Sharif Digital Repository

Boiler–turbine units may show quasiperiodic behavior due to the bifurcation occurrence in the presence of harmonic disturbances. In this study, a multi-input–multi-output nonlinear dynamic model of a boiler–turbine unit is considered. Drum pressure, electric output, and fluid density are the state variables and adjusted at the desired values by manipulation of the input variables. Control inputs are the valve positions for fuel, steam and feed-water flow rates. To improve the quasiperiodic behavior of the system and bifurcation control in tracking problem, two controllers are designed: feedback linearization control and nonlinear sliding mode control (SMC). The feedback linearization... 

This paper presents sliding mode control and model reference adaptive control strategies for the tape transport mechanism. A nonlinear multivariable MIMO model of the process, consisting of take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. The sliding mode control is applied for the nonlinear dynamic model of the process, while the model reference adaptive control deals with the linearized one. Moreover, in order to associate with the realistic model of system, design of controllers is accomplished with respect to parametric uncertainties. It is shown that both control strategies can guarantee asymptotic stability of the closed-loop... 

In the machining processes, vibration suppression is crucial in order to achieve the high precision as well as high-quality surface and increase of the material removal rate. In this paper, an adaptive sliding mode control approach is presented to supress the chattering phenomenon in the boring process in the presence of model uncertainties and unmodeled dynamics. The boring bar is modeled as a cantilever Euler–Bernoulli beam, which is actuated by a piezo-actuator located at the bar's end. As a more realistic model, the cutting tool is modeled as an added mass at the bar's end. In order to derive the equations of motion, mode summation method with inclusion the first three modes of vibration... 

In this paper, the modal-based indices are used in damage identification of the wind turbine blade. In contrast of many of previous researches, the geometric nonlinearity due to the large structural deformation of the modern wind turbines blade is considered. In the first step, the finite element model (FEM) of the rotating blade is solved to obtain the modal features of the deformed structure under operational aerodynamic loading. Next, the accuracy and efficiency of the various modal-based damage indices including the frequency, mode shape, curvature of mode shape, modal assurance, modal strain energy (MSE) and the difference of indices (between the intact and damaged blades) are... 

In this paper, a reduced order model for the nonlinear dynamic analysis of the wind turbine blade under operational loading is presented. The accuracy and efficiency of the proposed model are investigated through various static and dynamic analyses. A comprehensive straightforward formulation for the nonlinear beam model is developed based on different large deformation strain theories. Also, the fluid-structure coupling effects due to quasi-steady aerodynamics and gravitational forces are included. The new matrix expressions are introduced for direct conversion of the developed formulation into the reduced order model (ROM). Thereafter, the ROM based on the Galerkin method is developed... 

In this paper, an aeroelastic analysis of a rotating wind turbine blade is performed by considering the effects of geometrical nonlinearities associated with large deflection of the blade produced during wind turbine operation. This source of nonlinearity has become more important in the dynamic analysis of flexible blades used in more recent multi-megawatt wind turbines. The structural modeling, involving the coupled edgewise, flapwise and torsional DOFs, has been performed by using a nonlinear geometrically exact beam formulation. The aerodynamic model is presented based on the strip theory, by applying the principles of quasi-steady and unsteady airfoil aerodynamics. Compared to the... 

In this paper, thermo mechanical finite element analysis of orthogonal machining process with a flexible tool is carried out to study the dynamic behaviour of the machining system and its stability against chatter vibration. By combining the simulation of chip formation in metal cutting with the dynamic phenomena leading to chatter development, the influence of various phenomena, including thermal effects resulting from friction and plastic deformations on the stability of the process are investigated. The novelty of this model is in its ability to evaluate the effect of temperature rise in the cutting zone on the stability of cutting process. Process stability is analyzed and compared for... 

In this study, the artificial neural network (ANN) was used for the prediction of WDT. The inputs to network are molar mass and pressure, and the output is WDT at each input. A two-layer network with different hidden neurons and different learning algorithms such as LM, SCG, GDA and BR were examined. The network with 16 hidden neurons and Levenberg-Marquardt (LM) train function showed the best results in comparison with the other networks. Also, the predicted results of this network were compared with the thermodynamic models and better accordance with experimental data for ANN was concluded  

Acute hypotension episodes are one of the hemodynamic instabilities with high mortality rate that is frequent among many groups of patients. Prediction of acute hypotension episodes can help clinicians to diagnose the cause of this physiological disorder and select proper treatment based on this diagnosis. In this study new physiological time series are generated based on heart rate, systolic blood pressure, diastolic blood pressure and mean blood pressure time series. Statistical features of these time series are extracted and patients whom are exposed to acute hypotension episodes in future 1 hour time interval and whom are not, are classified based on these features and with the aid of... 

The crack growth process in columnar nanocrystalline samples is simulated using the molecular dynamics method. The effects of grain size, grain boundary, crystallographic orientation and crack tip position on the crack growth behavior are investigated. Different sets of samples with mean grain sizes ranging from 4 nm to 14 nm are prepared. Samples with a similar number of grains and identical dimensions are considered for examining the impact of grain boundary and crystallographic orientation. To assess the effect of the grain boundary, no constraint is considered on the position and orientation of grains, while only the grain orientations are changed to examine the effect of... 

