Understanding the superior mechanical properties of Mg-3Al-Zn alloy sheets:Role of multi-type unique textures

Mg-3Al-1Zn(AZ31)sheets were produced by transverse gradient extrusion(TGE)process.The flow behavior and dynamic recrystallization during extrusion were systematically analyzed.The microstructures,textures,and mechanical behavior of extruded AZ31 sheet were also analyzed and compared with conventional extruded(CE)sheet.The results showed that fine grain structure and multi-type unique textures were formed in TGE sheet because of the generation of extra flow velocity along transverse direction(TD)and flow velocity gradient along extrusion direction(ED)during extrusion.The basal poles gradually deviated away normal direction(ND)from edge to center of the TGE sheet along TD,and the largest inclination angle at center region reached around 65°.Furthermore,the basal poles inclined from ED to TD 40°-63°,except for the center region of TGE sheet.The TGE sheet presented higher ductility and strain hardening exponent(n-value),but lower yield strength and Lankford value(r-value)in comparison with the CE sheet.Both the basal<a>slip and tensile twins were easy to be activated during deformation,and the largest elongation of 41%and the lowest yield strength of 86.5 MPa were obtained for the ED-center sample in the TGE sheet.

Multi-type ant system algorithm for the time dependent vehicle routing problem with time windows

The time dependent vehicle routing problem with time windows（TDVRPTW） is considered. A multi-type ant system（MTAS） algorithm hybridized with the ant colony system（ACS）and the max-min ant system（MMAS） algorithms is proposed. This combination absorbs the merits of the two algorithms in solutions construction and optimization separately. In order to improve the efficiency of the insertion procedure, a nearest neighbor selection（NNS） mechanism, an insertion local search procedure and a local optimization procedure are specified in detail. And in order to find a balance between good scouting performance and fast convergence rate, an adaptive pheromone updating strategy is proposed in the MTAS. Computational results confirm the MTAS algorithm＇s good performance with all these strategies on classic vehicle routing problem with time windows（VRPTW） benchmark instances and the TDVRPTW instances, and some better results especially for the number of vehicles and travel times of the best solutions are obtained in comparison with the previous research.

Multi-type sensor placement and response reconstruction for building structures: Experimental investigations

Estimation of lateral displacement and acceleration responses is essential to assess safety and serviceability of high-rise buildings under dynamic loadings including earthquake excitations. However, the measurement information from the limited number of sensors installed in a building structure is often insufficient for the complete structural performance assessment. An integrated multi-type sensor placement and response reconstruction method has thus been proposed by the authors to tackle this problem. To validate the feasibility and effectiveness of the proposed method, an experimental investigation using a cantilever beam with multi-type sensors is performed and reported in this paper. The experimental setup is first introduced. The finite element modelling and model updating of the cantilever beam are then performed. The optimal sensor placement for the best response reconstruction is determined by the proposed method based on the updated FE model of the beam. After the sensors are installed on the physical cantilever beam, a number of experiments are carried out. The responses at key locations are reconstructed and compared with the measured ones. The reconstructed responses achieve a good match with the measured ones, manifesting the feasibility and effectiveness of the proposed method. Besides, the proposed method is also examined for the cases of different excitations and unknown excitation, and the results prove the proposed method to be robust and effective. The superiority of the optimized sensor placement scheme is finally demonstrated through comparison with two other different sensor placement schemes： the accelerometer-only scheme and non-optimal sensor placement scheme. The proposed method can be applied to high-rise buildings for seismic performance assessment.

Types of Ecological Revetments in Hydraulic Engineering

Compared with traditional bank protection, ecological revetments, as a new type of bank protection, can ensure the sustainable and healthy development of river ecology and has broad application prospects. In this paper, the design principles for ecological revetments and the factors that need to be considered in the selection of revetment plants were summarized; and the types of ecological revetments commonly used in water conservancy projects were summarized and classified according to the proportion of natural materials in revetment materials through domestic and foreign research and engineering examples, and their applicable scope and relevant merits were introduced. In conclusion, ecological revetments should get rid of its own limitations in the practical application process, and the river regulation scheme and revetment type should be selected comprehensively and flexibly combined with the status quo.

