A Semi-supervised Gaussian Mixture Variational Autoencoder method for few-shot fine-grained fault diagnosis.

In practical engineering, obtaining labeled high-quality fault samples poses challenges. Conventional fault diagnosis methods based on deep learning struggle to discern the underlying causes of mechanical faults from a fine-grained perspective, due to the scarcity of annotated data. To tackle those issue, we propose a novel semi-supervised Gaussian Mixed Variational Autoencoder method, SeGMVAE, aimed at acquiring unsupervised representations that can be transferred across fine-grained fault diagnostic tasks, enabling the identification of previously unseen faults using only the small number of labeled samples. Initially, Gaussian mixtures are introduced as a multimodal prior distribution for the Variational Autoencoder. This distribution is dynamically optimized for each task through an expectation-maximization (EM) algorithm, constructing a latent representation of the bridging task and unlabeled samples. Subsequently, a set variational posterior approach is presented to encode each task sample into the latent space, facilitating meta-learning. Finally, semi-supervised EM integrates the posterior of labeled data by acquiring task-specific parameters for diagnosing unseen faults. Results from two experiments demonstrate that SeGMVAE excels in identifying new fine-grained faults and exhibits outstanding performance in cross-domain fault diagnosis across different machines. Our code is available at https://github.com/zhiqan/SeGMVAE.

Stability and bifurcations of complex vibrations in a nonlinear brush-seal rotor system.

A brush seal has the advantages of adapting to different vibration conditions and increasing the stability of the nonlinear rotor system. In this research, the stability and bifurcations of complex vibrations in a brush-seal rotor system are studied. An analytical seal force model is obtained through the beam theory and mutual coupling dynamics of the bristles and the rotor. The interaction between the bristles and the rotor is clearly depicted by a geometric map. Periodic and chaotic vibrations as well as the corresponding amplitude-frequency characteristics are first predicted by a numerical bifurcation diagram and 3D waterfalls. Discrete dynamic eigenvalue analysis is adopted for a detailed investigation of the stability and bifurcations of nonlinear vibrations. Jumping, quasi-periodic, and half-frequency vibrations are warned during the speeding up and down process. Four separate nonlinear vibration evolving routes are discovered. Two period-doubling bifurcation trees evolving to chaos are illustrated for the observation of global and independent periodic vibrations. Nonlinear vibration illustrations are presented through displacement orbits as well as harmonic amplitudes and phases. Chaotic vibration and unstable semi-analytical vibration solutions are compared. The obtained results and analysis methods provide new perspectives on nonlinear vibrations in the brush-seal rotor system.

Design Approach for Tuning the Hybrid Region of 3D-Printed Heterogeneous Structures: Modulating Mechanics and Energy Absorption Capacity.

The functional hierarchical structures of the triply periodic minimal surface are receiving much attention in tissue engineering applications due to their lightweight and multifunctionality. However, current functionally graded structure design methods are not friendly to heterogeneous structures containing different orientations and different unit types and often face the problems of insufficient connection in the hybrid regions and low local stiffness. In this paper, an improved gradient structure design method was proposed, which solves the problem of insufficient connection between substructures by constructing hybrid region transition functions. Three improved heterogeneous structures were constructed using Primitive and Gyroid lattices and compared with the unimproved heterogeneous structure. Their mechanical properties, deformation mechanism, and energy absorption capacity were examined by finite element analysis and experiments. The results showed that the proposed design method can effectively solve the problems of insufficient connection and poor bearing capacity in the hybrid region between substructures. This method can not only ensure the full connection of the hybrid regions but also flexibly adjust the mechanical properties and energy absorption capacity as well as effectively expand the application range of the energy absorption. Overall, these findings provide valuable guidelines for designing gradient structures with disordered and hybrid features.

Mechanical properties of triply periodic minimal surface (TPMS) scaffolds: considering the influence of spatial angle and surface curvature.

