Slope Roughness Research Articles

MEASUREMENT OF SURFACE ROUGHNESS IN DESERT TERRAIN BY CLOSE RANGE PHOTOGRAMMETRY

As part of the measurements of desert terrain characteristics in the United Arab Emirates, made in support of a study of airborne radar, close range vertical stereophotographs of various natural surfaces were taken with a pair of Hasselblad MK70 metric cameras. The technique is described and the constraints imposed by the ground conditions and the need for rapid measurements are explained. Various terrain types are illustrated and the method is described whereby variables summarising surface roughness and surface slope were generated from profiles of the microrelief. From a more general discussion of current equipment and geomorphological applications of close range photogrammetry, it is concluded that this flexible technique is presently under utilised by field scientists.

A Study of the Effect of Lubricants on the Adherence of Molten Glass to Heated Metals

An improved kinetic test was devised by which the adherence of molten glass to metal may be evaluated. The results were expressed as the highest metal temperature at which the molten glass beads do not adhere. The variables of the test investigated were temperature of molten bead, height of fall of the molten bead, and slope and surface roughness of metal sample. The cumulative effect of the variables on the precision of measurement of the adherence temperature was found to be ±33° F. Several types of glass mold lubricants were investigated as to their effects on the adherence temperature and as to their persistence on heated metal surfaces. Several silicone lubricants were found to have high critical adherence temperatures while the graphitized oil base lubricant gave the best persistence.

Manifestation of the roughness-square-gradient scattering in surface-corrugated waveguides

We study a new mechanism of wave/electron scattering in multi-mode surface-corrugated waveguides/wires. This mechanism is due to specific square-gradient terms in an effective Hamiltonian describing the surface scattering, that were neglected in all previous studies. With a careful analysis of the role of roughness slopes in a surface profile, we show that these terms strongly contribute to the expression for the inverse attenuation length (mean free path), provided the correlation length of corrugations is relatively small. The analytical results are illustrated by numerical data.

Effective thermal conductivity of rough spherical packed beds

A new model is developed for predicting the effective thermal conductivity of regularly packed beds of rough, uniformly sized spheres immersed in a stagnant gas. Contact mechanics and thermal analyses are performed and the results are presented in the form of compact relationships. The present model accounts for the thermophysical properties of spheres and the gas, load, the rarefaction effects of the interstitial gas, gas temperature and pressure, and spheres diameter, roughness and asperities slope. The present model is compared with experimental data with the sphere diameter of 19.05, 25, and 50.4 mm and good agreement is observed.

Stochastic generation of geomorphological instantaneous unit hydrograph‐based flow hydrograph

The geomorphological instantaneous unit hydrograph (GIUH) can be represented as a sum of weighted probability density functions of the rainwater travel times for all plausible flow paths within a watershed. Using the kinematic‐wave routing procedure, the rainwater travel time for each overland or channel component is a function of the random channel length, slope and surface roughness coefficient due to their spatial variability. However, limited samples for random slope and surface roughness result in sampling errors which render the determination of statistical moments of component travel times as being uncertain. Hence, the resulting kinematic‐wave based GIUH (KW‐GIUH) is inevitably subject to uncertainty, which will be further transmitted to the design flow hydrograph. This paper develops a methodological framework to assess the uncertainty features of GIUH‐based flow hydrograph which, in turn, could be incorporated into constrained Gaussian simulation algorithm to generate randomly plausible design flow hydrographs.

Surface runoff and seed trapping efficiency of shrubs in a regenerating semiarid woodland in northern Ethiopia

