284 research outputs found
3D-Simulation of electromagnetic and temperature fields in the continuous induction heaters
The quasi-3-D model was developed for continuous induction heating of billets
with arbitrary cross section. This computer model is intended for evaluation of electrical and
thermal both stationary and non-stationary processes of stage and continuous working regime
an induction heater with magnetic and non-magnetic loading with any of cross section shape.
The combination of the most effective numerical methods for modeling induction heating
process was used in this software: Finite Difference Method (FDM), Finite Element Method
(FEM), Boundary Element Method (BEM), Integral Equation Method (IEM) and their
combination
Computer modeling of coupled electromagnetic, temperature and magnetohydrodynamic fields in the induction heating and melting devices
Computer modeling is necessary part of design new induction heating and melting devices [1]. One of the complicated technologies when it is necessary to simulate coupled electromagnetic, temperature and magnetohydrodynamic fields is heating and melting of titanium alloys in the alternating electromagnetic field. Thermal processing of titanium alloys in the inductor has some features that it is necessary to take into account on the designing of the advanced technology and equipment. Low thermal conductivity and high temperature losses at the surface result in maximum temperature inside of the billet that could under appropriate conditions exceed melting point. In this way it is possible to obtain liquid phase of titanium alloy inside of the billet and protect it from the contact with surrounding atmosphere. To get this it is necessary to choose the right regime of processing, frequency of current, power and thermal conditions. At the same time precise heating with very strong execution of the temperature profile during the heating time are essential for thermal processing of titanium alloys in this technology [2]. Mathematical model comprising computation of electromagnetic, temperature, MHD fields after getting melt zone and dynamic of its growth was developed. The calculation of the melting process has been carried out by the method “enthalpy-porosity” with application of models of turbulent currents k-ω SST in a non-static setting. Electromagnetic forces and heat sources have been defined by solving a harmonic task by the method of finite elements on a vector magnetic potential in the system “inductor – load” for each iteration of the hydrodynamic task. Experiments confirmed need in simulation of MHD fields to receive good coincidence. Using of the developed models for simulation of electromagnetic processing billets make it easy to develop and implement optimal heat processing systems for the crucibleless induction melting of titanium alloys.The calculations on the basis of the model and the analysis of physical processes with non-crucible melting of titanium alloys have also been carried out
The seed laser system of the FERMI free-electron laser: design, performance and near future upgrades
Abstract
An important trend in extreme ultraviolet and soft X-ray free-electron laser (FEL) development in recent years has been the use of seeding by an external laser, aimed to improve the coherence and stability of the generated pulses. The high-gain harmonic generation seeding technique was first implemented at FERMI and provided FEL radiation with high coherence as well as intensity and wavelength stability comparable to table-top ultrafast lasers. At FERMI, the seed laser has another very important function: it is the source of external laser pulses used in pump–probe experiments allowing one to achieve a record-low timing jitter. This paper describes the design, performance and operational modes of the FERMI seed laser in both single- and double-cascade schemes. In addition, the planned upgrade of the system to meet the challenges of the upgrade to echo-enabled harmonic generation mode is presented
Chaotic Observer-based Synchronization Under Information Constraints
Limit possibilities of observer-based synchronization systems under
information constraints (limited information capacity of the coupling channel)
are evaluated. We give theoretical analysis for multi-dimensional
drive-response systems represented in the Lurie form (linear part plus
nonlinearity depending only on measurable outputs). It is shown that the upper
bound of the limit synchronization error (LSE) is proportional to the upper
bound of the transmission error. As a consequence, the upper and lower bounds
of LSE are proportional to the maximum rate of the coupling signal and
inversely proportional to the information transmission rate (channel capacity).
Optimality of the binary coding for coders with one-step memory is established.
The results are applied to synchronization of two chaotic Chua systems coupled
via a channel with limited capacity.Comment: 7 pages, 6 figures, 27 reference
Controlled Synchronization of One Class of Nonlinear Systems under Information Constraints
Output feedback controlled synchronization problems for a class of nonlinear
unstable systems under information constraints imposed by limited capacity of
the communication channel are analyzed. A binary time-varying coder-decoder
scheme is described and a theoretical analysis for multi-dimensional
master-slave systems represented in Lurie form (linear part plus nonlinearity
depending only on measurable outputs) is provided. An output feedback control
law is proposed based on the Passification Theorem. It is shown that the
synchronization error exponentially tends to zero for sufficiantly high
transmission rate (channel capacity). The results obtained for synchronization
problem can be extended to tracking problems in a straightforward manner, if
the reference signal is described by an {external} ({exogenious}) state space
model. The results are applied to controlled synchronization of two chaotic
Chua systems via a communication channel with limited capacity.Comment: 8 pages, 2 figure
Two-colour generation in a chirped seeded Free-Electron Laser
We present the experimental demonstration of a method for generating two
spectrally and temporally separated pulses by an externally seeded, single-pass
free-electron laser operating in the extreme-ultraviolet spectral range. Our
results, collected on the FERMI@Elettra facility and confirmed by numerical
simulations, demonstrate the possibility of controlling both the spectral and
temporal features of the generated pulses. A free-electron laser operated in
this mode becomes a suitable light source for jitter-free, two-colour
pump-probe experiments
Scaling the mid-IR radiation at 7 ÎĽm - Two-stage double-pass 195 MHz narrow-bandwidth DFG laser system
We present a laser system based on difference frequency generation (DFG) to produce tunable, narrow-linewidth (<30 pm), and high-energy mid-IR radiation in the 6785 nm region. The system exploits nonlinear crystals (such as LiInS2, LiInSe2 and BaGa4Se7) and nanosecond pulses generated by single-frequency Nd:YAG and Cr:forsterite lasers at 1064 and 1262 nm, respectively. Various experimental configurations are used: single-pass and double-pass through the nonlinear crystal. Additional increments of the output energy can be obtained by performing two stage double-pass geometry
Frequency locking of modulated waves
We consider the behavior of a modulated wave solution to an
-equivariant autonomous system of differential equations under an
external forcing of modulated wave type. The modulation frequency of the
forcing is assumed to be close to the modulation frequency of the modulated
wave solution, while the wave frequency of the forcing is supposed to be far
from that of the modulated wave solution. We describe the domain in the
three-dimensional control parameter space (of frequencies and amplitude of the
forcing) where stable locking of the modulation frequencies of the forcing and
the modulated wave solution occurs.
Our system is a simplest case scenario for the behavior of self-pulsating
lasers under the influence of external periodically modulated optical signals
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