【作者】 孔巧玲；

【导师】 马捷；

【作者基本信息】 上海交通大学 ， 轮机工程， 2010， 博士

【摘要】 温差能驱动的水下滑翔机具有工作寿命长、构造简单、成本低、无噪音等特点,在海洋环境观测和水下军事侦察等方面具有重要的应用价值,已成为水下工程领域近几年来的研究热点。目前,国内外对热滑翔机的研究仍处于样机试制和实验阶段。温差能驱动的水下滑翔机,通过特殊的动力系统将海洋温差能转化为机械能,驱动滑翔机航行。其动力系统的工作特性将影响滑翔机从海洋温跃层获取能量的效率,而动力系统中的相变储能装置是实现水下滑翔机的长行程、无噪声的海洋探测工作的核心部分。本文对水下热滑翔机动力系统的相变储能装置的相变过程和影响因素进行研究,探讨滑翔机在水下运行时的动力性能及其对滑翔机整机性能的影响。首先,本学位论文利用数值模拟结合试验研究的方法,获取了固-液相变材料的体积变化规律及影响因素。在研究该问题中,所建立的数学模型,也适用于各种固-液相变材料体积变化规律的研究。所设计的实验方法,能够克服相变材料粘附管壁的困难,能够克服相变材料凝固体积变化量难以测量的困难。论文根据热滑翔机动力系统储能装置的物理模型,建立基于焓法的相变传热数学模型,采用液相分数场与温度场解耦的方法,模拟分析了影响动力系统储能装置传热效率的因素。研究结果表明,合理选择相变材料,提高相变材料的热物性能,增大动力系统与外界环境的温差,合理设计相变储能装置的结构尺寸,减小容器的半径或是增大滑翔机的运行速度,都可以提高动力系统的传热效率。热滑翔机通过动力系统中储能工质的体积变化来改变外胆的体积,从而改变滑翔机的整机净浮力,实现沉浮运动。储能工质的体积变化规律及影响因素决定了滑翔机动力系统的工作性能和滑翔机水下运行时的姿态控制。因此,本论文对相变材料的体积变化规律进行了实验研究和数值模拟分析。基于动力系统储能装置的相变传热模型,根据相变材料液相分数场的分布,推导出储能工质体积变化率的数学模型。通过实验验证和数值模拟分析,得到储能工质的体积变化规律。即储能工质在初始阶段具有较快的体积变化速率;其体积变化率跟相变速率有关,同时与相变过程中液相成分或固相成分有关;所有影响相变速率的因素均会影响体积变化速率。在外界压力的作用下,熔解过程的体积变化率小于凝固过程的体积变化率。在涉及承压较高的应用场合,应考虑压力作用的影响,以保证工作装置的正常运行。对给定体积的相变材料,增大Ste数(Ste ? c p?T /L)、Bi数( Bi ? hl /?)和减小圆柱形容器的尺寸,可以提高动力系统的输出功率。根据储能工质体积变化规律曲线,可求得最佳相变时间点和最优体积变化率,可以提高动力系统的综合性能。其次,本学位论文利用数值模拟方法,研究了运行于海洋温跃层间滑翔机的动力系统相变过程,获取了滑翔机运行中的体积变化规律、冷暖水层停留时间、动力系统阀门定时控制策略。通过滑翔机运行潜深优化、循环时间优化和输出功率变化规律研究,得到了提高滑翔机输出功率的途径。对滑翔机在赤道附近海域温跃层间的工作过程进行模拟优化,优化后的循环时间比未优化前减少了30%,滑翔潜深减小了40%。设计未达到100%体积膨胀率的行程,可缩短行程时间和减小滑翔潜深,提高动力系统输出功率,还可以预留部分相变材料作为能量损失补偿。再其次,本学位论文采用对浅跃层和深海跃层间工作的滑翔机进行研究的方法,获取了温跃层厚度和强度与滑翔性能之间的关系。浅跃层型的海洋温跃层,跃层的上界和下界温度对滑翔机的运行过程影响较大。跃层的上界温度越高,下界温度越低,相变速率越大,在冷、暖水层停留时间越短。深水跃层型的温跃层,其跃层的强度和上界温度对滑翔机的运行过程影响较大。跃层的强度越大,相变速率越快,滑翔机的潜深越小,循环所需的时间越短。跃层的上界温度越低,滑翔机需在暖水层停留的时间越长。最后,本学位论文采用动力系统工作性能与滑翔机水动力性能结合的方法,研究体积变化率与滑翔速度、攻角之间的关系,获取了动力系统输出功率与水下运行阻力之间的平衡关系,获取了提高整机性能的途径。滑翔机的水动力性能参数影响滑翔机运行姿态和动力系统的设计。滑翔机攻角和运行速度增大,滑翔机的水下运行阻力增大,滑翔机用于克服阻力所需的净浮力增大。相应地所需相变材料的体积变化率也随着增大。在给定的温跃层间运行的滑翔机,攻角增大,水下运行时的滑翔角减小,潜深、垂直运行速度和每循环所需的时间都随着增大。滑翔机的整机设计应根据具体的任务进行,按滑翔机运行速度、行程、潜深和负载能力等目标参数进行优化,以得到最优的整机综合性能。本论文的研究揭示了滑翔机动力系统的工作规律及其影响因素,指出提高动力系统输出功率的途径。通过滑翔机工作过程的模拟,结合实测海洋温跃层的温度分布,合理设计滑翔机在冷暖水层的停留时间,精确定时控制动力系统阀门的开闭,及时调整滑翔机运行姿态,保证滑翔机能够长时间的稳定运行。将滑翔机动力系统的工作特性与水动力性能参数给合起来,分析动力系统输出功率与滑翔机水下运行阻力间的平衡,得到影响滑翔机整机性能的因素,为合理设计动力系统相变材料体积变化率大小,以及对整机性能进行改进和优化设计提供了理论依据。更多还原

【Abstract】 The underwater glider propelled by ocean thermal energy has the property of long endurance, simple structure, low cost and low noise. It was widely applied in ocean environment monitoring and military detection. Recently it has become the research focus of underwater engineering. However, the related research is still at the stages of prototype design and field test. The thermal glider changes its net buoyancy by a special power system which can convert ocean thermal energy into mechanical energy and drive the glider moving. The working characteristics of the power system will influence the energy harvesting efficiency from the ocean thermocline while the phase change energy storage system of the power system is a key part for the glider to realize the long-term and non-noise ocean monitoring. The phase change process and the influencing factors of the power system were investigated in this thesis. And the dynamic performance of the underwater glider and the influence of the operating parameters on the whole performance of the underwater glider were discussed when it is operating in the ocean.Firstly, the numerical simulation and experimental study method was applied in this thesis to study the rule of the volumetric change rate for the solid-liquid phase change material. The influencing factors of the volumetric change