纵向通风下不同坡形隧道火灾烟气温度分布特性研究

为了解决不同纵向坡形隧道发生火灾时的烟流控制问题,以宝兰客运专线渭河隧道V形坡火灾通风为例,采用三维数值模拟方法,对不同坡形下烟气温度的分布特性进行研究。通过对V形坡、单面坡和人字坡等不同坡形隧道在不同纵向通风速度下的火灾工况模拟,对比分析隧道拱顶、一人高和3.0 m高处的温度分布特征。结果表明： 在火灾发生初期,当无纵向通风时,在变坡点火源车厢附近人字坡的温度最高,但随着离火源点距离的增大,V形坡的温度逐渐达到最大;当有纵向通风时,V形坡下游沿程的温度最高,且随风速增大,温度最高区域的分布范围逐渐扩大,而单面坡和人字坡的温度变化曲线基本一致,并在离火源点较远的下游区域趋于定值;在本研究范围内的坡形、坡度条件下,当纵向通风风速达到2 m/s 时,烟控效果最好。     

船体极限强度试验小比尺相似模型研究

基于薄壁梁理论推导了总纵极限强度试验的相似模型设计应该满足的条件,然后选取小相似比尺满足某实验室的加载条件,分别设计出某集装箱船的双层模型和单层模型.通过对三段形式模型的非线性有限元分析,验证实船与模型的中拱、中垂极限强度的相似性.相对而言,总纵极限强度试验更适合选用单层模型.     

初始缺陷角度对钢桥面纵肋顶板焊缝应力强度因子影响分析

初始缺陷在钢桥面板工厂焊接加工时难以避免,是影响钢桥面疲劳性能的重要内在因素。为研究初始缺陷角度对纵肋顶板焊缝疲劳开裂的影响,建立了包含典型初始缺陷工况条件下的有限元模型,分析得到了裂纹前缘应力强度因子。计算结果表明：竖向初始缺陷状态下的裂纹扩展能力最强;初始缺陷从竖向偏转至45°过程中,偏转角越大,张开型应力强度因子越小,滑开型和撕开型应力强度因子越大。断裂参数数值计算方法与分析结果可为相关钢桥面构造抗疲劳分析提供参考。     

预应力砼连续箱梁桥裂缝成因分析及防治措施

针对目前大跨径预应力砼连续箱梁普遍开裂的情况,从预应力筋的合理设置、计算方法的选取、温差应力的影响、应力控制值以及非预应力筋配置等几方面进行了裂缝成因分析,并提出了防止裂缝的设计建议和构造措施.     

杭州湾跨海大桥湿接头混凝土裂缝原因分析及防裂措施研究

杭州湾跨海大桥湿接头混凝土,由于恶劣的施工环境、特殊的结构及施工工艺,很容易产生裂缝。通过温度应力计算,分析了裂缝产生的原因,并研制出水化热降低剂,有效地降低了混凝土内部的早期温升,实践证明该措施对抑制湿接头混凝土裂缝效果明显。     

地铁车站使用阶段混凝土温度裂缝控制研究

以深圳地铁世界之窗站工程为背景,运用仿真模拟的方法,对明挖地铁车站混凝土结构的温度场和温度应力场进行多方面的对比研究。通过三维有限元计算模拟结构降温情况下结构中的温度场与温度应力场,分析构件中的温度梯度分布与混凝土结构开裂的关系,找到易于发生开裂的部位,提出温度筋的配置方式。通过算例对比,计算分析了三种不同约束条件下结构中的温度应力,得到在地铁车站设计中应合理设置伸缩缝和沉降缝的结论。     

城市轨道交通连续梁桥上无缝线路伸缩力计算

在总结既有文献的基础上,分析现场测试数据,根据梁轨相互作用原理,提出一种以边界和变形协调条件为基础来计算城市轨道交通连续梁上伸缩力的模型,解决了采用常量阻力无法得出城市轨道交通长连续梁伸缩力的问题。采用C＋＋语言编程计算。     

舰船甲板变形的理论研究

为了研究舰船甲板的变形,对其结构进行了简化,建立了舰船甲板受力的数学模型。分别在横向载荷、总纵弯矩及二者共同作用等3种情形下,对舰船甲板的变形特性进行了计算。计算结果表明,舰船甲板受力变形为mm级;在横向载荷作用下,舰首甲板变形最大;在总纵弯矩作用下,甲板的0.6~0.75间部位变形最大。     

Experimental research on dynamic vibration absorber with negative stiffness for longitudinal vibration control of propulsion shafting system北大核心CSCD

［Objectives］In order to control the first longitudinal vibration mode of propulsion shafting systems, a dynamic vibration absorber with disc spring negative stiffness is proposed and its experimental verification carried out. ［Methods］A test bench is established for the propulsion shafting system containing a dynamic vibration absorber with negative stiffness. According to the first longitudinal vibration mode of the shafting, a dynamic vibration absorber with negative stiffness integrated into the thrust bearing is developed. Vibration transmission tests under different rotational speeds, static thrusts and negative stiffness are then carried out, and acceleration response data on the thrust bearing foundation and shafting is obtained. ［Results ］ The results show that the developed dynamic vibration absorber with negative stiffness can achieve vibration suppression of 7.8 dB for the thrust bearing foundation in the first longitudinal mode of the propulsion shafting with a mass ratio of 1.6%, and the vibration control effect of the negative stiffness dynamic vibration absorber is maintained at 3.3 dB when the natural frequency changes by 5% and the thrust changes by 40%. The vibration response on the thrust bearing foundation and shafting do not deteriorate even at non-optimal negative stiffness. ［Conclusions］This study shows that a dynamic vibration absorber with negative stiffness can effectively suppress vibration transmission at the first longitudinal mode of a shafting under different rotational speeds. © 2023 Authors. All rights reserved.     

Weld toe versus root fatigue failure mode and governing parameters: A study of aluminum alloy load-carrying fillet joints

In load-carrying fillet welded connections, two fatigue failure modes are possible i.e. weld toe cracking and weld root cracking. The fatigue life associated with weld root cracking is typically much lower than weld toe cracking, exhibiting a wider scatter band, especially for welded aluminum alloys. This paper examines fatigue failure mode transition behaviors in load-carrying fillet welds made of aluminum and their governing parameters, among plate thickness, weld penetration, joint misalignment, weld material, and ultrasound impact peening(UIP). Through both experimental and theoretical studies, a quantitative fillet weld sizing criterion was proposed for avoiding weld root cracking in fillet-welded aluminum connections.