Abstract:

Pipe burst in urban water supply networks often pose serious threats to urban operation safety. Based on the pipe burst accident at Siping-Liyang Road in Shanghai on November 16， 2017， the pipe burst was modeled and analyzed by using the finite element method（FEM） with in-situ investigation and the damaged pipeline data collected from 3D laser scanning. The effect of pipe pressure and initial crack length on the stress concentration at crack tip was studied assuming the existence of some potential cracks in the pipe. The full failure process was also simulated from the initial crack to pipe burst by dynamic analysis. The results show that the stress concentration at crack tip grows as water pressure increases， the rate of which varies with crack length. The critical water pressure at crack tip failure decreases as crack length increases sharply. The central angle of initial crack length is evaluated to be more than 26° through the monitoring the data of pipe pressure around. The pipe failure simulation shows that the pipe shards rotate towards the pipe top with the development of crack and finally break along the pipe while the penetrating crack forms. The rotation and outward translation of the shards is considerably large due to external loads and internal pressure， and thus the burst of pipe causes great damage instantaneously.

Abstract:

Urban underground pipelines are the blood channels of the city. However， with the large number of drainage pipelines put into operation and their service life increasing， a series of hidden dangers of pipeline diseases have arisen， such as the overall structural deformation of the pipeline， internal surface cracking， and the insertion of foreign matters in the pipeline. Traditional disease image video capture， detection， and later disease classification and selection are conducted from a two-dimensional（2D） perspective， lacking consideration of three-dimensional spatial information （depth）. Aimed at the above three diseases， an experiment is conducted from generating depth maps and reconstructing three-dimensional（3D） pipeline diseases from 2D depth maps. A dual depth estimation method based on boosting-monodepth is proposed to improve the effect of depth maps， and finally a depth map with continuous and consistent images and clear outlines is generated. In terms of performance evaluation， Abs-Rel， RMSE， SqRel， ORD， D3R and other general indexes are compared with those of the traditional algorithm， and the results show that the boosting-monodepth is reduced by 30% at RMSE and increased by 18% at a threshold of δ< 1.25. Afterwards， the 3D point cloud of pipeline disease is reconstructed based on the depth map obtained， and 3D visualization is performed on CloudCompare. Finally， the disease depth is calculated using the random sampling consistent algorithm and compared with the real measured data to prove its effectiveness and accuracy.

Abstract:

Underground pipe networks are the critical infrastructures for urban and industrial energy supply. The predictive operation and maintenance （O&M） is the key issue for ensuring service throughout their life cycle. According to the failure damage mechanism of underground continuous pipelines， a stress analysis model is proposed based on the multi-source monitoring data fusion， and specific fusion algorithms are provided. A decision model for the first maintenance inspection plan is presented based on the time-dependent reliability， which considers the structural deterioration caused by uniform corrosion. A practical case showed that the fusion algorithm can successfully estimate unpredictable longitudinal bending stress and axial thermal stress， which demonstrates the effectiveness of the method proposed in this paper. The comparison result between the proposed model and existing model proves that the longitudinal bending stress cannot be ignored in the safety assessment and service life prediction of underground pipelines.

Abstract:

Cavities under urban roads have increasingly become a great threat to traffic safety. Most cavities are caused by the leakage of underground pipelines. Pipe penetrating radar（PPR） has been widely used in the cavity inspection near the underground pipeline. However， due to the attenuation of electromagnetic waves in the underground medium， it cannot accurately detect the upper surface of the cavity. This paper proposes a ground-pipeline penetrating radar joint detection technology to improve the accuracy of cavity inspection. An underground object detection platform is established to detect air and water-filled cavities with different sizes. In combination with the back-projection algorithm and antenna pattern correction， the cavity near the pipeline can be migrated by proposed joint imaging method. Laboratory experiment results show that the PPR has a higher resolution in cavity inspection compared with ground penetrating radar（GPR） detection. In addition， the undesired diffractive artifacts at the target edges can be suppressed while improving the migration accuracy with the proposed join imaging method. Both the top and bottom of the cavity as well as the reinforcement inside the concrete pipe can be reconstructed with high-resolution by the proposed joint imaging method. The result is helpful to promote the practical application of GPR and PPR to cavity inspection near the underground pipeline.

