جستجوی مقالات مرتبط با کلیدواژه « Wind tunnel » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

In most arid and semi-arid areas, the soils have a compact surface layer that is denser and less permeable than the underlying layers. These layers are referred to as surface coating when they are wet, and when they dry, they are referred to as surface crust. Surface crust can be divided into physical, chemical, and biological crusts depending on the nature of formation. Physical and biological soil crusts are the most significant types of soil crusts in arid and semi-arid regions. Two types of the physical crust are structural and depositional. Natural events, such as raindrops and the drying process, are the primary causes of the formation of surface crust. The process involves the creation of hard, thin layers on the surface of the soil. The thickness of the surface crusts is typically between 1 mm and 5 cm. Many researches have described different theoretical mechanisms for the formation of surface crusts in soil and reported their effective role in controlling wind erosion. The formation of crust in soil involves multiple stages, and the reaction of the soil surface to raindrop energy is divided into two main parts, as it was demonstrated. The first part involves the splashing of soil particles by raindrops' impact. A layer with a thickness of approximately 0. 1 mm is produced in this instance. The second component is composed of fine soil particles that penetrate the soil pores with water and cause the formation of a layer that is 2 mm thick. According to a study, soil loss control is not affected by the crust cover beyond 30%. There is a linear relationship between soil loss and surface crust coverage, as the surface crust cover develops gradually, soil loss differs between soil types.
 

During field surveys of dust storm sources in Khuzestan, it was observed that there are surface crusts that are strong enough to act as a barrier against wind erosion in certain locations. The 
suggestion was made to investigate the type and general characteristics of these surface crusts. The purpose of this study is to examine the general characteristics of these surface crusts and their effect on wind erosion control. The study was conducted by randomly obtaining 18 surface crust samples, each containing three sub-samples from a depth of 0 to 5 cm from the dust storm sources of Khuzestan province. After being air dried, they were then passed through a sieve of 2 mm. The factors of pH, EC, CaCo3, CEC, ESP, Ca, Mg, Po3-4 texture, initial moisture, and apparent density of the surface crusts were measured. The soil's sensitivity to crust formation was assessed by using soil stability index, Crusting Index, pressure resistance, and shear resistance. The stability of soil aggregates was assessed using the mean weight diameter and geometric mean diameter indices. Soil samples were collected and tested in a wind tunnel to examine the impact of these surface crusts on wind erosion control and the amount of soil loss and the speed of wind erosion were assessed. An orbital wind tunnel device was utilized for this purpose. Trays with soil were placed on the bottom of the tunnel in this manner. After the wind blew (speeds of 15, 10, 25 m/s) by measuring the difference in the weight of the tray before and after the wind blowing, the amount of erosion was calculated from a certain surface. Then, the threshold speed for wind erosion was determined. Statistical analysis was carried out using SPSS 26 software. The Kolmogorov-Smirnov test was used to verify data normality. Then, the data sets were entered into a step-by-step regression as independent components to determine their relationship with the index of crust formation and stability of soil aggregates, as well as the effect of crusts and stability of soil aggregates on the amount of wind erosion. The accuracy of the regression models was verified by using RMSE, RSE, MAE, and R2 statistics. The morphology of the crusts was finally determined by using a scanning electron microscope.
 

The results showed that the lowest amount of RMSE, and RSE statistics, and the lowest absolute error for evaluating the sensitivity of soil to crust formation in the dust storm sources of East Ahvaz, Southeast Ahvaz and Omidieh, Mahshahr and Hendijan, respectively belong to the index of compressive strength, soil stability and shear resistance. The scanning electron microscope images taken of the crusts of three dust storm sources indicated that small foreign matter is present in the soil's pores. The features of the sedimentary crust are displayed in all the images. The external materials in the crust structure reflect the different washing processes in soil particles, which cause adhesion and connection between the soil particles and make the crusts resistant to wind erosion. Based on the given explanations, it is possible that the crusts found in Khuzestan's dust storm sources are usually sedimentary crusts. Results also showed that the wind erosion threshold speed in the dust storm sources of East Ahvaz, South East Ahvaz and the sources of Mahshahr, Omidiye and Hendijan are 1. 44, 1. 62 and 2. 1 time their powdered state, respectively. These sources experience a soil loss of 3. 55, 2. 09, and 3. 01 times the intact crusts, respectively.

