Nirjuli, India
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Thermal design of oil filled distribution and power transformers is essential for obtaining the location of 'hot-spot' of the transformers. This study presents the analysis of 2D and 3D model for the simplified section of an oilfilled disc-type winding power transformer. Both models developed using COMSOL Multiphysics 5.1 were validated with the experimental and numerical results available in literatures. The analysis of the flow rate and the temperature distribution accurately reveals the location and the temperature of the 'hot-spot'. Further, the parametric study using the 3D model shows that the combined effect of variation in the vertical cooling duct width and the local cross-section area in the horizontal cooling duct has a significant influence on the location of the 'hot-spot' and a minor influence on its temperature (i.e. ±3%). The analysis results in this study shall be beneficial from the point of view of design development in transformers. © The Institution of Engineering and Technology 2017.

Pathak K.K.,NERIST | Giri A.,NERIST | Lingfa P.,NERIST
International Journal of Mechanical Engineering and Technology | Year: 2017

A computational study is carried out to find the heat transfer coefficients of a shrouded vertical array of heat sinks (fins). Heat transfer coefficients are calculated for different fin spacing. Effects of clearance, Grashof number and inlet velocities are reported. Results indicate that heat transfer coefficient first increases with fin spacing achieve a maximum and then decreasing or increasing with fin spacing depending upon the Grashof number and inlet velocities. For higher Grashof number coupled with higher inlet velocity heat transfer coefficient is maximum for non-dimensional fin spacing 0.2 and for lower Grashof number with lower inlet velocities the value of heat transfer coefficient is maximum at nondimensional fin spacing 0.4. Fluid velocity and temperature along the axial direction are sketched. Fin temperature variation is reported. © IAEME Publication.

Chatterjee S.,NIT | Kumar P.,NIT | Chatterjee S.,NERIST
Renewable and Sustainable Energy Reviews | Year: 2017

Owing to rapid depletion of fossil fuels and environmental hazard, different non-conventional sources of energy like wind, geothermal, nuclear, photovoltaic etc, have been taken into consideration for power generation. Environmental familiarness, reduced installation cost, improved power quality, abundant availability of source makes photovoltaic based distributed generation as one of the most popular alternative source of energy production. Improvement in power electronics technology makes synchronization of PV system with grid more viable. Power output from the PV module changes continuously with time depending upon the climatic condition. In order to get maximum output from the PV system different types of MPPT algorithm present in literature are studied and improvement proposed are described in this paper. Furthermore, different types of inverter topologies along with different grid synchronization technique and PWM topologies used to connect the PV system with the 3-phase AC grid are presented. In order to minimize the harmonic content of the inverter output, different types of filters used are presented in the proceeding section.Nextly different commonly used advanced islanding detection techniques for the safety purpose of PV based distribution generation system have been addressed and based on advantages and limitation of anti-islanding techniques, a comparison table has been presented. Afterward based on parameters like input, output voltage & current, MPP range, used standards etc, a comparison table between different commercially available grid tied PV inverters are presented in this paper. Finally, drawbacks of the prevailing grid connected PV system have been discussed. © 2017 Elsevier Ltd.

Wahengbam M.,NERIST | Marchang N.,NERIST
Proceedings - 2012 3rd National Conference on Emerging Trends and Applications in Computer Science, NCETACS-2012 | Year: 2012

Mobile Ad hoc network (MANET) is a new paradigm in wireless revolution, which is a self-configured network of wireless mobile nodes. Due to proliferation of miniature yet powerful mobile computing devices, it is gaining acceptance and popularity. However, MANET is vulnerable to security attacks due to its inherent characteristics such as dynamic topology, lack of a centralized coordinator and open wireless channel. In this paper, we analyze some security attacks of MANET and we propose to identify the attack by using an Intrusion Detection System (IDS). The proposed IDS uses fuzzy logic to detect malicious behavior and identify the attacks. © 2012 IEEE.

Hazarika N.,NERIST | Saikia M.,NERIST
2014 International Conference on Signal Processing and Integrated Networks, SPIN 2014 | Year: 2014

Transmitted images may have many different applications like commercial, military, medical etc. To protect the information from unauthorized access secure image transfer is required and this can be achieved by image data encryption. But the encryption of whole image is time consuming. This paper proposed a selective encryption techniques using spatial or DCT domain. The result of the several experimental, statistical analysis and sensitivity test shows that the proposed image encryption scheme provides an efficient and secure way for real-time image encryption and transmission. A chaotic logistic map is used to perform different encryption/decryption operation in this proposed method. © 2014 IEEE.

Singh T.J.,NERIST | Samanta S.,NERIST
Materials Today: Proceedings | Year: 2015

In recent years, the interest of using the fiber reinforced composites (FRCs) has increased due to its potential for replacing the traditional materials in various applications. Kevlar fiber, due to its unique properties such as higher strength to mass ratio and modulus, has become very popular as reinforcement in composite materials and its application has growth considerably. However, for enhancing its properties in various applications, a proper characterization is very important. Many researches have been conducted in recent years, for characterization of Kevlar fiber and its composites. In this paper, a state-of-the art review of these characterizations is presented. © 2015 Elsevier Ltd.

