Modeling and Simulation of Nano and Multiscale Composites

B. Ramgopal Reddy,K. Ramji 보안공학연구지원센터 2016 International Journal of Hybrid Information Techno Vol.9 No.3

Carbon nanotubes (CNTs) are being used extensively as reinforcing materials in polymer matrix composites because of their high strength, stiffness and resilience, as well as superior mechanical, electrical and thermal properties. Incorporating CNTs in polymer matrix composites can potentially enhance the strength and stiffness of composites significantly. In this paper, the effective elastic properties of nanocomposites (CNTs/Epoxy) at different volume fractions of CNTs and multiscale composites (Glass/CNTs/Epoxy) at 5% volume fraction of CNTs are evaluated using finite element method (FEM). 3-D finite element models using square representative volume element (RVE) incorporating necessary boundary conditions are developed. For validity the obtained results are compared with that of classical theories of equivalent material properties. Good agreement between them has been observed. Further the effect of CNT-integration in fiber-reinforced composites (three-phase) is also studied.

Numerical study of temperature dependent eigenfrequency responses of tilted functionally graded shallow shell structures

Chandra Mouli B,Ramji K,Vishesh R. Kar,Subrata K. Panda,Lalepalli Anil K,Harsh K Pandey 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.5

The free vibration frequency responses of the graded flat and curved (cylindrical, spherical, hyperbolic and elliptical) panel structures investigated in this research considering the rectangular and tilted planforms under unlike temperature loading. For the numerical implementation purpose, a micromechanical model is prepared with the help of Voigt’s methodology via the power-law type of material model. Additionally, to incur the exact material strength, the temperature-dependent properties of each constituent of the graded structure included due to unlike thermal environment. The deformation kinematics of the rectangular/tilted graded shallow curved panel structural is modeled via higher-order type of polynomial functions. The final form of the eigenvalue equation of the heated structure obtained via Hamilton’s principle and simultaneously solved numerically using finite element steps. To show the solution accuracy, a series of comparison the results are compared with the published data. Some new results are exemplified to exhibit the significance of power-law index, shallowness ratio, aspect ratio and thickness ratio on the combined thermal eigen characteristics of the regular and tilted graded panel structure.

Experimental evaluation of pumpjet propulsor for an axisymmetric body in wind tunnel

Suryanarayana, Ch.,Satyanarayana, B.,Ramji, K.,Saiju, A. The Society of Naval Architects of Korea 2010 International Journal of Naval Architecture and Oc Vol.2 No.1

Design of a Pump Jet Propulsor (PJP) was undertaken for an underwater body with axisymmetric configuration using axial/low compressor design techniques supported by Computational Fluid Dynamics (CFD) analysis for performance prediction. Experimental evaluation of the PJP was earned out through experiments in a Wind Tunnel Facility (WTF) using momentum defect principle for propulsive performance prior to proceeding with extensive experimental evaluation in towing tank and cavitation tunnel. Experiments were particularly conducted with respect to Self Propulsion Point (SPP), residual torque and thrust characteristics over a range of vehicle advance ratio in order to ascertain whether sufficient thrust is developed at the design condition with least possible imbalance torque left out due to residual swirl in the slip stream. Pumpjet and body models were developed for the propulsion tests using Aluminum alloy forged material. Tests were conducted from 0 m/s to 30 m/s at four rotational speeds of the PJP. SPP was determined confirming the thrust development capability of PJP. Estimation of residual torque was carried out at SPP corresponding to speeds of 15, 20 and 25 m/s to examine the effectiveness of the stator. Estimation of thrust and residual torque was also carried out at wind speeds 0 and 6 m/s for PJP RPMs corresponding to self propulsion tests to study the propulsion characteristics during the launch of the vehicle m water where advance ratios are close to Zero. These results are essential to assess the thrust performance at very low advance ratios to accelerate the body and to control the body during initial stages. This technique has turned out to be very useful and economical method for quick assessment of overall performance of the propulsor and generation of exhaustive fluid dynamic data to validate CFD techniques employed.

Performance evaluation of an underwater body and pumpjet by model testing in cavitation tunnel

Suryanarayana, Ch.,Satyanarayana, B.,Ramji, K. The Society of Naval Architects of Korea 2010 International Journal of Naval Architecture and Oc Vol.2 No.2

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at $4.5^{\circ}$ angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.

