Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
The mechanism and control of low-frequency road noise in a certain hatchback Car
Full text linkDuring the development of a hatchback car, a problem of ear-pressing noise caused by low-frequency road noise was encountered. Through the analysis of the vehicle’s transmission path, the mechanism of the problem, and experimental verification, it was confirmed that the low-frequency road noise problem inside the car was mainly caused by the road exciting the tire, transmitted through the suspension system to the subframe, arms, and other bottom plate components, and then transmitted to the body, causing the rear door bending mode to be excited and generate resonance, the body panel deformation squeezing the interior cavity, causing air pressure fluctuations in the car, and ultimately causing the low-frequency road noise ear-pressing problem. To solve the low-frequency road noise problem during vehicle operation, this paper studied the noise optimization scheme for the hatchback rear door, proposed a low-frequency road noise control solution, and successfully solved the low-frequency road noise problem of the hatchback car through in-vehicle verification, proving the effectiveness of the low-frequency road noise control solution and improving the driving comfort of the car, providing important guidance for NVH low-frequency road noise control
Design of a multifunctional UAV based on composite materials: integration of vacuum infusion, CFD analysis, and intelligent energy management
Full text linkThis study proposes an integrated design approach for a multifunctional UAV using composite materials, combining vacuum infusion, CFD-based aerodynamic analysis, and an STM32-based energy management system. CFD results showed a lift coefficient CL= 0.812, drag coefficient CD= 0.055, and L/D= 14.7, representing a 28 % improvement over aluminum structures. FEM analysis indicated a maximum stress of 312.4 MPa with a safety factor of 1.12, while vacuum infusion achieved 98.7 % resin impregnation, enhancing stiffness by 28 % and reducing weight by 25 %. The automated energy management system increased energy efficiency by 16.3 %, extending flight duration and improving operational stability
Experimental study of the effect of the cell size honeycomb core on the impedance of single-layer SAS
Full text linkThe study of the acoustic characteristics of sound-absorbing structures (SAS) seems to be an urgent task aimed at solving the problem of noise both in the cabin of aircraft and aircraft engine noise. Results of experimental study of the effect of the size of the cell edges of a fiberglass honeycomb core and the degree of perforation on the acoustic characteristics of single-layer sound-absorbing structures are presented. Tests of samples of sound-absorbing structures were performed on an interferometer type installation with a normal incidence of sound waves. The dependence of the acoustic characteristics of SAS on the size of the edge of the honeycomb filler is shown, in connection with the overlap of the holes of the perforated sheet of SAS with the edges of the honeycomb block. The dependence of the resonant frequency and the efficiency of the structure on the diameter of the holes of the perforated sheet are shown
Analysis of shimming performance and clearance influence under manipulation state
Full text linkDuring 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
Full text linkThe 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
Enhancing PLL performance in weak grids: a comparative analysis of backward and bilinear ADC with SOGI-PLL
Full text linkMost rectifiers using AC grid voltage assume that the voltage is ideal and has no distortion. However, in high-power systems such as water electrolysis, the grid voltage can be distorted. This situation is called a weak grid. In weak grids, the switching of rectifiers causes voltage distortion. Distorted voltage causes phase errors during observation, so it is important to measure voltage without distortion. There are two common methods to reduce errors during observation. One is using a hardware Low-Pass Filter (LPF) to reduce high-frequency switching distortion. The other is using a Second-Order Generalized Integrator (SOGI) Phase-Locked Loop (PLL) to separate the distorted component. Both methods are commonly used, but their performance changes depending on how they are applied. This paper compares the distortion reduction of the hardware LPF and the error caused by the digital method of the SOGI-PLL. Simulation results show that the hardware LPF reduces distortion by about 75 %, and the SOGI-PLL can have up to 6.7 % error depending on the digital method. These results are verified through PSIM simulation
Small sample fault diagnosis method based on dual convolutional kernel feature fusion and channel attention weighted temporal convolutional network (DCK-CAM-TCN)
Full text linkIn actual industrial environments, equipment failures often occur sporadically during operation, resulting in insufficient labeled data for training. To address the issues of difficult feature extraction and poor generalization caused by insufficient data in small-sample fault diagnosis, a small sample fault diagnosis method based on dual convolutional kernel feature fusion and channel attention weighted temporal convolutional network (DCK-CAM-TCN) is proposed. Firstly, dual convolution kernels are employed to extract signal features, with the large kernel capturing low-frequency components and the small kernel extracting additional features to enhance the network's expressiveness. Secondly, the channel attention mechanism adaptively adjusts the feature responses of each channel, enabling the network to focus on the most informative and relevant features while suppressing unimportant ones. Finally, the Temporal Convolutional Network (TCN) is utilized to capture dependency features within long time series, further improving the model's ability to process sequential data. Experimental results demonstrate that the DCK-CAM-TCN model significantly outperforms traditional Convolutional Neural Networks (CNNs) and other comparison models in small-sample scenarios. The results indicate the significant advantages of the DCK-CAM-TCN model in small-sample fault diagnosis
