Abstract
The paper analyzes the capabilities of an automatic rotary platform of the "Flyuger" type to reduce micro-accelerations in a protected area when it is installed on a small spacecraft of the ..."Aist-2" type. The micro-accelerations field of the working volume of scientific equipment of the "Growth installation" type has been modeled. The comparison with flight test data is made. The results of the work can be used in the design of small technological spacecraft.
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•This paper proposes a method to obtain scaling laws for rotor systems.•The power in scaling laws is represented by a function related to scaling factor.•The proposed method can ...predict the dynamic characteristic in partial similitude.•Testing for both prototype and model is carried out to verify the proposed method.•The proposed method can improve prediction accuracy compared with existing methods.
Similitude theory is widely used to predict the structural responses of the full-size prototype through scaled models and is categorized into complete and partial similitude according to the way of scaling parameters. Partial similitude is more flexible in practical design engineering, but its accuracy still needs to be improved. This study presents an improved partial similitude approach, which can be used to establish the scaling laws and understand the scaling behaviors of rotor systems. The aim is to overcome the insufficient accuracy of the existing methods in predicting the dynamic characteristic of rotor systems. The power in scaling laws is represented by a function, which is related to the scaling factor of the prototype to be predicted. In this work, the power function is developed by incorporating the Levenberg–Marquardt method and sensitivity analysis. The accuracy and effectiveness of the proposed partial similitude method are validated through numerical and experimental case studies, where the distortion in geometrical dimension is considered. The dynamic characteristic of prototypes is predicted through the scaled model. Furthermore, the accuracy of the proposed method is evaluated by using the existing methods. Both the numerical and experimental case studies indicate that the proposed method achieves higher accuracy than the existing methods in predicting the dynamic characteristic of rotor systems.
The journal-thrust coupled bearing in diesel engine operates under complex load and high working temperature. Under extreme working conditions, it supports the crankshaft and prevents its axial ...movement through the lubrication of journal and thrust parts. This study is mainly aimed to establish the thermal elastohydrodynamic (TEHD) lubrication analysis model for textured journal-thrust coupled bearing, which considered the thermal and pressure coupled effects in the lubrication process by proposing the flow, pressure and thermal continuity conditions between the journal and thrust parts. A specific coupled bearing testing equipment was set up and the experimental results validated the correctness of the TEHD lubrication model. Necessity of considering thermal and pressure coupled effect was confirmed through comparison of different models. Apart from that, parametric analyses were conducted to explore the influences of thermal and pressure coupled effects on lubrication performances and dynamic characteristics under different eccentricity ratio of journal part, geometry film thickness of thrust part and surface topography (mainly realized by texture distribution of thrust part).
•The journal-thrust coupled bearing in diesel engine is found necessary to consider the flow, pressure and thermal continuity conditions of the common boundary.•After considering the coupled effect mentioned above, the bearing capacity, maximum temperature, stiffness and damping of journal and thrust parts are improved.•With the reduction of geometry oil film thickness, the coupled effect has more significant influence on lubrication performances and dynamic characteristics, and the trend of each part is different. Similarly, the coupled effect also has a similar influence with the change of texture distribution.
Abstract
The purpose of this paper is to study the characteristics of recoil motion of a new suggested recoil system designed for the Russian 120- mm PM-38 mortar, rather than the conventional ...fixed-barrel mortar system. The new recoil system enables to reduce the total force imparted by the mortar system to the carriage, with the purpose of the mortar can be mounted on tracked/wheeled vehicles. The paper presents the suggestion of the new recoiling mortar system along with the discussion of the presentation of constructional considerations and constraints. The dynamic characteristics of recoil motion have been modelled with the aid of a new mathematical model that have been established using MATLAB software. As a result of the suggestion of the new recoiling mortar system, the maximum recoil resistance force is predicted to be reduced by more than 60% compared to that in the traditional fixed-barrel mortar system. In addition, the maximum recoil distance was predicted to be around 26 cm.
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•Indoor PM2.5 varied largely in different urban microenvironments.•Restaurants suffered from severe indoor PM2.5 pollution due to the strong internal emissions.•Cooking activities ...could significantly increase indoor PM2.5 levels in short time.•Outdoor penetration contributed mostly to indoor PM2.5 of public and household places.
People generally spend most of their time indoors, making a comprehensive evaluation of air pollution characteristics in various indoor microenvironments of great significance for accurate exposure estimation. In this study, field measurements were conducted in Kunming City, Southwest China, using real-time PM2.5 sensors to characterize indoor PM2.5 in ten different microenvironments including three restaurants, four public places, and three household settings. Results showed that the daily average PM2.5 concentrations in restaurants, public spaces, and households were 78.4 ± 24.3, 20.1 ± 6.6, and 18.0 ± 4.3 µg/m3, respectively. The highest levels of indoor PM2.5 in restaurants were owing to strong internal emissions from cooking activities. Dynamic changes showed that indoor PM2.5 levels increased during business time in restaurants and public places, and cooking time in residential kitchens. Compared with public places, restaurants generally exhibit more rapid increases in indoor PM2.5 due to cooking activities, which can elevate indoor PM2.5 to high levels (5.1 times higher than the baseline) in a short time. Furthermore, indoor PM2.5 in restaurants were dominated by internal emissions, while outdoor penetration contributed mostly to indoor PM2.5 in public places and household settings. Results from this study revealed large variations in indoor PM2.5 in different microenvironments, and suggested site-specific measures for indoor PM2.5 pollution alleviation.
