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Analysis and synthesis of a controllable crank-slider mechanism with parallel springs for frame saws
Get PDFFrame saws suffer from large unbalanced inertia forces, limiting operating speed and requiring heavy construction. This study aims to overcome these limitations by synthesizing a dynamically balanced main drive mechanism using a novel approach based on prescribed motion laws. The methodology involves proposing a crank-slider mechanism featuring a cam-actuated variable-length crank. The mechanism configuration with parallel spring is analyzed allowing for balancing inertia forces, achieved using a prescribed cosine slider motion law. For the considered configuration, the required variable crank length function (cam profile) and associated mechanism parameters (connecting rod length, spring stiffness) are analytically synthesized. The results of the carried-out numerical modeling demonstrate successful synthesis of a near-circular cam profile and very low pressure angles for the case studied. These findings show that synthesizing the saw drive kinematics based on force balancing requirements can theoretically eliminate inertial loads, offering the potential for higher speeds of saw frames and reduced loads. The synthesized near-circular cam profile suggests a pathway towards simpler manufacturing. The implications of successfully implementing such dynamically balanced frame saw mechanisms are potentially transformative for the sawmilling industry. Eliminating the primary inertial forces removes the major obstacle to increasing operating speeds. This could allow frame saws to operate closer to the optimal cutting speeds for wood (e.g., 40-50 m/s), leading to significant gains in productivity
Research on friction characteristics of drill string in whole well section of gas drilling based on finite element method
Get PDFDuring gas drilling, the drill string friction is directly related to the safety of drilling and tripping. When the drill string reaches the horizontal section, the friction problem is prominent, which greatly increases the risk and difficulty of trajectory control in the horizontal section. The purpose of this paper is to study the frictional characteristics between drill string and wellbore wall. Firstly, the dynamic mathematical model of drill string in gas drilling is established, a new boundary conditions between wellhead and bottom hole is proposed. Secondly, the governing equation of drill string system is established by using Lagrange equation. Thirdly, the improved Generalized-α method is used to solve the dynamic equation of drill string system. Finally, the effects of weight on bit (WOB) and rotational speed on friction torque of drill string system are analyzed, as well as the effects of different borehole curvature and friction coefficient on friction characteristics of drill string. The findings indicate that as the WOB and rotational speed increase, the lateral motion range and friction torque of the drill string gradually rise; With an increase of borehole curvature and friction coefficient, the friction resistance of the drill string increases obviously. Additionally, it is observed that the average friction resistance of the drill string is greater in horizontal sections compared to vertical and deflecting sections. The average lifting friction on the drill string is less than the lowering friction. Theoretical research plays a crucial role in guiding the optimization of drilling parameters and the implementation of friction reduction
Influence of the supporting surface inclination angle on the locomotion conditions of a vibration-driven system
Get PDFThis paper investigates the influence of supporting surface inclination angle on the locomotion of a capsule-type robot driven by an imbalanced rotor, considering dry anisotropic friction. Using Lagrange’s second-order differential equations, a mathematical model is developed, and numerical simulations are performed with Wolfram Mathematica software. The scientific novelty lies in the comprehensive analysis of how inclination angle, coupled with anisotropic friction, affects the capsule’s motion, including the derivation of analytical conditions for maintaining a “non-detachable” motion regime and preventing backward slippage. Key results include the establishment of relationships for the maximum permissible angular velocity of the imbalanced rotor as a function of surface inclination angle and friction coefficient. It is found that this velocity is maximal on horizontal surfaces and decreases with increasing inclination, while higher backward friction coefficients allow for greater rotor speeds. The practical value of these findings is significant for the design and control of vibration-driven robots, particularly for applications such as pipeline inspection, monitoring, and cleaning, where reliable navigation across varied inclinations is crucial
