation, a localized version of the predetermined control is also examined, and it is found to work as effectively as the continuous case. Finally, the present predetermined control is confirmed to work well in a three-dimensional flow too.

FULLY NONLINEAR AND DISPERSIVE MODELING OF SURF ZONE WAVES: NON-BREAKING TESTS

With the objective of modeling coastal wave dynamics taking into account nonlinear and dispersive effects, an accurate nonlinear potential flow model is studied. The model is based on the time evolution of two surface quantities: the free surface position and the free surface velocity potential (Zakharov, 1968). The spectral approach of Tian and Sato (2008) is used to resolve vertically the velocity potential in the whole domain, by decomposing the potential using the orthogonal basis of Chebyshev polynomials. The model mathematical theory and numerical development are described, and the model is then validated with the application of three 1DH test cases: (1) propagation of nonlinear regular wave over a submerged bar, (2) propagation of nonlinear irregular waves over a barred beach, and (3) wave generation and propagation after an abrupt deformation of the bottom boundary. These three test cases results agree well with the reference solutions, confirming the model's ability to simulate accurately nonlinear and dispersive waves.

Quantifying Water Pollution Sources in a Small Tile‐drained Agricultural Watershed

AbstractThis paper evaluates the quantity and quality dynamics of surface and drainage waters in a small, 7.1 km2 agricultural watershed, located in the crystalline complex of the Czech Republic. Concentrations and monthly solute loads of amonium nitrogen (NH4‐N), nitrate nitrogen (NO3‐N), phosphate phosphorus (PO4‐P) and total phosphorus (Ptot) from ten watershed's subcatchments with different soil, land use and tile drainage characteristics were compared for the period March–October from 2009 to 2011. The results and relevant processes were described using regular monitoring as well as event‐based sampling approaches, methods of runoff separation and regression techniques. The average baseflow comprised 35–50%, whereas interflow and overland flow were 50–65% of the total runoff. The highest concentrations of NO3‐N were detected in waters originating from cultivated and tiled subcatchments; those of NH4‐N, PO4‐P and Ptot came from subcatchments containing settlements and water ponds. In the monitored sites within the watershed, non‐point pollution sources produced on average 23% of NH4‐N, approximately 45% of NO3‐N, 24% of PO4‐P and about 26% of Ptot of total monthly solute loads. The differences in the share of monitored subcatchments in the total load from non‐point pollution sources varied from month to month and were caused mainly by miscellaneous hydrological conditions and natural as well as man‐altered runoff characteristics. The obtained results confirmed that used methods count for a useful approach for discerning water pollution sources and their dynamics in small, tile drained watersheds.

A unified generic theory on discontinuity factors in diffusion, SP3 and transport calculations

A theory is presented that unifies the calculation of discontinuity factors in diffusion, SP3 and transport calculations. The idea of Even Parity Discontinuity Factor (EPDF) was recently introduced for transport calculation using homogenized pin cells. In this paper a rigorous method is worked out to numerically calculate and implement the angular dependent EPDF while using angular flux without parity decomposition. This is made possible by converting EPDF forth and back to an equivalent Angular Flux Discontinuity Factor (AFDF) during the transport calculation. In order to save the required data storage to make the method practical, the angular independent EPDF is also introduced that can still preserve the cell reaction rate but greatly simplifies the calculation. The angular independent EPDF can be uniquely determined by using only the reference value of the cell surface net current without the need of knowing the reference value of the surface flux. The EPDF so determined is called the Prime EPDF. The EPDF can be renormalized by demanding a certain surface quantity to match its reference value after EPDF application. If the EPDF is generated with a single assembly model, the Prime EPDF and the Renormalized EPDF will have identical effect on the cell interface boundary conditions except for that on the assembly boundary surface when the assembly is placed in a core model. The EPDF theory suggests that the normalization target should be the sum of the incoming and outgoing partial currents on each surface.This angular independent EPDF theory can be easily applied to SP3 and diffusion calculation as special cases. Here the EPDF can be applied directly without the need of the supporting AFDF. Both the Prime EPDF and the Renormalized EPDF options apply to these special cases. For SP3 calculation the theory shows that both the zeroth order and the second order flux moments in SP3 should share the same EPDF, thus removing the fundamental ambiguity of how to define and calculate the SP3 discontinuity factors. For diffusion calculation the theory gives an EPDF defined differently from the conventionally adopted discontinuity factor.The theory has been tested to work well on a series of mini-core benchmark problems with severe heterogeneity. The tests are made for the Method of Characteristics (MOC) transport calculation, the SP3 calculation and the diffusion calculation. Both pin-cell homogenization and assembly homogenization cases are covered in the tests. Comparison is made on the results using the Prime EPDF, the Renormalized EPDF, the conventional discontinuity factor and the SPH (super homogenization) factor. Generally speaking, for cases with homogenized pin cells the Prime EPDF gives the best accuracy while for cases with homogenized assemblies the Renormalized EPDF gives the best accuracy.

