Experimental Study of Thickness Gradient and Flow Simulation in VARTM Process

Tushar Gajjar,Dhaval B. Shah,S. J. Joshi,K. M. Patel 한국섬유공학회 2020 Fibers and polymers Vol.21 No.2

Vacuum assisted resin transfer moulding (VARTM) process is widely used for manufacturing composite products. It is very difficult to manufacture a composite component with small dimension tolerance using VARTM process. In this research paper, carbon fiber reinforced polymer (CFRP) flat plates have been manufactured using the VARTM process with a different combination of process parameters. The carbon fiber laminates with different thickness have been manufactured using the VARTM process. The thickness of manufactured components has been measured at different locations using noncontact type 3D scanning techniques. The warpage has been determined for each manufactured components. The compaction pressure has been measured using pressure gauge at a different location during manufacturing. The thickness variation, pressure variation and volume fraction have been determined across the length for each manufactured components for different thickness laminates. The mould filling time has been calculated using the numerical approach in ANSYS Fluent software and the same has been compared with experimental results. The percentage difference between the experimental and numerical approach has been found within 5 %.

Electronic, Magnetic and Optical Properties of 2D Metal Nanolayers: A DFT Study

Prabal Dev Bhuyan,Sanjeev K. Gupta,Deobrat Singh,Yogesh Sonvane,P. N. Gajjar 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4

In the recent work, we have investigated the structural, electronic, magnetic and optical properties of graphene-like hexagonalmonolayers and multilayers (up to fi ve layers) of 3 d -transition metals Fe, Co and Ni based on spin-polarized density functionaltheory. Here, we have taken two types of pattern namely AA-stacking and AB-stacking for the calculations. The bindingenergy calculations show that the AA-type confi guration is energetically more stable. The calculated binding energies of Fe,Co and Ni-bilayer monolayer are − 3.24, − 2.53 and − 1.94 eV, respectively. The electronic band structures show metallicbehavior for all the systems and each confi gurations of Fe, Co and Ni-atoms. While, the quantum ballistic conductancesof these metallic systems are found to be higher for pentalayer than other layered systems. The density of states confi rmsthe ferromagnetic behavior of monolayers and multilayers of Fe and Co having negative spin polarizations. We have alsocalculated frequency dependent complex dielectric function, electronic energy loss spectrum and refl ectance spectrum ofmonolayer to pentalayer metallic systems. The ferromagnetic material shows Different permittivity tensor ( ɛ ), which is dueto high spin magnetic moment for n-layered Fe and Co two-dimensional (2D) nanolayers. The theoretical investigation suggeststhat the electronic, magnetic and optical properties of 3 d -transition metal nanolayers off ers great promise for their usein spintronics nanodevices and magneto-optical nanodevices applications.

Vitamin D Trajectory after Total Knee Arthroplasty: A Method for Quick Correction in Deficient Patients

Rajesh N Maniar,Adit R Maniar,Ditesh Jain,Nishit Bhatnagar,Arpit Gajjar 대한정형외과학회 2021 Clinics in Orthopedic Surgery Vol.13 No.3

Background: It has been widely reported that vitamin D (vit D) affects preoperative, postoperative, and long-term outcomes after total knee arthroplasty (TKA). Our aim was to study vit D trajectory after TKA and compare effects of oral versus intramuscular (IM) supplementation in insufficient patients and assess its effects on immediate functional recovery in the first 2 weeks after TKA. Methods: Vit D levels < 30 ng/mL are considered insufficient. We prospectively enrolled 60 patients (20 per group): group I, vit D sufficient patients; group II, vit D insufficient patients given IM supplementation (cholecalciferol 6,00,000 IU); and group III, vit D insufficient patients given oral supplementation (cholecalciferol 600,000 IU). Vit D levels, knee flexion, Timed Up and Go (TUG) test results, and visual analog scale (VAS) score were recorded preoperatively and postoperatively on day 3 and 14. Results: In group I, mean preoperative vit D significantly dropped at postoperative day (POD) 3 and POD 14 (p = 0.001). In group II, mean preoperative vit D rose at POD 3 and rose significantly at POD 14 (p = 0.001). In group III, mean preoperative vit D increased significantly at both POD 3 and POD 14 (p < 0.001). Also, in group III, the rise in vit D was significantly higher than that in group II both at POD 3 and POD 14 (p < 0.05). In group III, 19 of 20 insufficient patients became sufficient on POD 3 and all 20 by POD 14. In group II, even by POD 14, only 11 of 20 insufficient patients became sufficient. Functional parameters (flexion, change in flexion, TUG test results, and VAS score) were comparable (p > 0.05) in all groups. Changes in TUG test showed a significant increase in group II (48.5 seconds) when compared to group I (35.5 seconds) at POD 3 (p < 0.05), suggesting a slower recovery. It remained comparable (p > 0.05) between group III and group I. Conclusions: We found that vit D insufficient patients can be rapidly supplemented on the morning of surgery with a large dose of oral cholecalciferol 600,000 IU, and the effect was consistent over 2 weeks after surgery. Orally supplemented vit D insufficient patients also showed functional recovery comparable to vit D sufficient patients. IM supplementation increased vit D levels only at 2 weeks and the rise was significantly lower than oral supplementation. Interestingly, approximately 25% of vit D sufficient patients who were not supplemented after TKA became insufficient in the first 2 weeks postoperatively.

Multi-Secondary Transformer: A Modeling Technique for Simulation - II

Patel, A.,Singh, N.P.,Gupta, L.N.,Raval, B.,Oza, K.,Thakar, A.,Parmar, D.,Dhola, H.,Dave, R.,Gupta, V.,Gajjar, S.,Patel, P.J.,Baruah, U.K. Journal of International Conference on Electrical 2014 Journal of international Conference on Electrical Vol.3 No.1

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (${\mu}S$ order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.