Numerical simulation on sand sedimentation and erosion characteristics around HDPE sheet sand barrier under different wind angles

For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.

Utilizing sediment grain size characteristics to assess the effectiveness of clay–sand barriers in reducing aeolian erosion in Minqin desert area,China

The clay–sand barriers in Minqin desert area,China,represent a pioneering windbreak and sand fixation project with a venerable history of 60 a.However,studies on evaluating the long-term effectiveness of clay–sand barriers against aeolian erosion,particularly from the perspective of surface sediment grain size,are limited and thus insufficient to ascertain the protective impact of these barriers on regional aeolian activities.This study focused on the surface sediments(topsoil of 0–3 cm depth)of clay–sand barriers in Minqin desert area to explain their erosion resistance from the perspective of surface sediment grain size.In March 2023,six clay–sand barrier sampling plots with clay–sand barriers of different deployment durations(1,5,10,20,40,and 60 a)were selected as experimental plots,and one control sampling plot was set in an adjacent mobile sandy area without sand barriers.Surface sediment samples were collected from the topsoil of each sampling plot in the study area in April 2023 and sediment grain size characteristics were analyzed.Results indicated a predominance of fine and medium sands in the surface sediments of the study area.The deployment of clay–sand barriers cultivated a fine quality in grain size composition of the regional surface sediments,increasing the average contents of very fine sand,silt,and clay by 30.82%,417.38%,and 381.52%,respectively.This trend became markedly pronounced a decade after the deployment of clay–sand barriers.The effectiveness of clay–sand barriers in erosion resistance was manifested through reduced wind velocity,the interception of sand flow,and the promotion of fine surface sediment particles.Coarser particles such as medium,coarse,and very coarse sands predominantly accumulated on the external side of the barriers,while finer particles such as fine and very fine sands concentrated in the upwind(northwest)region of the barriers.By contrast,the contents of finest particles such as silt and clay were higher in the downwind(southeast)region of the sampling plots.For the study area,the deployment of clay–sand barriers remains one of the most cost-effective engineering solutions for aeolian erosion control,with sediment grain size parameters serving as quantitative indicators for the assessment of these barriers in combating desertification.The results of this study provide a theoretical foundation for the construction of windbreak and sand fixation systems and the optimization of artificial sand control projects in arid desert areas.

Cost analysis of sand barriers in desertified regions based on the land grid division model

Sand barriers are the most widely used mechanical implements for wind-blown sand control and desertification prevention.However,there is no standard quantitative cost analysis of the sizes and materials required for sand barriers.In this study,based on the original land grid division model for optimal resource utilization,we calculated the total side lengths of square and regular hexagonal sand barriers with the sizes of 1.0 m×1.0 m,2.0 m×2.0 m,and 3.0 m×3.0 m in a desertified region of the Shapotou area on the southeastern edge of the Tengger Desert,China.Then,through literature review and social survey,we obtained the material cost and material utilization amount of sand barriers with different materials and sizes.Finally,we calculated the costs of square and regular hexagonal sand barriers comprised of wheat straw,corn stalk,Salix mongolica,poly lactic acid,magnesium cement,and high-density polyethylene,with the sizes of 1.0 m×1.0 m,2.0 m×2.0 m,and 3.0 m×3.0 m.The results show that the material cost of regular hexagonal corn stalk sand barriers with the size of 3.0 m×3.0 m is the lowest,while the material cost of square magnesium cement sand barriers with the size of 1.0 m×1.0 m is the highest.When using the same material,the cost of regular hexagonal sand barriers is lower than that of square sand barriers with the same size.When using the same size,the cost of sand barriers with corn stalk material is lower than that of sand barriers with other materials.Based on the above analysis,we can conclude that the economic benefits of regular hexagonal sand barriers are greater than those of square sand barriers.This study provides a theoretical basis for accurately calculating the material cost of sand barriers,particularly for the estimated cost of mechanized sand barrier engineering projects.

Progress and Problems of Development Research and Application of Sand Barriers

Due to the restrictions on the conditions for afforestation and sand control,the development research,and application of sand barriers have accelerated in recent years,but some problems that cannot be ignored have emerged in practice. In this paper,the functions of wind prevention,sand blocking and fixation,improving soil physical and chemical properties and increasing plant diversity of sand barriers,accretion coefficient and capacity between sand barriers,and mobile sand barriers were analyzed firstly,and then several issues that should be noted in the development and application of sand barriers were proposed. The results show that sand barriers can fix sand on the spot and maintain the stability of sand surface. As an auxiliary measure before afforestation on a mobile sand surface,they are practical and feasible. The biggest drawback of sand barriers is that they are easy to be saturated. Although they can increase plant diversity and surface roughness,they lose the function of blocking sand flow after being saturated,and their function of in-situ sand fixation also rapidly decreases with the degradation of sand barriers. Mobile sand barriers overcome the disadvantage of sand barriers being easy to be saturated to some extent,but the cost greatly increases. In terms of desertification prevention and control by plants,plants are used as sand barriers to study their functions of sand blocking and sand fixation in many researches and practices,but the more important ecological functions of adjusting temperature on sand surface and achieving surface thermodynamic equilibrium of plants are ignored.

