Three-dimensional discrete element flexible undrained loading method based on dynamic geometry

Abstract

The invention belongs to the technical field of three-dimensional discrete element loading, and aims to solve the technical problems that a hexagonal unit is mostly adopted in the current discrete element three-axis undrained loading and volume monitoring process, adjacent particle pointers need to be repeatedly read through id numbers, a large amount of vector operation is carried out, and the computing power is wasted. The invention provides a three-dimensional discrete element flexible undrained loading method based on dynamic geometry, and the method comprises the steps: simplifying a hexagonal basic unit in a conventional flexible film loading process into a simpler triangular unit through introducing a geometry unit; and in combination with the specific area and normal vector extraction advantages of the geometer poly unit, the load application and volume dynamic monitoring process in the non-drainage loading process of the flexible film is effectively simplified, and the related research of the discrete element three-dimensional flexible film is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional discrete element loading, and in particular relates to a three-dimensional discrete element flexible undrained loading method based on dynamic geometry. Background Art

[0002] The Discrete Element Method (DEM) is a numerical method used to simulate the mechanical behavior of granular materials. This method treats the material as consisting of a large number of discrete particles and simulates the macroscopic mechanical behavior of the material by calculating the interaction forces between the particles.

[0003] Triaxial testing is a commonly used experimental method in geotechnical engineering, used to determine the mechanical properties of soil under complex stress states. The test simulates the stress state of soil in actual engineering by applying confining pressure and axial stress. Under undrained loading conditions, the pore water pressure in the soil will change with the loading process, thereby affecting the effective stress and mechanical behavior of the soil. Undrained loading is often used to study the strength, deformation characteristics and liquefaction of saturated soils. Since the response of soil under undrained conditions is greatly affected by pore water pressure, it is necessary to precisely control the test conditions to obtain reliable results. Applying the discrete element method to triaxial undrained loading simulation can deeply study the micromechanical mechanism of granular materials and its influence on macroscopic mechanical behavior. Through DEM simulation, microscopic phenomena such as contact force between particles, changes in pore water pressure and particle rearrangement can be analyzed in detail, thereby revealing the mechanical response mechanism of soil under undrained conditions.

[0004] Discrete element triaxial undrained loading is mainly divided into rigid loading and flexible loading. Rigid undrained loading refers to the use of rigid boundaries (such as rigid walls) to apply confining pressure and axial stress in triaxial tests. The characteristic of a rigid boundary is that the boundary itself does not deform, and the shape of the boundary remains unchanged during loading. Flexible undrained loading refers to the use of flexible boundaries (such as rubber membranes) to apply confining pressure and axial stress in triaxial tests. The characteristic of a flexible boundary is that the boundary can deform as the soil deforms, which can better simulate the free deformation behavior of the soil in actual engineering.

[0005] However, satisfying undrained loading conditions for flexible membranes often requires a large number of particles, and real-time volume detection is required to update the confining pressure. Current discrete element triaxial undrained loading and volume monitoring processes often use hexagonal elements, which require repeated reading of adjacent particle pointers by ID number and perform numerous vector operations, resulting in a waste of computing power. Therefore, a simple and efficient method for loading and volume detection of three-dimensional flexible membranes is needed. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a three-dimensional discrete element flexible undrained loading method based on dynamic geometry. By simplifying the existing hexagonal basic units into triangular units and using the convenient centroid position and area query functions of geometrypoly, the process of constructing vector operations based on particle positions is greatly simplified.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A three-dimensional discrete element flexible undrained loading method based on dynamic geometry includes the following steps:

[0009] Step 1: Determine the initial size of the rock and soil standard sample; specifically, use a rigid wall to generate the initial rock and soil standard sample;

[0010] Step 2: Generate a rigid wall, then generate a standard geotechnical specimen in the rigid wall. Based on the rigid wall servo control technology, preload the standard geotechnical specimen, assign contact-related parameters, and then store the result file.