rate were analyzed. The numerical model established in this thesis is suitable for studying the volumetric change rate of any other types of solid-liquid phase change material. And the experimental method can prevent the solid phase change material adhereing to the cylinder wall which cause measuring difficulty for the volumetric change rate during solidification process.According to the physical model of the power device of the thermal glider, a numerical model of the phase change heat transfer was established based on enthalpy method. The numerical equation was solved by decoupling the liquid fraction with the temperature field. The influencing factor of the heat transfer rate for the energy-storage power system was analyzed. The simulation results showed that the heat transfer rate of the power device can be enhanced improved by improving the properties of the phase change material, increasing the temperature difference between the devices and the surrounding, decreasing the diameter of the container or improving the gliding speed.The thermal glider changes the outer bladder volume by changing the volume of the energy-storage material during phase change process. Accordingly it changes the net buoyancy of the whole vehicle and gliding up and down in the ocean. The rule and effects of volume change for the energy-storage material decide the working performance of the power device and the gliding attitude of the glider. Therdfore the volume change rule of the energy-storage material was experimentally studied and numerical analyzed in this thesis.Based on the numerical model of the energy-storage device of the power system and according to the profilel of liquid fraction field, the numerical model of the volumetric change rate of the phase change material was deduced. By experimental verification and numerical simulation, the rule of the volumetric change rate during phase change process was discussed. The volume changes fast at the initial stage of the phase change process. The value of the volumetric change rate of the phase change material is related to the phase change rate. It is also related to the mass fraction of the liquid phase change material. All the factors affecting the phase change rate will influence the volumetric change rate.The volumetric expansion rate is less than theoretical value under an external pressure. While a high pressure situation is taken into consideration, the numerical model should be modified by adding a function calculating density varying with pressure to ensure that the model operates properly.For a certain volume of phase change material, the output power can be improved by improving Ste number (Ste ? c p?T /L), Bi number( Bi ? hl /?) and reducing the radius of the cylinder container. According to the curve of the volumetric change rate, the optimal time and volumetric change rate of the energy storage material can be determined. It can improve the comprehensive performance of the power device when the glider is operating with the optimal volumetric change rate.Secondly, the phase change process of the power system was studied when the glider was operating within the ocean thermocline by numerical simulation method, attending the results of the volumetric change rate, the time of staying at the cold and warm water layer, and the valve timing control method of the power system. Several methods to improve the output work of the glider were attained by studying the gliding depth optimization, the cycle time optimization