Research on 3D Simulation Design and Dynamic Virtual Display of Clothing Flexible Body

4 Garment industry design development problems and visualization mapping analysis software as a tool 5 to analyze the status of domestic and foreign research, followed by the current situation of the front-end 6 and back-end rapid response of the garment industry, the research problem of this topic, through the 7 garment design modeling (fabric physical model and design, human body and fabric collision detection 8 analysis, garment fabric rendering and flexible body 3D garment simulation model) and garment 9 dynamic virtual display Research to build an effective solution to the problem. It is found that the real 10 effect of garment fabric can be truly restored in the design stage, and the development speed can be 11 improved and the labor cost can be reduced, while the cost waste problem of proofing materials can be 12 solved by using dynamic simulation display, and the selection rate and design level of products . 13


Introduction
Clothing is a very important item in people's life, clothing, food, housing and transportation ranked first.China has the world's most complete apparel industry chain foundation, from planning, design, sampling, production, logistics and sales links, all with advanced level.However, most of the enterprises are serving international brands, and also do OEM services for some domestic brands, lacking the ability to actively give brand services to customers, while the design development sampling time of enterprises is at least about 10-15 days, which leads to a long time for the whole product line, and the efficiency of rapid response is very low.With the development of digital technology and the addition of artificial intelligence, the traditional apparel design method has failed to meet the needs of rapid response development of enterprises, and needs to break this restriction to digitally open up the content of rapid apparel design and virtual display of products.This paper starts from the problems that appear in the design and development of the apparel industry, extends to the status quo of the front-end and back-end rapid response of the apparel industry, and elaborates on two aspects of apparel design modeling and dynamic virtual display, such as apparel 3D flexible design, real-fabric restoration, 3D model modeling and flexible virtual dynamic display, which can intuitively show the dynamic display of apparel products, fabric feeling and samples, and can solve the efficiency of the design stage low efficiency, high cost and long time in the design stage, and indirectly improve the digital design level of enterprises.

Design development issues in the apparel industry and subsequent display, selection and production links
After the reform and opening up, a large amount of information from foreign garment design flowed into the country, and through the integration and development of the domestic industry, a The researchers obtained the domestic research situation by searching the CNKI database.Specifically, as shown in Figure 4 and Figure 5, 22 valid literatures were obtained by using the 3D simulation design of clothing as the key word.After using the VOSviewer to analyze, as shown in Figure 4, it can be found that several bright spots are the areas with the closest relationship between the key words, among which the 3D model of clothing, 3D model technology, and personalized design element database are the most relevant to this topic, It can be found that China pays attention to the research of modularization in the theme of 3D simulation design of clothing, especially the details and aesthetics.Figure 5 shows the visual retrieval analysis with the key word of dynamic virtual display of clothing.We can see that there are many relationship points with virtual display as the core, among which virtual reality, style design and virtual exhibition are related to this topic.It can be found that there are few dynamic virtual displays related to clothing, and the related areas are all on the branch line.Through the analysis of the research status quo at home and abroad by the visual analysis software, we can know that although some scholars at home and abroad have made some research on 3D simulation design and dynamic virtual display, most of them prefer technical models, detailed research and more elaborate specific 3D simulation design and dynamic virtual display content from the clothing ontology with less images, and have not found any impact on the clothing design content.Therefore, the research of this topic will provide a new method and new idea for clothing design, reduce the cost and development time investment, and the impact on the clothing industry is a research of great value.

