Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Flow separation and vortical dynamics generated by second-order Stokes waves propagating over a submerged rectangular breakwater supported on a rubble mound were investigated using particle image velocimetry (PIV) technology and numerical model based on Reynolds–averaged-Navier–Stokes equations (RANS). Experimental wave surfaces show nonlinear deformation before and after the structure. The asymmetry and skewness of the weatherside wave profile are –0.21 and 0.04, respectively, which indicates a steep front face and gentle rear face. The asymmetry and skewness of the leeside wave profile are –0.39 and 0.99, respectively, which indicates more significant lack of symmetry relative to vertical and horizontal axes. Phase-averaged velocity and vortex fields calculated from PIV data show that clockwise and counterclockwise vortices are generated periodically on the weatherside and leeside of the structure. However, these vortices are not fully developed. The subsequent flow reversal moves the vortices towards the free surface or the structure to make them dissipated. The weatherside vortex pair is confined within a relatively narrow region of about 0.5 times Keulegan–Carpenter number from the weatherside of the structure, which implies smaller wave energy dissipation. Meanwhile, the leeside vortex pair is confined within a relatively wide region of about 1.0 times Keulegan–Carpenter number from the leeside of the structure, which indicates greater dissipation of wave energy. In addition, a small circulation system is found above the upstream shoulder of the rubble mound and its movement is confined within two times the unperturbed wave particle trajectory, which may lead to local scouring. A numerical wave flume was established based on RANS–VOF mode and then verified by experimental results. The applicability of different wave-making methods and the effect of energy dissipation by sponge layer were analyzed. The RANS–VOF model was then used to further study the flow separation of shear boundary layers. Numerical results show that the supply of vorticity mainly comes from the shear boundary layers at the surface of the structure. The adverse vorticity in the shear boundary layers is induced by the adverse pressure gradient imposed by the movement of the vortices previously shed from the structure. The generation, shedding, stretching, advection and dissipation of vortices is expected to significantly change the local flow around submerged structures and hence cause local scour as well as additional loading. Therefore, the effect of the complex flow induced by vortices should be taken into account in engineering design.

The double steel plate composite shear wall structure is widely used in the high-rise buildings due to its advantages of good integrity, high rigidity and high shear bearing capacity. In this paper, the mechanical characteristics of L-shaped section double steel plate composite shear wall structure were analyzed. The finite element software ABAQUS was used to model and analyze the L-shaped section double steel plate composite shear wall, and the results were compared with the experimental results, through the finite element parametric modeling, the influence and characteristics of the main parameters such as axial compression ratio, steel plate thickness, steel plate strength grade, concrete strength grade, end H-beam size and other parameters on the hysteretic performance of the shear wall were studied. Results showed that the finite element model fit well with the test results; the bearing capacity of specimens increased with decreasing height–width ratio; increasing the thickness of the steel plate and the size of the H-beam at the end, increasing the strength grade of the steel plate and the strength grade of the concrete would increase the bearing capacity of the L-shaped section double steel plate composite shear wall; the strength of the concrete and the addition of H-shaped steel at the flangeless web were the main factors affecting the bearing capacity. It is recommended that the design axial compression ratio of the L-shaped section double steel plate composite shear wall should be restricted under 0.4.

In order to study the effect of Nano–particles on the low organic waste activated sludge fermentation performance. The WAS were fermented in the nanometer CuO (Nano–CuO) and nanometer ZnO (Nano–ZnO) fermentation systems. The results showed that the hydrolytic acidizing property of Nano--ZnO fermentation system was significantly higher than Nano--CuO fermentation system. Protease increased with the addition of Nano--ZnO and Nano--CuO, and the maximal value was 25.15 EU/mg VSS (Nano--CuO) and 46.71 EU/mg VSS (Nano--ZnO), respectively. The α--glucosidase increased firstly and then decreased with the addition of Nano--ZnO and Nano--CuO, the maximal value were 0.0037 EU/mg VSS of 10 mg/L (Nano-- CuO) and 0.0039 EU/mg VSS of 1 mg/L (Nano--ZnO), respectively.Alkaline phosphatase and acid phosphatase declined with the Nano–ZnO and Nano–CuO addition however the Nano–ZnO system was higher than Nano–CuO system. The coenzyme 420 declined with the increase of Nano–ZnO but increased with the increase of Nano–CuO . Theterrimonas , chryseolinea and ferruginibacter were enriched in Nano–ZnO fermentation system which resulted in the higher SCFAs production.

