Model test method for the amount of water shipped on the open cargo hold of an open box ship in waves

Abstract

The present invention discloses a method for model test of the amount of water boarding on the open cargo hold of an open box ship in waves, which includes: Step 1, simulating the test environmental conditions and test objects; Step 2, conducting tests, including preliminary tests and basic tests; Step 3, evaluating the test results. The present invention has a wide application range and high accuracy of test results.

Description

Technical Field

[0001] The present invention relates to the technical field of ships, and in particular to a model test method for wave load on an open cargo hold of an open box ship in waves. Background Art

[0002] With the changing global economic and trade landscape, the demand for open container ships has surged. IMO and classification societies have mandated that open container ships take into account the impact of waves on open cargo holds.

[0003] Existing technologies for determining the amount of wave action in open cargo holds include numerical simulation and physical model testing. Numerical simulation includes computational fluid dynamics (CFD) and empirical formula calculations; physical model testing includes wave tank testing and offshore ship testing. Computational fluid dynamics (CFD) uses specialized software to construct digital models of ships and waves to simulate the wave action. Empirical formula calculations use formulas summarized based on a large amount of test data and actual sailing experience to estimate the amount of wave action. Offshore ship testing involves installing measuring equipment on the actual ship to record the amount of wave action during navigation. Wave tank testing involves creating a scaled ship model in a water tank, using a wave maker to simulate different sea conditions, and measuring the amount of wave action using pressure sensors, flow meters, and other equipment.

[0004] Computational fluid dynamics (CFD) technology relies on reasonable assumptions and empirical formulas for model accuracy, has limited ability to simulate complex wave phenomena, and has difficulty accurately capturing dynamic changes.

[0005] The empirical formula calculation technology has a narrow scope of application and is usually based on specific ship types, sea conditions and test conditions, resulting in a significant decrease in calculation accuracy.

[0006] Offshore ship testing technology is high-risk, as severe sea conditions pose a threat to the safety of ships, personnel, and equipment, and is also costly.

[0007] Due to the late development of wave tank testing technology in China, there is a lack of accurate grasp of how to accurately simulate environmental conditions such as waves and ship speed, how to realistically construct the structural characteristics of a real ship, how to fully assess the trim and center of gravity range of a ship in actual operation, and how to design the test process. The accuracy and reliability of the tests are difficult to guarantee. Risk avoidance often results in excessive test conditions, resulting in high costs and low efficiency; and overly conservative test subjects and condition simulations, affecting the economic efficiency of the ship. During the test period, reasonable measures are not taken in a timely manner, resulting in increased test frequency and delays in the design and construction cycle.

[0008] The paper "Research on a Method for Evaluating Waves on Deck for Determining the Freeboard of Open Container Ships" (authors Sun Anlin et al., China Shipbuilding, Vol. 60, No. 3 (Total No. 231)) discloses a method for evaluating waves on deck for determining the freeboard of open container ships. This existing technology has the following deficiencies:

[0009] The prior art proposes that "for the remaining 5 open cargo holds, flexible waterproof materials are used for covering to collect the accumulated water caused by the incoming waves", which has the problem of overly conservative object simulation and cannot improve the economy of the ship.

[0010] The paper "Influence of DNV•GL New Specification on the General Design of Open Multi-purpose Ships and Measures to Reduce Incoming Waves" (authors He Xinyu et al., Ship & Boat, No. 3, 2021, Serial No. 192) discloses the research on the general design requirements of open multi-purpose ships. The prior art has the following deficiencies:

[0011] First, the prior art proposes that "when selecting GM values for the ship in all wave directions, the GM value corresponding to the resonance of the rolling period and the spectral peak period in the beam sea is selected. If the GM value corresponding to the resonance exceeds the maximum value of the ship's limit GM curve, the maximum value of the limit GM curve can be selected. For the 3 wave directions with relatively poor results, the maximum value of the limit GM curve is taken again"; it has the problem that the method of taking the initial metacentric height value leads to overly safe test results.

