SS Cape May Crane Senior Design Project

Transcription

1 SS Cape May Crane Senior Design Project MAE 435 Project Design and Management II Fall 2012 Final Report December 3, 2012 ODU Faculty Advisors Dr. Han Bao Dr. Gene Hou By: Henok Amenu Jeremy Pedigo John Alderson Emmanuel Laryea Kenneth Morgan

2 Abstract In this project, the group was to design the installation plan for a crane to be mounted on a single Container Adapter Frame (CAF), enabling the SS Cape May (AKR-5063) cargo ship to load and unload standard cargo containers, without requiring a dockside crane while in port. Previous groups recommended welding a series of plates onto the CAF to secure a mobile crane on top for cargo use. The primary objective for the current group was to reduce overall costs and CAF modifications necessary, while staying within the expectations set up by the customer. Throughout the project, the group researched two main methods to mount a stationary crane on top of a CAF. By choosing a stationary crane, the group's design would already have a lower initial cost. However, as the CAFs were not purposely built to have a crane mounted to them from the beginning, the group knew the uniquely shaped CAF surface would need to be modified so the crane could be mounted safely. The extent of the modifications and flexibility of design were topics intended to be discussed with the customer. However, due to reassignment personnel working between the Cape May and its owner, contact could not be made during the project period. Using the knowledge at hand, and any available information about the CAFs, the group moved on to complete the project by their deadline. Contact was made with a crane manufacturer to help select a suitable crane that would fit on the CAF and have the reach to move cargo containers on, off, and around the ship. A crane was chosen and the group began analysis and design of a way to mount the crane to the CAF securely. The first finalized method was installation of a flat plate to mount the crane, but with a drawback of likely removing the CAF's mobility in the process. The second method was to install a more complex bridge plate on the CAF to keep the mobility system operational and allow for relocation of the crane. Both proposals undercut the previous group's cost estimate, accomplishing the primary goal i P a g e

3 Table of Contents Abstract..Page i Table of Contents...Page ii List of Figures and Tables..Page iii Introduction Page 1 Project Proposal..Page 5 Methods.....Page 6 Cost estimation...page 15 Results Page 17 Discussion..Page 18 Conclusion..Page 21 Appendix A Page 22 Appendix B Page 24 Appendix C Page 33 ii P a g e

4 List of Figures Figure 1: 2D CAF Drawing...Page 2 Figure 2: SS Cape May Cargo Elevator...Page 3 Figure 3: MacGregor Deck Jib crane and Weight Specifications.Page 6 Figure 4: MacGregor supplied Crane Base...Page 8 Figure 5: Lift and Rail System to move the CAF.Page 9 Figure 6: Loading Configuration for Reaction Forces to resist Tip..Page 10 Figure 7: Multiple CAFs shown on deck..page 11 Figure 8: Plate Design 1 on CAF (Inventor Image)..Page 12 Figure 9: Plate Design 2 on CAF (Inventor Image)..Page 13 List of Tables Table 1: Comparison of Applied Load and Moment....Page 14 Table 2: Cost Considerations for each Plate Design.Page 15 Table 3: FEA Results for each Plate Design...Page 17 iii P a g e

5 Introduction The SS Cape May (AKR-5063) is one of Military Sealift Command's two Heavy Lift Ships. The Cape May is officially owned by the Department of Transportation's Maritime Administration (MARAD), and is berthed in Norfolk, VA. The ship was designed and built in the early 1970s. It was purchased by MARAD in July of Over its years of service, the Cape May was modified to include a Container Adaptive Frame (CAF) system, to facilitate storage and organization of standard 30' x 40' cargo containers, as well as granting it the ability to hold much larger cargo on a semi-mobile platform (i.e. a 100' Coast Guard Cutter). The CAF is a large frame made of plate steel. It is approximately 47 L x 33 W and can support upwards of 400 tons. The CAF weights 38 tons. (Figure 1) 1 P a g e

6 Figure 1: 2-D CAF Drawing 2 P a g e

7 As time has progressed, the functionality of the Cape May has seen the need for adaptation. Its original functions were that of a sea barge ship. The ship utilizes its 2000-ton capacity elevator to lift preloaded barges into the cargo bay (Figure 2). Once the cargo is on board, the Cape May utilizes a rail system to relocate cargo to various sections of the ship. The ship is Figure 2: SS Cape May Cargo Elevator equipped with a crane, but at only a 3-ton capacity it does not serve the purpose of loading and unloading cargo. Cargo capacities can range from 1 ton to 33 tons (maximum standard weight of shipping container). While these functions are diverse, direct loading and unloading of cargo is currently dependent on a dockside crane being available at any location the Cape May makes 3 P a g e