Abstract:

The cold wave disaster impact law and fortification standards of urban water supply system were studied in Shanghai as an example. First， the extreme cold waves in Shanghai from the end of 2020 to the beginning of 2021 were studied， focusing on the analysis of water supply system pressure， flow， pipeline maintenance， and other water supply facility function damages during cold waves. Using the meteorological data of the past 60 years， the statistical analysis of meteorological cold wave events in Shanghai over the years was conducted， and the distribution patterns of six cold wave characteristic indicators， i.e.， the minimum temperature of the day， 24h cooling， 48h cooling， 72h cooling， process minimum temperature， and duration， were given. The Poisson distribution was used to calculate the recurrence period and the probability of exceeding the annual minimum temperature in Shanghai， and the recommended standards for temperature setting of exposed facilities such as water meters were given. The correlation analysis was performed by temperature data and pipeline maintenance data， and the temperature benchmarks that adversely affect the operation of pipelines were identified from the perspective of maintenance rate. The research results of this paper can provide theoretical support for the safe operation and management of the water supply industry in Shanghai.

Abstract:

There are problems of incomplete information and lack of means in monitoring the operation safety of urban water supply pipeline networks. First， pipe loss data was analyzed to understand the influencing factors of water supply network operation safety. Protective monitoring and preventive monitoring were proposed for different purposes. Monitoring indexes were established， including the operation status， pipe structure， and environment conditions. Then， the path loss of wireless signal transmission for buried pipelines in the soil was studied. Finally， a monitoring system was deployed at the emergency repair site of Shanghai Water Supply Network. The results indicate that there are lots of pipe loss at the location involving the intersection， overlapping pipelines， and alternating load. They are the key locations for monitoring. The volumetric water content of soil is the main factor affecting the path loss of wireless signals. The path loss of sandy soil is smaller than that of clay soil at a high water content. The multi-hop network can effectively improve the penetrability of wireless network. The compactness of the backfill below the pipeline has a great impact on the later settlement of the pipeline. Therefore the quality of the backfill should be ensured. Structural monitoring can precede leakage， pressure， and flow change of water supply network for safety warnings.

Abstract:

A series of visual modeling experiments of soil slopes stabilized with anchored piles and anchor cable frame beams were conducted based on the transparent soil technology. Particle image velocimetry （PIV） was employed to investigate the displacement fields and failure processes of slopes at bar loading. The results show that anchored piles and anchor cable frame beams can enhance the ultimate bearing capacity of slopes. Its slip surface is deeper than that of an unreinforced slope. For the reinforcement of pushed landslides， the upper anchor cable works first. After it has been pulled out， the anchor cables that followed in turn exert effect until being pulled out. The stability of slopes stabilized with anchored piles and anchor frame beams is not conservative when the ultimate pullout resistance of all anchor cables is considered simultaneously as a component of the slip resistance. It is suggested that when checking the overall stability of the pushed landslide stabilized with anchored piles and anchor cable frame beams， the factor of safety of the uppermost anchor cable should be checked simultaneously to make it meet the factor of safety required by the project， thus ensuring the stability of the whole reinforced slope.

Abstract:

In order to study the pre-compression stress distribution and the crack resistance performance of the negative moment region of the post-connected prestressed composite girder bridge， two continuous composite test girders were designed. One was a post-connected composite girder whose concrete slab in the negative region was designed as a fully prestressed concrete slab， and the other was a normal composite girder without prestress. The mechanical behavior of the girders in the process of tensioning prestressed tendons and static loading were tested， and the stress state and crack distribution of the sections in the negative moment region were obtained. The test shows that the pre-compression stress is borne by the concrete slab because the steel girder and the concrete slab are not connected. The pre-compression stress of the concrete section is unevenly distributed along the transverse direction. The initial cracking load of the post-connected prestressed composite girder and the cracking load outside the group stud hole are 3.1 times and 5.0 times that of the normal composite girder， respectively. The post-connected prestressed composite girder suppresses cracks that penetrate the concrete slab along the transverse direction and improves the crack resistance performance in the negative moment region. The average crack spacing of concrete is approximately equal to the spacing of transverse rebars. The stress state of the post-connected prestressed composite girder after cracking is similar to that of the normal composite girder.