[0012] Second, the prior art proposes that "measure the incoming wave volume in all wave directions, 1 hour for each working condition, and then repeat the measurement in the 3 wave directions with relatively poor results. The additional trim value needs to be added to the open sea-keeping model test". It has the problems of a large number of test conditions and long test time caused by the possible superposition of 8 additional trim test conditions on the 8 horizontal trim test conditions.

[0013] For the above problems, no effective solutions have been proposed yet. Summary of the Invention

[0014] In order to overcome the above defects existing in the prior art, the present invention provides a model test method for the incoming wave volume of the open cargo hold of an open box ship in waves.

[0015] The present invention solves the above technical problems through the following technical solutions:

[0016] A model test method for the incoming wave volume of the open cargo hold of an open box ship in waves, which includes:

[0017] Step 1, simulate the test environmental conditions and the test object;

[0018] Step 2, conduct tests, including preliminary tests and basic tests;

[0019] The loading plans during the tests include a first loading plan and a second loading plan;

[0020] The first loading plan includes the combination of the deepest draft T1 for open sea navigation, the horizontal trim TR1, and the metacentric height value GM1 corresponding to the deepest draft of the open sea on the limit curve of the initial metacentric height;

[0021] The second stowage plan includes the combination of the deepest draft T1 in open sea navigation, the longitudinal trim TR1, and the initial metacentric height GM2. GM2 is the value of the initial metacentric height corresponding to the resonance between the actual ship's rolling period and the spectral peak period. If the resonance initial metacentric height value is greater than the maximum initial metacentric height value GM3 on the initial metacentric height limit curve or the maximum initial metacentric height value GM4 corresponding to the deepest draft loading condition of the actual ship in open sea, then one of GM3 and GM4 is selected as GM2.

[0022] The preliminary tests include: adjusting the ship model to the first stowage plan, not arranging containers in the open cargo holds, establishing the preliminary test conditions, respectively measuring the water inflow into each open cargo hold of the ship model under all preliminary test conditions, and determining the most unfavorable cargo hold for each of the five wave directions of head sea, bow quartering sea, beam sea, stern quartering sea, and following sea.

[0023] The basic tests include: establishing the basic test conditions, dynamically adjusting the container arrangement in the open cargo holds according to the wave direction. Under any wave direction, the most unfavorable cargo hold obtained from the preliminary test for this wave direction is simulated as having no containers, and the other open cargo holds are fully loaded with containers above the open deck. The ship model is respectively adjusted to the first stowage plan and the second stowage plan, and the water inflow into each open cargo hold of the ship model is respectively measured under all basic test conditions, and the most unfavorable wave direction and the maximum hourly water inflow height of the open cargo hold are determined.

[0024] Step 3, evaluate the test results.

[0025] [[ID=,13]]Furthermore, in step 1, the simulation of the test environmental conditions includes simulating the wave spectrum and the wave direction, and the simulation of the test object includes determining the ship model used to simulate the actual ship, determining the stowage plan of the ship model corresponding to each test condition and debugging it, and determining the test speed. Determining the stowage plan of the ship model corresponding to each test condition includes: determining the draft, longitudinal trim, initial metacentric height, longitudinal moment of inertia, transverse moment of inertia, natural rolling period, and decay coefficient of the stowage plan corresponding to each test condition.

[0026] Furthermore, in step 1, the ship model can use a spare propeller and a spare rudder instead of the designed propeller and the designed rudder.

[0027] Furthermore, in step 2, when the natural rolling period of the actual ship is twice the encounter period, under the stern quartering sea and following sea conditions, increase the minimum maneuvering speed by 1 or 2 kn, and determine the propeller speed N S 1 corresponding to this speed in still water. S 1 for the test.

