A bed load stratification and partitioning simulation method for a mountain river fluidized bed physical model

Abstract

This invention proposes a method for simulating bed load stratification and zoning in a moving-bed physical model of a mountain river. The method includes: sampling the bottom sediment of the simulated river section, classifying the sediment types, and stratifying and zoning the bottom sediment distribution; calculating representative gradations for each type of sediment, classifying the sediment components, and calculating the proportions of each component; constructing a formula for calculating sediment similarity scales, calculating the particle size of model sand for each component, and preparing model sand for each type of sediment; constructing a physical model, laying pre-prepared model sand according to the sediment type in each layer, and conducting moving-bed tests for verification. This method achieves accurate simulation of bed load movement under complex bed conditions in mountain rivers, effectively solving the challenges of model sand selection, model sand laying, and accurate bed load simulation in moving-bed physical models, and enriching and developing moving-bed physical model design methods.

Description

Technical Field

[0001] The invention belongs to the field of mountain river hydrodynamic sediment simulation methods, and in particular relates to a mountain river fluidized bed physical model bed load stratification and partitioning simulation method. Background Art

[0002] Mountain rivers have rapid flows and steep slopes, resulting in large sediment particles on the bed surface, often dominated by bedload movement. Due to irregular bank boundaries, the river often alternates between shallow shoals and deep troughs, resulting in a complex and diverse distribution of bed sediments. Simulating bedload movement in moving-bed physical models often requires a single bed to accurately reflect the complex in-situ bed distribution, and setting a bed distribution identical to that found in the field is difficult to achieve in practice. Simulating bedload movement in moving-bed physical models with complex bed distributions remains a challenge in the study of water-sediment dynamics in mountainous rivers. Summary of the Invention

[0003] The present invention aims to solve the problems faced by traditional moving bed physical model design, such as the difficulty in selecting suitable model sand to simulate the movement of bed load and the complex bed distribution of mountain rivers, and provide a layered and zoned bed load simulation method for the moving bed physical model of mountain rivers. The purpose is to provide a scientific and effective method for simulating the movement law of bed load in the moving bed physical model of mountain rivers.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A bed load stratification and partitioning simulation method for a mountain river fluidized bed physical model, comprising:

[0006] Sediment samples were collected from the simulated river section, and the sediment types of the sampled bodies were classified according to the sediment particle size, and the sediment distribution was stratified and zoned;

[0007] Calculate the average gradation of each type of sediment as the representative gradation of the corresponding type of sediment, group the sediment particle size of each representative gradation, and calculate the proportion of each particle size component;

[0008] A sediment particle size scale is established based on the condition that sediment initiation is similar. The statistical proportion of each particle size component is divided by the sediment particle size scale to obtain the proportion of each particle size component of the model sand. Model sands of various types of sediment are prepared based on the proportion of each particle size component of the model sand.

[0009] A dynamic bed physical model of the simulated river section is constructed, and the prepared model sand is laid according to the sediment types in each layer and area.

[0010] To optimize the above technical solutions, specific measures taken also include:

[0011] Furthermore, the bottom sediment sampling of the simulated river section is specifically carried out as follows:

[0012] Arrange multiple sampling points along the center line of the riverbed surface;

[0013] Drilling exploration is carried out vertically on the riverbed, with the drilling point located on the center line of the river channel; the surface thickness is calculated based on the drilling sampling, and the deep layer below the surface is sampled once.

[0014] Furthermore, the classification of sediment types in the sampled body according to sediment particle size is specifically as follows:

[0015] The sampled bodies were sieved, and the gradation curves of each sampled body were drawn. The median particle size of each sampled body was obtained using the gradation curves. According to the median particle size, the sampled bodies were divided into three sediment types: deep trough type, shallow shoal type and coarsened type according to the sediment particle size standards of 0.1-1 mm, 1-10 mm and 10-70 mm.

[0016] Furthermore, the bottom sediment distribution is divided into layers and zones, specifically:

[0017] The riverbed is divided into two layers vertically: the upper layer is the surface layer, the thickness of which is determined according to the surface thickness of the drilling sampling statistics; the lower layer is the deep layer, the thickness of which is determined according to the maximum scouring and silting thickness;

[0018] For the surface layer, the surface layer was divided into zones according to the sediment type of each surface sampling body.

