【作者】 刘斌；

【导师】 梁兴雨； 张志军；

【作者基本信息】 天津大学 ， 动力工程， 2019， 硕士

【摘要】 作为目前来说使用范围最广的动力装置,内燃机由于其独特的运动形式以及结构决定了其会产生振动。在随着发动机逐渐向高速、大功率发展的同时,振动噪声已逐渐成为判断发动机性能优劣的一个重要参数。而对船舶来说,发动机更成为最主要的振动噪声的源头。舷外机,是在近海广泛应用的一种动力推进装置,因为安装在舟、艇尾部艉板处而得名。然而舷外机由于其发动机布置方式以及工作环境与车用发动机不同,所以会产生更加复杂的振动噪声问题,再加上舷外机的机体直接暴露在外面,导致舷外机会产生非常剧烈的振噪问题。所以对舷外机开展振噪研究,对发动机产生的振动和噪声问题进行探讨,并对其进行优化是非常有必要的。本课题来源于校企合作项目,采用仿真和试验的方法围绕一台三缸舷外柴油机,针对其整机表面的振动和噪声进行评价,并对其进行优化。本文主要研究内容如下:首先,在发动机零件Pro/Engineer三维模型的基础上进行整机的装配建模,检查零件模型的装配干涉,验证发动机零件模型几何参数设计的正确性与合理性。然后建立舷外机整机及零部件的有限元模型,包括发动机机体、气缸盖、气门室罩壳、油底壳、齿轮室罩壳等主要构件,并对其进行模态分析,确定其固有频率和阵型。同时,建立曲轴活塞连杆系统的动力学模型,通过定义约束、运动关系并在其上施加载荷,计算得到该动力系统响应以及机体主轴承处受到的作用力,为接下来计算整机表面结构响应和噪声提供基础数据。其次,通过整机的有限元网格建立整机的声学网格,采用边界元法和基于模态的声学传递向量法,将动力学结果施加到整机上面,对舷外柴油机整机声振响应进行计算,同时在外声场中选取特征点计算其辐射噪声,为接下来的减振降噪优化提供思路和理论依据。然后根据振动噪声的计算结果,采用在动力学系统中设计添加单平衡轴对整机进行优化。最后,根据舷外机的结构特点,在专门的实验台架上,对改进后的舷外柴油机样机进行了一系列振动噪声方面的测试实验,包括振动试验、噪声试验和噪声源识别的试验。并对试验结果和模拟结果进行对比,验证模型模拟的结果正确性。测试结果表明,改进后的舷外机满足了计划设定的开发目标,优化后的整机噪声声功率在低频段最高可降低2d B(A)左右。更多还原

【Abstract】 As the most widely used power device,internal combustion engine is determined to generate vibration due to its unique form of motion and structure.With the development of engine to the direction of faster speed,stronger power and higher efficiency,noise and vibration has gradually become an important parameter to judge the performance of engine.For ships,the engine becomes the most important source of noise and vibration.Outboard engine is widely used in boats near the beach.Due to the different engine layout and working environment from vehicle,the more complicated vibration and noise problems are caused than vehicle.In addition,the outboard engine body is directly exposed to the environment.All of these factors lead to very severe vibration and noise problems.Therefore,it is necessary to carry out vibration and noise research on outboard engine,discuss the vibration and noise problems generated by the engine,and optimize them.This research project is funded by the school-enterprise cooperation project.It uses both simulation and experiment method to evaluate the vibration and noise of a threecylinder outboard diesel engine,and optimizes it in effective ways.The main contents of this paper are as follows:First of all,based on the three-dimensional model of engine parts in Pro/Engineer,the assembly modeling of the whole engine is built up,the assembly interference of the model is checked,and the correctness and rationality of the geometric parameter of engine model are verified.Then the finite element model of outboard engine is established,including the finite element model of engine block,valve cover shell,oil pan and other main components.The modal analysis is carried out to find out its natural frequency and formation.At the same time,the dynamic model of the crankshaft piston connecting rod system is established then by defining the constrain and the motion relationship,the response of the power system and the force received at the main bearing of the body are obtained.It provides the basic data for the calculation of the structure acoustics response and noise of the whole engine.Secondly,the acoustic mesh of the whole machine is established based on the finite element model of engine.The boundary element method and the modal-based acoustic transfer vector method are used to calculate the acoustic and vibration response,and the characteristic points are selected to monitor the radiated noise in the external acoustic field,which provides data support for the next optimization of structure.Finally,the whole machine is optimized by adding a single balance shaft to the dynamic system and optimizing the structure on the surface of the engine.At last,according to the structural characteristics of the outboard engine,a series of performance experiments on the prototype engine after improvement were carried out on a special experimental bench,including vibration test,noise test and noise source identification test.The experimental results and simulation results are compared to verify the correctness of the model simulation results.The test results show that the improved outboard engine meets the development goals set in the plan,and the optimized acoustics power of the whole engine is less than 2d B(A)at low frequency.更多还原