Abstract:The rock medium has obvious elastic-plastic deformation characteristics and fracture mechanics behavior at different loads. In order to simultaneously describe the continuous field of elastic-plastic deformation and the discontinuous field of fracture mechanics behavior of rock， a non-ordinary state-based peridynamics （NOSBPD） elastic-plastic model based on the Hoek-Brown strength criterion is proposed in this paper. First， based on the material correspondence in the non-local deformation framework， the NOSBPD elastic-plastic constitutive equation with the Hoek-Brown strength criterion is established. The stress increment corresponding to a given strain increment is obtained through the return mapping algorithm of the principal stress space， and the corresponding incremental model integration algorithm is given. Then， a fracture criterion based on equivalent plastic strain is proposed， which can realize the characterization of the mechanics behavior of the whole process of rock elastic-plastic fracture. Finally， the zero-energy mode problem of NOSBPD simulation is eliminated by introducing a non-uniform deformation state. Based on the comparison and analysis of the numerical simulation results in this paper with the finite element method and experimental data， the correctness of the model proposed is verified. This paper provides an effective analysis method for the study of elastic-plastic fracture mechanics behavior of rock.

Abstract:The peridynamics method has great advantages in solving crack propagation problems due to its automatic tracking of crack tips by breaking bonds， but it also faces the problems such as numerical oscillations and boundary errors. In order to solve the above defects， this paper first discussed the NOSB-PD method with the meshless Galerkin weak-form framework. Next， it introduced the peridynamics differential operator approximation and fully compared and analyzed the difference between the PDDO approximation and the reproducing kernel particle method （RKPM） approximation. Then， it proposed the RKPM-PD coupling algorithm with a higher numerical accuracy and gave the implicit iterative process of the RKPM-PD method. Finally， it verified the effectiveness of the algorithm in solving three-dimensional crack propagation problems by using several numerical examples.

Abstract:The governing equation of the original peridynamics is derived from the energy equation of work done by conservative forces， which cannot reasonably reflect the viscoelastic deformation behavior of materials and the energy dissipation of the system. To solve this problem， a peridynamics method considering the work done by non-conservative forces is proposed. The theoretical framework includes two parts： viscoelastic interaction of material points and its motion equation， and rate dependent fracture criterion of bond. In describing the movement of material points， based on the understanding of the deformation mechanism of concrete， the viscoelastic interaction model between material points is proposed. The viscoelastic motion equation is established by using the Hamilton’s principle considering energy dissipation. Using the viscoelastic peridynamics method and the energy density equivalent method of continuum mechanics， the determination methods of elastic parameters and viscous parameters are proposed. In terms of describing bond fracture and material strength， the rate dependent fracture criterion of bond is developed by using the dynamic uniaxial S criterion of concrete. Numerical experiments are conducted to investigate the functions and advantages of the viscoelastic peridynamics method proposed. The results show that the peridynamics method proposed can reasonably reflect the influence of loading rate on the deformation， strength， and cracking behavior of concrete.

Abstract:The concrete cut-off wall has been widely used in high embankment dams constructed in the overburden in China. The local failure of the wall embedded in the soil may occur since it is subjected to the giant water pressure， earth pressure， and the uneven settlement between the soil and the concrete. Generally， discrepancies of structure dimensions across diverse scales and accurate descriptions of the complicated failure involved in this process are crucial but difficult to be considered. In this paper， based on the multi-scale homogenization method of peridynamics， an equivalent damage model of concrete cut-off wall in high embankment dams was proposed. The concept of the model was given， and based on the damage mechanism of the cut-off wall， the aforementioned equivalent damage model was established. This model is characterized by its simplified formula， few parameters with valid physical meanings， and unified expressions of the tension and compression damage. The new index number renders the model to be capable of more accurately simulating the damage evolution process of concrete. The model proposed is easy to be employed in engineering practices. After the validation of the model proposed through concrete material tests and an eccentric three-point bending concrete beam test， it was employed to analyze the failure of the cut-off wall in a high gravel earth core rockfill dam in 3D.