[0028] Furthermore, in step 2, the stowage plan during the test includes the third stowage plan; the third stowage plan includes the combination of the deepest draft T1 in open sea navigation, the additional longitudinal trim TR2, and the initial metacentric height value GM1 corresponding to the deepest draft on the initial metacentric height limit curve.

[0029] Further, in step 2, the loading plan during the test includes the fourth loading plan; the fourth loading plan includes the combination of the deepest draft T1 during open - sea navigation, the additional trim TR2, and the initial metacentric height GM2, where GM2 is the initial metacentric height value corresponding to the resonance between the actual ship's rolling period and the spectral peak period; if the resonance initial metacentric height value is greater than the maximum initial metacentric height value GM3 on the initial metacentric height limit curve or the maximum initial metacentric height value GM4 corresponding to the deepest draft loading condition of the actual ship in the open sea, then one of GM3 and GM4 is selected as GM2.

[0030] Further, in step 2, the test also includes conducting additional tests; establishing additional test conditions; when conducting additional tests, the ship model is adjusted to the third loading plan, the containers are arranged in the same way as in the basic test, and the additional tests are carried out in the most unfavorable wave direction obtained from the basic test. The requirements for the additional tests are the same as those for the basic test; subsequently, the ship model is adjusted to the fourth loading plan and tested according to the test method under the third loading plan.

[0031] Further, in step 3, the evaluation includes: comparing with the evaluation criteria and the countermeasures taken when exceeding the evaluation criteria.

[0032] Further, the evaluation criteria are that the maximum hourly water ingress height of any open cargo hold measured in the test should not exceed the maximum allowable value specified for each navigation area.

[0033] Further, the countermeasures taken when exceeding the evaluation criteria include: preferentially conducting test conditions in more unfavorable wave directions. For test conditions that exceed the evaluation criteria, additional measures such as increasing the simulated cargo covers stacked on the hatch coaming of the cargo hold or on the open deck are used to reduce the water entering the empty cargo hold, and step 2 is repeated for testing.

[0034] The beneficial effects of the present invention are as follows:

[0035] The method of the present invention can simulate complex wave phenomena and accurately capture dynamic changes. The method of the present invention has a wide range of applications and can be applied to open - top container ships in all navigation areas to simulate the ship motion response in various navigation area sea conditions, and the test results have high accuracy. The method of the present invention can avoid the problem of high technical risks in sea trials of actual ships, prevent bad sea conditions from threatening the safety of ships, personnel and equipment, and reduce costs.

[0036] The method of the present invention establishes the loading methods of the ship model under the test conditions of preliminary tests, basic tests, and additional tests, and gives the determination methods of parameters such as draft, trim, initial metacentric height, longitudinal moment of inertia, transverse moment of inertia, natural rolling period, and decay coefficient.

[0037] The present invention adopts the technical feature that "GM1 is the metacentric height value corresponding to the deepest draft of the open part on the limiting curve of the initial metacentric height; GM2 is the metacentric height value corresponding to the resonance between the actual ship's rolling period and the spectral peak period; if the resonance metacentric height value is greater than the maximum metacentric height value GM3 on the limiting curve of the initial metacentric height or the maximum metacentric height value GM4 corresponding to the deepest draft loading condition of the actual ship's open part, then one of GM3 and GM4 is selected as GM2". GM1 and GM4 fully consider the variation range of the metacentric height of the actual ship's operation when loading light and heavy goods, overcome the problem that the test results are on the safe side caused by the existing method of obtaining the metacentric height value, and ensure the accuracy of the test.

[0038] The present invention adopts the technical feature that "through preliminary tests, the most unfavorable cargo holds for each of the five wave directions of head sea, bow quartering sea, beam sea, stern quartering sea, and following sea are obtained, and the container arrangements in each test condition and each open cargo hold are dynamically adjusted according to the wave direction change". This method of arranging containers in the open cargo hold fully considers the loading requirements of the actual operation of the ship, overcomes the problem of overly conservative simulation of the test object in the existing technology, and improves the economy of the ship.