[0019] Furthermore, the average gradation of each type of sediment is calculated as the representative gradation of the corresponding type of sediment, and the calculation formula is as follows:

[0020] ;

[0021] in, for n The average gradation of the samples of the same sediment type represents the average gradation of the corresponding type of sediment; For the i The gradation of the sample body; n is the number of sampling bodies of the same sediment type, x is the sediment particle size, b To be infinitely close to x The convergence coefficient, 0.1mm <b<x<100mm;

[0022] The sediment particle size grouping for each representative gradation is to group the calculated representative gradations into particle size groups according to 0.1-1 mm, 1-5 mm, 5-20 mm and 20-70 mm.

[0023] Furthermore, the calculation formula of the sediment particle size ratio is:

[0024] ;

[0025] in, is the sediment particle size ratio, is the sediment bulk density ratio, is the dry bulk density ratio of sediment, is the vertical scale of the model.

[0026] Furthermore, the construction of the moving bed physical model of the simulated river section is specifically as follows:

[0027] Determine the model's horizontal scale based on the simulation scope and laboratory scale , combined with the model vertical scale , a moving bed physical model of the simulated river section was constructed, the model elevation error was within 1mm, and grooves were reserved in the model for laying model sand.

[0028] Furthermore, the model sand prepared according to the type of sediment in each layer and area is specifically:

[0029] The model sand is laid in two layers, the lower layer is laid first, and the lower layer is laid according to the sediment type of the deep sampling body during drilling exploration, and the laying thickness is greater than the maximum scouring and silting thickness; the upper layer is laid second, and the upper layer is laid according to the zoning of the surface layer, and the laying thickness is the surface thickness calculated by drilling sampling statistics.

[0030] Furthermore, after laying the prepared model sand, a moving bed test is conducted on the moving bed physical model of the simulated river section under typical annual flow conditions, specifically:

[0031] According to the flow similarity scale and scouring and silting time scale Release flow to verify the scouring and silting of the riverbed of the dynamic bed physical model of the simulated river section; is the vertical scale of the model, is the model horizontal scale, is the dry bulk density ratio of sediment, is the sediment bulk density ratio, is the sediment particle size ratio;

[0032] If the deviation of the total erosion and deposition of the entire river section in the model is within ±20%, the model validation is successful;

[0033] If the deviation of the total amount of scour and sedimentation in the entire river section of the model exceeds ±20%, the scour and sedimentation patterns will be compared with the prototype terrain: for areas where the scour amount in the model is greater than that of the prototype terrain, the model sand particle size will be increased; for areas where the sedimentation amount in the model is greater than that of the prototype terrain, the model sand particle size will be reduced.

[0034] The beneficial effects of the present invention are as follows: based on the on-site sediment distribution and particle size classification, the present invention divides the sediment into zones in the plane and layers in the vertical direction. Each layer uses the same representative gradation for generalized sand selection, and scouring and silting verification is performed, achieving accurate simulation of bedload movement. The present invention has undergone rigorous correlation demonstration and model testing verification, and the results are reliable. The present invention can be applied to the simulation of bedload movement in mountainous rivers, effectively solving the difficult problem of bedload movement simulation under complex sediment conditions in mountainous rivers, and enriching and developing the design methods of moving bed physical models. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 3 is a diagram showing the arrangement of sampling sections (points) for bottom sediment sampling in a simulated river section in the embodiment.

[0036] Figures 2a to 2d is a graph showing the gradation of sediment samples of various types in the embodiment; wherein, Figure 2a This is a deep trough sediment gradation curve. Figure 2b This is a shallow-type sediment gradation curve. Figure 2c is the coarsening sediment gradation curve. Figure 2d It is a sediment gradation curve diagram of geological survey sampling.

[0037] Figure 3 It is a graph of median particle size along the cross section in the embodiment.

[0038] Figure 4 1 is a generalized curve diagram of the prototype sand and sediment gradation in the embodiment.

