| 1. |
- Chen, Zheng wei, et al.
(författare)
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Reducing the aerodynamic drag of high-speed trains by air blowing from the nose part: Effect of blowing speed
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- To reduce the aerodynamic drag of high-speed trains, this work proposes an air blowing configuration on the head and tail cars of high-speed trains. The variation in the aerodynamic drag and slipstream velocity is analyzed under different blowing velocities, and the flow mechanism for train aerodynamic performance alteration is explained. The results show that under the blowing speeds of Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, where Ut is the train speed, the total drag coefficient (Cd) decreases by 5.81%, 10.78%, 13.70%, and 15.43% compared to the without-blowing case, respectively. However, with the increase in the blowing speed, the reduction trend of Cd tends to be smoother; namely, the decrement ratio compared to the previous blowing speed for the head car is 9.08%, 0.11%, 0.60%, and 1.14% for Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, respectively. The blowing measure generates an air gap between the coming flow and train surface, consequently causing a reduction in the viscous and pressure drag. In addition, the structure size and strength of the wake flow under different blowing cases show a decreasing trend from Ub = 0.00Ut to 0.10Ut and then an increasing trend from Ub = 0.10Ut to 0.20Ut. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of Ub = 0.10Ut is recommended. Under this blowing speed, the reduction ratio of the aerodynamic drag is 9.18%, 12.77%, 10.90%, and 10.78% for the head, middle, tail car, and total train, respectively.
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| 2. |
- Ding, Li, et al.
(författare)
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Somatic mutations affect key pathways in lung adenocarcinoma
- 2008
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 455:7216, s. 1069-1075
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Tidskriftsartikel (refereegranskat)abstract
- Determining the genetic basis of cancer requires comprehensive analyses of large collections of histopathologically well-classified primary tumours. Here we report the results of a collaborative study to discover somatic mutations in 188 human lung adenocarcinomas. DNA sequencing of 623 genes with known or potential relationships to cancer revealed more than 1,000 somatic mutations across the samples. Our analysis identified 26 genes that are mutated at significantly high frequencies and thus are probably involved in carcinogenesis. The frequently mutated genes include tyrosine kinases, among them the EGFR homologue ERBB4; multiple ephrin receptor genes, notably EPHA3; vascular endothelial growth factor receptor KDR; and NTRK genes. These data provide evidence of somatic mutations in primary lung adenocarcinoma for several tumour suppressor genes involved in other cancers--including NF1, APC, RB1 and ATM--and for sequence changes in PTPRD as well as the frequently deleted gene LRP1B. The observed mutational profiles correlate with clinical features, smoking status and DNA repair defects. These results are reinforced by data integration including single nucleotide polymorphism array and gene expression array. Our findings shed further light on several important signalling pathways involved in lung adenocarcinoma, and suggest new molecular targets for treatment.
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| 3. |
- Lv, Dazhou, et al.
(författare)
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Numerical study on transient aerodynamic characteristics of high-speed trains during the opening of braking plates based on dynamic-overset-grid technology
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- The safety of high-speed trains is considerably compromised by increasing speed trends. Thus, braking plate technology has been applied to high-speed trains. The purpose of this study is to clarify the evolution law of the flow field of the vehicle during the opening of the braking plate and analyze the influence of the plate movement on the aerodynamic performance of the train. In this study, the flow field was computed using incompressible Navier–Stokes equations and the shear-stress transport (SST) k–ω turbulence model, and the unsteady flow over the opening brake plates was simulated using moving overlapping grids and dual time-stepping. The numerical method was verified through comparison with wind tunnel data (error <8%). The results reveal that the upstream braking plate significantly decreases the aerodynamic forces of the downstream plate during opening of the plates and causes the aerodynamic drag of the downstream braking plate to fluctuate significantly when it increases. The operation of the braking plate produces a small increase in the drag force of the train body (2.6%), but it significantly decreases the lift force of the train body (by up to 94%), especially during the opening of the braking plates. The flow field in the upper part of the train is significantly changed by the opening of the braking plate. In particular, the pressure in the cavity of the braking device changes sharply, and the surface is subjected to a large pulse pressure.
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| 4. |
- Niu, Jiqiang, et al.
(författare)
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Aerodynamic simulation of effects of one- and two-side windbreak walls on a moving train running on a double track railway line subjected to strong crosswind
- 2022
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- High-speed railway lines are widely distributed worldwide. The surrounding wind environment of such railway lines is complex, which significantly affects the safety of high-speed train operations. Using a combination of the computational fluid dynamics method of improved delayed detached eddy simulation and sliding grid technology, the effects of one- and two-side windbreak walls on the unsteady aerodynamic performance of a high-speed train running under a crosswind on a double-track railway line with an embankment and the flow-field characteristics around the train were systematically studied. The grid independence and numerical methods used in this study were verified. The results showed that when the windbreak wall was absent, the aerodynamic performance of the train running on the upstream railway line was the poorest, while the train running on the downstream railway line exhibited large aerodynamic fluctuations. The windbreak wall significantly reduced the aerodynamic force and its fluctuation; the one- and two-side windbreak walls had different effects on the unsteady aerodynamic performance of trains running on the upstream and downstream railway lines under a crosswind. The one-side windbreak wall could restrain the aerodynamic fluctuation of the train more and is thus preferred from the perspective of construction effort and cost.
