Vibrations of loosely supported tube bundles subjected to Streamwise Fluidelastic Forces

热交换器是许多行业的重要组成部分，包括发电、石化、纸浆和造纸。这些装置包含大量排列成阵列的管子。这些装置的目的是在内部和外部冷却和加热流体之间交换热量。大量的能量以高压和热的形式传递。如果这个能量的一小部分转化为振动，一种机械能的形式，管的完整性将受到损害。***流体弹性不稳定性（FEI）是最具破坏性的激励机制，其特征是超过一个临界流速，就会发生非常大的管响应。这些大的振动将导致毁灭性的故障，需要避免。这些故障表现为疲劳、管开裂和支承处的微动磨损。微动磨损的发生是由于管撞击其支撑。***过去人们认为FEI只在横向（升力）方向上起作用。因此，设计指南的重点是防止横向不稳定。所有的核蒸汽发生器都是按照这些准则制造的。在操作蒸汽发生器时，流向（阻力）不稳定性从来没有被认为是重要的。在最近一些替代的核蒸汽发生器（如圣奥诺弗雷核电站的那些）发生毁灭性故障后，这种信念被打破了。这些蒸汽发生器的设计寿命为40年，但实际上只持续了11个月。对这些故障的调查证实，流向（阻力）不稳定是造成管对管微动磨损和失效的原因。这些失败的严重程度在学术界和工业界引起了冲击波。在一家工厂，设备损坏和生产成本损失的价格接近10亿美元。在这些事件之后，研究界和工业界都做出了巨大的努力来理解这一现象。***最近的一些研究已经毫无疑问地证实了流向FEI可以发生。这一机制尚不完全清楚，也没有可用的分析或数值工具来预测它。因此，迫切需要开发一种能够预测该机制稳定性阈值的模型。***提出的研究将开发一个综合的时域模型，以捕获横向和流向的FEI激励。然后，开发的模型将用于研究管与支架间隙、滑动支架摩擦以及管与支架之间的预紧力的影响。该模型将通过数值模拟来研究这些影响。然后，这些模拟将用于评估在役热交换器的结构完整性，并为未来热交换器单元的设计提供指导。**

Heat exchangers are important components in many industries, including power generation, petrochemical, and pulp and paper. These devices contain large numbers of tubes arranged in arrays. The purpose of these devices is to exchange heat between internal and external cooling and heating fluids. A great deal of energy is transported in the form of high pressure and heat. If a fraction of this energy is transformed into vibrations, a form of mechanical energy, the tube integrity will be compromised. ***Fluidelastic instability (FEI) is the most devastating excitation mechanism, characterized by a critical flow velocity beyond which a very large tube response occurs. These large vibrations will cause devastating failures, and need to be avoided. These failures manifest as fatigue, tube cracking, and fretting wear at the supports. Fretting wear occurs as the result of tubes impacting against their supports. ***In the past it was thought that FEI prevails only in the transverse (lift) direction. Design guidelines therefore focused on designing against instability in the transverse direction. All nuclear steam generators were made using these guidelines. Streamwise (drag) instability was never considered to be of importance in operating steam generators. This belief has been shattered after recent devastating failures in some replacement nuclear steam generators such as those at SONGS (San Onofre Nuclear Generation Station). These steam generators were designed to last for 40 years and instead, lasted for only 11 months. Investigating these failures has confirmed that streamwise (drag) instability was responsible for the damage caused by tube-to-tube fretting wear and failures. The magnitude of these failures sent shockwaves through the academic and the industrial community. In one plant, the price in terms of equipment damage and lost production costs was close to one billion dollars. In the wake of these incidents, both the research community and industry have made great efforts to understand this phenomenon.***A few recent studies have confirmed beyond any doubt that streamwise FEI can occur. This mechanism is not fully understood, and there are no analytical or numerical tools available to predict it. There is therefore a pressing need to develop a model that can predict the stability threshold of this mechanism.***The proposed research will develop a comprehensive time domain model that captures both transverse and streamwise FEI excitations. The developed model will then be used to study the effect of tube-to-support clearance, sliding support friction, and tube preload against the supports. This model will be used to study these effects through numerical simulations. These simulations will then be used to assess the structural integrity of in-service heat exchangers, and provide guidelines for the design of future heat exchanger units. **