Ahmed Mahdi Kridi | University of Baghdad (original) (raw)

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Papers by Ahmed Mahdi Kridi

The effected of the long transmission line (TL) between the actuator and the hydraulic control va... more The effected of the long transmission line (TL) between the actuator and the hydraulic control valve sometimes essentials. The study is concerned with modeling the TL which carries the oil from the electro-hydraulic servovalve to the actuator. The pressure value inside the TL has been controlled by the electro-hydraulic servovalve as a voltage supplied to the servovalve amplifier. The flow rate through the TL has been simulated by using the lumped π element electrical analogy method for laminar flow. The control voltage supplied to servovalve can be achieved by the direct using of the voltage function generator or indirect C ++ program connected to the DAP-view program built in the DAPcard data acquisition connected to PC, to control the value of pressure in a selected point in the TL. It has been found that the relation between the voltage value and the output flow rate from the servovalve in most of the path is a linear relation. The MATLAB m-File program is used to create a representation state of the mathematical model to find a good simulation for the experimental open loop control test.

Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Eu... more Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Euler equation. An algorithm based on finite difference McCormack's technique is used to solve the subsonic-supersonic flow problem with and without by-passing. Trials on by-pass locations were also made. Operation without bypass shows the movement of the normal shock wave upstream which refers to an off-design operating regime. At a distance of 1.271 m measured from the cowl lip, the region of normal shock wave was localized near the throat which approximately represents the on-design perform 0ance condition (cells 8-9). When the flow is bypassed from the rear passages, the normal shock wave is sucked inside the flow passage save poor performance. Results show that by-passing provides a fast reaction to maintain a steady performance which meets the requirements of ondesign operation. The Mach number variation corresponding to each case is presented. Results show that the tendency to u...

Numerical solutions of two dimensional Euler equations are obtained for transonic and supersonic ... more Numerical solutions of two dimensional Euler equations are obtained for
transonic and supersonic flows. The shock capturing method is employed to solve
compressible Euler equations by using MacCormack's time marching method that
an explicit finite-difference technique. The test case chosen is that of a transonic
and supersonic flow through a channel with a circular arc bump on the lower wall,
half wedge and extended compression corner. Computational results accurately
reproduced the flow field. In three cases, contour plots showing the important
features of the flow-field are presented. The algorithm is tested for steady-state
inviscid flows at different Mach numbers ranging from the transonic to the supersonic
regime and the results are compared with the existing numerical solutions. The
method incorporates bounded high resolution of discontinuities and is therefore well
suited to all flow regimes ranging from transonic to supersonic.

Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Eu... more Two-dimensional, supersonic flow field computation with by-pass holes has been
conducted using Euler equation. An algorithm based on finite difference
McCormack's technique is used to solve the subsonic-supersonic flow problem with
and without by-passing. Trials on by-pass locations were also made. Operation
without bypass shows the movement of the normal shock wave upstream which
refers to an off-design operating regime. At a distance of 1.271 m measured from the
cowl lip, the region of normal shock wave was localized near the throat which
approximately represents the on-design perform 0ance condition (cells 8-9). When
the flow is bypassed from the rear passages, the normal shock wave is sucked inside
the flow passage save poor performance. Results show that by-passing provides a
fast reaction to maintain a steady performance which meets the requirements of ondesign
operation. The Mach number variation corresponding to each case is
presented. Results show that the tendency to unity Mach number near the cowl lip
sector can be achieved using by-pass expelled. The influence of by-pass on the total
pressure recovery and relative pressure is also discussed.

The determination of aerodynamic coefficients by shell designers is a critical step in the develo... more The determination of aerodynamic coefficients by shell designers is a critical step in the development of any projectile design. Of particular interest is the determination of the aerodynamic coefficients at transonic speeds. It is in this speed regime that the critical aerodynamic behavior occurs and a rapid change in the aerodynamic coefficients is observed. Two-dimensional, transonic, flow field computations over projectiles have been made using Euler equations which were used for solution with no special treatment required. In this work a solution algorithm is based on finite difference MacCormack’s technique for solving mixed subsonic-supersonic flow problem. Details of the asymmetrically located shock waves on the projectiles have been determined. Computed surface pressures have been compared with experimental data and are found to be in good agreement. The pitching moment coefficient, determined from the computed flow fields, shows the critical aerodynamic behavior observed in free flights.

