Research On Several Typical Problems Of Yarn Dynamics

In this dissertation,“yarn” is a long and thin textile flexible body formed by entangled short fibers or bundle filaments.With enhancing the speed of textile,the action of “Coriolis force” and air resistance has a significant influence on the dynamic characteristics of the moving yarn,as well as the dynamic viscoelasticity of the yarn.Meanwhile,the independent-frequency material and contact parameters of the yarn can no longer be ignored in the high-speed changing process.Yarn is an intermediate product from fiber to textile,and its quality directly affects the processed textiles’.During processing,the moving yarn is in contact with mechanical parts or the homogeneous yarn,which leads to the yarn completed its corresponding actions.It is difficult to investigate the yarn dynamics owing to the large overall motion and large deformation during processing.In this dissertation,the characteristics of macro motion of the yarn during processing were analyzed.Several typical problems of yarn dynamics were summarized and put forward into four categories,namely: the problems of mechanical parameter characteristics and uniform motion of the yarn,the problems of variable speed and limited acceleration of the yarn,the problems of contact impact of the yarn,and the problems of dynamic coupling of the yarn.The main works of this dissertation are as follows:（1）Based on the Kelvin model and harmonious strain excitation,the calculation formulas of the values of the dynamic elastic modulus and dynamic viscous coefficient of the yarn were derived.The cross-sectional profiles of the filament bundle under the same process tension were measured,and the equivalent diameter of the filament bundle was calculated.According to the equivalent diameter obtained from the experiment,the values of the dynamic elastic modulus and viscoelastic coefficients of the filament bundle were determined through the yarn dynamics tester,and the results showed that the constitutive parameters of the filament bundle are nonlinear and frequency-dependent.Based on the catenary principle and the finite element method,the motion string model which can be used for yarn dynamics with two ends constrained and the yarn finite element model which can be used for yarn dynamics of complex motion were established,respectively,and the dynamic characteristics of the yarn under uniform motion and rotation were investigated.The critical speed of uniform motion yarn considering transverse air resistance and the relationship between winding tension,winding radius and rotation speed of the uniform rotation yarn were obtained,respectively.（2）Based on Hamilton principle,the nonlinear dynamic equation of transverse vibration of the axially moving yarn was derived,and dynamic characteristics of the moving filament bundle were simulated.Under satisfying the conditions of the same tension and environment of the yarn,the model of the accelerated moving yarn was established,and the instantaneous limited value of acceleration of the moving yarn under the action of traction can be obtained.In order to understand the dynamic characteristics during rotation,the forces of the yarn balloon in the rotation process were analyzed,and the curve equations of the yarn balloon were derived,considering the action of the tension,“centrifugal force”,“Coriolis force” and air resistance.For the stable system of the rotating balloon,the shape curve of the yarn balloon was obtained by numerical calculation.The influence on the balloon shape was analyzed by changing the height of the balloon and the rotating speed of the yarn balloon.Finally,based on the research above,a design method for the high-speed ring spinning was proposed,and the range of the yarn balloon height corresponding to increasing the spindle speed was also given.（3）Based on the Hertz theory,the contact force model between yarns,mechanical parts and packages was established,and the radial equivalent elastic modulus coefficient of the filament package was determined through the experimental test.According to the contact characteristics between yarns,the contact force model of the homogeneous yarn was established.Furthermore,the friction coefficients between the filament bundle and the mechanical roller,the homogeneous filament bundle,the package surface and the paper tube were measured through the tests.Finally,based on Hertz contact force model and Direct damping model,the impact force model between the yarn and the mechanical component was established,which lays a foundation for the study of the dynamic behavior of the impact process between yarn and mechanical parts.（4）Taking the analysis of the dynamic characteristics of the rotating yarn balloon as an example,the air-flexible coupling between the yarn and the airflow was studied.Based on the established mathematical model of the yarn balloon,the air velocity outside the rotating yarn balloon close to the balloon and the balloon shape curve were measured through experimental tests.The dynamic characteristics of the yarn balloon considering the airflow around the yarn balloon during rotation were studied.By comparing the yarn balloon curve obtained by simulation and experiment,the results showed that the yarn balloon model proposed in this dissertation is correct and effective.In addition,the polyester filament winding system was used as an example to study the rigid-flexible coupling between the filament bundle and mechanical parts.The dynamic equations were established considering dynamic coupling between the moving filament and mechanical components.According to the forced non-resonance method of the linearized single-degree-of-freedom system,the identification formulas of dynamic contact parameters between the contact roller and the filament package were derived.The values of the equivalent contact stiffness coefficient and contact damping coefficient under the same process conditions were obtained through experiment and simulation.The dynamic characteristics of the filament bundle during reversing were simulated and analyzed.The results showed that the filament bundle is in a non-contact state during reversing in the winding process,and the large fluctuation of the filament bundle tension is caused by the small fluctuation of contact force between the blade and the filament bundle.The occurrence of these two situations will affect the high-speed and precise winding of the filament,which needs to require accurate analysis and then precise control of the dynamic characteristics of the polyester filament winding system.The dissertation focused on the moving yarn,and the four typical problems of yarn dynamics were proposed.Based on the moving string model and the finite element model of the yarn,the system model of the moving yarn was established,considering the material properties of the yarn.The dynamic characteristics of the moving yarn in the process of rotating and winding were investigated through numerical simulation and experimental tests.After those studies,a designed method of the high-speed ring spinning was proposed,and the influence of the rotary vane and the filament tension on the moving filament of the polyester filament winding system during reversing was explored.The research work in this dissertation can lay a solid foundation for the study of yarn dynamics and the high-speed and precise winding of the yarn.