Abstract The Yellow River Estuary is the primary depositional zone for sediments from the Yellow River Basin and supports a key wetland ecosystem in the warm temperate zone. However, pressures from river, marine and anthropogenic activities have led to challenges related to flood discharge, delta morphology and wetland ecological function. This study employed statistical analysis, remote sensing, numerical modelling and physical experiments to calculate the thresholds for water and sediment necessary to sustain channel discharge capacity, maintain delta equilibrium and meet wetland ecological water demands. A multi‐objective collaborative allocation model for water and sediment in the Yellow River Delta was developed and applied. Results indicate that lower incoming sediment coefficients during flood seasons enhance flood discharge capacity. Increased sediment load and coarser grain sizes accelerate the expansion of estuarine sand spits. The critical sediment load to maintain area balance is approximately 1.31 × 10 8 t for the Qingshuigou Nature Reserve (QSGNR) and 0.59 × 10 8 t for the Diaokouhe Nature Reserve (DKRNR). Delta imbalance continues to worsen due to erosion in the DKRNR and accretion in the QSGNR, with the imbalance coefficient reaching 0.1202 in 2020. Total annual ecological water demand for the delta wetlands is about 367.18 × 10 6 m 3 , with 288.8 × 10 6 m 3 allocated to QSGNR and 78.38 × 10 6 m 3 to DKRNR. The flood discharge capacity competes with both the delta landform equilibrium and the wetland ecological function, whereas the delta landform equilibrium and the wetland ecological function are synergistic. In low‐flow years, priority should be given to maintaining flood discharge capacity while meeting wetland water needs. In normal and high‐flow years, appropriately increasing water and sediment diversion to the Diaokou River can help mitigate delta imbalance trends and satisfy wetland ecological water needs. This research offers scientific guidance for the multi‐objective allocation of water and sediment in the Yellow River Estuary.

Accurately assessing habitat quality is crucial for ecosystem conservation. The Remote Sensing Ecological Index (RSEI), which incorporates soil moisture (WET), was widely used to assess regional habitat quality. However, in coastal wetlands, the performance of the WET index is often undermined due to high soil salinity caused by seawater intrusion. Therefore, a Water-Salt Stress (WSS) index was developed by integrating WET and salinity (SI) to quantify the combined water-salt stress on vegetation. Replacing WET with WSS, an improved index, Water-Salt Stress Remote Sensing Ecological Index (WSRSEI), was established for habitat quality assessment. Results show higher WSS (> 0.7) in tide-influenced coastal areas and lower WSS (< 0.4) near inland channels. In high-WSS zones, WSRSEI was significantly lower than RSEI. The correlation between WSS and WSRSEI (R 2 = 0.850) was substantially stronger than that between WET and RSEI (R 2 = 0.345), confirming WSS as a superior index. Long-term analysis (1985–2025) revealed a slight overall decline in the delta's WSRSEI (from 0.631 to 0.621). Habitat quality improved in the Qingshuigou Nature Reserve (WSRSEI: 0.565 to 0.627) due to sediment input and post-2008 ecological water supplementation, but declined in the Diaokou River Nature Reserve (0.621 to 0.554) due to coastal erosion and saltwater intrusion. Engineering structures such as levees and farm dikes effectively mitigated seawater intrusion. Since 1985, the expansion of aquaculture ponds, bare land, and built-up areas has been a major factor in the overall decline of habitat quality. This study provides a refined methodological framework for coastal habitat quality assessment.

Sediment coarsening in submerged deltas is commonly attributed to seabed erosion because of insufficient sediment input. The Yellow River subaqueous delta (YRSD) has exhibited distinct coarsening patterns following both accretion and erosion events. To investigate these contrasting mechanisms, grain size distributions, elevation changes, and bottom shear stress patterns were analyzed across the delta from 1992 to 2022. The results revealed distinct sedimentary patterns among the abandoned YRSD, active YRSD, southern Laizhou Bay, and adjacent Bohai Sea, with average median grain size (D50) increases of 17, 17, 6, and 0 μm, respectively. Sediment coarsening occurred primarily from 1992 to 2000, when the river mouth position was artificially altered and fluvial sediment grain size increased from 16 to 29 μm. From 1992 to 2015, the active YRSD experienced accretion at a rate of 7.8 mm/yr. Moreover, the abandoned YRSD and southern Laizhou Bay experienced significant erosion. The erosion rates were −5.1 and −1.0 mm/yr, respectively. This led to the identification of two mechanisms of sediment coarsening: erosion-driven coarsening in sediment-deficient areas and accretion-driven coarsening where the input sediment grain size increased. Although marine processes did not intensify during this period, the bottom shear stress distribution changed substantially due to morphological evolution, with correlation coefficients between grain size and shear stress showing increasing trends in littoral zones. This strengthening relationship, coupled with the declining fluvial sediment load, demonstrates the YRSD transition from river-dominated to wave-dominated processes, providing important insight into delta evolution under changing sediment regimes. The insights gained can guide Yellow River Delta management through targeted strategies and provide essential evidence for predicting delta evolution.

