Maintenance, Reliability and Condition Monitoring
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Bifurcation and chaos analysis of the floating raft vibration isolation system with quasi-zero-stiffness isolators
Get PDFThis paper presents an investigation into the nonlinear dynamic behaviors of the floating raft isolation system coupled with quasi-zero-stiffness isolators subject to multiple disturbance sources. First, the coupling effects between the excitation source and isolation system are considered. Also, the floating raft isolation model under multiple excitations and its motion equation are deduced, and then the dynamic responses are mainly investigated by using the techniques of time history diagram, spectrum diagram, phase diagram and Poincaré map, and the bifurcation diagram. Finally, the bifurcations of the mechanical isolation system with different parameters are analyzed through numerical methods, especially the effect of center distance and mass ratio. The result predicts that the floating raft shows an alternate phenomenon of periodic motion, quasi-periodic motion, and chaotic motion when the center distance and mass ratio vary. The motion state of the floating raft vibration isolation system is more sensitive to the mass ratio than to the center distance. The horizontal and rotational response of the system becomes very intense in the chaotic state, and the response amplitudes in the horizontal and vertical directions reach the same order of magnitude. Above all, the dynamic characteristics can provide the theoretic supporting for the dynamics, vibration control and its parametric optimization of the floating raft isolation system coupled with quasi-zero-stiffness isolators. This study will lay down the requirements for the engineering design and application of floating raft isolation equipment in large vessel
Simulation analysis of coupling mechanism between transient flow field characteristics of bubble collapse and metal deformation based on surface micromorphology
Get PDFIn the process of modifying titanium alloy oral implants using cavitation water jet, the collapse of bubbles releases significant energy. This phenomenon is accompanied by micro-jets and shock waves, which induce changes in the three-dimensional microscopic morphology of the implant surface. The loose and porous surface of the implant will increase the adhesion area of the cells, which is more conducive to the combination of the oral implant with the surrounding bone tissue. In order to explore the coupling mechanism between the instantaneous energy of bubble collapse and the surface deformation of titanium metal, based on different flow field and solid field model parameters, the numerical analysis software Ansys and the fluid-structure coupling simulation method are used to establish the numerical simulation model of single bubble collapse on the near curved wall. In order to explore the coupling mechanism between the instantaneous energy of bubble collapse and the surface deformation of titanium metal, the bubble growth process is ignored. Based on different flow field and solid field model parameters, this paper adopts the numerical analysis software Ansys and the fluid-structure coupling simulation method to establish the numerical simulation model of single bubble collapse on the near curved wall. The effects of flow field parameters and wall morphology on the transient flow field of bubble collapse and the effect of metal surface modification are revealed. The results show that when the initial bubble diameter is 180 μm, the instantaneous collapse high pressure reaches 7.24 GPa, and the maximum stress on the titanium surface is 689 MPa, which is 1.57 times higher than that under the bubble diameter of 60 μm. When the bubble collapses away from the wall, due to the weakened constraint of the wall, more intense energy is released, but the energy decays rapidly in the propagation process, and the energy loss when it reaches the wall is more serious. In this paper, the surface micromorphology is simplified into a near-curved shape. After the modification, the flow obstruction on the near-curved concave wall inhibits bubble collapse, resulting in an increase in bubble collapse time. The stress and deformation caused by a single bubble collapse are concentrated within a radius of 1mm and a depth of 5 μm
Denoising for ECG signals based on VMD and RLS
Get PDFElectrocardiogram (ECG) signals often encounter various types of noise interference, which annihilates their waveform characteristics and exhibits strong instability. To facilitate clinical diagnosis and analysis, it is necessary to perform denoising processing in advance. A denoising method for ECG signals based on variational mode decomposition (VMD) and recursive least square (RLS) has been proposed. VMD was used for the modal decomposition of noisy ECG signals, and the recursive least square (RLS) algorithm was used for adaptive filtering of various intrinsic mode functions (IMFs) components. The problem construction, solution, and decomposition characteristics of VMD were analyzed. The IMFs filtered by RLS were reconstructed. This achieved the elimination of interference noise in the ECG signal. The Sym8 wavelet basis, LMS, NLMS, RLS, and VMD-RLS denoising method were compared by using ECG signals including Gaussian white noise, baseband drift, electrode motion, electromyographic interference, and electrical interference noise. The experimental results showed that the VMD-RLS denoising method has significantly better denoising performance than the other four methods, achieving better values in the quantitative evaluation indicators. This algorithm improved convergence speed and signal estimation accuracy, and it has good effectiveness, superiority, and practicality. Therefore, the VMD-RLS denoising method can enable doctors and researchers to analyze and diagnose ECG signals of heart diseases more accurately