Study on Geometrical and Working Properties of the Parabolic Moldboard

Three forms of model parabolic bulldozing plate were designed and manufactured. Their macroscopic soil-engaging surface directrixes consist of parabolic curve and the cutting angle were 50°, 55°and 60°respectively. The working resistance was measured by a homemade indoor soil bin. The parabolic moldboard model with a cutting angle of 55° has the least working resistance. On this basis, the parametric equations of three kinds of macroscopic soil-engaging surface of parabolic type moldboard were established. The intrinsic geometrical quantities of the macroscopic soil-engaging surfaces, including the first base quantity (E, F, & G) and the second base quantity (L, M, & N), were calculated. Compared with the working resistance test results of the three moldboard models, it is found that there is a specific range of E value in first base quantities and L value in second base quantities which can make the soil-engaging surface to obtain lower resistance. This research provides a reference for the resistance-reducing and energy-saving design of macroscopic soil-engaging surface of moldboard.

Upper washita river experimental watersheds: reservoir, groundwater, and stream flow data.

Surface and groundwater quantity and quality data are essential in many hydrologic applications and to the development of hydrologic and water quality simulation models. We describe the hydrologic data available in the Little Washita River Experimental Watershed (LWREW) of the Southern Great Plains Research Watershed (SGPRW) and Fort Cobb Reservoir Experimental Watershed (FCREW), both located in southwest Oklahoma. Specifically, we describe the flood retarding structures and corresponding stage, discharge, seepage, and consumptive use data (), stream gauges, and groundwater wells and their corresponding stream flow (; LWREW ARS 522-526 stream gauges) and groundwater level data (SGPRW groundwater levels data; LWREW groundwater data; ; ), respectively. Data collection is a collaborative effort between federal and state agencies. Stage, discharge, seepage, and consumptive use data for the Fort Cobb Reservoir are available from the Bureau of Reclamation and cover a period of 1959 to present. There are 15 stream gauges in the LWREW and six in the FCREW with varying data records. There were 479 observation wells with data in the SGPRW and 80 in the LWREW, with the latest records collected in 1992. In addition, groundwater level data are available from five real-time monitoring wells and 34 historical wells within the FCREW. These data sets have been used for several research applications. Plans for detailed groundwater data collection are underway to calibrate and validate the linked Soil and Water Assessment Tool (SWAT)-MODFLOW model. Also, plans are underway to conduct reservoir bathymetric surveys to determine the current reservoir capacity as affected by land use/land cover and overland and stream channel soil erosion.

Hyperexponential and nonmonotonic retention of polyvinylpyrrolidone-coated silver nanoparticles in an Ultisol

The increasing application of engineered nanoparticles (ENPs) has heightened the concern that these ENPs would eventually be released to the environment and may enter into life cycle of living beings. In this regard, it is essential to understand how these ENPs transport and retain in natural soils because they are considered to be a major repository for ENPs. Herein, transport and retention of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (PVP-AgNPs) were investigated over a wide range of physicochemical factors in water-saturated columns packed with an Ultisol rich in clay-size particles. Higher mobility of PVP-AgNPs occurred at larger soil grain size, lower solution ionic strength and divalent cation concentration, higher flow rate, and greater PVP concentrations. Most breakthrough curves (BTCs) for PVP-AgNPs exhibited significant amounts of retardation in the soil due to its large surface area and quantity of retention sites. In contrast to colloid filtration theory, the shapes of retention profiles (RPs) for PVP-AgNPs were either hyperexponential or nonmonotonic (a peak in particle retention down-gradient from the column inlet). The BTCs and hyperexponential RPs were successfully described using a 1-species model that considered time- and depth-dependent retention. Conversely, a 2-species model that included reversibility of retained PVP-AgNPs had to be employed to better simulate the BTCs and nonmonotonic RPs. As the retained concentration of species 1 approached the maximum solid-phase concentration, a second mobile species (species 2, i.e., the same PVP-AgNPs that are reversibly retained) was released that could be retained at a different rate than species 1 and thus yielded the nonmonotonic RPs. Some retained PVP-AgNPs were likely to irreversibly deposit in the primary minimum associated with microscopic chemical heterogeneity (favorable sites). Transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis suggested that these favorable sites were positively charged sites on montmorillonite edges and goethite surfaces in the soil. Overall, our study highlights that the transport and especially retention of PVP-AgNPs are highly sensitive to the physicochemical factors, but mathematical modeling can accurately predict the fate of these ENPs in porous media which is important for better understanding the fate of these ENPs in point of exit and in the environment.

