查看更多>>摘要：The aerodynamic admittance of a rail vehicle was investigated by wind tunnel test. Aerodynamic force was measured in the cases of three typical railway structures, including on the flat ground, above an embankment, and on a bridge, under two turbulent flow fields. First of all, three-component aerodynamic coefficients of the vehicle on each structure were obtained under uniform flow with respect to three wind attack angles and four wind direction angles. Secondly, the aerodynamic forces on the vehicle and the corresponding wind speed were evaluated to establish an aerodynamic admittance function of the vehicle. The aerodynamic admittance of the rail vehicle approximated a constant value in the low-frequency domain, but decreased with the reduced frequency increasing. The effects of the different reduced frequencies on the drag are greater than the lift admittance of the vehicle, while moment admittance stays steady-state. Finally, in order to reflect the unsteady characteristics of the buffeting force on the vehicle, the aerodynamic admittance functions of the vehicle were fitted to the expression of the frequency response function of a mass-spring-damping system, which was then verified. Furthermore, the effects of flat terrain and mountainous terrain were investigated, revealing that the influence of turbulence intensity on aerodynamic admittance is significant.
查看更多>>摘要：Generating an inflow turbulence satisfying the near-ground wind characteristics of the atmospheric boundary layer is an important prerequisite to accurately predict the wind effects on buildings and structures using large eddy simulation (LES). An inflow turbulence generation method named as reusable wind tunnel replication method (RWTR) for LES is presented in this paper. The validation study is performed by numerical simulation of a real wind tunnel. And then the RWTR method is applied to a large eddy simulation to study the wind effects on a standard high-rise building, including the flow field characteristics, wind pressure and base bending moment. The advantages and limitations of the RWTR method are discussed by comparing of the calculated results with available wind tunnel measurements and previous numerical simulation results. Several suggestions are provided to improve the performances of this inflow turbulence generation method. The research results are helpful in the evaluation of wind effects on buildings using LES, for which the inflow turbulence matching the characteristics of near-ground turbulence can be conveniently generated based on the proposed method.
Kim, JihoonJang, Kyeong SikLee, Kwan-SupRyu, Jaiyoung...
19页
查看更多>>摘要：This study investigated the variations in aerodynamic drag and the pressure wave effects caused by more than two pods operating in a Hyperloop tube. Three speeds, i.e., 100, 200, and 300 m/s, and two distances between two separate pods, i.e., 43 and 86 m, were simulated using SST k-omega turbulence model. The results indicate that drag of single- and multi-pod systems have similar tendencies that increase with increasing pod speed. For pod speed exceeding the critical Mach number, irrespective of the connectedness or separation of the pods, the last pod always experiences the highest drag. Otherwise, at lower speeds, the differences between the drag acting on each of the pods is negligible. The distance between two pods has a minor influence of less than 4% on the drag. The effects of two different pod shapes, i.e. rectangular and semicircular, on the drag of three connected pods are also small. The average drag per pod was calculated, and it was observed that when more pods were operated, the average drag reduced significantly. The operation of the connected-pod system creates a slightly lower drag than that of a separate-pod system.
查看更多>>摘要：The difference in natural wind characteristics of the tunnel-bridge (TB) and tunnel-flat ground (TF) infrastructure may result in varied aerodynamic behaviours of the high-speed railway train (HSRT). Hence, continuous natural wind sampling is conducted on typical TB and TF sites by using three ultrasonic and one three-cup anemometers. The mean and fluctuating wind characteristics of the two sites are compared and discussed in detail based on field measurement data. The main results can be concluded as follows: Firstly, the prevailing wind direction on the TB site is perpendicular to the running direction of the HSRT due to the occlusion effect, whereas the mean direction on the TF site is easily deflected by the near-ground vegetations and other obstacles. Secondly, the turbulence intensities of the TF site are larger than those of the TB site, and the lognormal distribution is applicable for describing the probability distribution of measured turbulence intensity on the two sites. Thirdly, the von Karman spectrum accurately depicts the wind energy distribution of the TB and TF sites in the frequency domain, whereas the empirical spectrum adopted by the specification show inferior accuracy. Lastly, the coherence distance of the TB site is considerably longer than that of the TF site. The coherence distance of u and v components of the TB site is seven times longer than a train body (approximately 25 m), and that of u component of the TF site is shorter than two times of a train body.