Research Questions and Objects
The status quo of rapid response in the front and rear of the clothing industry Since the 1980s, the garment industry has experienced nearly half a century of development, forming a more professional and complete chain at the front and back ends.Based on the current development of digital technology and artificial intelligence, researchers analyze from the following two aspects: ① With the development of digital technology, the chain of front end and back end of clothing has changed.For example, in the front end of clothing, some digital software, such as 3DCLO, Marvelous Design and other design software with great design space, have been used to improve the design quality.However, it is just a simple design, not related to the selection of accessories in front, ordering, production and sales in the rear, At the same time, the purchase price of this digital design software (different from traditional Photoshop, AI, CorelDRAW) is relatively high.Most of the large brands that can afford to buy it are large brands, and small and medium-sized brands (enterprises) will not invest so much money to buy it.Therefore, we can think of the changes in the design stage.It is still small.Most enterprises still have traditional design models, such as design, proofing, ordering, etc.This also leads to the loss of the ability and opportunities for small and medium-sized brands to provide active services to large customers (providing innovative design products, digital design and other content), and they will be eliminated in a long time.
② At present, most domestic clothing brands still use the on-site ordering mode to provide the proofing products for key customers to choose in the form of exhibition.This mode is limited by many factors, and the selection rate of products is very low, leading to the waste of proofing products, which increases the development cost and also prolongs the time for the entire product development.If the order mode is not improved, the development of the enterprise will be subject to many restrictions.
Therefore, the design mode and ordering mode adopted by most domestic brands at the design stage can not adapt to the development of the digital technology era, and can not change the traditional design and ordering methods in a new way, then the result will be worse.This is also the research problem of this paper.

How to Solve the Problems of Traditional Fashion Design Method and Order Mode
Based on the previous analysis of relevant literature and clothing industry content, the researchers will solve the problem that the traditional clothing design methods and ordering mode cannot adapt to the development of the digital era from two directions.The details are as follows: ① Fashion 3D simulation design and modeling.Different from the traditional fashion design mode, the researchers make the effect of clothing products present the simulation content in the design stage, including the rendering of fabrics and human bodies, tend to be real.The specific contents include obtaining physiological parameters of clothing body, style detail design, physical model and design of fabric, collision detection and analysis of human body and fabric, clothing fabric rendering and 3D simulation model of clothing, etc.The key step in the whole content is the effect simulation of fabric physical model, which relates to the real style and characteristics of surface rendering.
② Dynamic virtual display of clothing.The research of this content is mainly to provide customers with electronic clothing dynamic display, and place it in different environments.At the same time, based on the 3D simulation effect of the front clothing, we strive to achieve the most real clothing dynamic and scene simulation, which can be directly sent to customers in the form of online conference or email for selection, directly omitting the ordering process of clothing development, saving the cost of sample clothing and reducing the time cost.This section uses geometric modeling algorithm to build a three-dimensional clothing dynamic virtual display model.

Methods
In this topic, the clothing flexible body refers to the 3D model of the simulated clothing, which has the texture and visual sense of the real clothing, and requires a variety of algorithms, models and.Therefore, this section will analyze from two directions: fashion design and modeling, and dynamic virtual display research.

Fashion Design and Modeling
Fashion design and modeling is the first and most basic step in this research.The key to this step is to integrate the four contents of human modeling data acquisition -clothing module databasefabric and human body collision test, fabric rendering simulation.Specifically, as shown in Figure 6, clothing design and modeling includes five processes: human body modeling (feature point extraction), clothing module database, human body and fabric collision detection and analysis, fabric physical model and rendering, and flexible clothing 3D simulation model.Among them, human body and fabric collision detection and analysis, fabric physical model and rendering use physical fabric model algorithm for simulation, and related contents will be described later.In order to enhance the accuracy and order of this research, the researcher takes the women's dress as the design subject, connecting the following process analysis, and will also more clearly express the content related to design modeling dynamic display.

