Stationary Mode Of Operation Research Articles

Linear controller design for chance constrained systems

This paper is concerned with the design of a linear control law for a linear system with stationary additive disturbances. The objective is to find a state feedback gain that minimizes a quadratic stage cost function, while observing chance constraints on the input and/or the state. Unlike most of the previous literature, the chance constraints (and the stage cost) are not considered on each input/state of the transient response. Instead, they refer to the input/state of the closed-loop system in its stationary mode of operation. Hence the control is optimized for the long-run, rather than for finite-horizon operation. The controller synthesis problem can be cast as a convex semi-definite program (SDP). The chance constraints appear as linear matrix inequalities. Both single chance constraints (SCCs) and joint chance constraints (JCCs) on the input and/or the state can be included. If the disturbance is Gaussian, this information can be used to improve the controller design. The presented approach can also be extended to the case of output feedback. The entire design procedure is flexible and easy to implement, as demonstrated on a short illustrative example.

Effects of the cathode grain size and substrate fixture movement on the evolution of arc evaporated Cr-cathodes and Cr-N coating synthesis

The influence of the cathode grain size and the operation mode of the substrate fixture on the microstructure evolution of the Cr cathodes and the resulting Cr-N coating synthesis is studied. Hot isostatic pressed Cr cathodes with three different grain sizes were arc evaporated in a nitrogen atmosphere and Cr-N coatings were deposited on cemented carbide substrate at 2 and 4 Pa nitrogen pressure, respectively. The Cr cathodes before and after arc discharging are composed of polycrystalline α-Cr regardless of the grain size. A converted layer forms on the Cr cathode surface and its microstructure differs with the cathode grain size. A stationary mode of the substrate fixture results in ditches covering the cathode surface while a single rotating mode does not. The increased grain size of the virgin Cr cathodes enhances the quantities of the ditches. The possible causes are addressed. At 2 Pa nitrogen pressure, the Cr-N coatings deposited with the single rotating mode of the substrate fixture comprise only cubic CrN phase while the ones deposited with the stationary mode of the substrate fixture contain a mixture of hexagonal Cr2N and cubic CrN phases. By the increasing grain size of the Cr cathode, the droplet density of the Cr-N coatings increase somewhat while the hardness decreases for the Cr-N coatings deposited with stationary mode at 2 Pa nitrogen pressure. At the same stationary operation mode of the substrate fixture, the hardness of Cr-N coatings deposited at 4 Pa nitrogen pressure decreases ∼5 GPa in comparison to coatings at 2 Pa nitrogen pressure due to the decreased fraction of hex-Cr2N and the increased droplet density.

Delimitation of application of stationary and non-stationary models of the gas pipeline operation

The author of work offers way of delimitation of preferable application of a stationary model, and model which describes non-stationary process of gas pipeline operation. Scientifically reasonable choice of a settlement model is key question for gas pipelines calculation. The importance of such differentiation in practice is that it makes sense to use simpler stationary model if variability of parameters is not big and doesn't entail inadmissible errors. The author of work shows this way on concrete models: standard calculation of a stationary operating mode of gas pipeline, offered, for example, in norms of design and calculation of well-known system of equations which describes non-stationary process by the way with variable coefficients. This way of calculation was significantly modified by author for accounting of heat exchange, and also, for gravity influence. The specified adjustment is described in detail in other publication of author. In offered way of differentiation of scopes of stationary and non-stationary models of gas pipeline hydraulic calculation, comparison of results of calculation of both models according to same regime data is used. Results of calculation of both models have to be compared in sizes of calculated losses of energy of gas compression in gas pipeline. The choice, for example, of this parameter is caused by that in solution of specific objective concerning gas transport, size of losses of energy of gas compression in gas pipeline defines main part of expenses of energy carriers at compressor station. Therefore it is key indicator in an assessment of an operating mode of gas transmission system and in choice of most economically expedient option of an operating mode. The essence of definition of required border consists in that distinctions of results of calculation for both methods which are exposed to differentiation, are comparable to errors of these methods. The application of offered way is shown on calculation of concrete example. For all counted parameters, settlement ratios are offered, and results of calculation, for reviewed example, presented by numbers or graphically.

A multifunction gyro inclinometer with the principal axis of the two-axis angular rate sensor aligned in the wellbore diametrical plane

The paper describes and analyzes a fundamentally new kinematic scheme of a strapdown gyro inclinometer (GI) which allows for both continuous and stationary modes of GI operation for all possible trajectories of wellbores. The output parameters of the GI are independent of start-up errors of the two-axis angular rate sensor in all practical applications.

Thermal Explosion of a Gas Mixture in a Porous Hollow Cylinder

A nonstationary model of gas combustion in a porous cylindrical heat generator with allowance for heat losses inside the body and from the outer surface is proposed and numerically analyzed. The flow pattern is demonstrated to depend on the ratio of the outer and inner radii of the working region. Critical conditions separating the stationary operation mode and the thermal explosion are found.

