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- 摘要
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- 实验方案
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Enhanced Voltage and Frequency Stability for Power Systems with High Penetration of Distributed Photovoltaic Generation
摘要： Distributed solar photovoltaic (PV) has shown a large-scale development in Germany with a total capacity of 22.5 GW connected to the low voltage networks in 2015. This paper deals with the quantitative assessment of the impact of a high penetration of small PV units embedded in distribution networks on the voltage and frequency stability of the larger interconnected system. In particular, the effect of the various requirements regarding voltage control, frequency control and active power control during contingency situations is analyzed using a fully-integrated EMT-type model for the PV power plant. Simulations on a representative benchmark test network are used to assess and quantify the overall impact and to identify appropriate measures to improve the voltage and frequency stability of the power system. Finally, the proposed improvements are evaluated considering the present developments in Germany.
关键词： Photovoltaic,low voltage networks,transmission system,EMT-simulation,Germany
更新于2025-09-12 10:27:22
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Design and Manufacturing of a Protective Nozzle for Highly Reactive Materials Processing via Laser Material Deposition
摘要： Laser Material Deposition (LMD) is a near-net-shape additive process. Powder particles are usually employed as filler material, which is injected through a powder nozzle (coaxial or off-axis) and then completely molten by a laser beam. The possibility to add material on complex 3D surfaces makes LMD a key process in the repair and wear/corrosion protection applications. The present work is focused on the improvement of the design & manufacturing of a LMD nozzle, what introduces two main advantages: the possibility to process a wider variety of materials by generating a protective atmosphere and the improvement of the efficiency of the nozzle. The results of numerical simulations are used for optimizing the design of the protective cone of the LMD nozzle, which is then manufactured and experimentally validated. Finally, the proper performance of the resultant nozzle is tested depositing Ti6Al4V.
关键词： efficiency,reactive materials,protective atmosphere,simulation,laser material deposition,oxidation-free,laser cladding,coaxial nozzle
更新于2025-09-12 10:27:22
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3D grain growth simulation and experimental verification in laser beam melting of IN718
摘要： A predictive grain structure model originally used for selective electron beam melting (SEBM) is adapted to laser beam melting (LBM). Single lines with varying welding speeds were molten in a base plate made of polycrystalline IN718. The heat input is calculated with an analytical heat source model and the resulting melt pool geometry is compared with micrographs and high-speed camera shots. A typical welding microstructure is predicted by the grain growth model and confirmed with Electron Backscatter Diffraction (EBSD) measurements. With increasing line energies, a rising fragmentation of the grains is observed. This phenomenon is explained by an analyzation of the thermal gradients at the time of solidification of the grains.
关键词： additive manufacturing,laser beam melting,cellular automata,grain growth simulation
更新于2025-09-12 10:27:22
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Simulation of molten pool dynamics and stability analysis in laser buttonhole welding
摘要： Molten pool dynamics in laser buttonhole welding with wire feeding and laser beam oscillation were studied using computational fluid dynamics (CFD). The simulation results, such as temperature fields and molten pool velocities, were used to analyze the characteristics of molten pool dynamics. The dynamics in the rear part of the molten pool area were significantly reduced in comparison to those in the front when a buttonhole (a cavity in the molten pool) was present.
关键词： buttonhole welding,beam oscillation,laser welding,seam quality,numerical simulation
更新于2025-09-12 10:27:22
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Weld pool shape observation in high power laser beam welding
摘要： The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
关键词： high power laser beam welding,transient weld pool shape,bulging,numerical process simulation
更新于2025-09-12 10:27:22
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Inconel 718 laser welding simulation tool based on a moving heat source and phase change
摘要： Modern aerospace industry demands the union of different Inconel 718 parts ensuring the quality of the joint. Therefore, in the present work a novel fiber laser welding model that considers wobbling strategy is developed. The heat source model definition and solid-liquid phase change phenomena are taken into account as bead is considered liquid zone during the melting, getting a robust-but-simple tool for prediction of bead and heat affected zone geometries depending on process parameters. One of the main drawbacks is the maximum welded bead width, which is limited by the beam spot. In order to overcome this handicap, wobbling strategy allows covering a wider area by combining elliptical and linear motions. Optimal relation between these orbital and translation speeds is defined for minimum overlap among consecutive wobble rings. Likewise, temperature rise at welded joint is estimated by existing and modified heat source models after relying on experimental validation.