Body Modeling and Clothing Module Database
Human modeling is the basis of garment simulation model, without the acquisition of human physiological feature points, it can not accurately establish the human parameter model.Human modeling is to form a virtual 3D model of a real human body through parameterization.At present, there are many methods to obtain the 3D model of a human body.The common methods are: the first is to capture the visual points of a human body from multiple angles with high-definition cameras in a closed space, obtain the spatial point cloud coordinates of the human body through image processing technology, and then use the splicing algorithm to form a human model, This requires high quality of environment and camera, as shown in Figure 7; The second is to use Kinect photosensitive capture camera equipment to convert scanned images into body size data using data cleaning and compression technology, and use multiple algorithms such as ray casting algorithm to obtain the coordinates of spatial point cloud, and finally build a human model (Izadi S et al.,20121;Gao Liwei et al.,2018) as shown in Figure 8; The third method is to establish a point cloud model by acquiring data of multiple human parts, and at the same time, compare it with the existing human model database, and select a closer human model for fine-tuning reconstruction, as shown in Figure 9.At present, the three methods are the best and have the highest utilization rate.In enterprises, the first and second methods are commonly used, and the third method is mostly used for college research.However, some problems have also been encountered.From this topic, the researchers believe that integrating the second and third methods to extract and model human body data is the best method with high accuracy, and can fine tune relevant data in the later stage.Specifically, (Mao Tianlu&Wang Zhaoqi, 2005)use the ray cast by the non-contact three-dimensional scanning equipment (photosensitive capture equipment) to the human body, use the sensor to receive the reflected ray, use the photoelectric conversion element to obtain the digital signal, and then use the image processing technology to obtain the spatial point cloud coordinates, which are converted into human body size data; According to the 24 physiological parameters of the human body obtained, different human skeleton models are constructed using the SMPL model, as shown in Figure 10.Human body shapes and features can be divided into different categories and sizes to achieve personalized and accurate customization (Loper, M et al.,2015).) , ), ,Through the algorithm model training of attitude parameters W, J, P in multi pose dataset, shape parameter S , T The multi shape dataset algorithm model is trained in many aspects, and the parameters and nodes will be optimized finally to meet the application needs most suitable for the subject research.At the same time, different human models can be formed according to different shapes and postures to meet the needs of personalized customization.
After the manikin is determined, the clothing module database can be used for a certain degree of combination design from the database, including fabric library, body library, accessories library, printing and embroidery library and parts (styles) library, as shown in Figure 12.At the same time, the content of the module database can be edited and adjusted.For the clothing modules attached to the manikin, secondary design (combination) can be carried out according to the needs of researchers.

Physical Model and Design of Fabric
Fabric simulation is an important step in the process of 3D flexible simulation of clothing.It is also the attempt and preparation of the subsequent flexible simulation model.At present, there are three methods for fabric simulation model: physical method, geometric method and hybrid method.The most commonly used, simplest and most valuable method is physical method.It takes a long time to calculate the speed and position of particles by analyzing the force of particles in the model, but the results are real.The most commonly used physical model is the spring mass model, which is simple, effective and easy to implement.The particle represents the movement track of the unit, and finally forms the movement deformation route (shape) of the fabric.There are several types of specific spring particle models: a. tensile spring, b. square grid, c. shear spring, d Bending spring, the four spring mass models have different characteristics, which are used in physical modeling.These spring mass models form the internal power of the fabric mechanical system, and are also the cause of minor changes in the fabric, such as fabric stretching, shaking and wrinkles.
In the process of spring mass model simulation, the fabric is separated into many mass points, and the mass points are connected by many small springs.The model needs to calculate their tension and bending coefficients, and reasonably distribute the mass points.Therefore, before calculating the physical model of the spring mass point, it is necessary to add physical data information to the model, which is the basis for the movement, force and structural bending deformation of the spring mass point, According to the relevant physical information of fabric stress, the researchers put forward the associated parameters table of fabric simulation physical model, as shown in Table 1.The whole table will be divided into three parts: internal factors, external factors and other parameters, which are closely related to the four spring mass models, and clearly understand that they play a decisive role in the simulation fabric of the spring mass model.   1 are applicable to ordinary fabrics.If special fabric effects, shapes or materials are involved, the parameters in the table will change accordingly.
Therefore, to build a spring mass model (physical model of fabric), first of all, we need to build a mechanical system.Generally, the movement process of the mass is in accordance with Newton's second mechanical law (Xiang Yu, 2012), and the formula is： The cloth is mainly affected by gravity, wind, collision force and the performance of the fabric itself.These factors affect the calculation rate of the spring particle model, which is constantly changed in the process.Then, the velocity and position of the next particle of the cloth are calculated through Newton's second law of mechanics, where m represents the weight of the particle, f G represents that only gravity is considered in this topic, f in represents the total internal force of the particle, and y represents the current position of the spring particle (Xiang Yu, 2012).
The particle is affected by wind, gravity and particle coordinates, quantity and position.The researchers calculate the deformation force of the particle spring by using Hooke's law (Zilch. 2021).The formula is: ∆ χ is the expansion and contraction of the mass spring The mass will consume energy in the process of moving or moving, and the spring mass will vibrate in the process of consumption, affecting the running track, so damping force is required to simulate and eliminate such vibration [9], the formula is: C d is the damping parameter, υ Is the motion direction of the mass spring Through the above analysis, formulas (1), ( 2) and ( 3) are converted into formula (4): The entire physical model equation is a nonlinear differential equation.At the same time, the explicit midpoint method is used to calculate the motion and spatial coordinates of the spring particle, and the calculation is repeated iteratively, that is, the physical motion of the fabric can be simulated.
For the model system established by spring mass, during the movement process, due to the characteristics of spring structure, the spring will appear excessive stretching, which will eventually affect the effect, and even lead to distortion of cloth simulation.The researchers believe that this pain point problem can be solved by improving the position correction.Specifically, by changing the speed of the particles on both sides of the spring and the position coordinates of the particles on both sides of the spring, the hardness and softness of the cloth can be reflected to achieve the desired simulation effect (Xiang Yu, 2012).

