2018-01-20T02:24:55Z
http://ijstm.shirazu.ac.ir/?_action=export&rf=summon&issue=235
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
A non model-based damage detection technique using dynamically measured flexibility matrix
Although a numerous methods exist for detecting damage in a structure using measured modal parameters, many of them require a correlated finite element model, or at least, modal data of the structure for the intact state as the baseline. For beam-like structures, curvature techniques, e.g., mode shape curvature and flexibility curvature have been applied to localize damage. An approximate flexibility matrix can be derived using a small number of vibration modes whose columns are referred to as flexibility shapes. In this paper, a damage localization method based on changes in flexibility shapes as well as its curvature is developed. Differential Quadrature Method (DQM) has been implemented to obtain the curvatures of flexibility shapes. It was shown that the method works well using the damaged model alone. To reduce the potential error due to differentiation of experimental data, a moving curve fit method has been implemented on flexibility shapes. The capability of the proposed method is demonstrated through numerical and experimental case studies.
modal analysis
modal testing
Damage detection
2011
04
28
137
149
http://ijstm.shirazu.ac.ir/article_891_ff95c4d5dd9ff75fe5df987720eca9ab.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
Part A: experimental investigation of unsteady supercavitating flows
The present experimental study is the first part of an investigation of unsteady cavitating flows. In the second part, the proper numerical modeling of such flow fields is introduced in order to remove the deficiencies of customary computational models. This study focuses on supercavitation initiation and its transitional process to partial cavitation and, finally, noncavitating flow as the body bears acceleration from rest and deceleration in a water test tank. Using a high speed camera, cavitation bubble status and motion characteristics of the body displacement after being launched in the prepared test tank are recorded and extracted. After processing the recorded images, body motion parameters including, speed, acceleration and consequently the total drag force in addition to cavitation bubble length and diameter were derived. Due to the high acceleration imposed on the body (7000g), during the short interval of launching time, the model design is a complex process compromising low weight and high strength. Some aspects of the test set up and model modification, as well as the proper data processing are explained in this paper.
From the experiments, it is observed that in the accelerating phase, as the velocity increases it is equivalent to lowering the cavitation number, the length of cavitation bubble is also increased, which is consistent with the expectations. However, in the decelerating phase this trend is reversed, which is totally unexpected. Finally, the experimental results are compared with the results of steady state flow field solutions and the difference between the two sets of results is huge. This deficiency is related to the dynamics of unsteady cavitating flow that is discussed in the second part of this paper.
cavitation
experiment
unsteady
2011
04
28
151
165
http://ijstm.shirazu.ac.ir/article_892_6157fd397c92c08cfdffad00ca8acbef.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
Part B: numerical investigation of unsteady supercavitating flows
The present numerical study is the second part of an investigation of unsteady cavitating flows. In the first part, cavity formation, establishment and disappearance were recorded using a high speed camera. Cavitation bubble length and diameter were extracted in accelerating and decelerating phases of model flight. Comparison of the experimental results with those of the steady state flow field solution showed an unacceptable agreement. In the present study a more realistic unsteady cavitating flow field simulation of the first part of the experiments is performed. The actual velocity variation of the experimental test is used in a dynamic mesh, unsteady flow field solution. Numerical results including the length and diameter of partial cavitation bubble in the accelerating phase had fairly good agreement with the experimental results. This is in contrast to the steady numerical results presented in the first part, which had a significant difference with the experiments. The maximum error of the length and diameter of the supercavitation bubble of the first part of the experimental and present numerical results is less than 10%, while the usual steady results are totally unacceptable.
cavitation
numeric
unsteady
2011
04
28
167
182
http://ijstm.shirazu.ac.ir/article_893_dbc45ad4cb20d445660d1ae14830a8e5.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
Maintenance performance evaluation of power generation system of a thermal power plant
The present research deals with the opportunities for the availability predictive modeling of a thermal plant using the Markov process and probabilistic approach. These opportunities will be identified by evaluation of a power generation system of a thermal power plant. This feasibility study covers two areas: development of a predictive model and evaluation of performance with the help of the developed model. The present system under study consists of four subsystems with three feasible states: full working, reduced capacity working and failed. Failure and repair rates of all subsystems are assumed to be constant. After drawing a transition diagram, differential equations are generated and then a probabilistic predictive model using Markov approach has been developed, considering some assumptions. The availability matrix for each subsystem is also developed, which provides various availability levels for different combinations of failure and repair rates of all subsystems. On the basis of this study, the performance of a power generation system is evaluated. The developed model helps in the comparative evaluation of alternative maintenance strategies.