Abstract:

Granite residual soil can be used as backfill in reinforced soil structure， and its water content has an important effect on its mechanical properties. Taking the granite residual soil in Zengcheng District， Guangzhou as the research subject， large-scale direct tests are conducted to analyze the shear characteristics， shear strength， and volume deformation properties of the residual soil and its interface with different water contents （13%， 19%， 25%， and 32%） and normal stresses （50， 100， 150， and 200kPa）. The test results show that when the water content is 13% and the vertical stress is 50kPa， the shear stress of residual soil-geogrid interface increases first and then decreases with the increase of shear displacement， and the shear stress increases with the increase of shear displacement in other conditions. The geogrid reinforcement can alleviate the shear softening of granite residual soil which decreases greatly after the shear stress reaches the peak value. The interface shear strength decreases greatly with the increase of water content， and the interface shear strength coefficient increases first and then decreases with the increase of water content. When the water content is 19% and 25%， the reinforcement effect is the best. The interface cohesion increases first and then decreases with the increase of water content， and the interface friction angle decreases with the increase of water content. At a water content of 13% and 19%， the soil-reinforced interface dilates at a vertical stress of 50kPa， and the bulk strain is mainly shear shrinkage under other conditions.

Abstract:

Groundwater inverse problems such as groundwater contaminant identification and aquifer parameter inversion problems are usually restricted by the computational load. In order to reduce the computational cost of groundwater inversion， the surrogate method is a feasible solution. In this paper， imitating the image recognition process of the convolutional neural network， the groundwater flow movement and contaminant transport problem is transformed into an image regression problem of the functional relationship between input image （hydraulic conductivity field， pollution source information， etc.） and output image （groundwater level， contaminant concentration， etc.）. The surrogate model of groundwater flow movement and contaminant transport is constructed by using AR-Net-WL based on the DenseNet network. The case study shows that， for the overfitting of the surrogate model， a 10% improvement in accuracy can be obtained by selecting training samples as large as possible. When there are no conditions to increase the training sample， AR-Net-WL with an optimal regularization coefficient can also achieve a good performance with fewer training samples （500 training samples） and can accurately predict the groundwater flow movement and contaminant transport.

Abstract:

To describe the route choice behavior of passengers under the condition of urban rail transit operation disruptions， a passenger route choice model was proposed. According to the different effects of operation disruptions， passengers were classified into different types and the corresponding route choice strategies were given. Then， the calculation method of generalized time cost was determined based on the travel time and travel cost. Considering the impact of the disruption duration on passengers， the value principle of passenger reference point in disruptions was constructed. Finally， a passenger route choice model was proposed based on the cumulative prospect theory and the nested logit model. The experimental results show the validity and accuracy of the model is less than 10% of the relative error between the calculated results and the questionnaire data. The passenger’s route choice changes dynamically with the change of disruption duration. It changes sharply in the short-time duration and is relatively stable in the long-time duration. The higher the passenger’s acceptance of travel cost， the more inclined they are to choose the route with a short travel time. The lower the endurance of passengers to disruptions， the more sensitive they are to the comprehensive value of the route.

Abstract:

In order to explore the aerodynamic noise characteristics of high-speed maglev trains， a TR08 high-speed maglev train was taken as the research object. Considering the compressibility of air， detached eddy simulation （DES） was used to calculate the transient flow field around the train. Based on the Lighthill acoustic analogy theory， the acoustic finite element method was used to calculate the aerodynamic noise. The accuracy of the numerical model was verified by comparing the online test data with the numerical simulation results. The results show that the aerodynamic noise of the high-speed maglev train is a kind of broadband noise. The noise sources are mainly distributed in the areas with a strong air separation and turbulence， such as the streamlined shoulders of the head and tail cars. When the train speed is 600 km·h^-1， the equivalent continuous A-weighted sound pressure level reaches 107.5dB（A） within the train passing time where the position is 25m from the track centerline and 3.5m above the track surface， and the noise peak is 101.9dB（A） which is at the center frequency of 1 600Hz in the 1/3 octave band.

Abstract:

Experiments of static tension and cycle tension-tension fatigue are performed for the carbon fiber reinforced plastics （CFRP） bonding， riveting， and rivet-bonding joints. The strength and deformation behavior of the three types of joints are analyzed， the load when the joint reaches infinite cycle life is predicted， the contribution of bonding and riveting to the rivet-bonding joints is discussed， the interaction of laminate， adhesive layer， and rivet in the tensile failure process of CFRP riveted joint is analyzed， the failure mechanisms of the three types of joints under static tension and tension-tension fatigue are summarized， and three methods to improve the riveting strength are proposed. The results show that for the same CFRP laminate， it is the bonding that decides the rivet-bonding joint strength when the shear strength of adhesive is higher than that of rivet. Rivets play a role of “secondary protection” for the rivet-bonding joints. The median fatigue life of the investigated CFRP rivet-bonding joint at a static maximum load of 80%， 65%， 55%， and 45% is 8 174， 22 568， 95 014， and 331 916 times， respectively. At a load of 37.1%， the tensile fatigue life of the joint can reach 10⁶ times. Rivet hole cracking is the main failure modes of CFRP rivet and rivet-bonding joints. Adding gaskets on the riveting side and coating the surface of rivet holes can improve the riveting strength by about 30%.

