Gongcheng Kexue Yu Jishu/Advanced Engineering Science

With the rise of development and utilization of marine resources, inclined pile foundation with good horizontal bearing capacity has been widely used as marine structures such as cross-sea bridge, offshore platform and high pile wharf. Under the action of strong nonlinear superposition of wave and current, severe local scour will occur around the inclined pile, which will reduce the safety of the structure and even lead to structural damage. In order to understand the influence of inclination angle on the scour characteristics of downstream inclined piles under different wave heights and flow velocities, and the difference from that of vertical piles, local scour tests under combined waves and current and pure current were carried out in the wave-current flume. By conducting tests on α=0°, 10°, 20° and 30° downstream inclined piles, the influence of inclination angle on scour duration, relative time scale and scour hole morphology was studied. The influence of dimensionless parameters Fr, KC and Ucw on maximum scour depth of downstream inclined pile was analyzed, and detailed comparison was made with previous vertical pile data. The results showed that when the pile was inclined to downstream, inclination angle had an important influence on the scouring characteristics of pile under combined waves and current. Compared with the vertical pile, with the increase of inclination angle, development rate of scour depth, scale and depth of scour hole gradually decreased, while ralative time scale increased gradually. For the 20° downstream inclined pile, when d50=0.403 mm，Uc=0.206 m/s，H=7 cm, the time for maximum scour depth point to be transferred from lateral front to front was about 60 min, which was much longer than that of a vertical pile. The dune of downstream inclined pile was distributed symmetrically along the central axis and had a bimodal structure, and the scour hole shape was obviously different from that of a vertical pile. Under the condition of moveable bed, regular sand waves were formed on the bed surface, the scour hole scale was further reduced, and the double peaks were more obvious. The relative scour depth of downstream inclined pile was the function of dimensionless parameters Fr, KC and Ucw, which was consistent with the trend for a vertical pile’s fitting curve.

Deflection is the basic data of bridge health monitoring. It can provide quantitative information for both structural safety evaluations and maintenance purposes. By analyzing the relationship between the displacement and its first and second derivatives (inclination and curvature), a method to detect the local stiffness damage of the structure by using the area difference of curvature of the deflection curve before and after the damage was proposed. The area enclosed by the curvature curves before and after damage was divided into several elements, and the ratio of the square of each element area to the sum of the square of all elements area was used as the damage location parameter ΔAκ. The peak value of ΔAκ can locate the damage. As a theoretical example, a simply supported T–beam bridge model with different degrees (5%～50%) and different numbers of local stiffness damage was simulated. By calculating ΔAκ value of each element, the damage in the structure was accurately detected. The method was also applied on a PMMA model bridge in the laboratory. The results showed that ΔAκ value at the damage location was much larger than that at the undamaged location, which could accurately locate the minor local stiffness damage in the structure, and ΔAκ was independent of the damage degree. The damage could be clearly located even in the case of measurement noise. This method is helpful to improve the efficiency of daily safety inspection of bridge, quantify the inspection data, objectify the identification results, and promote the application in actual bridge engineering.

Pipe jacking synchronous grouting is an important method to reduce formation disturbance and final settlement. In order to obtain the relationship between the grouting pressure and the final settlement, find out the reasonable grouting pressure and grouting amount in the actual project to reduce the disturbance of the surrounding stratum, and provide theoretical and experimental supports for the improvements of the synchronous grouting technology, the stratum–mud interaction and the mechanism of settlement from the perspective of the structural characteristics of soil particles and bentonite molecules were analyzed, theoretical assumptions for the four stages of settlement were put forward. Then, the geotechnical engineering centrifuges and self-developed pipe jacking projects were used to simulate the pipe jacking under different grouting pressures on-site. Through the comparative analyses of the settlement curves, the conclusions of the theoretical analysis part were verified. Finally, the relevant parameters such as the grouting pressure in the experiment were applied to the pipe jacking project in Suzhou Donghui Park and the settlement measurement points were arranged on-site, further verified the conclusions. Researches showed that the settlement after grouting can be divided into four stages: soil collapse stage, seepage loss stage, mud skin formation stage and grout uplift stage. The soil collapse stage was short and the settlement speed was fast. Seepage loss stage lasted for a long time and the total settlement was large, which was the main part of the formation settlement. At the mud skin formation stage, the bentonite molecules accumulated on the mud–stratum contact surface to form mud skin, and the slurry was not permeated into the stratum and the settlement of the stratum slowed down. Finally, at the grout uplift stage, the grouting pressure of the mud acted on the mud skin to push the overlying soil and produce settlement compensation. The size of grouting pressure and grouting amount had a great influence on the final settlement. Small grouting pressure and grouting amount would increase the settlement caused by soil collapse and seepage loss, while large grouting pressure would cause excessive settlement compensation effect, even could cause surface uplift. Selecting a reasonable grouting pressure and grouting amount was very important and effective for controlling stratum settlement. It could be used in various pipe jacking projects on-site.

