Crack Identification of Curved-Elements Using Wavelet Packet

Wavelet Transform (WT) and Wavelet Packet Transform (WPT) approaches have shown great promise in the field of signal analysis in recent decades. The main merit of these methods is their capability in localization of each signal in distinct time or space interval. However, the frequency resolution of such transformation is relatively poor in high frequency regions. The WPT, which is an extended form of the WT, provides a complete level-by-level signal decomposition. Therefore, a frequency analysis creates an arbitrary time. In this study, dynamic transient analysis is performed employing a finite element software (ANSYS) on a beam and acceleration time history of various points is investigated. Then, the captured signals are decomposed to the wavelet packet components using MATLAB and energy rate index is calculated for each component utilizing a wavelet packet rate index (WPERI). The results indicate that not only are the obtained index values sensitive, but they also are precise for the crack identification.

Radial stresses at the metal-coating interface of ship composite elements

В работе выполнена сравнительная оценка радиальных напряжений на границе раздела слоев металла и полимерного покрытия судовых композиционных элементов. Поле напряжений создается при изготовлении судовых композиционных элементов с большой кривизной рабочих поверхностей. Учтено влияние на адгезионную прочность действия факторов внешней среды. При эксплуатации морских судов характерно влияние на композиционные элементы воздуха, морской воды, нефтепродуктов. Проведены экспериментальные исследования композиционных криволинейных элементов с радиусом кривизны 300 мм. Подтверждена корректность предложенной расчетной зависимости. Показано, что основной причиной появления радиальных напряжений в композиционных элементах является различие коэффициентов Пуассона и линейного расширения материалов. Результаты проведенного исследования можно использовать для расчета радиальных напряжений на границе раздела слоев в зависимости от характеристик прочности судовых композиционных элементов. In this paper, a comparative assessment of radial stresses at the interface between metal layers and polymer coating of ship composite elements is performed. The stress field is created in the manufacture of ship composite elements with a large curvature of the working surfaces. The influence of environmental factors on the adhesive strength is taken into account. When operating marine vessels, the influence of air, sea water, and petroleum products on the composite elements is characteristic. Experimental studies of composite curved elements with a radius of curvature 300 mm were conducted. The correctness of the proposed calculation relationship was confirmed. It is shown that the main reason for the appearance of radial stresses in composite elements is the difference between the Poisson coefficients and the linear expansion of materials. The results of this research can be used to calculate radial stresses at the interface of layers depending on the strength characteristics of ship composite elements.

Numerical Study of a Customized Transtibial Prosthesis Based on an Analytical Design under a Flex-Foot® Variflex® Architecture

This work addresses the design, analysis, and validation of a transtibial custom prosthesis. The methodology consists of the usage of videometry to analyze angular relationships between joints, moments, and reaction forces in the human gait cycle. The customized geometric model of the proposed prosthesis was defined by considering healthy feet for the initial design. The prosthesis model was developed by considering the Flex-Foot® Variflex® architecture on a design basis. By means of the analytical method, the size and material of the final model were calculated. The behavior of the prosthesis was evaluated analytically by a curved elements analysis and the Castigliano theorem, and numerically by the Finite Element Method (FEM). The outcome shows the differences between the analytical and numerical methods for the final prosthesis design, with an error rate no greater than 6.5%.

An Innovative Construction Technique for Curved Structures

The masonry building Heritage is appreciated for its aesthetic and historical value all around the world. The widespread presence of curved elements, such as arch, vault and dome express the relevant constructive abilities in the different historical epochs. These curved elements are characterized by architectural beauty, structural strength (especially against the gravity loads), thermal comfort and fire resistance. On the other hand, curved structures required scaffolding in order to be erected. The design, the construction and the dismantling of the scaffolds is typically time-consuming and expensive. In addition, the on-site working risk is related to time-interferences (e.g. in manpower working, at the same time, over and under scaffold). This technology dates back to the Era of the Roman Empire and it is currently still used, despite its limitations and disadvantages. In the present paper, an innovative technique (recently patented), aiming for the construction of a curved structural member without scaffolds, is proposed and illustrated. It consists in a Hinged Lifting Arch (HLA), using FRP (Fiber Reinforced Polymer) bonded strips. In details, a series of blocks are cut following an arch geometry and then aligned on the ground-floor in order to bond a composite on their top surface. Moreover, the impregnation of the polymeric adhesive is not allowed at the extremities of each block. The fiber sheet is applied continuously along the entire extrados. In this sense, hinges are introduced, in fact, the FRP-connected blocks are able to easily rotate, in the opposite direction, around the contact ends (i.e. hinge). Finally, the middle block is lifted-up and the arch takes the desiderated shape. In the first experimental demonstration, the natural calcareous stone was used, even if the proposed technique is totally material-independent. Moreover, an analytical model is proposed and discussed for designing the proper aspect ratio of the blocks in order to ensure the full mutual contact when the HLA is totally lifted up. The advantages of the proposed technique are related to the absence of scaffolds and improved seismic strength against horizontal loads thanks to the presence of the FRP, which limits the occurrence of hinges at the extrados.

An Analysis of Stiffness Matrices of Tube Elements to Assess the Correctness of Modeling Curved Elements of Pipeline Systems

Large-scale work to create a Russian engineering analysis system involves the implementation of a considerable number of specialized tasks, each of which requires an individual approach and specific solutions. The calculation of pipeline systems that can most easily be performed in the version using rods is no exception. Such an approach is the most effective in terms of increasing the speed of calculations, increasing the dimension of the tasks performed, and most importantly, in simplifying the modeling procedure. In this paper, the authors consider the option of determining the stiffness matrices of a spatial element for modeling of pipes, which underlie the full engineering analysis of pipeline systems. Verification examples that confirm the reliability and correctness of the obtained solutions are presented.

Experimental study of flexural-torsional deformations and stability of curved elements of steel arches with l-shaped cross-section

The method and results of experimental studies of flexural and torsional displacements, as well as the stability of curved elements of steel arches with I-shaped cross-section are presented.The author presents graphs of the dependence of flexural-torsional movements on the load for three different loading schemes obtained during the experiment. The limit loads on the core elements of the arches were obtained. The results of the experiment were compared with the theoretical study.