Inferring Multi-Type Birth-Death Parameters for a Structured Host Population with Application to HIV Epidemic in Africa

Human Immunodeficiency Virus (HIV) dynamics in Africa are purely characterised by sparse sampling of DNA sequences for individuals who are infected. There are some sub-groups that are more at risk than the general population. These sub-groups have higher infectivity rates. We came up with a likelihood inference model of multi-type birth-death process that can be used to make inference for HIV epidemic in an African setting. We employ a likelihood inference that incorporates a probability of removal from infectious pool in the model. We have simulated trees and made parameter inference on the simulated trees as well as investigating whether the model distinguishes between heterogeneous and homogeneous dynamics. The model makes fairly good parameter inference. It distinguishes between heterogeneous and homogeneous dynamics well. Parameter estimation was also performed under sparse sampling scenario. We investigated whether trees obtained from a structured population are more balanced than those from a non-structured host population using tree statistics that measure tree balance and imbalance. Trees from non-structured population were more balanced basing on Colless and Sackin indices.

Study on the Effect of Multi-Type Current Transformers Hybrid Operation on Differential Protection of the Bus Based on Dynamic Simulation

This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.

Energy Dissipation Within the Wave Run-Up at Stepped Revetments

To understand the processes and energy dissipation performance caused by turbulence during the wave run-up over a stepped revetment,hydraulic model tests with steady flow conditions are conducted and correlated with unsteady flow conditions of the wave run-up within a short time frame.Under irregular waves,the run-up reduction over a stepped revetment is dependent on the Iribarren number and decreases for decreasing Iribarren numbers.Velocity gradients are found to be similar in a steady and unsteady flow regime near the pseudo-bottom.

基于Stacking集成算法的抛石护岸水毁破坏预测研究

抛石护岸在顶冲等极端情况下易发生水毁破坏,给人民的生命财产带来威胁。通过水槽试验获取496组样本数据,利用互信息(MI)筛选出6个关键特征属性,并采用支持向量机(SVR)、广义回归神经网络(GRNN)和随机森林(RF)等机器学习算法构建多个预测模型。然后,将这些模型作为基学习器,结合BP神经网络(BPNN)作为元学习器,采用Stacking集成学习方法构建抛石护岸破坏程度预测模型。最后,通过决定系数(R^(2))、均方根误差(R_(RMSE))及平均绝对误差(M_(MAE))等评价指标对模型性能进行评估。结果表明,Stacking模型在抛石护岸破坏高度、长度、范围上的平均R^(2)为0.98、RRMSE为0.02、M_(MAE)为0.03,相较于单一模型(SVR、GRNN、RF),Stacking模型的R_(RMSE)、M_(MAE)皆为最小,R2最高。在抛石护岸水毁破坏程度的预测中,融合的Stacking模型展现出更高的准确性与稳定性。

滨水生态驳岸对水体的净化效果研究——以南昌市象湖湿地公园为例

为研究滨水生态驳岸对水体的净化效果,本文以南昌市象湖湿地公园生态驳岸为例,通过重新构建生态驳岸植物群落等工程改造,监测和评价生态驳岸工程改造前后示范段的近岸水体净化效果。结果表明,改造前,区域内各水体的污染程度均较严重,原硬质驳岸、自然缓坡和木桩驳岸的近岸水质均为地表水Ⅴ类或Ⅴ类以下,以总氮为主要污染物,而总磷的污染程度较小。改造完成后,区域内的主要水体水质上升为地表水Ⅲ类,透明度明显增大;仅有局部的微小区域水质仍为Ⅴ类,但其污染指数已有明显降低。因此,生态驳岸的营建和滨水地带植物群落的合理布局,结合污染控制,能够较好地保护和重建水陆边缘地带的自然生态过程及岸栖生物栖息环境,有效地发挥其生态系统边缘效应,形成自然优美、生态功能持续稳定的湖泊湿地景观。

