Sharif Digital Repository

Purpose - Dimensional accuracy analysis of wax model created by room temperature vulcanization (RTV) silicone rubber molding to be used in investment casting is presented. The purpose of this paper is to discuss the effective parameters of dimensional accuracy in RTV tooling technique. Design/methodology/approach - After producing a pattern by stereolithography (SLA) and then creating the RTV silicone rubber mold by the SLA pattern, dimensional accuracy of wax models produced by RTV tool are analyzed. Design of experiments (DOE) using the Taguchi approach is used for analysis and determination of optimum condition. Findings - Experiments show that the dimensional accuracy in RTV technique is... 

Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generation due to their lower capital and operational costs and higher reliability as compared with doubly fed induction generators. This paper presents a vector-control scheme for a BDFIG operating as a variable-speed generator. The proposed vector controller is developed on the power-winding stator-flux frame and can be used to control both the speed and the reactive power. The machine model and the control system are developed in MATLAB. The test results show that the proposed controller has good dynamic performance when changes in speed and reactive power are applied. © 2009 IEEE  

The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8 pole stator windings and a nested-loop rotor cage. The rotor cage has six nests equally spaced around the circumference and each nest comprises three loops. All the rotor loops are short circuited via a common end-ring at one end. The vector model is derived based on the electrical equations of the machine and appropriate vector transformations. In contrast to the stator, there is no three phase circuit in the rotor. Therefore, the vector transformations suitable for three phase circuits can not be utilised for the rotor circuit. A new vector transformation is employed for the rotor circuit... 

In this study, we presented a method for distributing data storage by using residue number system for mobile systems and wireless networks based on peer to peer paradigm. Generally, redundant residue number system is capable in error detection and correction. In proposed method, we made a new system by mixing Redundant Residue Number System (RRNS), Multi Level Residue Number System (ML RNS) and Multiple Valued Logic (MVL RNS) which was perfect for parallel, carry free, high speed arithmetic and the system supports secure data communication. In addition it had ability of error detection and correction. In comparison to other number systems, it had many improvements in data security, error... 

A routing algorithm defines a route which packet traverses to get to destination. In this research we study some kind of routing algorithms that are used in internal connections networks of multi-processor and multi-computers systems. Then we discuss about some routing algorithms which have been implemented network on chip architecture. First, we present a group of routing algorithms based on various criterions, and review so-called category. Afterwards, we study adaptive and deterministic routing algorithms and express circular model applying in internal connections networks and its governing rules in order to prevent dead lock. Then we survey adaptive algorithms such as Deflection routing,... 

This paper presents a generalized vector control system for a generic brushless doubly fed (induction) machine (BDFM) with nested-loop type rotor. The generic BDFM consists of p1/p2 pole-pair stator windings and a nested-loop rotor with N number of loops per nest. The vector control system is derived based on the basic BDFM equation in the synchronous mode accompanied with an appropriate synchronization approach to the grid. An analysis is performed for the vector control system using the generic BDFM vector model. The analysis proves the efficacy of the proposed approach in BDFM electromagnetic torque and rotor flux control. In fact, in the proposed vector control system, the BDFM torque... 

This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p1/p2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupled-circuit model, which is the most detailed model for the BDFM, while maintaining the... 

The paper presents a novel vector control structure for the Brushless Doubly-Fed Machine (BDFM) which is derived based on the machine synchronous operation. In fact, the synchronous operation of the BDFM provides an efficient approach for determining the required reference angle in the machine vector control structure. The utilization of such reference angle makes the vector control structure presented in this paper different from and, in fact, more effective than the existing rotor flux and stator flux orientation schemes proposed for the machine. The results of implementing the vector control scheme in simulations confirm the effectiveness of the proposed approach for the BDFM control  

Wireless sensor networking remains one of the most exciting and challenging research domains of our time. Sensor nodes are arranged in the clusters and relay nodes could have been used as cluster head with more power, but this method has a Low Speed for networks with many sensors. In another method Storage and forwarding nodes are used to transfer the data from sensors to the base station. In this method, the data might have been failed due to the damage of the storage node. In this article, a hybrid method has been used to improve the network quality, which in that network, in addition to the forwarding and storage nodes, there is also cluster head. The purpose of this article is to solve... 