Analysis of Collision Detection Between Human Body and Fabric
Cloth simulation technology is a very important step in virtual clothing, so the collision and processing between human body and fabric are also the most time-consuming part of the cloth simulation process.When clothing is worn on the human body, many collision phenomena will be encountered when simulating the wearing effect, such as the crossing and collision between the mannequin and cloth, and between cloth and cloth.Therefore, collision detection is a key problem in the simulation process.The simplest method of collision detection is to pass through the basic geometric elements in the mannequin and fabric.
At present, there are two commonly used collision detection methods: spatial decomposition and hierarchical bounding box.Specifically, the spatial decomposition method is to divide the virtual space centered on the human model into multiple cells with equal volume, and cross test the crossing between cells occupying the same cell or adjacent cells; Hierarchical bounding boxes are used to divide multiple parts of the human body model by using the bounding boxes with large volume and simple modeling to form multiple bounding boxes of different sizes.When the bounding boxes cross each other, the objects between the two bounding boxes will be cross calculated.At the same time, the bounding boxes also have some hierarchical structures, such as bounding boxes along the coordinate axis, bounding balls, and directional bounding boxes.
In this study, the author combines the advantages of the two methods.Aiming at the cross collision between the mannequin and the fabric, the author makes use of the advantages of hierarchical bounding boxes (two or more bounding boxes cross each other -wrapping objects<mannequin>cross calculation), and uses hierarchical spatial decomposition (spatial decomposition of multiple color cells) to improve the order, three-dimensional and flexibility between the mannequin and the fabric, It reduces the irrelevant elements in cross testing and improves the speed and efficiency of collision detection.Specifically, first of all, the author takes the female body model as an example, and uses the hierarchical bounding box and static ellipsoid fitting to build a static key frame screen.Figure 15 shows the hierarchical bounding box and the static ellipsoid fitting diagram (Xiang Yu, 2012).On the right side are two randomly selected key frames, which are the area sets corresponding to the bounding box coordinates.Among them, a is the schematic area of the elliptical bounding box, which is expressed in green, and different parts of the human body are wrapped in regular shapes; b is the ellipsoidal fitting interpolation area.When the number of model keyframes is small, the connection between keyframes is not smooth.In order to reduce the interference between fabrics and affect the intersection between the mannequin and fabrics, linear interpolation is inserted between two frames; c is the node of the mannequin.The node coordinates around the mannequin are constructed according to the interpenetration position and elliptical structure.The node coordinates can better simulate and pass through the external features of the fabric.