[0011] Step 3: Based on the result file of step 2, the rigid wall is deleted and the granular flexible membrane is generated by combining step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated. In order to meet the regular arrangement of particles and facilitate the retrieval of adjacent particles, the granular flexible membrane is generated layer by layer according to the standard sample size of the rock and soil mass and the geometric size formula between the granular flexible membranes.

[0012] Step 4: Generate a corresponding geometry network based on the particle flexible membrane. The particle flexible membrane and the geometry network are used together to apply flexible confining pressure to the standard rock and soil specimen, and the volume change of the standard rock and soil specimen is monitored. Since the particles in step 3 are arranged in a regular pattern, the corresponding ID number of each particle can be used to find the corresponding adjacent particles, and a geometry network is generated based on the particle position. The particle pointer corresponding to each triangular geometry poly unit is stored to facilitate real-time position update and call.

[0013] Step 5: Apply vertical loading to the standard geotechnical specimen, monitor the volume change of the standard geotechnical specimen, and dynamically adjust the pressure of the granular flexible membrane based on the volume change to achieve constant volume. Combined with step 4, the geometry network is adjusted in real time based on the particle position of the granular flexible membrane. Based on the particle pointer stored in step 4 for each geometry poly unit, the poly position can be updated to be consistent with the particle. By monitoring the sample volume in real time, the confining pressure value is modified according to the pore pressure growth formula caused by the volume increment to meet the requirement of constant volume during the loading process.

[0014] Preferably, in step 1, the initial dimensions include the height and cross-sectional diameter of the standard rock and soil sample.

[0015] Preferably, in step 2, the relevant parameters include pre-compression stress, contact type, elastic modulus and strength parameter.

[0016] Preferably, step 3 comprises the following steps:

[0017] Step 3.1: Based on the result file of step 2, delete the rigid wall and generate new loading walls at the top and bottom of the standard rock and soil specimen;

[0018] Step 3.2: Generate the granular flexible membrane by combining the initial size of the rock and soil standard sample in step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated.

[0019] Preferably, in step 3.2, the corresponding spatial coordinate formula of the particle flexible film to be generated is:

[0020]

[0021] Where H is the height of the standard sample of rock and soil, R is the cross-sectional radius of the standard sample of rock and soil, r is the radius of the granular flexible membrane, n h is the number of vertical layers of the granular flexible membrane, and N is the number of particles in each circle of the granular flexible membrane.

[0022] Preferably, step 4 comprises the following steps:

[0023] Step 4.1: Generate the corresponding geometry network based on the particle flexible membrane, and store the particle pointer corresponding to each geometrypoly unit in the geometry network in the corresponding geometrypoly unit;

[0024] Step 4.2: Load the standard rock and soil specimen with flexible confining pressure through the granular flexible membrane and geometry network;

[0025] Step 4.3: Based on step 4.2, monitor the volume change of the standard sample of rock and soil. The volume calculation formula of the standard sample of rock and soil is:

[0026]

[0027] Among them, S bottom is the area of ​​the newly loaded wall at the top and bottom of the standard rock and soil sample; h is the real-time height of the standard rock and soil sample; S ABC is the area of ​​infinitesimal triangle ABC, l oabc is the distance from the center of the standard rock and soil specimen to the infinitesimal triangle ABC.

[0028] Preferably, step 5 comprises the following steps:

[0029] Step 5.1: vertically load the standard sample of rock-soil, and monitor the volume change of the standard sample of rock-soil in real time;

[0030] Step 5.2: based on the monitored volume change of the standard sample of rock-soil, dynamically adjust the pressure of the particle flexible membrane, and then load the flexible confining pressure on the standard sample of rock-soil according to the method of step 4.2;

[0031] Step 5.3: every time interval, traverse all geometrypoly units, retrieve the current position of the corresponding particle on the particle flexible membrane according to the particle pointer stored in step 4.1, and update the position of the vertex of the geometrypoly unit in the geometry network.