8 port. This quickly limits the usefulness of the ship, as not all ports the Navy may send it to will have crane facilities to offload cargo. From this problem, MARAD sought to find a solution by fitting the Cape May with its own crane. Old Dominion University's Mechanical Engineering Department was tasked with finding possible solutions and proposing the changes and associated costs to MARAD for consideration. This project objective would mean that the student design team representing the university would have to create a proposed solution and research the costs and labor required to implementing an effective strategy for outfitting the Cape May with a functional cargo crane. MARAD originally proposed a specific mobile crane to serve as the cargo crane, and the design team was tasked with determining the feasibility and costs associated with that idea. The new project objective was to try to find a solution that was less expensive than the latest proposal, primarily regarding the cost of the crane system. Any solution was primarily tasked with giving the Cape May the ability to load and offload standard cargo containers with an onboard crane. The secondary task was to minimize the costs and modifications required to the ship to fit it with a cargo crane. In the end, this solution would increase the Cape May's usefulness by reducing the facility requirements of any port the ship docks in, thereby increasing the number of ports the ship can dock in and successfully load and unload cargo to and from. 4 P a g e

9 Project Proposal The design team has proposed a method with the primary goal of reducing the entire additional cost of the crane significantly from the last design team s project path. The previous team proposed to purchase a Grove mobile crane and modify the CAF to allow for placement of the crane on the CAF. Modifications included adding steel plates to the CAF for the outriggers of the crane to rest on during lifts. Although the process of adding plates and modifying the CAF was not that costly, the mobile crane that was proposed could have easily cost well over $1 million on its own. The current design team planned to take a different approach that would see the removal of the mobile crane idea and replacement with a stationary crane design. Along with the stationary crane, there were plans to modify the CAF to allow centering of the crane on top of the CAF. This plan would reduce the initial cost at the end of the process from the expensive alternative the previous group proposed. 5 P a g e

10 Methods The project was completed using multiple engineering principles, methods, and programs. The main reason for choosing a fixed, supported crane for the design was the projected overall project price reduction. To supply the crane, the design team reached out to Cargotec ( who Figure 3: MacGregor Deck Jib crane and Weight Specifications supplied drawings for a GL deck jib crane (Figure 3). Although the crane was not being designed in this project, there was a minimum requirement for the boom length with regards to reach and overall lifting capacity. The ship was estimated to measure 98 feet across the deck, 6 P a g e

11 with the center of the CAF lying a distance of about 24.5 feet from the edge of the deck. This meant the requirement of at least a 54.5-foot crane boom to be able to lift a 30 by 40 container from the edge of the dock. However, this would be at a boom angle of zero degrees. When the boom is not at zero degrees, Equation 1 of Appendix A must be used. With a max boom angle of 18.9 degrees, this yielded an operating radius of 61 feet, which was beyond the 54.5-foot minimum needed to lift a standard container over the wall of the ship. Beyond the boom length, the crane had an overall height of 28.9 feet, weighing in at a total weight of 37 tons. The crane house itself, which would sit on the base plate, and center of the CAF, weighs 25 tons. Comparing that 25-ton weight to the 9 tons of the jib, or boom, and the 3 tons of the cables, it was clear that the weight of the crane house would be the driving factor for design. The crane can support up to 40 tons. Since this crane was not a variable boom length crane, the design team did not have to account for decreased lifting capability with longer operating radius. With that said, the maximum moment applied to the crane would be when the boom angle is zero degrees and the load is at the maximum. See Figure 3 for a drawing of the MacGregor crane. 7 P a g e

12 With choosing a fixed crane, the base was a single support column (Figure 4), which would make placement of the crane critical to the CAF. Two areas on the CAF were considered for placing the crane. The first area was to the left or right of the center of gravity. The driving factor for this placement was the fact that in order for the CAF to remain functional, the center Figure 4: MacGregor Supplied Crane Base must remain unmodified. This was because of the lift and rail system (Figure 5) that moves each CAF. The second area was directly in the center and would deem the CAF immovable. An alternate solution to center placement was designing the base plate to keep the functionality of the lifting device. The design team chose to place the crane at the center of the CAF. This 8 P a g e

13 decision was made over the other option to reduce the applied forces and help prevent tipping of the CAF during loading of the crane. These considerations served as the parameters for placing the crane at the center of the CAF. Figure 5: Lift and Rail System to move the CAF 9 P a g e