Figure.16 Visualization diagram of color annotation space decomposition and cross collision pressure perception
The second step uses the hierarchical space decomposition method to detect the collision between the mannequin and the fabric, which is also based on the first step of the hierarchical bounding box method.As shown in Figure 16, A in the figure is the schematic diagram of the hierarchical space decomposition method of color labeling(Yang Yan,2006).In this paper, the color enclosure centered on the human body is wrapped with an irregular polygonal cube.In order to accurately calculate the contact value between the convex point of the fabric and the polygonal cube, the three-dimensional space is divided into multiple small squares with the same color and volume.Each small square has unique coordinate information Unique color representation.When the mannequin is in motion, the clothing cloth and polygon color cube cross collide, and the coordinates will mark the coordinate hierarchy between the color bounding body and the human body and fabric e.Specifically, the whole model coordinate diagram A includes three parts: human body model coordinate, clothing cloth coordinate and polygon color cube enclosure coordinate.Specifically, three collision forms are judged through algorithms, including the coincidence of human body model coordinate and clothing cloth coordinate, the coincidence of clothing cloth coordinate and polygon color cube enclosure coordinate, and the coincidence of human body model and polygon color cube enclosure coordinate, At the same time, there are also some self collisions between cloth, including the intersection of cloth points and faces.In the whole process, firstly, the Sweep and Prune algorithm is used to detect the physical method of AABB bounding box, and at the same time, the separating axis theorem algorithm is used to optimize.Adjust the intersection of polygon cube's face, line, and point with cloth and human body model, and determine whether they intersect according to the overlapping shadow area.
B is the cross pressure perception map of clothing fabric and mannequin, and it is also the embodiment of the duplicate coordinates of the two.Different colors are used to represent the size of cross pressure.a/b/c/d in the figure represents the pressure value of different parts of the human body, and C represents the maximum pressure value, which is orange red.It is divided into the joint between the crotch and the fabric, and the joint between the shoulder and neck points and the fabric; The yellow area indicates that the pressure value is next, and the lowest pressure value is the blue area.The expression of the pressure sensing map also highlights the concrete embodiment of the coordinate intersection and fusion of the color space, polygonal cube enclosure, human body model and multiple parts of the fabric in A, which is the best expression of a collision detection method.Through 3D modeling and algorithm simulation, the researchers simulated the pressure perception visualization map of the mannequin wearing clothing fabric, as shown in Figure 17, which is divided into four directions: front, back and left and right sides, so that the collision monitoring pressure value of each part can be clearly understood.

Figure.17 Visualization diagram of pressure point perception Clothing Fabric Rendering
Cloth rendering is an important part of 3D flexible design of clothing.Traditional cloth rendering uses machines to scan the fabric, and secondary design and processing is carried out through AI or PS to make the desired style.However, because the size proportion is often inconsistent with the actual, it consumes time and costs.Before the appearance of digital physics engine, this method was a common method for garment enterprises to build fabric databases.Before analyzing digital rendering of fabrics, researchers first proposed several factors affecting fabric rendering, as shown in Table 2: The material definition and direction to be considered in the fabric rendering shown in Table 2 are important factors that affect the digital scanning and rendering in the later stage.Before rendering, we should first understand and be familiar with the material definition of fabric, including fabric appearance, physical attributes and data attributes.In terms of fabric appearance, we mainly focus on the color, texture, luster and other contents of the fabric, such as silk luster, cotton texture, etc; The physical properties of fabrics include elasticity, bending, pressure and other properties, such as the elasticity of knitted fabrics and the bending degree of wool fabrics; Fabric data attributes include composition, yarn count, etc.For example, when rendering, consider the appearance of the components.The researcher is familiar with the material definition and direction attribute of the fabric.Starting from this topic, the researcher proposes the relevant process of fabric rendering, as shown in Figure 18.The whole process includes four parts: digital fabric creation, texture mapping, texture redesign and color scheme, and realistic rendering.Specifically, the establishment of digital fabric is mainly to scan the fabric with high definition through digital scanning equipment to form a high definition base map; Secondly, the base map is processed by Substance Alchemist tool and AI algorithm to generate normal, yarn texture height and other contents, and impurities, shadows and other contents on the base map can be removed to finally generate texture maps; Then use relevant software to redesign the texture map and adjust the color matching of the fabric, such as Adobe IIIustrator, Adobe Dimension, etc.This step is related to the diversity and accuracy of the fabric; Finally, by matching the size, light and camera pigment of the fabric, and then through PBR rendering, the conventional PBR rendering is mainly applied to such fabrics as cotton fabrics and wool fabrics, and the special PBR rendering is mainly applied to silk fabrics with shiny and high linear requirements.In the specific implementation process, relevant algorithms in the Unity Shader tool are applied to render.Figure 18 shows the silk fabric effect in the fabric rendering.

