Experimental and Computational Studies on the Reentry Capsule Aerodynamics with a Flap

Senthil Kumar,J K Prasad,Kim H D 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

Flow field around a typical reentry capsule has been investigated adopting experiments and computations. The reentry capsule has the flap which could be useful to obtain control force. All the studies have been made at a free stream Mach number of 2 and Reynolds number of 30 X 106. Experiments consisted of schlieren flow visualization and measurement of axial force only. Three dimensional computation has been made using FLUENT and adopting k-ω turbulence model. Effect of angle of attack and flap angle has been obtained. Based on present study, it is observed the flap increases the axial force.

Improved Thermal Stability of Green InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes with an AlGaN/GaN Short-Superlattice-Inserted Structure

Y. S. Lee,M. Senthil Kumar,T. V. Cuong,J. Y. Park,J. H. Ryu,S. J. Chung,E.-K. Suh,C.-H. Hong 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1

We report an amelioration of the electrical, thermal and optical performances of green InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with AlGaN/GaN short- superlattice (SSL)-inserted structure grown using metal-organic chemical vapor deposition. Ac- cording to an atomic force microscopic study, the GaN template with the SSL-inserted structure shows a signicant reduction in pit density compared to the conventionally-grown template. The insertion of the SSL is also found to alleviate the eect of threading dislocations on the degradation of the electrical performance and promotes the stability of the K-factor and a low thermal resis- tance under a long-term acceleration test. A relatively higher optical output power is obtained for SSL-inserted InGaN/GaN green LEDs at high injection currents. We report an amelioration of the electrical, thermal and optical performances of green InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with AlGaN/GaN short- superlattice (SSL)-inserted structure grown using metal-organic chemical vapor deposition. Ac- cording to an atomic force microscopic study, the GaN template with the SSL-inserted structure shows a signicant reduction in pit density compared to the conventionally-grown template. The insertion of the SSL is also found to alleviate the eect of threading dislocations on the degradation of the electrical performance and promotes the stability of the K-factor and a low thermal resis- tance under a long-term acceleration test. A relatively higher optical output power is obtained for SSL-inserted InGaN/GaN green LEDs at high injection currents.

Characteristics of p-Type GaN Formed by Two Different Types of Mg Diffusion

Chung Sangjo,Karunagaran B,Muthusamy Senthil Kumar,Suh E. -K 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1

Two different types of magnesium (Mg) diffusion onto intentionally undoped n-type GaN, resulting in p-type GaN formation, have been employed in this work. Secondary-ion mass spectroscopy (SIMS) measurements reveal a uniform Mg concentration for both methods of diffusion up to a depth of 1.5 μm in GaN. Hall measurement data indicate that all the diffused and annealed samples consistently show p-type conductivity with hole concentrations in the range of 5 7 × 1016/cm3 and with mobilities <50 cm2/V·s. The measured dark current of the samples almost exponentially increases with the reciprocal temperature with an activation energy of 144 meV or 168 meV in the temperature range from 170 K to 250 K. The photoluminescence (PL) spectra of Mg diffused GaN show a broad violet emission at around 3.15 eV. This broad peak may be attributed to Mg acceptors. In the photocurrent (PC) measurements on the Mg/Au film deposited on n-type GaN, an additional broad peak was observed at around 1.2 eV, and this peak may be related to the yellow luminescence.

Influence of interface on the behavior of infilled frame subjected to lateral load using linear analysis

Senthil, K.,Satyanarayanan, K.S. Techno-Press 2016 Coupled systems mechanics Vol.5 No.2

Two dimensional numerical investigations were carried out to study the influence of interface thickness and their pattern on the behavior of reinforced concrete frames subjected to in-plane lateral loads using commercial finite element tool SAP 2000. The linear elastic analysis was carried out on one and two bay structural systems as well as the influence of number of stories was studied by varying the number of stories as single, three and five. The cement mortar was used as interface material and their effect was studied by varying thicknesses as 6, 8, 10, 14 and 20 mm. The interface was recognized as one sided, two sided, three sided and four sided and their effect was studied by removing the interface material between the reinforced concrete frame and masonry infill. The effect of lateral loads on infill masonry wall was also studied by varying assumed loads as 10, 20, 30, 40, 50 and 60 kN. The behavior of infilled frames studied has revealed that there is a maximum influence of interface thickness and interface pattern corresponding to 10 mm thickness. In general, the lateral displacement of frame is increased linearly with increase in lateral loads.

Energy absorption of fibrous self compacting reinforced concrete system

Senthil, K.,Satyanarayanan, K.S.,Rupali, S. Techno-Press 2016 Advances in concrete construction Vol.4 No.1

The objective of the present work is to evaluate the influence of two different methods of improving the ductility of Reinforced Concrete Frames and their influence on the full range behavior of the frames with M40 grade of concrete. For this purpose one fourth scale reinforced concrete square frames are experimentally tested subjected to static cyclic loading for three cases and monotonic loading for one case. The parameters are varied as method introducing ductility to the frame viz. (i) by using conventional concrete (ii) adding 1% of steel fibres by volume of concrete at hinging zones (iii) using self-compacting concrete with fibres at hinging zones. The energy absorption by ductile and non-ductile frames has been compared. The behavior of frames tested under cyclic loading have revealed that there is a positive trend in improvement of ductility of frames when fibrous concrete is used along with self-compacting concrete.

