Characteristics Of Sand Transport Research Articles

Characterizing sand transport with various micro‐ridge spacings and heights

AbstractIn arid regions, the use of ridge cover as a traditional agricultural strategy has been effective in mitigating soil wind erosion. However, few studies have focused on the sand transport characteristics of different micro‐ridge spacings and heights. This study aimed to identify the mechanism by which ridges change the near‐surface sand transport. In a controlled wind tunnel environment, the aeolian sand flux structure and sand transport flux (qz) at heights from 0 to 0.7 m were measured. The results showed that, compared with no ridges, ridge covering could significantly modify the structure of aeolian sand flux near the surface, yielding a substantial reduction in the proportion of sand transport to the total sand transport in the 0‐ to 0.1‐m height layer. In the absence of ridges, blown sand was mainly concentrated in the 0‐ to 0.1‐m height layer, and qz decreased exponentially as the height increased. With various micro‐ridge spacings and heights, when H was less than 0.1 m and L was more than 15H, the blown sand also remained concentrated in the 0‐ to 0.1‐m height layer, and qz decreased exponentially as the height increased. When H increased to 0.15 m from 0.1 m and L decreased from 15H to 5H, the height of the blown sand was concentrated in the 0.3‐ to 0.4‐m layer. The blown sand layer of most ridge structures was concentrated at a height of 0.1–0.4 m, and the structure of the aeolian sand flux resembled an ‘elephant nose effect’. The total sand transport rate of all ridge structures was significantly lower than that with no ridges, indicating that a reasonable ridge structure can effectively prevent wind erosion.

Wind regime and aeolian sand transport in Khuzestan Sand Sea

The Khuzestan Sand Sea extends from the Wasit and Maysan provinces in Iraq (22%) to the Ilam (10%) and Khuzestan (68%) provinces in Iran. In order to determine wind regimes and sand transport characteristics, hourly wind data records from 21 meteorological stations for the period 2000–2016 were analyzed using aeolian-sediment transport methods. The analysis of the wind energy based on drift potential (DP) revealed rather large spatial variations in the Khuzestan Sand Sea. The Iraqi part of the desert, as well as the southern regions of the Ilam province and the western edge of the Khuzestan province were characterized by particularly high wind energy (DP greater than 400), while towards the central area of the Khuzestan Sand Sea near Ahvaz city a sharp decrease to DP less than 200 was detected. In the southern and southeastern parts of the Khuzestan Province, the wind energy increased again and the DP reached more than 200 vector units. The temporal analysis of the DP showed no considerable temporal trends between 2000 and 2014 in this study area. The dune morphology analysis revealed a bimodal wind regime, which was also supported by the dominance of sand sheets and transverse dunes. Additionally, the local topography has an important influence on the formation of topographic dunes in the southeastern parts of the Sand Sea.

Large-eddy simulation of sand transport under unsteady wind

Aeolian sand movement contributes to evolution of surface landforms on Earth and Mars, as well as on Venus and Titan. Most natural landforms in arid regions are molded by wind with a general feature of unsteadiness. Many researches have improved our cognition of saltation in unsteady flow, but it is probably true that this issue is not yet fully analysed. In this paper, we conducted three-dimensional numerical simulations of wind-blown sand under unsteady wind conditions. The trajectories of sand particles are simulated by using a Lagrangian model. Particle motion, particle-bed interaction and wind modification have been taken into account. Results indicate that the characteristics of sand transport in unsteady and steady wind conditions profoundly differ; the sediment transport in unsteady conditions is significantly enhanced and increases with the amplitude of the sinusoidal wind fluctuations; the time series of sediment transport reveals a sine-like variation which lags behind the variation of the wind with a time delay of about 1 s (response time of saltation to wind variation). In unsteady conditions, sand transport shows an ‘overshoot’ which is embodied in the initial wave of the sediment transport. The impact of unsteady sediment transport should be paid more attention in future Aeolian research.