A solar chimney has been analyzed by solving its governing equations and compare with the simulat... more A solar chimney has been analyzed by solving its governing equations and compare with the simulated results. The solar absorbent of the chimney is selected as a black painted concrete, which is useful as an energy saver at night. The numerical simulation using ANSYS, based on solving the governing equations with suitable assumptions and boundary conditions for many variables such as the collector area, the chimney height, the ambient temperature, and the exit area of the chimney. The results shows that the chimney height and base area are very important parameters for improving the gained power, and it is also important to choose the region with suitable mean ambient temperature. And economically there are limitations to collector and chimney sizes to get suitable profit output power and any increment in system size becomes a small percentage increment in profit output power. The results compared with some experimental data from other results researchers and there is a good agreement between simulated and calculated results.

In this research, the Buoyancy heat transfer and flow patterns in a partially divided square encl... more In this research, the Buoyancy heat transfer and flow patterns in a partially
divided square enclosure with staggered partitions have been studied numerically.
The partitions were distributed on the lower and upper surfaces of the box in
staggered manner. The height of the partitions was varied. The conduction heat
transfer through the fins (partitions) was also included. It is assumed that the
vertical walls of enclosure were adiabatic and its horizontal walls were maintained
at uniform but in different temperature. The problem was formulated in terms of
the stream function-vorticity procedure. The numerical solution based on the
transformation of the governing equations by using finite difference method was
obtained. The effect of increasing the partition height and Rayleigh number on
contour maps of the stream lines and temperature were reported and discussed. In
addition, the research presented and discussed the results of the average Nussult
number of the enclosures heated wall at various Rayleigh number and
dimensionless partition heights. The results showed that the mean Nussult number
increases with the increasing of Rayleigh number and decreases with the
increasing of partition heights. The distributed heat by conduction through the
partition increases with the increasing of the partition height especially at
(H/L ≥ 0.3). A comparison between the obtained results and the published
computational studies has been made and it showed a good agreement with
percentage error not exceed (0.54%).

The effected of the long transmission line (TL) between the actuator and the hydraulic control va... more The effected of the long transmission line (TL) between the actuator and the hydraulic control valve sometimes
essentials. The study is concerned with modeling the TL which carries the oil from the electro-hydraulic servovalve to
the actuator. The pressure value inside the TL has been controlled by the electro-hydraulic servovalve as a voltage
supplied to the servovalve amplifier. The flow rate through the TL has been simulated by using the lumped π element
electrical analogy method for laminar flow. The control voltage supplied to servovalve can be achieved by the direct
using of the voltage function generator or indirect C++ program connected to the DAP-view program built in the DAPcard
data acquisition connected to PC, to control the value of pressure in a selected point in the TL. It has been found
that the relation between the voltage value and the output flow rate from the servovalve in most of the path is a linear
relation. The MATLAB m-File program is used to create a representation state of the mathematical model to find a
good simulation for the experimental open loop control test.

