Progresses and future directions on yardangs

Background,aim,and scope Yardang is a kind of typical wind-eroded landform in arid zones both on Earth and other planets.Their geomorphic process records the surface changes and climate,which may play a vital role in exploring the coupled landform-atmosphere system in arid zones.Recently,significant progresses have been made in this research field,and a review is still absent,which is the aim of the paper.Materials and methods Previous studies on the distribution,composition,morphology,and climatic driving force of yardang landform were reviewed.Results Earth yardang’s three evolutionary models were generalized:morphology evolution model,altitude evolution model and climate driven evolution model.Extraterrestrial yardang and its evolution are also summarized:the morphology is dominated by long ridges on Venus and Titan,and three yardang evolution hypotheses and an indirect dating method based on stratigraphic contact have been studied on Mars.Discussion In this study,firstly,the definition and morphology of yardang were described to define its characteristics.Secondly,we argue that yardang evolution has two dimensions:short-term variation and longterm variation.In the short-term variation,the morphological evolution of yardang on earth can be divided into four stages:embryonic stage,juvenile stage,mature stage,and demise stage.In the long-term variation,the evolution of yardang on earth is climate-driven,i.e.,it is controlled by atmospheric circulation changes during glacial-interglacial periods.Thirdly,yardang research on extraterrestrial bodies was also summarized:yardang has been found on Mars,Venus,and Titan,and the research focus by far are on geomorphology only.Conclusions(1)Yardang landform is an erosion landform with alternating ridges and troughs,with main form of whale back shape and fluctuations in the range of aspect ratios;(2)the short-term variation of yardang is manifested in its morphological evolution and height change,while the long-term variation is climate-driven;(3)based on Earth yardang,extraterrestrial yardang research has been carried out on Mars,Venus,and Titan.Recommendations and perspectives We then proposed that:(1)yardang formation ages,due to the erosion characteristics,are difficult to constraint;(2)the wind erosion capacity in the yardang areas might have been severely underestimated,making it essential to re-evaluate the previous paleoclimate reconstruction in the closed basins with limited chronological data;(3)yardang evolution is driven by climate change,but the coupling relationship between the yardang geomorphy and the air circulation is still unclear.Finally,future research directions:(1)more chronological data are needed,as well as the wind erosion capacity for yardang initiation and development;(2)the co-evolution of mid-low latitude landforms involved in yardang long-term variation and its relationship with global atmospheric circulation.

Numerical Study on the Probability of Fatigue Failure of a Semi-Submerged Platform Structure

On the basis of Miner's linear cumulative damage theorem, random variables are introduced to evaluate objectively the fatigue damage of a semi-submerged platform structure and a method is presented to analyze the fatigue reliability of the structure in its design life. The reliability of the method is verified through numerical examples and some conclusions are drawn, which have certain guiding and reference value for design and inspection.

DYNAMIC CHARACTERISTIC ANALYSIS OF A 3-D SEMI-SUBMERGED BODY AS A FLUID-STRUCTURE INTERACTION SYSTEM

An Arnoldi's method with new iteration pattern,which was designed for solving a large unsymmetric eigenvalue problem introduced by displacement-pressure FE (Finite Element) pattern of a fluid-structure interaction system,was adopted here to get the dynamic characteristics of the semi-submerged body. The new iteration pattern could be used efficiently to obtain the Arnoldi's vectors in the shift-frequency technique,which was used for the zero-frequency problem. Numerical example showed that the fluid-structure interaction is one of the important factors to the dynamic characteristics of large semi-submerged thin-walled structures.

An analytical approximation of focusing-wave-induced load on a semi-submerged cylinder

Owing to the complexity of the physical mechanisms of rouge waves,the theoretical study of the rogue-wavestructure interaction problems still makes little progress.However,for regular-shaped structures,it is possible to give a theoretical analysis,if a relatively simple model of the rogue waves is used.The wave load,induced by a focusing wave which is known as an intuitive basic model of the rouge waves,upon a semi-submerged cylinder is studied analytically.The focusing wave is approximate by the Gauss envelope wave,an ideal model which contains most features of the rogue wave.The diffraction velocity potential is derived through the separation of flow field,and the formulas of the horizontal force and bending moment are proposed.The derived formulas are simplified appropriately,and validated through comparison against numerical results.In addition,the influence of parameters,such as the focusing degree,the submerging depth and the wave focusing position,is thoroughly investigated.

