Buckling limit evaluation for reactor vessel of KALIMER liquid metal reactor under lateral seismic loads

The purpose of this paper is to evaluate the buckling limit of a conceptually designed reactor vessel of the Korea advanced liquid metal reactor (KALIMER). For evaluation of the critical buckling load, evaluation formulae and numerical simulation methods using finite element analysis are used. In the numerical simulation methods, eigenvalue buckling analysis, and non-linear buckling analysis with and without plasticity effects are carried out. From the calculated results of the critical buckling load in the KALIMER reactor vessel, it is shown that plasticity behavior significantly affects the buckling strength but the initial geometrical imperfections have little effect on it. In checking the buckling limits of the KALIMER reactor vessel for safe shutdown earthquake (SSE) lateral seismic load using the ASME B and PV Section III, Subsection NH, a non-seismic isolation design does not satisfy the buckling limit requirements but a seismic isolation design sufficiently satisfies the requirements. From the experimental verification tests performed for the cylindrical shells of the reduced scale, it is confirmed that the non-linear numerical simulation method used in the buckling strength evaluation can assure accurate results for buckling strength and buckling mode shape.     

The buckling behavior of U-shaped bellows under pressure loads

Bellows exhibit unique buckling behavior because of their peculiar shape. The buckling behavior and buckling criteria of bellows subjected to pressure loads are examined analytically and compared with test results. Under internal pressure, two different buckling modes can occur, namely, in-plane squirm and column squirm. On the other hand, under external pressure, bellows deformation is different from that under internal pressure.

The authors investigated various types of buckling behavior of bellows by means of simplified methods of analysis and finite-element analyses and conducted validation tests under various conditions. On the basis of these analytical and experimental studies, a rational method for evaluation of the buckling of bellows is proposed.     

Fracture behaviour of large scale pressure vessels in the hydrotest

Within the Nordic Countries a four-year research programme in the area of elastic-plastic fracture mechanics was initiated in 1985. This programme aims to assess the leak-before-break (LBB) criteria for pressure vessels and piping. The main experimental effort of the programme is to rupture large size pressure vessels, one having dimensions resembling those of a nuclear reactor pressure vessel, under internal pressure. Artificial flaws were made on the inner wall of the vessels. The dimensions of the flaws were defined by calculations so that the LBB condition was just anticipated during the test. For the time being two tests have been performed. The first test with a large pressure vessel was pressurized by water at 60°C, which was the lowest acceptable temperature for the hydrotest. In this paper experimental details including flaw preparation, instrumentation and material characterization are described. The fracture behaviour as well as experimental results of the tests are reported and compared to the analytical solutions of the analyses.     

Centrifuge modeling to evaluate natural frequency and seismic behavior of offshore wind turbine considering SFSI

Understanding of dynamic response of offshore wind turbine is important to reduce vibration of offshore wind turbine induced by structural and environmental loadings. Although dynamic characteristics of the offshore wind turbine such as natural frequency and seismic behavior are affected by foundation and soil conditions, there are little experimental studies about the dynamic behavior of offshore wind turbine with consideration of proper soil–foundation–structure interaction (SFSI). The goal of this research is to evaluate the natural frequency and seismic behavior of offshore wind turbine with a monopod foundation considering SFSI. Scaled model of offshore wind turbine and monopod foundation is produced for this research. Geotechnical centrifuge tests in fixed‐based and SFSI condition were performed to measure natural frequency in each case. Also, a series of seismic loadings with different intensities are applied to observe seismic behaviors of the offshore wind turbine during the earthquake and permanent changes after the earthquake. Experimental results show apparent natural frequency reduction in SFSI condition compared with the fixed‐based condition, non‐linear changes in dynamic response during a series of earthquakes and permanent changes occurred in natural frequency and rotational displacement after earthquakes. Copyright © 2017 John Wiley & Sons, Ltd.     

Experimental creep life assessment of tubular structures with geometrical imperfections in welds with reference to fast reactor plant life

Creep damage is a major life limiting factor for components operating at high temperature. For the fast breeder reactor (FBR), the hot sodium pool components and the steam generator are critical in determining the operating temperatures from structural mechanics considerations. Therefore, creep fatigue damage at various critical locations is estimated based on viscoplastic analyses, in compliance with the high temperature design rules of RCC-MR. In addition, welded joints of steam generator tubes with spigots made of modified 9Cr–1Mo and the welds of fuel pins made of 20% cold worked stainless steel to annealed end plugs, which have certain geometrical imperfections in the welds are also critical and the applicability of existing design rules to these components needs to be investigated carefully. Towards assessing the life of such tubular components realistically, accelerated tests were conducted simulating the creep damage to rupture. The generated test data were investigated by applying the existing creep damage assessment procedure recommended in the design code RCC-MR and the results demonstrated that with the recommended multiaxial creep damage assessment rule, the creep crack initiation lives have been predicted accurately. Further, the extrapolated life predicted by applying an appropriate Larson–Miller parameter indicates that the circumferential welds in the steam generator tubes and fuel pins are not life limiting factors in the design.     