14 When adding a crane to any type of structure, the maximum forces created are of importance. The design group looked at two different configurations of loading to determine the maximum forces created as a reaction to loading (both with the crane at the center of the CAF). The first was when the crane is positioned in the transverse direction. The second was when the crane is positioned in the longitudinal direction. These configurations provided the basis on which to model the system for Finite Element Analysis with respect to the worst-case scenario. See methods section on Finite Element Analysis. A minimum reaction force was found in order for the CAF to resist tipping when loaded in these worst case scenario configurations. Simple summation of moment and vertical forces on the CAF were used. The requirement for no-tip Figure 6: Loading Configuration for Reaction Forces to Resist Tip condition was zero moment at one of the contact points between the CAF and the ship s deck (Reaction Force 1 Location). See Equation 2 in Appendix A for calculations and Figure 6 for the loading configurations. 10 P a g e

15 Figure 7, illustrates how much of the surface of the CAF is empty space with support beams taking the actual load. Figure 7: Multiple CAFs shown on deck That setup prompted another design consideration of adding a support base plate to the CAF for the crane's base to be placed upon. Considerations for the base plate included material type for the corrosive environment and geometry. A base plate was necessary for both mounting options. Once final selections are made, the items must be attached to the CAF. The crane must be 11 P a g e

16 attached to the base plate and the base plate to the CAF. A weld joint was the chosen method of attachment based off supplements supplied with the crane, although it would make the crane harder to move to another CAF should the chosen CAF become defective. Again, the center of the CAF was chosen for placement of the crane. Because of this, the design team proposes two different base plate options. The first plate is solid across the center of the CAF. This solution Figure 8: Plate Design 1 on CAF (Inventor Image) would prevent movement of the CAF once the crane is installed (Figure 8). The second plate is recessed across the lift lug area, allowing for the CAF to remain functional once the crane is installed (Figure 9). Steel was chosen as the material for the base plate. It was selected for its availability; high ultimate tensile and yield strengths; to keep all material between the CAF, crane, and base plate common; as well as for its ability to be welded using gas, resistance, or oxyacetylene welding methods. The type of steel would be a plain, low carbon steel. An example of a plain carbon steel would be 1018 steel. The material exhibits yield strength of P a g e

17 kpsi, ultimate tensile strength of 49.5 kpsi and modulus of elasticity of 30 Mpsi. The team chose low carbon because the amount of hardness provided with medium or high carbon steels was not needed. This also would provide cost savings as low carbon steel is generally less expensive than higher carbon steels. Figure 9: Plate Design 2 on CAF (Inventor Image) Both designs were analyzed using the Finite Element Analysis software Patran (MSC Software, Santa Ana, California). In order to analyze the design, certain assumptions had to be made. The first of the assumptions was that the CAF supports were modeled as simple beams. To be a simple beam, the beam must represent characteristics in which the width is one tenth or less than the length. The second assumption was that all of the weight of the crane house, cables, boom, and max capacity load acted at the crane base where it would attach to the base plate. The last assumption took in to account the moment created by the max capacity load and weight of the boom and cables. The design team assumed that the max load and weight of the boom and 13 P a g e

18 cables created a moment at the base equivalent to placing all of the weight of these items at the end of the boom. The second and third assumptions would create results that are more conservative than if no assumptions were made at all. The crane comes in at a total weight of 37 tons (74,000 lbf), and the max capacity of the crane is 40 tons (80,000 lbf). Adding these two weights results in a downward force of 77 tons (154,000 lbf). To calculate the applied moment at the base, the team took the weight of the load, boom, and cables and assumed them to be a distance of 20 m from the line of action of the downward force. The weight of the crane house was not included because it passes directly through the base resulting in no net moment. Therefore, the moment that the base was calculated to see was kip-ft. The downward force was calculated to be 154 kip. These values were compared to the supplied downward force and moment included in the crane dimensions. The crane supplier calculated a downward force of 202 kip and a moment of kip-ft. Since the forces supplied by the crane manufacturer were larger, the design team decided to use those values in the analysis. The attachment method used was continuous welding of the plate to the CAF and was taken into account for in FEA. See Figure 3 and Appendix A, Equation 3 and Table 1 for component weights and calculations. Supplied Values Calculated Values Percent Difference Downward Force 2.02*10 5 lbf 1.54*10 5 lbf 23.7% Moment 9.148*10 6 lbf-ft 6.826*10 6 lbf-ft 25.4% Table 1: Comparison of Applied Load and Moment 14 P a g e

