조류발전 터빈의 날개 형상 최적화를 위한 CFD의 활용

Madhan Kumar,남권우(Gwon Woo Nam),오승진(Seung Jin Oh),서정화(Jeonghwa Seo),Abdus Samad,이신형(Shin Hyung Rhee) 한국해양환경·에너지학회 2017 한국해양환경공학회 학술대회논문집 Vol.2017 No.4

Fabrication and Electrochemical Corrosion Behavior of PEO Coatings on Strip-Cast AZ31Mg Alloy in 3.5% NaCl Solution

Madhan Kumar, Arumugam,Hwan Kwon, Sun,Chul Jung, Hwa,Park, Young Hee,Kim, Hea Jeong,Shin, Kwang Seon American Chemical Society 2014 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.53 No.23

<P>The generation of compact plasma electrolytic oxidation (PEO) coatings with outstanding corrosion resistance is essential for the widespread application of Mg alloys. In the present investigation, PEO ceramic coatings formed at different silicate concentration and oxidation time on AZ31 Mg alloy were studied, and the resultant surface structures of the oxide films were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. X-ray photoelectron spectroscopy and thin film-X-ray diffraction analysis of ceramic coatings showed that the surface coating is mainly composed of Mg<SUB>2</SUB>SiO<SUB>4</SUB>, and MgO with different amount based on oxidation time. Further, the potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) measurements were used to characterize corrosion behavior of PEO coated substrates in 3.5% NaCl solution. The results revealed that PEO coatings processed with 0.2 M silicate showed better performance due to its dense and compact coating with fewer structural imperfections in comparison to others.</P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ie404329s'>ACS Electronic Supporting Info</A></P>

Wave Energy Harvesting Turbine: Effect of Hub-To-Tip Profile Modification

Kumar, P. Madhan,Halder, Paresh,Samad, Abdus,Rhee, Shin Hyung Korean Society for Fluid machinery 2018 International journal of fluid machinery and syste Vol.11 No.1

The present paper investigates the leading edge (LE) undulations of a Wells turbine blade through numerical analysis. The aspiration for this modification came from humpback whales, which have uneven protrusions at the LE of their pectoral flippers. The flippers help whales to maneuver during swimming. The work is performed by using three-dimensional steady, incompressible Reynolds Averaged Navier-Stokes (RANS) equations with turbulent closer model. The LE of the turbine blades is modified with undulations of three different amplitudes: 1mm, 2.5mm, and 4mm. The results show that the undulation changes the turbine performance. The amplitude 2.5mm gives the peak performance. The comparison between blades with different amplitudes and the reference blade has been discussed throughout this study.

Solution processed n-In2O3nanostructures for organic-inorganic hybrid p-n junctions

Kumar, G. Mohan,Kumar, A. Madhan,Ilanchezhiyan, P.,Kang, T. W. The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.19

<P>Solution processed organic-inorganic bulk hybrid heterostructures are nowadays considered as the most promising elements to perform efficient optoelectronic functions. In this regard, In2O3 based hybrid heterostructures were fabricated using polypyrrole and their role as efficient interfacial layers was studied using polypyrrole/ZnO nanowires. The In2O3 nanostructures were synthesized through a facile wet chemical approach at an average scale of less than 10 nm in cubic phase. The presence of O and In related defects was studied through emission spectra; these were also found to exhibit their predominance in Raman measurements. The n-type characteristics and donor density value of around 1020 cm-3 were evaluated for the In2O3 specimens via Mott-Schottky plots. The role of In2O3 nanostructures as active/interfacial layers was then studied using the current-voltage characteristics obtained across the hybrid heterostructures made of polypyrrole/In2O3, polypyrrole/ZnO and polypyrrole/In2O3/ZnO. Organic-inorganic p-n diodes were obtained via in situ chemical polymerization, drop casting and hydrothermal routes. Cyclic voltammograms and Nyquist plots were used to study the reduction mechanism taking place in the nanostructures that actually results with the formation of metallic In, which plays a vital role in establishing the required conduction electrons. The same has been reasoned for the improved rectification characteristics observed across the diodes.</P>

Electrochemical synthesis and surface protection of polypyrrole-CeO₂ nanocomposite coatings on AA2024 alloy

Kumar, A. Madhan,Babu, R. Suresh,Ramakrishna, Suresh,de Barros, Ana L.F. Elsevier 2017 Synthetic metals Vol.234 No.-

