Analysis of flow and aerodynamic noise behaviour of a simplified high-speed train bogie inside the bogie cavity

Aerodynamic noise becomes significant for high-speed trains but its prediction in an industrial context is difficult. The flow and aerodynamic noise behaviour of a simplified high-speed train bogie at scale 1:10 are studied here through numerical simulations. The bogie is situated in the bogie cavity and cases without and with a fairing are considered, allowing the shielding effect of the bogie fairing on sound generation and radiation to be investigated. A two-stage hybrid method combining computational fluid dynamics and acoustic analogy is applied. The near-field unsteady flow is obtained by solving the unsteady three-dimensional Navier-Stokes equations numerically using delayed detached-eddy simulation and the data are utilized to predict far-field noise signals based on the Ffowcs Williams-Hawkings acoustic analogy. Results show that when the bogie is located inside the bogie cavity, the shear layer developed from the cavity leading edge interacts strongly with the flow separated from the bogie upstream components and the cavity wall. Therefore, a highly turbulent flow is generated within the bogie cavity due to flow impingement and recirculation within the cavity. It is found that, for noise calculated from the bogie surface sources of both cases, the directivity exhibits a lateral dipole pattern with dominant radiation in the axial direction. Compared with the no fairing case, the noise level is about 1 dB higher in the bogie symmetry plane along the axle mid-span for the fairing case where a stronger flow interaction is produced around the bogie central region. Moreover, the noise radiated to the trackside is predicted based on a permeable integration surface close to the bogie and parallel to the carbody side wall. The results show that the bogie fairing is effective in reducing the noise levels in most of the frequency range due to its shielding effect and a noise reduction around 3 dB is achieved for the current model case by mounting a fairing in the bogie area

Influence of cilostazol on thromboangiitis obliterans in rats and the mechanism involved

Purpose: To study the effect of Cilostazol on rat thromboangiitis obliterans (TAO), and the mechanism of action involved. Methods: Rats (N = 45) were injected with sodium laurate to establish the model of TAO, and then divided into Sham group (n = 15), TAO group (n = 15) and TAO + cilostazol group (n = 15). After administration of cilostazol, TAO lesions in the rats were graded, and the femoral arteries were stained by hematoxylin-eosin (H&E) to determine the degree of vascular lesions. The status of vascular endothelial cells was determined using transmission electron microscopy. Furthermore, the expression and transcription levels of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) proteins were evaluated by Western blotting and real-time polymerase chain reaction (RT-PCR) respectively. Results: In contrast to Sham group, TAO group exhibited symptoms such as changes in skin temperature and color, and limb swelling and thanatosis, while in the TAO + cilostazol group, the damage was reversed, vascular and vascular endothelial cell lesions were significantly ameliorated (p < 0.05), and the transcription and translation levels of HIF-1α and VEGF significantly suppressed (p < 0.05). Conclusion: Cilostazol alleviates sodium laurate-induced TAO lesions in rats via HIF-1α/VEGF pathway. This study may provide new insights for the treatment of TAO. Keywords: Cilostazol; Hypoxia-inducible factor/vascular endothelial growth factor pathway; Thromboangiitis obliterans; Limb swelling; Thanatosi

Flow simulation and aerodynamic noise prediction for a high-speed train wheelset

Aerodynamic noise becomes significant for high-speed trains and its prediction in an industrial context is hard to achieve. The aerodynamic and aeroacoustic behaviour of the flow past a highspeed train wheelset, one of the main components of a bogie, are investigated at a scale 1:10 using a two-stage hybrid method of computational fluid dynamics and acoustic analogy. The near-field unsteady flow is obtained by solving the Navier-Stokes equations numerically through delayed detached-eddy simulations and the results are fed to predict the far-field noise signals using the Ffowcs Williams-Hawkings acoustic analogy. Far-field sound radiated from the scaled model is also measured in a low noise open-jet anechoic wind tunnel. Good agreement is achieved between numerical and experimental results for the dominant frequency of tonal noise and the shape of the spectra. Results show that turbulent flow past the wheelset is characterized by three-dimensional streamwise and spanwise vortices with various scales and orientations. Vortex shedding and flow separation around the wheelset are the key factors for the aerodynamic noise generation. It is found that the radiated tonal noise corresponds to the dominant frequencies of the oscillating lift and drag forces from the wheelset. The directivity of the noise radiated exhibits a typical dipole pattern. As the inflow velocity increases, the shedding frequency scales with the freestream velocity and the axle diameter to yield a Strouhal number of 0.18 while the noise levels increase noticeably. For the current wheelset case investigated without considering the ground effect, the inclusion of wheelset rotation increases the radiated noise levels slightly with similar directivit

Flow behaviour and aeroacoustic characteristics of a simplified high-speed train bogie