Cavitation studies on axi-symmetric underwater body with pumpjet propulsor in cavitation tunnel

Suryanarayana, Ch.,Satyanarayana, B.,Ramji, K.,Rao, M. Nageswara The Society of Naval Architects of Korea 2010 International Journal of Naval Architecture and Oc Vol.2 No.4

A pumpjet propulsor (PJP) was designed for an underwater body (UWB) with axi-symmetric configuration. Its performance was predicted through CFD study and models were manufactured. The propulsor design was evaluated for its propulsion characteristics through model tests conducted in a Wind Tunnel (WT). In the concluding part of the study, evaluation of the cavitation performance of the pumpjet was undertaken in a cavitation tunnel (CT). In order to assess the cavitation free operation speeds and depths of the body, cavitation tests of the PJP were carried out in behind condition to determine the inception cavitation numbers for rotor, stator and cowl. The model test results obtained were corrected for full scale Reynolds number and subsequently analyzed for cavitation inception speeds at different operating depths. From model tests it was also found that the cavitation inception of the rotor takes place on the tip face side at higher advance ratios and cavitation shifts towards the suction side as the RPS increases whereas the stator and cowl are free from cavitation.

Design optimization of 3PRS parallel manipulator using global performance indices

S. Ramana Babu,V. Ramachandra Raju,K. Ramji 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.9

This paper presents an optimal kinetostatic design method for a general 3PRS (Prismatic-revolute-spherical) spatial parallel manipulator by formulating a multi-objective optimization problem considering the performance indices are as the objective functions. Three performance criteria--Global conditioning index (GCI), Global stiffness index (GSI) and workspace volume-were formulated and the effect of actuator layout angle on the performance indices was studied. A multi-objective evolutionary algorithm based on the Control elitist non-dominated sorting genetic algorithm (CENSGA) was adopted to find the final approximation set. The optimal geometric parameters that yield minimal compliance with larger workspace volume and improved dexterity are suggested for a general 3PRS parallel manipulator. For the optimal design, it is shown that global isotropy and global stiffness of the platform is improved at the cost of workspace reduction.

Cavitation studies on axi-symmetric underwater body with pumpjet propulsor in cavitation tunnel

Ch. Suryanarayana,B. Satyanarayana,K. Ramji,M. Nageswara Rao 대한조선학회 2010 International Journal of Naval Architecture and Oc Vol.2 No.4

A pumpjet propulsor (PJP) was designed for an underwater body (UWB) with axi-symmetric configuration. Its performance was predicted through CFD study and models were manufactured. The propulsor design was evaluated for its propulsion characteristics through model tests conducted in a Wind Tunnel (WT). In the concluding part of the study, evaluation of the cavitation performance of the pumpjet was undertaken in a cavitation tunnel (CT). In order to assess the cavitation free operation speeds and depths of the body, cavitation tests of the PJP were carried out in behind condition to determine the inception cavitation numbers for rotor, stator and cowl. The model test results obtained were corrected for full scale Reynolds number and subsequently analyzed for cavitation inception speeds at different operating depths. From model tests it was also found that the cavitation inception of the rotor takes place on the tip face side at higher advance ratios and cavitation shifts towards the suction side as the RPS increases whereas the stator and cowl are free from cavitation.

Experimental evaluation of pumpjet propulsor for an axi-symmetric body in wind tunnel

Ch. Suryanarayana,B. Satyanarayana,K. Ramji,A Saiju 대한조선학회 2010 International Journal of Naval Architecture and Oc Vol.2 No.1