Abstract:Considering effectively reducing the amount of calculation without reducing the solution accuracy， and based on the principle of effective stress， a coupling method of finite volume method and peridynamics is proposed to simulate the hydraulic fracture propagation in saturated porous fractured media. First， the effectiveness of the method proposed is verified by a porous media seepage simulation example. Then， the ability and main characteristics of this method to simulate crack propagation in saturated fractured porous media driven by fluid are further verified by several numerical examples. The simulation of five working conditions shows that the confining pressure difference can induce the fracture propagation of hydraulic fracturing. At the same time， the numerical simulation results of the coupling method are compared with other numerical， analytical， or experimental results， which further indicates that the coupling method proposed can effectively simulate the mechanical propagation and rock fracture process.

Abstract:Research on the over-fire performance of aluminum alloy gusset （AAG） joints can provide a basis for evaluating the bearing performance of aluminum alloy reticulated shells after fire. The tensile tests of 6061-T6 aluminum alloy after fire were conducted and the formula of reduction coefficient of mechanical property after fire was given. The bearing performance tests of 12 pieces of 6061-T6 aluminum alloy gusset joints after fire were performed. The bending capacity and the possible failure modes of aluminum alloy gusset joints after fire were presented. The test results indicate that the material property of aluminum alloy and the mechanical property of aluminum alloy gusset joints show a three-fold trend with the change of fire temperature. Parametric analysis was carried out based on the numerical model to study the influence of material properties， over-fire temperature， and size specifications on the bearing performance of aluminum alloy gusset joints after fire. Finally， through numerical fitting， the calculation formula of the bending stiffness and the bearing capacity of aluminum alloy gusset joints after fire and the four-line model of moment-rotation curve were obtained.

Abstract:To investigate the strain rate effect and acoustic emission characteristics of carbonaceous slates， a series of uniaxial compression tests were conducted at four different quasi-static strain rates （8.50×10^-6s^-1， 1.70×10^-5s^-1， 1.70×10^-4s^-1， and 3.34×10^-4s^-1）， and the acoustic emission signal was measured simultaneously. Based on the test results， the effects of strain rate on the stress-strain relationship， energy dissipation， and acoustic emission characteristics were analyzed， and the mechanism of these strain rate effects was explored. In addition， the closing stress σ_cc and the crack damage stress σ_cd were determined based on the evolution of dissipative energy density during loading； the closing stress σ_cc was defined as the starting point of the flat section of the dissipative energy curve， and the crack damage stress σ_cd was defined as the end point. The results show that in the quasi-static strain rate range， the elastic modulus and peak strength of carbonaceous slates first increase and then decrease with the strain rate， reaching their maximum values at the rate of 1.7×10^-4s^-1. The ratio of closure stress， crack initiation stress， and crack damage stress to the peak stress were about 0.37， 0.55， and 0.74， respectively， which do not change with the strain rate. The strain rate also has a significant impact on the acoustic emission signal. With the increase of strain rate， the proportion of main frequency in the range of 0~50 kHz increases and that in the range of 100~250 kHz gradually decreases. The failure mode also gradually changes from tensile failure to shear failure.

Abstract:In this paper， the specification parameters of 55 kinds of coated fabric membrane materials commonly used in engineering at home and abroad are counted， including warp and weft yarn density， fineness， grammage， thickness， etc.. The mechanical test results accumulated were sorted out， and data of the basic mechanical properties of coated fabric membrane materials were obtained. The multivariate statistical method was used to analyze the structure parameters and test results of coated fabric membrane materials， including the correlation analysis of mechanical properties and the influencing factors of mechanical properties. The influence of various parameters on these strength indexes of membrane materials was determined， and the further linear regression analysis was conducted. The regression models of tensile strength and tear strength were established respectively， which could be further applied to membrane material production and membrane structure design.