The absolute nodal coordinate formulation (ANCF) is a high accuracy technique to simulate the dynamics of flexible multi-body systems in large deformations and large overall motion. In computer-aided design (CAD) systems, the B & eacute;zier curve is a refined modeling method achieved by modifying control points and weights. Combining with B & eacute;zier curves and ANCF planar beams, this paper proposes a new B & eacute;zier planar beam model by adding additional control points in the crosssection direction from the computational geometry (CG). With respect to the distortion problem of the traditional ANCF element in describing quadratic curves such as circles and ellipses, the rational B & eacute;zier planar beam element presented in this paper accurately represents quadratic curve configurations. The paper proposed that the B & eacute;zier higher-order planar beam element employs the B & eacute;zier curves to represent the warping and stretching of the cross-section. Based on the modeling theory and interpolation strategy of B & eacute;zier planar beam elements, five models were proposed for selection. A thorough investigation of accuracy and convergence is conducted in the comparison study to comprehensively assess the five models and offer reasonable suggestions on their application. The results in geometric nonlinear static and dynamic problems show that compared to the ANCF first-order planar beam element, the lower-order model improves the efficiency under the same accuracy, and the higher-order model slightly reduces the efficiency to obtaining a accuracy close to that of the plane element. This paper proposes the new element that integrates the ANCF method and isogeometric analysis in two-dimensional planar problems, which provides a theoretical foundation for the integration of computer aided design and computer aided analysis.

Land subsidence in river deltas, particularly in the Yellow River Delta (YRD), represents an urgent environmental concern driven by both human activities and natural factors. This study provides a comprehensive analysis of land subsidence in the YRD region from 2019 to 2022 using multi-temporal InSAR data from Sentinel-1A. Results reveal that the maximum annual subsidence rate in the YRD exceeds 200mm/a, with the primary subsidence area located in the northeastern part of the delta, forming a subsidence funnel of approximately 200 km2 and displaying distinct spatial heterogeneity. Human activities, especially saltwater extraction and oil exploitation, are the main drivers of land subsidence. Areas heavily influenced by human activities show significantly greater subsidence than well-protected ecological zones. The study reveals pronounced seasonal variations in land subsidence across the YRD, with subsidence rates in summer being substantially lower than those in spring, autumn, and winter. By introducing the concept of equivalent precipitation, the research confirms that runoff exerts a regulatory effect on land subsidence, although its impact is considerably weaker than that of precipitation. This study proposes a novel explanatory mechanism: the expansion-contraction properties of surface soil explain how seasonal hydrological conditions influence subsidence patterns. During rainy summers, surface soil absorbs water and expands, partially offsetting subsidence caused by deep extraction. These findings provide valuable insights into the interactions between human activities and natural factors in complex deltaic systems, offering a scientific basis for subsidence monitoring and sustainable resource management in the YRD region.

