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Vol. 103

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2021-06-12 PIER M Vol. 103, 15-26, 2021. doi:10.2528/PIERM21040905

The Analytical Formula for Calculating the Self-Inductance for the Circular Coil of the Rectangular Cross-Section with a Non-Uniform Current Density

Slobodan Babic, Matthew Smith, Nikiforos Fokas, Yuriy Langer, and Jerry P. Selvaggi

In this article we give an analytical formula for calculating the self-inductance for circular coils of rectangular cross-section which has a non-uniform current density. Recently, the formula for calculating this important electromagnetic quantity was published in the form of the single integral whose kernel function was asum of elementary functions. However, a new formula is obtained in the form of elementary functions, single integrals, and the complete elliptic integral of the first, second and third kind. Although its development looks tedious, we obtain a rather user-friendly expression for the calculation. From the general case, the self-inductance of the thin disk coil (pancake coil) with the nonuniform current is obtained in a remarkably simple form. The results of this work are compared with different known methods, and all results are in the excellent agreement. Our approach has not been found in the literature.

2021-06-09 PIER M Vol. 103, 1-13, 2021. doi:10.2528/PIERM21040902

Prestress Monitoring of Internal Steel Strands Using the Magnetoelastic Inductance Method

Lei Liu, Senhua Zhang, Jianting Zhou, Hong Zhang, Huiling Liu, Kui Tan, and Leng Liao

Monitoring the prestress of prestressed steel strands is important but difficult. The magnetoelastic inductance (MI) method is used to monitor the prestress. A coupling model was established to describe the correlation among stress, magnetism, and inductance. A prestress monitoring system based on the MI effect was proposed. To verify the feasibility of the method, experiments were carried out. The results showed that influenced by the hydration heat of the grouting materials, the fluctuation range of the inductance was 1.033%. When the hydration came to an end, the inductance approached the initial inductance. For internal steel strands, the obtained inductance-prestress relationship was similar to the relationship of external steel strands. Thus, the prestress of the internal steel strands could be monitored by the MI method.