In forest restoration areas in northern Ethiopia, natural regeneration of Olea europaea ssp. cuspidata only occurs under pioneer shrubs. To assess the impact of erosion on the spatial distribution of Olea recruits, secondary dispersal of olive seeds by surface runoff was determined in and near the micro-environment of two important pioneers ( Acacia etbaica and Euclea racemosa). We hypothesized that (1) Olea seeds deposited under the protective crowns of shrubs are less likely to be lost by surface wash than seeds in the bare inter-plant areas and (2) that seeds in the latter are more prone to be translocated by runoff to microsites under shrubs than to open areas. Runoff experiments were conducted in August–September 2003 in ten 3 × 3 m 2 plots laid out around isolated shrubs in two sites. Twenty-eight marked tracer seeds were dropped at the upper end of each plot at 0.10 m intervals. Ten seeds marked in another way were deposited under the crown in each plot simulating seed dispersal by birds. The seeds were collected after the rainy season and their positions recorded. In a third experiment, mulch under shrubs was removed and ten marked seeds were deposited under each crown. Rainfall simulation experiments were conducted with a maximum intensity of 120 mm h − 1 for a 10 min duration. For all experiments, seed movement was analyzed in relation to slope and shrub variables. Seed movement was limited in one site, where only 21% of the seeds were translocated. Movement was significantly higher in the other site (61%) although it had a lower slope gradient. The number of seeds moved by surface runoff was not significantly related to shrub species, slope gradient or slope roughness. There was a strong linear relationship between the distance parallel to the contour from the shrub center to the seed and the extent of the downhill translocation. No seeds moved to a position under a shrub crown and no shrub lost a seed deposited under its crown. Simulated rainfall after mulch removal resulted in a seed loss of nearly 33%. Micro-topographic structures under shrubs, especially under E. racemosa, cause some soil and sediment retention, but more importantly divert runoff water and concentrate flows to rills alongside shrubs. From an eco-geomorphological point of view, shrubs show poor seed trapping efficiency contradictory to expectation. Seeds in sediment flows are deposited in the bare inter-plant areas. However, seeds under shrubs are not likely to be lost by surface wash. Surface runoff has little effect on the general pattern of the primary seed rain. Since Olea recruits were exclusively found under shrubs and not in the spaces between shrubs in the studied field sites, it appears plausible that seeds deposited in the open field are almost without doubt lost to post-dispersal seed predation, unsuccessful germination or seedling predation and mortality. Recovery of O. europaea in degraded shrubland communities therefore depends upon directed dispersal of seeds under shrubs by frugivorous birds.

An experimental investigation of thermal contact conductance of stainless steel at low temperatures

An investigation is carried out to study the effects of surface topography and interfacial temperature on the thermal contact conductance of the pressed stainless steel 304 contacts in the range 125–210 K and 1–7 MPa. The surface roughness of test specimens is between 1.5 μm and 17.6 μm. A theoretical model is used to predict the results and gives a reasonable agreement. The combined effect of phonon conductivity and electronic conductivity to thermal conductivity at low temperatures is described using a proposed correlation. The small contact conductance at low temperatures can ascribe to the decreased thermal conductivity and the increased hardness. It is demonstrated that rms roughness and mean absolute slope are both needed for evaluating contact heat transfer.

Bagnold Scaling, Density Plateau, and Kinetic Theory Analysis of Dense Granular Flow

We investigate the bulk rheology of dense granular flow down a rough slope, where the density profile has been found to show a plateau except for the boundary layers in simulations [Silbert et al., Phys. Rev. E 64, 051302 (2001)]. It is demonstrated that both the Bagnold scaling and the framework of kinetic theory are applicable in the bulk, which allows us to extract the constitutive relations from simulation data. The detailed comparison of our data with the kinetic theory shows quantitative agreement for the normal and shear stresses, but there exists a slight discrepancy in the energy dissipation, which causes a rather large disagreement in the kinetic theory analysis of the flow.

Effect of local slopes of roughness during contact between solids

In this work we propose to deal with the study of static sealing. The latter is modelled in a microscopic scale with finite elements method. The numerical simulations are related to the contact between conical asperities of a rough surface and a smooth rigid plan. It thus makes it possible to observe the local behaviours of the asperities during their crushing and to draw conclusions on the influence of various parameters such as the attack angle. If it is possible to deal with only a few asperities, the finite elements method does not allow us to succeed a full three-dimensional study. We thus propose in this work a simplified approach to solve this contact problem and to perform its generalisation to a random morphology. This useful method considers the contact between the real surface, which roughness is modelled as a distribution of indenters with various attack angles, and a smooth rigid plan.

