Sharif Digital Repository

This paper discusses the identification process of engine dynamics and presents derived transfer function models including; thrust, shaft speed, compressor exit pressure and turbine exit temperature in relation to the fuel flow. Model identification approach, presented in this paper, is the first to consider frequency-sweep signals to excite dynamics, as well as to utilise windowing and smoothing techniques to reduce random errors in the spectral estimates. Here, frequency sweep provides a fairly uniform spectral excitation and chirp-z transform warrants the exact determination of the frequency responses that are robust to the uncertainties. The identified models are also validated with the... 

This paper aims to explore the dynamic behaviour of a nano-resonator under ac and dc excitation using strain gradient theory. To achieve this goal, the partial differential equation of nano-beam vibration is first converted to an ordinary differential equation by the Galerkin projection method and the lumped model is derived. Lumped parameters of the nano-resonator, such as linear and nonlinear springs and damper coefficients, are compared with those of classical theory and it is demonstrated that beams with smaller thickness display greater deviation from classical parameters. Stable and unstable equilibrium points based on classic and non-classical theories are also compared. The results... 

Due to their agile manoeuvrability and simplicity of construction, quadrotor are employed in a variety of applications. Most of their expenses are due to complex control systems, since, to reduce these expenses, low cost control methods which are based on linear models should be used to achieve an autonomous flight. First, the process of accurate dynamic modeling of a sample quad rotor which is simulated by MATLAB SIMULINK is presented. Then, a frequency sweep input stimulates the virtual model in order to identify a linear model based on frequency response analysis. Consequently, the desired linear model is obtained in both hover and yaw mode of motion. However, pitch and roll mode were too... 

System Identification is a key technology for the development and integration of modern engineering systems including unconventional flying vehicles. These systems are highly parametric with complex dynamics and nonlinearities. Ducted fans are special class of these vehicles that can take off vertically, hover and cruise at very low speed. In this paper, an exact equivalent linear system is found from the non-linear dynamic model of a ducted fan by use of frequency response identification. Here, power spectral density analysis is performed, using CIFER software, to evaluate the input-output responses in hover and to derive the transfer functions based on the coherence criterion. Then,... 

System Identification is a key technology for the development and integration of modern engineering systems including gas turbines. These systems are highly parametric with complex dynamics and nonlinearities. Small turbojet engines are special class of gas turbines that are suitable for scientific purposes and researches in the area of stability, performance, simulation and fuel control design. The motivation behind the presented study is to improve the speed, quality and cost of engine testing and to gain insight into alternatives to traditional identification methods for gas turbines. It discusses the identification of small turbojet engine dynamics by validating the thermodynamic model... 

In this paper, the nonlinear dynamic response of an inclined pinned-pinned beam with a constant cross section, finite length subjected to a concentrated vertical force traveling with a constant velocity is investigated. The study is focused on the mode summation method and also on frequency analysis of the governing PDEs equations of motion. Furthermore, the steady-state response is studied by applying the multiple scales method. The nonlinear response of the beam is obtained by solving two coupled nonlinear PDEs governing equations of planar motion for both longitudinal and transverse oscillations of the beam. The dynamic magnification factor and normalized time histories of mid-pint of the... 

This article aims at developing a semi-analytic approach for studying the free and forced vibrations of a pseudoelastically behaving shape memory alloy beam. Based on the Euler–Bernoulli beam theory, equations of motion were derived through Hamilton principle, and the obtained partial differential equations were decomposed by applying the Galerkin approach and were solved using Newmark integration method. A three-dimensional phenomenological model of shape memory alloy, which is capable of identifying the main properties of the shape memory alloy, was employed to model the behavior of the shape memory alloy beam. A closed-form numerical algorithm was introduced to simulate the governing... 

This paper investigates the applicability of frequency-domain system identification technique to achieve the equivalent linear dynamics of an autonomous underwater vehicle for control design purposes. Frequency response analysis is performed on the nonlinear and coupled dynamics of the vehicle, utilizing the CIFER® software to extract a reduced-order model in the form of equivalent transfer functions. Advanced features such as chirp-z transform, composite window optimization, and conditioning are employed to achieve high quality and accurate frequency responses. A particular frequency-sweep input is implemented to the nonlinear simulation model to achieve pole-zero transfer functions for yaw... 

Despite their simple structure and design, microcantilevers are receiving increased attention due to their unique sensing and actuation features in many MEMS and NEMS. Along this line, a non-linear distributed-parameters modeling of a microcantilever beam under the influence of a nanoparticle sample is studied in this paper. A long-range Van der Waals force model is utilized to describe the microcantilever-particle interaction along with an inextensibility condition for the microcantilever in order to derive the equations of motion in terms of only one generalized coordinate. Both of these considerations impose strong nonlinearities on the resultant integro-partial equations of motion. In...