and the variation of the output work.The working process was analyzed and optimized when the thermal glider working within the ocean thermocline near the equator. After optimization the total time of a cycle decreases 30% and the gliding depth decreases 40%. The cycle time and depth can be decreased when the phase change material is partly melted when the volumetric expansion rate is less than 100%. The rest of the material can be set aside for the compensation of the energy loss caused by friction.Thirdly, the working process of the glider was studied in this thesis when the glider was operating within the shallow-water ocean thermocline and the deep-water ocean thermoclien. And the effects of the thickness and the strength of the thermocline on the gliding performance were attained.For the shallow-water ocean thermocline, the upper and lower bound of the thermocline influence the working process. The higher the warm water temperature and the lower the cold temperature, the faster the phase change rate, and the shorter the glider stays on both the warm and the cold water layer.For the deep-water ocean thermocline, the intensity and the upper bound temperature of the thermocline influence the working process. The stronger the intensity of the thermocline, the lower the gliding depth is and the shorter the cycle time needs. The lower the temperature of the top layer of the thermocline, the longer the glider stays in the warm water layer.Lastly, the relationship among the volumetric change rate, gliding speed and the attack angle was studied in this thesis by the method of combining working performance of the power system with the hydrodynamic performance of the glider. The balancing relationship between the output work of the power system and the gliding drag was analyzed and the methods to improve the comprehensive performance of the glider were put forward.The hydrodynamic parameters of the glider will influence the gliding attitude and the design of the power system. When the glider operate at different speed and glide angle, the net buoyancy needed increases with the attack angle. So is the volumetric change rate of the phase change material. For a certain ocean thermocline, the gliding depth, glide angle, gliding speed and the total cycle time increase accordingly. The design of the glider should be based on specific task and the gliding path should be optimized according to the parameters such as the gliding speed, distance, depth and load etc.The working process and the influencing factors of the power device of the thermal glider were presented in this thesis. Several methods to improve the output work of the power device were put forword. According to the actually measured temperature profile of the ocean thermocline the underwater working process can be simulated. By the simulation results, the time of the thermal glider staying in the warm water and cold water can be suitable selected. So the open-close timing of the valve in the power system can be pricesly controlled. The gliding attitude can be promptly adjusted to ensure the glider operateing stably in the ocean for the long endurance. The factors influencing the performance of the whole glider were also analyzed by combining the hydrodynamic parameters and the working characteristics of the power device. It provides theoretical fundament for suitably selecting the volumetric change rate of the phase change material, improving the performance and optimal design of the whole glide.更多还原