19 Cost Estimates Maintaining a low total cost of the project was one of the most important constraints for satisfying the customer (MARAD). The previous design team calculated a complete project cost using a used mobile crane of $610, Using a brand new mobile crane the project was calculated to cost $1,260, To accurately compare the two projects prices, the current design team referenced the welding costs and material costs (other than crane options) of the previous team. Welding labor was estimated at $50/hr and 18 hours labor. Material costs were estimated on a cubic foot basis. Plate A was modeled in FEA as 0.4 inches thick. However, the estimated cost of the plate was based off it being 0.5 inches thick due to the likelihood that it is more of a standard size used in materials. See Appendix A, Equation 4 for calculations of material costs. The cost considerations are as follows: Cost Considerations Design 1 Quantity Design 2 Quantity Crane $525, $525, Plate A $1, $1, Plate B $5, $11, Welding $ $ Total $527, $551, Table 2: Cost Considerations for each Plate Design 15 P a g e

20 From Table 2 it is notable that the two design options only differ by the addition of plate B, which added an extra $11, in costs. However, the bigger result from cost analysis was that the design team had indeed cut costs from the previous groups design by at least $59,369.77, comparing the previous group s least expensive option with the current group s most expensive option. Moreover, if the previous design team proposed the new crane option, instead of the used crane option, MARAD could see a cost savings of $709, P a g e

21 Results Upon loading each plate design into the FEA program and maintaining the loading force and moment between each design from the supplied values in Table 1, the team came to the values listed in Table 3. Based purely off the results listed, the design team would conclude that Design 1 was the more efficient choice in terms of max stress and deflection in the plate. While those results were favorable, Design 1 would deem the CAF immobile due to limitations put on the lift lug. Design 2 allowed for the use of the lift lug, and therefore movement of the CAF, between crane lifts. However, Design 2 had a high amount of stress under the loading conditions, though the deflection was still favorable. The 119 ksi in Design 2 would seem to fracture due to an ultimate tensile strength of only 49.5 ksi in steel. However, it could not be determined for certain because failure is also a function of material geometry, not simply material properties. The high stress in the analysis could be because that section of the plate did not have any support from the CAF s cross beams. It was standing on its own. This could be corrected by adding support that would not interfere with the lift lug. Design Max Stress (kpsi) Max Deflection (in) 1, Flat Plate , Bridge Table 3: FEA Results for each Plate Design 17 P a g e

22 Discussion As part of the Ready Reserve Force, the Cape May could potentially be put on active duty at any point in the future. The ship's storage capacity and aft submergible loading elevator make the vessel a dynamic transport ship with a variety of cargo and carrying options. However, for cargo not loaded from the sea, the vessel relies entirely on dockside shore cranes to load and unload main cargo. Without a doubt, the vessel's usefulness then becomes completely limited to the facilities at any port the ship is deployed to. The addition of an onboard cargo crane became an obvious solution to remove the primary limitation on the various deployment options the Navy could consider for the Cape May. While prior projects have explored options for crane installation aboard the ship, all have failed to be carried out by MARAD for one reason or another, and most recently because of too high a cost. The project group thus sought to find lower cost options that still allowed a cargo crane to be installed that could handle the defined load range and dimensions of a standard cargo container. After Cargotec gave the design group the crane specifications, the group performed analysis on the crane-to-caf interface and determined two primary design options based around feasibility of implementation and initial specifications given by MARAD. One of the finalized designs should simply and easily accommodate the crane onto the CAF. However it would likely force the CAF to be stationary due to the stated space requirements of the lift lug to move the CAF. The second option would allow the lift lug to be used without restriction, therefore making the CAF mobile as intended. However, the material stresses would be higher on the connection between the crane and CAF, and as a result, more support and expense would likely be necessary to ensure a stable interface. With either design option, the predicted costs were lower than the previous design group without sacrificing the main function of the crane. 18 P a g e

