Abstract:In this study, a hydrological model parameter optimization scheme was constructed in SWAT based on streamflow assimilation using the ensemble Kalman filter(EnKF)approach, in which the model simulation and streamflow observation errors were reasonably quantified and the model parameter evolution and over-fitting issues were effectively treated. Based on this scheme, the capacity of streamflow assimilation on SWAT model parameter optimization was evaluated in the upper Huai River above Huaibin hydrological station. The results showed that the updated parameter ensemble gradually converged and stabilized during the data assimilation process. The runoff process based on the stabilized parameter ensemble was close to the measured runoff. The deterministic coefficient at the outlet of the basin reached 0. 88. The results indicated that the EnKF based streamflow assimilation had the ability to optimize the parameters in SWAT. It was feasible to calibrate model parameters using data assimilation method.

Abstract:In order to study the effect of start-up combinations on the flow field characteristics of water-sediment in the inflow forebay of multi-sand water source pumping station, taking a typical pumping station in Jingdian irrigation area as a research object, the three-dimensional geometric model of the forebay of pumping station in the siltation condition was reconstructed by using reverse engineering technology based on the Realizable k-ε model and the Mixture model considering the phase slip. The numerical simulation of water-sediment two-phase flow in the in-situ pumping station forebay is carried out using FLUENT software and the reliability of the numerical model is verified by comparing the simulation and measured results. Based on this, the numerical simulations of the water-sand flow field characteristics of the pumping station forebay under non-siltation conditions with different start-up combinations were carried out. The results show that flow pattern disorder and serious sediment deposition exist in the forebay of in-service in-situ pumping station. The numerical simulation of flow pattern in in-situ forebay agrees well with field measurement results. The significant mainstream effect and a large low speed recirculation zone exsit in forebay of in-service prototype pumping station. With the start-up of the units at both ends of the pumping station, the diffusion effect of the mainstream in the forebay is improved, the flow field distribution tends to be symmetrical, and the sediment silt situation is slightly improved.

Abstract:In order to investigate the evolution mechanism of scour process around the mono-pile foundation of a tidal stream turbine, a series of physical tests in a flume were conducted. The influence mechanism of flow intensity were studied and the results were compared with that induced by a single mono-pile. The experimental results reveal that the scour process around the mono-pile foundation of a tidal stream turbine gradually develops with a periodic fluctuation. The presence of the rotor is found to accelerate the scour process and deepen the maximum scour depth. Meanwhile, the maximum scour depth increases linearly with the increasing flow intensity and the fluctuation amplitude also increases with the increase of flow intensity. Compared to the directional flow, the bidirectional flow reduces the scour depth around the mono-pile foundation of a tidal stream turbine. However, their difference gradually decreases with the increase of flow intensity.

Abstract:To study the effect of perforation rate of vertical baffle on the liquid sloshing characteristics, a six-degree-of-freedom motion simulation platform was used to conduct a series of sloshing lests in a rectangular tank with the bafles of different perforation rate. The external excitation frequency values are 0. 8~1. 2 time the first-order natural frequency of the tank. The results show that the perforated baffle with a porosity of 0. 1 is better than an unperforated bafle in reducing the maximum sloshing wave height and the maximum impact pressure at some places under different external excitation frequencies. The damping effect on sloshing of the perforated baffle increases with the decrease of the perforation rate. When the external excitation frequeney is the natural frequeney, the main frequency component of the sloshing wave height is the same as the external excitation frequency. When the external excitation frequency is not the natural frequency, the main frequeney of the sloshing wave height also has a frequency multiplication, and the frequency multiplication gradually disappears with the increase of the perforation rate.

Abstract:In order to investigate the anti-seepage characteristics of Sidraton particles under different cover conditions, three earth rock-fill dam models with different hidden trouble of leakage were constructed. Sidradon particles with different blanket thickness and different blanket area were covered in the seepage area of dam surface and the change of seepage flow with time was recorded. The experiment shows that after covering the Sidraton particles, the seepage flow of the three leakage models decreases exponentially with time. The seepage flow of the contact leakage model decreases the most, and the seepage flow of the reservoir bottom leakage model decreases slowly. With the increase of blanket thickness, the anti-seepage effect of the three leakage models is enhanced. For the contact leakage model and the concentrated leakage model, the anti-seepage effect decreases with the increase of the blanket area. Hydrated Sidraton particles with a good anti-seepage ability can be used to prevent and repair the leakage of dam.