关键词： Inconel 718,simulation,laser welding,wobbling
更新于2025-09-12 10:27:22
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Model assisted closed-loop control strategy for selective laser melting
摘要： Selective laser melting is a growing technology for the production of complex metal parts. However, the workpiece heat conduction differs for different points due to its geometry, which results in a varying melt pool temperature and a varying part quality. A desired closed-loop control of the melt pool temperature is currently missing, because the production machines have no suitable sensors or the slow measurement hinders the in-process control. For this reason, a novel control approach is presented and verified by a proof-of-concept experiment. The control consists of a model-based feedforward control using a finite element heat simulation in combination with a robust feedback control employing a pyroelectric sensor. Simulation and experimental results prove a reduction of the temperature deviation of up to 73 % compared to an open-loop approach for the tested demonstration geometry. The feedback control concept is further shown to be capable of achieving cycle durations <50 μs, which enables in-process control.
关键词： Control,feedback control,simulation,modelling,selective laser melting
更新于2025-09-12 10:27:22
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Multiscale Electrothermal Simulation of Quantum Cascade Laser Operation
摘要： Quantum cascade lasers (QCLs) are high-power coherent light sources in the midinfrared and terahertz parts of the electromagnetic spectrum. They are systems in which the electronic and lattice systems are far from equilibrium, strongly coupled to one another, and the problem bridges disparate spatial scales. We present our ongoing work on the far-from-equilibrium transport of charge and heat in QCLs.
关键词： Quantum cascade lasers,far-from-equilibrium,electrothermal simulation,multiphysics,multiscale
更新于2025-09-12 10:27:22
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[IEEE 2019 34th Symposium on Microelectronics Technology and Devices (SBMicro) - Sao Paulo, Brazil (2019.8.26-2019.8.30)] 2019 34th Symposium on Microelectronics Technology and Devices (SBMicro) - High-Efficiency GaAs Solar Cell Optimization by Theoretical Simulation
摘要： Theoretical simulations of solar cell current-voltage characteristics provide important information for a better design of the device structure, such as layers thicknesses and doping levels, in order to obtain high photovoltaic conversion efficiency. The inclusion of precise material parameters is critical to obtain reliable results and detailed understanding of the simulated device operation. In this study, GaAs solar cell structures were simulated by drift-diffusion model with SCAPS-1D in order to optimize the performance under 1 sun illumination. Moreover, we used the published results of some devices as references to infer their structures, as the details are normally not completely disclosed by the authors. To do so, an optimization study was required to probe different materials, thicknesses and doping levels for the layers. With the inferred structure, it was possible to evaluate the possibility of improvements through variation of the structure parameters to achieve even higher efficiencies.
关键词： Theoretical Simulation,Optimization,GaAs Solar Cell,SCAPS-1D
更新于2025-09-12 10:27:22
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Determination of sensitivity and thermal efficiency in laser assisted metal-plastic joining by numerical simulation
摘要： Laser-assisted joining of plastics and metals requires the formation of a melting layer in the thermoplastic material, which enables the wetting and the penetration of the metal surface. In this paper, a generally valid description of the melting layer is given based on material-specific temperatures and numerical simulation. Furthermore, the sensitivity of the melting layer to process parameters, material properties and geometrical parameters is provided. Based on these results, the thermal efficiency of the process was examined depending the major factors metal thickness and absorbed laser beam power.
关键词： thermal degradation,laser welding,LAMP,metal-plastic hybrid,thermal joining,hybrid joints,numerical simulation
更新于2025-09-12 10:27:22