密松水电站副厂房结构抗震分析

水电站副厂房是设置重要电气设备和工作人员工作的主要场所,其抗震安全性直接关系到整个电站的安全运行,以密松水电站副厂房为例,采用振型分解反应谱法对其结构进行抗震计算分析,给出了结构自振特性及在地震作用下的动应力、动位移,并采用最不利组合法将动力计算结果与静力计算结果进行叠加,对叠加后的结构应力及位移进行评估分析。结果表明,高地震烈度下,副厂房结构上部纵、横梁底部应力较大,建议在这些部位增大梁截面尺寸或加强配筋,以保证副厂房结构的安全运行。     

缅甸高震区某进水塔抗震与稳定性研究

鉴于进水塔结构在地震作用下的安全性关系到整个电站的安全和效益,以缅甸高震区某进水塔结构为例, 采用振型分解反应谱法计算分析了进水塔结构的自振特性、动位移、动应力,并将静动力计算结果进行了叠加, 评估了进水塔结构抗震性能,在此基础上分析了结构抗滑、抗倾覆稳定性。结果表明,该进水塔结构的变形、强 度及稳定性均能满足要求,可为工程设计提供参考依据。     

广义塑性模型在海洋砂土中的适用性研究

为研究广义塑性模型在海洋砂土中的适应性,采用静、动三轴仪对海洋砂土进行了固结排水剪切及固结不排水循环剪切试验,根据试验结果拟合出砂土的广义塑性模型参数,并利用此参数对动模量和阻尼比试验进行了数值模拟,比较了试验结果与模型拟合结果的差异。结果表明,计算结果与试验测定的动模量、阻尼比与动应变的变化规律一致,该模型能很好地反映砂土单调加载的应力－应变特性及小应变阶段的循环加载条件下的变形特性。     

低温环境中水工沥青混凝土动态抗压性能研究

为研究低温环境中水工沥青混凝土在地震作用下的动力特性及破坏模式,在不同温度和应变率下对水工沥青混凝土现场芯样进行了动态抗压试验,深入分析了温度和应变率对水工沥青混凝土的破坏形式、应力应变特性、峰值应力及弹性模量等力学性能的影响。结果表明,随着应变率的增加,水工沥青混凝土的破坏模式由微裂纹破坏、拉剪破坏过渡至劈裂破坏,应力应变曲线由应变硬化型向应变软化型转变,抗压强度和弹性模量也随之增大;随着温度的降低,水工沥青混凝土强度和刚度明显增大,具有明显的低温硬化效应。此外,基于试验结果建立了沥青混凝土的动态本构模型,该模型参数较少且与试验结果吻合度较高,具有一定的实用性。     

新型预制装配式混凝土剪力墙水平缝受力性能的数值分析

为解决装配式剪力墙钢筋外伸及湿作业影响工程质量的问题,设计出了一种无外伸钢筋且利用钢预埋件焊接的干连接方式的新型装配式剪力墙,并采用Abaqus有限元法模拟分析新型装配式剪力墙水平缝干连接方式时水平缝的受力性能,再通过与Abaqus有限元法模拟的现浇剪力墙、试验现浇剪力墙的滞回曲线、骨架曲线、延性系数、耗能能力、刚度退化等进行了对比分析。结果表明,在低周反复荷载的作用下,该新型预制装配式剪力墙结构虽然在耗能能力、抗震能力等方面比现浇剪力墙略弱,但接近于现浇剪力墙结构,受力性能较好,抗震性能较好。     

海上风机支撑结构疲劳性能试验研究

  目的  针对海上风机支撑结构的疲劳问题,进行了外加强环过渡段结构疲劳性能的试验研究。  方法  采用简化的支撑结构1/5缩尺模型进行了静力与疲劳试验,获得了模型的热点应力和疲劳寿命;并根据DNV的海上风机规范,采用不同类型单元对试验模型进行了有限元分析和疲劳寿命估算,将规范方法的计算结果与试验进行了比较。  结果  结果表明:试验结果和规范方法之间的差异主要源于S-N曲线的选取。  结论  最后根据试验数据,在DNV规范的基础上给出两种改进的疲劳校核方案,可为实际应用提供指导。     