Abstract:The linear dispersion and shoaling coefficients of a set of high-order Boussinesq-type equations are optimized, which significantly improves the linear dispersion and linear shoaling performance of the original equations. The sum of error squares between the phase velocity of the high-order Boussinesq-type equations and the linear wave phase velocity is minimized to optimize the dispersion coefficients of the equation for kh=6. 28, with k as the wave number and h as the water depth. The shoaling coefficients are determined according to the linear shoaling analysis. The linear dispersion and shoaling performance of the Boussinessq-type equations with different sets of coefficients is presented. A numerical model with a time difference format of mixed fourth-order Adam-Bashforth-Moulton is constructed based on non-staggered grid. The numerical model is applied to simulate the wave propagation and evolution on the submerged breakwater, and the simulation results using the optimized coefficients proposed by present work are in much better agreement with the experimental data.

Abstract:In view of the permeable sloping breakwaters in the practical engineering, wave transmission characteristics of the sloping breakwater were analyzed without considering the overtopping, by using the combined methods of physical experiments and numerical simulations. The relationship between the wave transmission coefficient of sloping breakwater and multiple wave parameters for breakwater and incident wave were mainly discussed, including the particle size of core material and relative dike width of breakwater body as well as the wave height, wave period, and wave steepness of incident waves. The semi-empirical formulas of wave transmission coefficient under regular wave and irregular wave actions for a sloping breakwater were fitted, respectively. Good agreement between the calculated results and the experiment results was achieved, which demonstrates that the proposed formulas can estimate the wave transmission coefficient of permeable sloping breakwater.

Abstract:The large eddy simulation model is used to simulate the three-dimensional sinusoidal oscillating jet in the cross flow environment. The differences of motion characteristics and dilution law between the non-oscillating jet and the oscillating jet in the cross flow environment were analyzed, and the influence of oscillating parameters of the jet was discussed. The results show that the shape of oscillating jet is obviously different from that of non-oscillating jet in the cross flow environment, and its trajectory is bent, showing an obvious “intermittent effluent cloud” phenomenon. Compared with the non-oscillating jet, the impact height and bending degree of the oscillating jet are significantly increased, and the mixing with surrounding water is intensified. With the increase of oscillating amplitude, the impact height and minimum dilution of the jet increase. In general, the oscillating jet is beneficial to the dilution of pollutants in the cross flow environment.

Abstract:For long-span suspension bridge, in order to evaluate the expansion function of bridge more accurately and discover the disease in time, based on the general evaluation method of expansion joint and bearing status based on monitoring data, the evaluation of expansion joint and bearing are integrated, and a status evaluation method based on the monitoring data for key restraint devices of suspension bridge is proposed. Wavelet separation method is used to separate the displacement data. The consistency of temperature displacement and the variation range of data details of suspension bridge are analyzed. After segmenting the natural day reasonably, the correlation analysis and break analysis of temperature and displacement are carried out in each continuous period. The method is used to evaluate a large suspension bridge, and the evaluation results are compared with the results of special inspection in the same period. The results show that the evaluation method is reasonable and feasible, which can assist the status evaluation of key restraint devices of suspension bridge.

Abstract:A finite element model of the steel plate girder bridge segment was established to study the cracking characteristics of the stiffener-to-web weld. Under the most unfavorable position of vehicle load, the normal stress and shear stress characteristics of web gap under different transverse load positions and the influence of crack length on the out-of-plane deformation of web were analyzed. The stress intensity factors at the crack tip and the deepest point of crack were compared under different crack lengths, which revealed the influence of crack length on the stress characteristics and the growth rate of crack front. The results show that when the crack is along the side of the surrounding weld end under the joint action of bending moment and shear force, the crack is mainly of type I crack, and when the crack is far away from the side of the weld end and extends to the web, the crack depth grows faster. When the crack penetrates the web, the out-of-plane deformation of web increases obviously, the shear stress of the web becomes more obvious, and the crack propagation rate increases obviously.