Abstract:

To fill the gap in research and standards on fan filter units （FFU）， this paper proposed the reference limits of each performance index of FFU based on both the accumulated multitude of testing data of commercial FFUs and the user requirements of domestic semiconductor industries. After the subjective importance of each performance index is determined， the weight calculation was conducted by adopting the analytic hierarchy process （AHP）. Summarizing the test data， it is found that the performance of the fan filter units under normal working conditions has been improved year by year， which is shown by the significant reduction of equipment energy consumption， better uniformity of surface wind speed， stronger stability of equipment， and lower noise. After the subjective importance of each performance index was clarified， the weight was calculated by the analytic hierarchy process. The weight of energy performance index （EPI） is the largest weight， followed by the airflow velocity uniformity， the filter resistance， and others. In combination with the performance test data of FFUs， the device with the largest weight ratio was calculated as the optimal device by using the total hierarchical ranking.

Abstract:

For the discrete-time system with actuator fault， and the state equation and output equation are affected by external disturbance， the reduced-order observer design method and interval estimation method based on the zonotope theory are studied， and an interval-observer-based actuator fault detection method is proposed. First， the original system is decomposed into two reduced-order subsystems by an appropriate state equivalent transformation， so that one subsystem can directly decouple the disturbance. Then， under the assumption that system has no actuator fault， a reduced-order observer design method is proposed for the subsystem without disturbance to obtain the asymptotic convergence state estimation of the original system. Next， a Luenberger observer is designed for another subsystem， and by combining it with the zonotope theory， an interval estimation method for measurable output is proposed. Afterwards， based on the interval estimation of the measurable output， a new actuator fault detection method is proposed by constructing a new residual. Finally， a simulation example is given and analyzed to verify the effectiveness of the method.

Abstract:

In order to reveal the impact of small group search behavior on the evacuation process， two different search strategies for social small groups were designed， and the calculation method of individual panic mood was defined based on the personality model. Meanwhile， the entropy theory was introduced to quantitatively characterize the perception of evacuation individuals on the degree of chaos in the surrounding population. An evacuation model for social group was established considering individual panic and crowd chaos. The simulation results show that social group search behavior is related to small group number and search strategies， and will aggravate the degree of panic and population chaos， and thus affect the evacuation efficiency.

Abstract:

Aiming at express network designing and based on the real data from the network designing practice of a domestic benchmarking express enterprise， this paper discussed the research of the multi-layer multi-service-leveled hybrid hub-spoke network design in the Chinese situation and the influence mechanism of low-carbon on the network design. It constructed hub-spoke network design decision models in both the situations of carbon tax and carbon trading. In combination with the real data， it solved the models by adopting Lingo 14， and analyzed the connection between the cost-minimizing target and the low-carbon target， as well as the influence mechanism between them. The comparison between the results illustrates that the pursuit of low-carbon， energy conservation and emission reduction will not impose extra influence on the traditional network structure that pursues the minimal cost.

Abstract:

In order to evaluate the real effect of government industrial policy incentives， in this paper a full sample of high-tech enterprises in Shanghai Zhangjiang High-Tech Park from 2012 to 2018 is used， and a panel data regression model and a Cox proportional risk model are applied to analyze the main factors affecting the growth and exit risks of high-tech enterprises from a dynamic perspective. The research result show that enterprises with high-tech recognition will indeed improve their level of development， profitability and innovation， but the enhancement effect varies significantly. In addition， the strength of the research and development subsidies and tax incentives of government is inversely related to the exit risk of high-tech enterprises. Besides， from the innovation dimension， the scale of enterprise innovation and the number of patents can more robustly reflect the relationship between innovation and the recognition of high-tech enterprises. Therefore， the central and local governments need to take these factors into account when optimizing the recognition criteria and improving the incentive policies system.