Soil is considered one of the most valuable natural resources and the existence of life on the surface of the earth depends on the existence of soil in addition to water and air. Soil stability is an important factor in the health of the soil system and it is a prerequisite to perform processes such as the cycle of elements in the soil. Soil erosion is a serious problem and threat in different regions of the world, and therefore protecting and preventing soil erosion as a non-renewable natural resource is of high priority. To prevent soil erosion, there are various physical, mechanical, and chemical methods.  Due to their high cost and harmful effects on the environment, today much attention is paid to biological methods that are friendly to the environment. This study aimed to investigate the potential of urease producing bacteria on biological stabilization and prevention of soil erosion.

Soil samples were collected from the Bazoft area in Chaharmahal va Bakhtiari provinces and transported to the laboratory. The enrichment and selective method was used to screen urease producing bacteria in the urea agar base culture medium. The activity of the urease was investigated by the electrical conductivity method and three strains with the highest urease activity were selected and used in further steps. The selected strains were identified by molecular methods, colony PCR by using 14f and 1492r universal primers, and sequencing. The compressive and shear strength was estimated in inoculated soils after 14 days.  The wind erosion threshold velocity was measured in the wind tunnel. The soil loss was estimated at different wind speeds (17.3, 22.09, and 27/20 m/s) in the inoculated soils.

The urease-producing bacteria were identified by changing the color of the culture medium from yellow to pink. The results showed that the soils of this area have a high potential for urease producing bacteria. Three species were selected based on their urease activity and identified as Bacillus thuringiensis (RIFR-U3), Bacillus sp. (RIFR-U7), and Exiguobacterium sp. (RIFR-U10). The compressive and shear strength increased in soil inoculated with the selected bacteria compared to the control.  The highest compressive (1.56± 0.241 kg/cm2) and shear strength (2.066±0.18 kg/cm2) were detected in the soils inoculated with Bacillus sp. (RIFR-U7) and Exiguobacterium sp. (RIFR-U10) strains, respectively. The wind erosion threshold velocity was 12.19 m/s. The soil loss was less in the inoculated soils with bacteria compared to control and Bacillus sp. (RIFR-U7) had the highest efficiency in preventing soil loss.

The increased compressive and shear strength showed that these selected strains are moderate to good stabilizers for increasing compressive strength and very good for increasing shear strength. The wind tunnel results showed that Bacillus sp. (RIFR-U7) inoculated soil was more resistant to wind erosion compared to the other two strains and controls. In conclusion, it seems that different strains or a combination of them can be used based on what characteristic of the soil is to be improved or the purpose of resistance against which erosion.

The purpose of this research is to study the feasibility and method of using xanthan biopolymer as an alternative for oil mulch in controlling or mitigating soil wind erosion. Xanthan is a biodegradable biopolymer made of Polysaccharides which is produced by bacteria and is used as stabilizer. The ability of different concentrations of xanthan in reducing the erosion, was examined by wind tunnel tests at speed of 7 to 15 m/s. To do so, xanthan gum suspension was sprayed on the surface of sand samples collected from sandy hills of Segzi plain in Isfahan and samples resistance to wind erosion were tested by wind tunnel after being dried. The test results indicated that a resistant crust is formed on sample surface due to spraying xanthan biopolymer, so that 2 gr/m2 of this biopolymer can reduce erosion up to 98 percent compared to untreated sample. Application of xanthan doesn’t need any advanced equipment and it can be sprayed cold. Cost of mulching with oil mulch in March 2020 to March 2021 was estimated to be 13 times more than mulching with xanthan gum. According to environmental standards, this biopolymer is also safe for using on soil resources.