<P><B>Abstract</B></P> <P>A facile approach based on electrochemical polymerization was used to synthesize polypyrrole/CeO<SUB>2</SUB> (PPy/CeO<SUB>2</SUB>) nanocomposite on an AA2024 alloy surface. CeO<SUB>2</SUB> nanoparticles (NPs) embedded in the PPy matrix were observed using FESEM micrographs with EDX analysis. IR and UV–vis spectroscopy were used to characterize the synthesized PPy/CeO<SUB>2</SUB> nanocomposite. The Raman spectra reflected the interactions between the π-conjugated structure of PPy and CeO<SUB>2</SUB> NPs. TGA thermograms revealed improved thermal stability of the synthesized nanocomposite and were used to determine the amount of nano ceria incorporated in the PPy matrix. The electrochemical corrosion behavior of the coated alloys in 0.6M NaCl solution was examined through potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) measurements. From these electrochemical studies, a larger shift of E<SUB>corr</SUB> in the positive direction with a high amount of CeO<SUB>2</SUB> in the nanocomposite was obtained, as well as a maximum corrosion protection efficiency of 99.64% by incorporating 3% of CeO<SUB>2</SUB> NPs in the PPy coatings. EIS studies also confirmed the enhanced corrosion protection behavior of PPy/CeO<SUB>2</SUB> coatings with higher R<SUB>ct</SUB>, R<SUB>f</SUB> and lower CPE<SUB>dl</SUB> values compared to those of pure PPy coatings. The results showed that the PPy coatings with CeO<SUB>2</SUB> nanoparticles can be potential coating materials for the corrosion protection of AA2024 alloys substrates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polypyrrole coatings with nanoceria were prepared through electrochemical route. </LI> <LI> Raman studies confirm the interaction between π-conjugated PPy & nano CeO<SUB>2</SUB>. </LI> <LI> TGA reveals improved thermal stability of the synthesized nanocomposite. </LI> <LI> Uniform distribution of nano CeO<SUB>2</SUB> was confirmed by EDX mapping analysis. </LI> <LI> Corrosion test confirms better surface protection of PPy/Ce than pure PPy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Multi-fidelity optimization of blade thickness parameters for a horizontal axis tidal stream turbine

Kumar, P. Madhan,Seo, Jeonghwa,Seok, Woochan,Rhee, Shin Hyung,Samad, Abdus Elsevier 2019 RENEWABLE ENERGY Vol.135 No.-

<P><B>Abstract</B></P> <P>Cross-sectional geometry of a horizontal axis tidal stream turbine (HATST) blade was optimized using surrogate models and computational fluid dynamics (CFD) analysis. The blade thickness parameters of a 100 kW class HATST model, i.e., relative thickness and maximum relative thickness location, were varied to examine change of turbine performance in terms of power coefficient. Multiple surrogates such as response surface approximation, radial basis function, Kriging and weighted average surrogates were implemented to the CFD analysis results with design parameter variation to search the optimal design. It was found that the Kriging model was suitable for this HATST optimization problem as it produced the smallest cross-validation error and high accuracy. The optimized design enhanced the power coefficient by 17.9%, which shows a way to implement the present approach to tidal stream turbine design and optimization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Blade profile of a HATST was optimized using surrogate models and computational fluid dynamics analysis. </LI> <LI> The numerical method for the turbine performance analysis was validated by comparisons with experiments. </LI> <LI> Kriging surrogate model showed the best performance in optimizing the turbine blade profile. </LI> <LI> The blade thickness was increased to reduce adverse pressure gradient on the suction side. </LI> </UL> </P>

High performance photodiodes based on chemically processed Cu doped SnS₂ nanoflakes

Mohan Kumar, G.,Xiao, Fu,Ilanchezhiyan, P.,Yuldashev, Sh.,Madhan Kumar, A.,Cho, H.D.,Lee, D.J.,Kang, T.W. Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.455 No.-

<P><B>Abstract</B></P> <P>In this work, Cu doped SnS<SUB>2</SUB> nanoflakes were synthesized through a simple hydrothermal method. The influence of Cu doping on the structural, optical and electrical properties of SnS<SUB>2</SUB> were investigated in detail. Optical properties explores the Cu doping in SnS<SUB>2</SUB> crystal lattice to result with a red-shift in absorption spectrum, which benefits visible-light absorption. Photodiodes were further fabricated by spin coating Cu doped SnS<SUB>2</SUB> nanoflakes on p-type silicon (Si). Electrical and photoelectrical parameters of Cu doped SnS<SUB>2</SUB> nanoflakes were determined by studying their impedance and current–voltage (I–V) characteristics, respectively. The diodes were found to exhibit excellent rectifying behavior and good sensitivity on par to pristine photodiodes. Impedance results identified the resistance of device to reduce considerably on Cu doping. The enhanced photoelectrical properties of the heterojunctions has been ascribed to Cu ions, which act as effective dopant and contribute to the varied carrier concentration in SnS<SUB>2</SUB>. Finally the obtained results suggest the potential of Cu-doped SnS<SUB>2</SUB> for application in photodetection and sensors applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu doped SnS<SUB>2</SUB> nanoflakes were synthesized in hexagonal phase. </LI> <LI> Nature of charge carriers/carrier density was determined using Mott-Schottky plots. </LI> <LI> Photodiode based on Cu doped SnS<SUB>2</SUB> nanoflakes were fabricated on p-Si substrate. </LI> <LI> Photodiode revealed improved photocurrent and responsitivity values under illumination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Evidencing enhanced charge-transfer with superior photocatalytic degradation and photoelectrochemical water splitting in Mg modified few-layered SnS₂