Experimental results of reducing harmful vibrodynamic effects caused by the interaction between rolling stock and track through the use of elastic under-sleeper pads in the rail joint zone
Full text linkIn the current era of independent development and market relations, the importance of railways continues to grow steadily. This, in turn, places great responsibility on the system of measures aimed at ensuring railway reliability. However, despite the advantages and advancements of the railway industry, it still faces technical complexities that can lead to track deterioration. In heavily loaded and high-speed railway sections, the interaction between the rolling stock and the track causes various issues in the rail joint zones – such as the development of defects and irregularities, deterioration of track geometry, reduction of track stability, as well as problems related to noise and vibration that must be mitigated. To address these challenges, scientific studies and experimental investigations have been conducted on the installation of elastic under-sleeper pads in the rail joint zones. These studies aim to modify the vertical stiffness transferred from the wheelsets of the rolling stock to the track structure, reduce harmful vibrations and oscillations, and thereby ensure uniform stability along the entire track. The conducted research, testing, and their results are presented in this article
Analysis of the influence of vibration phenomena in pump systems on electrical energy consumption and operational efficiency
Full text linkDespite the long-standing recognition of vibration phenomena as a critical factor affecting both mechanical reliability and energy performance, yet their influence on electrical energy consumption remains insufficiently quantified. Excessive vibration, originating from rotor imbalance, shaft misalignment, bearing wear, and hydraulic instabilities, can result not only in accelerated component degradation but also in significant increases in energy demand and reductions in hydraulic efficiency. Understanding the quantitative relationship between vibration intensity and pump energy performance is therefore essential for both predictive maintenance strategies and energy efficiency improvements in pumping systems. This paper presents an experimental investigation of the effect of vibration on the electrical energy consumption and operational efficiency of centrifugal pumps. Five industrial pump types, with rated powers ranging from 15 to 75 kW and capacities from 100 to 320 m3/h, were tested under controlled conditions. Measurements were carried out using UT310A vibration testers, an ultrasonic flow meter, and a Fluke 1777 Power Quality Analyzer. Vibration signals, volumetric flow rates, pressure heads, and three-phase electrical parameters were simultaneously recorded under partial load, nominal load, and overload conditions. Hydraulic power and efficiency were then calculated, while statistical analyses-including correlation and regression models-were applied to determine the relationship between vibration intensity and electrical performance. The results revealed a strong positive correlation between increasing vibration levels and higher electrical energy demand. In particular, RMS vibration acceleration was found to be a reliable predictor of additional energy losses, while efficiency was observed to decrease as vibration intensity increased. These findings not only confirm the detrimental effect of mechanical instability on energy consumption but also provide a methodological framework for integrating vibration monitoring into energy management practices. By bridging the gap between mechanical diagnostics and energy performance analysis, the study contributes new insights that can support the development of predictive maintenance systems, improve pump reliability, and promote more sustainable operation of pumping stations
Vibration-resistant mixed binders using man-made burnt rocks for transport infrastructure
Full text linkThis study presents the characteristics of man-made wastes, specifically burnt rocks formed by the self-combustion of coal-bearing waste dumps, whose chemical and mineralogical composition depends on the origin of the basin. The aim of this research is to assess the feasibility of using these burnt rocks as components of mixed mineral binders and to evaluate their influence on mechanical and dynamic performance parameters. A comprehensive analysis of their physical, chemical, and structural properties was carried out, demonstrating their compatibility with conventional binder materials. The novelty of this study lies in the first systematic use of locally available burnt rocks (glyage) in vibration-resistant binder compositions for transport infrastructure, expanding the raw material base of construction materials while reducing environmental impact. The developed binders achieved compressive strengths up to 17.6 MPa, sufficient for structural layers of pavement bases and subgrade stabilization. Moreover, these mixed binders can modify the dynamic stiffness and damping behavior of pavement structures under moving vehicle loads, establishing a scientific link between binder composition and vibration control in transport engineering. These results are directly relevant to vibration engineering, as the dynamic stiffness and damping behavior of the developed binders influence vibration propagation and attenuation in transport pavements, ensuring longer service life and reduced noise and deformation under dynamic traffic loads