Morphological evolution of a large sand bar in the Qiantang River Estuary of China since the 1960s

A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November since the 1960s,this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP)implemented in the last decades.The results show that three timescales,namely the seasonal,interannual and decadal timescales,can be distinguished for the sand bar evolution.The first two are related to the seasonal and interannual variations of river discharge.During high discharge seasons or years,erosion took place at the upper reach and sedimentation at the lower reach.Consequently,the bar apex shifted seaward.The opposite development took place during low discharge seasons or years.The decadal timescale is related to LRNP.Due to the implementation of LRNP,the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached;whereas the lower reach has been accumulated seriously and the accumulation still continues.Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established.Compared with the earlier stage of LRNP,the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m.The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.

Sand barrier morphological evolution based on time series remote sensing images:a case study of Anhaiao,Pingtan

The morphological evolution of the sand barrier in the Anhaiao coastal zone of Pingtan from 1996 to 2018 was studied.Tidal correction was used to refine the location of the coastline.A standard deviation ellipse method was applied to further analyze the movement of the barrier head with the axis and rotation angle.A natural neighbor interpolation(NNI)method was carried out to calculate the terrain of the intertidal area,and the erosion and deposition characteristics were illustrated based on the terrain.The results showed that the northern part of the sand barrier facing the lagoon area was deposited over the whole studied period,while erosion has always occurred in the southern part of the sand barrier facing the open sea.The erosion and deposition were slightly different on both sides of the barrier head due to hydrodynamic turbulence.The middle sand barrier moved 102.60 m away from its original location in 1996,and the end of the barrier moved 65.45 m.The head of the sand barrier continued moving 379 m to the northwest.Consequently,the preliminary morphological evolution of the sand barrier corresponding to the distance and direction of movement was detected.

Effects of sand sedimentation and wind erosion around sand barrier:Numerical simulation and wind tunnel test studies

Based on numerical simulations,this study highlights the sedimentation and erosion problems around a sand barrier through the relationship between the shear stress of the surface around the sand barrier and the critical shear stress of sand grains.The numerical simulation results were verified using data measured by the wind tunnel test.The results showed that when the porosity was the same,the size and position of the vortex on the leeward side of the sand barrier were related to the inlet wind speed.As the wind speed increased,the vortex volume increased and the positions of the separation and reattachment points moved toward the leeward side.When the porosity of the sand barrier was 30%,the strength of the acceleration zone above the sand barrier was the highest,and the strength of the acceleration zone was negatively correlated with the porosity.Sand erosion and sedimentation distance were related to wind speed.With an increase in wind speed,the sand grain forward erosion or reverse erosion areas on the leeward side of the sand barrier gradually replaced the sedimentation area.With an increase in porosity,the sand sedimentation distance on the leeward side of the sand barrier gradually shortened,and the sand erosion area gradually disappeared.The sand sedimentation distance on the leeward side of the sand barrier with 30%porosity was the longest.The numerical simulation results were in good agreement with the wind tunnel test results.Based on the sand erosion and sedimentation results of the numerical simulation and wind tunnel test,when the porosity was 30%,the protection effect of the High Density Polyethylene(HDPE)board sand barrier was best.

Grain Size Analysis of a Growing Sand Bar at Sonadia Island, Bangladesh

Sonadia is one of the most important islands of Bangladesh. South-eastern shore of the island, which is a growing sand bar, has to encounter continuous and rapid morphological changes. So study of the sediment characteristics of this Sand Bar is very important. In the present study, grain size analysis of this Sand Bar has been done on the basis of laboratory analysis. Sediment samples were collected from 9 (Nine) stations and texture analysis of sediment was completed following a standard procedure of sieve analysis of sand samples. The average value of median (MD), mean (M), standard deviation (s), skewness (SK) and kurtosis (K) of sediment of the Sand Bar of Sonadia Island was 1.93, 1.87, 0.44, 0.11 and 1.88 respectively. Highest median, mean, standard deviation, skewness and kurtosis of Sand Bar of Sonadia Island was 2.98 (Station 2, Lower Shore), 2.68 (Station 1, Lower Shore), 0.83 (Station 1, Middle Shore and Station 2, Lower Shore), 0.65 (Station 2, Lower Shore) and 3.59 (Station 1, Lower Shore) respectively. Lowest median, mean, standard deviation, skewness and kurtosis of Sand Bar of Sonadia Island was 1.42 (Station 9, Middle Shore), 1.45 (Station 9, Middle Shore), 0.30 (Station 5, Lower Shore and Station 8, Lower Shore), 0.04 (Station 5, Upper Shore) and 0.94 (Station 6, Upper Shore) respectively.

