195 research outputs found
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
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
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
МЕТОДИКА ПРОВЕРКИ В НАЗЕМНЫХ УСЛОВИЯХ ЛИНЕЙНОГО РАЗРЕШЕНИЯ ПО АЗИМУТУ В РАДИОЛОКАТОРЕ С СИНТЕЗОМ АПЕРТУРЫ КОСМИЧЕСКОГО БАЗИРОВАНИЯ
By working out of a radar with the aperture synthesis of the aerial (RAS) of space basing there is a necessity of its debugging and verification at the land conditions. The most difficult verification task is requirement performance on resolution maintenance of RAS on an azimuth. It is caused by the given resolution provided in RAS at an orbit during stable moving in space with a speed about 7,6 km/s. The verification method of maintenance of the demanded linear resolution of RAS on an azimuth in land conditions with turned synthesis of aerial aperture is offered. It operates when RAS is unmoved and objects of resolution are placed at a moving ship.При разработке радиолокатора с синтезом апертуры антенны (РСА) космического базирования возникает необходимость его отладки и проверки в наземных условиях. Наиболее сложно проверить выполнение требования по обеспечению разрешающей способности РСА по азимуту. Это обусловлено тем, что разрешающая способность по азимуту обеспечивается в РСА при его стабильном перемещении на орбите в космосе со скоростью около 7,6 км/с. Предложена методика проверки обеспечения требуемого линейного разрешения РСА по азимуту в наземных условиях с использованием обращенного синтеза апертуры, когда РСА неподвижен, а объекты разрешения размещены на движущемся носителе, в частности, на плавсредстве
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