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Titanium alloy is widely used in aerospace and other fields due to its low density, high specific strength, corrosion resistance, and other advantages. With the development of selective laser melting additive manufacturing technology, it is possible to manufacture triply periodic minimal surface porous structures. The effects of structural parameters on the mechanical properties of a Ti-6Al-4V Diamond (D)-type triply periodic minimal surface structure are studied. According to the characteristics of porous structures, the Gibson Ashby fitting formulas of D structures are modified using the concept of equivalent cross-sectional areas. The influence of cell size and surface thickness on the compressive modulus and strength of a D structure is discussed. Prediction formulas of the mechanical properties based on cell size and surface thickness are established by combining the relative density with the structural parameters. On this basis, the density optimization method is applied to the lightweight design of a rocket-related assembly based on D structure filling. The design results verify the feasibility of a lightweight design based on triply periodic minimal surface structure filling. [ABSTRACT FROM AUTHOR]

Featured Application: Voltage Regulation in Distribution Systems. Due to fluctuating characteristics of loads, dynamic reactive power optimization over a certain time period is essential to provide effective strategies to maintain the security and economic operation of distribution systems. In operation, reactive power compensation devices cannot be adjusted too frequently due to their lifetime constraints. Thus, in this paper, an online reactive power optimization strategy based on the segmentation of multiple predicted load curves is proposed to address this issue, aiming to minimize network losses and at the same time to minimize reactive power-compensation device adjustment times. Based on forecasted time series of loads, the strategy first segments each load curve into several sections by means of thresholding a filtered signal, and then optimizes reactive power dispatch based on average load in each section. Through case studies using a modified IEEE 34-bus system and field measurement of loads, the merits of the proposed strategy is verified in terms of both optimization performance and computational efficiency compared with state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Norton equivalent circuit is a commonly used model in estimating harmonic current emissions of harmonic sources. It however cannot reflect the mutual coupling relationships among voltage and current in different harmonic orders. This paper proposes a new method to identify parameters in a coupled harmonic admittance model. The proposed method is conducted using voltage and current measurements and is based on least square estimation technique. The effectiveness of the method is verified through time-domain simulations for a grid-connected converter and also through field data obtained from a ±800 kV converter station. The experimental results showed that the proposed method presents higher accuracy in terms of harmonic current emission estimation compared with three Norton-base methods. [ABSTRACT FROM AUTHOR]

An electrical thermal storage (ETS) device for space heating is designed in this study. The proposed device is charged by the off-peak electricity and releases its thermal energy to warm the space all day long. The natural convection occurring in the flow channel drives the flowing of air to be heated up and warm the space. The dynamic process of a fully charging/discharging cycle of the device is tested. Meanwhile, a three-dimensional model is developed to simulate the transient thermal behavior. It is found that the experimental and numerical results agree with each other which indicates the validation of the proposed numerical model. The results show that the temperatures of the bricks and the outlet air can be as high as 1002 K and 835 K, respectively. The natural convection occurring in the flow channel transfers 40.4% of the total electrical heating energy to the space for the charging process and 26.9% for the discharging process. Heat losses to the space through the adiabatic material shares 13.3% of the total heating energy for the charging process and 7.2% for the discharging process. Based on those findings, three methods are recommended to improve the device in the successive research. [ABSTRACT FROM AUTHOR]

A piezoelectric bimorph beam, as an upgraded cantilever beam structure, can be used to detect gas content and build a micro-actuator, among other functions. Thus, this beam is widely applied to microelectromechanical systems (MEMS), transformers, and precision machinery. For example, when photoacoustic spectroscopy is performed to detect oil-soluble gas in transformers, a micro-cantilever beam can be used to detect gas content. The dynamic characteristics of piezoelectric bimorph beams, such as resonant frequency, are important indexes in the applications of these beams. The equivalent circuit model for a piezoelectric bimorph beam is examined in this study and an admittance test is performed on the beam to accurately, quickly, and economically measure and analyze its dynamic characteristics. Then, the least squares method is applied to obtain the characteristic curves of the admittance circle, amplitude frequency, and phase frequency; identify the dynamic characteristics of the piezoelectric bimorph beam (e.g., resonant frequency); and determine the parameters of the equivalent circuit. The resonant frequency of the piezoelectric bimorph beam is 207.67 Hz based on the result of the admittance circle test, which is basically consistent with the results of microscope image method (i.e., 207.85 Hz) and the theoretical calculation (i.e., 222.03 Hz). This finding proves the validity of the proposed test method. This method cannot only improve the detection speed of piezoelectric bimorph beams, but can also provide a fast detection strategy for testing the characteristics of such beams during photoacoustic spectroscopy., Competing Interests: The authors declare no conflict of interest.