Figure.18 Fabric Rendering -Silk Fabric Effect Flexible 3D Garment Simulation Model
The establishment of 3D simulation model of garment flexible body is the core content of this topic, and also an important link for garment enterprises to actively design and serve key customers.At present, there are many methods for 3D modeling of clothing.This topic adopts the point line surface trinity modeling method, which is time-saving and effective.Therefore, according to the previous chapters and the particularity of 3D modeling of clothing flexible body, the researchers propose the flow of 3D clothing simulation model of clothing flexible body suitable for this topic, as shown in Figure 19, which is the flow of 3D clothing simulation model of flexible body (Liu Yan,2003).Specifically, the whole process is divided into five modules.The first module is a customized manikin.According to the manikin designed using the SMPL model method, match the corresponding size of the target clothing, such as women's 160/68A, men's 180/92A.At the same time, according to the characteristics of the target clothing, customize the design of the manikin, such as a little wider shoulder, a little more waist circumference, a little bigger chest circumference, etc.The second module is to select the data points of the clothing parts.This module exactly selects multiple data points reflecting the clothing shape according to the customized manikin and corresponding to the needs of the target clothing, as shown in Figure 20.The clothing shape is set as the women's bodice top, and the data points of the target clothing shape are selected.The selected position points are respectively 10 cm below the armpit, mastoid, side waist point, belly button and neck center, The purpose is to better control the surface modeling of the clothing form after the connection is formed, and reduce the number of unnecessary surfaces.There are four surfaces in the figure ,   The fourth module is to build the clothing surface model (Liu Yan,2003).Specifically, this step is the most complex and key step in the whole model construction, mainly including fabric stress structure analysis, pressure fitting points, fabric mapping and property rendering, screen Z-axis carving, low mold foreskin, etc; The fabric stress structure and pressure fitting point are mainly carefully drawn on the clothing softness and fitting degree, so that the bending degree and hardness of the fabric can maintain a certain state of confrontation, so as not to lose the sense of support of the clothing form, as shown in Figure 22; Cloth mapping and property rendering are mainly based on the previous cloth rendering for UV mapping.According to the shape effect of the target clothing, the pre rendered fabric map is placed in the clothing model to make it fit.The space between the human body and the cloth covered by the cloth can be replaced by the conventional shadow mapping algorithm, which can make the space between the cloth and the human body more fit and more realistic; Screen Z-axis carving can not be clearly drawn based on the relationship between the side seam of the target clothing form, the upper edge of the clothing and the human model.Generally, we use the XY axis direction, so we use the Z-axis view of screen coordinates for interpolation and careful drawing, as shown in Figure 23; The low mode foreskin simulates the clothing effect to a certain extent through the lighting effect and depth buffer algorithm, so that the contrast between the clothing and the front and back pixels of the human body can form a certain visual gap and enhance the stereoscopic sense.The fifth module is engine rendering, which is used to work on lighting, materials, clothing shape effects and other aspects through the unity rendering engine.As shown in Figure 24, we have constructed the primary clothing form.Through the mapping relationship between the position point coordinates (XYZ) and the texture coordinates, as well as the calculation of the lighting model, the middle form of the clothing is formed.It can be seen that the fabric is a grid texture, which cannot meet the needs of researchers.Therefore, we render again through the material characteristics, background environment (reflective, etc.), lighting model and depth buffer algorithm, After several rendering adjustments, the final shape of the target garment is finally constructed.The above is the specific workflow of the rendering engine.Due to the different shapes of the target clothing, there will be some differences in the workflow (Audio and Video Development, 2021).

Research on dynamic virtual display
According to the completion of the previous contents, the final content is to form a dynamic virtual exhibition of clothing after stitching the plates.This section studies the dynamic display of the clothing after the sewing is closed.The dynamic virtual display link can truly show the real state of the clothing before the proofing process, save costs, reduce development time, and play an important role in the whole clothing supply chain.At the same time, the saved costs can be used in the research and development link, making the product more competitive.

