Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
Study on the variation mechanism of non-linear stiffness of rubber O-ring
Full text linkO-ring dampers can be used as vibration-damping elements for short-life, low-cost engines, and the selection of a suitable rubber superelastic-viscoelastic ontological model to study their stiffness and damping is an important prerequisite for determining their vibration-damping characteristics. The superelastic-viscoelastic constitutive model consists of two models, superelastic and viscoelastic, in which the superelastic model reflects the static characteristics of the O-ring. Therefore, it is the basis of the study of dynamic characteristics to carry out the research on the static stiffness of the O-ring and to select an accurate superelastic model to describe its deformation and recovery characteristics under different working conditions. Based on the fact that the O-ring is in a small deformation range in the damper and the applicability of finite element simulation, the Mooney-Rivilin superelastic constitutive model is selected in this paper. Establish a three-dimensional finite element model of the O-ring damper, focusing on the analysis of the effect of temperature on the O-ring material properties and damper structure, to reveal the mechanism of non-linear stiffness change of the O-ring damper. At the same time, the accuracy of the hyperelastic model is verified by the test method, which lays a foundation for the study of the dynamic stiffness and damping characteristics of the O-ring. The results show that in the pre-compression state, there is a large contact pressure between the O-ring and the inner and outer rings of the damper. The contact pressure increases linearly during the compression process, and the stiffness of the O-ring changes linearly. In the non-pre-compression state, the contact pressure is 0, the contact pressure increases nonlinearly during the compression process, and the stiffness of the O-ring shows obvious nonlinear characteristics. In addition, the static stiffness of the O-ring increases with the increase of pre-compression amount, increases with the increase of material hardness, and decreases with the increase of temperature. The above research provides a reference for selecting the appropriate O-ring material size and installation conditions in the project to ensure that the O-ring can effectively withstand pressure during use
The properties of self-compacting fine-grained concrete mixtures for energy-efficient vibration-free construction technologies
Full text linkThe article presents the results of the development and research of self-compacting fine-grained concrete mixes for energy-efficient vibration-free construction technologies. The main focus is on selecting optimal compositions that ensure the required level of mobility and self-compaction through a rational ratio of components and the use of complex modifying additives. The results of research into the rheological characteristics of concrete mixtures, as well as the physical and mechanical parameters of the materials obtained, are presented. The patterns of the influence of the composition and structure of concrete on its density, strength, water absorption and deformability have been established. The results obtained confirm the possibility of creating effective self-compacting fine-grained concretes with high structural homogeneity and reduced energy consumption during production and laying
Stress-strain state of a welded high-strength steel pipeline in the presence of surface defects
Full text linkThe construction of main pipelines is now predominantly carried out using high-strength steels. This makes it possible to increase pipeline capacity while maintaining the existing pipe geometry. However, the issue of ensuring the strength of such pipelines in the presence of surface defects is still relevant. This is especially true for pipeline segments that are located in hard-to-reach places, and therefore, it is difficult to repair and restore. At the same time, the introduction of high-strength steels involves a complex system of material alloying and special thermo-mechanical strengthening technologies. As a result, special structures of increased strength can be produced, but they are sensitive to reheating, in particular when welding technologies are used. This is due to the formation of a special zone of thermal deformation influence in the vicinity of the weld. Material properties of the pipes differ from their original characteristics. The stress-strain state is formed, which also affects the strength of the welded pipeline. The nature of the stress-strain state of welded joints of pipes made of high-strength materials differs from the well-studied stress distributions in pipelines built in the past sixty-eighty years of the past century. In particular, several localized maxima of stresses can be located not only on the weld axis but also in the zone of thermal deformation influence. Therefore, it is important to evaluate the effect of weld stresses in welded joints of high-strength steel pipes on the strength of the pipeline in the presence of surface defects. Since the defect may be located at an arbitrary distance from the weld axis, the predicted strength of the welded pipeline segment can vary significantly
Enhancing the Carrying capacity of complex mountain railway sections through the optimization of train mass standards
Full text linkIt is known that the current train mass standards for railway sections often do not allow locomotives to fully utilize their tractive power. This limits the throughput and Carrying capacity of the railway sections. This article examines the issues of increasing the carrying capacity of freight trains by optimizing train mass standards, using the “Angren-Pop” railway section, which has the most complex profile in “Uzbekistan Railways” JSC, as an example. Updated optimal train mass standards have been proposed for freight trains operating on the “Angren-Pop” railway section, and experimental tests have been carried out based on these standards, followed by their implementation in practice. Based on traction calculations, the interstation travel times of trains for the updated mass standards have been determined. Methods for effectively increasing the transport capacity of the section have been recommended by implementing measures such as increasing the train mass standards and interstation running speeds of freight trains, as well as systematically organizing the use of electric locomotives with high tractive power
Kinematic synthesis of a cam-follower mechanism of a novel internal combustion engine