实景三维技术在敦煌雅丹地貌数字化存档中的应用

敦煌雅丹地貌因其珍贵和独特成为地质遗迹的典型代表,是一种稀有且无法再生的地质自然遗产。针对雅丹地貌的管理、保护与无具象化参考资料的问题,本文提出了一种融合多源数据进行多尺度实景三维建设的方法,在保证重建效率的同时,与传统倾斜摄影测量相比增强了模型细节。模型精度检测表明,本文所提实景三维建设方法能有效地记录敦煌雅丹地貌的几何构造和纹理细节,通过该技术对敦煌雅丹地貌进行数字化保存,可为今后修缮与重现提供重要依据。

Wind regime for long-ridge yardangs in the Qaidam Basin, Northwest China

Yardangs are typical aeolian erosion landforms,which are attracting more and more attention of geomorphologists and geologists for their various morphology and enigmatic formation mechanisms.In order to clarify the aeolian environments that influence the development of long-ridge yardangs in the northwestern Qaidam Basin of China,the present research investigated the winds by installing wind observation tower in the field.We found that the sand-driving winds mainly blow from the north-northwest,northwest and north,and occur the most frequent in summer,because the high temperature increases atmospheric instability and leads to downward momentum transfer and active local convection during these months.The annual drift potential and the ratio of resultant drift potential indicate that the study area pertains to a high-energy wind environment and a narrow unimodal wind regime.The wind energy decreases from northwest to southeast in the Qaidam Basin,with the northerly winds in the northwestern basin changing to more westerly in the southeastern basin.The strong and unidirectional wind regime for the long-ridge yardangs in the northwestern Qaidam Basin results from the combined effects of topographic obstacles such as the Altun Mountains and of the interaction between the air stream and the yardang bodies.Present study suggests that yardang evolution needs such strong and unidirectional winds in high-or intermediate-energy wind environments.This differs from sandy deserts or sandy lands,which usually develop at low-or intermediate-energy wind environments.Present study clarifies the wind regime corresponding to the long-ridge yardangs'development,and lays firm foundation to put forward the formation mechanisms for yardangs in the Qaidam Basin.

A new approach to study terrestrial yardang geomorphology based on high-resolution data acquired by unmanned aerial vehicles(UAVs): A showcase of whaleback yardangs in Qaidam Basin, NW China

Yardangs are wind-eroded ridges usually observed in arid regions on Earth and other planets. Previous geomorphology studies of terrestrial yardang fields depended on satellite data and limited fieldwork. The geometry measurements of those yardangs based on satellite data are limited to the length, the width, and the spacing between the yardangs; elevations could not be studied due to the relatively low resolution of the satellite acquired elevation data, e.g. digital elevation models(DEMs). However, the elevation information(e.g. heights of the yardang surfaces) and related information(e.g. slope) of the yardangs are critical to understanding the characteristics and evolution of these aeolian features. Here we report a novel approach, using unmanned aerial vehicles(UAVs) to generate centimeterresolution orthomosaics and DEMs for the study of whaleback yardangs in Qaidam Basin, NW China. The ultra-high-resolution data provide new insights into the geomorphology characteristics and evolution of the whaleback yardangs in Qaidam Basin. These centimeter-resolution datasets also have important potential in:(1) high accuracy estimation of erosion volume;(2) modeling in very fine scale of wind dynamics related to yardang formation;(3) detailed comparative planetary geomorphology study for Mars, Venus, and Titan.