Damage mechanism and stress response of reinforced concrete slab under blast loading

Senthil, K.,Singhal, A.,Shailja, B. Techno-Press 2019 Coupled systems mechanics Vol.8 No.4

The numerical investigations have been carried out on reinforced concrete slab against blast loading to demonstrate the accuracy and effectiveness of the finite element based numerical models using commercial package ABAQUS. The response of reinforced concrete slab have been studied against the influence of weight of TNT, standoff distance, boundary conditions, influence of air blast and surface blast. The results thus obtained from simulations were compared with the experiments available in literature. The inelastic behavior of concrete and steel reinforcement bar has been incorporated through concrete damage plasticity model and Johnson-cook models available in ABAQUS were presented. The predicted results through numerical simulations of the present study were found in close agreement with the experimental results. The damage mechanism and stress response of target were assessed based on the intensity of deformations, impulse velocity, von-Mises stresses and damage index in concrete. The results indicate that the standoff distance has great influence on the survivability of RC slab against blast loading. It is concluded that the velocity of impulse wave was found to be decreased from 17 to 11 m/s when the mass of TNT is reduced from 12 to 6 kg. It is observed that the maximum stress in the concrete was found to be in the range of 15 to $20N/mm^2$ and is almost constant for given charge weight. The slab with two short edge discontinuous end condition was found better and it may be utilised in designing important structures. Also it is observed that the deflection in slab by air blast was found decreased by 60% as compared to surface blast.

A review on the application of plastic waste in the reinforced concrete structures

K. Senthil,Suresh Jakhar,Manish Khanna,Kavita Rani Techno-Press 2024 Advances in materials research Vol.13 No.2

Concrete is the most significant material in the construction industry which is required to construct several facilities like roads, buildings, and bridges etc. which leads to the economic development of a country. But now days, in view of sustainable development and environmental problems, plastic waste management is one of the major environmental issues due to its non-biodegradable nature which allows it to stay in the landfills until they are cleaned up. To overcome all these concerns, plastic waste may be used as a substitute of natural fine and coarse aggregate in concrete and a valuable solution to utilize the plastic items which causes several problems. In order to, present study is focused on the affecting properties of concrete as workability, compressive strength, and tensile strength of concrete with using plastic waste and without using plastic waste. Based on the detailed literature, it was observed that the plastic waste is not affecting the quality and consistency of concrete. However, as the number of PVC particles in the mixture increased, the drying shrinkage values decreased and the inclusion of plastic flakes can mitigate drying shrinkage cracking which leads the higher durability of concrete. Based on the comprehensive literature, it was also observed that the plastic aggregate found to be suitable for low and medium strength concrete. However, the investigation on the application of plastic aggregate in the high strength concrete is found limited. It was concluded that the optimum percentage of the plastic aggregate was found about 20%.

Computation of stress-deformation of deep beam with openings using finite element method

Senthil, K.,Gupta, A.,Singh, S.P. Techno-Press 2018 Advances in concrete construction Vol.6 No.3

The numerical investigations have been carried out on deep beam with opening subjected to static monotonic loading to demonstrate the accuracy and effectiveness of the finite element based numerical models. The simulations were carried out through finite element program ABAQUS/CAE and the results thus obtained were validated with the experiments available in literature. Six simply supported beams were modelled with two square openings of 200 and 250 mm sides considered as opening at centre, top and bottom of the beam. In order to define the material behaviour of concrete and reinforcing steel bar the Concrete Damaged Plasticity model and Johnson-Cook material parameters available in literature were employed. The numerical results were compared with the experiments in terms of ultimate failure load, displacement and von-Mises stresses. In addition to that, seventeen beams were simulated under static loading for studying the effect of opening location, size and shape of the opening and depth, span and shear span to depth ratio of the deep beam. In general, the numerical results accurately predicted the pattern of deformation and displacement and found in good agreement with the experiments. It was concluded that the structural response of deep beam was primarily dependent on the degree of interruption of the natural load path. An increase in opening size from 200 to 250 mm size resulted in an average shear strength reduction of 35%. The deep beams having circular openings undergo lesser deflection and thus they are preferable than square openings. An increase in depth from 500 mm to 550 mm resulted in 78% reduced deflection.

An Algorithm for Energy Efficient Cooperative Communication in Wireless Sensor Networks

( K. Senthil Kumar ),( R. Amutha ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.7

In this paper, we propose an algorithm for energy efficient cooperative communication in wireless sensor network (WSN). The algorithm computes the appropriate transmission distance corresponding to optimal broadcast bit error probability, while taking the circuit energy consumption and the number of cooperating nodes into consideration. The algorithm guarantees minimum energy consumption by choosing higher value of bit error probability for cooperative phase and lower value of bit error probability for broadcast phase while maintaining the required end-to-end reliability. The simulation results show that the proposed algorithm provides significant energy saving gain when compared with traditional fixed distance schemes and is suitable for applications demanding energy efficiency with high quality of reception.

Selective and low potential electrocatalytic oxidation of NADH using a 2,2-diphenyl-1-picrylhydrazyl immobilized graphene oxide-modified glassy carbon electrode

Pillai, K. Chandrasekara,Shalini Devi, K. S.,Senthil Kumar, Annamalai,Moon, Il-Shik Springer-Verlag 2018 Journal of solid state electrochemistry Vol.22 No.11