[0039] The present invention adopts the technical feature that "the basic test conditions are first tested under all wave directions and then under beam sea, and the additional test conditions are tested under the most unfavorable wave direction obtained from the basic test". The 6 basic test conditions and 2 additional test conditions fully evaluate the influence of the most unfavorable wave direction and the superposition of the most unfavorable wave direction and the most unfavorable ship model loading, overcome the problem of a large number of test conditions and long test time caused by the possible superposition of 8 horizontal trim test conditions and 8 additional trim test conditions in the existing technology, and improve the test efficiency while ensuring the accuracy of the test.

[0040] The method of the present invention provides countermeasures when the evaluation of the green water volume on the open cargo hold of the ship is unreasonable, ensuring the smooth completion of the test. Specific embodiments

[0041] The following gives a preferred embodiment to more clearly and completely illustrate the present invention.

[0042] A model test method for the green water volume on the open cargo hold of an open-top container ship in waves, which includes:

[0043] Step 1, simulate the test environmental conditions and the test object;

[0044] Step 2, conduct tests, including conducting preliminary tests and basic tests;

[0045] The loading plans during the tests include the first loading plan and the second loading plan;

[0046] The first stowage plan includes the combination of the deepest draft T1 during open sea voyage, the longitudinal trim TR1, and the metacentric height GM1 corresponding to the deepest draft on the extreme metacentric height curve.

[0047] The second stowage plan includes the combination of the deepest draft T1 during open sea voyage, the longitudinal trim TR1, and the metacentric height GM2, where GM2 is the metacentric height value corresponding to the resonance between the actual ship's rolling period and the spectral peak period; if the resonance metacentric height value is greater than the maximum metacentric height value GM3 on the extreme metacentric height curve or the maximum metacentric height value GM4 corresponding to the deepest draft loading condition of the actual ship in the open condition, then one of GM3 and GM4 is selected as GM2.

[0048] The preliminary test includes: adjusting the ship model to the first stowage plan, not arranging containers in the open cargo holds, establishing the preliminary test conditions, measuring the water inflow of each open cargo hold into the ship model in all preliminary test conditions respectively, and determining the most unfavorable cargo hold for each of the five wave directions of head sea, bow oblique sea, beam sea, stern oblique sea, and following sea.

[0049] The basic test includes: establishing the basic test conditions, dynamically adjusting the container arrangement in the open cargo holds according to the wave direction change. Under any wave direction, the most unfavorable cargo hold obtained from the preliminary test for this wave direction is simulated as having no containers, and the other open cargo holds are fully loaded with containers above the open deck. The ship model is adjusted to the first stowage plan and the second stowage plan respectively, measuring the water inflow of each open cargo hold into the ship model in all basic test conditions respectively, and determining the most unfavorable wave direction and the maximum hourly water inflow height of the open cargo hold.

[0050] Step 3, evaluate the test results.

[0051] Among them, Step 1 belongs to the pre - test preparation stage, Step 2 is the test stage, and Step 3 is the test result evaluation stage. When conducting the test in Step 2, it should be carried out under the test environmental conditions and test objects in Step 1. Therefore, the content described in "the pre - test preparation stage" below is also the conditions to be met when conducting the test in the test stage of Step 2.

[0052] To avoid repetition, when the following text quotes the previous content, the way of using the serial number of the quoted content plus quotes to replace the quoted content is adopted. For example, when the following text quotes "1.1.2" in the previous text, at this time, "1.1.2" in the following text represents the content in "1.1.2 Wave direction angle" in "1. Test pre - test preparation stage"; the specific content of "1.1.2 Wave direction angle" will not be repeated in the following text.

[0053] 1. Test pre - test preparation stage

[0054] 1.1 Simulation of environmental conditions

[0055] The simulation of the test environmental conditions includes simulating the wave spectrum and the wave direction.