An active control method of trailing edge flap is investigated for suppressing high frequency vibration of wind turbine blades. The structure is modeled as composite blade beam with circumferentially asymmetric stiffness (CAS) configuration, which is based on the analysis of the elastic flap-wise/twist displacements and incorporates the angle control of trailing-edge flap driven by a stepping motor. Aerodynamic expressions of the aeroelastic system are based on a novel quasi-steady model suitable for trailing-edge flap. The partial differential aeroelastic equations of the aeroelastic system are solved based on the discretization function of Galerkin method. The high-frequency vibration of the blade is successfully suppressed by the active control based on the swing angle of the trailing-edge flap. The active control is realized by H∞ algorithm using linear matrix inequality (LMI) design and state observer design. Time-domain stability analysis and robust control method is investigated to realize displacement response analysis and robust performance analysis, and input signal display of trailing-edge flap angle. The optimization is investigated to mechanism of LMI is to optimize uncertain robust performance parameters based on the selection of robust control parameters, so that the controlled displacement and control input are kept within reasonable ranges. In order to reduce the influence of state variable detection error in full state feedback, state reconstruction and state observer are used to improve the control performance. At the same time, the reliability and robustness of H∞ control algorithm based on LMI are verified by comparisons of the results of high-frequency vibration control using different robust performance parameters and different wind speeds. Based on a real-time OPC technology of S7–300 PLC and WinCC configuration software, a process control experiment is adopted to verify the feasibility of the control algorithm in the engineering application. A real-time engineering application feasibility scheme is provided for the control method that cannot be conventionally implemented in the controller hardware due to the complexity of the intelligent control algorithm.

Hysteresis is one of the important characteristics of automatic adjustment of river system, while there are few studies on the law of sediment delayed response in the Three Gorges Reservoir (TGR). Based on the delayed response model, the measured data were analyzed and the delayed response model was modified by considering the sediment concentration and sediment particle size in order to construct the delayed response model in accordance with the characteristic of sediment deposition in TGR. Firstly, the changes of water and sediment conditions and sediment deposition characteristics since the impoundment of TGR were counted, and the influence of cascade reservoirs in the upper Yangtze River was analyzed. In order to simulate and analyze the sedimentation delayed response law in different periods of TGR, the existing model was used and modified. Based on the existing and modified response model simulation results, it can be seen that 1) The modified response model can better simulate the sediment deposition process of TGR after the impoundment of cascade reservoirs because of the consideration of sediment concentration and sediment particle size. 2) After the impoundment of cascade reservoirs, the fluctuation range of inflow and sediment decreases, the sediment inflow of TGR is more concentrated in flood season, both of which make the channel adjustment rate increase, the delayed response time of sediment deposition in TGR is shortened from the early 4 years to the early 3 years. 3) After the impoundment of cascade reservoirs, the influence weight of sediment concentration on the sediment deposition process increases, while the influence weight of flow and water level in front of dam decreases. By using the modified model, it can be seen that the inflow of sediment concentrates more in the flood season, which make the delayed response time of sedimentation in TGR shorten, and the influence weight of sediment on the sediment deposition increases.