Figure.25 3D dynamic virtual display process of clothing
As shown in Figure 25, it is the flow chart of 3D dynamic virtual display of clothing.Specifically, the whole process is divided into five parts.The first part is the skeleton setting of the mannequin.According to the dynamics of the target clothing, the skeleton skin is constructed, including the rotation angle and radian of each part of the upper and lower limbs.At the same time, the motion direction and angle of the target dynamics are matched to confirm the shape displayed by the skeleton structure in the action frame (Zhang Shasha, 2019).The second part is to use the model in CLO clothing modeling software to set the parameters of the target clothing, such as hair style, face, height, fat and thin, expression and gender, as well as particle spacing, resolution, etc., to make basic preparations for dynamic display (Wang Cong,2022), so that it can more vividly and accurately display the characteristics of the target clothing, which can improve the probability of successful selection.The third part is human motion simulation.This part needs to achieve consistency between the actions of clothing and human bones.3DMAX is used to establish systematic and regular forms of human walking, running, turning and other actions as well as actions between bones to form animation key frames.At the same time, the format is exported to Obj format, and then converted to fbx format to prepare for the next step (Zhang Shasha, 2019).The fourth part is to import the completed action model into 3DCLO software, and then select mannequins, clothing prints, sewing prints and other links in repeated operations for dynamic simulation.The fifth part is dynamic simulation.Click the animation solution button, set the solution time, and conduct animation synthesis simulation; After simulation, the whole dynamic picture may not meet the user's requirements in terms of chroma, background, etc. Premiere software picks up the human body, renders the background, chroma, brightness, etc., and finally sets special effects, designs in the direction of unified color, lens transition, etc. (Wang Cong,2022), so as to achieve a more complete dynamic virtual display, Let the company's target customers see a more realistic clothing design effect before making sample clothes.As shown in Figure 26, the screenshot of dynamic virtual display of round neck five part sleeve long skirt is derived according to the previous virtual display process.There are 10 screenshots in total, and the researcher selects 6 screenshots here

Discussion and Results
Based on the description and analysis of the two modules of clothing design modeling and clothing dynamic virtual display, the researchers can express the design process well and smoothly in the whole process, including modeling and dynamic display, and better display the two contents of clothing 3D simulation design, digital fabric effect and dynamic environment virtual display to target customers, so as to save proofing costs, reduce research and development time, and improve the efficiency of the entire supply chain, At present, it is more suitable for small and medium-sized clothing enterprises and some large clothing enterprises.However, there are also some problems in this process, such as the heavy workload of overall design and simulation, involving many AI problems; For example, it is difficult to capture the accuracy of physiological parameters of human models, which involves multiple human models of different shapes and ages; The 3D modeling of clothing takes a long time, involving the training of multiple algorithms; There is much interdisciplinary content knowledge, which is a variety of challenges for researchers in the direction of design.The research goal of this topic is to build a 3D model of clothing and research on the integration of dynamic virtual display.At the same time, the research terminal can provide the target customers with visual product development design and dynamic display, which shows the real effect of clothing design after proofing.This is also a way for small and medium-sized clothing enterprises to actively promote services for target customers, which can increase customers' trust and feelings towards the enterprise.As shown in Figure 26, it is a flow chart for 3D flexible body modeling, dynamic virtual display and key customer service of clothing.Specifically, the whole flow chart is divided into three parts: clothing design and 3D modeling, 3D dynamic virtual display of clothing and service for target key customers.Among them, the clothing design and 3D modeling part includes human modeling and clothing module database, physical model and design of fabric, collision detection analysis of human body and fabric The five sub modules of garment fabric rendering and flexible 3D garment simulation model are circular and have sustainable characteristics; The second content is 3D dynamic display of clothing, including five sub modules: skeleton setting of mannequin, human motion simulation, etc.The five sub modules are also circular; The first two parts have the relationship of research iteration.If one part of the content does not meet the requirements, it can be traced back to the previous part for redesign; The third part is target customer service, which is composed of three modules: complete clothing simulation effect, 2D visual template and virtual show dynamic display.This is the purpose and value of this research.The whole process can be studied iteratively.If the target customers put forward their ideas in details, they can go back to the first part again for redesign, which will be completed quickly and efficiently, and the whole process can be traced back to the source, This is of great value and significance to the rapid response system of many small and medium-sized garment enterprises in China.

