Numerical Analysis And Experimental Research Of Shock Response In The Head/Disk System

A hard disk drive (HDD), a kind of important storage devices, is made of disk, head, slider, suspension, shaft, spindle motor, etc, where the head is attached at the end of the slider. When a HDD is working, the slider (head slider) is flying over a high rotating disk, this makes a HDD excuting read/write functions. The distance between the slider and the disk is called the flying height of the slider, and this flying height in today’s HDD is less than10nm. In the process of work, th relative position between the head and the disk changes due to the movement, collision and falling of HDD, which influences on the performance of HDD. Therefore, the research work of the shock response in head/disk system has important significance for controlling and improving the work performance of HDD.The FK-Boltzmann model has a complex expression, and it is not easy to solve it by using numerical methods. In this thesis, a piecewise linear function is used to approximate the flow rate function in FK-Boltzmann model, and a new model called linearized flow rate (LFR) model is derived. By numerical examples, the relative errors between the FK-Boltzmann model and the LFR model are small, and the calculation efficiency of the LFR model is about20%higher than that of the FK-Boltzmann.In this thesis, the finite volume method is used to discretized the gas film lubrication, a discontinuous height factor is introduced to solve the problems of gas flow resulted from the discontinuous height on boundary of control volume. The discretized equation is solved by line-by-line Gaussian iteration with combining the chasing method. Meantime, a grid density function, which variable is pressure gradient of the slider, is defined and used to allocate many grids in large pressure gradient area. It ensures a reasonable distribution grid. Multigrid method is used to improve the efficiency of solving gas film lubrication equation. The gas film lubrication must be solved repeatly in the process of studing the dynamic characteristics of the head/disk interface; a low computational efficiency may cause a decline in the whole computing process. In this thesis, a5-layer multigrid method is used, and the initial value is given on the third layer grid. The calculation results show that the multigrid method can well improve the computational efficiency of numerical method. Numerical results show that this type of method combined the finite volume method, adaptive grid technique, multiple grid method, can improve effectively the speed of solving the gas film lubricatioin, which saves much time for studying of dynamical characteristics in the head/disk interface.In order to simulate the shock response in the head/disk interface, a finite element model including the disk, slider, suspension, shaft, cover, etc, is established in software Ansys. The film bearing capacity changes over time, and the gas film lubrication is solved by our program for obtaining the film bearing capacity. The film bearing capacity is applied to the finite element of HDD system. Therefore, a call between our program and the software Ansys is needed, and the calculation pareameters are passed between them. This problem is solved successfully by the LS-DYNA restart function. The dynamical characteristics in the head/disk interface are simulated in the case of the HDD subjected to different waveform, amplitude, period of the acceration impact load. Numerical results show that the increasing of the impact load amplitude will lead to the increasing of changing amplitude of flying parameters, and the increasing of the period will delay the changing of the flying characters. But, the wareform has a little influence on the flying parameters.Based on the relationship between the read back voltage signal and the distance between the slider and the disk, an experimental platform is set up. The Hitachi HDD in the numerical simulation is the testing object. The distance between the head and the disk is obtained when the cover of HDD is subjected from different displacement load with different amplitude and period. The testing results are compared with thosed of numerical simulation in the same conditions, and the comparing results show that the maximum relative error is7.69%.In a word, new gas film lubrication, the LFR model, is derived, and is efficiently solved by finite volume method, adaptive grid method and multiple grid method. The dynamic charateristics of the Hitachi HDD is simulated by using software Ansys and LS-DYAN solver when the cover of the HDD is subjected from different acceleration shock load with different wareform, amplitude and period. An experimental platform is set up for verifying the validity of the numerical simulation.