Aerodynamic Study of a NACA 64418 Rectangular Wing under Forced Pitching Motions

The aerodynamic behavior of a pitching NACA 64418 rectangular wing was experimentally studied in a subsonic wind tunnel. The wing had a chord c = 0.5 m, a span which covered the distance between the two parallel tunnel walls and an axis of rotation 0.35 c far from the leading edge. Based on pressure distribution and flow visualization, intermittent flow separation (double stall) was revealed near the leading edge suction side when the wing was stationary, at angles higher than 17° and Re = 0.5 × 106. Under pitching oscillations, aerodynamic loads were calculated by integrating the output data of fast responding surface pressure transducers for various mean angles of attack (αm (max) = 15°), reduced frequencies (kmax = 0.2) and angle amplitudes Δα in the interval [2°, 8°]. The impact of the above parameters up to Re = 0.75 × 106 on the cycle-averaged lift and pitching moment loops is discussed and the cycle aerodynamic damping coefficient is calculated. Moreover, the boundaries of the above parameters are defined for the case that energy is transferred from the flow to the wing (negative aerodynamic damping coefficient), indicating the conditions under which aeroelastic instabilities are probable to occur.

Segment Stress Characteristics and Ground Deformation Caused by Constructing Closely Spaced Parallel Tunnels under a Complex Geological Condition

Ground deformation and additional stress on the segments of the firstly constructed tunnel may change significantly due to the construction of another tunnel, which is closely spaced with the existing one. A poor geotechnical condition possibly leads to the interaction between such closely spaced tunnels even making it harder to build such tunnels. A practical project located in Guangzhou City, China, consists of such two parallel tunnels with the smallest distance of 2.6 m, which sat on an upper-soft and lower-hard stratum. A 3D finite element model has been proposed to numerically investigate the behavior of these two parallel tunnels. The numerical results predicted by the FE model are in close agreement with that obtained from the field monitoring system, indicating the accuracy of the proposed FE model. The FE model was then used to further analyze the effect of reinforcing piles in eliminating the detrimental effect on both ground deformation and additional stress of the segments of the existing tunnel as a result of the construction of the new parallel tunnel. The research results obtained from the present paper can provide technical support and guidance for urban subway construction.

Numerical Analysis on Influence of Subway Double-Hole Parallel Tunnel Deployment on Surrounding Soil Distortion

construction of near double-hole parallel tunnels frequently occurs in city subway evacuation. Studying the dynamical behaviors of the parallel tunnel construction, performing systematic numerical analysis and grasping mutual influences of different factors on the tunnel evacuation and different effects of surface sedimentation has important theoretical meaning and application value for the building technology of the parallel double-hole tunnel. This paper establishes a three-dimensional numeral model, analyzes influences of three main influence factors (tunnel distribution form, tunnel burying depth and tunnel gap) on the surrounding soil and surface sedimentation in double-hole tunnel synchronous evacuation. The conclusions indicate that the vertical distribution has the biggest influences on tunneling in horizontal distribution, vertical distribution and tilted distribution of two tunnels, followed by tilted distribution. The horizontal distribution has the minimal influence. With growth of the tunnel gap, the mutual influence between two tunnels will become smaller. With growth of the tunnel burying depth, the influences on tunneling will become bigger.

Numerical Analysis on Mutual Influences in Urban Subway Double-Hole Parallel Tunneling

mutual influence of the double-hole tunnel evacuation of urban subways is one of key issues involving the subway construction safety. The asynchronous one-direction evacuation, synchronous one-direction evacuation and opposite evacuation methods are frequently used in double-hole tunnel evacuation. This paper establishes three-dimensional numerical model by using the finite element analysis software MIDAS/GTS v2.01 and mainly studies the mutual influences of tunnels in the asynchronous one-direction evacuation and synchronous one-direction evacuation. The following conclusions are concluded based on computing. The preliminary conclusion is that the influential distance between the evacuation section of two tunnels is 3D (D is the tunnel diameter) in the parallel tunnel asynchronous evacuation, namely when the lagging distance is more than 3D, the lagging evacuation tunnel will not affect the advance evacuation tunnel section. The asynchronous evacuation of the vertical distribution tunnel is divided into the up tunnel first evacuation and down tunnel first evacuation. For up tunnel first evacuation, the influence range of the lagging distance is 5D. For down tunnel first evacuation, the influence range of the lagging distance is 1D. For up tunnel first evacuation on the slope, the influence range of the lagging distance is 5D. On the whole, the influence of two tunnels in up tunnel first evacuation is bigger than it in down tunnel first evacuation. The numerical analysis results will have important theoretical meaning and application value for building technology of the parallel double-hole tunnel.

The Vibration Influence on the Surrounding Ground by Four-Holes Parallel Tunnel

With the development of thetimes, the floor space has been unable to meet human requirements, bututilization of urban underground space has become a kind of choice to solvevarious problems. In recent years, many international organizations andresearch institutions have begun to develop urban underground space, and otherissues have been discussed in a number of meetings. As a new type of transportation, subwaycan effectively solve traffic congestions. This paper applies a kind of computer-aided Engineering,like ANSYS, to establish three-dimensional finite element model offour-hole parallel tunnel, Loadingthe subway train, andthen calculating, finally analyzing rules of vibrationof the surrounding ground of four-hole parallel tunnel when the subway is working.