Journal of Vibroengineering
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Mechanical deformation mechanism and verification of sections at junctions of light and dark tunnel in a mountain area
Get PDFProjects involving junctions of light and dark tunnel in mountainous areas are complex engineering problems that combine tunnel structure, slope rock-soil mass and protection projects. Such junctions suffer from a complex and changeable load. The stress and deformation of the junction varies under different conditions. Thus, it is a major source of inconvenience for construction and monitoring operations. In this paper, according to the load conditions at a junction of light and dark tunnel, we divide the junction hole into thrust, compression, and combined thrust-compression types. Three types of structures were simulated by numerical analysis, and we explored the structural deformation and stress of these types of tunnel under different condition. Thus, in any construction process, the mechanical deformation mechanism and the weak point in the structure should be worked out. Based on the weak parts, some monitoring points were installed, and four fields for monitoring were chosen. The monitoring results show that the actual deformation, stress and structural failure location are basically consistent with the numerical simulation results. The deformation mechanism of light and dark tunnel junction obtained can provide the basis for selecting the treatment measures and controlling the structural deformation. Furthermore, the results can also be used as a reference for similar engineering design, construction and site monitoring projects
Analyzing dynamic disturbance fragmentation mechanism of surrounding rock in roadway roof
Get PDFIn this paper, a numerical simulation is conducted to analyze an engineering practice pertaining to the in panel 2347, the discussion is focused on the following aspects: the influence of fault mining activation on fragmentation of surrounding rock in roof, surrounding rock failure of unsupported roadway under static load alone, surrounding rock failure of unsupported roadway under dynamic load and static load combination, damage of surrounding rock in supporting roadway under dynamic load and static load combination. The results show that, for the roadway surrounding rock with obvious dynamic disturbance, the compressive stress value can eliminate the influence of the tensile stress wave generated by the reflection of the compressive stress disturbance wave on the roadway wall. In the roadway support, it should provide a certain compressive stress to the surrounding rock of the surrounding roadway wall. An anchor support surrounding rock can significantly inhibit the tensile crack, shear the crack expansion and dislocation slip of coal gang, and it can also alleviate the tensile, compressive and shear failure of the roof carbonaceous mudstone. Because the dynamic load has a significant damage to the carbonaceous mudstone between roof anchors, it is necessary to reduce the anchor spacing and row spacing or enhance the stiffness and active stress of the protective surface member
A novel measurement method of toe debris thickness for bored piles based on one-dimensional wave theory
Get PDFThe existence of toe debris at the bottom of the bored pile will reduce the bearing capacity of the pile. This paper develops a novel equipment to measure the thickness of toe debris for bored piles. The equipment consists of a test rod, test hammer, velocimeter, transmission cable and data receiving and processing device. Based on the one-dimensional wave theory, the mechanism of the sudden change of the velocity time curve received at the top of the test rod is analyzed, which is caused by the change of the wave impedance at the interface between the test rod and the sediment, thus the feasibility of the equipment is verified in theory. Finally, numerical simulations of toe debris under various working conditions are carried out to verify the reliability of the equipment. The results show that the test curves are sensitive to the materials of test rod using proposed equipment when the thickness of toe debris is equal or greater than 50 cm, and the test values are all larger than actual values, which meet the requirement of relevant specifications. The test results are more accuracy when the thickness of toe debris is less than 50 cm. when the excited force is large, not only the sudden change is easy to be discriminated, but also the test accuracy can be assured. The remainder toe debris meet the requirement of relevant specifications after clearing pile hole according the proposed method. And the device is not affected by the properties of the sediment material, which indicates that the proposed equipment can perform well to test the thickness of toe debris
Graphical PID tuning method for uncertain fractional-order multivariable systems
Get PDFIn this paper, a graphical tuning method for controllers parameters based on the open-loop fractional transfer function (FO-EOTF) method is proposed for fractional-order parameter uncertain multivariable system. The FO-EOTF method is proposed to transform the parameter uncertain fractional-order multivariable system into a set of independent parameter uncertain fractional-order univariate systems and determine the parameters regions of the univariate systems. The gain phase margin tester is used to further guarantee the robust performance of the controlled system. Finally, simulation result from the numerical simulation is presented to demonstrate the effectiveness of this method
Seismic responses and dynamic characteristics of boom tower crane basing on measured strong earthquake excitation
Get PDFWith the wide use and longer life cycle of tower crane, the risk of coming across earthquake during service period increases. Hence, the seismic responses and dynamic characteristics of tower crane are becoming more important. In this paper, seismic responses and dynamic characteristics of boom tower crane were analyzed basing on measured strong earthquake excitation. The finite-element models of boom tower crane were established on Ansys platform. Key locations of max stress with different working conditions were confirmed. The stress and displacement of key nodes were compared and analyzed in time-history response with measured earthquake excitation. It was found that the sensitivities of different modes to the change of jib angle were distinct. Meanwhile the change of jib had a greater effect on dynamic characteristics of tower crane than the change of required lift capacity. When the jib was in small angle, numerical results showed that the lifting heavy object could be regarded as inertial damper, which absorbed earthquake energy and reduced displacement of tower crane partly. The results are of practical significance for seismic design and the layout of stability monitoring stations in tower crane
Experimental study of IERSFDs for vibration reduction of gear transmissions