[0056] 1.1.1 Wave spectrum

[0057] 1.1.1.1 The model test shall be carried out in long-crested irregular waves. The JONSWAP spectrum (i.e., Joint North Sea Wave Project, English name: Joint North Sea Wave Project, abbreviated as JONSWAP) can be used for the test. For ships operating only in restricted sea areas, other wave spectra approved by the competent authority can be used.

[0058] 1.1.1.2 For ships sailing in different navigation areas, the test shall generate waves with the significant wave height in accordance with Table 1 under the most unfavorable wave period (zero-crossing).

[0059]

[0060] 1.1.2 Wave direction angle

[0061] The model test shall be carried out for at least the following wave direction angles:

[0062] (1) Head sea (wave direction angle is 180°);

[0063] (2) Bow quartering sea (wave direction angle is 135° or 225°);

[0064] (3) Beam sea (wave direction angle is 90° / 270°);

[0065] (4) Stern quartering sea (wave direction angle is 45° or 315°);

[0066] (5) Following sea (wave direction angle is 0° / 360°).

[0067] 1.2 Simulation of the test object

[0068] 1.2.1 Integrity of the ship model

[0069] 1.2.1.1 For the test model, in addition to requiring the shape of the underwater part to be similar to that of the actual ship, the shape of the above-water part (including structures such as freeboard, upper deck, bulwark, superstructure up to the cab, deckhouse, wave shield, wave baffle, hatch coaming of cargo hold, chimney, etc. that affect seawater entering the cargo hold) also meets the similarity with the actual ship.

[0070] 1.2.1.2 The openings on the above structures and the gaps between the structures, such as the observation holes and mooring holes on the wave shield, also meet the similarity with the actual ship.

[0071] 1.2.1.3 The self-propelled unconstrained model is used for the test, and the appendages such as propeller, rudder, bilge keel, etc. should be similar to those of the actual ship.

[0072] 1.2.1.4 The ship model can use a spare propeller and a spare rudder to replace the designed propeller and the designed rudder, which is convenient for designers to flexibly adjust the test schedule.

[0073] 1.2.1.5 When individual cargo holds are equipped with hatch covers, in the model test, this cargo hold can be simulated as having a hatch cover, and containers can be arranged on it, and seawater is not pumped into this cargo hold.

[0074] 1.2.2 Loading plan and debugging method of the ship model corresponding to each test condition

[0075] 1.2.2.1 During the test, the draft of the ship model is adjusted to the position corresponding to the deepest draft of the actual ship in open water navigation. That is: during the test, according to the scale ratio, the draft of the ship model is adjusted to a position similar to the deepest draft T (minimum freeboard) of the actual ship in open water navigation.

[0076] 1.2.2.2 The longitudinal trim of the ship model is adjusted to a horizontal longitudinal trim.

[0077] 1.2.2.3 When the longitudinal trim in the deepest draft operation of the actual ship in open water navigation exceeds the range of ±0.5% of the ship length L, a loading plan with additional longitudinal trim should be added, and additional test conditions should be added. Among them, the ship length L refers to the ship length defined in the current "International Convention on Load Lines". The additional longitudinal trim is the same as the additional longitudinal trim in the probabilistic damage stability calculation of the actual ship according to the current "International Convention for the Safety of Life at Sea".

[0078] 1.2.2.4 Debugging method for the initial metacentric height GM of the ship model:

[0079] (1) In the preliminary test condition, it is adjusted to GM1 corresponding to the deepest draft in open water navigation on the GM limit curve. The GM limit curve is obtained from the probabilistic damage stability calculation of the actual ship according to the "International Convention for the Safety of Life at Sea".

[0080] (2) In the basic test condition, first, in the five wave directions of "1.1.2", keep the initial metacentric height GM1 in item (1) of this article unchanged and conduct basic tests in the five wave directions; then, in the beam sea of "1.1.2", adjust it to GM2 corresponding to the resonance of the actual ship's rolling period and the spectral peak period and conduct basic tests in the beam sea.

