The Dynamics Behavior Research Of Middle-Ear Structure Based On Analytical Method And Numerical Simulation

The life science is highly developped in the 21th century, the research of mechanics and structure engineering has entered in life science gradually. Middle ear structure is a fine and complex structure in life body. It generates transmission vibration in acoustic motivation, and transforms acoustic energy into kinetic energy to afferent inner ear. This is a set of power transmission process involving solid dynamics and hydrodynamics theory. At present, middle ear diseases and conduction deafness which are caused by middle ear lesions aren't still solved in ear medical science. However, due to the dynamics behavior in the process of human hearing transmission is not taken into account when middle ear diseases are studied by medical treatment only, treatment effect isn't fine. The paper research middle ear by analytical method and numerical simulation based on mechanics theory because middle ear structure is complex structure including ossicular chain and soft tissue(tympanic membrane, ligaments and tendons)。The motion equation of vibration framework is derived by analytical method; it is simulated by numerical method that whole system of middle ear structure includes skeleton and soft tissue. A new numerical method----- natural element method (NEM) is introduced, and overcomes the shortcomings which are element cell distortion and entanglement in simulating hyperelastic large deformation of soft tissue in living body by finite element method. Ear life body of viscoelasticity and hyperelasticity can be well simulated. Main contents of the article are as follows:1. The mechanical vibration characteristics and physical laws of the middle ear vibration system are analyzed from the view of mechanism. the motion equations of tympanic membrane(TM) ossicular chain and artificial ossicles are derived by the variation principle. The correctness of the motion equations are verified by the comparison with experimental results. Physical laws of parameter variation are gained by the motion equations. Elastic modulus change is the most sensitive to effect of vibration information in middle ear structure (the displacement of stapes footplate). It is the basis of parameter optimization in numerical simulation.2. In order to improve the computational efficiency of natural element method, interpolating function is constructed by edge element of Voronoi figure which replaces body elements. Integration method of background cell is applied in integral scheme, and the minimum number of integral point is determined by the method which is applied on FEM. Integral points is arranged by the demand that points are close in edge of integral domain and loose in center of integral domain.Finally, examples ( patch test etc) verify the method and moreover the results prove it correct and reliable accuracy.3. The Discrete form of dynamics problems of three-dimensional NEM is obtained, apply No 1 integral form which is composed of centered difference and Newmark average acceleration .Decoupled recursion is obtained, and furthermore improves the computational efficiency that NEM solves dynamics problems. The examples verify the currency of natural element method discrete format and decoupling algorithm.4. Dynamics action of sound transmission in whole system of middle ear structure including skeleton and soft tissue is simulated by NEM. Results show that NEM simulates the character that sound wave leads to vibration of middle-ear structure with little points in simulation computing; NEM simulates soft tissue in life body, especially hyperelastic large deformation of ligaments is well simulated than finite element method. Calculation results are well concord of experiments than those of finite element method.5. Because middle ear structure is simulated and analyzed, the better knowledge of analytical equation is obtained compared with that of single component, the conclusion—"elastic modulus is reducing and the displacement is increasing"which is gained by analytical equation is condition and range. Change of elastic modulus in ossicular chain is accordance with the conclusion of analytical equation in transmission motion which TM drives ossicular chain. But stiffness of TM is too little and can not drive malleus motion, displacement of stapes is reducing when elastic modulus of TM reduces fixed value.6. Based on the above analytical model and numerical model, according to middle ear diseases of clinical medicine---- TM perforation , ossicular chain fracture, connecting method of artificial ossicular and connecting location of artificial ossicular, pathological theory is explained by dynamics action of every component in sound transmission-----location of TM perforation and ossicular chain fracture is appeared the maximum location of stress and strain, and its sound transmission is the best when artificial ossicular is connected to TM umbo.7.Typical middle ear disease is simulated and analyzed by numerical simulation------ the mechanism and treatment outcome of which tympanosclerosis result in hearing loss is operated. Hardening of soft tissue (ligaments and tendons) is described by increasing elastic modulus, removal of Hardening tissue is described by deleting connections of soft tissue and temporal bone. The results showed ossicular motion can be recovered by resecting hardening ligaments and sound power is leaded in inner ear.The numerical model, analytic equation and the results of theoretical analysis can provide a theoretical reference for surgical research on conductive hearing loss from the view of crossing research of mechanics and biological structure. This is the preliminary attempt which mechanics and principle of structural analysis has entered into the research field of life body.