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| 5. |
- Niu, Jiqiang, et al.
(författare)
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Investigation of aerodynamic behaviour of a high-speed train on different railway infrastructure scenarios under crosswind
- 2022
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Ingår i: Wind and Structures, An International Journal. - 1598-6225 .- 1226-6116. ; 35:6, s. 405-418
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic behaviour of a CRH high-speed train under three infrastructure scenarios (flat ground, embankment, and viaduct) in the presence of a crosswind was simulated using a 1/8th scaled train model with three cars and the IDDES framework. The time-averaged and instantaneous flow field around the model were examined. The employed numerical algorithm was verified through a wind tunnel test, and the grid and timestep resolution analyses were conducted to ensure the reliability of the data. It was noted that the flow around the rail line was different under different infrastructure scenarios, especially in the case of the embankment, which degraded the aerodynamic performance of the train under the crosswind. The flow around the train on the flat ground and viaduct was different, although the aerodynamic performance of the train was similar in both cases. Moreover, the viaduct accidents were noted to have the most critical consequences, thereby requiring the most attention. The aerodynamic performance of the train on the windward track of the embankment under the crosswind was worse than that of the train on the leeward track. But for the other two infrastructure scenarios, the aerodynamic performance of the train on the windward track is relatively dangerous, which is mainly caused by the head car. These observations suggest that the aerodynamic behaviour of the train on an embankment under a crosswind must be carefully considered and that certain wind protection measures must be adopted around rail lines in windy areas.
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| 6. |
- Niu, Jiqiang, et al.
(författare)
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Numerical investigation on application of train body airflow diversion device to suppress pressure waves in railway high-speed train/tunnel system
- 2023
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Ingår i: International Journal of Rail Transportation. - : Informa UK Limited. - 2324-8386 .- 2324-8378. ; 11:4, s. 490-507
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Tidskriftsartikel (refereegranskat)abstract
- The development of the high-speed maglev train (HSMT) is important for the future of high-speed rail transit. A pressure wave (PW) is a common aerodynamic effect in high-speed railway tunnels. For HSMTs with a speed of 600 km/h, the amplitude of PW in the tunnel can be very big, which maybe far exceed the current design strength standard of the train body structure and seriously threatens the safety of the railway train/tunnel structure and passenger ear comfort. Therefore, aerodynamic PWs caused by a two-dimensional axisymmetric model with an ellipsoidal nose passing through a tunnel was investigate, and the numerical method adopted in this study was validated by two scaled moving model tests. The PWs caused by trains in four cases and the effects of train speed and tunnel length were analysed and compared. Some results show that diversion device significantly reduces the amplitude of the PWs (Delta C-p) on the train surface and tunnel wall. The diversion device on the train tail (C4) not only changes Delta C-p, but also changes the waveform. The diversion device on the train tail (C3) and diversion device on both train head and tail which are connecting each other (C2) mainly reduced the Delta C-p. When the decrease in both PWs on the train surface and tunnel wall is considered, C2 has the best effect. With an increase in the train speed, the effect of C2 on restraining the PW on the train surface and tunnel wall increases to a certain extent. However, the restraining effect on the micro-pressure wave (MPW) at the tunnel exit does not exceed 5%. The suppression effect of C2 on Delta C-p on the train surface and tunnel wall decreases with an increase in the tunnel length. However, it does not change the distribution law of Delta C-p along the train and tunnel. This study can provide a reference for the design of the body of HSMTs and the suppression of PW in tunnels.
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| 7. |
- Shao, Xinyuan, 1997, et al.
(författare)
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Near-wall approximations to speed up simulations for atmosphere boundary layers in the presence of forests using lattice Boltzmann method on GPU
- 2022
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Forests play an important role in influencing the wind resource in atmospheric boundary layers and the fatigue life of wind turbines. Due to turbulence, a difficulty in the simulation of the forest effects is that flow statistical and fluctuating content should be accurately resolved using a turbulence-resolved CFD method, which requires a large amount of computing time and resources. In this paper, we demonstrate a fast but accurate simulation platform that uses a lattice Boltzmann method with large eddy simulation on Graphic Processing Units (GPU). The simulation tool is the open-source program, GASCANS, developed at the University of Manchester. The simulation platform is validated based on canonical wall-bounded turbulent flows. A forest is modelled in the form of body forces injected near the wall. Since a uniform cell size is applied throughout the computational domain, the averaged first-layer cell height over the wall reaches to ⟨Δy+⟩=165. Simulation results agree well with previous experiments and numerical data obtained from finite volume methods. We demonstrate that good results are possible without the use of a wall-function, since the forest forces overwhelm wall friction. This is shown to hold as long as the forest region is resolved with several cells. In addition to the GPU speedup, the approximations also significantly benefit the computation efficiency.
