Journal of Engineering and Thermal Sciences
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Analysis on the influence of blade pitch angle on dynamic characteristics of the rotor system
Full text linkAt present, few studies focus on variable-pitch fans for small-to-medium turbofan engines, with most relying on hydraulic actuation that fails to meet strict environmental and efficiency demands. This paper analyzes an electrically actuated lead-screw servo-motor-driven variable-pitch fan rotor: at 1×10⁷ N/m support stiffness, the first critical speed exceeds the operational range and pitch angle’s influence is negligible, peak unbalance response is 1.22×10⁻⁶ m linearly decreasing with pitch angle, and vibration analysis avoids resonance. Results confirm the electric pitch-change concept’s feasibility
Optimal control of lane changing problem of intelligent vehicle
Full text linkLanes changing is one of the basic behaviors of vehicle driving, which has a significant impact on road traffic safety and stability. Aiming at the problem of slow convergence rate in solving the optimal control problem of vehicle lane changing, an optimal lane changing control method based on hp adaptive pseudospectral method is proposed. By establishing a vehicle kinematic model, boundary constraints, and path constraints, combining with the physical process of vehicle lane changing the proposed method discretizes the control and state variables to transform the multi constraint optimal control problem into a nonlinear programming problem and the minimum vehicle lane changing time is set as the performance objective function. And also, the proposed method is compared with traditional solving methods. The simulation results show that the proposed method can effectively solve the optimal feasible lane changing trajectory and complete the lane changing maneuver process in the shortest possible time
Study on vortex-induced vibration response of large-scale two-lay steel trusses bridge under large wind angle of attack
Full text linkWith the advancement of urbanization, two-lay trusses bridges are widely used because of their good traffic capacity and structural performance. However, the aerodynamic behavior of this beam type is still in the exploratory stage. The local microclimate characteristics at the bridge site in mountainous cities are obvious, and it is easy to form a large wind angle of attack, which has a significant impact on the vortex-induced vibration (VIV) performance of the bridge. Therefore, this study takes a long-span two-lay steel trusses bridge in a mountainous city as the engineering background, and uses wind tunnel test and numerical calculation methods to study the changes of the static three-component force coefficient and VIV response of the main beam in the construction and completion state under the action of high wind angle of attack. The results show that the three-component force coefficient curves under different wind speeds are close to each other, and the Reynolds number effect is not obvious. The vibration test shows that the vertical bending VIV first occurs at +3° and +5°, and then two torsional VIV with different amplitudes occur. Both vertical bending and torsional VIV are simple harmonic vibrations with a single frequency, and the vertical bending VIV frequency is locked at 2.227 Hz, and the torsional VIV frequency is locked at 4.289 Hz, which are close to the natural frequency of the test model. Compared with +3°, the maximum amplitude of vertical bending VIV under +5° increases by 30.0 %, while the maximum amplitude of torsional VIV under high and low wind speed increases by 16.6 % and 12.7 % respectively, and the locking range is longer. It can be seen that the wind angle of attack has a significant effect on the VIV response of the main beam in the completion state. Especially, the trusses beam at a large angle is more sensitive to VIV, and it is more prone to large-scale and large-amplitude VIV. The research results can provide a theoretical basis for the aerodynamic shape optimization and provide a reference for the design of related bridges
Improved CEEMD-based correction method for low-frequency shock response spectrum in large dual-wave shock tester devices
Full text linkThe shock response spectrum (SRS), calculated from a shock acceleration signal, is a critical indicator of shock environments. However, under intense loads, acceleration sensors are prone to trend term errors that can cause significant drift in the low-frequency spectral lines of large dual-wave shock tester devices. To address this issue, the complementary ensemble empirical mode decomposition (CEEMD) method was employed to decompose acceleration signals and restore the actual shock environment. Intrinsic mode functions (IMFs) were cross-correlated and compared to a predefined threshold to identify the effective IMF components required to reconstruct the signal. K-means clustering was employed to further validate the effectiveness of the IMFs for enhanced selection accuracy. Finally, the reconstructed acceleration signal was used to calculate a corrected SRS. The proposed approach demonstrated significant improvements over the traditional CEEMD algorithm. The corrected SRS exhibits a 5.6316 dB/oct slope in the low-frequency band, reflecting an equal displacement trend. The maximum error at the corresponding frequency was less than 6 % in comparison to the relative displacement response measured by low-frequency spring oscillators. This improved CEEMD correction method can effectively restore the actual shock environment of a dual-wave shock tester device, offering a valuable reference for evaluating shock resistance in onboard equipment
Study on the interaction state between polymer modifiers and asphalt based on precise grinding
Full text linkTo clarify the impact of resin modifier fineness on the performance and interaction of modified asphalt, this study selects resin modifiers to prepare modified asphalts. The effects of the fineness parameters of resin modifiers on the road performance of modified asphalts are investigated. The segregation tests and Han curves are employed to analyze the influence of modifier on the compatibility of modified asphalt. The scanning electron microscopy is utilized to characterize the interaction between resin modifiers and asphalt. The results indicate that resin modifiers improve the high-temperature performance and deformation resistance of asphalt binder but lead to the adverse effect on low-temperature performance. Adjusting the particle size of the modifier could improve the modification effect of resin modifiers on asphalt binder