Design of a Pump-Jet Propulsor (PJP) was undertaken for an underwater body with axi-symmetric configuration using axial flow compressor design techniques supported by CFD analysis for performance prediction. Experimental evaluation of the PJP was carried out through experiments in Wind Tunnel Facility (WTF) using momentum defect principle for propulsive performance prior to proceeding with extensive experimental evaluation in towing tank and cavitation tunnel. Experiments were particularly conducted with respect to Self Propulsion Point (SPP), residual torque and thrust characteristics over a range of vehicle advance ratio in order to ascertain whether sufficient thrust is developed at the design condition with least possible imbalance torque left out due to residual swirl in the slip stream. Pumpjet and body models were developed for the propulsion tests using Aluminium alloy forged material. Tests were conducted from 0 m/s to 30 m/s at four rotational speeds of the PJP. SPP was determined confirming the thrust development capability of PJP. Estimation of residual torque was carried out at SPP corresponding to speeds of 15, 20 and 25 m/s to examine the effectiveness of the stator. Estimation of thrust and residual torque was also carried out at wind speeds 0 and 6 m/s for PJP RPMs corresponding to self propulsion tests to study the propulsion characteristics during the launch of the vehicle in water where advance ratios are close to Zero. These results are essential to assess the thrust performance at very low advance ratios to accelerate the body and to control the body during initial stages. This technique has turned out to be very useful and economical method for quick assessment of overall performance of the propulsor and generation of exhaustive fluid dynamic data to validate CFD techniques employed. Design of a Pump-Jet Propulsor (PJP) was undertaken for an underwater body with axi-symmetric configuration using axial flow compressor design techniques supported by CFD analysis for performance prediction. Experimental evaluation of the PJP was carried out through experiments in Wind Tunnel Facility (WTF) using momentum defect principle for propulsive performance prior to proceeding with extensive experimental evaluation in towing tank and cavitation tunnel. Experiments were particularly conducted with respect to Self Propulsion Point (SPP), residual torque and thrust characteristics over a range of vehicle advance ratio in order to ascertain whether sufficient thrust is developed at the design condition with least possible imbalance torque left out due to residual swirl in the slip stream. Pumpjet and body models were developed for the propulsion tests using Aluminium alloy forged material. Tests were conducted from 0 m/s to 30 m/s at four rotational speeds of the PJP. SPP was determined confirming the thrust development capability of PJP. Estimation of residual torque was carried out at SPP corresponding to speeds of 15, 20 and 25 m/s to examine the effectiveness of the stator. Estimation of thrust and residual torque was also carried out at wind speeds 0 and 6 m/s for PJP RPMs corresponding to self propulsion tests to study the propulsion characteristics during the launch of the vehicle in water where advance ratios are close to Zero. These results are essential to assess the thrust performance at very low advance ratios to accelerate the body and to control the body during initial stages. This technique has turned out to be very useful and economical method for quick assessment of overall performance of the propulsor and generation of exhaustive fluid dynamic data to validate CFD techniques employed.

Performance evaluation of an underwater body and pumpjet by model testing in cavitation tunnel

Ch. Suryanarayana,B. Satyanarayana,K. Ramji 대한조선학회 2010 International Journal of Naval Architecture and Oc Vol.2 No.2

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at 4.5º angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll. Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at 4.5º angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.

Safety of delayed umbilical cord clamping in preterm neonates of less than 34 weeks of gestation: a randomized controlled trial

( Anubhuti Rana ),( Krishna Agarwal ),( Siddarth Ramji ),( Gauri Gandhi ),( Latika Sahu ) 대한산부인과학회 2018 Obstetrics & Gynecology Science Vol.61 No.6

Objective There is concern regarding the safety of delayed cord clamping (DCC) in babies born at less than 34 weeks' gestation. Therefore, the primary objective of this study was to compare the rates of hyperbilirubinemia and polycythemia during initial 7 days in infants born at less than 34 weeks' gestation and randomized to receive DCC by 120 seconds or early cord clamping (ECC) within less than 30 seconds. Methods One hundred pregnant women were randomly subjected to DCC or ECC at the time of birth in a tertiary referral hospital setting. Blood samples were obtained from each newborn at 48 hours and 7 days for hematocrit measurement. Serum bilirubin levels were estimated once the infant had clinically significant jaundice or at 72 hours. For the statistical analysis, the χ² test, Student's t-test, or Wilcoxon rank sum test was used. Results The hematocrit was significantly higher in the DCC group than in the ECC group (P<0.001). None of the babies had polycythemia. Mean total serum bilirubin level was 6.6 mg/dL in the DCC group and 8.7 mg/dL in the ECC group (P<0.001). There was no increased risk of hyperbilirubinemia in the DCC group. Conclusion DCC benefits preterm neonates with no significant adverse effects.