Print ISSN: 1681-6900

Online ISSN: 2412-0758

### Volume 25, Issue 2, April 2007, Page 23-241

##### Applying the Principle of Maximum Energy Dissipaition in Impact Problems

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 23-33

In this study a dynamic model has been developed for two legs walking machine
for analysing the impact process. Energy dissipation in impact process due to leg
contact with the surface was determined. Then the principle of maximum energy
dissipation was applied to find the vertical and horizontal reaction at the points of
contact of legs with the surface. Also the relation between the angle of compass
(legs angle see fig1), the angular velocity prior impact and the vertical and
horizontal reactions at the points of contact is studied in order to determine the
optimum angle that gives a stable walking process and reduces vibration.

##### The Boundary Element Method Versus The Finite Element Method For Solving Two-Dimensional Continuum Problems

Damluji; Omar al-Farouk S. al; Mohammed Yousif Fattah

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 132-152

Stress analysis problems in geomechanics are ideally suited to the method of boundary
elements, as this technique usually requires a very small number of nodes by
comparison to finite elements. As only the surface of the continuum needs to be
discretized, problems extending to infinity can be described by a very small number
of elements on the soil surface or around a tunnel or excavation . In addition, the
boundary conditions of the infinite domain can be properly defined using boundary
elements, as the technique is based on fundamental solutions valid for unbounded
domains.
Herein, a comparison is made between the finite element method and the boundary
element method in solving two-dimensional stress analysis problems. It is concluded
that the results of the boundary element method are greatly improved when
increasing the number of elements, especially at the regions of stress concentration. A
good agreement can be obtained between the results of the two methods. One must
keep in mind that in the boundary element method, errors due to discretization are
restricted to the boundaries compared to the finite element method where the entire
domain needs to be discretized. This advantage makes the use of the boundary
element method easier and faster.

##### Surface matrix based Machining Planes Determination for Milling Process (Roughing Stage)

Laith A. Mohammed

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 153-167

This paper deals with machining plane determination process for CNC milling
machining. Three methods, Matrix, 3D contour matrix and flow line are
presented. All methods depend on the data set point of the surface matrix of
the workpiece to be machined. All methods can be used to automate the
CAD/CAM operation for roughing process in milling machining. Two surface
examples are included to illustrate all methods. By a comparison among the
three presented methods, a conclusion has been reached that the presented 3D
contour matrix method requires maximum number of blocks to build G-codes
program for CNC tool path programming. It means that, this method requires
longer time to accomplish tool paths. On the other hand the other two
methods require minimum number of blocks of G-codes and shorter time for
roughing.

##### Features of Spot-Matrix Surface Hardening of Low-Carbon Steel Using Pulsed Laser

Khawla S. Khashan; Oday A. Hamadi

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 168-175

In this work, results of spot hardening in low-carbon steel by using a pulsed
Nd:YAG laser are presented. These results include determination of
hardening depth, diameter of hardened spot, aspect ratio and heat-affected
zone width with varying laser energy density. In order to determine the effect
of irradiation profile on the overall achievable hardness, the profiles of
overlapping, adjacent and separated hardened spots are compared and the
percent coverage of the workpiece as a function of the laser-hardened spot
dimensions.

##### Fabrication and Characterization of Cu2S /Si Heterojunction Photodetector Based on Spray Pyrolysis of Cu2S on Si

Khaled Z. Yahiya; Yasmeen; Z. Daood; Saria D. Ahmed

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 176-182

In the present work fabrication and characterization of Cu2S/Si
heterojunction photodiodes made by spray pyrolysis method using aqueous
solution of CuCl2.2H2O onto n-type silicon substrates made. The external
quantum efficiency of heterojunction was ٣7% at wavelength of 850nm. The
experimental results show peak relative responsivity around 100mA/w , and
maximum value of detectivity D* (2*1011cm.Hz1/2.w-1).