查看更多>>摘要：Crosswind associated with rainfall is a common weather condition, which threatens the operational safety of trains. This paper focuses on an investigation of the effect of crosswind associated with rainfall on train aerodynamics. The methodologies for reproducing the turbulent wind speed and instantaneous rainfall intensity are first described, and the calculation method of unsteady aerodynamic forces of trains operating in a wind-rain environment is set up using the quasi-steady method and weighting function method. Then the CFD technology is used to obtain the aerodynamic load coefficients of a train exposed to a wind-rain environment, and the computational model is verified with the experimental results. Finally, the unsteady aerodynamic load time histories, as well as the corresponding statistical characteristics of the train are investigated. The results demonstrate that the aerodynamic load coefficient is a function of yaw angle, rainfall intensity and wind velocity relative to the train under wind-rain conditions. The aerodynamic loads approximately obey normal distribution both for the quasi-steady method and weighting function method. The mean values of aerodynamic loads obtained by the two methods are almost the same, whereas the standard deviations computed by the weighting function method are smaller than those computed by the quasi-steady method. The dimensionless standard deviations of aerodynamic loads increase with the rainfall intensity, and are approximately linearly related to the rainfall intensity. The wind velocity relative to the train also has an impact on the dimensionless standard deviations of aerodynamic loads, and the impact becomes more obvious when the rainfall intensity increases. The dimensionless standard deviations of the aerodynamic loads can be expressed as quadratic polynomial functions of yaw angle, rainfall intensity and wind velocity relative to the train.
van Vuren, Petrus JansenSinganallur, Nagendrakumar BalasubramanianKeck, HannaEschbaumer, Michael...
7页
查看更多>>摘要：Epithelial tissue or vesicular fluid from an unruptured or recently ruptured vesicle is the sample of choice for confirmatory laboratory diagnosis of foot-and-mouth disease (FMD). However, in 'FMD-free' countries the transport and downstream processing of such samples from potentially infected animals present a biosafety risk, particularly during heightened surveillance, potentially involving decentralised testing in laboratories without adequate biocontainment facilities. In such circumstances, rapid inactivation of virus, if present, prior to transport becomes a necessity, while still maintaining the integrity of diagnostic analytes. Tongue epithelium collected from cattle infected with FMD virus (FMDV) of serotype O (O/ALG/3/2014 - Lineage O/ME-SA/Ind2001d) or A (A/IRN/22/2015 - Lineage A/ASIA/G-VII) was incubated in the PAXGene Tissue System Fixative (pH 4) and Stabiliser (pH 6.5) components respectively, in McIlvaine's citrate-phosphate buffer (pH 2.6) or in phosphate-buffered saline (PBS, pH 7.4) at room temperature for 2, 6, 24 or 48 h. Following incubation, tissues were homogenised and tested by virus isolation and titration using LFBK alpha V beta 6 cells. The integrity of FMD viral RNA was assessed by RT-qPCR (3D(pol) coding region), Sanger sequencing of the VP1 region and transfection of LFBK alpha V beta 6 cells to recover infectious virus. Viable virus could be recovered from samples incubated in PBS for at least 48 h. The PAXgene Tissue System Stabiliser component yielded variable results dependent on virus serotype, requiring at least 6 h of incubation to inactivate A/IRN/22/2015 in most samples, whereas the Fixative component required up to 2 h in some samples. McIlvaine's citrate-phosphate buffer rapidly inactivated both viruses within 2 h of incubation. There was no demonstrable degradation of FMD viral RNA resulting from incubation in any of the buffers for up to 48 h, as assessed by RT-qPCR, and 24 h by sequencing and transfection to recover infectious virus. McIlvaine's citrate-phosphate buffer (pH 2.6) is easy to prepare, inexpensive and inactivates serotype A and O FMDV in epithelial tissue within 2 h, while maintaining RNA integrity for downstream diagnostic processes and virus characterisation.