Mohan Kumar, G.,Cho, H.D.,Ilanchezhiyan, P.,Siva, C.,Ganesh, V.,Yuldashev, Sh.,Madhan Kumar, A.,Kang, T.W. Elsevier 2019 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.540 No.-

<P><B>Abstract</B></P> <P>Recently there has been immense interest in the exploration of richly available two-dimensional non-toxic layered material such as tin disulfide (SnS<SUB>2</SUB>) for potential employment in energy and environmental needs. In this regard, we report on the synthesis of few-layered Sn<SUB>1−x</SUB>Mg<SUB>x</SUB>S<SUB>2</SUB> nanosheets through a facile one-step hydrothermal route to address all such functions concerning photocatalysis and photoelectrochemical conversion. The crystalline order and structure of processed layered Sn<SUB>1−x</SUB>Mg<SUB>x</SUB>S<SUB>2</SUB> were initially found to exhibit a strong influence on their physicochemical properties. Their optical properties attest the Mg doping in SnS<SUB>2</SUB> to benefit us with enhanced visible-light absorption via red-shift in their absorption edge. In the photoluminescence spectrum the emissions observed along visible and red region signifies the association of Mg related trap states in Sn<SUB>1−x</SUB>Mg<SUB>x</SUB>S<SUB>2</SUB>. Next, the photocurrent and electrochemical impedance spectroscopic results revealed the Mg doping to promote the effective charge transfer process (which was beneficial to enhance their photocatalytic activity). Consequently, the layered Sn<SUB>0.98</SUB>Mg<SUB>0.02</SUB>S<SUB>2</SUB> made photoanodes displayed 1.7 fold higher photocurrent density under simulated solar radiation with respect to their undoped counterpart. Furthermore, the layered Sn<SUB>0.98</SUB>Mg<SUB>0.02</SUB>S<SUB>2</SUB> nanosheets exhibits enhanced visible light decomposition of organic dye while compared with pristine SnS<SUB>2</SUB> nanosheets. The value of rate constants obtained for the Sn<SUB>0.98</SUB>Mg<SUB>0.02</SUB>S<SUB>2</SUB> nanosheets was found to be 1.4 times higher than that of pristine SnS<SUB>2</SUB>. Finally, the results obtained through the present study projects the huge potential of layered Sn<SUB>0.98</SUB>Mg<SUB>0.02</SUB>S<SUB>2</SUB> nanosheets for future multifunctional applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigation on the Controlled Degradation and Invitro Mineralization of Carbon Nanotube Reinforced AZ31 Nanocomposite in Simulated Body Fluid

A. Madhan Kumar,S. Fida Hassan,Ahmad A. Sorour,M. Paramsothy,M. Gupta 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.1

Magnesium (Mg) based implant materials are believed to be the perfect candidates for biomedical applications due to theirversatile properties. However, regulating their corrosion/degradation rate in the biological surroundings is still a noteworthytask. Suitable strategies to overcome this task is to wisely select alloy elements with improved corrosion resistanceand mechanical characteristics. An attempt has been made to enhance the corrosion and biocompatibility performance ofmagnesium alloy AZ31 containing carbon nanotubes (CNTs) as reinforcement and evaluate its degradation and invitromineralization performance in physiological medium. Corrosion behavior of AZ31 alloy with CNTs reinforcement wasinvestigated using electrochemical methods, weight loss, and hydrogen evolution in SBF during short and long-term periods. The obtained results revealed that the corrosion resistance of AZ31 alloy enhanced significantly due to the incorporationof CNTs. Hydrogen evolution test and weight loss tests revealed that the presence of CNTs improves the stability of theMg(OH)2 and efficiently regulate the degradation behavior in SBF. Surface characterization after immersion in SBF revealedthe rapid formation of bone-like apatite layer on the surface, validated a good bioactivity of the AZ31 nanocomposite samples.

Electrical property studies on chemically processed polypyrolle/aluminum doped ZnO based hybrid heterostructures

Mohan Kumar, G.,Ilanchezhiyan, P.,Madhan Kumar, A.,Yuldashev, Sh.U.,Kang, T.W. Elsevier 2016 Chemical physics letters Vol.649 No.-

<P>A hybrid structure based on p-type polypyrolle (PPy) and n-type aluminum (Al) doped ZnO nanorods was successfully constructed. The effect of Al doping on material properties of wurtzite structured ZnO were studied using several analytical techniques. To establish the desired hybrid structure, pyrrole monomers were polymerized on hydrothermally grown Al doped ZnO nanorods by chemical polymerization. The current-voltage characteristics on the fabricated PPy/A1 doped ZnO heterostructures were found to exhibit excellent rectifying characteristics under dark and illumination conditions. The obtained results augment the prescribed architecture to be highly suitable for high-sensitivity optoelectronic applications. (C) 2016 Elsevier B.V. All rights reserved.</P>