Aesthetic evaluation of yardang landforms landscape:the Dunhuang Yardang National Geo-park example

Dunhuang Yardang National Geo-park, situated in the Gansu Province of northwestern China （40°25′36″N-40°33′10″N, 93°00′00″E-93°13′30″E）, was chosen as a research locality of aesthetics evaluation of yardang landforms landscape. The yardang landforms landscape is a composite structural system of patch-corridor-matrix, with four landscape unit elements as dense group, sparse group, single body and remnant. The study of the landscape aesthetics spatial pattern of Dunhuang Yardang National Geo-park shows that yardang dense group, sparse group and single body provide the greatest contribution to the aesthetic value of yardang landforms landscape. Yardang bodies are scarce, unique, irreplaceable, and priceless resources in yardang landforms areas. However, they are easily destroyed under the influence of the natural and artificial factors. Therefore, when the tourism potential of yardang landforms landscape is exploited, the protection should be fully improved.

多空间分辨率Google Earth影像和Canny边界算法的雅丹地貌边界提取

雅丹形态特征能反映雅丹地貌的发育过程和演化阶段,对研究雅丹地貌至关重要,但目前关于雅丹地貌边界提取的高精度、低成本方法很少。本文首先采用Canny边界算法,将高空间分辨率Google Earth影像(1.19 m)重采样为一系列不同空间分辨率(3、5、8、10、12、15 m)的影像;然后针对不同空间分辨率的影像提取不同大小的雅丹地貌边界;最后将不同结果合并,取得了良好的效果。结果表明:①尽管无法识别阴影,但Canny边界提取方法的总体精度为89.23%,Kappa系数为0.72,这一结果与面向对象方法的中等分割尺度(138)取得的精度结果相近;②使用Canny边界提取算法提取雅丹地貌边界中位数宽度,与影像空间分辨率呈很好的线性关系(R^(2)=0.95),随着空间分辨率的降低,Canny边界算法提取的雅丹地貌边界总长度呈明显的对数递减(R^(2)=0.904)。

雅丹地貌形成年代研究方法简评与应用

雅丹地貌形成年代是确定其侵蚀速率和侵蚀量的重要依据,也是深入认识其形成发育过程及其与环境关系的前提。然而作为侵蚀性地貌类型,雅丹地貌的形成年代问题一直困扰着研究人员,成为雅丹地貌研究中的一大瓶颈问题。介绍和分析了已有的雅丹地貌形成年代研究方法,并简要评述其优缺点,然后,将部分方法应用到敦煌雅丹国家地质公园区的雅丹地貌形成年代的研究中,得出该区域雅丹地貌开始形成的年代不晚于10.87kaBP,不早于(39.15±3.88)kaBP,最后对雅丹地貌形成年代学研究需努力的方向做出展望。

地表风化作用对楼兰地区雅丹地貌发育的影响

风蚀是雅丹地貌发育的主要控制因素,但在特定环境中,其他环境因素也可能起重要作用。通过对楼兰地区雅丹地貌野外调查、测试及室内实验分析,探讨风化作用对雅丹发育的影响。结果发现:新疆罗布泊地区广泛发育雅丹地貌,其中楼兰地区雅丹相对较为矮小,主要发育于全新世沉积岩上,地表没有植被或松散沉积物等覆盖,地层裸露。楼兰雅丹体为黏土质粉砂岩,干燥条件下较为坚硬(硬度> 20 kg·cm^(-2)),抗风蚀能力较强,但是雅丹体表层岩性发生明显软化(硬度<10kg·cm^(-2))。这主要是由于罗布泊地区少量且集中的降水、显著的昼夜温差以及强烈太阳辐射等相互作用造成的。从这些广泛存在的松软层表明,雅丹体表层风化作用速度快于风蚀作用,而表层首先进行的风化作用,对雅丹风蚀作用起很大的促进作用,明显加速了楼兰地区雅丹地貌的发育。因此,受少量降水、昼夜温差和强烈的太阳辐射等影响的风化作用对楼兰地区雅丹地貌发育具有重要的影响。