Analysis and optimization of dynamic characteristics of the supporting frame structure of small fishing boat
Get PDFThe dynamic characteristics of the support frame structure are critical factors influencing the safety and stability of small fishing boat. A prestressed modal analysis model of the support frame was established using the finite element method to evaluate stress, deformation, natural frequency, and modal shapes under maximum bending load conditions. To validate the accuracy of the simulated natural frequencies, the support frame was freely suspended using wide elastic ropes, and a hammering test method was employed, achieving a maximum error of less than 7.5 %. Based on a multi-objective optimization approach, optimal designs with varying thicknesses were developed to minimize stress peaks and maximize natural frequencies without increasing mass. Combining the results from strength and modal analyses, structural improvements such as adding local reinforcing ribs were proposed. Modal simulations confirmed that the optimized design can effectively mitigate low-frequency vibrations and enhance structural reliability
Study of the aerodynamics of a full-scale tractor-trailer
Get PDFThe wind tunnel campaign evaluated 10 configurations of a tractor-trailer combination using a Volvo VNL860 tractor and the 30 ft NRC trailer. The test results include balance measurements of drag force, side force, and yawing moment. The baseline tractor-trailer combination had a blockage-corrected drag coefficient of 0.457 at 0° yaw and a wind-averaged drag coefficient of 0.527. The combined removal of the side extenders, their extensions, and the roof air deflector (in Configurations 6 and 7) resulted in the largest increase in drag (6 % relative to baseline) of all of the aerodynamic packages that were evaluated. The smallest change in drag coefficient resulted from the removal of the tractor skirt extensions (aerodynamic package 4), but it should be noted that the tractor skirt extensions were only evaluated at 0 yaw and would have more of an effect at higher yaw angles. The purpose of this paper is to study the drag coefficient of the entire Tractor through wind tunnel experiments. At present, there are few tests on the resistance coefficient of Tractors, and there are also few published papers on this topic. By removing Aerodynamic packages, this helps to understand the impact of different Aerodynamic packages on the overall drag coefficient of the vehicle
The importance of using geosynthetic materials in ensuring anti-erosion stability of railway embankments
Get PDFRailway embankments are key elements of transport infrastructure whose stability depends on soil, hydrogeological, and climatic factors. Wind and rainfall erosion threaten slope integrity, causing soil loss and potential landslides. This study integrates field experiments and modeling to assess erosion mechanisms and the effectiveness of geosynthetic geomats for slope protection. Tests on the Bukhara-Miskin railway section determined wind and rainfall thresholds for soil displacement and evaluated geomat performance by slope stability, vegetation density, and runoff resistance. Reinforced slopes showed almost no soil washout, with vegetation density of 4000-5500 kg/ha – over 200 % higher than traditional seeding. Geomat use reduced erosion by up to 80 % and improved ecological resilience, offering a reliable, cost-effective, and sustainable solution for long-term railway slope stability
An ensemble model with convolutional neural network by DS evidence fusion for bearing fault diagnosis
Get PDFBearing fault diagnosis is crucial for ensuring the safety and reliability of rotating machinery. In recent years, artificial intelligence technology based on machine learning has made substantial progress in the field of bearing fault diagnosis. Most existing models for bearing fault diagnosis are built using big data and deep learning algorithms and can achieve high diagnostic accuracy with sufficient fault data. However, there still exist two open issues, 1) in practical engineering, acquiring fault sample data is challenging, and it is difficult to obtain a sufficient number of samples to train the hyperparameters of deep learning models. 2) Fault diagnosis models based on individual classifiers rely heavily on prior knowledge for signal feature extraction and the selection of network structures and parameters, making it difficult to guarantee the model’s effectiveness. This paper proposes an integrated diagnostic model called DS-ELM that employs multiple extreme learning machine modules with different parameters as subclassifiers. The outputs of these modules are then fused via DS evidence fusion theory to obtain the final diagnostic result. This ensemble model has better flexibility and robustness which significantly improves the accuracy and stability of the diagnostic model. Overall, the proposed DS-ELM provides a new solution for bearing fault diagnosis. In addition, the superiority of the reported technique is confirmed via experimental bearing fault data from Case Western Reserve University