Abstract:An overview of the latest research progress on the interaction between submerged berms and waves is given from two aspects， the evolution of submerged berms under the effects of waves and the wave dissipation effect of submerged berms. Classic experimental studies of the interaction between submerged berms and waves are reviewed， and their research background， scaling criteria， and main conclusions are introduced. The development process and core idea of “process-based profile evolution model”， which is suitable for the simulation of medium- and long- term evolution of submerged berms， are expounded. Suggestions on the engineering application of submerged berms are given from the aspects of longshore length， nourishment location， and lifetime design. The limitations of conclusions and methodologies of existing studies are discussed， and future research prospects are proposed.

Abstract:Aiming at the early crack at the edges and corners in the design life of the traditional rigid pavement structure， based on the experiment result of the full-scale tests in FAA’s NAPTF CC1 and CC2， combined with the Westergaard theorical solution， a balance-stiffness design concept and a structural stiffness concept are proposed in this paper， that is， increasing the structural stiffness in the slab edges and slab corner， balancing them with the centroid of the slab approximately. According to the result of the full-scale test CC6， the effect of crack alleviating of this concept has been verified， and the rigid pavement with flexible base can also reach the same goal. The general form of the rigid pavement structure and a prototype structure considering engineer application has been proposed based on the balance-stiffness design concept. The research results can provide a theoretical basis for the balance stiffness design of rigid pavement structures.

Abstract:To take proper measures to manage the overtaking behavior on urban roads， a method is proposed to recognize high-risk overtaking vehicles online based on quantitative indicators. First， the traffic wave theory is employed to classify overtaking on urban roads. Enlightened by the types， a multi-dimensional index system is constructed to illustrate the essential features of urban-road overtaking. Then， based on license plate recognition data， a method is introduced to calculate these indexes online. Finally， with the real data， the effectiveness of the index system and its calculation are verified to recognize high-risk overtaking. According to the analysis results， both the correlations between the overtaking number and volume and the overtaken number and volume can be fitted by the polynomial， which would help identify volume-sensitive segments. The K-means algorithm is used to cluster the overtaking vehicles into three types according to the difference between the planning speed and the overtaking speed. Given the type， the actual speed and the overtaking speed difference are suitable for evaluating the overtaking risk. It is found that high-risk overtaking frequently occurs in the unfavorable phases resulting from inappropriate signal control coordination between adjacent intersections. Moreover， overtaking with high risk is also prone to be found among the vehicles passing by the end of green light at downstream intersections and the first vehicles passing during green light at upstream intersections.

Abstract:In order to explore the diffusion law and influencing factors of water vapor in asphalt mixture， a penetration water vapor diffusion test device was designed， and three types of asphalt mixtures with porosities of 7%， 17%， and 24% were prepared. Water vapor diffusion tests were conducted at 25℃， 30℃， and 40℃， respectively. The results show that the diffusivity of water vapor in asphalt mixture increases with the increase of temperature. The porosity plays a dominant role in the diffusion of water vapor in asphalt mixture at a lower temperature （25℃ and 30℃）， and temperature plays a dominant role at a higher temperature （40℃）. The diffusivity of two porous asphalt mixtures is obviously higher than that of dense asphalt mixture. The amount of water vapor accumulation in asphalt mixture increases with the increase of porosity and decreases with the increase of temperature. The TSR decreases with the increase of water vapor accumulation. The results indicate that both porosity and temperature have a significant effect on diffusivity， and the higher the temperature， the more significant the effect of porosity on the diffusivity. The higher the porosity， the more significant the effect of temperature on diffusivity. The water stability of dense asphalt mixture is more affected by water vapor diffusion.

Abstract:Pipe damages will lead to the infiltration of groundwater into sewer systems， which seriously affect the efficiency of urban sewage treatment in areas where the groundwater level is higher than the buried depth of the pipeline. Cities with busy traffic and high-rise buildings make it difficult to dig damaged pipes. In addition， the physical detection method is very labor-intensive and even hard to perform. Therefore， in areas with high groundwater level， a particle swarm optimization methodology in conjunction with hydraulic model computation and water level monitoring was proposed to identify sewer defect. The method was demonstrated in the sewer system of a certain city. The damage points were determined by quantified groundwater infiltration flow based on water level monitoring and flow calculation， with a relative error less than 5%. Meanwhile， the influence of the monitoring points on the optimization model was discussed. 60% of the total nodes was selected as the optimal number， and the location precision rate and location recall rate are 75% and 94%， respectively.