水位变化条件下植被对下荆江河段岸坡稳定性影响分析

针对下荆江河段典型的上黏下砂二元岸坡,选用香根草-高羊茅组合植物护坡型式,综合考虑植物根系锚固作用及植被蒸腾作用,利用GeoStudio软件模拟岸坡强度指标和热力学指标,运用单因子分析方法研究河道水位下降幅度M、水位下降速率R、初始水位I因素对岸坡稳定性的影响,并运用灰色关联分析方法对比三种因素对岸坡稳定性的影响程度。结果表明:在水位下降过程中,岸坡稳定安全系数先快速下降,后趋于稳定;岸坡稳定性受水位快速下降的影响最大,当下降速率小于1 m/d时,素土岸坡能保持在基本稳定状态;当下降速率大于3 m/d时,岸坡失稳破坏。植被有助于提升岸坡的稳定性,有植被岸坡与素土岸坡相比,其稳定安全系数最大可提升4.33%;岸坡稳定安全系数与M、R、I三种影响因素的关联度在有植被条件下依次有所下降,最大降低3.73%。本文研究结果明确了水位变化条件下植被对下荆江岸坡的稳固效果,可为生态护岸工程的设计提供基础支撑。

软体排沉排水流结构与排体动力特性数值模拟

针对软体排沉排施工时容易出现撕排和断排的问题,本文基于k-ωSST湍流模型,采用分区耦合算法对顺水沉排过程进行双向流固耦合模拟。分析了不同水流条件下绕流流场、涡流结构与排体动力特性,并结合室内水槽试验验证模型计算精度。结果表明:水流流经排体后发生流动分离,导致沿排宽中轴线形成对称的回流区。排体迎水面流速随水深增加呈指数型递增,排体后方高速尾流带的最大流速相较平均流速可增大40%~50%。当雷诺数增加,主体涡流结构由靠近床面侧逐步向水面处发展。此外,排体所受应力沿横向呈条带状分布,峰值集中于排体与翻板交界处及排头梁附近。研究结果可为完善排体结构设计、改进沉排施工工艺提供理论指导。

钢板桩加固岸坡变形与桩土相互作用机理研究

针对航道开挖过程中护岸边坡板桩变形及桩土相互作用机制,通过选取典型断面进行现场试验的方法,对板桩结构位移、土压力及临近土体变形等关键物理量参数进行监测,并结合理论计算方法对板桩结构及后方岸坡土体稳定性进行了详细分析,探究了复杂地质条件下桩后土体变形与主动土压力的内在关联,得到了部分有益结论。板桩护岸后方边坡土体水平位移随开挖进行逐渐增加,边坡达到平衡状态时不同深度土体位移约为0.8~1 mm,板桩桩顶水平位移变化量约为1.2 mm。航道开挖过程中板桩主动侧土压力随开挖的进行逐渐减小,不同埋深位置桩侧土压力减小值约为1 kPa,与理论计算结果比较发现现场试验结果均较小,说明上述理论计算方法对于本试验结构形式而言土压力计算略偏保守。

内河航道板桩-浆砌块石结构共同护岸机理研究

在内河高等级航道建设中,新建板桩-原有浆砌块石共同护岸成为一种新型的护岸结构。通过对该护岸结构的离心模型试验研究,分析了板桩与原有结构之间无连接(J1)、刚性连接(J2)时,原有护岸结构位移、板桩桩侧土压力及桩身弯矩。试验结果表明,刚性连接时,原有结构后倾、下沉位移远小于无连接情况,板桩稳定性大幅度提升;开挖过程中J1,J2条件下板桩除了产生平移位移、还有转动位移,J1以转动为主,J2以平移为主;受U型板桩形状影响,开挖过程中板桩两侧土体形成土拱,同一深度不同位置板桩土压力有较大区别,土压力变化也有较大差异;开挖过程中,J2条件下桩身范围内土压力变化较一致,J1条件下随桩身深度增加,桩侧土压力变化幅度增加;J1条件下最大弯矩位于桩身下部、J2条件下位于桩身上部,且J2最大弯矩大于J1最大弯矩。

基于神经网络的多向波作用下直立堤越浪量预测模型

海岸工程中常采用直立堤的结构形式,波浪作用下的越浪量影响因素众多,特别是考虑实际多向波的作用,目前并没有统一的计算方法。利用神经网络方法在计算回归问题上的优势,构建反向传播神经网络模型,采用物理试验数据构建训练集,建立多向波浪作用下直立堤越浪量的预测模型。通过与测试集、经验公式以及其他物理模型试验结果的对比,显示了本模型具有良好的预测精度,可满足工程设计需要。利用该模型进一步分析波浪入射角度和方向分布宽度对波浪越浪量的影响规律,弥补了试验数据不全造成的变化规律不明显的问题。

