Mathieu stability of offshore Buoyant Leg Storage & Regasification Platform

Chandrasekaran, S.,Kiran, P.A. Techno-Press 2018 Ocean systems engineering Vol.8 No.3

Increasing demand for large-sized Floating, Storage and Regasification Units (FSRUs) for oil and gas industries led to the development of novel geometric form of Buoyant Leg Storage and Regasification Platform (BLSRP). Six buoyant legs support the deck and are placed symmetric with respect to wave direction. Circular deck is connected to buoyant legs using hinged joints, which restrain transfer of rotation from the legs to deck and vice-versa. Buoyant legs are connected to seabed using taut-moored system with high initial pretension, enabling rigid body motion in vertical plane. Encountered environmental loads induce dynamic tether tension variations, which in turn affect stability of the platform. Postulated failure cases, created by placing eccentric loads at different locations resulted in dynamic tether tension variation; chaotic nature of tension variation is also observed in few cases. A detailed numerical analysis is carried out for BLSRP using Mathieu equation of stability. Increase in the magnitude of eccentric load and its position influences fatigue life of tethers significantly. Fatigue life decreases with the increase in the amplitude of tension variation in tethers. Very low fatigue life of tethers under Mathieu instability proves the severity of instability.

SPLIT MAP AND IDEMPOTENT SEPARATING CONGRUENCE

CHANDRASEKARAN, V. M.,LOGANATHAN, M. 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.18 No.1

Let T be a regular semigroup and let S be a regular subsemigroup of T. In this paper we study the relationship between the idempotent separating congruence on S and the idempotent separating congruence on T, when T and S are connected by a splitmap ${\theta} : T {\to} S$.

STRUCTURE OF COEXTENSIONS OF REGULAR SEMIGROUPS BY RECTANGULAR BANDS

Chandrasekaran, V.M. 한국전산응용수학회 2003 Journal of applied mathematics & informatics Vol.12 No.1

In this paper, we described the structure of coextensions of regular semigroups by rectangular bands.

Long-term drought modifies carbon allocation and abscisic acid levels in five forest tree species

Chandrasekaran Umashankar,Kim Kunhyo,Byeon Siyeon,Huh Woojin,Han Ah Reum,Lee Young-Sang,김현석 한국생태학회 2023 Journal of Ecology and Environment Vol.47 No.4

Background: This study analyzed the drought responses of five forest tree species grown in Korean peninsula, Korean fir Abies koreana (Ak), eastern white pine Pinus strobus (Ps), keyaki Zelkova serrata (Zs), tulip tree Liriodendron tulipifera (Lt), and Japanese elm Ulmus japonica (Uj). Physiological (chlorophyll, root collar diameter [RCD]) and biochemical responses (non-structural carbohydrates, proline, lipid peroxidase and abscisic acid [ABA]) of the plants grown under mild (MD) and severe drought (SD) were compared. Results: In this study, three soil moisture regimes: control (100% precipitation), MD (60% reduction in precipitation) and SD (20% reduction in precipitation) were applied. Soil moisture content showed high water content in control site compared to MD and SD. A decline in RCD was found for Korean fir, keyaki, and tulip plants, with eastern white pine and Japanese elm showing no significant decline to the prolonged drought exposure (both MD and SD). Total chlorophyll showed a significant decline in Korean fir and tulip, with the sugar levels indicating a significant increase in Korean fir and keyaki species under SD compared to control plants. Non-significant decline in sugar level was noted for eastern white pine and Japanese elm. High accumulation of ABA, malondealdehyde and proline was noted in Korean fir, tulip, and keyaki under SD compared to control. Signs of tree mortality was only observed in Korean fir under MD (38%) and SD (43%). Conclusions: The observed findings indicate the drought responses of five tree species. The majority of the morpho-physiological (especially mortality) and biochemical variables assessed in our study indicate superior long-term drought resistance of Ps and Uj compared to the highly sensitive Ak, and moderately sensitive Lt and Zs. The results provided will help species selection for afforestation programs and establishment of sustainable forests, especially of drought-tolerant species, under increased frequency and intensity of spring and summer droughts.

