Effective swimming strategies in low Reynolds number flows

The optimal strategy for a microscopic swimmer to migrate across a linear shear flow is discussed. The two cases, in which the swimmer is located at large distance, and in the proximity of a solid wall, are taken into account. It is shown that migration can be achieved by means of a combination of sailing through the flow and swimming, where the swimming strokes are induced by the external flow without need of internal energy sources or external drives. The structural dynamics required for the swimmer to move in the desired direction is discussed and two simple models, based respectively on the presence of an elastic structure, and on an orientation dependent friction, to control the deformations induced by the external flow, are analyzed. In all cases, the deformation sequence is a generalization of the tank-treading motion regimes observed in vesicles in shear flows. Analytic expressions for the migration velocity as a function of the deformation pattern and amplitude are provided. The effects of thermal fluctuations on propulsion have been discussed and the possibility that noise be exploited to overcome the limitations imposed on the microswimmer by the scallop theorem have been discussed.Comment: 14 pages, 5 figure

Diagnosing Disk-Space Variation in Distribution Power Transformer Windings Using Group Method of Data Handling Artificial Neural Networks

Monitoring centers in the smart grid exchange the collected data by sensors and smart meters to monitor the current conditions and performance of electric power components. Distribution Power Transformers (DPTs) have a key role in maintaining the integrity of power flow in the smart grid. Online monitoring of DPTs to detect possible faults can potentially increase the reliability of modern power systems. Mechanical defects of DPTs are the major issues in their proper operation that must be detected in their early stage of occurrence. One of the most effective solutions for diagnosing mechanical defects in DPTs is Frequency Response Analysis (FRA). In this study, an appropriate condition monitoring scheme for DPTs is developed to identify even minor winding defects. Disk-Space Variation (DSV), a common DPT windings fault, is applied to the 20 kV-winding of a 1.6 MVA DPT in various locations and with different severity. Their corresponding frequency responses are then computed, and all four components of the frequency responses, i.e., amplitude, argument, and real and imaginary parts, are evaluated. Different data-driven-based indices are implemented to extract appropriate feature vectors in the preprocessing stage. Group Method of Data Handling (GMDH) Artificial Neural Networks is proposed to assist monitoring centers in interpreting FRA signatures and identifying DPT defects at primary stages. GMDH has a data-dependent structure, which gives high flexibility to modeling nonlinear characteristics of FRA test results with different data sizes. It is demonstrated that the proposed approach is capable of accurately determining the fault location and fault severity. The proposed Artificial Intelligence (AI)-based approach is used to extract essential features from frequency response traces in order to detect the position and degree of Disk-Space Variation (DSV) in the DPT windings. The experimental results verify the effectiveness of the proposed methods in determining the severity and location of DSV defects

A New High Voltage Gain Active Switched-Inductor Based High Step-Up DC–DC Converter With Coupled-Inductor

This paper propounds a new high step-up DC-DC topology based on the active switched-inductor (A-SL) technique, which utilizes a coupled inductor (CI) for performance enhancement. Among the features of the presented topology are the following: (a) Better voltage gain (VG) and efficiency, (b) Since there are low voltages across power switches, it is possible to reduce the amount of power that is lost as a result of using MOSFETs with a low voltage rating and reduced internal resistance, (c) By reducing the turn ratio of the CI, the VG is enhanced, (d) Through the series connection of a capacitor with the CI primary winding, zero DC bias is achieved, and the core saturation problem is solved, (e) Input current division between input inductors and switches, (f) There is no limitation on duty cycle ( 0< D< 1 ), and (g) Simple switching patterns and simultaneously driven switches. The propounded converter&#x2019;s operation principle and steady-state analysis are explained in detail, and parasitic elements&#x2019; effects on VG and efficiency are examined. In addition, the VG, the number of components, and the voltage tension on power switches, diodes, and capacitors are compared and analyzed. An experimental laboratory prototype with 30V input and 400V output voltage is used to verify the validity of the study and the performance of the propounded topology