小角度缠绕复合材料护岸管桩抗弯性能试验与设计

本文提出一种新型复合材料护岸管桩。该护岸管桩由纤维缠绕工艺制备的复合材料缠绕管制成。通过四点弯曲试验,得到试件的破坏模式以及荷载-位移关系,以此分析缠绕角度±55°、±15°以及是否浇筑混凝土对护岸管桩抗弯性能影响。结果表明:纤维缠绕角度由55°减小为15°与浇筑混凝土都能极大提高复合材料护岸管桩的刚度和抗弯承载力。在此基础上进行复合材料护岸管桩嵌固端深度计算公式推导,并给出护岸管桩的设计流程以及应用建议。这为之后复合材料护岸管桩应用于护岸工程提供了参考。

长江王家洲崩岸治理及护岸效果分析

通过分析长江上下三号河段近期河势变化趋势,由于受上游河势变化影响,王家洲岸坡易发生崩塌后退,需实施整治工程。为解决王家洲崩岸问题,对崩岸段采取岸坡防护加固措施。工程实施后,结合新近护岸测图,对该区域水文和地质进行了研究,分析了河道演变,并采用了平面法、横断面法和冲淤分析法,综合分析王家洲护岸工程实施后的效果。结果表明:护岸工程的实施保障了岸坡的稳定,历经多次洪水考验。实际说明护岸段近岸河床及岸坡相对稳定,护岸效果较好,并结合工程实践经验,提出后续建议和保护措施。

插板桩护岸桩顶位移过大原因探讨

插板桩护岸桩顶位移远超规范规定限值,整体倾向河中心,观感不佳,且插板桩有失稳风险。通过探讨插板桩护岸桩顶位移过大的具体原因,总结了相关经验教训,为同一类型其他河道整治护岸工程提供参考与借鉴。

湿地驳岸生态修复与应用效果研究

研究针对湿地驳岸的水体污染物,采用香根草、水葱、菖蒲、美人蕉4种水生植物对水体中的氨氮和总磷污染物进行修复,开展了不同季节和不同水生植物对湿地驳岸的水体中的营养物质进行修复。对植物的生物量和水体中的总氮、铵态氮、硝态氮及总磷进行了分析。验证四种水生植物对湿地驳岸的水体的生态修复能力和效果。实验结果表明,水生植物的生物量对氨氮的去除率会有影响,但是两者之间相关性不强,说明水生植物对水体的净化能力除了和植物本身的生长有关系,还和其它因素有关联。

软弱土地区城市道路河道生态护岸设计

南充市顺庆区荆溪河沿岸滨河路及护岸建设过程中,大部分河段存在较厚的软塑粉质黏土。该层土物理力学性质较差,对道路建设和护岸稳定极为不利。滨河路是拟建的休闲景观大道,因此该工程在保证道路和护岸安全的前提下,提出生态需求。根据场地工程地质情况,选取了斜坡式生态护岸形式,即表面采用绿化混凝土护坡与客土绿化,坡脚采用格宾石笼护脚,针对较厚的软塑粉质黏土区域采取水泥土搅拌桩进行加固处理。监测结果表明护岸方案整体稳定性及不均匀沉降满足要求。

一种新型双曲弧面海堤护坡结构的防浪消能效果

研发新型海堤护坡结构对守护人民生命安全、提高海堤工程稳定性具有重要意义。针对钱塘江河口潮流强劲,而传统海堤护面光滑,难以对强大冲击浪进行有效缓冲的工程问题,设计研发了一种具有双曲弧面结构的海堤护坡结构,采用室内水力试验和数值模拟等手段对其防浪效果、压强分布特征进行分析。研究结果表明,新型海堤护面结构通过有效引导、改变冲击浪的流向及流态,既能起到较好的消能作用,又能增强钱塘江大潮的观景效果,为复杂水流条件下海堤护坡结构设计提供了新的工程思路。