Browsing by Author "Getachew, Dereje"

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    Sliding Mode Control of a 2 DOF Of Freedom Robot Arm Using Permanent Magnet Synchronous Motor
    (2018-03) Getachew, Dereje; Mengesha, Mamo (PhD)
    This thesis study aims at the problem of modeling and control of a two DOF robot arm using Permanent magnet synchronous actuators. Permanent magnet synchronous actuator have been used in various industrial and domestic applications because of its advantages like simple structure, large torque, long use. Trajectory tracking is a very difficult topic in robot arm control. This is due the nonlinearities and input couplings present in the dynamics of the arm caused by dynamics changes rapidly as the manipulator moves within its working range. Moreover, for a robot with gear transmissions, the gears have nonlinearities such as hysteresis, backlash, friction, and nonlinear elasticity. In industrial applications such complex systems are controlled using the traditional PID controllers. However, a major drawback of the linear PID control is failed to track the desired trajectory of the robot arm when the nonlinear system dynamics is dominant. In this thesis sliding mode controller is modeled to overcome the shortcomings of PID controller. The SMC is designed to control the joint trajectory of the robot. SMC adopts a switching function, and these results in high-frequency oscillations (the so-called chattering) in the control signal. To reduce chattering, saturation function is used. The simulation is carried out using Level-2 MAT-LAB s-function and Simulink. PID controller is designed for the comparison purpose with SMC without disturbance and parameter variation and the result shows Steady State error of SMC is 0.029% for joints one and 0.0098% for joint two and increased to 15% and 24% respectively overshoot remain the same, rise time is decreased by 0.16sec, and settling time is decreased by 0.4sec for both joints when PID controller is used. The SMC and PID with disturbance and parameter variation also tested and results show that the performances with disturbance and parameter variation are almost the same for SMC. The control input voltage is increased by 0.03v and 0.02v for joint one and two respectively for SMC. However the amplitude of the control effort of PID controller with disturbance and parameter variation is much larger when compared to the control effort without disturbance and it is increased by 18v and 6.5v. Generally from the result it is possible to conclude that SMC has better performance, more stable and robust than PID controller.
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    Synthetic Unit Hydrograph Derivation Using Giuh And Giuh Based Nash Iuh Models forUngauged Catchments in Abbay
    (Addis Ababa University, 2011-06) Getachew, Dereje; Ayalew, Semu(PhD)
    Geomorphologic instantaneous unit hydrograph (GIUH) can be used as a transfer function for modeling the transformation of excess rainfall into surface runoff, in which excess rainfall is a production function to the hydrologic system. These models can be used to predict the temporal variation of the surface runoff at the outlet of ungauged catchment, which is useful in the hydrologic engineering applications. In this study the two types of geomorphologic approaches were studied, GIUH and GIUH based Nash IUH models, for unit hydrograph derivation from the observed data. The geomorphological characteristics of a catchment were related with the shape and scale parameters of the Nash IUH to derive the complete shape of the GIUH based Nash IUH model; and GIUH was developed from geomorphological characteristics of the catchments and probability density function of travel time of rainfall excess to the catchment outlet. These two models were developed in seven catchments in Abay basin (Fettam, Hoha, Neshi, Uke, Andassa, Azuari and Jedebe) with range of areas 161 to 573km2. In this study, velocity was set as a calibration parameter to calibrate the simulated unit hydrograph with the observed unit hydrograph in both models. A regionalized streamflow velocity equation was developed from the simulated data with R2 equal to 0.89 and 0.96 for GIUH and GIUH based Nash IUH model respectively. Then, these equations were applied on chemoga catchment, which was considered as ungauged catchment, to observe the reliability of the models. The performances of the calibrated models were evaluated using Nash-Sutcliffe efficiency (NSE), Error (ERR), percentage error in peak discharge (PEP) and percentage error in time to peak (PETP). From model evaluation results, GIUH model efficiency (EFF) varies from 81.95 to 97.9 percent while GIUH based Nash IUH model efficiency varies from 75.68 to 97.51 percent. GIUH model is efficient in peak discharge estimation (R2=0.988) than GIUH based Nash IUH model (R2=0.884). In general, the result of both GIUH and GIUH based Nash IUH models are almost comparable and their results are acceptable but the GIUH model is superior. ii Moreover, a simple GIUH based regional triangular unit hydrograph equations were developed and compared with the SCS triangular unit hydrograph. The R2 value in peak discharge estimation using SCS method is 0.48 while using GIUH method is 0.95. This implies that the derived GIUH based regional triangular unit hydrograph equation is quite different from SCS triangular unit hydrograph and GIUH has better efficiency. Finally, this paper concludes that, the regionalized GIUH based equation for peak discharge, time to peak and base time of the triangular unit hydrograph can be used, within the errors specified in this research paper, for any ungauged catchment found in neighbor of the study area having similar character and varying in areas from 161 to 573km2. Further work may in the future be required to explain any non linear relationship of rainfall runoff and homogeneity of the catchments. KEY WORDS: Geomorphologic Instantaneous Unit Hydrograph (GIUH), Nash IUH Model, ILWIS (Integrated Land and Water Information System), Rainfall-Runoff modeling, Ungauged Catchment.