[0032] Compared with the prior art, the present application has the beneficial effects that:

[0033] (1) Unlike the conventional rigid triaxial undrained loading method, the present application uses flexible membrane loading to better reflect the free deformation behavior of soil under real loading conditions;

[0034] (2) Unlike the hexagonal microelement in the existing flexible membrane loading technology, the present application uses triangular basic microelement, so that the unit is more fine and the description of the mechanical behavior of the flexible membrane is more accurate;

[0035] (3) The present application adds the design of geometry network, and due to the superiority of geometrypoly in calculating the centroid position and area, complex vector operation is omitted, the process of applying particle confining pressure and monitoring volume of the flexible membrane is greatly simplified, and the calculation efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Schematic diagram for generating particle triangular unit and relative position numbering;

[0037] Figure 2 Id number lookup method for corresponding particles around particles with different initial positions of the present application;

[0038] Figure 3 Principle diagram for monitoring the volume of the sample through poly triangular unit;

[0039] Figure 4 Schematic diagram for generating rigid wall sample;

[0040] Figure 5 Stress change diagram for the servo control preloading process of the rigid wall;

[0041] Figure 6 Schematic diagram of the flexible membrane particle sample;

[0042] Figure 7 Schematic diagram of the geometry network sample based on triangle micro-elements;

[0043] Figure 8 Schematic diagram of the force vector of the granular flexible membrane after the confining pressure is applied;

[0044] Figure 9 The geometry network and volume monitoring curve after loading is completed;

[0045] Figure 10 The particle morphology and stress-strain curve of the sample after loading is completed. DETAILED DESCRIPTION

[0046] The following is a diagram of the embodiment of the present invention. Figures 1 to 10 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0047] An embodiment of the present invention provides a three-dimensional discrete element flexible undrained loading method based on dynamic geometry, which specifically includes the following steps:

[0048] Step 1: Determine the initial size of the rock and soil standard sample; specifically, use a rigid wall to generate the initial rock and soil standard sample; the initial size includes the height and cross-sectional diameter of the rock and soil standard sample. In the embodiment of the present invention, the height of the rock and soil standard sample is 160mm, the cross-sectional radius is 40mm, the particle radius of the rock and soil standard sample is 1-2.5mm, the initial porosity is 0.34, and the generated rigid wall sample is as follows: Figure 4 As shown;

[0049] Step 2: Generate a rigid wall in the discrete element software PFC, and then generate a geotechnical standard sample in the rigid wall. Based on the rigid wall servo control technology, preload the geotechnical standard sample through the rigid wall, assign contact-related parameters, and then store the result file. Generally, in order to ensure the results of the key steps, the current state will be stored after the operation. The result file is a storage operation performed after the geotechnical standard sample is generated, and the result file is a .sav file that is convenient for calling the storage; the stress changes during the preloading process are as follows: Figure 5 As shown; related parameters include pre-compression stress, contact type, elastic modulus and strength parameters, and the specific settings are shown in Table 1 below. In the embodiment of the present invention, the initial pre-compression stress is set to 1KPa, and the vertical stress and horizontal stress change during the equilibrium process;

[0050] Table 1 Mechanical parameters of discrete element rock and soil samples

[0051]

[0052] Step 3: Based on the result file of Step 2, the rigid wall is deleted and the granular flexible membrane is generated by combining Step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated. To ensure the regular arrangement of particles and convenient retrieval of adjacent particles, the granular flexible membrane is generated layer by layer according to the standard specimen size of the rock and soil mass and the geometric size formula between the granular flexible membrane. To prevent the granular flexible membrane from breaking during the loading process, the contact bond strength of the flexible membrane is set to 1e300, and the contact stiffness is also determined according to the corresponding properties of the flexible membrane. The specific parameters are shown in Table 1 above.

[0053] In the embodiment of the present invention, step 3 specifically includes the following steps:

[0054] Step 3.1: Open the PFC software, retrieve the result file from step 2, delete the rigid wall using the wall delete command, and generate new loading walls at the top and bottom of the standard rock and soil specimen using the wall generate command.