##### The Effect of Initial Temperature on Burning Velocity of Hydrogen – Air Mixtures

M. N. Hamid; Arkan F. Said

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 183-194

In present work, the burning velocity of hydrogen-Air mixtures varies
with hydrogen concentration and initial temperature of the unburned
mixture. Laminar flame speed has been measured experimentally inside tube
using the optical technique. The experimental work was carried out in a prepressure
period in order to apply the density ratio method for calculation of
laminar burning velocity. Mixture strength and unburned mixture
temperature dependence of burning velocity is represented by empirical
function over the ranges of hydrogen concentration (xH2 = 10 – 70 %) and
unburned temperature (Tu = 298K– 348K), which is extended to (473K)
through the previously published data all at a pressure of (1 atm). In
overlapping ranges, the results show good agreement with those previously
published.

##### Prediction of Delay at a Parking Garage Facility Using STARSIM Simulation Package

Emad A. Ismail; Ali M. K. Al-Ubaidy

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 195-209

The main objective of the present paper is to predict the average delay values
for delayed vehicles at the adjacent entrance and exit gates combination of a
parking garage using a simulation package named STARSIM. Flow level,
number of lanes at each approach of the major road, number of lanes at the
entrance and exit gates, and proportion of parking vehicles from the major
road are taken as the most important factors that affect the performance of the
gates of the car park in term of average delay to be predicted in this paper.
These traffic and geometrical conditions are used to generate a range of delay
values, and the effect of these conditions on the performance of the entrance
and exit gates, in term of delay, is discussed and presented figuratively.

##### Nonlinear Finite Element Analysis of Reinforced Concrete Beams with Large Opening under Flexure

Ihsan A. S. Al-Shaarbaf; Nabil A-M. J. Al-Bayati; Dhar I. A. Al-Kaisy

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 210-228

This paper describes a three- dimensional nonlinear finite element model
suitable for the analysis of reinforced concrete Beams with Large Opening
under Flexure. The 20-node isoparametric brick elements have been used to
model the concrete. The nonlinear equations of equilibrium have been solved
using an incremental-iterative technique operating under load control. The
solution algorithm used was the modified Newton-Raphson method. The
numerical integration has been conducted using the 27-point Gaussian type
rule. The reinforcing bars are idealized as axial members embedded within
the concrete element and perfect bond between the concrete and the
reinforcement has been assumed to occur. The behavior of concrete in
compression is modeled using an elasto-plastic work hardening model
followed by a perfectly plastic response, which is terminated at the onset of
crushing. In tension, a smeared crack model with fixed orthogonal cracks has
been used with the inclusion of models for the retained post-cracking tensile
stress and the reduced shear modulus. Different types of reinforced concrete
beams with large rectangular transverse openings have been analyzed and the
finite element solutions are compared with the experimental data. Generally,
good agreement has been obtained between the numerical and experimental
material parameters such as concrete compressive strength, amount of
longitudinal tensile reinforcement and opening size on the load-deflection
response have been carried out to study their effect on the over all behavior of
reinforced concrete beams with Large opening under Flexure.The finite
element solution revealed that the ultimate load and post-cracking stiffness
increase with the increases of concrete compressive strength, increases with
the increase of the bottom steel reinforcement amount and decreases with the
increase of length or depth of opening.

##### Laplace Transformation for Determining The Linear Equivalence of The Periodic Sequence

Engineering and Technology Journal, 2007, Volume 25, Issue 2, Pages 229-241

The research presents a proposed method with an algorithm written in
Matlab language to determine the linear equivalence of the pseudo-random
periodic sequences mathematically by using the Laplace transform. The
proposed method enables the computation of the linear equivalence to
determine the degree of the complexity of any periodic sequences produced
from linear or nonlinear key generators. The procedure can be used
comparatively greater computational ease and efficiency. The results of this
algorithm are compared with Berlekamp-Massey (BM) method and good
results are obtained where the results of the Laplace transform are more
accurate than those of (BM) method for computing the linear equivalence (L)
of the sequence of period (p) when (L) is greater than (p/2). Some examples
are given for consolidating the accuracy of the results of this proposed
method.