Experimental Determination of Optimal Construction of Current Limiting Transformers Using HTS Tapes and Rings

The current limiting or self-limiting transformer (CLT, SLT) is a multifunctional device which combines the functions of a usual power transformer with the functions of a current limiter. Various constructions of the CLT and fault current limiters (FCL) were investigated in order to realize the optimized constructional outline. Small scale devices were investigated with one or more YBCO rings and BSCCO tape(s). The rings were placed on one or two limbs of the devices. The HTS ring was replaced with HTS tape in order to realize a new FCL construction. The main goal is to decrease the leakage field and to increase the mainfield reactance. The magnetizing current is to be reduced. The upscalability i.e. increase of the power rating is investigated as well. The CLT was investigated experimentally for both sudden short circuit and steady state (transformer) operation modes in cases of several selected configurations. The activation currents of the devices were determined in cases of sudden short circuit and transformer operation modes. The results are used to find the optimum constructional outline realization of the current limiting transformer.

Adaptive algorithms to estimate parameters of the optimal policies of inventory control under limited stock-out

Consideration was given to the inventory control by the criterion for minimum of the cumulative mean costs over a sufficiently long planning horizon in conditions of uncertain demand characteristics. Adaptive algorithms to estimate the parameters of the optimal two-level control policies oriented to the supply systems with high level of customer servicing were constructed for the stationary mode of operation.

Analyses of the ammonia response of integrated gas sensors working in pulsed mode

WO 3–Cr, SnO 2–Pd and TiO 2–Cr nanoparticles have been prepared following a sol–gel route. The additive-modified nanostructured metal oxides have been deposited on hotplate platforms by microdropping. Functional gas test of the sensitive layers to ammonia has been performed in stationary and pulsed mode of operation. The pulsed mode fastened the regeneration of the surface yielding an enlargement of the sensor response and a decrease of the transient time. The improved sensing response to ammonia was particularly marked for the WO 3–Cr based gas sensor.

Optimization of Control of Doubly Stochastic Nonordinary Flows in Time-Sharing Systems

Control of conflicting flows in a class of time-sharing algorithms with regard for orientation and readjustment is studied. Probabilistic properties of flows are determined by the Markov environment. Conditions for the existence of a stationary operation mode of the system are determined and interpreted graphically. Optimization by the minimum of mean sojourn cost in a control cycle is studied. Imitation modeling is used to estimate the characteristics that cannot be found analytically.

Mathematical model and numerical simulation of the dynamics of flocculated suspensions in clarifier–thickeners

We formulate a mathematical model for continuous sedimentation–consolidation processes of flocculated suspensions in clarifier–thickener units. The governing equation of this model is a scalar, strongly degenerate parabolic equation in which both the convective flux and the diffusion term depend on parameters that are discontinuous functions of the depth variable. A simple finite-difference scheme for the numerical solution of the model is introduced. We perform a limited analysis of steady states as desired stationary modes of operation. Finally, numerical examples illustrate that the model realistically describes the dynamics of flocculated suspensions in clarifier–thickeners.

A Model of Continuous Sedimentation of Flocculated Suspensions in Clarifier-Thickener Units

The chief purpose of this paper is to formulate and partly analyze a new mathematical model for continuous sedimentation-consolidation processes of flocculated suspensions in clarifier-thickener units. This model appears in two variants for cylindrical and variable cross-sectional area units, respectively (Models 1 and 2). In both cases, the governing equation is a scalar, strongly degenerate parabolic equation in which both the convective and diffusion fluxes depend on parameters that are discontinuous functions of the depth variable. The initial value problem for this equation is analyzed for Model 1. We introduce a simple finite difference scheme and prove its convergence to a weak solution that satisfies an entropy condition. A limited analysis of steady states as desired stationary modes of operation is performed. Numerical examples illustrate that the model realistically describes the dynamics of flocculated suspensions in clarifier-thickeners.

Universal plasma electron source

The construction of universal plasma electron sources that allows to generate both focused electron beams and large cross-section beams within stationary and pulse mode of operation is proposed, without any essential change in the construction of the source. The special feature of the source is the stability of electron beam parameters over a wide range of pressure (up to 10−2mbar), which makes it possible to use it in difficult vacuum conditions caused by intensive gas emission from the treated surface. High stability of the focused electron beam parameters is achieved due to a special configuration of electric and magnetic fields in the region of electron extraction. Generating large cross-section beams, a weak dependence of beam parameters of gas pressure, is achieved by using the method of double-grid stabilization of the emitting plasma surface. Physical processes causing an increase in parameter stability are discussed.

Application of the Principle of Design of Adaptive Systems with a Reference Model to Problems of Monitoring of a Current State of Transmission Shafts

A possibility of monitoring a current state of transmission shafts on the basis of an adaptive system with a reference model is considered. Using a gas-turbine engine as an example, a problem is solved for the estimation of a torsion angle of the shaft that transmits the torque of a free turbine through the reduction gear to the propeller in the condition of a finite value of the torsion stiffness of the shaft. The torsion angle specifies the current state of the shaft and can be used for the advanced disengagement of the engine in the event of the breakup of the transmission. It is shown that the suggested adaptive system of estimating the torsion angle of the shaft ensures a high dynamic accuracy in the stationary and nonstationary modes of operation of the engine. The mathematical modeling confirmed the serviceability of the system under conditions that are close to actual ones, in particular, under the action of random noise of the measurement.