玉门关西雅丹地貌的分布和特征及形成时代问题

玉门关西雅丹地貌位于玉门关以西６８ ｋｍ的疏勒河故道北面北山剥蚀残丘准平原的东西向断层谷地中（９０°００′～９０°１０′Ｅ， ４０°３０′～４０°３４′Ｎ），该区雅丹地貌组成的古湖相地层被推测形成于中更新世甚至早更新世，中更新世末的新构造运动湖水向西撤退，随即被晚更新世的戈壁砾石层覆盖。晚更新世末发育了东西向古河道，以后由蒙古高原南下的强劲北风吹蚀而成，雅丹一般高２０～４０ ｍ，最高可达１００ ｍ，形态丰富多姿，为世界上所少见的大中型、密集的、形态奇特的雅丹地貌景观，是旅游观光和科研的宝地。

柴达木盆地鸭湖地区水上雅丹地貌成因研究

本文通过对青海柴达木盆地鸭湖地区构成水上雅丹的地层序列和沉积相、地层形成时代、地层形成后演化为雅丹地貌的构造条件、气候条件和人为因素的研究,认为构成研究区水上雅丹的地层为中新世上油砂山组,所含介形虫组合指示其形成时代为中新世晚期;沉积相和孢粉组合分析揭示本区在中新世晚期为温暖干旱的气候下的古湖环境,接受湖相和湖泊三角洲前缘沉积;上新世在区域构造抬升和干旱化气候的双重作用下,古湖逐渐萎缩;更新世在极端干旱和强劲的季风环境中,被抬升到地表的上油沙山组上部地层在风蚀为主的外营力作用下形成雅丹;晚更新世末期—全新世由于末次间冰期的到来,气候转向温暖湿润,湖水再次入侵。近年人类活动改变了湖泊分布格局,导致湖泊淹没了部分陆地上的雅丹,呈现为奇特的水上雅丹地貌景观。

罗布泊东阿奇克谷地雅丹地貌与库姆塔格沙漠形成的关系

阿奇克谷地位于罗布泊洼地之东,93°E以西,东西长约150km,南北宽20～30km。为新生代北山与阿尔金山之间的地堑凹地的一部分,与东面河西走廊的地堑凹地相通。根据出露的雅丹地层河湖相沉积样品所作的ESR测年(227 2～1009 4kaBP)和本区的地质地貌特征可将阿奇克谷地演化与库姆塔格沙漠的发育史归纳为4个时期。①早更新世至中更新世罗布泊古湖扩大时期,东部湖湾宽约50～60km,向东延伸至93°15′E或更东;②中更新世晚期山地上升与古湖湾退缩消失时期,距今30万年前左右,青藏高原强烈隆升,阻挡了海洋水汽的进入,亚洲内陆加速变干,由于阿尔金山的左旋向东滑动,在北面古湖区地层发生了与阿尔山斜交的羽毛状断裂谷群,并因东北向的断裂上升与东西向的河西地堑谷地斜交,阻断了疏勒河水不再向西流入罗布泊,使东部湖湾向西退缩并逐步消失;③中更新世晚期至晚更新世初,暴雨径流与强烈的风蚀作用时期,阿奇克谷地北部的洪积湖相沉积台地支沟口形成雅丹土丘群,谷地南面库姆塔格沙漠北面羽毛状断裂谷群形成雅丹垄脊和风蚀谷,谷地中央呈现出季节性的盐碱沼泽和零星雅丹土丘;④晚更新世末至全新世库姆塔格沙漠扩大,向北埋没了羽毛状断裂谷(风蚀谷)和雅丹垄脊,形成了世界上独特的羽毛状沙丘。

柴达木盆地东南部雅丹地貌形态参数研究

雅丹地貌的外部形态特征是其对所处环境适应的表现,对雅丹地貌形态参数进行研究可以推测雅丹体所受内外营力的性质。以柴达木盆地的东南部为研究区域,通过对该区雅丹地貌形态参数的相关性分析,得出该区雅丹地貌长与宽的相关系数r=0.882 4,为强相关关系,采用最小二乘法拟合得出长/宽(R)=3.04。并通过与其它区域雅丹地貌的研究结果对比,发现全世界范围内雅丹地貌的形态参数长与宽均具有较强的相关性,而长/宽(R)值则具有区域差异性。从雅丹地貌成因的层面对这一现象进行分析,认为雅丹地貌形成因素的相似性,决定着雅丹体外部形态的相似性,即体现为长与宽的强相关性。同时又由于形成因素的区域差异性使得长/宽(R)值在不同的雅丹地貌分布区具有不同的数值。

