STC加筋砂水平循环剪切与竖向激振特性试验研究          下载免费PDF全文

鲁洋  刘斯宏  张雨灼  徐小东 《地震工程学报》2015,37(2):494-499

随着中国汽车工业的发展,大量废旧轮胎带来的"黑色污染"问题日益显著。提出一种采用废旧轮胎柱(Scrap tire columns,STC)的加筋土结构,并初步探究其作为基础减隔振材料的可行性。通过室内水平循环剪切试验和竖向激振试验研究STC加筋砂(STCRS)的水平循环剪切和竖向激振特性。结果表明,最大剪应变为1%时STCRS的等效阻尼比未加筋前增加约10%,等效动剪切模量减小20%~25%,水平向减振性能得以提高;STCRS的竖向加速度衰减呈现出速度快、幅值大的特点,竖向减振效果较未加筋砂显著提高。STC加筋砂作为基础减振材料是可行的,且为原形废旧轮胎的资源化利用提供新思路。  相似文献   

考虑挤土效应时楔形桩纵向振动阻抗研究          下载免费PDF全文

吴文兵  谢帮华  黄生根  徐学连 《地震工程学报》2015,37(4):1042-1048

基于复刚度传递多圈层平面应变模型,研究考虑桩周土挤土效应时成层地基中楔形桩的纵向振动问题。首先根据桩周土体的纵向成层情况并考虑楔形桩的变截面特性,将桩土系统沿纵向划分为有限个微元段,对每个微元段的桩周土体建立复刚度传递多圈层平面应变模型,并通过剪切复刚度递推方法求得桩周土作用在桩身的剪切复刚度;然后将求得的剪切复刚度代入桩身纵向振动控制方程,运用Laplace变换技术和阻抗函数递推方法,推导得到考虑桩周土挤土效应时成层地基中楔形桩纵向振动时桩顶复阻抗的解析解;最后,采用参数研究方法在低频范围内分析挤土效应对桩顶复阻抗的影响及其规律。  相似文献   

城市地铁爆破开挖对浅埋地下大直径管道的安全影响研究     

赵建平  宋晓东 《震灾防御技术》2015,10(3):531-538

在城市浅埋地铁爆破开挖中,经常遇到地下管网、涵洞等构筑物,而爆破地震效应对其影响范围和程度的正确评价就显得尤为重要。本文以长沙地铁爆破开挖为例,以现场实测数据为基础,采用有限单元法,对爆破振动下大直径混凝土污水管道的动力响应、变形和动应力等进行了计算,评价了爆破地震对管道的安全影响。研究表明:管道在控制爆破作用下是偏于安全的;爆心距是影响管道受到爆炸作用力影响大小的最主要因素;对于以实测数据为基础,采用加速度激励的时程分析方法以爆破振动对埋地管道的影响进行评价,是一种可行且较为精确的方法。  相似文献   

衬砌隧道中移动轴向激励作用下两相多孔介质动力响应     

包汉营  陈文化 《岩土力学》2018,39(10):3735-3742

为了研究衬砌隧道中地铁振动在饱和地层中的传播情况,采用移动轴向激励模拟技术,建立了隧道-衬砌-两相介质的动力分析模型;利用波函数展开法、傅里叶变换法等,推导了频域内衬砌隧道移动轴向激励作用下两相多孔介质动力响应的解析解,并给出了两相多孔介质临界速度的经验公式;通过离散快速傅里叶逆变换得到了时-空域内两相介质的动力响应。结果表明：无衬砌隧道中移动的轴向常激励作用下,两相介质临界速度只与介质的剪切模量和密度有关,且数值接近其剪切波速的1.1倍;对于衬砌隧道,介质的临界速度随着衬砌剪切模量的增大而增大,随着衬砌密度的增大而减小,衬砌对振动向介质中的传播有一定的削弱作用,衬砌剪切模量与介质剪切模量相差越大,削弱越明显;动力响应频率越接近激振频率,其幅值越大,所对应的临界速度越小。  相似文献   