Fire and the evolution of steep, soil-mantled landscapes

Recent burns in the western United States attest to the signif- icant geomorphic impact of fire in mountainous landscapes, yet we lack the ability to predict and interpret fire-related erosion over millennial time scales. A diverse set of geomorphic processes is often invoked following fire; the magnitude of postfire erosional processes coupled with temporal variations in fire frequency dic- tate the extent to which fires affect sediment production and land- scape evolution. In the Oregon Coast Range, several models for long-term rates of soil production and transport have been tested and calibrated, although treatment of fire-related processes has been limited. Following recent fires in the Oregon Coast Range, we observed extensive colluvial transport via dry ravel, localized bed- rock emergence due to excess transport, and talus-like accumula- tion in adjacent low-order valleys. Soils exhibited extreme but dis- continuous hydrophobicity, and no evidence for rilling or gullying was observed. Using a field-based data set for fire-induced dry rav- el transport, we calibrated a physically based transport model that indicates that soil flux varies nonlinearly with gradient. The post- fire critical gradient (1.03), which governs the slope at which flux increases rapidly, is lower than the previously estimated long-term value (1.27), reflecting the reduction of slope roughness from in- cineration of vegetation. By using a high-resolution topographic data set generated via airborne-laser swath mapping, we modeled the spatial pattern of postfire and long-term erosion rates. Postfire erosion rates exceed long-term rates (which average 0.1 mm·yr 21 ) by a factor of six, and subtle topographic variations generated local patches of rapid postfire erosion, commonly.1 mm·yr 21 . Our sim- ulations indicate that fire-related processes may account for ;50% of temporally averaged sediment production on steep hillslopes. Our analysis provides a mechanistic explanation for the coincident early Holocene timing of increased fire frequency and regional ag- gradation in Oregon Coast Range drainage basins. Given the sen- sitivity of steep hillslopes to fire-driven transport, changes in cli- mate and fire frequency may affect soil resources by perturbing the balance between soil transport and production.

Seafloor geomorphology of convergent margins: Implications for Cascadia seismic hazard

We compare the geomorphology of several convergent continental margins to constrain the seismic hazard of the Cascadia margin offshore Oregon, and present the possibility of a slow earthquake mechanism for a characteristic Cascadia event. The Cascadia seafloor has a very delicate bathymetry, with well‐preserved landslides and noneroded slopes approaching 20°, unusual for a margin that produces M∼9 earthquakes. Three‐dimensional seismic and multibeam bathymetry data from the Nankai Trough suggest ubiquitous erosion over the entire margin with a smooth lower slope, devoid of large landslides, as would be expected on an accretionary margin that produces M∼8.5 earthquakes. The accretionary Makran (Pakistan) and Kodiak (Alaska) margins have evidence of mass wasting and smooth lower slopes that lack large landslides. The nonaccreting Nicaraguan, Sanriku, and Aleutian margins have large, well‐preserved landslides that add roughness elements to the slope, and have produced anomalously large tsunami, suggesting a slow source mechanism. Quantitative analysis of the lower slope roughness suggests the Cascadia has a characteristic geomorphology substantially different than the other sedimented convergent margins. The geomorphology, heat flow, pore pressure regime, and accounts of the 1700 “megathrust” event suggest a possible characteristic earthquake with a slow source mechanism. Rupture velocity would be high enough to be tsunamigenic, but accelerations would be low such that downslope erosion is minimal. To make the distinction between a slow and rapid source mechanism is critical in planning for seismic hazard in the Pacific Northwest.

Parametric evaluation of 3D dispersion of rockfall trajectories

Abstract. The capability of evaluating and managing rockfall related risks is largely based on numerical modelling. Nevertheless, the reliability and accuracy of rockfall models is greatly affected by the strong uncertainty and spatial variability which characterise all the relevant parameters. In particular, 3D effects related to the variability of slope geometry and micro-topography play a major role in controlling the dynamics of falling blocks. The most important 3D effect is the "lateral dispersion" of rockfall trajectories, largely affecting the way we model rockfall dynamics, design countermeasures and assess rockfall hazard. Nevertheless, the dependence of lateral dispersion on different controlling factors has been hardly ever systematically evaluated. In this paper, the influence of different controlling factors on the dispersion of rockfall trajectories has been systematically evaluated by performing 3D parametric modelling. Numerical simulations have been performed through a new software code able to use both a lumped mass and an hybrid (kinematic-dynamic) approach. Parametric modelling has been performed at different spatial resolutions using sets of biplanar simplified slopes characterised by different mean inclination and roughness. Model results outlined a complex dependence of lateral dispersion phenomena on slope mean gradient (macro-topography), slope roughness (micro-topography) and the spatial resolution of the model (model-dependent topography). Furthermore, the sensitivity of model results in terms of kinematic variables of motion (i.e. velocity and height to the ground) to the factors controlling lateral dispersion has been evaluated, resulting in practical constraints on countermeasure design and hazard assessment.

