Journal of Mechanical Engineering, Automation and Control Systems
Not a member yet
1200 research outputs found
Sort by
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
Self-synchronisation of vibration exciters of a biharmonic vibration drive
Get PDFThe paper considers the practical possibility of self-synchronisation of two biharmonic unbalanced vibration exciters mounted on a solid body with plane oscillations. The problem is solved by the method of direct separation of motions. The equations for slow processes of establishing synchronous modes of rotation of the exciters are obtained; expressions for vibration torque; the vibration coupling coefficient and the condition for the existence of an synphase mode of motion. It is shown that the latter condition is relatively “soft”. An expression for the vibration torque is obtained for the case of “stuck” velocity of a biharmonic exciter in the resonance zone of a vibration machine. Recommendations for selecting the parameters of the vibration drive are given. The analytical conclusions are confirmed by computer modelling
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
Numerical study on sloshing in coaxial shells
Get PDFSloshing in coaxial shells partially filled with liquid is investigated using reduced boundary element method. Conical shells are considered as storage tanks. An ideal and incompressible fluid is assumed in the shells. The spectral boundary problem for the liquid vibrations in rigid shells is solved. The results demonstrate the high accuracy of the presented approach
Prestressed modal and fatigue characteristic analysis of pedal machine support
Get PDFTo ensure the reliability and stability of the pedal machine support under prolonged operational conditions, prestressed modal analysis and fatigue characteristic analysis were conducted using the finite element method. A coupling module integrating intensity and mode was constructed and imported into Workbench via intermediate data files to facilitate grid division, material property definition, and load application. Through simulation and calculation, the first four natural frequencies and modes of the model were determined, aligning with vibration response test results. The stress field analysis showed that the maximum stress experienced by the model was 93 MPa, meeting static strength requirements. Furthermore, fatigue life and safety factor of the support frame were assessed under fatigue analysis conditions. The conclusions indicate that the structure exhibits robust safety characteristics in compliance with fatigue load requirements
Simulation analysis of helicopter rotor blade based on fluid-structure coupling
Get PDFSince the helicopters are required to fulfil many different attitudes during actual flight and are exposed to low amplitude and high number of cycles of vibration loads for a long period of time, the stresses on its rotor structure will be more complicated, which will lead to the rotor blades being subjected to larger stresses and causing fatigue damage. This paper proposes a combination of fluid-solid coupling and nCode fatigue simulation of helicopter rotor blade structure to study the stress distribution, danger point and fatigue life of rotor blades in hovering and forward flight state, so as to provide a reference basis for the judgement of helicopter rotor blade fatigue damage and the enhancement of safety performance. The results show that the maximum stress of the helicopter in the forward flight state is larger than that in the hovering state, and the maximum stress of the rotor blade in the forward flight state of the helicopter is located at the root of the blade as 166.89 MPa; and the fatigue life in the two states is obtained by the joint simulation method of Workbench-nCode, and the fatigue life in the forward flight state is reduced by 0.726 % compared with that in the hovering state. Therefore, the combined method of fluid-solid coupling and nCode fatigue simulation proposed in this paper can provide an effective research method for the design and optimisation process of helicopter rotor blades
Stability analysis of civil air defense tunnel under blasting vibration
No full textBased on a large section drilling and blasting excavation project, the dynamic response characteristics of civil air defense tunnels are analyzed by combining field monitoring and numerical simulation. The dynamic response features include particle vibration velocity, main frequency, displacement, and stress, and the stability criterion of the tunnel is analyzed. A safety criterion model based on the ultimate tensile strength of materials is established. The results show that the frequency of the X, Y, and Z directions is mainly distributed in 90-140 Hz. The effective stress increases first and then decreases along the axis of the roadway. The stress near the explosion source is large and the relative reduction is also large. By fitting the relationship between blasting vibration velocity and maximum principal stress, the safe vibration velocity criterion based on tensile strength is obtained, and the safe threshold of vibration velocity is 19.62 cm/s. It can be assumed that blasting does not affect the structure
A one-dimensional high-order dynamic model for twin-cell box girders with deformable cross-section
No full textA one-dimensional high-order dynamic model for single-box twin-cell box girders is presented together with the pattern recognition algorithm. The model takes into account the deformable cross-section and can accurately predict its 3D dynamic behaviors. The cross-section deformation is captured by basis functions satisfying displacement continuity condition, which is essential to construct the initial model formulation based on the Hamilton principle. The axial variation patterns of generalized coordinates are decoupled by solving the eigenvalue problem. On this basis, the combinations of basis functions are obtained to bring out cross-section deformation. The cross-section deformation, hierarchically organized and physically meaningful, are used to update the basis functions in the reconstructed high-order model. Numerical analysis has verified the accuracy and applicability of the reconstructed one-dimensional high-order model
Research on citrus segmentation algorithm based on complex environment
Get PDFAiming to address the low efficiency of current deep learning algorithms for segmenting citrus in complex environments, this paper proposes a study on citrus segmentation algorithms based on a multi-scale attention mechanism. The DeepLab V3+ network model was utilized as the primary framework and enhanced to suit the characteristics of the citrus dataset. In this paper, we will introduce a more sophisticated multi-scale attention mechanism to enhance the neural network’s capacity to perceive information at different scales, thus improving the model’s performance in handling complex scenes and multi-scale objects. The DeepLab V3+ network addresses the challenges of low segmentation accuracy and inadequate refinement of segmentation edges when segmenting citrus in complex scenes, and the experimental results demonstrate that the improved algorithm in this paper achieves 96.8 % in the performance index of MioU and 98.4 % in the performance index of MPA, which improves the segmentation effectiveness to a significant degree
Numerical modelling of the warping behaviour at the first layer-build plate interface in 3D-printed models produced via the fused deposition modelling process
Get PDFThe material structure of 3D-models printed via the fused deposition modelling (FDM) technique is mainly affected in the z-direction of the 3D-print as a result of the layer-by-layer approach which tend to exhibit a deformation behavior corresponding to a type of transversely orthotropic material. Moreover, uncontrolled parameters such as printing temperature and printing speed have been reported to adversely affect 3D-print quality leading to undesired effects such as distortion and warpage. The additive manufacturing process is a relatively new field in advanced manufacturing where further research and innovation are required to overcome the limited strength and structural performance observed in presently 3D-printed components. In line with the above, this study proposes the numerical investigation of the warping behavior in PLA (Polylactic acid) - based 3D printed models by considering the finite element method (FEM) software of LS-DYNA. The warping investigation was specifically centered on the cooling cycle prevailing between the layer-by-layer structures. The findings of this study showed that warpage would most likely occur in the thermal process model corresponding to abrupt change in temperature due to a buildup of strain between the bottom most layers of the 3D model and the build plate. The findings of this study, which shed light on the warping behaviour in 3D-models, has direct implications on the final quality of 3D-printed components