水平成层场地动剪应变与震动速度关系解析     

李瑞山  袁晓铭  李程程 《岩土力学》2018,39(10):3623-3630

以SHAKE2000为代表的频域等效线性化是目前主流的土层地震动计算方法。由于该方法在软土场地计算结果严重不合理,其改进方法成为目前研究热点,主要采用频率相关法,但一直没有取得实效。对频率相关法中土体动剪应变和震动速度成恒定比例关系的基本假定进行研究,从波动方程推导出了均匀全空间单向行波、单一均匀半无限场地、成层场地等3种典型场地中土体剪应变与震动速度关系的精确解答,通过数值试验研究了这一假定的合理性与偏差程度。结果表明：动剪应变和震动速度成恒定比例关系这一假定只有在无边界均匀介质单向行波情形下才成立,对于实际成层土场地,动剪应变与震动速度关系强烈依赖于波的频率和观察点的位置,如果在土层地震反应分析中忽略反射波而采用单向行波恒定比例假定将会使计算结果产生显著偏差;动剪应变与震动速度成恒定比例关系的假定导致的偏差达4个量级,即使对于单一均匀半无限空间模型偏差也十分显著;对实际土层地震动的求解,该假定在理论上定性错误,定量上偏差不可接受,必须放弃而另寻其他途径。  相似文献   

超声波振动下不同应力条件对岩石强度影响的试验     

尹崧宇  赵大军 《吉林大学学报(地球科学版)》2019,49(3):755-761

振动有助于碎岩,以往关于振动碎岩机理的研究大多在低频率段展开。为填补超高频率段下振动碎岩机理的空白,采用单轴动静组合加载模式,开展了超声波振动下不同应力条件对岩石强度影响的试验研究,其中超声波振动频率为20kHz,预压范围为100～500N。研究结果表明:当预压小于200N时,岩石内部应力状态无法满足强度准则,岩石强度下降不明显;当预压大于等于200N时,岩石强度随振动时间的增加而逐渐降低且存在最优预压力值(400N)使得岩石强度最低。缩短振动频率与岩石固有频率的差值有利于提高超声波振动碎岩效率。  相似文献   

From outwash to coastal systems in the Portneuf–Forestville deltaic complex (Québec North Shore): Anatomy of a forced regressive deglacial sequence          下载免费PDF全文

Pierre Dietrich  Jean‐François Ghienne  Mathieu Schuster  Patrick Lajeunesse  Alexis Nutz  Rémy Deschamps  Claude Roquin  Philippe Duringer 《Sedimentology》2017,64(4):1044-1078

Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km²) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km³) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year^?1), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year^?1), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations.  相似文献   

Numerical benchmark studies on drag and lift coefficients of a marine riser at high Reynolds numbers     

《Applied Ocean Research》2017

Numerical benchmark studies on drag and lift coefficients of a marine riser have been organized by the 27th ITTC Ocean Engineering Committee. The purpose of the studies was to benchmark the capabilities of CFD methods through quantitative comparisons and validation studies against the model test results of a circular cylinder by MARIN. Studies were focused on the drag crisis phenomenon for the stationary smooth cylinder in the critical Reynolds number regime. Eight organizations have participated in the studies by using RANS, DES and LES methods. An overview of the model test results, test cases, submissions and comparison results are presented in this paper. Conclusions and recommendations are made for future studies.  相似文献   

涡激振动实验中的流速增大装置研发与性能研究          下载免费PDF全文

姚宗  陈刚  杨建民  胡志强  付世晓 《海洋工程》2017,35(6):1-9

拖曳水池中进行立管涡激振动实验时,为了保证采样时间长度,难以达到较高的Re数。流速增大装置可以在不提高拖车车速的情况下增大立管外的流速。利用这种流速增大装置还可实现流速分层流场中细长柔性立管涡激振动实验。经过对流速增大装置中的进流段曲线进行优选,发现Witozinsky曲线的总体性能最好。在对流速增大装置进行水池实验和数值模拟后,发现流速增大区域的流速增大倍数接近进流段收缩比,流速增大区域流场比较稳定、均匀,流速增大装置对其外的流场影响很小。此流速增大装置不但可应用于拖曳水池中的立管涡激振动实验,还可以应用于对流速要求较高的水下航行体的水池试验,如鱼雷、水下机器人等。  相似文献   

Two Improvements on Numerical Simulation of 2-DOF Vortex-Induced Vibration with Low Mass Ratio     

KANG Zhuang  NI Wen-chi  ZHANG Xu  SUN Li-ping 《海洋工程》2017,(6):764-772

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson''s work, the maximum amplitude of the cylinder with low mass ratio m*=2.6 can reach as large as 1.5D to be called as the “super-upper branch”, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.  相似文献