Volume 26, Issue 4, November 2014
Index of content:
- Technical Articles
A complete model of keyhole and melt pool dynamics to analyze instabilities and collapse during laser welding26(2014); http://dx.doi.org/10.2351/1.4886835View Description Hide Description
A complete modeling of heat and fluid flow applied to laser welding regimes is proposed. This model has been developed using only a graphical user interface of a finite element commercial code and can be easily usable in industrial R&D environments. The model takes into account the three phases of the matter: the vaporized metal, the liquid phase, and the solid base. The liquid/vapor interface is tracked using the Level-Set method. To model the energy deposition, a new approach is proposed which consists of treating laser under its wave form by solving Maxwell's equations. All these physics are coupled and solved simultaneously in Comsol Multyphysics®. The simulations show keyhole oscillations and the formation of porosity. A comparison of melt pool shapes evolution calculated from the simulations and experimental macrographs shows good correlation. Finally, the results of a three-dimensional simulation of a laser welding process are presented. The well-known phenomenon of humping is clearly shown by the model.
Experimental evaluation and theoretical investigations of fiber Raman amplifiers and its gain optimization based on single forward pump26(2014); http://dx.doi.org/10.2351/1.4889955View Description Hide Description
In this paper, we perform the experiment evaluation and the optimization of forward pumped fiber Raman amplifiers. The pumping configuration characteristics and optimum single mode large-effective-area fiber lengths for the system are presented within the framework of the undepleted pump approximation. It is found that achievable optimal span length and Raman gain in optimized forward pumped is about 52 km and 3.92 dB (2.42 dB) using an efficient particle swarm optimization (PSO) method at signal wavelength 1500 nm, higher than that without using PSO in signal wavelength 1300 nm for 200 mW pumping power. The experimental results showed that the gain flatness of the forward Raman amplifier can be maintained over a wide wavelength with a gain ripple lower than 0.4 dB.