Axial Compressive Behavior of Square Ice Filled Steel Tubular Stub Columns

Concrete has many limitations in the building construction in cold areas. However, there is abundant ice in those regions. Therefore, using ice as a substitute for concrete has been explored by researchers. Inspired by the idea of square concrete filled steel tube (CFT), a new column form termed square ice filled steel tubular (IFT) column is proposed in this study. It consists of a square outer steel tube with the inner space filled with ice. A total of eighteen stub columns were made and tested under axial compression, including three circular plain ice specimens, nine square IFT specimens and six hollow square steel tubes, to demonstrate the advantages of the composite column. The width-to-thickness (B/t) ratio of the steel tubes varies from 39.5 to 77. The test results confirmed that the ice core is effectively confined by the steel tube, and the inward local buckling of the steel tube is suppressed by the inner ice, leading to higher strength and better ductility of the square IFT specimens compared with hollow steel tubes and plain ice columns. A simplified axial bearing capacity equation for square IFT stub columns is proposed and it provides reasonable and accurate predictions of the test results

Behavior and Modeling of Circular Large Rupture Strain FRP-Confined Ice under Axial Compression

The application of concrete is severely limited in construction in cold areas. However, the local ice has functioned as a potential substitute for concrete for a long time. In order to make efficient use of ice to overcome its weaknesses of low strength and poor ductility, an innovative type of ice-filled large rupture strain (LRS) fiber-reinforced polymer (FRP) tube column was developed. The system consists of external LRS FRP tubes filled with plain ice or sawdust-reinforced ice. This paper presents an experimental investigation into the axial compressive behavior of such composite stub columns with circular sections. The test results confirmed that the axial compressive behavior of the ice cores was greatly improved because of the LRS FRP confinement, as well as the addition of sawdust in ice. The axial stress–strain curves of the LRS FRP-confined ice exhibited monotonically ascending bilinear shapes. Both the compressive strength and the ultimate axial strain of the confined ice were significantly enhanced with an increase of the thickness of the LRS FRP tube. A theoretical model for the LRS FRP-confined ice is proposed, in which the dilation properties (i.e., lateral strain–axial strain relation), as well as the entire axial stress–strain responses of the inner ice cores, are explicitly modeled with reasonable accuracy

Zero-voltage-switching buck converter with low-voltage stress using coupled inductor

This study presents a new zero-voltage-switching (ZVS) buck converter. The proposed converter utilises a coupled inductor to implement the output filter inductor as well as the auxiliary inductor which is commonly employed to realise ZVS for switches. Additional magnetic core for the auxiliary inductor in traditional ZVS converters is eliminated and hence reduced cost is achieved. Moreover, thanks to the series connection between the input and output, the switch voltage stress in the steady state is reduced and thus the ZVS operation can be easier achieved. Then the leakage inductor current circulating in the auxiliary switch is decreased, contributing to reduced conduction losses. In particular, low-voltage rating devices with low on-state resistance can be adopted to further improve efficiency in applications with non-zero output voltage all the time, such as the battery charger. Furthermore, the reverse-recovery problem of the diode is significantly alleviated by the leakage inductor of coupled inductor. In the study, operation principle and steady-state analysis of the proposed converter are presented in detail. Meanwhile, design considerations are given to obtain circuit parameters. Finally, simulations and experiments on a 200 W prototype circuit validate the advantages and effectiveness of the proposed converter

Fault-Tolerant Converter with a Modular Structure for HVDC Power Transmitting Applications

For the high-voltage direct-current (HVDC) power transmission system of offshore wind power, dc/dc converters are the potential solution to collect the power generated by off-shore wind farms to HVDC terminals. The converters operate with high-voltage gain, high efficiency, and fault tolerance over a wide range of operating conditions. In this paper, an isolated ultrahigh step-up dc/dc converter with a scalable modular structure is proposed for HVDC offshore wind power collection. A flyback-forward converter is employed as the power cell to form the expandable electrically isolated modular dc/dc converter. The duty ratio and phase-shift angle control are also developed for the proposed converter. Fault-tolerant characteristics of the converter are illustrated through the redundancy operation and fault-ride-through tests. Redundancy operation is designed to maintain high operation efficiency of the converters and fault-ride-through operation improves the converter reliability under harsh operating conditions. Analytical studies are carried out, and a 750-W prototype with three modular cells is built and experimentally tested to verify the performance of the proposed modular dc/dc converter

Porous Organic Polymers: An Emerged Platform for Photocatalytic Water Splitting

Porous organic polymers (POPs), known for its high surface area and abundant porosity, can be easily designed and constructed at the molecular level. The POPs offer confined molecular spaces for the interplay of photons, excitons, electrons and holes, therefore featuring great potential in catalysis. In this review, a brief summary on the recent development of some current state-of-the-art POPs for photocatalytic water splitting and their design principles and synthetic strategies as well as relationship between structure and photocatalytic hydrogen or oxygen evolution performance are presented. Future prospects including research directions are also proposed, which may provide insights for developing POPs for photocatalytic water splitting with our expectations

Multiple Open-Circuit Fault Detection and Isolation Using Universal Low-Cost Diagnosis Circuits for Reconfigurable Dual-Active-Bridge Converters

Compared with single-switch open-circuit faults (SOCFs), multiple switches open-circuit faults (MOCFs) of power electronic devices (PEDs) due to high voltage or current stress, false triggering, and manufacturing tolerance have become more challenging. To address this issue, a reconfigurable dual-active-bridge (R-DAB) converter is presented with a fast, accurate, robust, and low-cost fault detection (FD) and fault isolation (FI) scheme to accommodate both SOCFs and MOCFs. Compared with the standard dual active bridge (DAB) topology, the proposed R-DAB will utilize a center-tapped high-frequency transformer and two symmetrical auxiliary inductors, where inherent half-bridge conduction branches are capable of maintaining uninterrupted operations. The proposed FD and FI scheme is straightforward and universal since only the center-tap current in the primary and secondary bridge is monitored as the universal fault signature. Moreover, a simple and low-cost fault diagnostic circuit was designed, which can detect and isolate various open circuit faults (OCFs) of PEDs under varying input and output conditions, without using expensive voltage and current sensors. This sensorless fault diagnosis technique can achieve the fastest fault detection and isolation speed reported so far, which is within a couple of \boldmath $\mu s$ for various OCFs. Experimental results were acquired from an R-DAB prototype under various OCFs to validate the effectiveness of the proposed technique

Automated cattle counting using Mask R-CNN in quadcopter vision system

The accurate and reliable counting of animals in quadcopter acquired imagery is one of the most promising but challenging tasks in intelligent livestock management in the future. In this paper we demonstrate the application of the cutting-edge instance segmentation framework, Mask R-CNN, in the context of cattle counting in different situations such as extensive production pastures and also in intensive housing such as feedlots. The optimal IoU threshold (0.5) and the full-appearance detection for the algorithm in this study are verified through performance evaluation. Experimental results in this research show the framework's potential to perform reliably in offline quadcopter vision systems with an accuracy of 94% in counting cattle on pastures and 92% in feedlots. Compared with the existing typical competing algorithms, Mask R-CNN outperforms both in the counting accuracy and average precision especially on the datasets with occlusion and overlapping. Our research shows promising steps towards the incorporation of artificial intelligence using quadcopters for enhanced management of animals