This study aims to investigate the hydrogen production process using an integrated system based on solar energy. This system includes an evacuated tube collector to absorb solar energy as input energy of the system. A parametric analysis was conducted to determine the most important design parameters and evaluate these parameters' impact on the system's objective functions. For identifying the optimum system conditions, multi-objective optimization was performed using particle swarm optimization (PSO) algorithm. The results obtained from the parametric analysis show that an increment in the collector mass flow rate and the turbine inlet temperature, as well as a decrement in the collector... 

In this article, a modified version of the Lee model is utilized to research the effect of variation of the geometric parameters of the electrode system on the amount of the soft X-ray radiation (SXR) yield. The parameters are the anode radius and length, the cathode radius, and the number of rods in the cathode. It will be seen that increasing the anode radius causes an increase in the SXR yield. This is because of the constancy of the ratios of the pinch radius and length to the anode radius and length, respectively. Since the SXR yield scales to the pinch current, increasing the anode length brings a reduction in the yield. When the number of the cathode rods is increased, then the formed... 

The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux oriented reference frame. The rotor flux oriented reference frame is well known in the standard AC machines analysis and control. Similar benefits can be sought by employing this method for the BDFM The vector model is implemented in MATLAB/SIVIULINK to simulate the BDFM dynamic performance under different operating conditions. The predictions from the vector model are compared to those from the coupled circuit model in simulation. The results are shown for the cascade mode of operation. © 2008 IEEE  

Background: Wearing unloader knee orthoses for the long term may have a side effect on knee adduction moment (KAM). Research question: This study sought to determine whether equipping an unloader knee orthosis with vibrators improves its effectiveness in pain, stiffness, function, and reducing the KAM. Methods: The authors performed a clinical evaluation with the Western Ontario and McMaster Universities (WOMAC) questionnaire and instrumented gait analyses on 14 participants with medial compartment knee osteoarthritis in two testing sessions: before wearing the orthosis and after 6 weeks of use. Results and significance: Wearing both orthoses for 6 weeks significantly improved (p < 0.05)... 

This paper proposes a decentralized algorithm to organize an ad-hoc sensor network into clusters. Each sensor operates independently, monitoring communication among others. Those sensors which have many neighbors that are not already part of a cluster are likely candidates to creating a new cluster by declaring themselves to be a new cluster-head. The Clustering Algorithm via Deadline Timer (CADT) provides a protocol whereby this can be achieved and the process continues until all sensors are part of a cluster. Because of the difficulty of analyses simplified models are used to study and abstract its performance. A simple formula to estimate the number of clusters which will be formed in an... 

This paper presents different applications of a vector model developed by the authors in Brushless Doubly-Fed Machine (BDFM) studies including analysis, control and simulations. The BDFM considered consists of a nested-loop type rotor. The vector model, which considers all the loops in each rotor nest, is derived using BDFM coupled-circuit model equations and by applying appropriate vector transformations. Three vector transformations are employed for the derivation of vector model corresponding to two three-phase windings in the stator and the rotor circuit. Each transformation consists of an angle which is, in general, unspecified and must be assigned appropriately depending on the... 

Thermal expansion and hot deformation are two phenomena causing dimensional errors in investment casting. This error occurs in dimensions between the die and wax pattern. Therefore, the wax's thermo-physical and thermo-mechanical properties, the metal die features, and the process parameters affect the dimensions of the wax pattern. Some important effective process parameters are the injection temperature, die temperature, and holding time. In this paper, the effect of injection parameters on the dimensional accuracy of the wax model created by a metallic die is studied. The Taguchi formulation based on the design of experiments is applied to obtain the optimum condition in achieving the... 

Alumina-zirconia nanostructured coatings were formed on 7075 Al alloy through Plasma Electrolytic Oxidation (PEO) operated in aDC potentiostatic mode. The composite coatings were produced in the range of 425-500 V in an alkaline electrolyte containing 4 g/LK2ZrF6. Tribological properties of coatings were investigated using dry sliding wear test against WC balls with a pin-on-disc tribometer. Wear rates were evaluated using optical profilometer. It was shown that the nanostructured alumina-zirconia composite coatings can be formed at voltages 450 V. The coating thickness and roughness were in the range of 15.2-24.2 μm and 0.68-2.35 μm, respectively. The distribution of Al, Zr and O in the...