Abstract:In order to study the impact of the construction process on the prestressed concrete cylinder pipe(PCCP)under the action of an earthquake, a PCCP seismic response analysis method considering the impact of the construction process is proposed: a nonlinear finite element model that considers the impact of the PCCP construction process is established and the alive and death element technology is used to realize the finite element analysis of the PCCP from the ground stress balance to the application of prestressed steel wire prestress, pipe laying, and backfilling to determine the degree of compaction. As an index to measure the construction quality of backfills, based on the viscoelastic artificial boundary theory, equivalent nodal force ground motion input method and static-dynamic boundary conversion method, the analysis considers the construction process and the impact of different backfill compaction quality on the PCCP seismic response analysis. The results show that the stress of the pipeline is affected by the gravity of the backfill and itself. The hoop compressive stresses of the inner and outer concrete pipe tops, the outer units of the pipe bottom, and the inner units of the pipe waist are larger considering the influence of the construction process than those of the pipe top without considering the construction process. The hoop compressive stress of the inner unit of the tube bottom and the outer unit of the tube waist is smaller than the construction process without considering the construction process; under the the earthquake, the backfill soil is evenly compacted, and increasing the compression degree of the backfill soil can reduce the axial tensile stress at the PCCP socket. The more uneven the degree of backfill compaction, the greater the maximum value of the horizontal and vertical rotation angles between the pipes, and the impact of the backfill compaction quality on the vertical rotation angle is greater than the impact on the horizontal direction.

Abstract:In order to investigate the dynamic mechanical properties of roller compacted concrete, a series of dynamic compression tests have been carried out on roller compacted concrete cylindrical specimens with different diameters by the split Hopkinson compression bar(SHPB). The test results show that the roller compacted concrete material has a significant strain rate effect, as well as size effect, despite the dispersion of test results at high strain rates. That is to say, for the specimens with same size, the dynamic compressive strength increases with increasing strain rate, and the compressive strength enhancement increases with increasing specimen size when subjected to same loads. Moreover, recent studies have revealed that the above dynamic compressive strength enhancement is mainly the result of the coupling effect of strain rate effect due to material properties(namely true strain rate effect), lateral inertia effect, and end friction effect. It is of great significance to figure out the true strain rate effect of roller compacted concrete material for the better prediction of the dynamic response of roller compacted concrete structures under impact load. Based on the assumption that the real strain rate effect, lateral inertia effect and end friction effect are not related to each other, this paper quantitatively evaluates the enhancement of compressive strength caused by the lateral inertia and end friction constraints effect by numerical simulation and semi-theoretical derivation. Then the dynamic compressive strength enhancement is eliminated, and the true strain rate effect of roller compacted concrete material is obtained by the regression analysis of the corrected DIF data. The results show that the obtained true strain rate effect of roller compacted concrete is relatively close to the model proposed by Fib code and Hao.

Abstract:Using the centrifuge equipment, the contact crushing test of sandstone spherical particles was carried out, and the crushing morphology, cone-shaped core size and crushing rate were studied to explore the contact crushing characteristics of spherical particles under multi-point contact conditions. The crushing morphology of samples can be divided into two-block type and three-block type, in which the two-block type is the main type, and the multi-point contact is the necessary condition for the three-block type failure. Combined with the existing research results of single point contact crushing of spherical particles, the empirical formulas of cone-shaped core size and the empirical formula of crushing rate of spherical particles are established by the fitting method, and are validated by the test. It is found that increasing the number of contact points can effectively reduce the particle crushing rate under the same load.

Abstract:The effects of material filling rate, vertical stress, amplitude of shear strain and other factors on the dynamic characteristics of single soilbag were studied by the cyclic shear test of single soilbag under the condition of variable shear strain amplitude using a large indoor shear system. The results showed that when the vertical stress is 80 kPa, the greater the material filling rate, the better the damping effect of the single soilbag. Considering the construction efficiency and other factors, it is suggested that 90% should be used as the optimal filling ratio of the single soilbag. When the vertical stress is greater, the dynamic shear modulus of the single soilbag is large and the greater the horizontal shear displacement amplitudes, the greater the damping ratio of the single soilbag. In other word, when the disturbance is small, the single soilbag has the ability to maintain its own stability, while the disturbance is large enough, the single soilbag uses its own flexibility to lift the damping and dissipates a large amount of vibration energy.

Abstract:In order to better solve the drop problem of cleaning robot caused by the lack of effective boundary detection and satisfy the requirement of full coverage cleaning, a navigation method based on the hierarchical cost map is proposed for the cleaning robot of photovoltaic(PV)systems. On the layer of the traditional hierarchical cost map, the boundary layer of the PV array is added to establish the cleaning area, according to the analysis of the working environment of the robot, so that the working space of the robot can be constrained in the PV array. Then, the navigation strategy combining the bow shape cleaning path and multi-point navigation is adopted to realize the full traversal of cleaning area. Moreover, the second round of cleaning judgment is introduced to remove the residual contaminants on the surface of PV array, which improves the cleaning efficiency of robot. The experimental results show that the proposed navigation method can solve the drop problem of robot due to the failure of boundary detection, and the robot can effectively complete the full coverage cleaning work.