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This article focuses on improving the control structure of electronic capacitor (EC), formed by a bidirectional dc–dc converter terminated with small auxiliary capacitance. Typical application of such a system is mimicking the dynamic behavior of a bulk dc-ink capacitor while actually employing a component with much lower capacitance value. It was previously revealed that EC may be treated as output-voltage regulated wide-input-range converter feeding a bidirectional power load. Dual-loop voltage-current linear cascaded regulator, typically employed for EC terminal voltage control, imposes slow unstable mode when absorbing power from the dc-link. This article demonstrates that performing a transformation from voltage–current to power-energy domain by feedback linearization-based nonlinear control simultaneously eliminates the unstable mode and increases control bandwidth. Revealed findings are well-supported by simulations and experiments.

We consider modeling wellbore acoustic fields induced by the flow noise in the zone of the formation inflow. The influence of the reservoir’s properties, geometry, and phase composition of the fluid on the acoustic field in the wellbore is investigated. Using numerical modeling, we showed that these factors significantly influence the spatial-frequency pattern of the spectrum, and certain frequencies of the spectrum are strongly amplified. We present the modelling results for various examples of reservoirs with oil and gas wells.

Active capacitance reduction circuits (ACRCs) are dc–dc converters, terminated by a small auxiliary capacitor, typically utilized to replace bulk electrolytic capacitors in dual-stage grid-connected power conversion systems. Electronic capacitors are ACRCs supporting “plug-and-play” operation in addition to the ability to emulate virtually any finite capacitance at dc-link connected terminals. Despite excellent steady-state functionality, all ACRCs possess the poor response to steplike no-load-to-full-load (and vice versa) transients due to the fact that the auxiliary capacitor utilized (and thus corresponding energy stored) is much smaller than the bulk dc-link capacitor being replaced. Nevertheless, in grid-feeding applications where fuel cells of photovoltaic generators act as a power source, the rate of generated power change is limited. This is also true regarding some off-grid systems such as LED lighting with dimming, where sudden load changes are unnecessary and electronic capacitors seem to be directly applicable in such systems. Therefore, this paper reveals the limits of steplike and ramplike load variations, tolerable by a system equipped with an electronic capacitor, based on its power rating and auxiliary capacitance value utilized. Examples are given for typical systems with 400-V dc link, connected to 50-Hz mains. The validity of presented findings is well-supported by simulations and experiments.

A novel method for controlling direct voltage regulated active dc-link capacitance reduction circuits (ACRC) is proposed in this paper. Instead of forcing the dc-link voltage of the power conversion system to follow a constant reference, the ACRC imposes dc-bus voltage in proportion to the integral of its input current. Consequently, it resembles an adjustable value capacitor from the dc-link side. Therefore, as opposed to existing control strategies, the proposed method simultaneously allows the dc-link voltage to reflect the power balance of the system and the pulsating power component to be diverted into significantly reduced auxiliary capacitance via a bidirectional dc–dc converter. As a result, replacing bulk dc-link capacitance by the proposed circuitry does not require any modification of existing grid-connected power conversion system controllers, thus allowing plug-and-play operation. The proposed approach is validated by application to a commercial power factor correction front end by both simulations and experiments.

The first results of the multidisciplinary expedition onboard research vessel Akademik Nikolaj Strakhov in the Barents Sea in August-September 2018 are given. On 41 stations the hydrophysical sounding was carried out, sampling of the bottom sediments was done using both grab and gravity corer. As a result of geophysical investigations the areas with the signs of modern dangerous natural processes were identified. Four seismic bottom stations were installed in the Pechora Sea.

Рассматривается задача моделирования акустических полей, индуцированных течением флюидов в околоскважинной зоне пласта. Проведено исследование влияния свойств пород-коллекторов, геометрии и фазового состава флюида на акустическое поле в скважине. С помощью численного моделирования показано, что эти факторы существенно влияют на пространственно-частотную картину спектра, и выявлено значительное усиление амплитуды на определенных частотах спектра. Представлены результаты моделирования для различных случаев резервуаров с нефтяными и газовыми скважинами.

The paper presents a simplified algorithm for fast modeling of many typical finite element models using visual programming tools. Authors provide recommendations for creating a parametric finite element model in the Dynamo Sandbox and Autodesk Robot Structural Analysis software. This method was used to find the most geometry rational and lightweight steel structure for given initial conditions of architectural requirements. On the example of one-story industrial steel frame building a detailed work of the algorithm was described to select the lightest structure of all calculated options. As a result of the study, addiction was derived for the total weight of the structure and single frame from count of frames and its spacing. A dependency graph of the full structure weight to the number of frames was derived and conclusions were made about the optimal spacing of the frames and number of frames in the steel structure for the given initial conditions.

We present an approach of passive acoustic logging data interpretation to estimate wellbore fluid holdup variation along the wellbore due to the fluid inflow. The algorithm uses machine learning methods for the analysis of acoustic fields generated, in particular, by flow noise in the reservoir near wellbore zone. The method is designed using acoustic fields generated by numerical simulations. The study of simulation results shows the significant influence of wellbore resonances on acoustic field spectrograms and on intensity distributions along the wellbore. The interpretation results demonstrate that the suggested machine learning model predicts water holdup in a zone after the water inflow with high accuracy. The predictions of water holdup before the water inflow interval are less accurate because resonance characteristics are less sensitive to them. We also studied the influence of passive acoustic logging data distortion by contaminating noise on the model learning and on prediction accuracy for the developed interpretation algorithm. As expected, the estimation of water holdup before the water inflow interval is more sensitive to signal interference. The novelty of the suggested approach to passive acoustic logging data interpretation is in using resonance structures of the acoustic noise spatial frequency characteristics to locate the inflow interval and to estimate the oil and water volume fractions. The resonances contain a clear fingerprint of the fluid holdup variation in wellbore fluid, as shown by our study, and the corresponding information can be interpreted by the machine learning algorithms.

This Letter proposes a simple realisation of a circuit (referred to as electronic capacitor) capable of emulating large capacitance of controllable value while utilising a much smaller capacitor and a DC–DC converter. The circuit may be used in a plug-and-play fashion instead of any real large capacitor within the control bandwidth. The proposed control algorithm forces the terminal voltage of the DC–DC converter to follow the well-known capacitance equation by sensing the terminal current and simultaneously compensates conversion losses by an auxiliary control loop. The proposed algorithm is successfully verified by emulating bulk DC-link capacitance of a commercial power factor correction front end.