Advanced design strategies and applications for enhanced higher-order multisegment denatured pascal curve gears
Get PDFThe existing Pascal curve gears suffer from limited flexibility in pitch curves and restricted changes in transmission ratios. This has impeded the application in a range of mechanical systems that require more adaptable gear solutions. For this, a design procedure for higher-order multisegment denatured Pascal curve gear is proposed. This innovative design offers greater flexibility in pitch curves and allows for a broader range of transmission ratios. The analysis of the transmission ratio confirms the theoretical predictions and highlights the effectiveness of the proposed gear design in achieving variable transmission ratios. The transmission mechanism of the higher-order multisegment denatured Pascal curve gear is analyzed and the unified mathematical expression of the families of Pascal curve gear is derived. The non-circular gears with free-form pitch curves can be obtained from higher-order multi-segment denatured Pascal curves by adjusting design parameters to unify different types of pitch curves. This approach provides significant flexibility in achieving specific transmission characteristics. Then the transmission characteristics are discussed. To further validate the design, the visual analysis and design software of the higher-order multisegment denatured Pascal curve gear is compiled based on Visual Basic, and is verified with the example. The novelty Pascal curve gears is applied to drive the differential velocity vane pump. The displacement, instantaneous flow rate, and pulsation rate of the differential velocity vane pump are calculated. The novelty drive mechanism could meet the requirements and have good performance. The application shows that the higher-order multisegment denatured Pascal curve gear is feasible in practice
Analysis of shimming performance and clearance influence under manipulation state
Get PDFDuring the roll control process of an aircraft, shimmy often occurs, usually manifested as high-frequency and low amplitude vibrations. In order to better analyze the essential causes of landing gear shimmy, this paper establishes a flexible shimmy dynamics model for the nose landing gear and analyzes the influence of the hydraulic stiffness of the control actuator. The analysis shows that a decrease in stiffness will reduce the stability of the system, and the shimmy frequency will decrease, but the frequency will be higher than the reduced shimmy state. Finally, the system damping ratio is compared to evaluate the stability of the system. Based on the above model and combined with clearance theory, a set of shimmy dynamics model considering the influence of clearance was established. The results show that radial clearance has almost no effect on shimmy; The presence of axial clearance can cause equal amplitude vibration in the system, and increasing the clearance value can cause an increase in amplitude; When the initial swing angle of the system is different, the system will gradually swing to the same amplitude of vibration; There is a coupling effect between system stiffness and clearance values, and as the system stiffness decreases, its amplitude will increase nonlinearly
Load transfer mechanism of flexible drill string with hinges based on dynamic relaxation method
Get PDFThe flexible drill string with hinges is a unique structure for drilling ultra-short radius horizontal wells. In this paper, spatial beam elements are used to simulate the flexible drill string and outer tube, universal joint connection elements are used to simulate hinge joints, and contact gap elements are used to simulate the random contact between the flexible drill string and the outer tube. A nonlinear mechanical analysis model is established for the contact of the flexible drill string with hinges in the outer tube, and the dynamic relaxation method is adopted to solve the model. The correctness of the model and method is verified by an example with analytical solutions. Numerical calculations are conducted on six types of hinge rotation limits and six different single section lengths of flexible drill strings in the inclined section. The results illustrate that the contact force between the flexible drill string and the outer tube is discontinuous and randomly distributed along the axis. The hinge rotation limit is increased from 3° to 5.5°, the axial force transmitted to the bottom of the flexible drill string is reduced from 16.7 kN to 1.5 kN, and the torque transmitted to the bottom has little changed, and its values are close to 1900N·m. When the hinge rotation limit is greater than 5 degrees, the axial force loss rate is greater than 59.5 %. When the hinge rotation limit is 4 degrees, the axial force and torque transmitted to the bottom of the well have little change for flexible drill strings of different single section lengths