The Safety Assessment By Using The Reduced Scale Model Of Bridge-type Grab Ship Unloader

In the process of the bridge-type grab ship unloader’s working, it starts and brakesrepeatedly so that the steel structure suffers from relatively strong vibration and shockfrequently. Therefore, it’s very important to calculate the mechanical strength and maintainthe overall stability of the steel structure. However, to the large structure of the shipunloader, there are complex loading and poor working conditions. Unfortunately, themanpower, economy and the capacity of equipment are limited. So it’s difficult to organizefield trial. In order to reduce the test costs to make the design, manufacture, maintenance ofthe ship unloader possess related theoretical basis and experimental data, this paper takes a2250t/h bridge type grab ship unloader serving at Zhanjiang harbor as the specific object ofstudy and undertakes a series of studies on it such as analysis of its static and dynamicsimilarity theory, design and production of it’s scale model, modeling its three-dimensionalfinite element, simulation and conduction of model tests and so on. The specific researchmethods, results and conclusions are as follows:Through collecting considerable information about the port crane at home and abroadto understand the research status and development tendency; Through a field investigationon the2250t/h bridge type grab ship unloader serving at Zhanjiang port to master theoperating principle, composition of structure, main technical parameters and load type ofthe ship unloader. On these basis, according to the similarity principle to deduce the staticand dynamic similarity criterion of the ship unloader affected by extraneous factors byusing dimensional analysis method. The similarity criteria provides theoretical basis toassist the design and manufacture of the similar scale model.According to the static and dynamic similarity criterion of the2250t/h Bridge-typeGrab Ship Unloader, a1/40scaled-down model was designed and the assembly diagramand all parts drawing were drawn by using Pro/E software. Finally, a physical scale modelof the ship unloader steel structure which lays the foundation for the latter test researchinto the model was made by using appropriate sectional materials.On the basis of finishing designing and producing the scale model of the shipunloader’s steel structure, Pro/E was used to establish the three-dimensional solid model ofthe ship unloader’s prototype and its scale models, and Ansys workbench was used to establish their3D finite element models. Firstly, the static structural analysis of both wascarried out and the stress and strain fields were compared to verified the correctness of thestatic similarity criteria. Secondly, the modal analysis of both was carried out and themodal shape and frequency were compared to validate the correctness of dynamicsimilarity criterion. The research above provides theoretical basis to assist the design,manufacture and maintenance of the ship unloader.According to the results analyzed by Ansys work bench, experiment research into tothe strain characteristic and modal of the scale model of the ship unloader steel structurewas carried out. Through the strain tests in this model, we got the strain-time history curveof the five points on the boom and forestay in the process of the grab’s movement from thelifting position to the hopper position. The experimental results are in good agreement withthe computed results and they verify the rationality of the scale model and the correctnessof the analysis results about structural static; Through modal experiment research, thecurves of amplitude-frequency characteristics on the three directions of the end of the front,back girder and the tower top are obtained. The natural frequency identified are in goodagreement with the the computed results which verify the rationality of the model and thecorrectness of the analysis results about modal.According to the research above, we can draw the conclusion that the scale modeldesigned and manufactured is relatively in line with the static and dynamic similaritycriterion and the the test data in this model can be translate into prototype’s, which providetest data to assist the design, manufacture and maintenance of the ship unloader.