HYDROCHEMICAL STUDIES FOR SUSTAINABLE WATER RESOURCES OF SEMI- ARID CLIMATIC REGION DODBALLAPUR TALUK,BANGALORE URBAN DISTRICT, KARNATAKA STATE (SOUTH INDIA)

The 21 st century has been declared the century of water, and we have every responsibility to find proper solutions to water crisis witnessed all over the world. A large part of the world’s population especially people living in the developing countries is experiencing water stress resulting in water shortages and pollution. In many areas, water supplies for industrial, domestic and agricultural needs are dependent on groundwater. More than 85% of the rural water supply is being provided through groundwater. It is observed that areas experiencing declining water levels are also facing the problems of increase in the concentration of solutes, which may result in the deterioration of groundwater quality. In view of this, two sub-watersheds located in semi-arid region (water stressed region) in Southern India Karnataka State, Bangalore rural district, Dodballapur Taluk are taken up for intensive studies, broadly covering hydrologic, soils, water(surface and sub-surface) quantity and quality, water requirement of crops and the like.

Correlating computationally derived particle surface stress-strain states to mesoscale shock response

The results of FE simulations are presented, correlating the continuum and mesoscale shock response of a particulate system with particle surface stresses-strains. The objective of this work is to gain insight into how the complex responses at the meso/sub-mesoscale manifest to quantities that could be experimentally measured without perturbing the material, informing the design of possible mesoscale diagnostics. Three simulation setups were analyzed. First, the normal plate impact of monolithic silica quartz for continuum comparison purposes. Second, the normal plate impact of a 2D representative volume element (RVE) of randomly packed disks. Third, the normal plate impact of a 3D RVE of randomly packed spheres. In each of the RVEs a small coupon corresponding to an assumed mesoscale "sensor" was attached to the surface of a particle in the center of the RVE. Stress quantities from the sensor and existing continuum diagnostics were analyzed. The mesoscale quantities are highly heterogeneous and differ significantly from the continuum quantities. Difficulties regarding correlation of surface quantities to the average particle and system response are also discussed.

Scale criticality in estimating ecosystem carbon dynamics

Scaling is central to ecology and Earth system sciences. However, the importance of scale (i.e. resolution and extent) for understanding carbon dynamics across scales is poorly understood and quantified. We simulated carbon dynamics under a wide range of combinations of resolution (nine spatial resolutions of 250 m, 500 m, 1 km, 2 km, 5 km, 10 km, 20 km, 50 km, and 100 km) and extent (57 geospatial extents ranging from 108 to 1 247 034 km(2) ) in the southeastern United States to explore the existence of scale dependence of the simulated regional carbon balance. Results clearly show the existence of a critical threshold resolution for estimating carbon sequestration within a given extent and an error limit. Furthermore, an invariant power law scaling relationship was found between the critical resolution and the spatial extent as the critical resolution is proportional to A(n) (n is a constant, and A is the extent). Scale criticality and the power law relationship might be driven by the power law probability distributions of land surface and ecological quantities including disturbances at landscape to regional scales. The current overwhelming practices without considering scale criticality might have largely contributed to difficulties in balancing carbon budgets at regional and global scales.

Focused Ion Beam Fabrication and Atomic Force Microscopy Characterization of Micro/Nanoroughness Artifacts With Specified Statistic Quantities

Series of roughness patterns with predetermined statistic quantities, such as standard deviation of surface heights, autocorrelation length, and height distribution were fabricated by focused ion beam (FIB) lithography and characterized by atomic force microscopy (AFM). Template-matching analysis and comparisons of surface parameters were performed to ascertain the fabrication and measurement qualities. Results show that the root-mean-square (rms) residuals are approximately 4.8, 5.2, and 15.7 nm for the fabricated Gaussian, negatively skewed, and positively skewed surfaces with the dimension of 5120 nm × 5120 nm × 121 nm. For the surfaces with the same skewness but different autocorrelation lengths, the rms residuals have no significant differences. The surface parameters of the fabricated artifacts are in close agreements with their expected values. To further elucidate the geometric interactions between the tip and roughness structure in AFM measurements, blind tip estimations were carried out on the scanned images. The tip estimation deviation increases with the increase of autocorrelation length for the Gaussian surfaces. The skewed structures help to improve the estimation accuracy. By a proper design of the surface quantities, the artifacts can serve as reference areal roughness standards at the nanoscale and a kind of tip characterizers.

