Studies On Helicalization Design,Motion And Electromagnetic Properties Of Helical Structure

The helical structure is widespread in nature and life.Due to its structural characteristics of high flexibility,strong designability,and obvious chirality,it is widely used in biomedicine,metamaterial,aerospace,and other fields.The core of the helical structural design is how to relate the mechanical characteristics to its functional properties in its application area.At present,there are few studies to explain the formation mechanism of the helical structure,so it is urgent to build a mechanical model of the helical structure and predict the critical conditions of helicalization.The applications of the existing small-scale helical structures still mainly depend on the external field source,and it is difficult to improve the performance from their structural design.Under the action of internal stress or external environment,the variable configuration characteristics of the helical structure become extremely significant.However,the coupling mechanism between the large deformation characteristics and the functions of the helical structure is still unclear.Therefore,this thesis mainly takes the helical structure as the research object,and studies the helicalization of the linear structure,the motion performance in the flow field,and the electromagnetic characteristics of the helical structure,to explore the variable configuration characteristics of the helical structure and the influences on functional performance.It is of great theoretical and engineering significance to study the design and performance of the helical structure in the fields of biology,medicine,robotics,electromagnetism,etc.The mechanical model of the linear structure helicalization is established,including driven by internal force or external load.Based on the hypothesis of in-plane and out-plane decoupling in the helicalization process,the energy in the in-plane crimping process is analyzed and the nonlinearity is considered.The differential relations of internal force and displacement during bending and torsional deformation are established.The critical structural size,internal force,and displacement are obtained.The thermodynamic constitutive of shape memory polymer is studied,and the simulation method for analyzing the shape memory behavior is established based on the constitutive model.The thermodynamic behavior laws of helicalization and intelligent deformation driven by internal force are obtained.In addition,considering the helicalization of the structure under external load,a helicalization mechanical model under the combination of compression and rotation is established,and the force on the structure is analyzed.Taking internal force-driven helicalization as an example,the helicalization,unhelicalization,folding,and unfolding behaviors of the helical structures are characterized by experiments and simulations.The resistive force theory based on microscale fluid dynamics is established.The linear simplified relationship between force and velocity during the motion of the helical swimming structure is predicted.The correlations among the drag coefficient,helix geometry,and viscosity characteristics of the flow field are defined.A numerical calculation method to simulate the fluid dynamics of the helical structure based on the resistive force theory is proposed to ensure the accuracy of the results and greatly improve computational efficiency.The relationships among the thrust,drag,propulsive efficiency and dimensionless geometric parameters are obtained,and the influences of geometric configuration on the motion performance of the helical structure are clarified.A novel hierarchical helical swimming structure is designed,which significantly improves the motility on the premise of guaranteeing stability and resilience.The motion abilities of the hierarchical helical structures and the combinations are evaluated from different aspects,and a reliable motion performance control strategy is proposed.The electromagnetic properties of the helical structure are studied from theory,simulation,and experiment.Combining the effective medium theory and S-parameter inversion method,the method to obtain the electromagnetic parameters of the heterogeneous structures is presented.Based on the classical“sandwich”structure,a helical absorbing cell is constructed.The important electromagnetic parameters such as resonant frequency,absorptance,and RCS reduction are obtained.The axial mode helical antenna is established,and its electromagnetic parameters such as the S₁₁parameter,resonant frequency,gain,and direction pattern are obtained by experiment and simulation.The characteristics of its operating frequency band and radiation direction are discussed.The electromagnetic characteristics between the circularly polarized helical antenna and linearly polarized antenna are compared and analyzed.And the variation laws of electromagnetic properties,such as resonant frequency point and radiation direction,caused by different geometric structures are studied.The variable configuration characteristics of the helical structure are studied.The influences of the variable configuration on its motion and electromagnetic properties are investigated.The influence of the global curvature on the motion performance is revealed.A nested helical structural design is proposed.The influences of the nested design and unhelicalization on the motion characteristics of the helical structure are comprehensively analyzed,and the internal mechanism is explained.A guiding phase diagram is given.The effects of variable configurations on the electromagnetic properties are analyzed,such as folding and unfolding,lateral bending,helicalization and unhelicalization,and radial expansion and contraction.The variation laws of electromagnetic properties caused by configuration characteristics are obtained,such as resonant frequency,radiation mode,and gain.The effects of the configuration transition between the unfolded and folded state on the working frequency band,absorbing function,and quality factor of the helical absorbing structure are investigated.