Recently, receptance coupling substructure analysis (RCSA) is used for stability prediction of machine tools through its dynamic response determination. A major challenge is the proper modelling of the substructures joints and determination of their parameters. In this paper, a new approach for predicting tool tip FRF is presented. First, inverse RCSA formulation is extended so that the holder FRFs can be identified directly through experimental modal tests. The great advantage of this formulation is its implementation in arbitrary point numbers along joint length. Therefore, in comparison with previous inverse RCSA approaches, a more realistic joint model can be considered. In addition, due... 

Receptance coupling substructure analysis (RCSA) is extensively used to determine the dynamic response of milling tool at its tip for the purpose of prediction of machining stability. A major challenge in using this approach is the proper modelling of the joint between the substructures and determination of its parameters. In this paper, an inverse RCSA is developed for experimental extraction of tool-holder frequency response function (FRF) including joint parameters. The accuracy and efficiency of this method is evaluated through an analytical investigation. It is shown that the extracted holder FRF can provide a highly accurate prediction of the tool tip FRF. The developed method is used... 

Control problem in a biological system is the problem of finding an interventional policy for changing the state of the biological system from an undesirable state, e.g. disease, into a desirable healthy state. Boolean networks are utilized as a mathematical model for gene regulatory networks. This paper provides an algorithm to solve the control problem in Boolean networks. The proposed algorithm is implemented and applied on two biological systems: T-cell receptor network and Drosophila melanogaster network. Results show that the proposed algorithm works faster in solving the control problem over these networks, while having similar accuracy, in comparison to previous exact methods. Source... 

Power augmentation is known to be one of the important applications of Exoskeletons. This paper designs a control strategy to reduce the energy consumed by users in power augmentation mode. The strategy aims to calculate and apply the interaction force between humans and robots according to human intentions. To realize human intentions, the movement's kinematic characteristics and the user's muscular activity were used. The movement patterns were learned by the robot using a set of adaptive oscillators. The human movement pattern in each movement cycle was considered the basis for predicting human intention in the next cycle. Thereby, the robot's optimal path and interaction torque were... 

The high demand for radiotherapy services, combined with the limited capacity of available resources, patient unpunctuality, and series of appointments, makes Patient Appointment Scheduling (PAS) in radiotherapy centers very challenging. Although most centers use a First-Come-First-Serve (FCFS) policy for appointment scheduling, this approach does not consider patients’ behaviors, and consequently, it performs poorly. This type of inappropriate scheduling usually leads to inefficiency at the center and/or patient dissatisfaction. This study provides a data-driven approach to patient appointment scheduling to deal with the challenges mentioned above, and it considers patients’ histories of... 

In this study, 40% CaO/γ-Al2O3 catalyst was used for biodiesel production from corn oil. A transesterification reaction was done for 5h at a temperature of 65°C in the presence of corn oil, methanol (methanol to oil molar ratio of 12:1), and CaO/γ-Al2O3 catalyst (0.06g/g (6wt%)). Catalyst used in this study was synthesized using the sol-gel method. In this method, two parameters of gelation temperature and nitric acid concentration were used as variables in the catalyst synthesis step, and experiments were designed using central composite design (CCD). The results indicate that the optimal point is achieved at a gelation temperature of 70°C and... 

In mechanical assemblies, the performance, quality, cost and assemblability of the product are significantly affected by the geometric errors of the parts. This paper develops the statistical error analysis approach for dimensional control in automotive body multi-station assembly process. In this method, the homogeneous transformation matrices are used to describe the location and orientation of part and assembly features and the small homogeneous transformation matrices are used to model the errors. In this approach, the effective errors in automotive body assembly process are classified in three categories: manufacturing errors (dimensional and geometric tolerances), locating errors... 

To achieve high rate of data transfer, tape mechanisms must be able to transport the tape with a constant velocity for scanning. During this process, it is desired to make the rise time minimized without timing and data transfer errors. In this paper, three servo systems including the take-up and supply reel servos for tape tension control and capstan servo for speed control are considered. So, tape transport mechanisms can be described with a nonlinear multi-input multi-output system (MIMO). After state-space representation of the problem, feedback control is designed for tracking objective. It should be mentioned that an increase in the speed of time response of system corresponds to an... 

During the milling process, self-excited vibration or chatter adversely affects tool life, surface quality and productivity rate. In this paper, nonlinear cutting forces of milling process are considered as a function of chip thickness with a complete third order polynomial (instead of the common linear dependency). An optimal control strategy is developed for chatter suppression of the system described through nonlinear delay differential equations. Counterbalance forces exerted by actuators in x and y directions are the control inputs. For optimal control problem, an appropriate performance index is defined such that the regenerative chatter is suppressed while control efforts are... 

In this study, surface ECG recordings have been used to accomplish a non-invasive method which can predict spontaneous termination of Atrial Fibrillation (AF) and discriminate terminating (T) and non-terminating (N) AF episodes. The data set was provided by Physionet including holter recordings of 50 patients (20 training and 30 test sets). Concerning that most relevant information about the AF exists in the atrial fibrillatory wave, Several spectral and time-frequency parameters were extracted from the ECG signal after canceling the QRST complex. Also a temporal feature, RR interval variation, representing the ventricular activity was calculated. These parameters were evaluated using a...