A cost model analysis in the process of refining petroleum using supplementary variable technique
Get PDFThis paper presents a cost model analysis for refining petroleum using an MX/G(a , b)/1.MX/G(a , b)/1 queuing system with two stages of heterogeneous services under steady-state conditions. The study derives the total average cost per unit time for two distinct service phases: Phase I and Phase II. In the first case, the analysis focuses on the total average cost of the system when the server operates in Phase I with a probability of π1 at any given time, and in Phase II with a probability of π2. Additionally, the model incorporates holding costs, operating costs, renovation costs for both phases, and closure time costs. Finally, numerical tables and graphical representations are provided to illustrate the observations regarding the total average cost, renovation rate, and arrival rate
Object localization of channel robot using laser triangulation
Get PDFTrajectory tracking and Object Localization in robots are developing rapidly, but the tasks are becoming increasingly complex and significantly increasing the range of tasks for robotic systems. Cognitive tasks in domestic, industrial or traffic conditions require not only the recognition of objects but also their evaluation by classifying them without direct recognition. One of such spheres are tunnels that are physically difficult for humans to reach and require diagnostics. In such an environment, it is difficult to globally define the direction and goal, so it is necessary to interpret the locally obtained information. To solve such a problem, sensor fusion is widely applied, but sensors of different physical natures do not allow to obtain the necessary information directly, so there is a great need to use AI to interpret and control the received information and generate the robot's trajectory [1]. Local navigation systems require a wide range of sensors [4]. Various cameras and time-of-flight LiDAR lasers are widely used. For the aforementioned reasons, an economical local trajectory generation and tracking system is being developed, one of the most important components for object recognition is the laser triangulation method. The essence of this method is that the camera reacts to the projection of the laser light in front of it and interprets the obstacle depending on its distortion. In this way, the camera's resources are more concentrated, and at the same time, a simple RGB camera is enough for this method. Also, this method is perfect in the dark, when the laser light is more pronounced. In this paper, the laser triangulation method will be reviewed in detail, evaluating its advantages and disadvantages
Identification and characteristic statistics of surface microstructure of titanium metal based on cavitation water jet
Get PDFThe application of cavitation water jet technology to modify medical implant surfaces facilitates the formation of distinctive microporous structures, thereby enhancing the contact area between the implant and alveolar bone, and improving osseointegration. Therefore, the microstructure characteristics of the modified implant are one of the important evaluation indicators of the modification effect. This paper proposes a processing method for the identification and statistical analysis of surface micro-morphology images. The method incorporates techniques such as image enhancement, image segmentation, morphological image processing methods, and pixel matrix operations, enabling automated quantification of pit counts, the relative positions of the pits, and other topographic characteristics of the material surface. Simultaneously, the microstructure of each pit is spatially fitted and reconstructed to standardize measurement benchmarks for pit diameter and depth characteristics. This facilitates in-depth multi-dimensional analysis of material surface characteristic information and provides foundational support for further exploration of cavitation jet modification technology. In the study, the modification effect of processing time on the surface morphology of titanium metal was used as an application case. A surface morphology feature information database was established under different processing times, and statistical analysis was conducted on proportion, structural distribution, and other characteristics in the focus areas. The results show that the diameter and proportion distribution of the pits produced by cavitation jet modification tend to be stable when the jet pressure and standoff distance remain constant, while the depth of the pit increases with the increasing processing time
Bending of a piecewise homogeneous plate with a circular interfacial materials separation zone and radial crack considering the strip contact of its edges
Get PDFThe work presents a solution to the bending problem of an infinite piecewise homogeneous isotropic plate with an elastic circular washer and a radial through straight crack. It was assumed that under the action of an external loads at infinity, the edges of the crack are smoothly contacted on area of constant width (strip contact) on the upper base of the plate. The solution of the problem is built using the methods of the theory of functions of a complex variable and complex potentials and is reduced to a system of singular integral equations, which is numerically solved using the method of mechanical quadrature A numerical analysis of the problem is conducted and graphic dependencies of contact force, coefficients of intensity of moments and forces at various parameters of the problem were constructed
Analysis and experimental research on the reliability of the connection between large-diameter bridge piles and caps