Probability distributions of travel time and intensity of the earliest arrivals of a short pulse backscattered by a rough surface

Precise measurements of the travel times of backscattered waves, and especially the travel times of the first (i.e., earliest) arrivals, underlie a number of geophysical remote sensing techniques. In this paper, statistical properties of the travel time and intensity of pulses backscattered by a two-dimensional rough surface are investigated within the geometric optics approximation by adopting a method originally developed in the theory of excursions of a stochastic process. We assume a wave source located sufficiently far from a rough surface with Gaussian statistics, and show that the probability distribution functions of the normalized deviation of the travel time of the first and second backscattered pulses from the travel time in the absence of roughness, are functions of a single dimensionless parameter, T=γ2 0 H/(2πσ), where σ2 and γ2 0 are the variances of the rough surface elevation and slope, and H is the source altitude. Signals from the rough surface return to the source location earlier than from the mean plane by O(2σ/c), where c is the velocity of wave propagation. On average, the travel times of the first and second arrivals decrease as parameter T increases, with the travel time shift being proportional to . The time delay between the first and the second arrivals is inversely proportional to . The joint probability density functions (PDF) of the travel times and the intensities of the first two backscattered pulses are derived. This allows us to obtain the travel time PDF for signals exceeding the given intensity threshold. It is shown that the travel time and the intensity are strongly correlated: on average, earlier arrivals have smaller amplitudes.

Tidally-induced clouds of suspended sediment connected to shallow-water coral reefs

The Bay of Banten, West Java, Indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions. The sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration (SSC) around the reefs. Arrays of in situ calibrated optical backscatter (OBS) sensors were deployed across the reef slopes. Far field conditions were simultaneously monitored using an acoustic Doppler current profiler (ADCP) and a conductivity temperature and depth (CTD) probe, equipped with an OBS sensor. In addition, hydrographic surveys were conducted using the ADCP attached to a small fishing boat, navigating transects perpendicular to the reef islands. The direct influence of river plumes was found to be insignificant. Waves act only in the uppermost few meters of the reef slopes, where coral growth is most abundant and little sediment is available for resuspension. Tidal currents are the primary cause of high turbidity, which was inferred from peaks in the diurnal and semidiurnal frequency bands of SSC spectra, and the large depths where the turbidity variation sometimes initiates. The entrained sediment disperses upward across the reef slopes, which is likely due to a secondary current associated with bending of the flow along the curved, hydraulically rough reef slopes, in weakly stratified ambient waters. Changes in sediment availability, variable critical shear stresses for erosion and deposition, and the formation and evanescence of island wakes may explain the high variability of SSC at the reef slopes.

Backscattering of acoustic pulses from rough surfaces: Statistical properties of first arrivals

In a number of applications, including echo sounding of the ocean bottom, nondestructive evaluation of materials, and satellite altimetry, measurements of travel time and/or shape of a backscattered pulse are employed to retrieve information about position and properties of scatterers. When the scatterer is an extensive rough surface with sufficiently large slopes, the backscattered wave consists of numerous pulses, of which the earliest arrivals are often of primary interest. In this paper, the geometrical acoustics approximation is applied to study signal intensities and the difference between the travel times of waves scattered by a random rough surface and those reflected from the mean, plane boundary. For a Gaussian statistical distribution of roughness, probability density functions (PDFs) of the travel-time differences are found for the first and second arrivals in terms of variances of the surface roughness elevation and slope. The joint PDFs of the travel times and intensities are derived. It allows one to obtain the travel-time PDF for signals exceeding a given intensity threshold. It is shown that the travel time and the intensity are strongly correlated; on average, the earlier a signal arrives, the smaller is its intensity.

希薄気体流における流路の表面形状と下流側圧力の影響−真空用微小流量測定システムの製作−

The aim of this paper is to clarify the effects of surface roughness and downstream pressure on the rarefied gas flow through passages. Surface roughness is modeled by two-dimensional triangular roughness. In the calculation, molecules are assumed to scatter from slope of triangular roughness according to the cosine law. Conductance of rarefied gas flows through passages is calculated using the Monte Carlo method. In the experiment, a flow measurement system for rarefied gas is manufactured to measure flow rate through passages. Experiments and calculations are conducted in the near free molecule flow region. Results of this study are as follows; The manufactured flow measurement system can measure flow rates below 1 × 10 -4 [Pa·m3/sec] accurately. The conductance of rarefied gas flows is affected by the downstream pressure even if pressure difference is equal in two flows. The effect of surface roughness does not change with the downstream pressure of passages.

