Use of Finite Element Method in Optimization of Quay Crane's Grab

Advanced Materials Research Vol. 837 (2014) pp 346-350 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.837.346 Use of Finite Element Method in Optimization of Quay Crane’s Grab DRAGOMIR Cristina Constanta Maritime University, 104 Mircea cel Batran street, 900663, Constanta, Romania [email protected] Keywords: bulk, cargo, deformation, FEMAP, optimization, harbour, NX NASTRAN, port operator Abstract. This Finite element method is one of the most advanced calculating methods for approximation of accurate solutions to engineering problems. Optimization of grab’s quay cranes is necessary because most port operators use this type of equipment for loading and unloading bulk cargo. Initial research methods applied in this study are based on observations and surveys conducted on Bocşa 16 t - 32 m mobile quay cranes of MinMetal S.A. Constanta port operator. Modeling and analysis for grab’s structure optimization was made with FEMAP and NX NASTRAN - version 10.3.1 applications, which use the finite element method and finite element analysis. After calculations and analysis, the following optimizations resulted: -to increase the grab’s closing force (in order to minimize the loss of cargo between jaws and to increase digging force) the lower beam weight must be reduced. -to reduce the amount of cargo drained from the grab’s jaws at loading, rubber jaws barriers can be fixed or bars can be welded at grab’s jaws. - if cargo has high granulation, in order to reduce grab’s weight the plate of the jaw can be cropped. -cups’ supporting tie rods could be replaced by hydraulic cylinders. The greatest tension is located in the cups’ supportive arms and in the area where cups are attached to arms. Shafts’ tensions are larger than the grab’s metal structure and are located in shafts-arms contact areas, ie support bearings. In these areas, an optimization can be made by installing ball bearings to reduce friction. The largest deformations occur in the middle area of the arms. To increase safety in operation it is necessary to change the material of the four arms supporting cups, given that deformation of 89.7 mm (~ 9 cm) combined with external factors and / or shock loads can lead to permanent deformation or even material breaks. After changing the material, the model showed that the deformations in the middle area of the arms are substantially reduced, at only 4 mm. In the contact area of the upper arms with the two bars of the upper beam, hazardous tensions may be minimized if there are inserted bearings. Introduction Operations made within ports are determinant, through the complex connections they carry, for optimal development and production activities of the entire country. Current and future trend in solving loading and unloading, transport and handling of goods, materials and spare parts of quay cranes is to create effective machinery with reliable operation, increased productivity and with maintenance and operation easily to achieve [1]. When port operators don’t have the possibility to make large investments in acquiring new cranes, they choose to invest in repairs, optimization and improvement of the existing cranes. This paper presents a research made on Bocsa 16 t – 32 m mechanic quay cranes with grab of one port operator from Constanta Port. The scope of the research is to improve and further optimize the exploitation of such cranes. Finite Element Analysis in Optimization of Quay Crane’s Grab Literature Review. Many works cover the complex subject of finite element method. An overview of finite element methods that currently are used extensively in academia and industry was made by K.-J. Bathe [2]. The author described the method in general terms, presented the basic formulation All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 5.14.143.115-28/10/13,22:10:35) Advanced Materials Research Vol. 837 347 and summarized some issues regarding effective finite element procedures, pointing various applications using the method, as well as key challenges for the additional development of the method. O. C. Zienkiewicz and R. L. Taylor [3] described non-linear behaviour of materials while retaining the assumptions on small strain, covering in detail problems of viscoelasticity, plasticity and viscoplasticity. They also described a specific class of problems of structural mechanics and concluded with computer procedures used for solving non-linear problems. G. Dhatt, G, Touzot and E. Lefrançois [4] described approximations with finite elements, various tyoes of elements, integral formulation, matrix presentation of the finite element method, numerical methods and programming technique, as well as numerical examples of the sparse solver. J.N. Reddy [5] examined the mathematical underpinnings of finite element method, and provided a general approach of engineering application areas. Also, simulation softs using finite element analysis are used to study the plastics behavior at injection [6]. Quay Crane Grab. A clamshell or grab consists of hoist drum lagging, clamshell bucket, tag line, and wire ropes to operate holding and closing lines [7]. Fig. 1. Grab forces In Fig. 1 are represented the following forces that interact in a grab: - Hi is the closing force - S is the force in the cable. - F1 is the force in the upper beam; - F2 is the force in the articulation of bucket with bars; - F3 is the force in the lower beam; - i is the transmission ratio (for corn, with ρ = 760 kg/m3, i has values between 3...4, [3] we choose i = 3); - η is the efficiency of closing hoist (from calculations, η = 997) 348 Modern Technologies in Industrial Engineering Crane and Grab Modeling in FEMAP. Bocşa quay crane 16 t - 32 m with mobile arm was modeled in a CAD (computer-aided design) application with FEMAP. The virtual simulation was tested with NX Nastran FEA solver [8]. In the first stage of analysis, has been studied the crane’s grab virtual prototype obtained in the CAD application. Secondly, the problem was