Search

The application of non-stationary Lamb wave signals is a promising tool in various industrial applications where information about changes inside a structure is required. Phase velocity is one of the Lamb wave parameters that can be used for inhomogeneities detection. The possibility of reconstructing the segment of the phase velocity in a strong dispersion range using only two signals is proposed. The theoretical study is performed using signals of the A0 mode propagating in an aluminium plate at a frequency of 150 kHz, 300 kHz, 500 kHz and 900 kHz. The experiment was carried out at a value of 300 kHz. The studies conducted indicated that the maximum distance between two signals, at which the time-of-flight can be measured between the same phase points, is the main parameter for the two signals technique application. Theoretical and experimental studies were performed, and the mean relative error was calculated by comparing the obtained results with those calculated via the SAFE method. In the theoretical study, the mean relative error of 0.33% was obtained at 150 kHz, 0.22% at 300 kHz, 0.23% at 500 kHz and 0.11% at 900 kHz. The calculated mean relative errors δcph=0.91% and δcph=1.36% were obtained at different distances in the experimental study. The results obtained show that the estimation of the phase velocity in dispersion ranges using only two received signals was a useful tool that saved time and effort.

The identification of the main steps for the creation of a unified ecosystem from the institutional point of view and the framework for ecosystem design is presented and discussed. Based on the expertise and the knowledge gained during the time when the ELISE project had been implemented, a unified Kaunas city ecosystem is being designed using the Ecosystem Map method. As the review of the ELISE project reports helped to identify the main steps of each project partner in building ecosystems’ networks, Kaunas city chose to create a co-Creation Hub (c-CH), which is the first step in developing an ecosystem management model. The main tasks of such a hub are listed, and should involve the preparation of a long-term action plan involving not only the coordination of the stakeholder meetings, organisation of seminars, the preparation of new materials, and methodology but also the development of a clear strategy for each stakeholder based on national economy and government and municipality policies. The role of the c-CH is to ensure the ease of cooperation and knowledge distribution among stakeholders within the city, public authorities, and the national government. This approach could become a fundamental background tool for the regional and/or city municipal and stakeholder-based creation and development of unified ecosystem development.

The Lamb waves are named one of the promising solutions for future wind turbine blade (WTB) failure prevention. The compliance with safety assurance of WTBs by detecting structural changes during the manufacture and performing their monitoring during the service life are effective tools for environmental sustainability. This work presents the basic characteristics of Lamb waves and highlights two main unusual limitations—the dispersion and an infinite number of modes—as a great challenge that complicates the application of such waves. This requires the investigation and development of new signal processing methods (SPMs) for conducting accuracy assessments according to the requirements of ISO 17025. The general principles for the accuracy assessment of the signal processing methods applied to evaluate the dispersion of Lamb waves are presented here, and a suitable procedure for estimation of errors and uncertainties is proposed. These should facilitate the verification analysis of any signal processing method used for the dispersion evaluation of Lamb waves. This information allows determining parameters that define the measurement reliability and facilitates the application and utilisation of the proposed methods and their choice. Moreover, it is a necessary prerequisite for setting reliable testing, inspecting, and monitoring standards for WTBs certification.