As is the case with numerous other large rivers around the world, the construction and regulation of reservoirs have altered the water and sediment regimes of the Lower Yellow River (LYR) in China, which has significantly altered the LYR. Therefore, it is crucial to examine the impact of reservoir regulation on the erosion and deposition of the LYR channel on different temporalspatial scales, which has not been thoroughly investigated in previous studies. This study used 22 years of topographic data to examine the spatial variability of the evolution of the braided and transitional-meandering reaches of the LYR on interannual and seasonal scales. The results indicate that the LYR experienced significant siltation, which transformed into pronounced erosion after operation of the Xiaolangdi Reservoir (XLD) was initiated in 1999. The braided reach of the river downstream of the XLD had the highest annual rates of siltation and erosion, accounting for 81% and 73% of the total, respectively, within the LYR. From a seasonal perspective, the evolution of the LYR was characterized by a shift from deposition to erosion during flood season following the construction of the XLD. In contrast, the transitional-meandering reach of the LYR experienced constant erosion throughout the similar to 20-year study period. During the dry season, the LYR degraded continuously, with continuous erosion in the braided reach and siltation in the transitional-meandering reach, which lies farther downstream. The water and sediment regimes in the LYR have been significantly altered by the operation of the XLD, particularly through the Water and Sediment Regulation Scheme (WSRS), a coordinated management involving XLD and two other major reservoirs in the middle reaches of the Yellow River. The water and sediment regimes altered by the operation of the XLD have primarily contributed to the shift in the evolutionary behavior of the channel. Furthermore, the regulation of the XLD also resulted in a change to the sediment budget within the LYR. The present study offers a comprehensive and systematic examination of the spatial and temporal impacts of reservoir regulation on riverine erosion and siltation processes of large rivers. The findings have significant implications for the optimization of reservoir regulation strategies to sustain channel degradation and deltaic advancement.

The frequency and buckling characteristics of functional gradient (FG) beams with asymmetric material distribution in the temperature field are analyzed in this paper. Generally, the asymmetrical material distribution of FG beams results in a non-zero neutral axis and non-zero thermal moment. However, some previous studies adopted the treatment of homogeneous beams in which the neutral axis and thermal moment were set as zero. To this end, a comprehensive FG beam model with thermal effect is developed based on the absolute nodal coordinate formulation, in which Euler–Bernoulli beam theory, Lagrangian strain, exact curvature, thermally induced strain, and neutral axis position are considered. For the convenience of comparisons, the presented model can be simplified into three models which do not consider the neutral axis or thermal moment. The numerical results indicate that the influence of the neutral axis on the thermal axial force is minimal while that on the thermal moment is significant. In the case of the high temperature difference, frequency, critical temperature difference, unstable state, and the buckling type of the FG beams are misjudged when the neutral axis or thermal moment is ignored.

The Qingshuigou Channel, as the current tail channel of the Yellow River, formed by the diversion of the Diaokou River in 1976, has undergone a particularly dramatic spatio-temporal evolution, and its evolution processes and the underlying mechanisms are still unclear. On the basis of the flood season cross section data for the river downstream of the Lijin Hydrological Station from 1976 to 2017, the current study calculated the main channel morphological characteristics of the tail channel in different reaches using a reach-scale morphological parameter calculation method and K-means clustering analysis. An elevated riverbed index was proposed to identify the elevated riverbed situation of the river channel. The results show that from 1976 to 2017, the bankfull area experienced repeated processes of decrease and increase, and the main channel morphology gradually changed from wide and shallow to narrow and deep over time. For most of the time period, the conveyance capacity of the main channel gradually decreased from upstream to downstream. The elevated riverbed situation gradually became more severe along the river reach from 0 to 85 km away from Lijin, but was less severe in the reach more than 85 km downstream of Lijin. The most severe elevated riverbed situation appeared mainly in the range of 71–83 km below Lijin in 1991–1995. When the sediment-carrying capacity of the water flow was strong, the bankfull area of the main channel increased, and the elevated riverbed situation was alleviated. River channel projects have helped to maintain the narrow and deep shape of the main channel, but the installation of farm dikes have aggravated the elevated riverbed situation. At the same time, extension and diversion of the tail channel have changed the erosion base level, greatly affecting the evolution of the channel morphology. The current study has provided a typical case for exploring the processes and mechanisms of tail channel evolution.

The skew angle is an important feature for the rotating plate, which has a significant influence on the modal characteristics of the vibration. However, the variation of modal properties induced by the skew angle for a rotating cantilever plate has seldom been studied, and most work has been focused on the static behaviors or free vibration analysis of non-rotating skew plates in the existing literature. A novel dynamic model using a floating frame of reference (FFR) based on the absolute nodal coordinate formulation (ANCF) shell element is proposed to investigate the vibration behaviors of a rotating skew plate. The convergence and validation analyses are performed, and the results obtained by the present method are verified by comparing with those in the available literature. A detailed parameters investigation on the effects of skew angle, aspect ratio, hub radius and stagger angle on the variations of modal characteristics are demonstrated. The eigenvalue loci veering phenomena along with the corresponding mode shape variations are presented and comprehensively discussed. In addition, it is found that the skew plate may buckle due to the non-uniform centrifugal force, which leads to the zero fundamental frequency by the critical rotational speed.