[0055] Step 3.2: Generate a granular flexible membrane by combining the initial dimensions of the rock and soil standard sample from step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated. The initial dimensions of the rock and soil standard sample in this embodiment are: the height H and the cross-sectional radius R of the rock and soil standard sample. The parameters of the granular flexible membrane are: the radius r of the granular flexible membrane, the number N of particles per circle of the granular flexible membrane, the number n of vertical layers of the granular flexible membrane h .

[0056] According to the relationship between the cross-sectional perimeter of the particle flexible membrane and the radius of the membrane particle:

[0057] 2rN=2π(R+r)

[0058] Wherein, N is the number of particles in each circle of the granular flexible membrane, R is the cross-sectional radius of the standard specimen of the rock and soil mass, and r is the radius of the granular flexible membrane;

[0059] Arranging the above formula, the corresponding spatial coordinate formula of the particle flexible film to be generated is obtained as follows:

[0060]

[0061] Where H is the height of the standard sample of rock and soil, R is the cross-sectional radius of the standard sample of rock and soil, r is the radius of the granular flexible membrane, n h is the number of vertical layers of the granular flexible membrane, and N is the number of particles in each circle of the granular flexible membrane.

[0062] Combining the above formula with loop statements and ball create commands, the flexible film can be generated layer by layer. z Set to 200, and calculate n h is 100, r = 0.94 mm, and the flexible film sample is generated as Figure 6 shown.

[0063] Step 4: Generate a corresponding geometry network based on the particle flexible membrane. The particle flexible membrane and the geometry network are used together to apply flexible confining pressure to the standard rock and soil specimen, and the volume change of the standard rock and soil specimen is monitored. Since the particles in step 3 are arranged in a regular pattern, the corresponding ID number of each particle can be used to find the corresponding adjacent particles, and a geometry network is generated based on the particle position. The particle pointer corresponding to each triangular geometry poly unit is stored to facilitate real-time position update and call.

[0064] In the embodiment of the present invention, step 4 specifically includes the following steps:

[0065] Step 4.1: Generate the corresponding geometry network based on the particle flexible membrane. The core of this is to correctly find the ID number relationship between the particle and its adjacent particles, such as Figure 1 For ease of description, Figure 1 (1), (2), (3), (4), and (5) in the equation represent the relative positions of the particles to the initial particles. Taking particle E of the granular flexible membrane as an example, its corresponding two triangular geometry elements are EFG and EHI. It is worth mentioning that when the particles are located on both sides of the initial generated particles in each circle, such as particles F (left side of the dividing line) and J (right side of the dividing line), the retrieval formula for adjacent particles needs to be changed. The corresponding formula for the specific position is as follows: Figure 2 As shown. According to the ball.pos command, find the position of each particle of the triangular element, and generate the geometrypoly mesh corresponding to the triangular element according to the geometry.poly.create command. In order to facilitate subsequent position updates, the particle pointer corresponding to each geometrypoly unit in the geometry network is stored in the corresponding geometrypoly unit; according to the above content, the geometry network sample is generated as follows Figure 7 As shown;

[0066] Step 4.2: Use the granular flexible membrane and geometry network to load the standard rock and soil specimen with flexible confining pressure. Specifically, by traversing each triangular geometry element, the centroid coordinates and area of ​​the element can be quickly obtained through the geometry.poly command. If the confining pressure on the granular flexible membrane is P m, then the equivalent force on each microelement particle is (in Figure 1 Take triangle EFG in the figure as an example):

[0067]

[0068] Among them, P m is the confining pressure on the particle flexible membrane, F E is the equivalent force received by each microelement particle, S EFG is the area of ​​triangle EFG.

[0069] Apply an equivalent force to the membrane particles through the ball.appliedforce command. The force direction vector of each particle is as follows: Figure 8 As shown;

[0070] Step 4.3: Based on step 4.2, monitor the volume change of the standard sample of rock and soil. The volume calculation formula of the standard sample of rock and soil is:

[0071]

[0072] Among them, S bottom is the area of ​​the newly loaded wall at the top and bottom of the standard rock and soil sample; h is the real-time height of the standard rock and soil sample; S ABC is the area of ​​infinitesimal triangle ABC, l oabc It is the distance from the center of the standard rock and soil specimen to the infinitesimal triangle ABC, that is, the height corresponding to the base ABC in the infinitesimal tetrahedron ABCO.