Full text linkThis paper presents a kinematic synthesis of a groove-type disk cam that directly drives sliders in a novel internal-combustion engine architecture. The synthesis is formulated in an invariant (normalized) space and enforces zero acceleration at phase boundaries while embedding a quasi-constant-velocity segment in the mid-portion of the compression (retraction) phase. An arbitrary shaping function is introduced to generate a family of admissible motion laws; a constrained optimization (series truncated to four terms) minimizes the peak acceleration under a prescribed bound on velocity, yielding a PLM with a quasi-constant-velocity interval of approximately 39 % of the kinematic cycle (±5 %). The synthesized retraction law is paired with a sinusoidal approach (power) law to ensure zero endpoint accelerations for both phases. Cam profiles for the working and return strokes are constructed; maximum pressure angles remain within admissible limits across examined phase splits, including an experimental 65°/25° case. Compared with the sinusoidal baseline, the synthesized law retains a similar acceleration constant but reduces the velocity constant by approximately 31 %, indicating lower inertial loading and milder end-conditions that are favorable for mixture preparation and bearing lubrication. The results provide a compact, implementable route to motion programming for cam-driven reciprocators in internal-combustion engines and establish feasibility for multi-cylinder layouts
Graphical analytical modeling of the kinematic scheme of a rock-piston pump
Full text linkTwo kinematic diagrams are presented, consisting of two combined toggle mechanisms and a piston pump. Kinematic calculations of the moving link parameters for both kinematic diagrams resulted in the determination of the displacement of the working and idle stroke lengths S of the piston as a function of the toggle mechanism swing angle φ and the change in the toggle length and crank radius of the piston pump. The numerical value of the coefficient K of the average toggle mechanism slider velocity, K= 2, and the displacement of the piston stroke S were obtained: for a toggle-piston pump, S= 1.25, and for a crank-toggle mechanism, SK= 0.7 m. Various asymmetric phase angles were calculated for the working φp and idle φx strokes of the slider during rotation of the toggle mechanism crank for both kinematic diagrams. The relationship between the center distance α and the position of the fixed support point O1 of the crank axis of rotation to the support point O2 of the rocker arm is obtained. The numerical values of the stroke displacement SD, linear velocity VD, and acceleration αD of the pump piston for both kinematic diagrams of the rocker-piston pump mechanism are presented in tabular form by numerical values and in kinematic diagrams
Influence of angular speed of tedder on kinematic parameters of linter machine drive
Full text linkThis article investigates the influence of the tedder’s angular speed on the kinematic and power characteristics of the drive system of the 5LP linter machine. The linter machine is a complex technological unit used to remove residual fibres from the surface of cotton seeds. One of the key factors determining linting efficiency is the interaction between the tedder and the seed roller inside the machine’s working chamber. A detailed kinematic and force analysis is presented, taking into account the resistance forces generated by the seed roller during its movement and processing. Particular attention is given to the development of a calculation model that describes the interaction between the tedder blades and the seed roller. In this model, each blade is treated as a cantilever beam subjected to variable loads resulting from the non-uniform mass and density distribution of the seed material. The analysis demonstrates that variations in the mass and density of the seed roller significantly affect the load transmitted to the drive and the stability of the saw cylinder. The obtained results enable more accurate selection of drive parameters and optimisation of the operating modes of the linter machine. These findings are crucial for improving the productivity and reliability of the equipment, as well as for accounting for both transient and steady-state operating conditions in real industrial environments
Analysis and optimization of dynamic characteristics of the supporting frame structure of small fishing boat
Full text linkThe 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
Analysis of the natural characteristics of fiber-reinforced cantilever beams using 8-node solid elements
Full text linkA combined theoretical and experimental approach is employed to investigate the dynamic characteristics of fiber-reinforced cantilever beams. An 8-node element method establishes the theoretical model of the cantilever beam, allowing for the determination of its dynamic properties. A relevant experimental platform is constructed to test the fiber-reinforced cantilever beams, thereby validating the accuracy of the theoretical model. The results indicate that the theoretical model accurately predicts the dynamic characteristics of fiber-reinforced cantilever beams. Finally, based on the established theoretical model, the effects of cantilever beam length, width, and elastic modulus on the dynamic characteristics of the cantilever beam are discussed
Research on optimization of intelligent driving
Full text linkTrajectory tracking control is one of the most fundamental and important technologies in intelligent vehicles. In response to the problems of low accuracy and poor reliability in current intelligent vehicle path tracking control, the shortest time to complete path tracking of double lane changing was set as the control objective and the optimal control problem for vehicle path tracking is transformed into a nonlinear programming problem using the multi-interval Radau pseudospectral method, and then solved by the sequential quadratic programming method. Through Carsim and MATLAB/Simulink platforms, a joint control simulation of the control algorithm was conducted under double lane changing condition, and finally verified through virtual experiments. The joint simulation and virtual experiment results show that the intelligent vehicle path tracking control algorithm proposed in this paper has good tracking accuracy and driving stability while ensuring the target path tracking performance of the intelligent vehicle. The average values of lateral error and heading error are calculated to be 0.0912 m and 0.0263 rad, indicating that the lateral error and heading error of path tracking are controlled within a small error range during the path tracking process which indicating that the proposed method has high computational accuracy