Geometric features of the flame propagation process for an SI engine having dual‐ignition system

Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd.     

THE RELATION BETWEEN WETTING EFFICIENCY AND LIQUID HOLDUP IN PACKED COLUMNS

Liquid holdup and wetting efficiency in packed columns were determined using a tracer method. A new model was developed considering axial dispersion, and analysis was made using the moment technique. The saturated solution of KG was used as an inert tracer and total liquid holdups were determined in the first part of experiments. As an adsorbable tracer, dioxane was utilized in the second part of the work and wetting efficiencies were obtained. Adsorption equilibrium constant was determined by the experiments conducted in a liquid full bed. A model proposed between liquid holdup and wetting efficiency gave good agreement with the experimental results. Axial dispersion effects were also taken into account during the work. It was also shown that axial dispersion of liquid phase should be considered especially in the small scale trickle bed reactors. @KEYWORDS:Packed beds,Wetting efficiency,Liquid holdup,Tracer method,Moment technique,Trickle bed reactors.     

Methacrylate-functionalized POSS influence on cross-linking and mechanical properties of styrene-butadiene rubber

Iranian Polymer Journal - The addition of methacrylate-functional polyhedral oligomeric silsesquioxane (MA-POSS) nanoparticles to styrene-butadiene rubber (SBR) composites was evaluated in terms of...     

Investigating the influence of tool shape during FSW of aluminum alloy via CFD analysis

This paper describes the application of the CFD code, Comsol Multiphysics, to modeling the 3-D metal flow in friction stir welding of AA 2024-T3 aluminum alloy in order to investigate the influence of tool shape over the metal flow. Heat transfer and non-Newtonian flow equations were solved simultaneously. The results from the benchmark experiments found in the literature were used for validation purposes. Scrolled shoulders and threaded pins were given as kinematic boundary conditions. This made the computational problem an easy one. A welding engineer can predict the metal flow around the tool with different scrolls and threads under any welding conditions without making expensive experiments. Investigation of the velocity field before actual welding can save a lot of engineering hours.     

Two new control signal approaches for obtaining the MRAS-CDM and a real-time application

The coefficient diagram method (CDM) is one of the most effective control design methods. It creates control systems that are very stable and robust with responses without the overshoot and small settling time. Furthermore, all control parameters of the control systems are changed by varying some adjustment parameters in CDM depending on the demands. The model reference adaptive systems (MRAS) are the systems that follow and change the control parameters according to a given model reference system. There are several methods to combine the CDM with MRAS. One of these is to use the MRAS parameters as a gain of the CDM parameters. Another is to directly use the CDM parameters as the MRAS parameters. In the industrial applications, the system parameters can be changed frequently, but if the controller, by self-tuning, recalculates and develops its own parameters continuously, the system becomes more robust. Also, if the poles of the controlled systems approach the jw axis, the response of the closed-loop MRAS becomes more and more insufficient. In order to obtain better results, CDM is combined with a self-tuning model reference adaptive system. Systems controlled by a model reference adaptive controller give responses with small or without overshoot, have small settling times, and are more robust. Thus, in this paper, a hybrid combination of MRAS and CDM is developed and two different control structures of the control signal are investigated. The two methods are compared with MRAS and applied to real-time process control systems.     

Resource Leveling in Line‐of‐Balance Scheduling

Resource leveling involves minimizing resource fluctuations without changing the completion time of a project. A smooth distribution of resources minimizes logistical problems and results in cost savings. Line‐of‐balance (LOB) is a resource‐based scheduling system that is used in projects that exhibit repetitive characteristics, performs resource allocation as a matter of course, but does not deal with resource leveling. In the past, researchers experienced declines in productivity whenever they leveled resources in different linear scheduling models by adjusting activities’ production rates. The objective of this research is to develop a genetic algorithm‐based resource leveling model for LOB schedules that does not impact productivity negatively. This model is based on the “natural rhythm” principle, according to which a crew of optimum size will be able to complete an activity in the most productive way. The “natural rhythm” principle allows shifting the start time of an activity at different units by adjusting the number of crews without changing the duration of the activity in any one unit and without violating the precedence relationships between activities. An LOB schedule is established for a pipeline project and is used to illustrate the proposed resource leveling model. It was observed that the model provides a smoother resource utilization histogram. Performing resource leveling in LOB scheduling without sacrificing productivity is the major contribution of the proposed model.     

Evaluation of plate loading tests on some rock formations for assessing the ground bearing capacity

A significant proportion of the cost of winning minerals or aggregates in an open cast mine is related to the mass haul. The quality of the haul roads is an important factor in the efficiency and length of turn-round time. The paper reports a study into the use of plate loadings tests as a quick and easy means of establishing a preliminary bearing capacity. Various relationships have been obtained between bearing capacity and the results of field and laboratory tests. Good performance indices (r, RMSE, VAF) indicate they can be used for an initial assessment of the bearing capacity of rock units ranging from weak to strong. In addition, classes for bearing capacity of rock units have been suggested based on field observations and measurements.     

Effect of various demineralizing agents on mineral contents of cementum surfaces (an electron probe analysis)

The purpose of this investigation was to determine the surface morphology and mineral content of periodontally diseased cementum surfaces following root planing and conditioning with either citric acid, tetracycline HCL and minocycline HCL. Mineral contents of cementum surfaces were determined with an electron probe. All 3 demineralizing agents caused the exposure of the collagen matrix on the root surface but citric acid was the more effective. Calcium (Ca) and phosphorus (P) showed higher values in citric acid and minocycline HCL treated cementum surfaces compared to nondiseased cementum surfaces. The Ca and P were found to be in similar proportions in the tetracycline HCL treated group and nondiseased cementum surfaces. Although citric acid is a strong demineralizing agent, our specimens' cementum surfaces to which citric acid was treated showed high Ca and P content. In our opinion this difference about the effects of demineralizing agents on the surface morphology and surface element content was found to be related to the facts that whether the total amount of hypermineralized cementum as removed or not with root planing and the lacking criteria to detects the amount of this removal. Our findings suggest that these demineralizing agents can demineralize cementum surface after root planing but can not remove all of the hypermineralized diseased cementum. For this reason, it may be stated that it is more important to remove the pathologically altered cementum than applying various chemical agents.     

Seventh-order elliptic video filter with 0.1 dB pass band ripple employing CMOS CDTAs

In this paper, a CMOS realization of the current differencing transconductance amplifier (CDTA) is given, which is a newly reported active building block for current-mode signal processing. Current differencing stage of the CDTA element is realized using a differential current-controlled current source and in the output stage, floating current sources are used to convert intermediate voltage of z terminal to output currents. Due to the compactness of the circuit, it is capable of high-frequency operation and suitable for video signal-processing applications. The CDTA element is used in a current-mode anti-aliasing video filter, which is designed using operational simulation of a seventh-order passive elliptic filter, so the resulting active filter has the low sensitivity feature of its passive counterpart. The filter has 0.1 dB maximum pass band ripple as imposed by ITU video anti-aliasing filter standard. SPICE-simulation results of both the CDTA element and the seventh-order elliptic filter are given. Simulation results are found in close agreement with theoretical results.