Thesis Chapters by Ahmed Mahdi Kridi

The control concept on the electro-hydraulic servovalve system focuses on the pressure control, p... more The control concept on the electro-hydraulic servovalve system focuses on the pressure control, position control and velocity control. The servovalve and the system components are needed to be considered in the proposed control strategy. The control concepts on the electro-hydraulic servovalve systems in this work are divided into two parts:
1. Theoretical and experimental investigation for pressure control on the electro-hydraulic servovalve systems.
The pressure control study in this work is concerned with the modeling and controlling of the hydraulic fluid pressure value at the end of long transmission line (TL) by using the electro-hydraulic servovalve. The input voltage signals to the amplifier, designed by C++ program, are used to control the pressure reference signal at the end of TL. The electrical analogy method is used to simulate the effect of the TL, as well as the first order transfer function to simulate the servovalve effect. Therefore, the whole system is represented mathematically in MATLAB m-file program. The mathematical model is seen as a good simulation approach compared with the experimental open loop control test. The on-line adjustable control strategy, Ziegler & Nichols method and Astrom & Hagglund method, can be used experimentally to find the proportional and integral control gain values for acceptable control system behavior. The servovalve succeeds to reduce and overcome the negative effect of the TL on the hydraulic fluid pressure value at the chosen control point.
2. Theoretical and experimental investigation for velocity and position control by the electro-hydraulic servovalve system.
The C++ language programs are designed to control the position and velocity of the road simulator (single-rod, double acting linear cylinder actuator) with variable load (quarter car suspension system). The whole system is analyzed mathematically and experimentally. The mathematical model of the electro-hydraulic servovalve system is represented and analyzed successfully by designing the SIMULINK program.
The dynamics modeling of the servovalve and the single road cylinder actuator under variable load which are controlled as a closed loop position control method with existence of the actuator internal leakage is done successfully by using the SIMULINK environments. So, the transfer function and the state-space model of the system in open and closed loop control are presented. Also, the Bode diagram is done for the system as well as the stability characteristics are found for the system by the Nyquist Diagram.
The on-line adjustable PID control tuning is employed experimentally to find the best control gain values which are applied to the system. In the mathematical SIMULINK program, the PID gains values are tuned manually and automatically by computing a linear model of the plant. The tuning strategies are done automatically for the P, PI and PID strategies for three different response time values. The comparison figures in the P strategy show that the simulation programs give a good and accurate prediction results and enhance the system behavior. On the other hand, the PI strategy shows incompatible results between the actual test and the simulation program. The PID strategy shows a good prediction results. To analyze the actual fully system behaviors for a large spectrum frequency, the numbers of sinusoidal voltage input signal are used with unity compensator to create actual Bode plot. The tracking closed loop control method is done experimentally by designing C++ program and it is done theoretically by the SIMULINK simulation program for the system. The comparison result with the previous research clarifies that the mathematical solution method proposed in this dissertation shows that the prediction of the system behavior is acceptable and improve the system behavior.

The effected of the long transmission line (TL) between the actuator and the hydraulic control va... more The effected of the long transmission line (TL) between the actuator and the hydraulic control valve sometimes essentials. The study is concerned with modeling the TL which carries the oil from the electro-hydraulic servovalve to the actuator. The pressure value inside the TL has been controlled by the electro-hydraulic servovalve as a voltage supplied to the servovalve amplifier. The flow rate through the TL has been simulated by using the lumped π element electrical analogy method for laminar flow. The control voltage supplied to servovalve can be achieved by the direct using of the voltage function generator or indirect C ++ program connected to the DAP-view program built in the DAPcard data acquisition connected to PC, to control the value of pressure in a selected point in the TL. It has been found that the relation between the voltage value and the output flow rate from the servovalve in most of the path is a linear relation. The MATLAB m-File program is used to create a representation state of the mathematical model to find a good simulation for the experimental open loop control test.

Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Eu... more Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Euler equation. An algorithm based on finite difference McCormack's technique is used to solve the subsonic-supersonic flow problem with and without by-passing. Trials on by-pass locations were also made. Operation without bypass shows the movement of the normal shock wave upstream which refers to an off-design operating regime. At a distance of 1.271 m measured from the cowl lip, the region of normal shock wave was localized near the throat which approximately represents the on-design perform 0ance condition (cells 8-9). When the flow is bypassed from the rear passages, the normal shock wave is sucked inside the flow passage save poor performance. Results show that by-passing provides a fast reaction to maintain a steady performance which meets the requirements of ondesign operation. The Mach number variation corresponding to each case is presented. Results show that the tendency to u...

