مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    254-269
Measures: 
  • Citations: 

    0
  • Views: 

    278
  • Downloads: 

    0
Abstract: 

During the course of expansion in turbines, the steam at first super cools and then nucleated to become a two-phase mixture. This is an area where greater understanding can lead to improved design. This paper describes a numerical method for the solution of two-dimensional two-phase flow of steam in a cascade of turbine blading; the unsteady Euler equations governing the overall behavior of the fluid are combined with equations describing droplet behavior and treated by Jameson's fourth order Runge Kutta time marching scheme which modified to allow for two phase effects. The theoretical surface pressure distributions, droplet radii and contours of constant wetness fraction are presented and results are discussed in the light of knowledge of actual surface pressure distributions

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Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    270-276
Measures: 
  • Citations: 

    0
  • Views: 

    285
  • Downloads: 

    0
Abstract: 

We use two recent codings of binary trees by integer sequences called P-sequences and Ballot-sequences in order to generate binary trees in B-order and Ballot-order. These algorithms generate; each sequence in constant average time O(1). The ranking and unranking algorithms for both sequences with O (n2) time complexity are described

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Author(s): 

RANJBARAN M.

Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    277-282
Measures: 
  • Citations: 

    0
  • Views: 

    284
  • Downloads: 

    0
Abstract: 

In the past 10-15 years the need for the development of specifically engineered .structures of polymers has resulted in the proliferation of products manufactured using various coating and multilayer extrusion technologies. Initializing these technologies, great advantages can be achieved by combining polymers of widely dissimilar solid-state structures and properties into unique multilayer blends and composites. However, the manufacture of these products is not without problems. Many processes are currently hindered due to the occurrence of irregular interfaces and undesirable layer distribution. These irregularities are due to the different rheological properties of the material used and can significantly deteriorate the mechanical or optical properties of the product. Hence, to establish guidelines for the overall processing of multilayer coating and extrusion processes, a better understanding of interfacial instability and deformation of multilayer flow of polymeric fluid is required. In this research, an experimental apparatus has been developed for observing interfacial stability and deformation of multilayer pressure driven channel flows. This apparatus has been used to directly observe the deformation of the interface and growth of interfacial waves in order to enhance our understanding of the effect of viscoelastic forces on stability and deformation of multilayer viscoelastic flow. Due to synergetic effects of combining individual polymers, multilayer films and conjugated fibers have been progressively gaining interest in the past decade. In the manufacture of multilayer products, it is a well-known fact that the multilayer extrusion process is more economical than the conventional laminating process. These products are generally superior to their single component counterparts because of the combining materials with different properties into a single structure. This effect is readily observed in the food packing industry where packing films contain multiple layers, each of which contribute a specific barrier, mechanical or optical property to the resultant film. Interfacial instabilities that manifest themselves in form of traveling waves at the interface are the limiting factor in production of multilayer plastic structures. These interfacial waves result in a significant deterioration of the final products properties of interest (i.e. barrier, mechanical, optical, etc.), hence to better design and control these processes a comprehensive understanding of the interfacial instability phenomenon is required. This would facilitate the selection of materials with suitable rheological properties, proper design of co extrusion die and proper selection of layer ratio within the structure.

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Author(s): 

KERMANSHAH M. | ASGHARI G.

Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    1185-1198
Measures: 
  • Citations: 

    0
  • Views: 

    1153
  • Downloads: 

    0
Abstract: 

This study investigates validity of continuity assumption of error terms underlying multiple linear regression approach of trip generation models for infrequent trips. Since not many household members make daily trips for purposes like shopping or personal business, estimation of such trips with their discrete and non- negative nature and still close to zero averages, using conventional multiple linear regression, needs to be investigated This study employs a two-stage trip generation model, the probability of making/not making trip is modeled first by binary probit, then, number of trips for those who have already made trips are estimated by the weighted least square method The results are then compared with the results of single-stage regression model. The study findings show similarities in both sets of descriptive variables of the regression models. So, no justification was found for employing a very complex two-stage generation model.

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Author(s): 

AMIRSHAHI S.H. | RAFIEE S.H.

Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    1199-1209
Measures: 
  • Citations: 

    0
  • Views: 

    1207
  • Downloads: 

    0
Abstract: 

A Basic form of the Kubelka- tertiary blends of pre-color fibre without any limitation on the number of primaries. Similar to binary blends, the mechanism consists of two simultaneously independent processes. Firstly, the subtractive colour mixing of fibres provides a number of colour dots on the surface of samples. Then, the portative colour mixing of these dots produce the final observed or measured colour. The number of the created colours depends on the number of layers that are necessary to produce an opaque media. An increase in the fibres transparency leads to an increase of the number of colour dots on the surface. The probability of each colour existence depends on the percentages of fibres in blends. Nine layers are considered to provide the media for applying the basic form of the Kubelka; Munk equation due to the processing power of the accessible computer. The media is still translucent in some wavelengths and needs more layers to produce completely opaque substrate. The reflectance values of samples are determined by using this model as well as the Two Constant Kubelka-hunk theory. However, in comparison to the actual reflectance values of the blended samples, the results show that two constant theory leads to smaller error.

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Author(s): 

KABGANIAN M. | ABOLHASSANI A.

Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    1210-1219
Measures: 
  • Citations: 

    0
  • Views: 

    1655
  • Downloads: 

    0
Abstract: 

The present work neals with the study of stability of a vehicle model during a straight path maneuver with braking. The vehicle is represented as three degree of freedom system (longitudinal, lateral and yaw degrees of freedom). After extracting the model's differential equation in front wheel lock condition, sufficient condition for smoothness of system inertial matrix is used to prove exponential stability of vehicle in braking. Sensitivity analysis is performed by the aid of mentioned lemma, the results of analytical analysis are validated by a numerical model.

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Journal: 

AMIRKABIR

Issue Info: 
  • Year: 

    2003
  • Volume: 

    14
  • Issue: 

    56-C
  • Pages: 

    1220-1229
Measures: 
  • Citations: 

    0
  • Views: 

    1117
  • Downloads: 

    0
Abstract: 

Considering the increasing importance of Zinc-Nickel alloy coatings in car industries, extensive research has been done to obtain an optimum conditions for these coatings in various kinds of electrolyte baths, as well as studying their phisyco-chemical properties. In this paper the effect of different factors such as current density, pH and temperature of electroplating bath and the presence of metal ions in bath composition on the chemical composition Zinc-Nickel alloy coatings have been investigated Also some phisyco-chemical properties of these coatings have been studied.

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