Vibration control of SUV steering gear using acoustic black hole structure
Full text linkIn the steering system, the vibration generated by the steering gear can seriously affect human driving comfort, and effective vibration reduction is crucial. Acoustic black hole (ABH) is a vibration reduction and noise reduction technology that controls the consumption and aggregation of bending waves through thin-walled power function structure changes. A design scheme of embedding a 2D ABH plate in the steering column is proposed to address the vibration reduction issue of the steering gear. Using the finite element method, the natural frequency and velocity response curve of the steering gear is obtained. Then we embed a 2D ABH into the steering gear model. The steering gear model embedded with 2D ABH was subjected to finite element analysis to obtain the vibration characteristics and velocity response and acceleration curve of the steering gear after adding 2D ABH. The results indicate that the vibration velocity and acceleration of the steering gear embedded with ABH is lower throughout the entire frequency range. The maximum damping is around 510 Hz, and the minimum damping is around 294 Hz
Erratum: Vibrodiagnostics and dynamic operation of reinforced concrete sleepers under the influence of moving load
Full text linkResearch on modeling and dynamic characteristics of GTF transmission gearbox
Full text linkTaking a GTF star transmission gearbox as the research object, this paper innovatively introduces the Westgard decision diagram, which is widely used in medical clinical trials, and combines "relative error distance method of speed, transmission ratio and meshing force" to build a performance evaluation method of gearbox model based on multi-body dynamics. At the same time, the translation-torsional dynamics model of the gearbox is established by using the lumped mass theoretical method, and the key parameters such as output speed, gear meshing force and bearing vibration acceleration are obtained by the analysis of the two models. Comparing the simulation results of the multi-body dynamics model selected by the performance evaluation method with the analysis results of the concentrated parameter method, it can be seen that the performance of the multi-body dynamics model selected by the performance evaluation method is reliable and effective, and the analysis accuracy and analysis efficiency can be taken into account. The maximum absolute error of meshing force is 2.5771 N, and the absolute error of vibration acceleration at the bearing of input shaft and output shaft is controlled within 0.08 m·s-2 and 0.1 m·s-2, respectively. The model performance evaluation method proposed in this paper effectively solves the problem of the balance between simulation efficiency and accuracy of the traditional gearbox dynamics model, provides a new technical path for the performance evaluation of complex gear transmission systems, and provides a reliable theoretical basis and technical support for the design and optimization of gear transmission systems of high-end equipment such as aeroengines, and has important engineering application value
Challenges to properly accounting for cyclic response in transversely isotropic elastic soil idealizations
Full text linkThe way natural soils are deposited gravitationally inherently leads to an anisotropic microfabric. The elasticity of such anisotropic soils has typically been idealized as being transversely isotropic (or “cross anisotropic”). The importance of elastic anisotropy in geotechnical engineering applications has particularly been invoked in conjunction with predicting ground deformations associated with underground structures such as deep excavations and tunnels. The development of elastic constitutive relations for transversely isotropic geomaterials is complicated by the fact that the elastic material parameters are usually not constant. This paper briefly reviews the issue of elasticity in soils. Following a short overview of isotropic elastic idealizations, the more relevant topic of transversely isotropic idealizations is discussed, with emphasis not only on monotonic but also on cyclic response
Vibration characteristics testing and vibration reduction optimization design of four-wheel-drive micro-tiller handlebar assembly
Full text linkMicro-tillers are essential for agricultural operations in hilly and mountainous regions, yet their severe vibrations pose significant health risks to operators, including hand-arm vibration syndrome. This study presents an innovative vibration reduction solution through the installation of a damping spring isolator at the handle-frame connection point. Comprehensive vibration testing revealed that the vertical vibration under tillage conditions reached 2.15 m/s2 RMS, with spectral analysis identifying critical excitation frequencies at 39 Hz, 78 Hz, and 156 Hz. Constrained modal analysis demonstrated that the handle frame's third-order natural frequency of 41.02 Hz risked resonance with the engine’s 39 Hz excitation. The optimized isolator system, designed with a damping ratio of ξ= 0.2, successfully reduced this critical frequency to 34.87 Hz (15 % reduction), effectively avoiding resonance. Field validation showed significant vibration attenuation, with RMS values decreasing by 14.17 % (idle), 17.61 % (no-load), and 23.26 % (tillage), while achieving 19.3 % vibration energy absorption during operation. This research represents the first successful integration of isolation and damping mechanisms for micro-tiller handle frames, providing a cost-effective solution (< 1.5 % of machine cost) that significantly improves operator comfort and addresses long-standing ergonomic challenges in small-scale agricultural machinery. The solution's simple implementation without structural modifications makes it particularly suitable for widespread adoption in developing regions