To study the dynamic performance of C-type cold-formed thin-walled steel members under transverse impact loading, two groups of 12 members were selected for impact test. The deformation modes and displacement extremum of the test members were compared with the results of ANSYS/LS–DYNA finite element simulation and the results showed that the deformation modes of the two members were similar, and the difference of displacement extremum was less than 8.0%, which indicated that ANSYS/LS–DYNA finite element model could accurately and effectively simulate the dynamic response of the steel member. Then, the numerical model was used to analyze the influence of different impact parameters (density, velocity and angle) on the deformation mode and dynamic performance of C-type cold-formed thin-walled steel members successively. The results showed that the maximum impact force of members increased by 25.5%, the maximum vertical displacement was 20.30 mm, and the proportion of stable strain energy in the peak value was basically maintained at 60.0%, when the density of impactor increased by 2000 kg/m3 in the range of 2000～8000 kg/m3 when the velocity of the impactor increased by 3 m/s in the range of 3～9 m/s, the maximum impact force of the member increased by 79.1%, the maximum vertical displacement was 26.78 mm, and the proportion of the stable strain energy in the peak value basically remained at 60.0% when the impact angle of the impactor increased from 30° to 90°, the maximum amplification of impact force was 41.4%, the maximum vertical displacement was 20.09 mm, and the proportion of stable strain energy in the peak value was between 60.0% and 70.0%. Eventually, the deformation and degree of damage of the member were affected by the change of impactor density, velocity and impact angle, and the impact velocity had the most outstanding influence on the deformation of the member.

Creep deformation and stress relaxation are two properties of rock mass in underground engineering, but in many construction practices, rock mass is neither pure creep deformation nor pure stress relaxation, with stress and strain of rock masses simultaneously changed with time, which is time-dependent, and may ultimately cause failure. It’s hard to explain the phenomenon simply by creep deformation and stress relaxation, so it is a challenge for rock mechanics researchers. To ensure the long-term stability of underground engineering and its structures, it is necessary to further study the properties of rock mass in the generalized theory of rheological mechanics. In the linear viscoelastic theory, the creep compliance was obtained by creep deformation test while the relaxation modulus by stress relaxation test, and the two values were showing linear rheological features, in a reciprocal relationship with each other, and could be converted in each other under certain conditions, so they were no essential difference. But in non-linear viscoelastic theory, their relationship was not clear, and the generalized rheological theory by the stress-feedback controlling method provided the possibility to study mutual relationship. The generalized rheological tests of Tage tuff at 50%, 85% of the peak stress level, Sanjome andesite at 50%, 65% and 80% of the peak stress level were carried out by using the stress-feedback testing method, the generalized rheological direction coefficient for two rocks were 3.0, ±∞, –3.0, –1.0, –0.3, 0, 0.3, respectively. The experimental results showed that the generalized rheological law for two rocks was similar, and the variation of stress and strain obeyed the logarithms law. Based on the definitions of creep compliance and relaxation modulus in the linear viscoelastic theory, the generalized related strain and stress were defined, the calculating method for generalized rheological-compliance (GRC) and generalized rheological-modulus (GRM) was proposed. According to the testing results analyses, the proposed method was general, and creep compliance and relaxation modulus were two special forms of generalized rheological properties. It was found that GRC and GRM were relevant to viscoelastic deformation, had obvious characteristics of time-dependence, direction coefficient-dependence and non-linear rheology, and the ratio between GRC and GRM slightly decreased with time, which showed that the rock rigidity gradually reduced, and deformation quickly increased in pre-failure region. Consequently, the proposed method in this paper can further analyze the quantitative relationship between rock rigidity and plastic deformation, it is very valuable for further investigation of time effect and assessing the long-term stability of underground structures.