Aerodynamic noise becomes significant for high-speed trains and its prediction in an industrial context is difficult to achieve. The aerodynamic and aeroacoustic behaviour of the flow past a simplified high-speed train bogie at scale 1:10 is studied using a two-stage hybrid method comprising computational fluid dynamics and acoustic analogy. The near-field unsteady flow is obtained by solving the Navier-Stokes equations numerically with the delayed detached-eddy model and the results are used to predict the far-field noise through the Ffowcs Williams-Hawkings method. The sound radiated from the same scaled bogie model is measured in an anechoic open-jet wind tunnel. The aeroacoustic characteristics of tandem wheelsets are also investigated for comparison. It is found that the unsteady flow past the bogie is characterized by coherently alternating vortex shedding from the axles and more randomly distributed vortices of various scales and orientations from the wheels and frame. The vortices formed behind the upstream geometries are convected downstream and impinge on the downstream bodies, generating a highly turbulent wake behind the bogie. The noise predictions correspond fairly well with the experimental measurements for the dominant frequency of tonal noise and the shape of spectra. Vortex shedding from the axles generates the tonal noise with the dominant peak corresponding to the vortex shedding frequency. The directivity exhibits a dipole shape for the noise radiated from the bogie. Compared to the wheelsets of the bogie, the noise contribution from the bogie frame is relatively weaker

Resource Allocation for Hybrid NOMA MEC Offloading

Non-orthogonal multiple access (NOMA) and mobile edge computing (MEC) have been recognized as promising technologies for the beyond fifth generation networks to achieve significant capacity improvement and delay reduction. In this paper, the technologies of hybrid NOMA and MEC are integrated. In the hybrid NOMA MEC system, multiple users are classified into different groups and each group is allocated a dedicated time slot. In each group, a user first offloads its task by sharing a time slot with another user, and then solely offloads during a time interval. To reduce the delay and save the energy consumption, we consider jointly optimizing the power and time allocation in each group as well as the user grouping. As the main contribution, the optimal power and time allocation is characterized in closed form. In addition, by incorporating the matching algorithm with the optimal power and time allocation, we propose a low complexity method to efficiently optimize user grouping. Simulation results demonstrate that the proposed resource allocation method in the hybrid NOMA MEC systems not only yields better performance than the conventional OMA scheme but also achieves quite close performance as global optimal solution

Power Efficient IRS-Assisted NOMA

In this paper, we propose a downlink multiple-input single-output (MISO) transmission scheme, which is assisted by an intelligent reflecting surface (IRS) consisting of a large number of passive reflecting elements. In the literature, it has been proved that nonorthogonal multiple access (NOMA) can achieve the same performance as computationally complex dirty paper coding, where the quasi-degradation condition is satisfied, conditioned on the users’ channels fall in the quasi-degradation region. However, in a conventional communication scenario, it is difficult to guarantee the quasi-degradation, because the channels are determined by the propagation environments and cannot be reconfigured. To overcome this difficulty, we focus on an IRS-assisted MISO NOMA system, where the wireless channels can be effectively tuned. We optimize the beamforming vectors and the IRS phase shift matrix for minimizing transmission power. Furthermore, we propose an improved quasi-degradation condition by using IRS, which can ensure that NOMA achieves the capacity region with high possibility. For a comparison, we study zero-forcing beamforming (ZFBF) as well, where the beamforming vectors and the IRS phase shift matrix are also jointly optimized. Comparing NOMA with ZFBF, it is shown that, with the same IRS phase shift matrix and the improved quasi-degradation condition, NOMA always outperforms ZFBF. At the same time, we identify the condition under which ZFBF outperforms NOMA, which motivates the proposed hybrid NOMA transmission. Simulation results show that the proposed IRS-assisted MISO system outperforms the MISO case without IRS, and the hybrid NOMA transmission scheme always achieves better performance than orthogonal multiple access

Screening of specific diagnostic peptides of swine hepatitis E virus

© 2009 Zhao et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Flow between the train underbody and trackbed around the bogie area and its impact on ballast flight

The aerodynamic behaviour of flow past a simplified high-speed train bogie including the ground underneath with ballast particles at scale 1:10 is studied numerically. It is found that the flow around the bogie is highly unsteady due to strong flow separations and flow interactions developed there. Generally, the ballast particles distributed inside the wheels are situated in the stronger turbulent flow and are subject to much higher aerodynamic forces than the particles located outside the wheels. Moreover, these aerodynamic forces increase when the ballast particles are located downstream of the bogie cavity and reach the peak values close to the bogie cavity trailing edge. Force time-series are produced based on the simulations of an array of the ballast particles in a wind-tunnel setup and it shows that the ballast flight is apt to happen as the rear part of the bogie cavity passing the ballast bed. When the ballast particles become airborne, the fluctuating forces generated increase significantly. Therefore, the stronger unsteady flow developed around the bogie cavity, especially in the cavity trailing edge region, will produce larger fluctuating forces on the ballast particles, which will be more likely to cause ballast flights for high-speed railways