Mechanical Environment Analysis And Test Technology For Fiber Optic Gyroscope Strapdown Inertial Navigation System

Strapdown architecture has been widely adopted as a typical structure of Inertial Navigation System.With the aircrafts velocity steadily improving,the aircrafts experience the harsh aerodynamic noise environment during their flying back to the aerosphere.The Strapdown Inertial Navigation system(SINS)is under a severe,random,wider frequency range and multidirectional vibration mechanical environment.The harsh vibration environment causes the vibration magnitude of the inner inertial devices far exceeds the magnitude that can keep their accuracy,and causes the system performance unstable,the electron devices destroyed,and even leads to navigation function decline or loss.For the research of mechanical environment adaptability of the new type SINS,the dissertation introduces the dynamic optimal cycle design method that has the center part of structural dynamics analysis and mechanical environment test.The structural dynamic characteristics and dynamic response characteristics of the system is solved by introducing structural dynamic modeling and analysis techniques before the prototype was constructed and after the geometry model was designed.Mechanical parameters such as strength,stiffness and buckling stability of the existing design can be acquired,the distribution of stress,strain,displacement,velocity,acceleration and other mechanical properties of the structure can be shown in detail,and the mechanical weakness and the structural defect position of the system can be described intuitively.Then turn back to the first stage to modify and optimize the initial geometric design.The optimum design obtained before the system prototype constructed with repeatedly revision,improvement and optimization.Finally,the prototype manufacture and mechanical tests verify the system design.The dynamic optimization cycle design method overcomes the blindness of the traditional method of "geometric design-prototype manufacturing-mechanical test-modified geometric design" which avoids the phenomenon of "under-test" or "over-design" to a largely extent,and reduces the schedule,cost,and quality.The dissertation takes the SINS preliminary design as an example,studies some key problems when adopting this method.The influences of the dynamic environment on SINS output were disused from three aspects: attitude algorithm,speed calculation and position calculation.The dissertation gives the vibration test result of the SINS prototype when system power on.The navigation output error and its magnitude of the system are given.The research shows that it is necessary to improve the anti vibration performance of the system from structure,material and vibration reduction.The dissertation summarizes the function of experimental method,analytical method and numerical method in solving the structural dynamics problems,and uses the analytical method and the finite element numerical method to solve the structural mechanical properties of a typical geometric structure.Result shows that the analytical method is correct,and the finite element numerical method has an accuracy and applicability performance to solve this kind of problems.According to the comparison results,the dissertation will adopt the two methods for our research: the finite element numerical method and the mechanical test method,and use the calculation result to verify from each other.CAD-CAE is the most suitable process to establish the finite element mathematical model of SINS.The dissertation shows the details about the important steps and settings to establish the model.The compound material theory was used to acquire some key mechanical parameters of the fiber ring,such as elastic modulus,Poisson ratio,density,etc.The modal analysis of the internal structure and the whole structure of SINS shows us the basic mechanical characteristics such as natural frequency and modal shape of the SINS preliminary design.In order to obtain the vibration magnitude and built the reasonable external force function,the dissertation analyzes typical environment of the SINS carrier,such as the working environment on ships and missiles,and gives algorithms and their corresponding settings of the analysis methods on the random and sinusoidal vibration response problems of SINS.In view of unreasonable factors of the SINS preliminary designs,the dissertation adopts some structural modifications to reach a reasonable structure and studies the structure optimization method of SINS from the modal characteristic frequency parameter,and then obtains the dynamic response and characteristics of the optimized structure from the harmonic response analysis and random vibration analysis respectively.The object of the test is the mechanical performance of the composite frame of SINS which be used to install all the inertial devices.It will show test conditions,such as test equipments,test preparations,vibration magnitude and directions after system test.Finally,compare sweep frequency vibration test and random vibration test results with the numerical results of finite element method,to verify the correctness of the finite element mathematical model and the dynamic response calculation results,and to find the error sources between the test and simulation results.