A Three-Dimensional Singular Model of a Magnetic Perpendicular Recording Head with Applications to Inter-Track Interference

Two-dimensional models of the read head are not suitable for simulating the replay of the extremely high density data that is expected to be achieved in hard drives using perpendicular recording. By matching a singular function approximation to the Fourier solution at the air-bearing surface (ABS), a three-dimensional analytic model of a shielded giant magnetoresistive head, with side shields, for perpendicular replay is derived in this thesis. An explicit expression for the potential in the ABS is presented and parameters in that expression are accurately estimated for a range of practical head dimensions. Using only a few terms of this singular potential model, the vertical field is accurate to within 2% of the sensor potential in the region of the medium for the majority of head dimensions suitable for magnetic recording. The expected increase in areal density in hard drives using perpendicular technology will require very narrow t racks which normally suffer from large inter-track interference (ITI) or crosstalk. This interference can corrupt the read data and reduce t he signal strength. Here, the effects of ITI across three tracks in a three-head system are modelled by applying the three-dimensional singular function model of the head field. The magnetisation patterns which cause the worst ITI are identified so that these codes can be prohibited. A coding constraints scheme, in which ITI is exploited to read from tracks which have widths that are just 70% of the width of the head, is presented

Linear frequency domain and harmonic balance predictions of dynamic derivatives

Dynamic derivatives are used to represent the influence of the aircraft rates on the aerodynamic forces and moments needed for flight dynamics studies. These values have traditionally been estimated by processing measurements made from periodic forced motions applied to wind tunnel models. The use of Computational Fluid Dynamics has potential to supplement this approach. This paper considers the problem of the fast computation of forced periodic motions using the Euler equations. Three methods are evaluated. The first is computation in the time domain, and this provides the benchmark solution in the sense that the time accurate solution is obtained. Two acceleration techniques in the frequency domain are compared. The first uses an harmonic solution of the linearised problem referred to as the linear frequency domain approach). The second uses the Harmonic Balance method, which approximates the nonlinear problem using a number of Fourier modes. These approaches are compared in the sense of their ability to predict dynamic derivatives and their computational cost. The standard NACA aerofoil CT cases, the SDM fighter model geometry and the DLR F12 passenger jet wind tunnel model are used as test cases. Compared to time accurate simulations an order of magnitude reduction in CPU costs is achieved for flows with a narrow frequency spectrum and moderate amplitudes, as the solution does not evolve through transients to reach periodicity