A Method to Minimize the Effort for Damper–Blade Matching Demonstrated on Two Blade Sizes

A method called PCR (Platform Centered Reduction) is designed to more effectively perform complex iterative and nonlinear calculations required for the dynamic response of turbine blades damped by dry friction contacts between rigid dampers and airfoil-to-neck platform. The key feature of PCR is to represent all nonlinear forces on the blade platform by means of only six degrees of freedom at a point located within the platform volume, regardless of the number of damper–platform contact elements. Despite reducing the effort and computational time by more than one order of magnitude, the method proves to be fully accurate by a check against the corresponding nonlinear Finite Elements (FE) calculation. It is also shown that the limit exciting force, indicating the upper capability to dampen vibrations, can be calculated with a simple linear modal analysis. In order to search for the best blade–damper match, the preferred graph represents relevant bending stresses on the airfoil against excitation forces. A detailed application of the method concerns two significantly different blade sizes, by varying parameters such as neck length and damper centrifugal force. Finally, it is emphasized that a final check by a complete FE analysis is still possible as a purely linear solution fed by sets of contact forces previously determined through the PCR at any desired frequency and excitation.

Numerical investigation of setup effects in the vertical holding capacity of finless torpedo anchors

This article presents a numerical-based study on the vertical holding capacity of a typical finless torpedo anchor embedded in a pure cohesive isotropic sol considering setup effects. A strategy based on two axisymmetric nonlinear finite elements (FE) models is proposed. In these models, the soil is represented with continuous solid elements with both plane translational and pore pressure degrees of freedom, which allow the modeling of the soil's strength regain after the installation of the anchor, i. e., the soil setup. The anchor is also modeled with solid elements, and its interaction with the soil is addressed with contact elements. Several analyses are conducted to evaluate setup effects, and, additionally, a parametric study on different soil undrained shear strengths and permeability coefficients is performed. The results obtained show that the permeability of the soil and its undrained shear strength have an important role in the setup process, and an inverse relationship between consolidation time and the permeability coefficient of the soil is observed. Finally, an analytical approach is calibrated with a reasonable agreement to the numerical results

Determination of destructive forces in a rod-cable arch

The aim of research - comparison the results of the experimental data with the computer modeling the work of the strengthened brick-cable arch. Methods. Experimental and theoretical methods of research. Results. Firstly, the tests on a small desktop models were performed, for the determination the nature of destruction of the construction. During them, it was discovered, that the arch crash is taking place because of the splitting the small size timber bricks, or as the result of the breaking its steel strengthening elements. Further, the computer model of the construction was created with the help of physically and geometrically nonlinear finite elements at LIRA-SAPR PC. The generated model was load by a concentrated force at its top zone, the same one, as it had been during the experiments before. On the results of the calculation, the maximum deformation was received, which are different from the experimental one on a value less then 10%, what suggests the nearness the computer model to the real construction. The highest compressive strengths of the arch and the largest stretching forces of its steel bands were determined during the further analysis of the model. Maximum splitting and stretching forces also were calculated theoretically, according to the formulas of SP 64.13330.2017 and SP 20.13330.2016. It was determined that the timber bricks have more than 7 times reserve of strength, and the steel bands over them - only times, and during the growth of external force, the arch will crash because of its steel sprengel bands breakage. By the results of the research, the calculation algorithm of such kind constructions was generated, at the base of LIRA-SAPR PC. It was recommended first, to determine deformation of the strengthened brick-cable arch, with further checking the timber elements for splitting and steel sprengel elements for maximum permissible stretching. The problem of stability the flat form of deformation for the brickcable arch are the same as for the glued one, because of the tight connection the timber bricks, with elimination their exit from the frontal plane.

An Empirical Formula for Predicting Elastic Ultimate Buckling Strength of Flat-Bar Stiffened Panels With Initial Imperfections

Elastic ultimate buckling strength is an important strength design criteria to estimate the safety margin of stiffened panels subjected to axial compressive load. Based on a series of Nonlinear finite elements analysis, an empirical formula is proposed to elastic ultimate buckling strength of stiffened panels with flat-bar stiffener in this study. The elastic ultimate buckling strength is defined as that in the loading process, a certain average compressive stress of stiffened panels when the Vonmises stress of structures firstly reach the yield stress. The range of geometrical sizes for numerical samples is discussed in order to ensure the applicability of presented empirical formula. The extent of models and initial imperfection, namely initial geometrical deformation are also taken into account. Ultimately, it is shown that there are a good agreement between the results of Non-linear finite element method and the proposed empirical formula.