Journal of Vibroengineering
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Numerical study on aerodynamic characteristics of high-speed trains with considering thermal-flow coupling effects
Get PDFIn order to conduct in-depth researches on rationality of air conditioning system equipment of a high-speed train as well as its pipeline system design, working conditions of the air conditioning system and distribution of aerodynamic characteristics including pressure, velocity and temperature in high speed trains should be computed carefully at the design stage. Therefore, the finite volume method was used to solve a governing equation of computational fluid dynamics. The aerodynamic characteristics of pipelines of the air conditioning system and the complete high speed train were computed, so the indoor distribution of wind velocity, temperature and gas concentration (carbon oxide, carbon dioxide, nitrogen and so forth) was obtained. The flow field index and the thermal comfort index were used to evaluate the indoor thermal comfort degree. In this way, whether rationality of the air conditioning system design and indoor aerodynamic characteristic could satisfy requirements for design specifications can be analyzed. Results show that: Under winter or summer working conditions, wind velocity was relatively high at the passageway door, where the maximum wind velocity was more than 1 m/s and would make passengers uncomfortable. Air flow velocity outside comfortable regions was more than 0.05 m/s, satisfying UIC553 standards. Velocity distribution was basically the same indoors, where wind velocity was large at positions perpendicular to the air supply hole, and the maximum wind velocity was more than 1 m/s, but wind velocity was uniform in the passenger region, which was basically lower than 0.2 m/s and satisfied UIC553 standards. In summer and winter working conditions, distribution of pressure, velocity and temperature was not uniform, where the maximum temperature gradient was near the air inlet in the compartment. Air components in the compartment satisfied requirements for comfort. The most uncomfortable regions in the compartment were concentrated at the passageway. Air supply holes distributed symmetrically on the train roof caused high air flow intensity, high wind velocity, low temperature and high humidity at the passageway in the compartment, so the thermal comfort was low, and it is feasible to adjust the layout of air supply holes appropriately
Erratum: Rubbing dynamics behavior of a flywheel shafting with a single point flexible support
Get PDFEffect of electrode location and thickness ratio of flange and web on I cross section piezoelectric cantilever beam for its actuation capability
Get PDFPresent work deals with the numerical investigation of a cantilever beam having I cross section made up of piezoelectric material for its actuation capability. The beam is modeled under the assumption of Euler’s Bernoulli equation. Eight cases are considered for different electrode locations. The beam was subjected to voltage loads at different locations. It was noticed that tip deflection increases with increasing applied voltage across the electrodes. Maximum tip deflection was achieved with the increase in voltage with particular electrode arrangement. In this report we have also demonstrated that for downward tip deflection, there are two values of thickness ratio of flange and web for a given tip deflection at a given applied voltage
An analysis on strip vibration coupled with torsional vibration of main drive system of rolling mill
Get PDFAccording to the movement mechanism of strip and rollers during the continuous rolling process, the main drive system of each stand was simplified to a single degree of freedom discrete model, and the strip was simplified to an axially moving Euler beam. Then, a nonlinear continuous-discrete coupled vibration model between transverse and longitudinal vibrations of strip and torsional vibration of main drive system was established. According to Hamilton’s principle, the nonlinear differential equations were established. Moreover, modified iteration method and Kantorovich averaging method were used to solve the differential equations. Depending on numerical calculation, the amplitude-frequency responses of strip vibration coupled with torsional vibration of main drive system were obtained. Finally, the influences of the axial velocity, the strip tension, the torsional stiffness, and the rotational inertia on the vibration characteristics were discussed. The results would provide a theoretical reference for control and analysis of rolling mill vibration in engineering practice
Study on aerodynamic characteristics and running safety of two high-speed trains passing each other under crosswinds based on computer simulation technologies
Get PDFWith the continuously increased running speed of high-speed trains, aerodynamic problems become more and more obvious. Running safety of trains under crosswinds is a serious problem among numerous aerodynamic problems. Aiming at this problem, this paper combines computational fluid dynamics with multi-body dynamics to study aerodynamic characteristics and safety problems when the high-speed train is running under crosswinds. Based on fluid software FLUENT, this paper computes the flow field of two high-speed trains passing each other under crosswinds. Meanwhile, with combining the multi-body dynamic software SIMPACK with theories, the paper establishes a multi-body dynamic model of the high-speed train, and applies random aerodynamic loads which act on the high-speed train to this model. Impacts of aerodynamic forces (force moments) on aerodynamic characteristics and running safety of each train compartment in the open air are analyzed. Analyzed results show that: when two high-speed trains are passing each other at the same speed of 350 km/h and the crosswind speed is 15 m/s, maximum pressure fluctuations are at observation points near the lateral windows of the head train; aerodynamic forces and force moments of the head train are more than those of the mid-train and tail-train; the high-speed train still has a high safety performance under crosswinds, where the maximum derailment coefficient is 1.9, the reduction rate of the wheel load is 1.1 and the overturning coefficient is 0.98, all of which are smaller than the limit value. More comprehensive factors are considered by the computational model in this paper. It can be used as an effective method to study and evaluate the performance of two high-speed trains passing each other under crosswinds
