Identification Of Loads On The Bearing Based On Support Reaction Force Meaurement

Load identification has always been a hot point in related engineering and scientificfields, and attracts worldwide attention. The identification is an indirect measurementprocess of loads, based on known dynamic characteristics and response information of acertain mechanical system. It belongs to the third inverse problem in the kinetics field, andis of great research value. It is important in real engineering problems to acquire the loadson a structure, though many of the loads are hard or even impossible to measure, and thishas promoted the emersion and development of load identification technology. Thistechnology has been in rapid progress since it was put froward in the1970s. Loadidentification methods can be divided into the frequency domain and time domainmethods, and the frequency domain methods were developed relatively earlier and morematurely. The identification principle in this thesis is based on frequency domain method.As ships become larger and larger and improved in performance, requirements forbetter vibration characters of ship’s propulsion shafting are higher and higher. It is easierto monitor the health and fatigue condition of a shafting system when loads on the rearbearing are detailedly obtained, and this is of great importance for the implication ofshafting’s operating conditions. What’s more, accurate acquisition of loads will helppeople know the dynamic characters and stability of the shafting system, and greatlysupport the design and improvement of the structure. In this thesis, the identificationprinciple of loads on ship’s rear support structure bearing is obtained in frequency domainmethod through formula derivation, and the characters of the shafting system got in laterresearch are discussed.Chapter I on the whole introduces the backgrounds and a profile of domestic andabroad research of content in this thesis. And some theories and test methods to be used inthe thesis are also briefly outlined, such as loads identification methods and modal testingexperiments.In Chapter II, the introduction and simplification of the support structure is firstlydisplayed, next is the detailed demonstration of the theories and methods above noted,including modal parameters and loads identification, admittance synthesis method andmodal testing experiments. This chapter is the theoretical base of the whole thesis, anddisplays each introduction in logical sequence.Chapter III is the main part of the thesis, and describes the formula derivation processof the principle of the identification of loads on the bearing of ship’s rear support structure.In this method, the support structure is composed of several beams and a bearing, and each beam has transverse vibration and longitudinal vibration problems to solve, then asynthesis can be done on the bearing’s dynamic functions. The formula derivation isperformed in direct problem and inverse problem and thus a calculation is done to verifytheir mutual inverse relationship. At the end of this chapter, some brief instructions onprogramming of the load identification principle are given.Chapter IV comprises the computation of frequency response functions of the supportstructure and the verification of the identification principle. The simplified finite elementmodel is established using APDL. Modal analysis and harmonic analysis are conductedand the simulation results are discussed. The simulation results are compared with thetheoretical data in Chapter III, and the identification principle is verified numerically.In Chapter V, the study objective is the shafting system, so the research here can beseen as an extension of that on the support structure. Loads on the screw propeller arederived based on the results in chapter III, and gross thoughts about relative identificationare given. In the next part, a finite element model is created of the shafting, and naturallysimilar process as in chapter IV is performed. In the end, discussions are made on thecharacters of the shafting system obtained through formula derivation as well assimulation analysis, and some improvements on structure design and processing aresuggested.Chapter VI deals with modal test experiments on the support and the shafting system.First of all, an introduction is given about modal test experiment, the methods of it and thedevelopment of it, and thus the aim of the test is drawn out. Then the two different testingsystems, measuring points layout and the test block diagram are described. In theexperiment on the support structure, the sensors are piezoelectric force transducers and animpact hammer is used to get excitation, while in that on the shafting system the sensorsare acceleration transducers and an exciter. What is next, the experiment processes of thetwo study objectives are introduced, and discussions on their results are made. What ismore, a comparison is done between the result data of the modal test experiments and thefinite element model. At the end, some discussions, analyses and conclusions are made onthe above results obtained.Chapter VII summarizes the whole content of research in this thesis, points out theinnovative highlights, and outlooks some further work in need to be done as well on loadsidentification of the rear bearing and the shafting system.