Structurally tuned lead magnesium titanate perovskite as a photoelectrode material for enhanced photoelectrochemical water splitting

Chandrasekaran, S.,Kim, E.J.,Chung, J.S.,Yoo, I.K.,Senthilkumar, V.,Kim, Y.S.,Bowen, C.R.,Adamaki, V.,Hyun Hur, S. Elsevier 2017 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.309 No.-

This is the first demonstration of four distinct types of Lead Magnesium Titanate (PMT) perovskites including spheres, flakes, hierarchical flower and thin microbelt shapes that were finely tuned via facile solution method to develop cost effective and high performance photoanode materials for water splitting. The influence of solvent effects during structural tuning, purity, morphology, optical absorption, structural phase transition and stoichiometric formation of the prepared Lead Magnesium Titanate perovskites has been discussed in detail. A remarkable observation is that the thin microbelts structured PMT perovskite (PMTT) exhibited an excellent water splitting performance and it is more sensitive to the illuminated visible light. Owing to the unique structural features, the photoconversion efficiency value of PMTT perovskite is ~3.9, 3.54, 2.85 and 1.52 times higher than those of other prepared PMT perovskites including pristine PbTiO<SUB>3</SUB>. The excellent water splitting performance of PMTT (thin microbelts) may be ascribed to the remarkable structural features that include a large surface area, high optical absorbance, more active sites and high interface area of the microbelts, which provide large contact areas between the electrolyte and highly active materials for electrolyte diffusion and a rapid route for charge transfer with minimal diffusion resistance. In addition, each thin microbelt is directly in contact with the Ni foam substrate, which can also shorten the diffusion path for the electrons. The demonstrated approach paves the way for low-cost and high-throughput production of next generation, high performance and highly active water splitting perovskite photocatalysts.

EXISTENCE RESULTS FOR NEUTRAL FUNCTIONAL INTEGRODIFFERENTIAL EQUATIONS WITH INFINITE DELAY IN BANACH SPACES

Chandrasekaran, S.,Karunanithi, S. The Korean Society for Computational and Applied M 2015 Journal of applied mathematics & informatics Vol.33 No.1

This paper is concerned with the existence of mild solutions for partial neutral functional integrodifferential equations with infinite delay in Banach spaces. The results are obtained by using resolvent operators and Krasnoselski-Schaefer type fixed point theorem. An example is provided to illustrate the results.

Response of triceratops to impact forces: numerical investigations

Chandrasekaran, Srinivasan,Nagavinothini, R. Techno-Press 2019 Ocean systems engineering Vol.9 No.4

Triceratops is one of the new generations of offshore compliant platforms suitable for ultra-deepwater applications. Apart from environmental loads, the offshore structures are also susceptible to accidental loads. Due to the increase in the risk of collision between ships and offshore platforms, the accurate prediction of structural response under impact loads becomes necessary. This paper presents the numerical investigations of the impact response of the buoyant leg of triceratops usually designed as an orthogonally stiffened cylindrical shell with stringers and ring frames. The impact analysis of buoyant leg with a rectangularly shaped indenter is carried out using ANSYS explicit analysis solver under different impact load cases. The results show that the shell deformation increases with the increase in impact load, and the ring stiffeners hinder the shell damage from spreading in the longitudinal direction. The response of triceratops is then obtained through hydrodynamic response analysis carried out using ANSYS AQWA. From the results, it is observed that the impact load on single buoyant leg causes periodic vibration in the deck in the surge and pitch degrees of freedom. Since the impact response of the structure is highly affected by the geometric and material properties, numerical studies are also carried out by varying the strain rate, and the location of the indenter and the results are discussed.