The present study investigated the effect of guar biopolymer on soil wind erosion. Assuming that Guar gum can control wind erosion, its ability to reduce soil wind erosion was examined by wind tunnel tests. Examined soil samples were gathered from sandy hills of Segzi plain, located in Isfahan Province. Then were prepared in plates with diameter of 23 cm treated with guar gum suspension so that 0.2, 0.4, 0.8, 1 and 1.2 gr of the biopolymer were scattered per square meter of sample surface. Wind tunnel tests were performed on samples at speed of 7 m/s to 15 m/s. The test results indicated that the resistant crust formed on soil surface due to spraying Guar suspension can highly increase soil resistance to wind erosion. 1.2 gr/m2 of Guar can reduce erosion up to 98 percent. Soil sieving analysis results pointed out that Guar gum causes enlargement of the soil aggregates and so in reduction of erosion and raise in threshold wind velocity from 7 to 10 m/s. Thus, using Guar gum can be considered as a suitable method for controlling soil wind erosion, after the field experiments.

 Due to the detrimental consequences of the application of stabilizers such as mulch and other protectives on the soil surface, including the wafting of bad smell, blackening of the ground, increasing thermal coefficient, warming of the whole area, and even destruction of plants and their unsustainability in nature, wide use of such stabilizers could not be considered as a useful solution to control wind erosion. Therefore, to solve the problem of sandstorms in Iran and get the desertschr('39') soil stabilized, this study proposes that deserts be coated with non-erodible materials (e.g., gravel, sandblasting, etc.)

Based on the purpose of this study, the effect of gravel cover with 30%, 50%, and 75% coverage on the sandblasting rate of MontazerQaem -TaleHamid desert was investigated using the wind tunnel. To investigate the effect of different gravel coatings on the sand particle transport rate, first, a sand sample was gathered from the Talle-Hamid area in Tabas, located 209 km off the Bafgh Railway, at 55/89 latitude and 32/93 longitude degrees, respectively, and the particle density of sand particles size was measured using standard ASTM D854-02. Its amount was found to be 2724 kg/m3. In the next stages, dry aggregation of sand particle size was first extracted from different parts of the MontazerQaem-Talle-Hamid track. According to the ASHTO T27 standard, at least 500 gr random fine sample particles should be collected from each site to sieve. Four samples were collected from sites that were 209, 213, 217, 222, and 222.7 km off Tabas. Having enumerated Standard-sized sieved particles, we used a vibrating machine to shake different particle diameters for at least 15 minutes. Furthermore, scales with a minimum accuracy of 0.01gr were used to weigh particles of different diameters. According to the standard of reconstitution for fine particles such as sand, the minimum sample size for sieving is 300gr, and the sample should be dried at 110 ° C in a three-stage oven. Then, these particleschr('39') transportation rate was measured at different wind speeds for uncovered gravel samples.

Initially, by increasing the wind speed from 1 m/s to 8 m/s, it was found that the particlechr('39')s creeping movement started at 6.9 m/s and its creeping speed was 6.9 m/s. The index sample was then placed in the wind tunnel for 5 minutes at different speeds of 9.9, 12.4, 17.2, and 22 m/s, and sand particle transportation was determined. It was also found that wind erosion increased by increasing wind speed polynomials. Subsequently, sands with 30-50% and 75% gravel cover were inserted into the wind tunnel for 5 minutes at wind speeds of 10.5, 15.7, and 22.9 m/s. Having determined the rate of wind erosion, we observed that the wind erosion rate decreased with an increasing percentage of gravel cover at a certain speed. We also found that the greatest effect on decreasing wind erosion rate occurred at wind speed 22.9 m/s, with the reduction percentage of erosion being 67.5%. The study results showed that the wind erosion rate decreased with an increasing rate of gravel cover at a certain speed, and the highest effect of graved on reducing wind erosion was reported for gravel cover of 75%. Therefore, covering the surface of a sandy desert with non-corrosive materials such as sand or gravel could be a practical solution for preventing wind erosion.

The effects of non-erodible coating or gravel on the rate of sand particle erosion were investigated via the wind tunnel, the results of which showed that the samples with gravel cover were effective in reducing wind erosion of sand particles. The greatest reduction in wind erosion rate was reported for the sites covered by 75% gravel. According to research conducted in the Chinese deserts, gravel cover with eroding sand particles and reducing wind velocity at the sand surface could well improve erosive sand levels. The present study also showed that at 22.9 m/s wind speed and 75% gravel cover, the erosion rate decreased by 67.5%. Therefore, to reduce the effects of sandstorms in Iran and stabilize the sandy desert area, non-erodible coating such as gravel would be recommended instead of mulch.