[0039] Figure 5 2 is a graph showing the gradation curves of various types of model sands in the embodiments.

[0040] Figure 6 Schematic diagram of the layered and zoned laying of model sand in the embodiment.

[0041] Figures 7a to 7c The verification diagram of the scouring and silting amount of each shoal in the embodiment; Figure 7a This is the verification diagram of the sedimentation volume of each beach section. Figure 7b This is the verification diagram of the scour volume of each beach section. Figure 7c It is a verification diagram of the erosion and siltation volume of each beach section. DETAILED DESCRIPTION

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] This embodiment proposes a method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model, specifically comprising the following steps:

[0044] 1. Sediment sampling and classification.

[0045] Sediment sampling was conducted in the simulated river section. Sediment sampling was conducted on the riverbed surface, with sampling points arranged along the river centerline and no more than 500m apart. Each sample (i.e., the sample collected at each sampling point) weighed more than 5kg. A vertical borehole exploration was conducted in the riverbed, with at least one borehole set up in the study section, located along the river centerline, to a depth of more than 5m. The surface layer thickness was calculated based on the borehole exploration column, and a single sample was taken from the deep layer below the surface. The sample weight was more than 5kg.

[0046] All samples were screened, and the gradation curve of each sample was drawn. The median particle size D was obtained using the gradation curve. 50 According to the median particle size, the sampled bodies were divided into three types of sediment: deep trough type, shallow shoal type, and coarsened type according to the standards of 0.1-1 mm, 1-10 mm, and 10-70 mm.

[0047] For the surface area of the riverbed, the surface riverbed is divided into zones according to the sediment types of each surface sampling body; the vertical area of the riverbed is divided into two layers, the upper layer is the surface layer, the thickness of which is determined according to the surface thickness calculated by drilling sampling statistics, and the lower layer is the deep layer, the thickness of which is determined according to the maximum scouring and silting thickness.

[0048] 2. Calculate the representative gradation and the proportion of each component.

[0049] For the same type of sediment, calculate the average value of its sediment gradation as the representative gradation of this type of sediment. The formula for calculating the average sediment gradation is:

[0050] ;

[0051] in, for n The average gradation of the samples of the same sediment type represents the average gradation of the corresponding type of sediment; For the i The gradation of the sample body, i Number each sampling point; n is the number of sampling bodies of the same sediment type, x is the sediment particle size (mm), b To be infinitely close to x The convergence coefficient, 0.1mm <b<x<100mm。

[0052] For the representative gradations of the three types of sediment, in order to facilitate the preparation of model sand and cover the composition characteristics of each type of sediment gradation, the three representative gradations are grouped into particle sizes of 0.1~1mm, 1~5mm, 5~20mm, and 20~70mm, and the proportion of each particle size component is calculated as the basis for selecting model sand.

[0053] 3. Establish a sediment similarity scale calculation formula and model for sediment selection.

[0054] Based on the condition of similar sediment initiation, the sediment particle size ratio is derived. :

[0055] ;

[0056] in, is the sediment bulk density ratio, is the dry bulk density ratio of sediment, The vertical scale of the physical model is determined based on the minimum water depth condition of the physical model. .

[0057] The sediment particle sizes of each particle size component of the model sand are calculated based on the sediment particle size scale. 、 、 、 , based on the proportion of each particle size component of the model sand being consistent with that of the prototype sand, model sand of various types of sediment is prepared.

[0058] 4. Model sand laying and verification test.

[0059] Determine the model's horizontal scale based on the simulation scope and laboratory scale , combined with the vertical scale of the model determined above A physical model of the simulated riverbed was constructed, with elevation errors controlled within 1mm. The model had recesses for laying model sand, which was laid in two layers: a lower layer based on the sediment types found at deep geological survey sampling points, and an upper layer based on the sediment zoning patterns at surface sampling points. The lower layer was laid first, with a thickness greater than the maximum scour and sedimentation depth of the riverbed; the upper layer was then laid, with a thickness equal to the surface cover layer.