Spatial configuration of sand and mud in the lacustrine nearshore sand bar deposits and its geological implications

Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact,causing complicated genesis and distribution of argillaceous sediments,as well as other issues.This paper investigates the spatial configuration of sand and mud in the sand bar reservoir,and analyzes its internal structure.Modern sand bar deposits in the Xiashan Lake,Shandong Province,China,were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag,China.The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud.Based on the alternate deposition characteristics of sand and mud in the longitudinal direction,lacustrine nearshore sand bars can be divided into three sedimentary combination patterns:thin-sand and thin-mud interbed pattern,thick-mud thick-sand pattern,and thin-mud thick-sand pattern.Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types.These include(semi-)deep lacustrine mud,sand and mud interbedded beach,argillaceous sediments in the water retention area behind the bar,and fall-silt seams that resulted from flood discharge.By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits,a depositional process-based argillaceous sediment composition model is proposed.Based on this,this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs,and introduces the typical stratigraphic structures of sand bars in two environments,i.e.,vertical superposition and lateral migration.In lacustrine nearshore sand bar reservoirs,the deposition and preservation degrees of mud mainly depend on three factors:accommodation space change,frequency of base-level cycles,and exposure-erosion time.These in turn influence the continuity and relative contents of sand and mud in reservoirs.The distribution of argillaceous sediments forms different orders of interlayers,which affects the heterogeneity and fluid percolation of sand bar reservoirs.Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs.Furthermore,this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans.

Characteristics of water alternating CO_(2)injection in low-permeability beach-bar sand reservoirs

Water flooding can be ineffective in highly heterogeneous low-permeability beach-bar sand reservoirs.The introduction of CO_(2)flooding helps boost the oil production of the reservoirs but only in an early stage.During the late stage of flooding,gas channeling would occur.Water alternating gas(CO_(2))(WAG)process can be used to delay gas channeling and improve the effect of CO_(2)injection,though its adaptability to beach-bar sand reservoirs remains unclear.In order to clarify CO_(2)injection characteristics in these reservoirs,experiments were carried out in high-temperature high-pressure NMR on-line displacement experiment apparatus to simulate different flooding modes on synthetic cores that can reflect the vertical heterogeneity of beach-bar reservoirs.Different CO_(2)injection modes were implemented on these cores and the displacement characteristics and residual oil distribution features during both WAG injection and continuous CO_(2)injection were analyzed quantitatively and qualitatively.The results show that the scheme of WAG injection after continuous CO_(2)injection can obtain better oil displacement efficiency than that of the scheme of continuous CO_(2)injection after WAG injection,but there is no significant difference in respect of oil displacement efficiency of WAG flooding between the mode of bar-injection e beach-production(injection into bar sand e production from beach sand)and the mode of beach-injection e beach-production(injection into and production from beach sand),with the former mode having a higher oil recovery rate.The wider pore-size distribution range of microscopic residual oil after WAG injection shows great potential of enhancing oil recovery from subsequent continuous gas injection.When WAG injection is implemented prior to continuous CO_(2)injection,the displacement effect of the latter is more significant.This research may provide a theoretical basis for CO_(2)EOR in this type of reservoirs.

Evolution Characteristics and Development Trends of Sand Barriers

Sand barriers are one of the main measures used to prevent desertification and have been widely used in desertification control. Here, we use bibliometric methods and content analysis to summarize sand barrier type, applications and research. Existing problems in research are pointed out and revolution characteristics and development trends of sand barriers are discussed. We conclude that three main driving factors have stimulated sand barrier study： demand, technology and development concept. Developing environmentally friendly technology and promoting industrialization of sand area economies are future directions for sand barrier research.

Mechanical Properties of Railway High-strength Manufactured Sand Concrete: Typical Lithology, Stone Powder Content and Strength Grade

In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.

Prediction of intrusive gas pores caused by resin burning in sand core for iron castings

In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process.Therefore,a gas generation and flow constitution model was established,in which the gas generation rate is a function of temperature and time,and the flow of gas is controlled by the gas release,conservation,and Darcy's law.The heat transfer and gas flow during casting process was numerically simulated.The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core.The gas pores in castings are predicted by the gas pressure,the viscosity and state of the melt for these dangerous points.Three distinct sand core structures were designed and used for the production of iron castings,and the simulated gas pore results were validated by the obtained castings.