Predictive GIS-Based Model of Rockfall Activity in Mountain Cliffs

Rockfall susceptibility has been analysed in mountain cliffs of the Cantabrian Range, North Spain. The main aim of this analysis has been to build a predictive model of rockfall activity from a low number of environmental and geological variables. The rockfall activity has been quantified in a GIS. The cartographic information used shows the spatial distribution of all the recent talus screes as well as their associated source areas in the rock-slopes. The area relation At/Ar (recent talus scree polygon/source basins) in the rock slopes has been used as the rockfall activity indicator. This relation has been validated in 50 pilot rock-slopes and compared with the relation number of recent rock fragments/source basin, obtained from field work. The environmental factors causing rockfall depend on the rock slope situation, and these are: altitude and sun radiation on the rock cliff. The geological factors considered are: lithology, relative position of the main discontinuities with respect to the topographic surface and two morphologic parameters: the roughness and slope gradient. A logistic regression analysis has been applied to a population of 442 limestone and quartzite rock cliffs. The dependent variable is the rockfall activity indicator, which allows the definition of two classes of rock cliff units: low and high activity. The independent variables are altitude, sun radiation (equinox radiation, summer solstice radiation, winter solstice radiation), slope roughness, slope gradient,anisotropy and lithology. Results suggest that it is possible tobuild a valid cartographic predictive model for rockfall activity in mountain rock cliffs from a limited number of easily obtainable variables. The method is especially applicable in massive rock slopes or in regions with uniform rock mass characteristics.

3D Visual Information Processing and Gait Control of a Quadruped Robot - for operation on a steep slope protected by a free frame -

Construction work on steep slopes is difficult and dangerous, but it is also difficult to automate work at such type sites. One reason is that construction sometimes calls for movement across a ""Free Frame"" - a structure built to keep a slope from collapsing - and because of the ups and downs of the natural slope, it is difficult to design a purposeful simple mechanism to move on this frame. We propose a sensor-based quadruped walking robot that moves on the slope without damage to the surface of the frame, and developed a TITAN VII prototype robot. We detail the techniques required by this type robot to move and work on steep slopes. Practical ways of A) detecting positions and orientations of frame surfaces on rough slopes and B) stepping over the frame and maintaining the stability of the robot using positioning, are presented and their effectiveness is verified through experiments.

Influence of surface roughness features on mixed‐film lubrication

AbstractAn optical technique (three‐dimensional spacer layer imaging) has been developed to map accurately lubricant film thickness in thin‐film elastohydrodynamic (EHD) contacts. This experimental technique has been used to study the influence of surface roughness features, asperity height, and slope on EHD film thickness and pressure. Single ridges transverse to the entrainment direction were used to represent asperities. It was found that the ridges with lower slopes generate films of greater minimum thickness. Below a certain entrainment speed, the minimum film thickness declined at a rate dependent on the ridge slope. At low speeds, the ridges with higher slopes entrapped a larger volume of lubricant ahead of the ridge and along the entrainment direction. For all speeds, the highest ridges entrapped the most lubricant. Both ridge slope and ridge height had a negligible effect on mean film thickness in the contact. Asperity pressure increased with higher ridge slope, but was not influenced by entrainment speed. An increase in pressure was found where lubricant is entrapped upstream of a ridge.

A semianalytical solution of the Saint‐Venant equations for channel flood routing

A semianalytical solution for channel hydraulic routing has been derived from the Saint‐Venant equations. The Saint‐Venant equations were converted into a nonlinear diffusion equation by introducing the Froude number. Subsequently, the mixing cell method is used to discretize a nonlinear diffusion equation in space, transforming it into a first‐order nonlinear ordinary differential equation where the optimal space interval is obtained to be the same as the characteristic reach length. The nonlinear ordinary differential equation was solved by integration with respect to time to achieve a nonlinear implicit algebraic equation. The resulting implicit equation is practical and easy to program on a computer. This method is based on the results of a numerical simulation using the Lambda scheme which indicates that the Froude number is only dependent on the channel roughness and bottom slope. The method was tested with numerical examples and compared with the Lambda scheme and observed data. The hydrographs produced by this method were of comparable accuracy.