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Conference Proceedings Vol. I, II, III

 事業名 海事シミュレーションと船舶操縦に関する国際会議の開催
 団体名 日本船舶海洋工学会 注目度注目度5


3. APPROACH OF IDENTIFYING METHODS FOR CHARACTERIZlNG SLOW SPEED MANEUVERING PERFORMANCE
 This study originally planned the following steps:
1. Survey senior mariners, simulator operators, etc.
2. Compile the information; identify common practices, rules of thumb, or formula
3. Evaluate and pick a set of maneuvers and indices
4. Demonstrate through fast-time simulation (if possible, a demo on simulator is desired)
5. Modify the maneuvers and indices based on feedback and re-test
6. Document and publish
 
 As the survey task progressed, a focus group meeting was held mainly due to the sparse return of the survey forms and the concern that the survey might not bring out the desired information. With dynamic exchange of information, ideas, and debate among the professionals knowledgeable about slow speed maneuvering, expert opinions could be collected in a relatively short time. Thus, after the results of survey were compiled for review and discussion, a focus group meeting was held to discuss and brainstorm results from a preliminary set of test maneuvers and performance indices.
 
3.1 Survey
 
 Many useful inputs and comments about slow speed maneuvers were gathered, nevertheless it was difficult to pin down the universally adopted maneuvers, test procedures and the indices, either by naval architects/math modelers or by mariners, for assessing slow speed maneuvering performance. Although the survey did not produce the information as hoped for, it did indicate that the formal assessment and reporting of slow-speed maneuvering performance is indeed an area that needs to be developed and established in the maritime community, It is also recognized that the criteria of slow speed maneuvering performance involves even more complicated issues. This pilot study only scratched the prerequisites for judging a vessel's slow speed performance.
 
3.2 Focus Group Meeting
 
 An information package was mailed to the participants before the meeting. The package included survey questionnaire responses and a collection of reference papers and documents to prepare them for the gathering. The meeting included a combination of presentation, discussion, and desktop computer demonstration. All was designed to obtain from the group of knowledgeable professionals a set of preliminary candidate maneuvers, their test procedures, and associated performance indices. The time for simulation demonstration, brainstorming session was insufficient, but many thoughts and rich information were gathered. Written comments on the preliminary candidate slow speed maneuvers were also received from several experts. Their comments, especially the extensive ones from Hensen [25], Norrbin [26], and Groh [27] have provided valuable inputs to formulate the modified suggestions found in Section 5 on slow speed maneuvers and their performance indices.
 
4. FINDINGS FROM THE INFORMATION GATHERING PROCESSES
4.1 Speed Effects on Maneuvering Hydrodynamics
 
 In the Focus Group Meeting, Ankudinov, Jakobsen, and Mazurkiewicz [28] presented the hydrodynamic aspects of slow speed maneuvering in deep and shallow waters. They explained the governing mechanisms of slow speed ship hydrodynamic and presented the supporting test data. Key points include:
 
・For the turning circle, as a rule of thumb, the Tactical Diameters (TD) from the SEA speed test and FULL (Full Maneuvering) speed test do not differ greatly. However, the TD of SEA or FULL speed test differs more noticeably from those of SLOW or DEAD SLOW speed tests. Jakobsen, et al [29] later offered more findings about the speed effect on turning performance. In general, the TD becomes larger for most ships as a function of Froude Number.
・For the MARAD full-form series [30], both sway damping coefficient ratio and yaw damping coefficient ratio drop as the Froude Number (based on water depth) becomes smaller.
 
 Jakobsen, et al [29] also implemented an important effect of speed on resistance into simulation modeling to improve its accuracy: the increase in resistance coefficient with decreasing ship speed for low speed operation. The resulting increase in propeller loading can cause an increase in propeller wash and thus make the rudder relatively more effective.
 
4.2 Different Views of Judging Maneuverability
 
 Relatively speaking, engineers and mariners seem to collect, use, describe and exchange ship maneuverability information in different ways; they judge maneuverability from different perspectives.
 