Characteristics of Aeolian Dune, Wind Regime and Sand Transport in Hobq Desert, China

A systematic study of the wind regime characteristics in a region can not only accurately grasp the dynamic factors of the development of aeolian geomorphology, but also provide a scientific basis for the prevention and treatment of regional sand disasters. Taking the Hobq Desert as the study area, the basic characteristics of dune are analyzed by using remote sensing images. Based on the annual meteorological data of six meteorological stations from 2009 to 2018, the spatial and temporal distribution characteristics of wind speed were obtained. With the daily wind data of three stations from 2009 to 2018, we have figured out the wind regime and sand transport characteristics of the Hobq Desert. The results show that the sand dune height of the Hobq Desert ranges large, the highest height is 5010 m and the lowest is 10 m. It decreases gradually from the west to the east. The height of dune mainly distributed below 1500 m, followed by 1500–2000 m. Migratory sand dunes in Hobq Desert accounts for 51.8% and is mainly distributed in the west of the desert. The distribution area of fixation sand dunes in Hobq Desert is the least, accounting for 8.3%. The migratory dune pattern is trellis dune, semimigrated dune and semifixed dune patterns include honeycomb dune, parabolic duneand brush dune, and fixation dune pattern is grass dune. Annual wind speed was greatest in the southeast and decreased moving to the northwest. The dominant wind direction was W and SW from 2009 to 2018 in the Hobq Desert, the average wind speed of the prevailing winds mainly distributed at 4–8 m/s. The frequency of wind speed exceeding 10 m/s is very low, with a maximum value of 10% or below. There is a low energy wind environment in the Hobq Desert, with intermediate annual directional variability and obtuse or acute bimodal wind regime. The resultant drift direction (RDD)at Dongsheng station was relatively constant from 2009 to 2018, it was about 350°. RDD differed significantly at Baotou and Linhestations were 181 ± 169° and 231 ± 121°, respectively.The relationship between drift potential (DP) and the average and maximum wind speed was expressed as a power function. DP was strongly correlated with them. There is no significant correlated between the temporal changes in DPandprecipitation and temperature from 2009 to 2018 in the Hobq Desert.

Experimental Study on Sand Transport Characteristics in Horizontal and Inclined Two-Phase Solid-Liquid Pipe Flow

AbstractAn experimental investigation on the hydraulic transport of sand particles in pipelines is presented in both horizontal and 30° upward inclined orientations. The pipe, with an internal diam...

Sand transport in multiphase flow mixtures in a horizontal pipeline: An experimental investigation

An inherent problem with both oil and natural gas production is the deposition of sand particles in pipeline, which could lead to problems such as excessive pressure drops, equipment failure, pipeline erosion, and production decline. The characterization of sand particles transport and sedimentation in different flow systems such as sand–multiphase mixtures is vital to predict the sand transport velocity and entrainment processes in oil and gas transportation pipelines. However, it seems that no model exists able to accurately characterize the sand transport and deposition in multiphase pipeline. In fact, in the last decade several researchers tried to extend the modeling of liquid-solid flow to gas-liquid-solid flow, but no significant results have been obtained, especially in slug flow condition due to the complexity of the phenomenon. In order to develop and validate a mathematical model properly formulated for the calculation of the sand critical deposition velocity in gas-liquid flow, more and more experimental data are necessary. This paper presents a preliminary experimental study of three phase flows (air-water-sand) inside a horizontal pipe and the application of the sand-liquid models present in literature. Significant observations were made during the experimental study from which several conclusions were drawn. Different sand flow regimes were established by physical observation and data analysis: fully dispersed solid flow, moving dunes and stationary bed. The critical deposition velocities were determined at different sand concentrations. It was concluded that sand transport characteristics and the critical deposition velocity are strongly dependent on the gas-liquid flow regime and on sand concentration.