East of Isfahan City, especially around Segzi Plain is one of the desert areas of the country that due to the flatness and soils sensitivity to wind erosion, there is high susceptibility to wind erosion. The aim of this study is to evaluate the possibility of using saline water of Segzi Plain and its effect on the soil strength properties, crust formation and its stability against wind erosion. In order to conduct this research, five soil samples with different textures were collected from top soil surface and were transferred to the laboratory along obtained saline water sample from surface aquifer. After determining some of the physical and chemical properties of samples, they were examined in wind tunnel with specified velocity for soil erosion tests. The first soil sample was flooded with saline water and the rest were treated with either spraying of undiluted saline water or spraying of diluted saline water with 2 to 1, 1 to 1 and 1 to 2 ratios of saline water to water. In this regard, parameters such as salinity of saline water, erosion threshold velocity of dried treated soil samples, maximum dry density, thickness, strength and sieve analysis of the crusts were determined. The results indicated that, as the salinity of saline water increases, the strength, thickness and maximum dry density of forming crust and wind erosion threshold velocity also increases in the model. Analysis of variance used to investigate the effects of soil texture, salinity of saline water, crust thickness and threshold velocity to control wind erosion showed significant difference in 1% level. Sample C1 with the highest percentage of fine grains had threshold velocity of 11 m.s-1, but sampleE1 with the lowest percentage of fine grains had threshold velocity 6.23 m.s-1. The presence of a high amount of sodium makes restrictions on the possibility of using saline water as mulch scientifically and practically but the results showed that the use of saline water can increase the density of dirt roads.

Dust storm is a meteorological phenomenon which is common in arid and semi-arid regions. Dust storms are also one of the environmental concerns in Iran. There are different methods to control this phenomenon which some of them have limitations. Application of mulches is one of the ways to control and prevent dust storms. This study, aims to evaluate the behavior of biological, chemical and mineral mulches during one week in laboratory conditions and six months to stabilize the source of dust storm and improve the persistence of these mulches in Ilam Province. In order to study dust storm stabilization by these mulches, different tests were carried out including wind tunnel test, light and temperature stress effect on strength, pressure resistance, aggregate stability and soil loss. Wind erosion resistance determined in laboratory conditions by wind erosion simulation in 25 m s-1 for 15 minute of each treatment for both, one week and six months. According to the results, strength, pressure resistance, aggregate stability and wind tunnel simulation, three formulation of F4, F13 and F14 (zantan polymer-calcium carbonate, polyvinyl acetate-calcium carbonate and zantan-polyvinyl acetate) were recommended for stabilization of dust storm in Ilam Province. Generally, for soil stabilization suitable formulation based on climatic, soil physical and chemical properties are needed for each region.

Due to the drought in recent years and the need to increase the efficient use of water in agriculture, the abiotic windbreak appears to be more suitable than biotic. In order to investigate the effects of lattice brick patterns in protection of the windbreak on the back, an experimental study was carried out in a wind tunnel. For this purpose, five lattice brick patterns with different densities, with density of 100% for the control in a randomized complete block design with four replications were studied. The results revealed that with increasing porosity in the windbreaks, while reducing wind speed and keeping the area protected; flow lines become parallel and vortex currents are not observed. While with reduced porosity, the wind streamlines the flow and becomes turbulent and reduces protection in the desired area. Also, results showed that the construction of windbreaks with a height less than the height of the protection structures (like a greenhouse), especially in high-density windbreaks, not only protect against winds not retained, but also with the formation of more rapid and vortex flows behind the windbreaks, the damage increases. Thus, attention to create optimum density with the use of appropriate lattice patterns is important in establishing abiotic brick windbreaks.