Rigidity of polyhedral surfaces, I

We study the rigidity of polyhedral surfaces and the moduli space of polyhedral surfaces using variational principles. Curvature-like quantities for polyhedral surfaces are introduced and are shown to determine the polyhedral metric up to isometry. The action functionals in the variational approaches are derived from the cosine law. They can be considered as 2-dimensional counterparts of the Schlaefli formula.

On surface elasticity theory for plane interfaces

A closed system of surface elasticity equations was derived in terms of surface quantities defined as integrals of respective excess bulk quantities normal to the interface. The equations were consistently linearized for the case of small strains. It is shown that these equations are more general than the Shuttleworth equations. Equations of this type were also derived for the particular case of an interface formed by a thin layer with constant properties. The derived equations were used to consider bending of a plate under pressure applied to both sides.

Surface critical exponents at a discontinuous bulk transition

Systems with a bulk first-order transition can display diverging correlation lengths close to a surface. This surface induced disordering yields a special type of surface criticality. Using extensive numerical simulations we study surface quantities in the two-dimensional Potts model with a large number of states $q$ which undergoes a discontinuous bulk transition. The surface critical exponents are thereby found to depend on the value of $q$, which is in contrast to prior claims that these exponents should be universal and independent of $q$. It follows that surface-induced disordering at first-order transitions is characterized by exponents that depend on the details of the model.

High density polyethylene and silane treated silicon nitride nanocomposites using high-density polyethylene functionalized with maleate ester: Mechanical, tribological and thermal properties

In this study, attempt has been made to improve the overall performance of high-density polyethylene (HDPE) composites by blending with silane treated silicon nitride (SN) using HDPE grafted dibutyl maleate as compatibilizer. A small quantity of surface modified nanoclay has also been added in order to improve the mechanical properties. The mechanical properties show that both silane modification of silicon nitride accompanied by nanoclay addition has led to the substantial enhancement in mechanical properties. In addition, compatibilization has further improved the mechanical properties showing 10% (w/w of silicon nitride) as optimal compatibilizer content. The wear results showed that, as SN content increased, the slide wear loss decreased. Addition of SN along with compatibilizer also improved the thermal stability of the nanocomposites.

Morphology and Mechanical Properties of PP/LLDPE Blends and Ternary PP/LLDPE/Nano-CaCO3 Composites

Mechanical and morphological properties of polypropylene (PP)/linear low density polyethylene (LLDPE)/ nano-sized calcium carbonate ternary composites were prepared using a twin-screw extruder. Modification of the filler nano-particle surface was pretreated with stearic acid and of the PP/LLDPE interface by melting high crystallizable, high density polyethylene. In this research, effects of modified linear low density polyethylene (LD) and nano-CaCO3 weight percentage on tensile strength, Young’s modulus and impact absorbed energy of composites were investigated. In addition, effect of the interaction between filler particles and polymer matrix was studied. Effect of quantity of microcracks on tensile properties of the composites was also discussed. Effect of nano-CaCO3 and LD on the quantity of microcracks and impact-fractured surface of PP composites was studied by scanning electron microscope (SEM). The impact-fractured surface morphologies were characterized by SEM to clarify the possible mechanisms for improving the fracture resistance.

Heterogeneous nucleation in multi-component vapor on a partially wettable charged conducting particle. I. Formulation of general equations: Electrical surface and line excess quantities

Thermodynamics is applied to formulate general equations for internal energies and grand potential for a system consisting of a dielectric liquid nucleus of a new phase on a charged insoluble conducting sphere within a uniform macroscopic one- or multicomponent mother phase. The currently available model for ion-induced nucleation assumes complete spherical symmetry of the system, implying that the seed ion is immediately surrounded by the condensing liquid from all sides. We take a step further and treat more realistic geometries, where a cap-shaped liquid cluster forms on the surface of the seed particle. To take into account spontaneous polarization of surface layer molecules we introduce the electrical surface and line excess quantities.

Formal conserved quantities for isothermic surfaces

Isothermic surfaces in \(S^n\) are characterised by the existence of a pencil \(\nabla ^t\) of flat connections. Such a surface is special of type \(d\) if there is a family \(p(t)\) of \(\nabla ^t\)-parallel sections whose dependence on the spectral parameter \(t\) is polynomial of degree \(d\). We prove that any isothermic surface admits a family of \(\nabla ^t\)-parallel sections which is a formal Laurent series in \(t\). As an application, we give conformally invariant conditions for an isothermic surface in \(S^3\) to be special.