Retraction: Multiple damage detection and localization in beam-like and complex structures using co-ordinate modal assurance criterion combined with firefly and genetic algorithms
No full textAcoustic characteristic analysis of the non-smooth surface fan of off-highway machinery
Get PDFCooling fan, as an important component of the Off-Highway machinery cooling system, is becoming the largest noise source when it is rotating fast. So, it is the key to suppress the noise from cooling fan in reducing noise in the Off-Highway machinery. In this study, we designed a kind of non-smooth surface cooling fan which could reduce noise strongly, by adding two kinds of non- smooth features on the smooth surface of the forward-skewed fan, and also combining the CFD virtual wind tunnel simulation with bench test to analyze features of flow field and noise. Comparing the experimental data shows that the new fan effectively suppressed the vortex of the power cabin; the effect to reduce noise is proportional to the rotate speed, and with the rated speed, the total noise is reduced 20.9 % and the peak noise is reduced 21.5 % than the original arc bending plate fan in wheel loaders
Numerical analysis on dynamic responses of single-storey buildings under seismic effects
Get PDFThe paper applies the commercial software ABAQUS to establish numerical models of an original single-storey building and a reinforced building, and conducts experimental test to verify correctness of the computation models. Damages and dynamic characteristics of two kinds of models under seismic effects are studied systematically. X-direction acceleration amplitudes of the wall obviously exceeded those in Y direction. In the same horizontal direction, accelerations of the left wall obviously exceeded those of the right wall. Compared with the original model, the X-direction acceleration amplitude is decreased by 15.4 %, and the Y-direction acceleration amplitude is decreased by 49 % in the left wall of the reinforced model. As for right wall of the reinforced model, the X-direction acceleration amplitude is decreased by 30.4 %, and the Y-direction acceleration amplitude is decreased by 17.6 %. In the X direction, the power amplification factors of the reinforced model were less than those of the original model, and the value was decreased by 30 % for the power amplification factors corresponding to 1.3 g. In the Y direction, the power amplification factors of the reinforce model were less than those of the original model under different seismic effects, wherein the value of the reinforced model was decreased by 33 % for the power amplification factors corresponding to 1.3 g compared with the original model. Under the seismic effect of 0.1 g, damages took place to four wall bodies of the model at earliest, but its value was small. With increased seismic input excitation, damage degree of the wall bodies was also gradually increased. Under the seismic effect of 0.8 g, damages to four wall bodies were serious. Under seismic effect of 1.3 g, damage values of 4 wall bodies reached the maximum value 0.99, and the single-storey building will fail. Damages values of four wall bodies of the original model were relatively concentrated; while damage values of four wall bodies of the reinforced model were disperse. Under each seismic effect, the overall damage value was smaller than that of the reinforced model. This result fully indicates that reinforcement can reduce damages of wall bodies and generate anti-seismic effects
Effect of the blade outlet angle on unsteady characteristics of a single channel pump
Get PDFTo study the effect of β2 on energy performance and unsteady characteristics of the single-channel pump, the experimental tests about the energy characteristics, head pulsation, pressure fluctuation and radial force have been conducted by the synchronous test. 3 different impellers with the blade outlet angle β2 of 8°, 16° and 25° respectively are studied. The results show that with the increase of β2 from 8° to 25°, the head increases gradually and the maximum increase amplitude reaches 22.6 %. As β2 changes from 8° to 25°, there is a maximum efficiency. The mixing loss at the impeller outlet can be decreased by reducing β2. With the increasing of β2, the minimum head in time domain gradually lag and the maximum head gradually advances. The pressure fluctuation in each measuring point shows the trend of increasing first and then decreasing with the increasing of the flow rate. With β2 increasing, the radial force also increases and the maximum increase amplitude of minimum radial force is larger than 8 %. The research can provide some reference for the optimization of single channel pumps
Experimental research and finite element analysis on the dynamic characteristics of concrete steel bridges with multi-cracks
Get PDFComplex bridges will inevitably have cracks in operation. Dynamic characteristics with crack structures have been researched central issues. In the past, few researches were conducted from the whole structure of bridges with multi-cracks. In the meanwhile, related experimental research and systematic numerical simulation were lacking. In addition, researches on cracks seldom considered the high-order vibration characteristics of structures with multi-cracks. Aimed at this problem, this paper selected the whole bridge structure which was widely applied in engineering to study dynamic characteristics. For the concrete steel bridge with two cracks, this paper established finite element models for concrete steel beam and bridge with cracks under three different conditions and obtained vibration frequency and three order modes through simulation. Then, this paper analyzed and verified the correctness of numerical simulation result through experiment. Based on the verified model, this paper conducted a systematic analysis and summary, and obtained the following findings: The vibration frequency of concrete steel beams with cracks was obviously affected by cracks. The higher the order was, the greater the impact of cracks on frequency would be and the smaller the impact of cracks on the amplitude of modes would be. With the increased crack depth, the impact on the vibration frequency of concrete steel beams was more obvious. Additionally, crack distance also had some impacts on the dynamic characteristics of concrete steel beams. Numerical simulation model and method in this paper provided foundation and reference for continuing to analyze concrete steel beams with other crack forms or other structural forms. In the meanwhile, the three-dimensional analytical contour in this paper could help engineers to more intuitively understand and valuably apply the change rule of impact of crack depth and position on concrete steel beams