Field observations of the vertical distribution of sand transport characteristics over fine, medium and coarse sand surfaces

AbstractThe vertical distribution of sand transport characteristics is an important issue in aeolian research. Surface characteristics affect sand transport processes, but their effects are not yet fully understood. To provide more data on this subject, we observed sand transport in 16 field experiments above surfaces covered by fine, medium and coarse sand. The sand transport rate over relatively coarser‐grained medium and coarse surfaces could be expressed as a Gaussian peak function: qz = a + b exp (−0.5[(|z – Ch|)/d]e), where qz is the measured sediment transport at height z above the bed and a, b, Ch, d, and e are regression coefficients. The measured sand transport flux peak values (Hh) were linearly related to Ch, and both values were significantly related to the mean surface grain size. However, for the relatively finer‐grained medium and fine sand surfaces, the sediment transport could be expressed as an exponential function. The cumulative sand transport below 0.1 m was directly related to the mean surface grain size, and the relationship could be expressed as the following exponential function: Cz = f + g exp –Mz/i, where Cz is the cumulative sand transport at height z above the bed, Mz is the mean grain size and f, g, and i are regression coefficients. Above 0.1 m, there were no significant relationships between the cumulative sand transport and the mean surface grain size. The mean grain size decreased with increasing height below the peak height and then increased with increasing height. The surface grain size distribution and proportions of the particles in different grain size categories controlled the mean grain size as a function of height. The observed changes in the sand transport rate and grain size with height will provide support for sand disaster mitigation, numerical modelling and studies of dune formation. Copyright © 2016 John Wiley & Sons, Ltd.

Monitoring Sand Transport Characteristics in Multiphase Flow in Horizontal Pipelines Using Acoustic Emission Technology

Monitoring Sand Transport Characteristics in Multiphase Flow in Horizontal Pipelines Using Acoustic Emission Technology

Identification of minimum transport condition for sand in two-phase flow using acoustic emission technology

This paper presents an experimental investigation using Acoustic Emission (AE) technology to monitor sand transport characteristics and identify the sand minimum transport condition (MTC) in two-phase flow. The sand concentration investigated ranged from 300lb/1000bbl to 700lb/1000bbl and superficial liquid velocity (VSL) had a range of between 0.1ms−1 and 1.2ms−1. The experimental findings clearly showed a correlation between MTC and AE energy levels.

Characteristics of sand transport around the submerged breakwaters installed in Songdo Beach, Busan, South Korean

ABSTRACT W.D. Lee, M.K. Kim, D.S. Hur, W.C Cho and J.S. Yoon, 2013 Characteristics of sand transport around the submerged breakwaters installed in Songdo Beach, Busan, South Korean, Journal of Coastal Research, Special Issue No. 65, pp. 2143–2148, ISSN 0749-0208.--> Songdo Beach, a pocket beach, is directly affected by wave activities. During the First Coast Repair Project (2000–2009), two submerged breakwaters were installed to reduce incoming wave energy and trap the sand eroded from the beach. After that the submerged breakwaters have played an important roll to determine the hydrodynamics behind the submerged breakwaters and the sand transport along the Songdo beach. For these reasons, five-year monitoring (2004–2008) was carried out for the prediction of shoreline change and for the maintenance of shoreline of Songdo beach. On the basis of the accumulated monitoring data, we analyzed the sand movement in Songdo beach to predict beach erosion. The results reveals that beach erosion occurs by the typho...

Inter-particle collision effects on the entrained particle distribution in aeolian sand transport

Based on the Boltzmann transport equation, a theoretical model for the particle concentration distribution was developed in the aeolian sand transport to account for the inter-particle collision effects near the sand bed surface. In order to assess the inter-particle collision effects on sand transport characteristics near the sand bed surface, a set of experiments were performed in a large-scale wind tunnel with a dimension of 12,000mm×400mm×600mm (L×W×H). Two types of sand samples were prepared by screening. The free-stream wind velocity in the wind tunnel was measured by HWA (Hot Wire Anemometer). The particle velocity, concentration, and Reynolds stress were obtained by PDPA (Phase Doppler Particle Analyzer). Experimental results showed that particle concentration emerged a turning point at about 2cm from the sand-bed surface. They agreed with the numerical simulation results very well. The collision rate of particles also emerged a turning point, and the location of the turning point was approximately consistent with that of the measured concentration and the Reynolds stress. Consequently, the inter-particle collision close to the sand-bed surface, which was the main factor that altered the characteristics of particle transport, could not be neglected.

