Flow Visualization and Scour Mechanism around Abutments

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Study of dimensionless quantities to analyse front and rear wall of keyhole formed during laser beam welding

Fluid flow mechanisms present in Keyhole (KH) during Laser Beam Welding (LBW) process influence the associated heat and mass transfer. In an attempt to describe these complexities for eventual optimization of LBW parameters, a dimensionless analysis using Mach (Ma), Raleigh (Ra), Reynolds (Re) and Marangoni (Mg) numbers have been carried out. This analysis describes hydrodynamics of melt and vapour phase appearing in the front and rear wall of KH. The non-dimensional hydrodynamic quantities describe the mechanism behind flow pattern present in melt-vapour in terms of ratio of convection–conduction heat transfer occurring within KH. The analysis shows that the higher Marangoni number indicates stronger Marangoni convection in the KH causing relatively higher capillary flow in the melt pool. The laminar-turbulent flow of melt-vapour in KH medium is described in terms of ratio of Reynolds and Mach numbers (Re/Ma). The pressure distribution in the KH accounts for the melt-vapour ejection rate. A relationship between depth and radius of KH has been obtained as a function of delivered laser power

Dynamics of plasma expansion in the pulsed laser material interaction

A pulse Nd: YAG laser with pulse duration 5-10 ns, beam radius at focal point 0.2-0.4 mm, wavelengths 1064 nm, 532 nm and 238 nm with linearly polarized radiation and Gaussian beam profile, was impacted on a thin foil of titanium metal for generating plasma plume. Numerically, the above parameters were linked with average kinetic energy of the electrons and ions in the laser-induced plasma. In the present model, electrons having higher velocities are assumed to escape from plasma, that forms a negatively charged sheath around the plasma. It is seen from present computations that the forward directed nature of the laser evaporation process results from the anisotropic expansion velocities associated with different species. These velocities are mainly controlled by the initial dimension of the expanding plasma. An attempt was undertaken to estimate the length of the plume at different ambient gas pressures using an adiabatic expansion model. The rate of the plasma expansion for various Ar ion energies was derived from numerical calculations. A numerical definition of this plasma includes events like collisional/radiative, excitation/de-excitation and ionization/recombination processes involving multiples of energy levels with several ionization stages. Finally, based on a kinetic model, the plasma expansion rate across the laser beam axis was investigated

Complexes of Co(II), Ni(II) & Cu(II) with 4-Methyl-2-aminothiazole & 4-Phenyl-2-aminothiazole

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Melt pool vorticity in deep penetration laser material welding

In the present study, the vorticity of melt motion in the keyhole and weld pool has been evaluated in case of high power CO2 laser beam welding. The circulation of vorticity is obtained as a function of Reynolds number for a given keyhole volume which is linked to Mach number variation. The shear stress and thermal fluxes present in the turbulent pool are linked to diffusivity and Prandtl number variation. It was shown that below a critical value of Rayleigh number, the conduction mode of melt transfer signifying beam absorption becomes dominant. Above this value, convective heat transfer indicates melting and evaporation occurring in the weld pool during laser welding. The evaporative recoil pressure expels the liquid while surface tension and hydrostatic pressure help to retain the melt in the keyhole cavity in this high power laser beam welding. The understanding of several hydrodynamic phenomena occuring in the weld pool is valuable not only for understanding basic mechanistic aspects but also for process optimization involved in laser beam welding

Thermal dynamics-based mechanism for intense laser-induced material surface vaporization

Laser material processing involving welding, ablation and cutting involves interaction of intense laser pulses of nanosecond duration with a condensed phase. Such interaction involving high brightness radiative flux causes multitude of non-linear events involving thermal phase transition at soild-liquid-gas interfaces. A theoretical perspective involving thermal dynamics of the vaporization process and consequent non-linear multiple thermal phase transitions under the action of laser plasma is the subject matter of the present work. The computational calculations were carried out where titanium (Ti) was treated as a condensed medium. The solution to the partial differential equations governing the thermal dynamics and the underlying phase transition event in the multiphase system is based on non-stationary Eulerian variables. The Mach number M depicts significant fluctuations due to thermal instabilities associated with the laser beam flux and intensity. A conclusive amalgamation has been established which relates material surface temperature profile to laser intensity, laser flux and the pressure in the plasma cloud

Post-COVID-19 Disease Associated with Mucormycosis and Guillain-Barré Syndrome: A Causal Association or Just a Coincidence?

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Originating from Wuhan, China, COVID-19 has rapidly spread worldwide. COVID-19 is primarily considered to be a respiratory illness, but with time there is enough evidence about the extrapulmonary manifestations of the disease. One of the neurological manifestations is Guillain-Barré syndrome (GBS). It may be associated with mucormycosis, with majority of cases occurring in India. Here, we report a case of a 40-year-old male patient, a known case of hypertension and diabetes mellitus who presented with the complaints of fever, cough and shortness of breath since May 10, 2021. He was found to be RT-PCR positive for COVID-19 on May 12, 2021. While recovering from COVID-19, on May 25, he was suspected to have rhino-orbital mucormycosis, which was confirmed on tissue specimen. While recovering from rhino-orbital mucormycosis, on July 26, the patient complained of weakness in bilateral lower limbs, followed by weakness in both upper limbs after 2 days. GBS was confirmed on nerve conduction study (NCS) and cerebrospinal fluid (CSF) examination. Patient was treated with intravenous immunoglobulin (IVIG), and while on treatment, the patient showed no significant improvement. Invasive ventilation was started in view of respiratory muscle involvement. The patient also developed autonomic dysfunction. He went into cardiac arrest and despite best efforts, couldn’t be revived. Currently, to the best of our knowledge, there is no data to tell that both mucormycosis and GBS can occur in association with COVID-19. This case aims to raise awareness among the healthcare providers for this type of association. COVID-19 may be a cause or it may just be a mere coincidence, needs further stud

Subarachnoid Hemorrhage as a Rare Presentation of Gestational Trophoblastic Neoplasia

Gestational trophoblastic neoplasia (GTN) is a rare group of malignancy that has varied clinical presentations. Hence, diagnosis is difficult, but if diagnosed on time, it has an excellent prognosis. Case summary: Here we present the case of a 24-year-old female who presented with recurrent intracranial hemorrhages. She was earlier misdiagnosed as tubercular cerebral vasculitic hemorrhage, but in her subsequent presentation after a thorough history, examination and investigation, she was diagnosed as GTN-choriocarcinoma. Conclusion: Subarachnoid hemorrhage is a rare complication of choriocarcinoma and any female in the reproductive age group with a prior history of abortion and who presents with bleeding manifestations of any organ system, should be suspected for choriocarcinom

Iron (III) perchlorate: A novel reagent for functional group as well as ring transformations in organic synthesis

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