In this paper, an extended three-dimensional (3D) model of the Yellow River Estuary (YRE) is established. It is based on a Delft 3D shallow-water high-resolution hydrodynamic model. The model is calibrated and verified by field observation data, which ensures its stability and accuracy, and provides a better simulation of the river plume in the estuary under different flow inputs. Since 2009, the spring flow pulse of the Yellow River can be divided into four types. The strong flow pulse is more conducive to the extension of the low salinity zone (LSZ). Doubling the peak discharge of pulse flow increases the LSZ area by 60%. The retardation time of salinity change in response to the flow pulse in estuary waters is weakly affected by the flow pulse intensity. The difference in shear front between the spring tide and the neap tide is the main dynamic mechanism contributing to the different retardation times. The average retardation time is 73 h during the spring tide and 55 h during the neap tide. In order to reduce the estuary salinity, it is suggested that the optimal time for the peak value of flow pulse in the river mouth is during the neap tide.

首先总结分析河流水位变化传统表征方法的优缺点,其次运用K线图理论确定水位K线图4个特征水位值的提取方法,最后依据1950—2019年黄河利津水文站相关实测资料,分别绘制基于1 a、10 a周期的3000 m3/s流量对应的水位K线图.结果显示:与传统的水位变化过程线相比,K线图既能显示单一周期和多个连续周期的水位变化趋势,也可以从中获取水位变化的其他重要信息,表征水位变化的效果十分理想.

为更全面地认识黄河尾闾河道形态的调整规律,基于1977—2017年利津水文站实测水沙资料以及典型断面资料,探讨黄河尾闾河道河床纵剖面形态在不同时期的变化过程,建立河床纵剖面凹度、纵比降与水沙条件的相关关系.研究表明:现行流路尾闾河道纵剖面主槽平均高程整体表现出先上升后降低的特征;纵剖面凹度在清8改汊前后,均表现出先增大后减小的特征,整体为"下凹"型;河道纵比降在流路改道(汊)后达到最大,在流路运用结束之前逐渐减小;尾闾河道纵剖面调整过程伴随着沿程、溯源的冲淤过程,与流路发展阶段和入海水沙过程密切相关,其中纵剖面凹度与汛期来沙系数有较密切的负相关关系;河道纵比降在不同时期对水沙条件表现出不同的响应规律,即当溯源淤积起主导作用时河道纵比降与汛期来沙系数有较好的负相关关系,当水流的挟沙能力起主导作用时则有明显的正相关关系.

Dynamic coupling modeling and analysis of rotating beams based on the nonlinear Green-Lagrangian strain are introduced in this work. With the reservation of the axial nonlinear strain, there are more coupling terms for axial and transverse deformations. The discretized dynamic governing equations are obtained by using the finite element method and Lagrange’s equations of the second kind. Time responses are conducted to compare the proposed model with other previous models. The stretching deformation due to rotating motion is observed and calculated by special formulations under dynamic equilibrium. The stretching deformation and the change of the associated equilibrium position are taken into account to analyze the free vibration and frequency response of the rotating beams. Analytical and numerical comparisons show that the proposed model can provide reliable results, while the previous models may lead to imprecise results, especially in high-speed conditions.

An improved modeling method for the dynamics analysis of rotating cantilever beams with free end mass is introduced. The proposed improved modeling method is based on the nonlinear Green strain theory in this study. By using the Hamilton principle and the Galerkin method, the discrete dynamic equations of the axial and chordwise motions are obtained. Meanwhile, the equations for free vibrations analysis of the rotating cantilever beam with free end mass are derived by introducing the equilibrium axial deformation into both axial and chordwise motions. Numerical simulations are performed to validate the proposed model, and the results are compared and discussed with the other modeling methods. The comparison shows that even a small free end mass has an important influence on the dynamic characteristics of the rotating beam. Furthermore, the influences of various parameters on the vibration frequencies and axial deformations of the rotating cantilever beams are analyzed, such as the angular speed, the free end mass to beam mass ratio, and the center body radius to beam length ratio. Under the same conditions, the influence of the free end mass on the variation in the first- and high-order frequencies with the increasing angular speed are different.