[0060] After the model sand is laid, a moving bed test is carried out under typical annual flow conditions. and scouring and silting time scale Release flow to verify riverbed scouring and sedimentation. If the planar morphology, thickness, and evolution of the dynamic bed model and the prototype terrain scouring and sedimentation areas are essentially similar, and the deviation of the total scouring and sedimentation in the entire river section is within ±20%, the model is successfully verified and can be used to simulate bedload movement under different operating conditions. If the deviation of the total scouring and sedimentation in the entire river section exceeds ±20%, it is necessary to compare the scouring and sedimentation morphology with the prototype terrain and fine-tune the model sand particle size in certain areas. In areas of the dynamic bed with significant scouring, the model sand particle size in these areas should be appropriately increased; in areas of the dynamic bed with significant sedimentation, the model sand particle size in these areas should be appropriately reduced.

[0061] Next, the preparation and laying of model sand for the design of the moving bed of the physical model of the Dongjiang Likou-Binglangtan section will be taken as an example, and this embodiment will be explained in conjunction with the accompanying drawings and specific implementation inferences.

[0062] The Dongjiang River, one of the three main streams of China's Pearl River system, is 138 km long. Its upper reaches feature a rocky, pebble-filled riverbed, but the flow slows to a sandy bed in the plains of the middle and lower reaches. The riverbed is variable in width, with continuous sandy shoals. The Likou-Binglangtan section studied in this case study is located at the junction of the upper and middle reaches of the Dongjiang River. It stretches 16.2 km and encompasses four shoals: the Menghutiaoqiang Shoal, the Guanyin Pavilion Shoal, the Lanpai Shoal, and the Hengling Shoal. The bedload can reach 180,000 tons annually, and the bottom sediments are complex and diverse. Traditional single-use sediment selection methods are difficult to simulate the actual dynamic bed morphology. Considering the research scope and laboratory conditions, a model horizontal scale of 120 was selected, the minimum water depth of the comprehensive model was greater than 3 cm, and the model vertical scale was selected as 50. The method used in this example simulates and lays out the complex bottom sediments of the study section, including the following steps:

[0063] (1) Sediment sampling and classification.

[0064] In the horizontal direction, riverbed samples were collected along the center line of the waterway in the Likou-Binglangtan section, with a sampling section set up every 500m, for a total of 23 sampling sections, and sediment samples were collected on the center line of the waterway in each section. In the vertical direction, drilling surveys were carried out at the Menghutiaoqiang Shoal, Guanyin Pavilion Shoal, Lanpai Shoal and Hengling Shoal, with one survey point at each shoal. The drilling point is located at the center line of the river channel, and the drilling depth is greater than 5m. Based on the statistical surface thickness of the drilling exploration column, samples are taken from deep layers below the surface. The sampling sections (points) are arranged as follows: Figure 1 shown.

[0065] All samples were screened, and the gradation curve of each sample was drawn. The median particle size D was obtained using the gradation curve. 50 According to the median particle size, the sample body is divided into three types of sediment: deep trough type, shallow shoal type, and coarse type according to the standards of 0.1~1mm, 1~10mm, and 10~70mm. The grading curves and classifications of each sampled sediment are as follows: Figures 2a to 2d shown.

[0066] Draw a chart showing the variation of the median particle size along the channel center. The channel is divided into 19 areas in the horizontal direction. The variation of the median particle size along the cross section is shown in the figure below. Figure 3 At the same time, through the analysis of drilling survey data, it was found that the bottom of the shallow riverbed below 1.5 m in the vertical direction is mainly coarse sand (D 50 =1-10mm), which is generally close to the shoal-type sediment gradation. Therefore, the bottom layer of the physical model moving bed should be paved with model sand that simulates the shoal type, and the paving range should be below 1.5 m of the riverbed (i.e., the model depth is below 3 cm).

[0067] (2) Calculate the representative gradation and the proportion of each component.

[0068] According to the formula (0.1 mm < b < x < 100 mm), construct a mathematical generalization model of sediment gradation, generalize the sediment gradation of various types, and through the generalization process, obtain three sediment gradation curves representing the average gradation composition of three types of sediment. The generalized curve of the prototype sediment gradation is as Figure 4 shown.