[0073] like Figure 3 As shown, the total volume of the standard rock and soil sample can be obtained by calculating the volume of each micro-element tetrahedron (such as ABCO) plus the volume of the two central cones.

[0074] Assuming that the coordinates of a certain poly element are (x, y, z) and point O is located at the origin, the volume of the element tetrahedron can be calculated by the area of ​​geometrypoly and the coordinates of the centroid according to the following formula:

[0075]

[0076] Among them, (x, y, z) is the coordinate of a certain poly element, S ABC is the area of ​​infinitesimal triangle ABC.

[0077] The volumes of the two central cones are calculated using the following equations:

[0078]

[0079] Among them, V1 is the volume of the two central cones, S bottomS is the area of the new loading wall body on the top and bottom of the geotechnical standard sample; h is the real-time height of the geotechnical standard sample; S

[0080] The volume calculation formula of the total volume of the geotechnical standard sample is:

[0081]

[0082] Wherein, S bottom S is the area of the new loading wall body on the top and bottom of the geotechnical standard sample; h is the real-time height of the geotechnical standard sample; S ABC S is the area of the microelement triangle ABC, l oabc S is the distance from the center of the geotechnical standard sample to the microelement triangle ABC, that is, the height corresponding to the bottom surface ABC in the microelement quadrangular pyramid ABCO, (x, y, z) is the coordinates of a poly microelement, and n is the number of microelement quadrangular pyramids.

[0083] Step 5: vertically loading the geotechnical standard sample, monitoring the volume change of the geotechnical standard sample, dynamically adjusting the pressure of the particle flexible film according to the volume change of the geotechnical standard sample, so as to realize the constant volume, and combining step 4, adjusting the geometry network in real time according to the particle position of the particle flexible film. According to the particle pointer stored in each geometry poly unit in step 4, the position of the poly can be updated to be consistent with the particle. Through real-time monitoring of the sample volume, the pore pressure growth formula caused by the volume increment is used to correct the confining pressure value to meet the requirement of constant volume during loading;

[0084] In the embodiment of the application, step 5 specifically comprises the following steps:

[0085] Step 5.1: loading the geotechnical standard sample by applying a vertical velocity to the wall body, specifically when the loading speed of the upper and lower wall bodies is 1.6 mm / s, the quasi-static loading requirement of the model can be met. According to the experimental requirements, the loading is stopped when the vertical strain of the sample reaches 0.2. Then the volume change of the geotechnical standard sample is monitored in real time according to the method in step 4.3;

[0086] Step 5.2: dynamically adjusting the pressure of the particle flexible film based on the monitored volume change of the geotechnical standard sample, and then loading the flexible confining pressure of the geotechnical standard sample according to the method of step 4.2;

[0087] When the geotechnical standard sample is subjected to vertical loading, the pore water pressure is caused, and the pore water pressure can be calculated by the following formula:

[0088] ΔP=E w Δε

[0089] Wherein, ΔP is the pore water pressure, E wis the bulk modulus of water, and Δε is the monitored volume strain.

[0090] Due to the influence of pore water pressure, the boundary flexible membrane is subjected to non-equilibrium pore pressure. In order to offset this effect and ensure constant volume, the current flexible membrane confining pressure P n The calculation formula is:

[0091] P n =P m +ΔP

[0092] Among them, P m is the confining pressure on the particle flexible membrane, and ΔP is the pore water pressure.

[0093] According to the calculated current flexible membrane confining pressure P n , adjust the loaded confining pressure accordingly, reset the force on the flexible membrane to zero, and then load the flexible confining pressure on the standard rock and soil specimen according to the method in step 4.2.

