Meccanica最新文献

This study investigates the effect of radial hydraulic forces on low-specific-speed centrifugal pump bearings and assesses the effectiveness of the double-volute balancing technique in mitigating these forces. Numerical simulations were conducted on centrifugal pumps with both single- and double-volute designs. Experimental validation confirmed the numerical findings, establishing the technique's efficacy. Additionally, while size limitations often restrict the use of double-volutes in small pumps, their potential benefits and encouragement for further exploration are discussed for these applications, highlighting the significance of the double-volute arrangement in designing and operating high-pressure radial-flow centrifugal pumps. The simulations demonstrated a notable decrease in the radial hydraulic forces with the implementation of the double-volute configuration. Consequently, adopting a double-volute centrifugal pump design resulted in a substantial reduction in the impeller-induced forces and forces exerted on the bearings, leading to an approximate 45% decrease in the hydraulic radial forces. This result explains the significant reduction in impeller-induced and bearing forces.

This paper presents a linear version of the reduced multibody system transfer matrix method, specifically designed for the exact analysis of free vibrations in hybrid models composed of Timoshenko beams, rigid bodies, and springs. The method is flexible, designed to handle various boundary conditions and any combination of beams, rigid bodies, and springs. We treat each beam segment and spring-supported rigid body as independent elements. Thus, viewing the overall model as a chain system simplifies the analysis. The essence of this method is the recursive transfer of mechanical information between elements, which is contained in the reduced transfer equations. The reduced transfer equations for the spring-supported rigid bodies and Timoshenko beams are derived in detail. The accuracy, high precision, and higher-order modal analysis capabilities of this method are validated through numerical examples. Furthermore, the improvement of the numerical stability by the segmentation strategy is analyzed, and the orthogonality between the augmented eigenvectors is proved mathematically and numerically. The concise, structured and highly programmable greatly simplifies the process of handling complex hybrid systems containing any number of Timoshenko beams and rigid bodies.

This paper presents a numerical implementation of phase field models in structures subjected to tensile stress in both quasi-static and dynamic fracture cases. It focuses on the AT1 model and the phase field regularized cohesive zone model (PF-CZM) to compare their performance. Within these models, we focus on implementing the irreversibility condition using the penalization method rather than (Miehe et al. in Comput Methods Appl Mech Eng 199(45–48):2765–2778, 2010. https://doi.org/10.1016/j.cma.2010.04.011)’s “History field” method. Moreover, we employed a staggered algorithmic implementation due to its proven robustness. Numerical simulations were conducted using the multi-physic finite element code, COMSOL Multiphysics. The geometries analyzed include a notched and un-notched confined beam under stretching load and a ring under internal pressure. The originality of this work is presented in two parts. The first part consists in the implementation of the penalization technique within COMSOL Multiphysics. Then we investigated the effects of parameters like cohesive softening laws, notch depth and shape, mesh sensitivity, and length scale sensitivity on the confined beam responses. The second part of this manuscript consists in studying the dynamic fragmentation of a ring under internal pressure. A new solution is proposed to capture crack nucleation and propagation without randomizing material parameters.

Morrow’s model has been widely used in recent years as part of new methodologies for assessing the fatigue life of metallic materials through the laws of thermodynamics. It is used to quantify the rate of dissipated energy in the fatigue process, represented by the hysteresis loop of the stress–strain diagram of the material. Then, the dissipated energy is used to quantify the entropy generation of the fatigue process. Morrow’s model is a function of the amplitude of the cyclic loading, and a few constants that represent material properties. However, despite its apparent simplicity, the material properties, when are experimentally obtained, usually exhibit dispersions that can lead to inaccurate calculations. In this work, the sensitivity of Morrow’s model to the variability of these parameters is evaluated. In order to assess the sensitivity, a constant amplitude value was set, and the quotient ({{sigma }_f^{'}}/{{sigma }_U}), the fatigue strength coefficient (sigma_f^{'}), the fatigue ductility coefficient ({ epsilon_f^{'}}) and the cyclic strain hardening exponent (n^{'}) were varied. A factorial design was conducted to determine the effects of the interactions of the material parameters on the response of Morrow’s model. The results showed that Morrow’s model is strongly sensitive to the above mentioned parameters, affecting its accuracy. In an extended case study, the fatigue fracture entropy and the fatigue life of Al2024-T3 were determined using material parameters from different sources in order to determine the influence of the material parameters in the assessment of the estimation of fatigue damage. The study allowed concluding that a meticulous statistical treatment is required when characterizing the material properties and the design engineer must be aware of possible inaccuracies if Morrow’s model is used for estimating fatigue life, specially in the new thermodynamic approaches.

Large amplitude vibration of transmission line seriously affects the structural safety. Due to the low bending stiffness of superhigh transmission tower, vortex-induced excitation combining with support motion induced by the tower will cause significant complex dynamic behaviors of the transmission line. To reveal dynamic behaviors, this paper newly proposes a suspended cable model of the transmission line subjected to the boundary motion and vortex-induced vibration. Dynamic mechanism and vibration energy transfer are focused in the condition of primary and subharmonic resonances. Innovative behaviors of the transmission line under two excitations are revealed. Firstly, vortex-induced excitation is very weak and support motion usually plays a dominate role in the dynamic responses. Large amplitude vibration of transmission line observed in practice should be caused more by tower tip motion and the vortex-induced vibration is the incentive. Secondly, different weak support motion can cause different effect on dynamic responses of transmission line under vortex-induced vibration reflecting by different lock-in phenomenon, which leads us the application of active control measure in engineering.

This study aims to numerically investigate the impact of entrance velocity distributions on wall shear stress in a simplified curved vessel model. The flow in a single-curved vessel is simulated with Reynolds numbers adjusted to a Newtonian blood-analog fluid in an external iliac artery (EIA) model. Simulations are conducted assuming a rigid wall and a steady-state flow regime using OpenFOAM®. Eight entry velocity conditions are implemented, including the effects of flow development, asymmetry, Dean-type secondary flow and rotation. Their influences on hemodynamics features are investigated, focusing on axial wall shear stress (WSS). In the examined configurations of EIA flow, the impact of entrance conditions on WSS distribution is moderate. The maximum WSS is consistently located at the bend exit on the outer wall, except in the case mimicking an upstream curved pipe in the opposite direction of the local curvature. While the entry condition affects the maximum WSS value, this value remains within the same order of magnitude. At (Re=560), the highest WSS value is given by the Poiseuille condition and reaches 4.9 times the value of the laminar straight flow. At (Re=1100), the maximum value provided by the Dean-type condition, particularly in the case mimicking an upstream curved pipe perpendicular to the local curvature, reaching 7.1 times the laminar straight flow, which exceeds the value of the Poiseuille condition by 17%. The results suggest that, to capture extreme WSS value, opting for Poiseuille flow as the entrance condition is a good choice for further studies on EIA flow. It has to be noted that results presented here tend to confirm the link established between exaggerated WSS and the endofibrosic plaque development.