defined. The next step was the mesh operation, the virtual prototype division in finite elements. Subsequently, the limit conditions were applied and finally the analysis was run and the results were interpreted. After importing the crane model in FEMAP, were defined materials from crane’s structure and the crane was loaded with cargo (Fig.2). In the model were introduced the following approximate weights of components (± 10%): 1. Upper Tower: 10-12 tons 2. Jib: 13-15 tons 3. Assembly which closes arms parallelogram: 1.5 tons 4. Crane’s beak: 5 tons 5. Rear counterweight: 4 tons 6. Two cables: 1 ton/each 7. Four rolls: 600 kg 8. Grab: 12 tons 9. Beak’s rolls: 200 kg / group reels. Fig. 2. Quay crane model Results of the Finite Element Analysis. After the finite element analysis with NX NASTRAN, were obtained the following results. In order to increase safety in operation, it is recommended to change the material of the four arms supporting the grab’s cups Advanced Materials Research Vol. 837 349 The greatest deformation occurs in the arms, in the middle area (median), where δarmsOL37= 89,7 mm (Fig. 3). This deformation in conjunction with external factors and / or shock loads can lead to permanent deformation or breakage of the material. Fig. 3. Deformation of the middle of grabs’ arms After proceeding the arms analysis, the tensions obtained for OL37 material are: σcr = 153 357,792 N/mm2 σmax = 30 685 504 N/mm2 compared to the tensions in the case of using AISI 4340 (an element from FEMAP and NX Nastran libray) in the grab’s arms: σcr = 133 019 712 N/mm2 σmax = 26 603 960 N/mm2 If the von Mises stress changes insignificant, deformations in arms are significantly reduced, reaching the value δarmsAISI=4,051 mm. As a result of the change of material from OL37 to AISI 4340, deformations in the middle of the arms are substantially reduced from about 9 cm to just 4 mm. After further calculations and analysis, there are required the following optimizations: 1. In order to increase the closing force of the grab (both to minimize loss of cargo through the grid, and to increase the digging force) lower beam weight has to be reduced. 2. The closing force Hi is maximum when the grab is opened and decreases as it closes, as Hi is proportional to the grab’s weight and with the gear ratio “i” of the hoist. For these reasons it is recommended a higher gear ratio. This, however, requires more cable wound on the drum, so a larger closing time, resulting in reduced productivity. If necessary a higher closing force, gear ratio “i” should be considered to the higher end of the range, i.e. i = 4. For a higher productivity (smaller closing time), then the value of “i” remains 3. 3. During operation of Bocşa 16 t - 32 m mobile quay cranes was found the following problem: an amount of cargo was falling from the grabs’ bucket. One solution would be to place rubber gaskets or welded bars on jaws of the grab bar in order to reduce the amount of material lost when loading the grab. It appears that rubber is not efficient, as it would break when unloading grain from old barges that have nails in the floor of the barn. Welding overlaid straps on the cups, to limit losses of cargo, do not affect the stress distribution in the grab. 350 Modern Technologies in Industrial Engineering 4. If cargo is large grain (eg corn cobs), in order to reduce grabs’ weight and to ease the lifting equipment, cutouts can be made in the jaws. In this way it can be extended the grabs’ operability and the weight of the empty grab decreases. 5. In grab modelling using FEMAP appear problems of tie rods bending . A solution would be replacing tie rods supporting cups with hydraulic cylinders, implying the following advantages: - if a pair of tie rods is replaced by a single hydraulic cylinder, the weight of the grab decreases; - due to hydraulic actuation, increases the closing force and the closing time is reduced; - hydraulic actuation provides a good closure of the cups and minimize cargo loss during operation. - hydraulic actuation can be separated on each cup, ensuring more precise control over every cup (together or separately). Conclusions and Future Research The finite element method was used in this research to analyze and propose optimization solutions to improve grabs of 16 t - 32 m mobile quay cranes. The use of finite element method showed that by changing the arms material of the grab from OL37 to AISI 4340, the deformations are substantially reduced. This result can be of high significance, as arms deformation in conjunction with external factors and/or shock loads can lead to permanent deformation or breakage of the grab’s material. Also, other findings resulted from the finite element analysis. A future research will approach the impact of external factors and shock loads on grab’s arms deformations. Nevertheless, a limitation of the research is that finite element method is convergent and can approach the solution of a problem as much of the exact solution, but can not reach it (except in rarely cases and only for very simple structures), nor may indicate deviations between the two solutions. References [1] C. Dragomir, A. Pintilie, Contributions at Quay Cranes Exploitation Optimization, Constanta Maritime University’s Annals, 18 (2012) 41-44. [2] K. J. Bathe,Finite Element Method, Wiley Encyclopedia of Computer Science and Engineering (2008) 1–12. [3] O. C. Zienkiewicz and R. L. Taylor, The Finite Element Method, fifth ed., ButterworthHeinemann (2000). [4] G. Dhatt, G. Touzot and E. Lefrançois, Finite Element Method, John Wiley & Sons, Hoboken (2012). [5] J.N. Reddy, An Introduction to the Finite Element Method, third ed., McGraw-Hill (2005). [6] T. D. Mîndru, Ş. Andrei, C. Burian, Finite Element Analysis of Samples Injected by Polyamide 6.6 Nature, Int. J. Modern Manufacturing Techn. Vol. IV, 2 (2012) 47-54. [7] Information on http://www.tpub.com/eqopbas/147.htm, accessed at 20.11.2012. [8] Information simularea. on http://www.adacomputers.ro/solutii/produse/seria-velocity/femap/ce-este-