In this work, the shape optimization of a single link revolute-jointed flexible manipulator is carried out. Manipulator link is considered as a Euler-Bernoulli beam and finite element based on Lagrange approach is employed for dynamic analysis. Sequential quadratic programming (SQP) method is applied to extremize the objective functions. Four different optimization problems are solved for comparative study of the model for vibration suppression. © 2013 Elsevier Ltd.

Maheshwari B.K.,Indian Institute of Technology Roorkee | Singh H.P.,NERIST | Saran S.,Indian Institute of Technology Roorkee
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2012

A study on liquefaction resistance of Solani sand reinforced with geogrid sheet, geosynthetic fiber, and natural coir fiber is reported. Tests were carried out on shake table (vibration table) with sand samples prepared at a relative density of 25%, with and without reinforcements. Synthetic geogrid sheets were used in three different combinations of three, four, and five layers. In case of fibers, the percentage of fibers by weight of dry sand were taken as 0.25, 0.50, and 0.75% and mixed randomly with the sand sample. Theliquefaction parameters, such as the maximum pore water pressure (Umax), maximum pore water pressure built-up time, stay time for Umax, and pore water pressure dissipation time were measured corresponding to various levels of accelerations varying from 0.1-0.4 g. Thefrequency of the dynamic load was kept constant at 5 Hz. The liquefaction resistance of sand was evaluated in terms of maximum pore water pressure ratio (ru max). Test results indicated that on inclusion of fibers and geogrid sheets into the sand samples, the ru max decreased. On increasing the fiber content and number of geogrid sheets, ru max decreasedfurther, and this decrease is significant at a small amplitude of excitation. The averageincrease in liquefaction resistance of sand reinforced with synthetic and coir fibers wasfound to be 88 and 91%, respectively, for 0.75% fiber content, whereas for five layers ofgeogrid sheets, this increase was about 31% at 0.1 g acceleration. © 2012 American Society of Civil Engineers.

Sivakumar P.,NERIST | Prasad R.K.,NERIST
Water Resources Management | Year: 2014

Pressure deficient condition occurs in the water distribution network (WDN) when the nodal demands are in excess of the design discharge as in the case of fire demand, pump failure, pipe breaks, valve failure etc. It causes either no-flow or partial-flow depending upon the available pressure head at the nodes. To evaluate the nodal flows in such condition, node flow analysis (NFA) gives reasonable results in comparison to demand-driven analysis (DDA) and head-dependent analysis (HDA). The NFA works on the predefined pressure-discharge relationship to evaluate the nodal flows. However, this approach requires human intervention and hence cannot be applied to large WDN. Recently, modified pressure-deficient network algorithm (M-PDNA) has been developed by Babu and Mohan (2012) for pressure-deficient analysis with EPANET toolkit. However, it requires modification of the source code of EPANET. In this study a relationship with the M-PDNA and node flow analysis (Gupta and Bhave 1996) has been investigated and it is found that M-PDNA is the simplified version of NFA. Further, the working principle of M-PDNA has been investigated with suitable examples of Babu and Mohan (2012). The theoretical basis of M-PDNA has not been investigated in terms of head-discharge relationship. Herein, a head-discharge relationship based on the working principal of M-PDNA is proposed. Some of the toolkits are also readily available to modify demand driven solver of EPANET 2 to suit for the pressure-driven analysis and then it can be used for analysing pressure deficient network. Also in this study, a modification in M-PDNA approach is proposed which does not require the use of EPANET toolkit which is found to be capable of simulating both pressure-sufficient and pressure-deficient conditions in a single hydraulic simulation. Using the proposed approach, pressure-deficient condition is analysed with constant and variable demand pattern. © 2014 Springer Science+Business Media Dordrecht.

Sivakumar P.,NERIST | Prasad R.K.,NERIST
Water Resources Management | Year: 2015

Generally, the water distribution networks are designed for peak demands so that under normal operating conditions pressure is adequate to meet the nodal demand however, due to this, the pressure remains excessive when the consumption is low. This leads to huge water leakages and pipe bursts due to excess available pressure. These excess of pressure can be reduced by operating pressure reducing valves. Moreover, the pressure deficient conditions of water distribution network depends on many factors such as excess demand (i.e., fire fighting demand), location and elevation of nodes, location and pressure setting values of pressure reducing valve, ageing of pipes (i.e., increase the pipe roughness) etc. In exceptional situations, pressure deficient condition also may occur when there is a fire demand while pressure reducing valves are in operating condition. The available literature of the pressure deficient condition as well as optimal location, number and their pressure setting values of pressure reducing valves are analysed by mathematical programming or optimization methods. Normally, it is cumbersome to the field engineers to use the any toolkit utility functions. Hence in this study, the pressure deficient condition is analysed via the method of modified pressure-deficient network algorithm without using EPANET toolkit functions which are coupled with pressure reducing valve operation. A benchmark problem is analysed and compared for the proposed method. Further, a real water distribution networks is analysed introducing fire demand at junction/distribution node using fixed and diurnal nodal demand pattern coupled with and without pressure reducing valve operation in a single hydraulic simulation. © 2014, Springer Science+Business Media Dordrecht.

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