23 Known final results of previous design groups were limited to the first preceding group only. Compared to this design group, the main difference was that that group designed for a mobile crane and planned to secure it to the CAF versus the current group that designed for a fixed crane and planned to mount it to the CAF. The two main drawbacks of the previous group's design were the expense of the mobile crane and the issues of mounting the mobile crane, with its immovable tires and supports, to the CAF, which has many open gaps in its surface. For the current group's design, reduced expense was achieved easily due to the lessened cost of the crane by not having a mobile platform underneath it. Mounting the crane was still complex, however the overall complexity modifications required to the CAF was decreased by aiming to design for a single surface modification where the crane's base would rest rather than multiple surface modifications where each of the mobile crane's supports would extend to. In the end, it was a comparison between the $1,260, estimated cost of the new mobile crane option and the $551, estimated cost of the new fixed crane option that would still leave the CAF with its mobility. Choosing the less expensive design option would save costs, but would likely make the CAF stationary, which MARAD would not prefer. Likewise, the previous group's design could save costs by using a used mobile crane, but at increased risk of higher maintenance and lower reliability. Therefore, in a comparison of the designs that were reliable and maintained functionality, the current group had the more cost-effective design. The design group was limited throughout the project by not being able to visit the Cape May and by not having contact with MARAD due to a change of personnel assigned to the ship. Had a visit been able to be arranged or contact to be made with MARAD: certain design criteria could have been clarified, the understanding of the CAF unit and its operation would have taken much less time to attempt to understand, and the range of flexibility of the design in areas such 19 P a g e

24 as the space required by the lift lug could have been explained. With a lack of ability to see or hear about the CAF and its limitations, work time was slowed in the early stages. A hope for clarification of the paramount goals of the crane design and allowable modifications to the CAF stalled the progress of the design group while waiting for an answer. After attempts at contact were put on hold, the design group's progress was further slowed by uncertainties about the CAF's design and limitations. Extensive research into the CAF system was done, however only refit design drawings and one study done with the CAF could be located. The study provided little insight, and the design drawings could only go so far at explaining the way the CAF functioned. By the end of the project, finalized design reflected a feasible option for MARAD to consider. However, there were potential design optimizations that could be made to save on modifications and costs, but without knowing if those optimizations were realistically feasible, they had to be discarded. The finalized design represents a logical option for MARAD to consider for the Cape May, and one that could be weighed against prior design options submitted by preceding groups. While the results of the design were essentially conclusive, future designs could build off of the current group's idea by attempting to optimize the interface between the crane and CAF to make it removable in case the crane would ever need to be moved to another CAF. Also, future groups could seek clarification of design limitations on the CAF's surface to decrease the materials required to make the interface, as well as the realistic extent of the necessary CAF modifications. Whatever the case, MARAD now has new options to consider in their search to expand the capabilities of the Cape May. 20 P a g e

25 Conclusion Based on the results that the design team formulated, it would be wise to carefully consider both of the design options for the addition of a crane to the Cape May. From the FEA of the CAF for both designs, it can be seen that both have their benefits and disadvantages. Design option 1 with the plate welded across the entire section of the center of gravity would see the CAF with little to no critical stresses, and showed that it could withstand the max stress and deflection. Unfortunately, this design would greatly limit the mobility of the CAF itself and could make it undesirable to the vessel s needs. Design option 2 would have the plates welded on two opposite sides of the CAF with a gap between them allowing the lift lugs to come through in the center and move the CAF. However, in this design option there appeared to be a high amount of stress present in the CAF, and the plates themselves, due to an extra layer of steel plate welded on top of the two plates. By adding a support beam that connects to both plates right beneath the connecting steel plate in the center, this high stress disability could be avoided, and the result would be a very stable and desirable base and crane overall. 21 P a g e

26 Appendix A: Equations and Calculations 1. Boom angle equation: 2. Summation of Moment and Vertical Forces: For configuration 1 For configuration 2 22 P a g e

27 3. Applied Downward Force and Applied Moment 4. Material Cost Estimation Current Team s Plate Sizes Plate A is ft 3 and plate B is ft 3 23 P a g e

28 Appendix B: FEA Images Design 1 with Loading in FEA 24 P a g e

29 Design 1 Deflection Under Loading 25 P a g e

30 Design 1 Stress Under Loading Top View 26 P a g e

31 Design 2 with Loading in FEA 27 P a g e

32 28 P a g e

33 Design 2 Stress Under Loading Top View 29 P a g e

34 Design 2 Stress Under Loading Side View 30 P a g e

35 Design 2 Deflection Under Loading Top View 31 P a g e

36 Design 2 Deflection Under Loading Side View 32 P a g e

37 References Metal suppliers online, LLC. (2012, December 2). Properties of 1018 (Carbon Steels 1018)[Online]. Available: Navsource, (2012, December 2). [Online]. Available: Patran. (2012, December 2). Complete FEA Modeling Solution. [Online]. Available: Cargotec. (2012, December 2). [Online]. Available: 33 P a g e

38 Appendix C: Project Gantt Chart 34 P a g e