Triply periodic minimal surface (TPMS) has a promising application in the design of bone scaffolds due to its relevance in bone structure. Notably, the mechanical properties of TPMS scaffolds can be affected by many factors, including the spatial angle and surface curvature, which, however, remain to be discovered. This paper illustrates our study on the mechanical properties of tissue scaffolds consisting of TPMS structures (Primitive and I-WP) by considering the influence of spatial angle and surface curvature. Also, the development of a novel model representative of the mechanical properties of scaffolds based on the entropy weight fuzzy comprehensive evaluation method is also presented. For experimental investigation and validation, we employed the selective laser melting technology to manufacture scaffolds with varying structures from AlSi10Mg powder and then performed mechanical testing on the scaffolds. Our results show that for a given porosity, the Gaussian curvature of the stretched TPMS structures is more concentrated and have a higher elastic modulus and fatigue life. At the spatial angle θ = 27°, the shear modulus of the primitive unit reaches its largest value; the shear modulus of the I-WP unit is positively correlated with the spatial angle. Additionally, it is found that the comprehensive mechanical properties of TPMS structures can be significantly improved after changing the surface curvature. Taken together, the identified influence of spatial angle and surface curvature and the developed models of scaffold mechanical properties would be of significant advance and guidance for the design and development of bone scaffolds.

Effect of Surface Curvature on the Mechanical and Mass-Transport Properties of Additively Manufactured Tissue Scaffolds with Minimal Surfaces.

The design of scaffolds for tissue engineering has to consider two trade-off properties: mechanical and mass-transport properties. This is particularly true for additively manufactured scaffolds with the structures of minimal surfaces, and notably, the influence of the surface curvature of the structure on the mechanical and mass-transport properties remains unclear. This work presents our study on the scaffolds designed with the structure of triply periodic minimal surfaces (TPMS), with a focus on discovering the influence of surface curvature on the mechanical response and the mass-transport property or permeability of the scaffolds. Based on the entropy weight fuzzy comprehensive evaluation method, a model representative of both mechanical and permeable properties of scaffolds was developed; scanning electron microscopy (SEM) and finite element analysis (FEA) were also used to reveal the influence mechanism of curvature on structural fracture and deformation behavior. AlSi10Mg samples of scaffolds designed with different surface curvatures were manufactured using selective laser melting (SLM), and their mechanical and permeable properties were examined and characterized by both experiments and simulations. Our results illustrate that at the same porosity, the more concentrated the curvature distribution of the same type of unit, the better trade-off mechanical and mass-transport properties the scaffolds have. Particularly, at the porosity of 55%, the compressive elastic modulus and permeability of the Dte structure are increased by 2.03 times and 1.95 times compared with the Diamond unit, respectively. The fusion structure can greatly improve permeability performance at the cost of mechanical properties. Our results also show that porosity has the greatest influence on mechanical and permeable properties, followed by the surface curvature. The study illustrates that the surface curvature has a significant influence on the mechanical and permeable properties of scaffolds, and that the developed scaffold performance evaluation scheme is an effective means for the optimization and evaluation of scaffold performance.

Effect of unit configurations and parameters on the properties of Ti-6Al-4V unit-stacked scaffolds: A trade-off between mechanical and permeable performance.

Scaffolds in tissue engineering can be created or printed nowadays with various structures that consist of a number of three-dimensional (3D) units stacked together periodically. The performance or properties of such scaffolds can be affected by the unit configurations and parameters, which, however, has not been well investigated and elucidated. This paper presents our study on the influence of unit configuration and parameters on the scaffolds performance by taking triply periodic minimal surfaces (TPMS) as the basic unit. The normalized values of elastic modulus, shear modulus and permeability were used to characterize the scaffold performance and analyzed by means of finite element analysis and CFD simulation, with focus on identifying the influence of unit configurations and parameters on the scaffold mechanical and permeable properties. Furthermore, by selective laser melting (SLM) printing technique, the cubic Primitive and IWP scaffolds with an oversize of 12 mm (2 × 2 × 2 units) were created and subjected to compressive tests. Both simulation and experiment results are in agreement to illustrate that unit configuration and parameters have significant influence on the mechanical and permeable properties of TPMS units. The methods and findings in the present work would serve as the base or rationales to regulate the unit configurations and parameters with trade-off solutions for given tissue engineering application.