[0081] (3) When the resonance GM2 in item (2) of this article far exceeds the maximum GM3 on the GM limit curve or the maximum GM4 corresponding to the deepest draft loading condition of the actual ship in open water navigation, then in the beam sea, select one of GM3 and GM4 as GM2 and conduct basic tests in the beam sea.

[0082] (4) Additional test conditions (if any), adjust to the initial metacentric height GM1 in item (1) of this article. First, conduct additional tests in the most unfavorable wave direction obtained from the basic tests; then adjust to the initial metacentric height GM2 in item (2) or (3) of this article above and conduct additional tests in the most unfavorable wave direction.

[0083] 1.2.2.5 Based on "1.2.2.1" to "1.2.2.4", establish the ship model loading plan corresponding to each test condition. Adjust the center of gravity, longitudinal moment of inertia, and transverse moment of inertia of the ship model to be similar to the actual ship according to each loading plan. The debugging parameters of the ship model for each loading plan are shown in Table 2.

[0084]

[0085] 1.2.2.6 If there is no clear requirement for the longitudinal radius of gyration of the ship model, it can be taken as 0.25Lpp; if there is no clear requirement for the transverse radius of gyration of the ship model, it can be taken as 0.35B.

[0086] 1.2.2.7 For each loading plan, conduct a free rolling decay test in still water at zero speed to measure the natural rolling period, decay coefficient, etc. of the ship model.

[0087] 1.2.3 Test speed

[0088] The ship model should be tested at least at the following speeds:

[0089] (1) The maximum sustained speed in head seas and bow quartering seas;

[0090] (2) The minimum maneuvering speed in quartering seas and following seas;

[0091] (3) Zero speed in beam seas.

[0092] Among them, the zero speed in beam seas is required to be in the state of the ship model without power.

[0093] 1.2.3.1 Method for determining the maximum sustained speed:

[0094] (1) According to the maximum continuous power of the main engine (SMCR), combined with the results of the calm water ship model speed performance test, predict the speed V in still water;

[0095] (2) Select 4 propeller speeds N1, N2, N3, N4 in still water, measure the corresponding speeds V1, V2, V3, V4, and interpolate the propeller speed N from V;

[0096] (3) In regular waves, with the propeller speed set to N respectively in the case of head seas or bow quartering seas, and keep the course stable by steering, measure the maximum sustained speed V considering stall in head seas W 1 and the maximum sustained speed V considering stall in bow quartering seasW 2.

[0097] 1.2.3.2 The minimum manoeuvring speed is calculated in accordance with the "Guidelines for Determining the Minimum Propulsion Power for Maintaining the Maneuvrability of Ships in Severe Sea Conditions (MEPC.1 / Cir.850 / Rev.2)":

[0098] V S = max(4, V ref - 10(A R - 0.009))

[0099] Where: V ref is the minimum reference course-keeping speed, obtained by the calculation method given in Table 3; A R is the ratio of the actual rudder area Ar of the ship to the underwater lateral immersed area A of the ship corrected for the width effect, A LS = A R = A r / A LS . In the following table, A F / A L is the ratio of the actual transverse wind area A F of the ship to the longitudinal wind area A L of the ship.

[0100]

[0101] 1.2.3.3 For the speeds V and V S in still water, the corresponding propeller revolutions N and N S are determined respectively. In the head sea and bow quartering sea conditions, the ship model is tested at the propeller revolutions N; in the beam sea condition, the ship model is tested at zero speed (stationary state); in the stern quartering sea and following sea conditions, the ship model is tested at the propeller revolutions N S .