Benchmark experiments on measurement of neutron and γ-ray leakage spectra and yields from three vanadium spheres

The results of measurements of the γ-ray and neutron leakage spectra from three vanadium spheres with diameter 10, 24 and 34 cm at their internal irradiation by 14-MeV neutrons are presented. The experiments are carried out in the framework of ISTC Project #910 in collaboration with FZK. All the spheres have the same geometry of the central hole 3 cm in diameter. The measurements were carried out by the time-of-flight technique. NaI(Tl) crystal with the dimensions of ∅150×100 mm was used as γ-spectrometer. The neutron leakage spectra were measured with two types of scintillation detector, and by a gas proportional counter at a stationary mode of neutron generator operation.

CuBr laser with a reduced energy input into a discharge

The operation of a CuBr laser with a small volume of the active medium for a reduced energy input into a discharge was studied. It was shown that switching the commutator to a smaller operating capacitor for a short time permits a 2.3-fold reduction (relative to the typical operating mode) of the power supplied to the discharge without sacrificing any output laser power. By the application of an additional 'dissociating' pulse, a stationary mode of laser operation was realised, whereby the pump pulse energy was lowered by a factor of 10 without loss in the output power.

Critical stability conditions in skimmed milk crossflow microfiltration: impact on operating modes

There exists a critical ratio (convection towards the membrane/erosion) in crossflow micro- filtration, MF, below which there is no marked fouling by colloidal particles and above which per- formance are altered: sharp increase of fouling, reduced operating time, large decrease in perme- ability and solute transmission. This paper outlines the impact of the critical ratio on skimmed milk MF processing (separation of casein micelles from the soluble proteins) and gives objective ele- ments (taking into account the critical ratio) for the selection of start-up procedures and stationary modes of operation: controlled transmembrane pressure or permeation flux; static or dynamic counter- pressure, the latter achieved by circulating the permeate co-current to the retentate to maintain an equal transmembrane pressure profile along the filtering path. Results showed that the controlled trans- membrane pressure mode of operation was appropriate for conducting skimmed milk filtration, since it prevented from sharp increase of the hydraulic resistance of fouling and maintained nearly constant performances (permeability, selectivity) over the course of the time. In order to determine the more appropriate counter pressure mode and to predict skimmed milk performances, a four step method was proposed : i) assessment of the critical ratio; ii) selection of the critical flux at the required wall shear stress; iii) determination of the corresponding critical transmembrane pressure in dynamic counter-pressure; iv) calculation of the MF performance in static mode taking into account the gradient of transmembrane pressure induced by the retentate pressure drop. hydrodynamics / crossflow microfiltration / operating mode / critical permeation flux / milk

A nondestructive method for measuring thermal parameters of hermetically sealed electron devices

The nonrestrictive method described is intended for measuring the quantity of heat coming from the surroundings into the working volume of the hermetically sealed device with a thermoelectric cooler. The method is based on the dependence of the thermal emf that appears across the thermopile leads of the thermoelectric cooler in the stationary operation mode on the thermal load on the heat-absorbing surface.

The 900 kN electromagnetic press with superconducting coils

Load-generating facilities based on the interaction of electromagnetic coils are, as a rule, compact and easily controllable. These are, for example, the electromagnetic presses intended for mechanical tests of various materials. A press with superconducting coils allows such testing at cryogenic temperatures. In this case, the operation expenditures decrease sufficiently for the stationary operation mode. To increase the efficiency and reliability of this facility, the load scheme of the coils in repulsion is preferable. In the paper, the optimum dimensions of such a magnet system are determined taking into account strength restrictions. The design peculiarities of the superconducting electromagnetic 900 kN press are considered.

Possibility of stationary and quasistationary modes of operation of an electroluminescence radiator

Using representations of the electrodiffusion mechanism of the degradation of electroluminescence radiators — semiconductor structures, operating in the prebreakdown mode, a model of the processes is constructed which regards electrodiffusion as the migration of charged impurities from one interstice to another. The solution of the system of differential equations obtained indicates the possibility of obtaining a quasistationary mode of operation of the radiator in which the volume part of the crystal is a supplier of a practically constant flow of impurities, which diffuse into the intense-field region and which then drift to the surface of the specimen. This mode of operation corresponds to a considerable slowing down in the aging process — the drop in the brightness of the prebreakdown electroluminescence structure, which may turn out to be useful from the practical point of view.

The design and performance of liquid filled stationary concentrators for use with photovoltaic cells

This paper discusses the design and practical application of dielectric filled stationary concentrators. The design adopted is a 3 × liquid filled lens-V trough concentrator fabricated as a thin walled plastic shell with total internal reflecting sides. The measured performance of both oil and water filled prototypes is in agreement with predicted performance. It is concluded that the dielectric filled LVT concentrator performs as well as the dielectric filled CPC in the stationary mode of operation and has advantages in relation to economy and ease of fabrication.