THEORETICAL ANALYSIS AND NUMERICAL SIMULATION OF TURBULENT FLOW AROUND SAND WAVES AND SAND BARS

Natural rivers usually possess sand waves and sand bars. In this article, the rapid distortion theory was used to study the turbulent flow over sand waves. The results show that the pre-existing sheafing motion and upstream anisotropy of the turbulence flow would have significant effect on the turbulent structures, and hence the memory effect should be taken into consideration. Furthermore, the 2-D mathematical model was employed to simulate the unsteady flow around the Taiping Sand Bar in the lower reach of the Yangtze River and the time step effect on the unsteady flow simulation with the implicit scheme was discussed at the same time. The results show that the implicit scheme keeps effective until the time step reaches a certain number, and the calculated water levels and velocities are in agreement with the observed data.

Preparation of Heavyweight Ultra-high Performance Concrete Using Barite Sand and Titanium-rich Heavy Slag Sand

The heavyweight ultra-high performance concrete(HUHPC)was prepared with barite sand partially replaced by titanium-rich heavy slag sand(THS)at replacement proportion of 0%,30%,50%,70%and 100%in this work.The results show that THS incorporation can effectively improve the mechanical properties and reduce the volume shrinkage of HUHPC.The HUHPC with 50%THS replacement reaches an apparent density of 2890 kg/m^(3)(for fresh HUHPC),28 d compressive strength of 129 MPa,28 d flexural strength of 23 MPa,28 d flexural toughness of 28.4,56 d volume shrinkage of 359×10^(-4) and,as expected,excellent durability.Microstructural investigation demonstrates that the internal curing of pre-wetted THS promotes the hydration of the surrounding cement paste thereby strengthening the interfacial transition zone,resulting in the“hard shell”formation around aggregate to“protect”the aggregate.Additionally,the“pin structure”significantly improves the cement paste-aggregate interfacial connection.The combination of“hard shell protection”and“pin structure”remarkably improve the mechanical properties of HUHPC produced with porous THS aggregate.

CHRONOLOGICAL RESEARCH OF SAND BARS ALONG THE SOUTH COAST OF CHINA

Ⅰ. INTRODUCTIONThere are many sand bars along the south coast of China, distributed from the south of Fujian, Guangdong, Hainan to Guangxi. After investigating and sampling more than 100 bars, the author has chosen 64 samples for dating and has collected 35 prevenient data in order to study the ages of the bars. The samples got from bars, from beds

Data-driven casting defect prediction model for sand casting based on random forest classification algorithm

The complex sand-casting process combined with the interactions between process parameters makes it difficult to control the casting quality,resulting in a high scrap rate.A strategy based on a data-driven model was proposed to reduce casting defects and improve production efficiency,which includes the random forest(RF)classification model,the feature importance analysis,and the process parameters optimization with Monte Carlo simulation.The collected data includes four types of defects and corresponding process parameters were used to construct the RF model.Classification results show a recall rate above 90% for all categories.The Gini Index was used to assess the importance of the process parameters in the formation of various defects in the RF model.Finally,the classification model was applied to different production conditions for quality prediction.In the case of process parameters optimization for gas porosity defects,this model serves as an experimental process in the Monte Carlo method to estimate a better temperature distribution.The prediction model,when applied to the factory,greatly improved the efficiency of defect detection.Results show that the scrap rate decreased from 10.16% to 6.68%.

Experimental and simulation research on hollow AZ31 magnesium alloy three-channel joint by hot extrusion forming with sand mandrel

Magnesium alloy is one of the lightest metal structural materials.The weight is further reduced through the hollow structure.However,the hollow structure is easily damaged during processing.In order to maintain the hollow structure and to transfer the stresses during the high temperature deformation,the sand mandrel is proposed.In this paper,the hollow AZ31 magnesium alloy three-channel joint is studied by hot extrusion forming.Sand as one of solid granule medium is used to fill the hollow magnesium alloy.The extrusion temperatures are 230℃ and 300℃,respectively.The process parameters(die angle,temperature,bottom thickness,sidewall thickness,edge-to-middle ratio in bottom,bottom shape)of the hollow magnesium alloy are analyzed based on the results of experiments and the finite element method.The results are shown that the formability of the hollow magnesium alloy will be much better when the ratio of sidewall thickness to the bottom thickness is 1:1.5.Also when edge-to-middle ratio in bottom is about 1:1.5,a better forming product can be received.The best bottom shape in these experiments will be convex based on the forming results.The grain will be refined obviously after the extrusion.Also the microstructures will be shown as streamlines.And these lines will be well agreement with the mold in the corner.

Flow field, sedimentation, and erosion characteristics around folded linear HDPE sheet sand fence: Numerical simulation study

Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.

Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image analysis.The results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly improved.For every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was 1-1.50.Moreover,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 d.The optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.