鱼卡(红柳)至一里坪铁路地质选线研究

研究目的:鱼一线地处柴达木盆地西北边缘地带,自然环境恶劣,地质条件复杂,线路穿越了世界上最大的雅丹地貌(俗称"魔鬼城"),风沙、盐渍土遍布,湖盆低洼地带存在软土、盐岩。在该地区进行地质选线对于降低后期勘察设计难度、减少投资、降低后期维护费用等方面起决定性作用。本文针对线路穿越风沙、软土、盐渍土、盐岩四类工程地质问题时,采取何种地质选线的技术原则进行了研究。研究结论:(1)在本次地质选线过程中,综合采用了遥感解译、地质调绘、钻探、试验等勘探方法,查清了沿线的工程地质条件;(2)对线位比选起决定性因素的工程地质条件主要有风沙、软土、盐渍土、盐岩,选线应遵循"绕避为主"的原则;(3)通过对北线方案(CK)、中线方案(C9K)、南线方案(C10K)三条线位进行比较,得出中线方案优于北线方案、南线方案,宜做为本线的推荐方案;(4)本研究能够为类似地区的工程项目选线研究提供一定的借鉴。

多伦县风蚀地貌及风蚀量评价研究

在多伦县沙漠化土地调查过程中,就其风蚀地貌进行了详细的研究。本文不仅论证了风蚀地貌的形成、类型和分布,而且以翔实的测定数据,并采用克拉瓦洛维克的风蚀强度公式计算了该地区不同景观类型区的风蚀量。以论据为基础,研讨了增加地表粗糙度的方法、成效以及防止或减缓风蚀的有效途径。

新疆罗布泊旅游资源特征

罗布泊曾为中国第二大内陆湖泊,随着自然环境的变迁以及塔里木河上游筑坝截流,使罗布泊无水流补给于1972年彻底干涸,干涸的罗布泊在卫星影像图上呈现出清晰的耳状环形图案,被称为神秘"地球之耳"。在罗布泊古湖周围分布有龙城、白龙堆、阿齐克谷地等雅丹地貌,面积达约3 000km2,是我国仅次于柴达木盆的第二大雅丹地貌分布区,由于其位于塔里木盆地东部的荒漠地带,人迹罕至,是世界最神秘的雅丹地貌。除丰富的地质遗迹景观外,在罗布泊还分布有楼兰古城遗址、米兰古城遗址、贵族墓等众多绚丽多彩的人文景观资源。这里原始古朴,是一块充满神秘色彩的地方,是未来旅游开发的热点地区之一。

00Cr22Ni5Mo3N双相不锈钢在某气田雅丹地貌土壤中的腐蚀行为

为考察00Cr22Ni5Mo3N双相不锈钢在中国西部某气田雅丹地貌环境的腐蚀行为及对其施加阴极保护的必要性,采用现场埋设试片的方法,通过对试片的腐蚀速率、腐蚀形貌分析,研究了其腐蚀行为特征。结果表明:00Cr22Ni5Mo3N试片在该土壤中的平均腐蚀速度低,适用于该气田集气管线,并无施加阴极保护的必要性。

超氯盐渍土在雅丹地貌铁路沿线固沙试验研究

以雅丹地貌新建铁路为例,研究当地超氯盐渍土在铁路沿线固沙中的应用。通过室内土工试验和微观分析结合的方法,研究超氯盐渍土的氯离子含量、含水率、液塑限、养护温度和抗压强度的关系。研究结果表明:随氯离子含量和含水率的提高,单键键能増大,单位体积键量减少,总键能减小,导致试件的抗压强度降低;抗压强度与最佳含水率之间呈抛物线关系。加温养护后,试件孔隙率增大,抗压强度降低。对于氯离子含量超过40%的盐渍土,不但要考虑毛细现象的影响,而且需采用固化剂对氯盐进行处理。研究结果对雅丹地貌新建铁路沿线的绿色固沙有所裨益。