Numerical solutions of two dimensional Euler equations are obtained for transonic and supersonic ... more Numerical solutions of two dimensional Euler equations are obtained for
transonic and supersonic flows. The shock capturing method is employed to solve
compressible Euler equations by using MacCormack's time marching method that
an explicit finite-difference technique. The test case chosen is that of a transonic
and supersonic flow through a channel with a circular arc bump on the lower wall,
half wedge and extended compression corner. Computational results accurately
reproduced the flow field. In three cases, contour plots showing the important
features of the flow-field are presented. The algorithm is tested for steady-state
inviscid flows at different Mach numbers ranging from the transonic to the supersonic
regime and the results are compared with the existing numerical solutions. The
method incorporates bounded high resolution of discontinuities and is therefore well
suited to all flow regimes ranging from transonic to supersonic.

Two-dimensional, supersonic flow field computation with by-pass holes has been conducted using Eu... more Two-dimensional, supersonic flow field computation with by-pass holes has been
conducted using Euler equation. An algorithm based on finite difference
McCormack's technique is used to solve the subsonic-supersonic flow problem with
and without by-passing. Trials on by-pass locations were also made. Operation
without bypass shows the movement of the normal shock wave upstream which
refers to an off-design operating regime. At a distance of 1.271 m measured from the
cowl lip, the region of normal shock wave was localized near the throat which
approximately represents the on-design perform 0ance condition (cells 8-9). When
the flow is bypassed from the rear passages, the normal shock wave is sucked inside
the flow passage save poor performance. Results show that by-passing provides a
fast reaction to maintain a steady performance which meets the requirements of ondesign
operation. The Mach number variation corresponding to each case is
presented. Results show that the tendency to unity Mach number near the cowl lip
sector can be achieved using by-pass expelled. The influence of by-pass on the total
pressure recovery and relative pressure is also discussed.

The determination of aerodynamic coefficients by shell designers is a critical step in the develo... more The determination of aerodynamic coefficients by shell designers is a critical step in the development of any projectile design. Of particular interest is the determination of the aerodynamic coefficients at transonic speeds. It is in this speed regime that the critical aerodynamic behavior occurs and a rapid change in the aerodynamic coefficients is observed. Two-dimensional, transonic, flow field computations over projectiles have been made using Euler equations which were used for solution with no special treatment required. In this work a solution algorithm is based on finite difference MacCormack’s technique for solving mixed subsonic-supersonic flow problem. Details of the asymmetrically located shock waves on the projectiles have been determined. Computed surface pressures have been compared with experimental data and are found to be in good agreement. The pitching moment coefficient, determined from the computed flow fields, shows the critical aerodynamic behavior observed in free flights.

A solar chimney has been analyzed by solving its governing equations and compare with the simulat... more A solar chimney has been analyzed by solving its governing equations and compare with the simulated results. The solar absorbent of the chimney is selected as a black painted concrete, which is useful as an energy saver at night. The numerical simulation using ANSYS, based on solving the governing equations with suitable assumptions and boundary conditions for many variables such as the collector area, the chimney height, the ambient temperature, and the exit area of the chimney. The results shows that the chimney height and base area are very important parameters for improving the gained power, and it is also important to choose the region with suitable mean ambient temperature. And economically there are limitations to collector and chimney sizes to get suitable profit output power and any increment in system size becomes a small percentage increment in profit output power. The results compared with some experimental data from other results researchers and there is a good agreement between simulated and calculated results.

In this research, the Buoyancy heat transfer and flow patterns in a partially divided square encl... more In this research, the Buoyancy heat transfer and flow patterns in a partially
divided square enclosure with staggered partitions have been studied numerically.
The partitions were distributed on the lower and upper surfaces of the box in
staggered manner. The height of the partitions was varied. The conduction heat
transfer through the fins (partitions) was also included. It is assumed that the
vertical walls of enclosure were adiabatic and its horizontal walls were maintained
at uniform but in different temperature. The problem was formulated in terms of
the stream function-vorticity procedure. The numerical solution based on the
transformation of the governing equations by using finite difference method was
obtained. The effect of increasing the partition height and Rayleigh number on
contour maps of the stream lines and temperature were reported and discussed. In
addition, the research presented and discussed the results of the average Nussult
number of the enclosures heated wall at various Rayleigh number and
dimensionless partition heights. The results showed that the mean Nussult number
increases with the increasing of Rayleigh number and decreases with the
increasing of partition heights. The distributed heat by conduction through the
partition increases with the increasing of the partition height especially at
(H/L ≥ 0.3). A comparison between the obtained results and the published
computational studies has been made and it showed a good agreement with
percentage error not exceed (0.54%).

