动车水箱焊缝随机振动疲劳寿命的时域法研究

动车车载设备较多采用焊接结构,在列车高速行驶过程中,焊缝处易发生疲劳失效。以往的分析对象多数主要是简单焊接结构,而对于复杂焊接结构,特别是随机振动时焊缝的疲劳寿命预测比较欠缺。为此,针对某包含焊缝及水的动车水箱有限元模型,采用模态叠加瞬态响应分析法,获得该焊接结构中各节点的应力-时间、加速度-时间响应曲线。结合焊缝S-N曲线、Miner线性累积损伤理论和雨流循环计数法,基于时域法估算母材及焊缝的随机振动疲劳寿命。结果表明:连接水箱上盖板和下箱体的焊缝处疲劳寿命最低,仅为17 min,根据预测结果给出了水箱的结构优化方案。通过与台架试验数据对比,表明该种焊缝疲劳寿命数值模拟算法具有正确性和有效性。

Numerical Analysis of the Flow Field in a Sloshing Tank with a Horizontal Perforated Plate

Liquid sloshing is a type of free surface flow inside a partially filled water tank.Sloshing exerts a significant effect on the safety of liquid transport systems;in particular,it may cause large hydrodynamic loads when the frequency of the tank motion is close to the natural frequency of the tank.Perforated plates have recently been used to suppress the violent movement of liquids in a sloshing tank at resonant conditions.In this study,a numerical model based on OpenF OAM(Open Source Field Operation and Manipulation),an open source computed fluid dynamic code,is used to investigate resonant sloshing in a swaying tank with a submerged horizontal perforated plate.The numerical results of the free surface elevations are first verified using experimental data,and then the flow characteristics around the perforated plate and the fluid velocity distribution in the entire tank are examined using numerical examples.The results clearly show differences in sloshing motions under first-order and third-order resonant frequencies.This study provides a better understanding of the energy dissipation mechanism of a horizontal perforated plate in a swaying tank.

The Effect of Netting Solidity Ratio and Inclined Angle on the Hydrodynamic Characteristics of Knotless Polyethylene Netting

Knotless polyethylene(PE) netting has been widely used in aquaculture cages and fishing gears, especially in Japan. In this study, the hydrodynamic coefficient of six knotless PE netting panels with different solidity ratios were assessed in a flume tank under various attack angles of netting from 0?(parallel to flow) to 90?(perpendicular to flow) and current speeds from 40 cm s^(-1) to 130 cm s^(-1). It was found that the drag coefficient was related to Reynolds number, solidity ratio and attack angle of netting. The solidity ratio was positively related with drag coefficient for netting panel perpendicular to flow, whereas when setting the netting panel parallel to the flow the opposite result was obtained. For netting panels placed at an angle to the flow, the lift coefficient reached the maximum at an attack angle of 50? and then decreased as the attack angle further increased. The solidity ratio had a dual influence on drag coefficient of inclined netting panels. Compared to result in the literature, the normal drag coefficient of knotless PE netting measured in this study is larger than that of nylon netting or Dyneema netting.

Experimental assessment of two-phase bubble pump for solar water heating

The research goal is to develop a new solar water heater system(SWHS) that uses a solar bubble pump instead of an electric pump.The pump is powered by the steam produced from an evacuated tube collector.Therefore,heat could be transferred downward from the collector to a hot water storage tank.The designed system consists of two sets of heat-pipe evacuated tube collectors,a solar bubble pump installed at an upper level and a water storage tank with a heat exchanger at a lower level.Discharge heads of 1 and 5 m were tested.The bubble pump could operate at the collector temperature of about 90-100 ℃ and vapor gage pressure of 80-90 kPa.It is found that water circulation within the SWHS depends on the incident solar intensity and system discharge head.Experimental investigations are conducted to obtain the system thermal efficiencies from the hourly,daily and long-term performance tests.The thermal performance of the proposed system is compared with conventional solar water heaters.The results show that the proposed system achieves system characteristic efficiency of 10% higher than that of the conventional systems using electric pump if taking the consumption of electric power into account.And the former is a zero carbon system.

Investigation of the Effect of Bulbuos Bow of Containership in Head Waves Using CFD

Reynold＇s averaged Navier-Stokes based CFD （computational fluid dynamics） technique WISDAM developed at The University of Tokyo is used to investigate and compare the hydrodynamic loads on container ship models SR108 and KCS in 120 degree regular oblique wave conditions. WISDAM has the capability of handling 6DOF （six degrees of freedom） in ship motions. Finite volume method with structured and overlapping grid system is employed. The flow variables are described in staggered manner, i.e., velocity components arc defined at the face center while pressure is at the cell center. Computational results agree favorably well with existing towing tank results especially for ship motions. Computational results also show that ship with bulbous bow experience higher hydrodynamic loads on bow section.