直接测力俯仰振荡翼型动态气动性能研究

在西北工业大学NF-3低速风洞二元实验段开展翼型俯仰振荡运动动态气动性能深入研究。实验模型为展向三段式测力模型,测力仅在模型中段进行以减小风洞侧壁干扰的影响。实验中采集模型的转动瞬态迎角、计算模型中段的惯性力和惯性力矩、并从天平采集数据中扣除以修正模型惯性对结果的影响。结果表明,迎角超过正向或负向静态失速迎角是升力系数和俯仰力矩系数产生大的迟滞环的必要条件。随着振荡缩减频率增大,动态失速会推迟,升力系数迟滞环增大,阻力系数增大,最大迎角附近的俯仰力矩系数减小。在迎角小于静态失速迎角或超过不大的迎角范围,随着缩减频率的增大,翼型振荡运动俯仰力矩系数上行时减小,下行时增大。随着振荡振幅的增大,翼型振荡运动动态升力系数和俯仰力矩系数的迟滞环增大。随着平均迎角的增大,翼型迎角更多地进入正向失速区,升力系数迟滞环增大,俯仰力矩系数最小值变小。雷诺数对升力系数、阻力系数和俯仰力矩系数迟滞环无明显影响;但是,在翼型模型下行过程,随着雷诺数的增大,升力恢复提前,同时迟滞环随雷诺数增大而减小。     

Analytical studies of four-inch pipe whip tests under BWR LOCA conditions

The purpose of pipe rupture studies in JAERI is to perform model tests on pipe whip, restraint behavior, jet impingement and jet thrust force, and to establish a computational method for analyzing these phenomena. This report presents the analytical results of 4-inch pipe whip tests under BWR LOCA conditions.Dynamic response analyses were performed using the general-purpose finite element program ADINA. The test pipe was modelled by straight beam elements and the four restraints were modelled by a single truss element. The analytical results were compared with the experimental results. Impact time and maximum total restraint force showed good agreement with experimental results. On the other hand, pipe strain and pipe deflection could not be predicted so well. The reason for this is that the sliding of the restraint during the pipe whip movement cannot be considered in the analyses.     

边坡动力响应特性及破坏过程的振动台试验研究

以某护坡工程中的岩土边坡为原型,设计并制备了坡高1 m、坡角45°的模型边坡,通过输入不同振幅的人工波、随机波和白噪声激励,采用大型振动台动力模型试验研究了边坡的动力响应规律及已知滑动面条件下的边坡失稳滑动机理。试验结果表明,不管是坡体表面或内部,加速度放大系数均随高程增加呈放大效应,相同高程的边坡表面放大系数略高于坡体内部,且呈现出一定的趋表效应;随着地震波加速度幅值的增加,结构面开始出现张开、闭合、滑移的运动状态,进而产生较大的位移并发生失稳破坏。     

开孔和补强对圆柱壳轴压屈曲的影响分析

  [目的]  早期的圆柱壳轴压屈曲试验结果与理论偏差较大,导致差异的因素较多,其中初始几何缺陷是产生差异的主要因素。  [方法]  文章采用一种专用的轴压屈曲试验平台,可以利用激光位移传感器扫描壳体三维实际形貌。屈曲试验轴压采用液压装置,轴压数据通过称重传感器读取。  [结果]  试验结果表明:开孔降低了圆柱壳轴压屈曲临界载荷,在开孔处插入圆管补强件,提高了圆柱壳轴压屈曲临界载荷。基于壳体形貌实测数据建立了有限元模型,利用Abaqus对圆柱壳、开孔圆柱壳和补强圆柱壳进行非线性屈曲有限元分析。  [结论]  模拟得到的规律与试验规律一致,壳体轴向载荷均是先呈线性增大后减小,开孔圆柱壳轴压屈曲临界载荷最小,含补强件圆柱壳轴压屈曲临界载荷次之,未开过孔的圆柱壳轴压屈曲临界载荷最大。对不同壳体的临界载荷模拟值与试验值进行了比较,其中最小的相对误差只有13.8%。说明运用此方法可以预测壳体轴压屈曲临界载荷,对壳体屈曲设计具有参考价值。     

A comparative study of usefulness for pad reinforcement in cylindrical vessels under external load on nozzle

The main purpose of this paper is to perform a comparative study of strength behavior for cylindrical shell intersections with and without pad reinforcement under out-of-plane moment loading on nozzle. Three pairs of full-scale test vessels with different d/D ratios were designed and fabricated for testing and analysis. A three-dimensional nonlinear finite element numerical analysis was also performed. The maximum elastic stress for each vessel under per unit moment on nozzle is provided. The plastic limit moment on nozzle is obtained by load–displacement and load–strain curves for each test vessel. The results indicate that the effect of pad reinforcement on decreasing maximum elastic stress and increasing plastic limit load is obviously effective. The study results will serve as the available data for understanding the usefulness of pad reinforcements and as the basis for developing an advanced design method by limit analysis for pad-reinforced cylindrical vessels under external loads on nozzle.     

