It is important to obtain accurate dynamic vibrations of steam turbine blades for safe operation. Strain gauge (SG) measurements cannot fully obtain vibrations of all blades and nodal diameter (ND) details. The blade tip timing (BTT) technique could resolve this problem because it has the advantage of measuring all blades’ vibrations. This article proposed an improved BTT technique for measuring synchronous vibrations of shrouded blades in a steam turbine based on fiber optical sensors with lenses. The newly developed sensor was equipped with a Plano-convex lens, and the optical path was specifically designed to collimate the beam within a large working distance from 4 to 19 mm and improve the measuring accuracy. A method to search the spectra of all peak vibration amplitudes of all the blades was proposed to obtain the ND details of synchronous vibration. Experimental results validated the efficiency and accuracy of the proposed methods and sensors. Comparison results of BTT measurements with SG measurements showed that the relative errors of normalized frequency and strain were small and acceptable.
Rising protectionism and globalization have led to new interest in new regionalism. The facilitation and liberalization of two-way direct investment between China and Pan-East Asian countries result in increasing exports between these countries. By studying the relationship between China’s investment and export trade in Northeast Asian and Southeast Asian countries, this paper explores the influence mechanism of China’s two-way foreign direct investment and export trade with Pan-East Asian countries. The study discovers that with the improvement of the bilateral economic development level, China’s Outward Foreign Direct Investment (OFDI) to Northeast Asia and Southeast Asian countries will significantly increase the scale of China’s export trade. Yet, the total value of the export creation effect decreases over time. China’s utilization of Inward Foreign Direct Investment (IFDI) has a significant inhibitory effect on export trade. The two-way interaction effect of China’s OFDI and IFDI is weak. As the level of IFDI in China increases, the effect of OFDI on exports increases—though this effect differs across regions and countries.
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