・Engineers are more mathematics oriented, thus more inclined to using indices for communication; mariners are more qualitative oriented; they often describe ship's performance in words.
・Traditionally many mariners have preferred using dimensional values during actions, especially those who are assigned to a single ship; e.g., the Advance and Transfer of a turning circle or the amount of squat are described in cables, yard, etc. The usage of the non-dimensional values favored by researchers is gradually adopted by mariners such as pilots who have to handle quite a few different vessels within a short period of time; the nondimensionalized information provides a logic basis for decision-making via extrapolation.
・For mathematical convenience, engineers usually use the Center of Gravity or Midship as the reference positions, while mariners would refer to the bridge or radar for judging position. Mariners also like to see track plots with swept path to visualize the space required for operation.
・The focus of treating a maneuver may be different between mariners and engineers. For example, Back & Fill is a space constrained maneuver to a mariner while it is a cross-quadrant maneuver to math modelers where they need to pay attention to the transition of propulsion and steering forces between quadrants.
・Mariners and engineers do use common terms referring to ship movements. However, the focus and attention level can be quite different. One example is the Pivot Point. Lewis [31] discussed it briefly from the hydrodynamics point of view. However, Hooyer [32] dedicated a chapter to Pivot Point in his shiphandling book and wove the discussions of its use all throughout the book.
 
4.3 Presenting Slow Speed Performance Information
 
 The slow speed performance information can continue to be presented in traditional tabulated format on paper. However, modern technologies should allow us to customize the information for different end users to serve them better in their own working context. Al-though this issue is far beyond the scope of this project, it is worthwhile to point out that
 
・Enabling technologies are abound to allow maneuvering performance and other vessel properties be intuitively presented
・A combination of system identification, simulation, and prediction technologies can offer timelier and better information for decision making
・Integrated mobile computing technology allows timely information delivered to the user when they request it and where they want to use it
・Customized presentation of maneuvering performance may facilitate bridging the communication gap between engineers and mariners
 
5. PROPOSED SLOW-SPEED MANEUVERS
5.1 Selection Considerations
 
 The following considerations were weighed when formulating the suggested Basic and Additional set of Slow Speed Maneuvers:
 
・The basic set of maneuvers shall serve as the common denominators that are applicable to all types of vessels and all types of engine/propeller/ rudder configurations.
・The number of maneuvers in the basic set should not be overwhelming. Economy plays a key role when acquiring full-scale test data. Only the "highly desirable" tests should be emphasized and the "nice to have" tests should be indicated as the tests of opportunity.
・The Basic set should reveal the slow speed maneuvering performance when the propeller and rudder operate within and during the transition between quadrants.
・ Preferably, the operation is familiar to mariners, so that no significant effort is required to get the concept across when it comes to field tests.
・Performance indices associated with a test maneuver should bear physical meaning that is easy to understand. The indices should also be easy to measure or derive
・Human factors/decisions should be taken out of the loop to delineate objective performance of the vessel.
 
5.2 Summary of Selected Maneuvers
 
Based on the requirements explained in Sec. 1.2, the gathered information and expert input described in Sec. 3 & 4, and the considerations above, eleven slow speed maneuvers are chosen as the basic set of slow speed maneuvering tests. They are
 
・Test for Minimum Effective Rudder (MER) angle
・Crash Stop from HALF AHEAD (HAHD)
・Acceleration/Deceleration Combination Test with speed starting from and back to Dead In Water (DIW)
・Backing/Stopping Combination Test with speed starting from and back to DIW
・35° Accelerating Turn starting from DIW with SLOW AHEAD (SAHD) bell
・35° Coasting Turn from SAHD speed
・20°/20° Overshoot Test from SAHD speed
・20°/20° Accelerating Overshoot Test from DIW with SAHD bell
・20°/20° Coasting Overshoot Test from SAHD or HA HD speed
・Back & Fill with Fill First
・Back & Fill with Back First
 
 For ships equipped with twin screws, two additional slow speed maneuvers starting DIW are suggested:
 
・Twist-A Differential Thrust (DT) test with equal but opposite throttle orders for starboard and port
・Twist with Full Rudder
 
 For a ship equipped with bow/stern thruster(s), IMO has a general guideline on what performance should be tested or estimated. Eight additional maneuvers are suggested here based on the IMO guideline:
 
・Bow Thruster Turn w. Throttle at STOP
・Stern Thruster Turn w. Throttle at STOP
・All Thrusters Twist w. Throttle at STOP
・All Thrusters Lift (Lateral Push) w. Throttle at STOP
・Bow Thruster Accelerating Turn w. SLOW ASTERN (SAST) bell
・Bow Thruster Accelerating Turn w. SAHD bell
・Stern Thruster Accelerating Turn w. SAHD bell
・Stern Thruster Accelerating Turn w. SAST bell
 
 The default test conditions for all these tests include: open deep and 1.2 depth/draft shallow water, calm weather, moderate uniform current, loaded and ballast draft. In designing the tests above, one could use other rudders and throttle commands. In most cases, there is no unique or obviously optimal way. A 35° rudder for turning and 20° rudder for overshoot test were adopted from conventional definitive tests. Other smaller rudder angles may be used for the complete investigation of maneuvering performance.
 