Seismic evaluation of offshore wind turbine by geotechnical centrifuge test

As offshore wind turbines are now planned to be installed at seismic activity areas around Asia in large numbers, understanding of the seismic behavior of offshore wind turbine has become essential to evade structural hazards due to earthquake. Although the seismic behavior of the structure is largely affected by soil‐foundation‐structure interaction (SFSI), there is only a few experimental data about this subject as conventional offshore wind turbines are mostly located in the area where earthquakes are scarce. Geotechnical centrifuge experiment can provide reliable experimental data for this subject as it can reproduce field stress condition of the soil and simulate earthquake motion in a scaled model test. In this research, three case studies using centrifuge model test were performed to evaluate the seismic behavior of offshore wind turbine during the earthquake and permanent deformation after the earthquake. The results were compared with conventional seismic evaluation methods. Monopile, Monopod, and Tripod foundations were chosen for the experiment. Peak acceleration and rotational displacement of the wind turbine for three cases were evaluated under various intensities of seismic loading applied by centrifuge‐mounted shaking table. Results were compared with conventional evaluation method for design acceleration and conventional rotational displacement criteria suggested in DNV‐OS‐J101.     

核电应急柴油发电机组辅助高温水循环泵抗震鉴定试验研究

为验证某核电站应急柴油发电机组辅助用高温水循环泵的抗震性能,根据国家相关规范标准进行了抗震性能试验研究。采用白噪声信号作为输入激励,分别测试了高温水循环泵在抗震试验前后的固有频率和阻尼比;根据高温水循环泵具体位置选定对应的反应谱,进行了5次运行基准地震试验和1次安全停堆地震试验。试验结果表明:该型高温水循环泵有足够的抗震强度,能够在规定的地震条件下正常运行,满足抗震性能要求。     

Observations of hydraulic stimulations in seven enhanced geothermal system projects

Numerous stimulation tests have been performed on Enhanced Geothermal System (EGS) or Hot Dry Rock (HDR) projects during the past three decades, however, there is much room for improvement in our knowledge and understanding of the mechanisms of stimulation. This paper investigated the hydraulic stimulation tests carried out on seven EGS or HDR projects where massive volume of fluid was injected into the long open section of the well with interval of tens to hundreds of meters in the crystalline formation. The key characteristic test and performance parameters were defined and collected through extensive survey of stimulation results. Attempts were made to carry out comparative analysis on reservoir conditions, test parameters and test observations. The analysis and discussion suggest that 1) the reservoir stress regime impacts the growth of stimulated region and the reverse faulting stress regime can be favorable for the layout of multiple well system as it may lead to a horizontally or sub-horizontally oriented stimulated zone; 2) the injection pressure for activating shear slip and the associated onset of seismicity is mainly field stress controlled; 3) there is strong dependency of injectivity on injection pressure and a high pressure makes a better hydraulic injectivity during stimulation and consequently afterwards for circulation; 4) the stimulated region and number of induced seismic events are mainly injection volume controlled and the potential strategy to reduce seismic risks is either to extend stimulation in time or to separate stimulation in space; and 5) the differential stress condition is one of the necessary factors to raise a large magnitude event (LME) and the difference of maximum injection pressure achieved over that at onset of seismicity is an important additional factor to induce LMEs.     

Preliminary experimental evaluation of a four wheel motors,batteries plus ultracapacitors and series hybrid powertrain

This paper reports the preliminary experimental evaluation of a four wheel motors series hybrid prototype equipped with an internal combustion engine coupled to a generator and an energy recovery system (batteries plus ultracapacitors). The paper analyses global efficiency (energy dissipated to overcome the dissipative forces on energy dissipated in fuel), autonomy in electric configuration, and the efficiency of the regenerative braking system. The tests were carried out in a test cell equipped with a chassis dynamometer. The tests were performed according to the current regulated procedures. A constant speed test was performed in order to evaluate the autonomy of the vehicle in the electric configuration. The results show that the real tank to wheels efficiency is about 30% for HOST as a series hybrid and 79% for HOST as an electric vehicle.