Micro-scale to nano-scale generators for energy harvesting: Self powered piezoelectric, triboelectric and hybrid devices

Chandrasekaran, Sundaram,Bowen, Chris,Roscow, James,Zhang, Yan,Dang, Dinh Khoi,Kim, Eui Jung,Misra, R.D.K.,Deng, Libo,Chung, Jin Suk,Hur, Seung Hyun Elsevier 2019 Physics reports Vol.792 No.-

<P><B>Abstract</B></P> <P>This comprehensive review focuses on recent advances in energy harvesting of micro-scale and nano-scale generators based on piezoelectric and triboelectric effects. The development of flexible and hybrid devices for a variety of energy harvesting applications are systematically reviewed. A fundamental understanding of the important parameters that determine the performance of piezoelectric, triboelectric and hybrid devices are summarized. Current research directions being explored and the emerging factors to improve harvester functionality and advance progress in achieving high performance and durable energy conversion are provided. Investigations with regard to integrating flexible matrices and optimizing the composition of the piezoelectric and triboelectric materials are examined to enhance device performance and improve cost-effectiveness for the commercial arena. Finally, future research trends, emerging device structures and novel materials in view of imminent developments and harvesting applications are presented.</P>

3D crumpled RGO-Co₃O₄ photocatalysts for UV-induced hydrogen evolution reaction

Chandrasekaran, S.,Choi, W.M.,Chung, J.S.,Hur, S.H.,Kim, E.J. North-Holland 2014 Materials Letters Vol.136 No.-

Three dimensional (3D) crumpled reduced graphene oxide (RGO)-Co<SUB>3</SUB>O<SUB>4</SUB> nanohybrids were synthesized via a novel and facile solution method for use in UV-induced hydrogen evolution reaction (HER). The synthesized RGO-Co<SUB>3</SUB>O<SUB>4</SUB> was calcined at a temperature from 300<SUP>o</SUP>C to 500<SUP>o</SUP>C to examine the effect of calcination on its HER activity. The 500<SUP>o</SUP>C-calcined 3D-crumpled RGO-Co<SUB>3</SUB>O<SUB>4</SUB> exhibited the highest photocurrent density under UV illumination due to the improved interfacial hole transfer and suppressed electron recombination. In addition, it also showed excellent durability even after 1000 cycles in acidic solution.

Influence of severe drought on mineral nutrient status in eastern white pine (Pinus strobus L)

Chandrasekaran Umashankar,변시연,김근효,허우진,한아름,이영상,김현석 한국산림과학회 2023 Forest Science And Technology Vol.19 No.3

The photochemical process of photosynthesis is significantly influenced by the availability of nutrients. The purpose of this research is to ascertain how photosynthetic pigment function is affected by nutrient elemental changes caused by severe drought stress. Using elemental analysis, we looked at the changes in mineral nutrient composition in eastern white pine (Pinus strobus L) seedlings 32 days after drought treatment. According to our findings, severe drought resulted in a significant and non-significant decrease in the contents of Chl “b and a”, respectively. The elemental composition of iron (Fe), zinc (Zn), magnesium (Mg), potas- sium (K), phosphorus (P) and nitrogen (N) was measured. After severe drought treatment, leaf nutrient status showed a significant decline in total N (control-1.57 ± 0.1; drought- 0.65 ± 0.07), P (control-959.4 ± 17; drought-645 ± 46), Mg (control-1030.4 ± 33; drought- 750.7 ± 76), and K (control-3062.5 ± 32; drought-1853.3 ± 198), with a non-significant decrease in leaf Fe (control-120.3 ± 20; drought-98.9 ± 28) and increase in leaf Zn (control-33.49 ± 2; drought-39.05 ± 4). A positive correlation was found between the content of Fe, P, Mg, K, and N in leaf Chl “b”, but only a positive correlation was found between the content of Zn in leaf Chl “a” during severe drought. During severe drought, nutrient reallocation has a sig- nificant impact on leaf chlorophyll levels, as evidenced by this correlation.