 The logic of choosing these basic and additional maneuvers was explained by Hwang in [33]. The test objective, conditions, procedure, and performance indices are described in the appendices of [33]. Note that the three Twist maneuvers in [33] have been combined into two tests in Table 3 for clarity. Table 2 and 3 summarize the purposes of the basic and additional sets of maneuvers.
 
 In order to facilitate the discussion in Sec. 6, the test procedure and performance indices for MER as well as the Back & Fill tests are included in the appendices of this paper. Note that these selections do not provide total information of slow speed maneuvering performance, but when they are tested systematically, they can provide quite comprehensive information, especially for math model validation and trouble shooting.
 
Table 2 Suggested Basic Slow Speed Maneuvers
NAME OF MANEUVER TEST PURPOSES
Minimum Effective Rudder (MER) - Least rudder angle that can be applied and still effect yaw-checking at speeds ranging from cruising to slow speed at cach engine order
Crash Stop from HALF AHEAD (HAHD) speed -Ship's stopping capabilities from a speed which is relevant in harbor operation
-Ship's dynamic response to throttle order when operating in transition from Quadrant 1→4
-Paddlewheel Effect/Stern Walk
Acceleration/Deceleration Combinations (Start from & back to Dead In Water) - Ship's dynamic response to throttle order when operating in transition from Quadrant 1→4→3
- Paddlewheel Effect/Stern Walk
Backing/Stopping Combtinations
(start from & back to DIW)
-Ship's dynamic response to throttle order when operating in transition from Quadrant 3→2→1
-Paddlewheel Effect/Stern Walk
35°Accelerating Turn Starting from DIW with SADH bell -Ship's ahead turning capability during acceleration at slow speed
35°Coasting Turn from SAHD speed -Ship's ahead turning capability at slow speed during deceleration with propeller(s) wind milling or possibly stopped
20°/20°Overshoot Test with SAHD approaching speed -Ship's yaw checking capability at a speed which is relevant in harbor operation
20°/20°Accelerating Overshoot Test Starting from DIW with SAHD bell -Ship's yaw checking capability during acceleration ahead at slow speed
20°/20°Coasting Overshoot Test with SAHD or HAHD approaching speed -Ship's yaw checking capability at slow speed during coasting ahead with propeller(s) wind milling or possibly stopped
Back & Fill with Full First (for both Starboard Filling and Port Filling) -Ship's maneuverability in tight space
-Interactions between hull, propeller, and rudder when operating in transition from Quadrant 1→4→3
Back & Fill with Back First (for both Starboard Backing and Port Backing) - Ship's maneuverability in tight space
-Interactions between hull, propeller, and rudder when operating in transition from Quadrant 3→2→1
 
Table 3 Suggested Additional Slow Speed Tests
NAME OF MANEUVER TEST PURPOSES
Twist from DIW
(A Differential Thrust test with equal but opposite throttle orders for starboard and port)
- Twin-screw ship twisting capability using propellers only. If ship gains headway, one propeller in Quad 1. the other propeller in Quad 4;If ship gains sternway, one propeller in Quad 2. the other propeller in Quad.3
Twist with Full Rudder from DIW - Twin-screw ship twisting capability assisted by rudder
   
Bow Thruster Turn with Throttle at STOP -Effectiveness of bow thruster with no initial ship speed
Stern Thruster Turn with Throttle at STOP - Effectiveness of stern thruster with no initial ship speed
All Thruster Twist with Throttle at STOP - Twisting capability using bow and stern thruster with no initial ship speed
All Thruster Lift(Lateral Push)Maneuver with Throttle at STOP - Lifting capability using bow and stern thruster with no initial ship speed
Bow Thruster Accelerating Turn with SAST bell - Effectiveness of bow thruster with accelerating sternway
Bow Thruster Accelerating Turn with SAHD bell - Effectiveness of bow thruster with accelerating headway
Stern Thruster Accelerating Turn with SAHD bell - Effectiveness of stern thruster with accelerating headway
Stern Thruster Accelerating Turn with SAST bell - Effectiveness of stern thruster with accelerating sternway







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更新日: 2020年10月17日

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