Dynamic Investigation On Soft Structures With Large Deformation Based On Absolute Nodal Coordinate Formulation

Soft robot is a novel type of continuum bionic robot which is made of soft materials,which is also a kind of large deformable complex soft structure with mutiple air chambers,and it is attracting more and more attention and becomes a new research topic and hotspot.Owing to materials nonlinearity of soft structure itself,coupled with geometric nonlinearity caused during motion process,air chambers structures’ complexity as well as volumetric locking problem that may occur in the numerical calculation,which makes its dynamic study face many difficulties.In addition,soft structures such as soft actuator and soft robot will encounter multiple point contact between adjacent two air chambers during movement and deformation process,how to build an accurate and effective mechanical model and study overall configuration and stress distribution is still a challenging conundrum.However,the traditional modeling approach base on small deformation and linear elastic theory is no longer able to describe dynamic characteristics of nonlinear hyperelastic soft structures.Therefore,it is necessary to establish an accurate dynamic model for soft structures with large deformation and conduct simulation analysis and experimental investigation on large deformation,large-scale motion and dynamic behaviors.It can establish a theoretical basis for research of soft robot,which has not only profound theoretical guiding significance,but also has broad practical application prospects.Previous existing researches mainly focused on these structures with linear elastic materials such as beams,plates,shells,whereas those investigations on modeling approaches for those same counterparts and soft structures with multiple air chambers which are made from hyperelastic incompressible materials are relatively less involved.This dissertation launches dynamic modeling and experimental study on nonlinear hyperelastic soft structures with large deformation based on absolute nodal coordinate formulation(ANCF).The main research contents and achievements are as follows:1.With respect to modeling for an incompressible silicone beam,an ANCF lower-order beam element is improved to solve a volumetric locking problem caused by a lower-order beam element.Further,an ANCF higher-order beam element is developed,and the combined use of the higher-order beam element with nonlinear material models is proposed to implement dynamic modeling and simulation analysis as well as experimental investigation on the silicone beam with large deformaion.The higher-order beam element can not only avoid the volumetric locking,but also accurately describe large deformation and large-scale motion of the silicone beam.The static and dynamic numerical examples as well as physical experiments validate feasibility and accuracy of the dynamic model.2.On the basis of the above beam element model,with respect to modeling for an incompressible silicone plate,an ANCF lower-order plate element is improved to eliminate stiffening effect generated by a lower-order plate element.Moreover,an ANCF higher-order plate element is also developed,and the higher-order plate element is combined with nonlinear constitutive model to enforce dynamic modeling and analysis as well as experimental investigation on the hyperelastic silicone plate.The higher-order plate element can not only eliminate stiffening effect,but also reflect configuration and strain variations of the silicone plate.Numerical simulation and experimental results demonstrate effectiveness and accuracy of the dynamic model.3.With regard to a multiple point contact problem between adjacent two air chambers of a pneumatic soft actuator with multiple air chambers and more complex structure,a more accurate mechanical model is established,and the interpenetration problem between adjacent two air chambers is solved.It can be found from a static experimental investigation that compared with the conventional beam model,this model can not only improve accuracy in simulating bending deformation of the soft actuator,but also describe the overall configuration variations,von Mises stress distribution and concentration phenomenon.4.Combining a multiple point contact model with a friction model effectively,a dynamic modeling approach for a pneumatic soft robot with multiple air chambers is proposed,and a corresponding dynamic model is established.The dynamic simulation investigation is implemented for crawling process of the soft robot,and a continuous forward crawling motion for the soft robot is successfully simulated,and the stick-slip nonlinear dynamic behavior is revealed.The combination of the motion control method with the digital image correlation(DIC)measurement technique is used,a corresponding crawling experiment for the soft robot is conducted,and the accuracy of the dynamic model is verified.5.The numerical algorithm for solving dynamic equations of the pneumatic soft robot is investigated.Aiming at the computational problem for the created nonlinear dynamic equations,and the established differential-algebraic equations(DAEs)are solved by adopting an implicit algorithm,and the detailed dynamic solution process is given.Combining parallel computing with sparse matrix technique,and a numerical solution for dynamic equations is realized,and computational efficiency is improved meanwhile ensuring computational accuracy.