[0069] According to Figure 4 the generalized curve diagrams of the sediment gradations of the three types shown, in order to facilitate the preparation of the model sand and cover the characteristics of the sediment gradation compositions of various types, divide the three representative gradations into particle size groups according to 0.1 - 1 mm, 1 - 5 mm, 5 - 20 mm, and 20 - 70 mm respectively, and calculate the proportion of each particle size component as the basis for selecting the model sand. The content proportions of each component are shown in Table 1.

[0070] Table 1 Proportion of each component of the prototype sand

[0071]

[0072] (3) Establish the calculation formula for the sediment similarity scale and select the sand for the model.

[0073] In this example, the horizontal scale of the physical model of the research river section is , and the vertical scale is . The model sand is selected as Shanxi anthracite washed clean coal with a specific gravity of about 1.45, then there are:

[0074] Sediment bulk density scale: ;

[0075] Sediment dry bulk density scale: ;

[0076] Sediment particle size scale: ;

[0077] Among them, is the measured sediment bulk density; is the bulk density of the model sand; is the sediment bulk density scale; is the measured sediment dry bulk density; is the dry bulk density of the model sand; is the sediment dry bulk density scale; is the vertical scale of the physical model. Determine the vertical scale according to the minimum water depth condition of the physical model; in order to prevent the model sand from being too fine and compacted, select pulverized coal with a light bulk density and large particles as the model sand, so as to determine the sediment bulk density scale and the sediment dry bulk density scale .

[0078] According to the sediment particle size ratio calculated above, the four segments corresponding to the model sand are: 0.015-0.15 mm, 0.15-1 mm, 1-3 mm, and 3-10 mm. The proportion of each component should be consistent with that of the prototype sand, as shown in Table 2.

[0079] Table 2 Model sand preparation

[0080]

[0081] At the same time, the sediment gradation diagram of the model sand can also be made, such as Figure 5 According to this composition ratio, model sands similar to various types of prototype sands can be prepared.

[0082] (4) Model sand laying and verification test.

[0083] The horizontal scale of the model is determined according to the simulation scope and laboratory scale. Combined with the vertical scale of the model determined above, a dynamic bed physical model of the study river section is constructed, and the model elevation error is controlled within 1mm. The model is equipped with grooves for laying model sand. According to the on-site sampling situation, the laying of model sand is divided into two layers, upper and lower. According to the vertical sampling results, the bottom sediment gradation below 1.5 m of the riverbed is similar to the shoal type gradation, so the bottom layer of the model is paved with model sand A that simulates the shoal layer gradation and is laid to 3 cm below the riverbed elevation. The upper layer of model sand is based on Figure 3 The plane sampling results are laid to the riverbed bottom elevation. The schematic diagram of the model sand layering and partitioning is as follows Figure 6 shown.

[0084] After the model sand was laid, the verification of sediment scouring and deposition was carried out from September 9, 2015 to August 8, 2017. The verification period was 23 months, including two medium flood processes, which can reflect the changes in scouring and deposition in this river section. During this period, 2016 was a major flood with an average flow of 1056m 3 / s, the maximum flow rate reaches 3620m 3 / s. According to the traffic similarity scale and scouring and silting time scale The simulation of the discharge and erosion and sedimentation in the river section is as follows: Figures 7a to 7c As shown in the figure, the planar morphology, thickness and change process of the dynamic bed model and the prototype terrain scouring and silting parts are basically similar, and the deviation of the total amount of scouring and silting in the entire river section is within ±20%, and the model verification is successful.

[0085] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A bed load stratification and partitioning simulation method for a mountain river fluidized bed physical model, characterized in that: include: Sediment samples were collected from the simulated river section, and the sediment types of the sampled bodies were classified according to the sediment particle size, and the sediment distribution was stratified and zoned; Calculate the average gradation of each type of sediment as the representative gradation of the corresponding type of sediment, group the sediment particle size of each representative gradation, and calculate the proportion of each particle size component; A sediment particle size scale is established based on the condition that sediment initiation is similar. The statistical proportion of each particle size component is divided by the sediment particle size scale to obtain the proportion of each particle size component of the model sand. Model sands of various types of sediment are prepared based on the proportion of each particle size component of the model sand. A dynamic bed physical model of the simulated river section is constructed, and the prepared model sand is laid according to the sediment types in each layer and area.

2. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 1, characterized in that: The bottom sediment sampling of the simulated river section is specifically as follows: Arrange multiple sampling points along the center line of the riverbed surface; Drilling exploration is carried out vertically on the riverbed, with the drilling point located on the center line of the river channel; the surface thickness is calculated based on the drilling sampling, and the deep layer below the surface is sampled once.

3. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 2, characterized in that: The classification of sediment types in the sample body according to sediment particle size is specifically as follows: The sampled bodies were sieved, and the gradation curves of each sampled body were drawn. The median particle size of each sampled body was obtained using the gradation curves. According to the median particle size, the sampled bodies were divided into three sediment types: deep trough type, shallow shoal type and coarsened type according to the sediment particle size standards of 0.1-1 mm, 1-10 mm and 10-70 mm.

4. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 3, characterized in that: The substrate distribution is divided into layers and zones, specifically: The riverbed is divided into two layers vertically: the upper layer is the surface layer, the thickness of which is determined according to the surface thickness of the drilling sampling statistics; the lower layer is the deep layer, the thickness of which is determined according to the maximum scouring and silting thickness; For the surface layer, the surface layer was divided into zones according to the sediment type of each surface sampling body.

5. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 1, characterized in that: The average gradation of each type of sediment is calculated as the representative gradation of the corresponding type of sediment, and the calculation formula is as follows: ； in, for n The average gradation of the samples of the same sediment type represents the average gradation of the corresponding type of sediment; For the i The gradation of the sample body; n is the number of sampling bodies of the same sediment type, x is the sediment particle size, b To be infinitely close to x The convergence coefficient, 0.1mm <b<x<100mm; The sediment particle size grouping for each representative gradation is to group the calculated representative gradations into particle size groups according to 0.1-1 mm, 1-5 mm, 5-20 mm and 20-70 mm respectively.

6. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 1, characterized in that: The calculation formula of the sediment particle size ratio is: ； in, is the sediment particle size ratio, is the sediment bulk density ratio, is the dry bulk density ratio of sediment, is the vertical scale of the model.

7. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 1, characterized in that: The construction of the moving bed physical model of the simulated river section is specifically as follows: Determine the model's horizontal scale based on the simulation scope and laboratory scale , combined with the model vertical scale , a moving bed physical model of the simulated river section was constructed, the model elevation error was within 1mm, and grooves were reserved in the model for laying model sand.

8. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 4, characterized in that: The model sand prepared according to the type of sediment in each layer and area is specifically: The model sand is laid in two layers, the lower layer is laid first, and the lower layer is laid according to the sediment type of the deep sampling body during drilling exploration, and the laying thickness is greater than the maximum scouring and silting thickness; the upper layer is laid second, and the upper layer is laid according to the zoning of the surface layer, and the laying thickness is the surface thickness calculated by drilling sampling statistics.

9. The method for simulating bed load stratification and partitioning in a mountain river fluidized bed physical model according to claim 1, characterized in that: After laying the prepared model sand, a moving bed test is conducted on the moving bed physical model of the simulated river section under typical annual flow conditions, specifically: According to the flow similarity scale and scouring and silting time scale Release flow to verify the scouring and silting of the riverbed of the dynamic bed physical model of the simulated river section; is the vertical scale of the model, is the model horizontal scale, is the dry bulk density ratio of sediment, is the sediment bulk density ratio, is the sediment particle size ratio; If the deviation of the total erosion and deposition of the entire river section in the model is within ±20%, the model validation is successful; If the deviation of the total amount of scour and sedimentation in the entire river section of the model exceeds ±20%, the scour and sedimentation patterns will be compared with the prototype terrain: for areas where the scour amount in the model is greater than that of the prototype terrain, the model sand particle size will be increased; for areas where the sedimentation amount in the model is greater than that of the prototype terrain, the model sand particle size will be reduced.

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