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| 8. |
- Shao, Xinyuan, 1997, et al.
(författare)
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Near-wall modeling of forests for atmosphere boundary layers using lattice Boltzmann method on GPU
- 2022
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 16:1, s. 2142-2155
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the simulation and modeling of the turbulent atmospheric boundary layers (ABLs) in the presence of forests are studied using a lattice Boltzmann method with large eddy simulation, which was implemented in the open-source program GASCANS with the use of Graphic Processing Units (GPU). A method of modeling forests in the form of body forces injected near the wall is revisited, while the effects of leaf area density (LAD) on the model accuracy is further addressed. Since a uniform cell size is applied throughout the computational domain, the wall-normal height of the near-wall cells is very large, theoretically requiring a wall function to model the boundary layer. However, the wall function is disregarded here when the forest is modeled. This approximation is validated based on the comparison with previous experimental and numerical data. It concludes that for the ABL conditions specified in this study as well as a large body of literature, the forest forces overwhelm the wall friction so that the modeling of the latter effect is trivial. Constant and varying LAD profiles across the forest zone are defined with the same total leaf area despite the varying one being studied previously. It is found that the two LAD profiles provide consistent predictions. The present forest modeling can therefore be simplified with the use of the constant LAD without degrading the model accuracy remarkably.
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| 9. |
- Venkatesh, Aravindhan, 1997, et al.
(författare)
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Coexistence of passive vortex-induced vibrations and active pitch oscillation triggered by a square cylinder attached with a deformable splitter plate
- 2024
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Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:4
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Tidskriftsartikel (refereegranskat)abstract
- To understand passive vortex-induced vibrations (VIV) coexisting with active structure motions, this paper numerically investigates the use of pure pitch oscillation to control a square cylinder mounted with a deformable splitter plate at the Reynolds number of 333. The oscillation is enforced with an amplitude of 3° and different frequencies from 0 to 6 Hz. Direct numerical simulations using a partitioned method with a semi-implicit coupling algorithm are performed. According to the trajectories of the splitter-plate tip displacement with respect to the lift or drag force coefficient, a specific lock-in regime determined by the frequency of the enforced pitch oscillation is identified. Further spectral analyses of the tip displacement and lift force show that the lock-in frequencies are equal to the enforced frequencies. Next to the lock-in regime, semi-lock-in regimes with narrow bandwidths are distinguished, exhibiting both lock-in and non-lock-in features. In the non-lock-in regimes, the frequencies of the most predominant peaks in the spectra are found near the natural frequency of the splitter plate of 3.236 Hz, and the frequencies of the two secondary peaks are distributed along the characteristic lines following the ratios of these frequencies to the enforced frequency, which are ±1. Thus, the interaction is dependent on the combined effects of the passive VIV and the actively enforced pitch oscillations. Moreover, the intersection points of the characteristic lines are located close to the upper and lower frequency limits of the lock-in regime, inferring the conditions for the lock-in onset.
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| 10. |
- Venkatesh, Aravindhan, 1997, et al.
(författare)
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Vortex-induced vibrations of a deformable splitter plate behind a square cylinder controlled by active pitch oscillation
- 2023
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Vortex-induced vibrations (VIV) widely occur in nature and are of interest for energy harvesting and bio-inspired propulsion. To understand passive VIV coexisting with active structure motions, this paper is motivated to numerically investigate the use of pure pitch oscillation to control a square cylinder mounted with a deformable splitter plate at the Reynolds number of 333. Direct numerical simulations using a partitioned method with a semi-implicit coupling algorithm are performed. According to the trajectories of the splitter-plate tip displacement with respect to the lift or drag force coefficient, a specific lock-in regime determined by the frequency of the enforced pitch oscillation is identified. Further spectral analyses of the tip displacement and lift force show that the lock-in frequencies are equal to the enforced frequencies. Next to the lock-in regime, semi-lock-in regimes with narrow bandwidths are distinguished, exhibiting both lock-in and non-lock-in features. In the non-lock-in regimes, the frequencies of the most predominant peaks in the spectra are found near the natural frequency of the splitter plate, and the frequencies of the two secondary peaks are distributed along the characteristic lines following the ratios of these frequencies to the enforced frequency, which are ±1. Thus, the interaction is dependent on the combined effects of the passive VIV and the actively enforced pitch oscillations. Moreover, the intersection points of the characteristic lines are located close to the upper and lower frequency limits of the lock-in regime, inferring the conditions for the lock-in onset.
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