Study on Soil Erosion by Wind Tunnel Experiment of Semi-Arid Steppe in Inner Mongolia

The characteristics of soil erosion of steppe in Inner Mongolia were studied in wind-tunnel tests. The results indicated that the soil in this region consists primarily of sand and coarse silt, with particle sizes mainly between 0.02 and 1mm, and it is defined as erodible sandy soil. The eroded sediments are mainly concentrated at heights of 0~24cm, and the extreme value of particle size is clearly in the range 100~300μm. Average particle size increased with increasing wind speed, and it decreased exponentially in the vertical direction, reflecting the characteristics of sand transport by wind. The relationship between wind erosion rate and wind speed assumes a power function with correlation coefficients greater than 0.9. A wind speed of 15m/s is a significance point above which wind erosion in this region becomes very large. Soil erosion rate decreases logarithmically as soil moisture content and vegetation coverage increase, and the 5% level of moisture content is a turning point.

Sand Transportations and Deposition Characteristics in Multiphase Flows in Pipelines

Sand management strategies become an important study to be performed as part of multiphase flow assurance assessments during oil and gas project life and especially for subsea multiphase flow network. This paper presents experimental works to investigate the sand transport characteristics and identify the sand minimum transport condition (MTC) in sand–water and sand–air–water flows in a horizontal and + 5 deg inclined pipelines. The used sand volume fraction, Cv, ranged from 1.61 × 10−5 up to 5.38 × 10−4. The sand minimum transport velocity in single-phase water flow was obtained visually and then compared with that calculated by previous correlations for slurry transport. It was found that in sand–water flow, the pipeline inclination had negligible effect on the minimum sand transport velocity. However, the transport characteristics of sand particles were found changed significantly by changing the pipe inclination, which could result in the change of air–water flow regime. It was observed that sand particles transport more efficiently in terrain slug than stratified wavy flow in +5 deg inclined pipes. The sand transport and settling boundary for different air–water flow regimes were generated for horizontal and +5 deg inclined pipeline.

Observations of wind‐blown sand under various meteorological conditions at a beach

Field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind‐blown sand transport under various weather conditions including a storm event. Data sets over periods of several hours included blown sand impact counts, three‐dimensional wind conditions, hourly precipitation, and moisture content of the sediment surface. The intermittent blown sand impact data shifted by 1 s ahead of the wind velocity correlated with the wind velocity during a no‐rainfall period (for an assumed dry surface) and in the longshore wind direction (for sufficiently long fetch length). The 5‐min mean wind velocity/impact counts relationship was well constrained by both second‐ and third‐order polynomial fitting of velocity under similar weather conditions. During a no‐rainfall period and in the longshore wind direction, the relationship between the wind velocity and sand flux estimated from the counts coincides with existing studies in wind tunnel experiments. The sand flux, however, decreased by 1 order of magnitude because of a change in the wind direction from longshore to cross‐shore and then by more than 1 order of magnitude because of an increase in the moisture content. Threshold wind velocity calculated using the time fraction equivalence method with the impact counts and the horizontal wind velocity in 5‐min sampling periods was approximately equal to the value predicted using Bagnold's equation during the no‐rainfall period and increased significantly during the rainfall phase. The sand flux sensor has several limitations for complex conditions in the field; however, it provides a number of characteristics of sand transport under various meteorological conditions.