[0094] Step 5.3: At every specified time step, traverse all geometry poly units, retrieve the current position of the corresponding particle on the particle flexible membrane according to the particle pointer stored in step 4.1, and adjust and update the position of the geometry poly unit vertex in the geometry network. The dynamic geometry mesh shape after cutting and the volume monitoring data during the cutting process are as follows: Figure 9 As shown. After shearing, the particle morphology and stress-strain curve of the sample are shown as follows. Figure 10 As shown, through Figure 9 and Figure 10 It can be seen that the three-dimensional discrete element flexible undrained loading method based on dynamic geometry proposed in the present invention has a good effect and can effectively control the volume to be constant during the loading process.

[0095] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A three-dimensional discrete element flexible undrained loading method based on dynamic geometry, characterized in that: The following steps are involved: Step 1: Determine the initial size of the standard sample of rock and soil; Step 2: Generate a rigid wall, then generate a standard geotechnical specimen in the rigid wall. Based on the rigid wall servo control technology, preload the standard geotechnical specimen, assign contact-related parameters, and then store the result file. Step 3: Based on the result file of step 2, the rigid wall is deleted, and the granular flexible membrane is generated by combining step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated; Step 4: Generate a corresponding geometry network based on the granular flexible membrane. Use the granular flexible membrane and the geometry network to load the standard rock and soil sample with flexible confining pressure, and monitor the volume change of the standard rock and soil sample. Step 5: Apply vertical loading to the standard rock and soil specimens, monitor the volume changes of the standard rock and soil specimens, dynamically adjust the pressure of the granular flexible membrane based on the volume changes of the standard rock and soil specimens, and combine with step 4 to adjust the geometry network in real time based on the particle positions of the granular flexible membrane.

2. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 1 is characterized in that: In step 1, the initial dimensions include the height and cross-sectional diameter of the standard rock and soil specimen.

3. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 1 is characterized in that: In step 2, the relevant parameters include pre-compression stress, contact type, elastic modulus and strength parameters.

4. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 1 is characterized in that: Step 3 includes the following steps: Step 3.1: Based on the result file of step 2, delete the rigid wall and generate new loading walls at the top and bottom of the standard rock and soil specimen; Step 3.2: Generate the granular flexible membrane by combining the initial size of the rock and soil standard sample in step 1 and the corresponding spatial coordinate formula of the granular flexible membrane to be generated.

5. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 4 is characterized in that: In step 3.2, the corresponding spatial coordinate formula of the particle flexible film to be generated is: Where H is the height of the standard sample of rock and soil, R is the cross-sectional radius of the standard sample of rock and soil, r is the radius of the granular flexible membrane, n h is the number of vertical layers of the granular flexible membrane, and N is the number of particles in each circle of the granular flexible membrane.

6. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 1 is characterized in that: Step 4 includes the following steps: Step 4.1: Generate the corresponding geometry network based on the particle flexible membrane, and store the particle pointer corresponding to each geometrypoly unit in the geometry network in the corresponding geometrypoly unit; Step 4.2: Load the standard rock and soil specimen with flexible confining pressure through the granular flexible membrane and geometry network; Step 4.3: Based on step 4.2, monitor the volume change of the standard sample of rock and soil. The volume calculation formula of the standard sample of rock and soil is: Among them, S bottom is the area of ​​the newly loaded wall at the top and bottom of the standard rock and soil sample; h is the real-time height of the standard rock and soil sample; S ABC is the area of ​​infinitesimal triangle ABC, l oabc is the distance from the center of the standard rock and soil specimen to the infinitesimal triangle ABC.

7. The three-dimensional discrete element flexible undrained loading method based on dynamic geometry according to claim 6 is characterized in that: Step 5 includes the following steps: Step 5.1: Apply vertical loading to the standard rock and soil specimens, and monitor the volume changes of the standard rock and soil specimens in real time; Step 5.2: Based on the monitored volume change of the rock and soil standard sample, dynamically adjust the pressure of the granular flexible membrane, and then load the rock and soil standard sample with flexible confining pressure according to the method in step 4.2; Step 5.3: At every specified time step, traverse all geometry poly units, retrieve the current position of the corresponding particle on the particle flexible membrane according to the particle pointer stored in step 4.1, and adjust and update the position of the geometry poly unit vertex in the geometry network.

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