Camouflage is widespread in nature, engineering, and the military. Dynamic surface wrinkles enable a material the on-demand control of the reflected optical signal and may provide an alternative to ...achieve adaptive camouflage. Here, we demonstrate a feasible strategy for adaptive visible camouflage based on light-driven dynamic surface wrinkles using a bilayer system comprising an anthracene-containing copolymer (PAN) and pigment-containing poly (dimethylsiloxane) (pigment-PDMS). In this system, the photothermal effect-induced thermal expansion of pigment-PDMS could eliminate the wrinkles. The multiwavelength light-driven dynamic surface wrinkles could tune the scattering of light and the visibility of the PAN film interference color. Consequently, the color captured by the observer could switch between the exposure state that is distinguished from the background and the camouflage state that is similar to the surroundings. The bilayer wrinkling system toward adaptive visible camouflage is simple to configure, easy to operate, versatile, and exhibits in situ dynamic characteristics without any external sensors and extra stimuli.
In this paper, the dynamic characteristics of MEMS gas bearing are investigated. Angular misalignment and rarefaction effect are introduced into the lubrication equation based on FK model. The ...partial derivative method is adopted to solve the lubrication equation. The comparison of the calculating results between continuous model and rarefied model shows that the rarefaction effect has obvious impact on the dynamic performance of MEMS gas bearing. Then the influence of misalignment on the dynamic coefficients of MEMS gas bearing is studied and the influence laws on 8 dynamic characteristic coefficients are obtained. Furthermore, the limit dynamic performances considering misalignment and rarefaction effect are discussed in detail.
•The rarefaction effect is introduced into the dynamic lubricated equation.•The rarefaction effect is introduced into the dynamic lubricated equation.•The analysis shows that the rarefaction effect has obvious impact on bearing’s dynamic performance.•The influence of misalignment on the 8 dynamic coefficients of MEMS gas bearing is studied.•The limit dynamic performances considering misalignment and rarefaction effect are discussed in detail.
•A general double-beam model with elastic supports is proposed.•A unified modal analysis method is proposed.•The dynamic stiffness of the system is discussed for the first time.•The contributions of ...the two beams to each mode is studied.
The double-beam system with several elastic supports is one of most significant mechanical models in engineering structures. Its dynamic characteristics are crucial for structural design, vibration control, health monitoring, and other dynamic issues. In the dynamic analysis of double-beam systems, since existing researches often need to make some assumptions or approximations to the displacement function, the accuracy and application range of the analysis results are limited. In view of this, this article proposes an exact modal analysis method for the double-beam system based on the dynamic stiffness method. It can consider the effect of boundary conditions, the differences in the material and structural of the two beams, the axial forces and other factors simultaneously without any approximation. During the analysis, the accuracy of the proposed method is verified first by comparing with finite element solutions. Then, the influence of elastic supports on modal characteristic is discussed, and the variation law of the dynamic stiffness in frequency domain is investigated. Finally, a dynamic stiffness-based method for determining the contributions of the two beams to each mode of the system is provided. The method can be extended to quickly obtain the frequency and mode shape information of the system without solving the frequency equation or characteristic equation.
•The full-size water-lubricated stern bearing are investigated experimentally.•A hydrodynamic model considering bidirectional shaft inclinations is established.•A 16 dynamic coefficients calculation ...method is proposed.•Horziontal shaft inclination has greater effect on bearing at low eccentricity.
This paper investigates the lubrication and dynamic characteristics of water-lubricated stern bearing (WSB) under service conditions. A test scheme of bearing film pressure distribution and spatial shaft position is proposed. The experiment reveals the pressure bias and bidirectional shaft inclination phenomenon of full-size WSB, according to which the transient fluid–solid coupling dynamic model of the bearing is established, considering bidirectional shaft inclination and lining deformation. The calculation method of 16 dynamic coefficients is proposed. Influences of eccentricity ratio, shaft inclination angle, and bearing structure parameters on lubrication and dynamic characteristics are explored systematically. Results indicate that the rotating shaft produces apparent horizontal deflection during the working condition of low speed and heavy load. Under the existence of attitude angle, the horizontal and vertical shaft inclinations both affect the film thickness and pressure distribution, especially at low eccentricity ratio, the horizontal shaft inclination has a greater impact on the bearing. As the length to diameter ratio increases or as the clearance ratio decreases, the effect of vertical shaft inclination on lubrication and dynamic characteristics of the bearing decreases, and that of horizontal shaft inclination increases. Research results are instructive for further study on the effect of misalignment on the structural design and optimization for such bearings.
The purpose of this paper is to investigate the static and dynamic characteristics of the high-speed water-lubricated spiral-groove thrust bearing (SGTB) considering cavitating and centrifugal ...effects. A turbulent flow lubrication model was established based on gas-liquid two phase flow, and the influence of cavitation and centrifugal force on the static and dynamic characteristics was analyzed for the SGTB. An experiment setup was developed to measure the static and dynamic characteristics of the SGTB. The result shows that the proposed model with cavitating and centrifugal effects is more accurate than that without those two effects, the effect of the cavitation and centrifugal force should be considered when the modified Reynolds number exceeds 0.3.
•The static and dynamic characteristics of high-speed water-lubricated SGTB is studied.•A turbulent flow lubrication model for the SGTB is established based on gas-liquid two phase flow.•All the static parameters and the dynamic coefficients reduce with the effect of cavitation and centrifugal force.•The effect of cavitation and centrifugal force must be considered when the modified Reynolds number exceeds 0.3.
