Meccanica最新文献

A multiscale topology optimization model of anisotropic multilayer periodic structures (MPS) is proposed using the isogeometric analysis (IGA) method. The integrative design of multiscale structures was realized in two stages: the distribution optimization of multilayer periodic materials, which determines the types, distribution, and volume fraction of microstructures, and parallel topology optimization, which optimizes the macrostructure and various microstructures simultaneously. To implement the multilayer periodic constraint, the relative density and sensitivity of the IGA control points were equally redistributed. The correctness and advantages of the proposed model were confirmed by comparing its results with those obtained using finite element methods, and the optimal IGA microstructures displayed smoother boundaries. In addition, the multiscale MPS of the cantilever was 3D printed, confirming the practicality of the proposed model. The influences of the regularization scheme, multilayer periodic constraints, and Poisson's ratio factor on the results of the multiscale multilayer periodic optimization were explored, and recommendations for proper values of these parameters were provided to enhance the structural stiffness.

Controlling a cable-driven parallel robot (CDPR) when a cable breaks is challenging. In this paper, a sliding mode adaptive PID control is designed to ensure a safe guidance of the load when a cable fails. Indeed, regardless when a cable breaks, this control makes it possible enchanting the guidance of the load inside the remaining wrench feasible workspace. In other words, it allows reducing the load oscillation and then increasing the safety of the recovery manoeuvre. Performances are evaluated through simulations by considering a spatial CDPR and comparing the results with a PID control.

To investigate the effect of gradient direction on mechanical properties and energy absorption capability of Gyroid lattice structures (GLSs), network-based and sheet-based lattice structures (G1-N768, G2-N768, G1-S768, G2-S768) of different gradient directions with an average porosity of 70% were established. The Al-Si10-Mg samples were manufactured through selective laser melting (SLM). Through compression tests and finite element analysis (FEA), the energy absorption, deformation behavior, and mechanical properties of the GLSs were evaluated. The data exhibited good consistency, and the deviations of yield strength, elastic modulus, plateau stress, densification strain and energy absorption could be controlled at about 10%. The results indicated that whether it is network-based or sheet-based GLSs, by changing the gradient direction, the deformation behavior could be transformed from layer-by-layer deformation (G1-GLSs) to uniform deformation (G2-GLSs), and thus realize the regulation of mechanical properties. At the same time, due to different topological configurations, stretch-dominated sheet-based GLSs (G1-S768, G2-S768) exhibited higher energy absorption capability and mechanical properties than bending-dominated network-based GLSs (G1-N768, G2-N768), and the energy absorption, yield strength and elastic modulus increased by 93.7%, 80.8% and 66.7%, respectively. In addition, the introduction of the Johnson–Cook model has effectively simulated the failure behavior of GLSs. This paper can offer theoretical guidance for the subsequent performance regulation and application of functionally graded GLSs.

Muscle injuries are the most common sports injuries in eccentric contraction. There are many factors that could influence the severity of muscle injuries, including strain, strain rate and stimulation. This study evaluated the interaction of these factors on the biomechanical properties of the muscle–tendon bundle and their role in injuries. A Hopkinson bar system, an MTS machine and an electrical pulse generator were utilized to collect eccentric contraction response data of over 150 frog muscle–tendon samples at strain rates ranging from 0.01 to 300 s⁻¹. The results have shown that the maximum eccentric stress has increased and peaked at the strain rate of about 150 s⁻¹. That peak value has then maintained at the following strain rates. In contrast, Young’s modulus reduced as the strain rate changed from 50 to 300 s⁻¹. That trend was in contrast to unstimulated muscle bundles. In addition, strain rate has significantly influenced stimulated tendon–muscle bundle fracture. Samples tend to rupture at a minor strain of about 3.5% with strain rates over 200 s⁻¹. Because of the increasing stiffness of the muscle area at high strain rates, increased strain in the tendon region resulted in frequent injuries in the tendon area. On the other hand, a maximum stress reduction was detected when the muscle bundles were stimulated at muscle strain greater than 0.2. The results showed that improper timing of stimulation could increase muscle injury. The study shows that the stimulation and strain rate dramatically impact muscle–tendon properties and the risk of injury.

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.