Get PDFIntegral elastic ring squeeze film damper (IERSFD) is proposed to reduce and isolate the vibration of the gear transmissions. IERSFD offers the performance of a low radial stiffness and high squeeze film damping. This paper presents a mechanical model of an IERSFD elastic damping support and a single-degree-of-freedom vibration isolation system for the gear system. An open single-stage spur gear system was built to experimentally study the vibration characteristics of gear transmissions with rigid supports and with IERSFD elastic damping supports filled with damping fluids of different viscosities. The experimental results show that the IERSFD can effectively reduce the peak vibration acceleration of the gear shafts and can guarantee the smooth operation of the gear assembly over a range of speeds. This work shows that an IERSFD can reduce the shock and vibration of the gears’ meshing. It effectively attenuates vibration for most of the gears’ frequency components. Within a limited viscosity range, the vibration reduction is more effective with the higher-viscosity IERSFD damping fluids tested
Vibroacoustic measurements and analysis of blasting works
Get PDFBlasting works cause short-term high-energy shock waves - acoustic, air (airblast) and paraseismic. The duration of the event can be up to 2-3 seconds, while the rise time to the peak value is directly related to the delay between the individual explosive material (EM) and the firing sequence and ranges from a few to several milliseconds. Their propagation in the environment can affect people, animals and construction structures located not only in the close but also further distance from their source. If EM is placed on the surface of the earth during the detonation, the shock wave spreads evenly in all directions in the half-space, and when the detonation follows in rock, the wave usually travels in one direction and is accompanied by a paraseismic wave. However, the sound heard when detonating is part of the wave spectrum in the band from 20 to 20000 Hz, while the airblast itself has a frequency of less than 20 Hz. Since at some distance from the detonated EM, the parameters of the airblast are close to the parameters of the acoustic wave, the method of spreading the acoustic wave depends to a great extent on atmospheric conditions, i.e. density, temperature and humidity of the air, and from wind speed and its direction. To get to know the essence of the phenomenon of the impact of blasting works, measurements are carried out considering the propagation conditions, i.e. meteorological conditions as well as vibration analysis in the ground itself and on the building substructure. This paper presents the results of research carried out by the Authors in terms of the correct assessment of the impact range (acoustic, airblast, paraseismic waves) during EM detonation placed on the surface
Influence of roll-to-roll system’s dynamics on axially moving web vibration
Get PDFIn this paper, a model for transverse web vibration in a roll-to-roll system is presented. Web axial tension and web axial speed, decisive parameters in the equation of motion that describes web vibration, are rigorously obtained by considering the two rolls-web coupled system’s dynamics, coupled with the equation of motion. According to the present analysis, the idealized simply-supported boundary conditions, commonly used in studies on vibrations of axially moving structures are not needed. Instead, a mathematical model comprised of the governing equation of web transverse vibration and the roll angular velocity – web axial tension relationship is solved as a coupled system. A finite-difference based algorithm is used for solving the coupled system of differential equations. It is worth noting that the web axial speed and web-transmitted tension are not constants when a certain amount of the web material is transferred from the unwinding roll to the winding roll; they vary nonlinearly after a short transient period. The transverse vibration response at selected points on the web span shows higher (lower) frequency fluctuations corresponding to lower (higher) transport axial speed. This behavior is significantly different from that of a vibrating web under constant axial speed and tension
The experimental study on influence of turbine wheel position and mass on rotor critical speed
Get PDFThe rotor critical speed of turbine generator unit when the amplitude of the rotor increases sharply, bring to unit certain harm, rotor critical speed calculation method often results with the actual error is bigger. Through Bode diagram method and frequency spectrum analysis method, the rotor critical speed measurement was carried out. Through the experimental results it was concluded that two methods the test results are basically identical, and bode diagram was determined the selection method of measuring rotor critical speed more accurate. By changing the rotor on the quality of the wheel and position change, the use of Bode diagram method for rotor critical speed measurement. It was concluded that with the increase of the quality of the rotor critical speed decreased, the impact is not big in the center of the deviation from the rotor position far; The same quality case, the farther wheel deviating from the center of rotor, the rotor critical speed increases faster. The test results can guide the engineering practice, for the calculation of the rotor critical speed, the simulation and experiment have certain reference function
Implementation of new high efficient input parallel output series partial power DC-DC converter for solar photovoltaic partial shading conditions
Get PDFThe proposed research suggests an improvised performance which is efficient and a reliable converter as a reasonable solar photo Voltaic (PV) approach. The proposed research helps in elevating the performance levels so that power extraction is maximized from the respective PV arrays specifically during the case of limited shading. In order to track the maximum amount of power from every solar PV string, connection of DC-DC converters is done amid the solar PV strings. By doing so, maximum power output can be ensured by the operation of each string irrespective of the occurrence of variation in the solar radiation amongst diverse strings. Usually, the DC-DC converter that would be employed for this purpose would process the string’s power completely. This Full Power Processing (FPP) architecture gives rise to extreme losses of conversion. Hence, the suggested work propound a Partial Power Processing (PPP) that processed a part of the total system power, while the rest of the power is straight away delivered to the output side, thus provides high conversion efficiency when compared to the existing DC-DC FPP converters. An input parallel output series structure having a novel Non-Isolated Partial Power Processing topology (NIPPP) is recommended and the operation’s details are elucidated depending on the operating principle. For the purpose of evaluating the performance of the converter, Matlab Simulink environmental platform are carried out. The closed loop prototype experimental approach is also carried out with the improvement of efficiency compared to conventional it appears in efficient manner