Three Dimensional Simulation Of Weft Knitted Fabric Based On Mass-Spring Model

Due to the complex structures of weft knitted fabrics and loop deformations resulted from the effect of the yarn tension when different kinds of stitches combined with each other,it is difficult for the designers to accurately predict the actual appearance of the fabrics.Though the current CAD(Computer Aided Design)system can effectively solve part of the above problems,there are still large discrepancies between the simulation effects and actual fabrics.This is because the real deformation behaviors caused by the change of yarn tension of fancy stitches in weft knitted fabrics cannot be simulated,which brings difficulties to design and manufacture of weft knitted fabrics.Therefore,the deformation behaviors of loops of weft knitted fabrics are analyzed and simulated in this work,which is used as modules of three dimensional(3D)simulation system.The system is applied to the weft knitting CAD system CKCAD 2.0.At first,according to the structural characteristics and physical properties of weft knitted fabrics,the cuboid mass-spring model is proposed based on traditional mass-spring model.By measuring the actual fabrics,the parameter relationships between bonding points coordinates and cuboid mass-spring model are obtained.According to the parameter relationships,the bonding points of basic and fancy stitches of weft knitted fabrics are built based on the cuboid mass-spring model,including plain stitch,rib stitch,interlock stitch,purl stitch,tuck stitch,miss stitch,loop transfer,plain laying-in stitch and accordion stitch.Then,the offsets of the bonding points in fancy stitches are studied by measuring the deformation displacement caused by the tension after the combination of fancy stitches and plain stitches,fancy stitches and fancy stitches.The measured fancy stitches include tuck stitches(single-row tuck,double-rows tuck and triple-rows tuck),miss stitches(single-row miss stitch,double-rows miss stitch and triple-rows miss stitch)and loop transfer(loop transfer which span one needle,two needles and three needles).After that,the proportional relationships between offsets and the structural parameter of the loop are calculated via the linear relationships between the bonding points and particles.In addition,the effect of different number of tucks,miss stitches and loop transfer on proportional relationships is also analyzed.The obtained proportional relationships are applied to the cuboid mass-spring model and the dynamic equation of the mass-spring model is solved by velocity-Verlet numerical integral method.The force of the particle and the force and displacement of its adjacent particles are calculated.The deformation behaviors of fancy stitches and its adjacent loops caused by yarn tension are simulated.To solve the problems of unreasonable insertion of yarns induced from the tension effect and the dislocation of loops,the collision detection method with cylinder bounding box is proposed in this work according to the geometric model of the yarn.When used for collision detection,this algorithm can closely surround the geometric objects,efficiently avoiding the complicated calculation and the lack of accuracy caused by the overlapping and voids of other bounding boxes.In order to improve the volume and realistic of the loop,the realistic rendering of 3D geometric model of the loop is realized by using 3 different methods in this work.The Non-Uniform Rational B-Splines(NURBS)surface and texture mapping functions in Open GL are respectively used to realize the loop shape with smooth surface and texture.The loop shape with yarn twist is achieved by combining the proposed algorithm of twist simulation with space objects rotating function.Based on the comparison of the simulation results under different illumination conditions with diffuse light,ambient light,mirror reflection and radiation light,the suitable illumination models for the simulation of weft knitted fabrics are obtained.Finally,combined with previous models and methods,the 3D simulation system of weft knitted fabrics with excellent interactive design interface is implemented based on Visual Studio 2010 and Open GL.The system can flexibly set the parameters of loop,yarn and elastic et al.and the viewing angle and paint methods are free transformed according to the requirements of users.The weft fabrics images with real mechanical deformation effect are generated.The running time of the system is further tested to ensure the real-time performance of the system.The practicability and efficiency of the proposed method and model are verified by comparing the simulation results and the real fabric.In conclusion,the 3D simulation of weft knitted fabrics in this work is carried out from the four aspects mentioned above.Starting from the deformation behavior simulation of the loop,the 3D simulation system of weft knitted fabrics with real fancy stitches deformation effect is achieved.The system not only can intuitively and efficiently help designers for weft knitted product development,but also provides technical support for dynamic virtual display and customizing knitwear.