Conclusion
At present, the impact of digital technology and intelligent algorithms on many industries has been very obvious.From the perspective of clothing, both the clothing design teaching in colleges and universities and the clothing design tools in enterprises have started to expand to the digital direction.At present, the design tools used by designers in enterprises still rely on manual drawing and 2D design software.At the same time, there are not many clothing designers in small and medium-sized enterprises, and expensive salaries will limit the number of people, which will lead to slow response in the design part; At the same time, most production and processing small and medium-sized garment enterprises will react slowly to the big order meeting, and can not lock this big customer for a long time, so they lack the trust and strength to let the big customer choose the enterprise.
At the same time, most small and medium-sized garment enterprises provide OEM services for foreign brands.Therefore, quick response and active introduction of design services are an effective way to obtain long-term orders.Therefore, based on this, the researchers propose how to design flexible 3D effect of clothing, 3D dynamic virtual display and virtual simulation of fabrics and human models from the two directions of 3D modeling of clothing flexible bodies and 3D dynamic virtual display of clothing.Through the research of this topic, the rapid reaction speed of clothing enterprises can be greatly improved, the R&D efficiency can be improved, the cost can be reduced, and the trust and reputation in front of large customers can be improved, Improve order durability.
The development of digital technology enables garment enterprises to better transform and adapt to the current trend of intelligent manufacturing.

Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Figure. 2
Figure.2 Analysis of keyword commonness based on 3D clothing simulation design as keyword retrieval result

Figure. 4
Figure.4 Analysis of keyword co citation based on 3D clothing simulation design as keyword retrieval result

Figure. 6
Figure.6 Associated content and process of fashion design and modeling

Figure. 10
Figure.10Female manikin derived from SMPL model(Loper, M et al.,2015)Among them, SMPL(Hypochondria 2022)(Skinned Multi Person Linear Model) is a naked, vertex based three-dimensional human model, which can accurately represent different shapes and postures of the human body.The SMPL model contains N=6890 vertices, 13,776 patches, 24 joint points (note: 23 joint points+1 root node), and the model parameters are determined by The calculation process consists of three steps: body parameters (vertex offset) -posture parameters (vertex offset) -skinning.The number of shape PCA based parameters is 4.28x10e6, and the number of pose PCA based parameters is 23x9=207.

Figure. 11 .
Figure.11Layout of 23 joint points in SMPL model Figure 11 is the schematic diagram of the joint point layout in the SMPL model, which is a normal posture.The coordinates of the human joint points are calculated by the formula ) ; ( ( ) J( s S B T J   + =

Figure. 12
Figure.12 Interface design of apparel module database

Figure. 14
Figure.14Type of spring mass model(Xiang Yu, 2012) Specifically, external factors include human factors and non-human factors.Human factors mainly refer to the effect of other forces on the fabric, including pulling, rotating, etc; (Xue Yuan et al.,2016)The non-human factors are mainly the wind force, air resistance and gravity in nature.The wind factor coefficient is rV rV w F  = ；The internal factors include three types of spring mass model, which are mainly related to spring elongation, tensile data, friction data and collision data, which are related to fabric folds; Other factors are mainly model correlation factors, mainly including the number of model particles, model structure and model difficulty.Therefore, model correlation factors involve the collision effect detection of fabrics and the setting of bending springs.The parameters in Table

Figure. 15
Figure.15 Schematic diagram of hierarchical bounding box and static ellipsoid fitting

Figure. 19
Figure.19 Flow of flexible 3D clothing simulation model and the left and right clothing pieces are distinguished by different colors( Gong Sui, 2018).The third module is to draw the internal and external linetypes of clothing on the basis of selecting the data points of clothing form parts in the second part, as shown in Figure 21.It mainly uses the curve equation to calculate from point to line, and constructs the structure in terms of cloth topology, wrinkle shaping, etc. to form a closed loop internal and external linetype structure of clothing.This is also the initial clothing form master.The linetype parameters are obtained by calculating the XYZ axis of the curve equation and each part point, Connect into line type; In this module, we should consider the rationality of clothing attachment to the mannequin and the reflection of normal state under the action of gravity.At the same time, in this step, we should also consider the characteristics of fabric, force direction, structure, pleating volume and other factors.

Figure. 20
Figure.20 Point selection of target clothing shape Figure.21Draw the inner and outer lines of clothing

Figure. 22
Figure.22 Adjustment of fabric stress structure Figure.23 Screen Z-axis engraving (interpenetration) and fitting point

Figure. 26
Figure.26 Dynamic virtual display screenshot of round neck five sleeve long skirt

Figure. 26
Figure.26 Flow chart of 3D flexible body modeling, dynamic virtual display and key customer servicess

Table . 1
Associated parameters of physical model of fabric simulation

Table . 2
Material definition and direction to be considered for fabric rendering