Effects of the Velocity and the Nature of the Inert Gas on the Stainless Steel Laser Cut Quality

Abstract: The effects of inert assisting gas nature and velocity on laser cut quality are investigated. A pure fusion cutting process just above melting point is considered, where the molten steel velocity is given as a function of the two acting forces represented by the pressure gradient and the frictional forces applied by the laminar gas flow. In the case of nitrogen assisting gas, the stainless steel melt film exhibits a visible separation point. The point where the melt flow is separated out from the solid wall depends strongly on the gas velocity. It is pushed down the cut surface when the gas velocity is increased. Furthermore, we have investgated the use of different inert gases (nitrogen, argon and helium) to blow the molten material out of the kerf, and it was noted that the argon and the nitrogen gases evacuate more easily the molten metallic film, compared to the helium gas from their cooling rates point of view. It is concluded that the two first gases are more efficient in laser cutting process of metals. We have studied a 4 mm stainless steel plate thickness without taking into account the transverse movement of the treated workpiece, the numerical solution is obtained by the volume of fluid (VOF) and solidification/melting models, implemented by Fluent CFD software

Calculation of resonant short-crested waves in deep water

International audienc

Three-dimensional periodic interfacial gravity waves: Analytical and numerical results

International audienceThe properties of fully three-dimensional gravity waves propagating on the interface between two finite layers of different densities are investigated. Solutions are calculated via a computer-generated perturbation expansion in wave steepness. Series solutions are analytically computed to third-order for general wave parameters, and numerically to 27th-order for five specific values of μ = 0 , 0.001 , 0.1 , 0.5 and 0.99, where μ is the ratio of the density of the upper fluid to that of the lower fluid. For near limiting waves, the series of frequency, kinetic energy and potential energy are summed using Padé approximants. For both two and three-dimensional cases, the present theory is found to coincide with previous theories such as two-dimensional interfacial standing waves, two-dimensional interfacial progressive waves and three-dimensional surface gravity waves respectively, showing the validity and general applicability of the solutions. The numerical results demonstrate the influence of the ratio density and thicknesses of the two fluids on the wave profile and wave frequency bifurcation. Particular attention is paid to the harmonic resonances where multiple solutions are possible

Semideterministic global optimization method: Application to a control problem of the Burgers equation

This paper has two objectives. We introduce a new global optimization algorithm reformulating optimization problems in terms of boundary-value problems. Then, we apply this algorithm to a pointwise control problem of the viscous Burgers equation, where the control weight coefficient is progressively decreased. The results are compared with those obtained with a genetic algorithm and an LM-BFGS algorithm in order to check the efficiency of our method and the necessity of using global optimization techniques

The Impact of Gravity vs Suction-driven Therapeutic Thoracentesis on Pressure-related Complications: The GRAVITAS Multicenter Randomized Controlled Trial

BACKGROUND: Thoracentesis can be accomplished by active aspiration or drainage with gravity. This article investigated whether gravity drainage could protect against negative pressure-related complications such as chest discomfort, re-expansion pulmonary edema, or pneumothorax compared with active aspiration. METHODS: This prospective, multicenter, single-blind, randomized controlled trial allocated patients with large free-flowing effusions estimated ≥ 500 mL 1:1 to undergo active aspiration or gravity drainage. Patients rated chest discomfort on 100-mm visual analog scales prior to, during, and following drainage. Thoracentesis was halted at complete evacuation or for persistent chest discomfort, intractable cough, or other complication. The primary outcome was overall procedural chest discomfort scored 5 min following the procedure. Secondary outcomes included measures of discomfort and breathlessness through 48 h postprocedure. RESULTS: A total of 142 patients were randomized to undergo treatment, with 140 in the final analysis. Groups did not differ for the primary outcome (mean visual analog scale score difference, 5.3 mm; 95% CI, -2.4 to 13.0; P = .17). Secondary outcomes of discomfort and dyspnea did not differ between groups. Comparable volumes were drained in both groups, but the procedure duration was significantly longer in the gravity arm (mean difference, 7.4 min; 95% CI, 10.2 to 4.6; P \u3c .001). There were no serious complications. CONCLUSIONS: Thoracentesis via active aspiration and gravity drainage both seem safe and result in comparable levels of procedural comfort and dyspnea improvement. Active aspiration requires less total procedural time. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT03591952; URL: www.clinicaltrials.gov