The effected of the long transmission line (TL) between the actuator and the hydraulic control va... more The effected of the long transmission line (TL) between the actuator and the hydraulic control valve sometimes
essentials. The study is concerned with modeling the TL which carries the oil from the electro-hydraulic servovalve to
the actuator. The pressure value inside the TL has been controlled by the electro-hydraulic servovalve as a voltage
supplied to the servovalve amplifier. The flow rate through the TL has been simulated by using the lumped π element
electrical analogy method for laminar flow. The control voltage supplied to servovalve can be achieved by the direct
using of the voltage function generator or indirect C++ program connected to the DAP-view program built in the DAPcard
data acquisition connected to PC, to control the value of pressure in a selected point in the TL. It has been found
that the relation between the voltage value and the output flow rate from the servovalve in most of the path is a linear
relation. The MATLAB m-File program is used to create a representation state of the mathematical model to find a
good simulation for the experimental open loop control test.

The control concept on the electro-hydraulic servovalve system focuses on the pressure control, p... more The control concept on the electro-hydraulic servovalve system focuses on the pressure control, position control and velocity control. The servovalve and the system components are needed to be considered in the proposed control strategy. The control concepts on the electro-hydraulic servovalve systems in this work are divided into two parts:
1. Theoretical and experimental investigation for pressure control on the electro-hydraulic servovalve systems.
The pressure control study in this work is concerned with the modeling and controlling of the hydraulic fluid pressure value at the end of long transmission line (TL) by using the electro-hydraulic servovalve. The input voltage signals to the amplifier, designed by C++ program, are used to control the pressure reference signal at the end of TL. The electrical analogy method is used to simulate the effect of the TL, as well as the first order transfer function to simulate the servovalve effect. Therefore, the whole system is represented mathematically in MATLAB m-file program. The mathematical model is seen as a good simulation approach compared with the experimental open loop control test. The on-line adjustable control strategy, Ziegler & Nichols method and Astrom & Hagglund method, can be used experimentally to find the proportional and integral control gain values for acceptable control system behavior. The servovalve succeeds to reduce and overcome the negative effect of the TL on the hydraulic fluid pressure value at the chosen control point.
2. Theoretical and experimental investigation for velocity and position control by the electro-hydraulic servovalve system.
The C++ language programs are designed to control the position and velocity of the road simulator (single-rod, double acting linear cylinder actuator) with variable load (quarter car suspension system). The whole system is analyzed mathematically and experimentally. The mathematical model of the electro-hydraulic servovalve system is represented and analyzed successfully by designing the SIMULINK program.
The dynamics modeling of the servovalve and the single road cylinder actuator under variable load which are controlled as a closed loop position control method with existence of the actuator internal leakage is done successfully by using the SIMULINK environments. So, the transfer function and the state-space model of the system in open and closed loop control are presented. Also, the Bode diagram is done for the system as well as the stability characteristics are found for the system by the Nyquist Diagram.
The on-line adjustable PID control tuning is employed experimentally to find the best control gain values which are applied to the system. In the mathematical SIMULINK program, the PID gains values are tuned manually and automatically by computing a linear model of the plant. The tuning strategies are done automatically for the P, PI and PID strategies for three different response time values. The comparison figures in the P strategy show that the simulation programs give a good and accurate prediction results and enhance the system behavior. On the other hand, the PI strategy shows incompatible results between the actual test and the simulation program. The PID strategy shows a good prediction results. To analyze the actual fully system behaviors for a large spectrum frequency, the numbers of sinusoidal voltage input signal are used with unity compensator to create actual Bode plot. The tracking closed loop control method is done experimentally by designing C++ program and it is done theoretically by the SIMULINK simulation program for the system. The comparison result with the previous research clarifies that the mathematical solution method proposed in this dissertation shows that the prediction of the system behavior is acceptable and improve the system behavior.