Probabilistic approach
Predictive model
transition diagram
markov approach and availability matrix
2011
04
28
183
195
http://ijstm.shirazu.ac.ir/article_894_78a1ed3c07cfab10015dda302992022d.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
IML robot grasping process improvement
This paper presents an example of how a differential pressure sensor can be used to improve grasping of in-mold-labelling (IML) robots. In order to minimize mold-open time on injection molding machines, shorter operation time is desirable. To achieve this goal, an analysis of grasping labels using the in-mold-labelling robots was done with different approaches to improving the grasping process by measuring pressure in the chambers of the cylinder which carries the tool for grasping labels. The approach that uses the differential pressure sensor has proved best.
IML robot
grasping
pneumatics
2011
04
28
197
207
http://ijstm.shirazu.ac.ir/article_895_eae563a12e3aa732c5a7abf1d0b9d657.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
Mixed convection simulation of inclined lid driven cavity using lattice Boltzmann method
In this study, the mixed convective heat transfer in a lid driven square cavity at different inclination angles is investigated numerically using lattice Boltzmann method with Boussinesq approximation. The vertical walls of the cavity are insulated, while the bottom (hot wall) and top (cold lid) surface are maintained at a uniform temperature. The study is carried out forRichardson numbers ranging from 0.01 to 10 and an inclination angle of cavity ranging from 90 to 90. TheseRichardson numbers are selected based on the inclusion of forced, mixed and natural effects. The result shows that the heat transfer rate is independent of the inclination angle for Ri of 0.01, whereas it changes when theRichardson number increases. Moreover, it has been found that this effect is positive for negative angles and negative for positive angles that are due to the effect of buoyancy force on flow field. In addition, the verity of Nusselt number andRichardson number are opposite because the natural convection changes to mixed or forced convection when theRichardsonnumber decreases. Consequently the Nusselt number increases.
Lattice Boltzmann Method
mixed convection
lid-driven cavity
Richardson number
2011
04
28
209
219
http://ijstm.shirazu.ac.ir/article_896_7b26928b129e7d61fc90e6b9b95b7dff.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
A novel approach to optimize grinding circuits- modelling strategy to monitor ball mill particle size distribution data at Lakan plant
Online monitoring and control of size distribution in any grinding circuit is a vital task in mineral processing plants. Flotation process efficiency depends on the size of feed materials and also fraction of the fine particles e.g. -38 microns. This paper presents a new approach to monitor the size distribution of Lakan Pb/Zn flotation circuit in Iran. A software monitoring size distribution has been developed, based on two main parameters named "n" which is reduction ratio in the mill and "b" which comes from Guadin equation, i.e. W=aDb. "n" depends on mill characters and feed function while "b" depends on ore, instruments, and other properties. Liberation and size fraction studies showed that the d80 of ground material should be -74 microns and weight of passing 38 microns materials should be 35-40%, which is the optimum condition for the flotation recovery. Finally, results obtained from ball mill circuit for "n" and "b" indicated that these parameters were equal to "nBall Mill=80-87" and "bBall Mill=0.84-1.1" at optimum condition. Under this condition, flotation recovery increases up to 75%, which is practically confirmed in Lakan flotation plant.
Monitoring
Modeling
Optimization
size distribution
Ball Mill
Lakan
2011
04
28
221
236
http://ijstm.shirazu.ac.ir/article_897_0f1cc7d9dedb631345d090c987262f93.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2011
35
1
Study of lubricant compressibility effect on hydrodynamic characteristics of heavily loaded journal bearings
By means of numerical techniques, the effect of lubricant compressibility on hydrodynamic behavior of heavily loaded journal bearings is studied in the present work. To reach this goal, the set of continuity and momentum equations for compressible two-dimensional lubricant flow in journal bearings are solved numerically by CFD method. The journal bearing under consideration has infinite length and the lubricant flow is assumed to be laminar and isoviscous. Although the lubricant is liquid, in the cases of high bearing loads, the variation of density with pressure may be important. Therefore, in the computations, the lubricant density is considered variable as a function of pressure. Considering the complex geometry in the physical domain, an attempt is made to transfer the set of governing equations into computational plane by means of conformal mapping. The transformed forms of equations are discretized by the control volume method and are solved using the SIMPLE Algorithm. Results show that the compressibility effect causes an increase in the generated hydrodynamic pressure, such that this effect is enhanced under the condition of high shaft rotational speed, small clearance and high eccentricity ratio.
Compressibility effect
journal bearings
hydrodynamics
CFD
2011
04
28
237
241
http://ijstm.shirazu.ac.ir/article_898_e672ccabcce72b84d2d7dc4f619f90f5.pdf