Abstract:Natural pyrethrins are encapsulated with silicon dioxide gel prepared via the sol-gel method using tetraethyl orthosilicate as precursor. Taking drug loading rate as the evaluation index， the response surface methodology is used to design the BBD （Box-Behnken design） experiment to determine the optimal preparation conditions as follows： pH is 9.02， the dosage of TEOS（tetraethyl orthosilicate） is 0.96 g， and the reaction temperature is 36.5 ℃. The drug loading efficiency and average particle size of the microcapsules are 38.0 % and 13.5 μm， respectively. The results show that the stability of encapsulated drug is significantly improved below 250 ℃. The drug loading efficiency decreases by only 6.2% after it is stored in the dark at 4 ℃ for four months. The microcapsules demonstrate a good sustained-release property， and can effectively reduce the quality loss of the drug at 100~200 °C. The microcapsules also exhibit a high insecticidal activity against Culex pipiens pallens and Aedes albopictus larvae， and are even slightly more effective against aphids and stick insects than the original drug， endowing them with a great application value.

Abstract:Noise pollution is an important environmental problem. It is always a challenging subject to study how to design sound-absorbing structures to reduce noise in the environment. Compared with the traditional material， metamaterials have attracted wide attention due to their excellent advantage in the low-frequency sound absorption. In this paper， two major mechanisms， i.e.， the acoustic viscosity theory and the heat conduction theory， of acoustic absorption are introduced. Next， the basic research methods of sound absorption structures are introduced， including the impedance analysis theory， the numerical calculation method， and the experimental technique. The impedance analysis theory includes the impedance matching theory and the complex frequency plane. Then， according to the current design and research status of sound absorption structures， this paper presents relevant works， introducing the research progress of design based on metamaterials， and analyzing the practical application and possible development direction. Finally， the absorber based on metamaterials is summarized from structure design， working frequency， structural size and absorber performance， and the challenges in practical application and working condition are analyzed.

Abstract:For the cold gas inflator， high refinement of ultimate load forecast is the key to the structural design of the generator. First， the zero curvature method and the RIKS method were used for burst disk hydro-burst test ultimate load calculation. Compared with the results of the real test， the refinement of both of the two methods are above 97%. Then， to solve the nonlinear contact convergence issue of the implicit algorithm， the explicit algorithm was used to solve ultimate load based on the status of stress matrix analysis results of the RIKS method. The method of stress matrix status analysis was proposed to judge the ultimate load of explicit algorithm results. In the explicit calculation， the stress change at the center of the burst disk is tracked and the corresponding load when plastic instability occurs in the thickness direction is defined as the ultimate load. The refinement of the ultimate load of the explicit algorithm is 97.4% in contrast to the real test judging by the method of stress matrix status analysis. Because of the involvement of the effect of nonlinear contact， the refinement of displacement of burst disk is better than that of the implicit method.

Abstract:Aimed at the problem of controlling the temperature of each stack in the multi-stack fuel cell system， a parallel connection thermal management subsystem is proposed and built. The outlet gas temperature of anode and cathode is taken as the correction term of the stack temperature， and a thermal balance analysis is conducted for the multi-stack fuel cell system. First， the model predictive control method is used to control the temperature. Then， several prediction models are established by using the system identification method， and the performance of the stack is predicted by switching between different prediction models. Finally， the test conditions are designed for simulation verification. The results show that under the corresponding temperature index， the model predictive control algorithm can be used to control the temperature of each stack in the multi-stack fuel cell system quickly and accurately， and the increase of prediction points can improve the control effect， reduce the overshoot， and shorten the regulation time.