most conventional methods use chemical polymers and petroleum products (particularly, in arid and semiarid zones) to stop dust storm which are considerably labor, cost and time consuming. Use of the chemical polymers have several drawbacks such as high price of chemicals and their potentially harmfulness to environment. Using bio polymers has received worldwide attention during the last two decades owing to their great potential as a soil additives to stabilize the soil. The results obtained from different types of biopolymers or biopolymer compositions implicitly represent them to be applicable for binding the soil particles at the surface of light soils. Application of biopolymer as a stabilizer has proved to be effective for prevention of dust storms by stabilizing soil structure. The objective of this study was to use and screen a series of biopolymers to quantify their effectiveness as dust stabilizer in the laboratory scale. In this study, 20 biopolymer stabilizers be used. In order to assess the influence of biopolymers upon topsoil stabilization, laboratory tests on unconfined compressive strength, wet aggrigate stability and erosion resistance of untreated and treated soil samples be performed. In laboratory the wind speed in the tunnel be gradually increased from 0 to 25.6 m/s during 15 minutes . The wind erosion, compressive strength and aggregate stability test results clearly indicated that S3, S4, S5, S6, S7, S8, S9, S10, S12, S14 specimens were useful to dust control, in the relatively arid and semiarid areas. The SEM image showed that when biopolymers were applied to soil, a part of them filled up the voids of soil, and other part stayed on the soil aggregates surface. The polyelectrolyte groups in its molecular structure had chemical reaction with positive ions of clay grain and create physicochemical bonds between molecules and soil aggregates with ionic, hydrogen, or Van der Waals bonds. Untreated sample hadn’t bonds between molecules and soil aggregate so, the compressive strength and aggregate stability were very weak in these samples.

Due to the difficult field operations in desert regions, in order to measure wind erosion, the use of devices with a high-performance, resistant to environmental conditions and need less maintenance is required. The main objective of this research was to design, manufacture, and evaluation of EDST (Eight Directional Sand Trap)", so that it could be used in areas exposed to wind erosion and sedimentation. The device is made of two parts including the sediment catch from the soil surface to a height of 60 cm and sediment holding tanks for the eight geographical directions. According to the obtained results, the catching efficiency of this sand trap varied in different examined wind speeds (1, 2, 3, 4 and 5 ms-1);so that the most efficiency was equal to 47.3% at 4 ms-1. In addition, the device efficiency in determining the direction of sediment transport increased by increasing tunnel’s wind speed and reached to the highest value (61.8%) at 5 ms-1. The comparison of cumulative curve of sediment grading inside the sand trap and sediment source in the wind tunnel showed that the device was selective to diameter, so that the trapping of particles whose diameter was more 1 mm was done with an efficiency of 86%. However, it was inefficient in tapping the particles smaller than 1 mm.

Wind erosion is one of the aspects of land degradation resulting in some problems especially for arid and semi-arid regions. Recognition of Sediment size Distribution (PSD) as well as transport mechanisms is important in modelling of wind erosion. In the present study، this topic was investigated on two soils taken from cropland and sand dune with different PSD، using wind tunnel. Results showed that compared to the original soil، the collected sediment had finer sizes، indicating a selective mechanism in transporting detachable particles. It was found that for cropland soil، increasing wind speed from 2 to 18 m/s at the height of 20 cm، the PSD of sediment approached to the original soil. This trend was reverse for sandy soil so that، for higher wind velocities، the frequency of fine particles was more than the original soil. The result of transport mechanisms indicated that compared to saltation as well as suspension، creeping was the least important mechanism. The contributing percentage of creeping for cropland and sandy soils was determined less than 10 and 1 %، respectively. For the cropland soil at wind speed of 2 m/s، suspension was the most important mechanism of transport and depends on soil''s PSD، 61. 1- 68. 5 % of particles were transported. Increasing wind speed up to 18 m/s، saltation with 50. 4- 53. 8 % was found as the main transport mechanism. Reversely، in the sandy soil at low wind speed، most of sediment (59. 3 %) was transported through saltation، whereas increasing the speed، suspension with 55. 3 % became the dominant mechanism. The finding of this study brings up the important of soil PSD on the PSD of sediment as well as transport mechanisms.