查看更多>>摘要：In this study, tests and simulations are used to investigate the changes in micro-pressure waves (MPWs) generated by high-speed trains passing through high geo-temperature tunnels. First, moving model tests of highspeed trains passing through local high-temperature tunnels are conducted, and then the simulation results are compared with the experimental results to verify the accuracy of the numerical algorithm. The results show that high temperature reduce the pressure gradient and alleviate MPWs. When the length of the high-temperature zone in the tunnel is within the streamlined length of the train (12.5 m), MPWs decrease as this length increases. When the length exceeds the streamlined length, MPWs basically no longer change. When the length equals the streamlined length and the air temperature in the tunnel reaches approximately 323 K, MPWs are reduced by 9.1%. This paper also presents the influence of the circumferential angle of the tunnel high temperature zone on MPWs. MPWs gradually decrease with increasing heating angle when the angle is less than 225 and remain basically unchanged when the angle is greater than 225. The results provide a method for mitigating MPWs and guidance for scholars who study MPWs mechanism in high geo-temperature tunnels.
Weiler, NinaSampaio, Kerstin LaibStanton, Richard JamesSinzger, Christian...
9页
查看更多>>摘要：Due to strictly cell-associated growth, experiments requiring cell-free virus are not applicable to recent clinical HCMV isolates to date. On the other hand, adaptation to cell-free growth is associated with undesirable changes in the viral gene regions RL13 and UL128. We had previously found that siRNA-mediated reduction of UL128 expression allowed transient release of cell-free virus by clinical isolates, and now hypothesized that virus yield could be further increased by additional knockdown of RL13. Despite the extensive polymorphism of RL13, effective RL13-specific siRNAs could be designed for three recent isolates and the Merlin strain. Knockdown efficiency was demonstrated at the protein level with a Merlin variant expressing V5-tagged pRL13. Knockdown of RL13 alone did not result in measurable release of cell-free virus, but combined knockdown of RL13 and UL128 increased infectivity in cell-free supernatants by a factor of 10-2000 compared to knockdown of UL128 alone. These supernatants could be used in dose-response assays to compare the effect of a neutralizing antibody on the various HCMV isolates. In summary, combined knockdown of RL13 and UL128 by specific siRNAs allows reliable release of cell-free infectivity from otherwise strictly cell-associated HCMV isolates without the need to modify the viral genome.
查看更多>>摘要：It is necessary to discuss particulate matter (PM) diffusion and distribution in open pit mines' dumping operation process. In this paper, the PM migration and distribution under different factors are studied through numerical simulation. The results showed that, the PM downwind diffusion distance decreased as PM density increased during the dumping process. Specifically, when the PM density was 4800 kg/m3, the PM downwind diffusion distance was approximately 58 m, and the PM could not easily be resuspended. The impact of the dumping angle on the PM diffusion distance in the downwind direction was minimal, whilst a large dumping angle increased the PM concentration near the dumping site. Meanwhile, wind speed diluted the PM concentration in the atmospheric environment to a certain extent, the average PM concentration at different heights in the atmospheric environment was lower than 50 mu g/m3 when wind speed reached 4 m/s. The starting mechanism of PM in the dumping operation process of open pit mines may be summarized as collision, wind force, and induced airflow. The results of the present study can provide a theoretical basis for PM control strategies and environmental evaluation in mine dumping operations.
查看更多>>摘要：Aerodynamic admittance is an important parameter for revealing the buffeting force on a vehicle. This paper is the first to present an experimental study on the admittances of moving vehicles under turbulence flow. The power spectrums of the wind velocity experienced by a moving point on the bridge and measured at a stationary point are investigated. The effects of wind velocity power spectrum types, vehicle motion states, and yaw angles on the aerodynamic admittance of a moving vehicle are evaluated, and a simple empirical equation is proposed to fit the aerodynamic admittance. The results indicate that the movement of the measured point has little effect on the vertical component spectrum, but a great effect on the longitudinal component spectrum. Moreover, the admittance defined by using the static wind velocity power spectrum will be underestimated at low frequencies. Static wind tunnel test will overestimate the admittance of the vehicle at low frequencies, and the peaks of the lift and side force admittances of the moving vehicle shift toward higher frequencies, and the value of the lift force admittance at low frequencies is sensitive to the moving speed.
NSTL
Elsevier