历史上的黄河入海流路具有"十年一改道"的演变特征,其流路稳定问题一直是黄河河口综合治理研究和实践进程中的热点、难点和焦点问题.本文基于对黄河入海流路失稳驱动因子的分析,以黄河入海流路失稳驱动力响应模型作为构建流路稳定评价指标体系的理论依据,以DSC模型(DrivingForce-State-Control,驱动力-状态-控制模型)作为描述框架模型,通过对15个要素、83个具体指标因子的筛选、调整和优化,分别构建了具有不同稳定目标特征值的基本判别指标体系和综合判别指标体系.利用两种判别指标体系对现状黄河入海流路的稳定状态进行了计算判断,结果表明:现状西河口水位(二)站在10000 m3/s流量时水位为10.52 m,距离12 m改道标准尚有1.48 m的上涨空间,其流路综合稳定状态评价值为0.259,流路稳定状态良好.

黄河入海流路自1976年5月改道至清水沟流路以来,其地貌形态一直处于剧烈的变化当中,以往的研究虽然关注了典型断面主槽的形态特征及过流能力的变化,但对于清水沟流路范围界限内河道断面整体形态及其沿程变化等地貌特征还缺乏系统研究.本文以2019年10月黄河口现行清水沟流路范围渔洼以下河段加测横断面为研究对象,辨识现状地貌分布特点和横断面沿程形态特征,并分析其成因.结果表明:黄河口地貌形成受自然演变和人类活动的影响,既具有主槽、滩地、堤防等河流地貌要素,又具有滩涂、潮沟、拦门沙等海洋地貌要素.在有堤防河段,主槽形态窄深,过流能力较强;在无堤防河段,主槽形态宽浅,过流能力较差;从滩槽高差、唇滩高差、滩地横比降三个指标来看,无堤防河段的"自然悬河"程度大于有堤防河段的"二级悬河"程度.黄河口悬河程度小于黄河下游大部分河段,但黄河口尾闾河道的滩地横比降依然远大于河道纵比降,若发生漫滩洪水将极易引起顺堤行洪,会对黄河口堤防安全造成极大威胁.

对黄河河口入海流路的稳定类型进行分类整理和概括总结,简要回顾其人工改道标准阈值的演化和确定过程,初步构建入海流路实施改道的阈值体系,利用实测资料对典型流量级改道水位阈值、河长阈值、海域容沙阈值及其河口容许累计来沙量阈值进行了论证分析和计算.结果表明:现状流量为3000 m3/s的改道水位阈值为10.58 m,河长阈值约为89 km,海域容沙阈值约为72.19亿m3,相应的利津站累计来沙量阈值约为120.65亿t.

基于黄河河口、现代黄河三角洲、黄河入海流路三者在概念定义上的异同,划定了黄河入海流路地貌单元分类研究的范围.在系统总结河口地貌研究现状的基础上,运用一般地貌学原理、"形态-成因"原则和等级系统原则,综合比较入海流路各地貌单元的存在形式、主要生成原因、发育规模和范围、以及对流路演变的影响权重.将整个流路系统视为Ⅰ级地貌,形成了包括河道、海岸、水下三角洲等三个Ⅱ级地貌,堤防、河槽、汊河、拦门沙、滩涂等16个Ⅲ级地貌的黄河入海流路的地貌分类系统.进一步构建了沟汊、滩涂、拦门沙等典型地貌单元类型的分类谱系.结合黄河河口及其三角洲的实际现状,提出了今后入海流路地貌发育的研究方向.

对黄河河口现行清水沟流路范围内不同汊河的形成、演化及其特征进行了梳理总结,围绕汊河不同运用方案的影响效应进行了论证分析.研究表明:现行清水沟流路范围内的汊河运用方案不适用于多汊河轮流行河模式、同时行河与轮流行河联合模式和同时行河模式,而采用单一汊河轮流行河模式可以充分发挥海洋输沙动力,保证河口海域向外海的较大输沙量,对延长清水沟流路使用年限更有利,更为科学和经济合理.在现行清8汊河达到改道标准后,应优先使用老河道汊河,该方案不仅有利于未来海岸线的均衡发展,而且更有利于延长清水沟流路的使用年限.