Dune sand transport as influenced by wind directions, speed and frequencies in the Ordos Plateau, China

The Ordos Plateau in China is a region with extensive wind erosion, severe desertification and various aeolian sand hazards. In order to determine aeolian sand transport in this region, the relationship between the sand transport rate and wind speed at 10 min frequencies was established by field observation in both the Qubqi Sand Desert and the Mu Us Sandy Land. Threshold wind speeds (2 m above the ground) for mobile, semi-fixed and fixed dune surfaces were estimated by field observations. The sand transport rate increased with the increase of the bare land ratio and near-bed wind speed. High-resolution meteorological 10 min average wind velocity data at 10 m above the ground were converted into velocity values at a height of 2 m to calculate sand transport potential based on three specific parameters decisive for sand transport: wind speed, duration and direction. The quantity of aeolian sand transported was calculated for various wind speed levels and directions, and the overall characteristics of sand transport on different dune surface types were determined by vector operation techniques. Sand transporting winds took place mainly in springtime. The prevailing wind directions were W, WNW and NW, with a frequency of more than 60% in total, and sand transport in these directions made up more than 70% of the total transport, corresponding to a general southeastward encroachment of aeolian sand in the study area. The relationship between wind frequency and speed can be expressed by a power function. High magnitude strong winds had a low frequency, but they played a dominant role in aeolian sand transport.

Influence des tempêtes sur la mobilité des dunes tidales dans le détroit du Pas-de-Calais

Influence of storms on tidal dune mobility in the Strait of Dover. The present paper deals with dune dynamics in a zone of the Strait of Dover located in the sea lane running into the North Sea. The dunes, widespread in this 35-m depth area, are mobile sedimentary structures (up to 40 m·yr −1) that culminate at a maximum of 22 m depth and endanger navigation as well as submarine man-made structures (cables, pipelines). Single- and multibeam bathymetric data, coupled with seismic data, allow us to follow dune displacements over different time scales. A net bedload parting zone has been displayed and divides the area into two parts, SE and NW. However, according to the considered time-scale, dune movements present variations in intensity and direction. Over a long-term period (decades), sedimentary dynamics fit the regional scheme of the residual tidal currents that induce transport toward the SW and the NE in the respective SE and NW parts of the studied area. Over a medium-term period (several years), meteorological data show that a high frequency of storm winds alters the residual sand transport characteristics by strengthening, slowing or reversing the effect of the tidal currents and can lead to the reversal of dune asymetry. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Strait of Dover / sedimentary dynamics / tidal dunes / storms

ESTIMATION USING A MOVABLE BED MODEL OF SHORELINE CHANGE CAUSED BY A RECLAMATION PROJECTED INTO THE SEA

Recently, many local airports in Japan are considering to extend their runways, so accommodating passenger traffic. But most airports are obliged to extend their runways into the sea on account of the shortage of land and complaints from their neighbors about jet-plane noise. Tokushima Airport is one of such local airports, which is situated on the coast along the Kie-Suido Channel as shown Figure 1. The length of the runway of Tokushima Airport is 1500 m at percent, so a plan to extend the runway by 600 m into the sea has been proposed by the local government. However, Matsushige beach, where the airport is located, is now so seriously eroded that offshore breakwaters are being constructed in the south and the northern part is used for sea-bathing. Therefore, it is necessary to estimate the change of beach profiles, especially of the shoreline, caused by the extension of the runway, and to find countermeasures against unfavorable change. A movable bed model was constructed to estimate such changes, because no numerical simulation using a computer has been developed to estimate changes of a complicated beach topography. Of course, the universal dynamic similarity does not hold for model studies on sand transport problems. Therefore, the characteristics of sand transport at the site are first clarified through analysis of the field observation data, and then the model scale, bed material, and test waves are determined in such a manner that the topographic variation in the model sea bed will become similar to that in the prototype. But, in general, it is difficult to make all of the variations of the sea bed in the model similar to that in the prototype. In this model experiment, the long term changes of the shoreline has been taken as the most important phenomena to be reproduced in the model.