Get PDFThis article investigated the construction conditions of the pile foundation in the Wuxing section of the “Shanghai Suzhou Huzhou” railway bridge project. To test the reliability of large diameter connectors, it has established a finite element model with ABAQUS software for numerical simulation. Based on on-site tests, the reliability of the connection between the pipe pile and the cover steel was studied. According to the simulation results, when the load is P= 900 kN, the displacements of A2 and A3 steel pipe piles are 55.8 mm and 60.1 mm, respectively. The load-displacement relationship shows a high-order curve distribution. According to the results of on-site experiments, the displacements are 77.9 mm and 60.2 mm, respectively. The load-displacement relationship is linear. The results for the simulation and on-site testing are consistent. This study provides a basis to the research on the reliability of the connection between large-diameter steel pipe piles
Lightweight small target detection based on aerial remote sensing images
Get PDFWith the upgrading of aviation space technology, the amount of information contained in remote sensing images in the aviation is gradually increasing, and the detection technology based on small targets has developed. For lightweight small targets, pixels per unit area contain more information than large targets, and their area is too small, which is easily overlooked by conventional detection models. To enhance the attention of such algorithms, this study first introduces a Control Bus Attention Mechanism (CBAM) in the fifth generation You Only Look Once (YOLOv5) algorithm to increase the algorithm’s attention to small targets and generate optimization algorithms. Then convolutional neural network is used to mark feature pixels of the optimization algorithm, eliminate redundant information, and generate fusion algorithm, which is used to generate redundant information with high similarity when the optimization algorithm surveys pixel blocks. The novelty of this study lies in using CBAM to improve YOLOv5 algorithm. CBAM module can extract important features from images by adaptively learning the channel and spatial attention of feature maps. By weighting the channel and spatial attention of the feature map, the network can pay more attention to important features and suppress irrelevant background information. This attention mechanism can help the network better capture the characteristics of small targets and improve the accuracy and robustness of detection. Embedding CBAM module into YOLOv5 detection network can enhance the network's perception of small targets. CBAM module can improve the expressive ability and feature extraction ability of the network without increasing the complexity of the network. By introducing CBAM module, YOLOv5 can better capture the characteristics of small targets in aerial remote sensing images, and improve the detection accuracy and recall rate. Finally, the proposed fusion algorithm is used for experiments on the Tiny-Person dataset and compared with the fifth, sixth, and seventh generations of You Only Look Once. When the fusion algorithm tests the target, the classification accuracy of Sea-person is 39 %, the classification accuracy of Earth-person is 31 %, and the probability of being predicted as the background is 56 % and 67 %, respectively. And the overall accuracy of this algorithm is 0.987, which is the best among the four algorithms. The experimental results show that the fusion algorithm proposed in the study has precise positioning for lightweight small targets and can achieve good application results in aerial remote sensing images
Open-source hand prosthesis: evaluation of mechanical feasibility and additive manufacturing potential
Get PDFThis study delves into the risks associated with 3D-printed hand prostheses lacking mechanical feasibility studies. Such unvalidated prostheses may exhibit various issues like durability shortcomings, anatomical incompatibility, functional safety concerns, manufacturing quality deficiencies, and health risks due to inappropriate materials. These issues can lead to damage or premature failure during use, discomfort, skin irritation, injuries, inability to withstand functional loads, and health hazards from toxic or allergenic substances. Therefore, ensuring the safety, quality, and effectiveness of these prostheses is crucial. The study focuses on a mechanical feasibility study conducted through Finite Element Analysis (FEA) simulations on an open-source hand prosthesis model. It evaluates mechanical properties, stress concentration areas, and displacement on the prosthesis surface. The methodology comprises three key steps: acquiring the virtual model, conducting computational simulations, and selecting the 3D printing material. The simulations assess the prosthesis’s ability to withstand compressive forces and identify stress concentration areas. Results from the study indicate that using PETG as the constituent material demonstrates mechanical viability and satisfactory performance under static force conditions. This finding underscores the importance of rigorous testing and adherence to standards in developing 3D-printed hand prostheses. Such studies contribute significantly to enhancing these devices’ safety and effectiveness, facilitating their broader adoption in healthcare settings. In summary, this study highlights the critical need for mechanical feasibility studies in the development of 3D-printed hand prostheses. It emphasizes the significance of following strict standards and regulations to ensure these devices’ safety, quality, and functionality. By doing so, it paves the way for the widespread use of these prostheses in healthcare, benefiting users and advancing the field of prosthetic technology