[0102] 1.2.3.4 When the natural rolling period of the actual ship is twice the encounter period, in the stern quartering sea and following sea conditions, the above minimum manoeuvring speed can be increased by 1 or 2 kn to avoid the problem of excessive water ingress into the open cargo hold due to resonant rolling and prevent the ship model from being damaged or even the test from failing. Determine the propeller revolutions N S 1 corresponding to this speed in still water, and conduct the test at the propeller revolutions N S 1.

[0103] 2 Test phase

[0104] During the test phase, it should be carried out under the conditions that meet the above "1. Preparatory stage before the test". The test content in the above "1. Preparatory stage before the test" is included in this test phase.

[0105] The overtopping test for the open cargo hold includes: preliminary test, basic test and additional test.

[0106] 2.1 General requirements

[0107] 2.1.1 The test time for each test condition shall correspond to at least 1 h of the full-scale ship time (except for the preliminary test), and each test condition may consist of multiple test voyages.

[0108] 2.1.2 In addition to measuring the usual parameters (model motion, speed, relative motion, rudder angle, etc.) for each test voyage, the amount of water entering each open cargo hold shall also be measured. The cumulative amount of water entering multiple times is the measured overtopping volume.

[0109] 2.1.3 After each test voyage, the water pumped into the hold shall be pumped out and measured so as not to have an obvious impact on the initial metacentric height, moment of inertia and displacement due to the accumulated water.

[0110] 2.2 Preliminary test

[0111] 2.2.1 The preliminary test is used to determine the most unfavorable cargo hold for each wave direction in "1.1.2", providing a basis for the container arrangement in the open cargo hold in the basic test and additional test (if any).

[0112] 2.2.2 The model is adjusted to the loading plan A001 in "1.2.2.5", and no containers are arranged in all open cargo holds. The test is carried out at the speed specified in "1.2.3" in the five wave directions in "1.1.2". The preliminary test conditions are shown in Table 4.

[0113]

[0114] 2.2.3 The test time for the preliminary test conditions does not need to correspond to 1 h of the full-scale ship time.

[0115] 2.2.4 Measure the amount of water entering each open cargo hold under the preliminary test conditions to determine the most unfavorable cargo hold for each wave direction. Taking the case of setting 3 open cargo holds as an example (assuming the hatch opening area of the first cargo hold is 400 m 2 , the hatch opening area of the second cargo hold is 800 m 2 , and the hatch opening area of the third cargo hold is 500 m 2 ). See Table 5 for details.

[0116]

[0117] As can be seen from the above table, the most unfavorable cargo hold in head seas is the first cargo hold, the most unfavorable cargo hold in bow quartering seas is the third cargo hold, the most unfavorable cargo hold in beam seas is the second cargo hold, the most unfavorable cargo hold in quartering stern seas is the second cargo hold, and the most unfavorable cargo hold in following seas is the third cargo hold.

[0118] 2.3 Basic Test

[0119] 2.3.1 The basic test is used to measure the amount of water entering each open cargo hold of the ship model under the basic test conditions, and to determine the most unfavourable wave direction and the maximum hourly flooding height of the open cargo hold.

[0120] 2.3.2 During the test, the container arrangement in the open holds of the ship model is dynamically adjusted according to the wave direction. That is, for a certain wave direction in "1.1.2", the most unfavorable cargo hold for that wave direction obtained from the preliminary test is simulated as empty of containers, while the other open holds are fully loaded with containers that are above the weather deck.

[0121] 2.3.3 The ship model remains loaded as A001. First, adjust the open hold container layout for each wave direction in "1.1.2." Then, conduct tests in that wave direction at the speed specified in "1.2.3." Conduct tests in the same manner for the five wave directions in "1.1.2." Adjust the ship model to loading plan A002 in "1.2.2.5." Arrange the containers in the same manner, and conduct tests in beam seas at zero speed.

[0122] The basic test conditions are shown in Table 6.

[0123]

[0124] 2.3.4 Measure the amount of water entering each open cargo hold under the basic test conditions and determine the most unfavorable wave direction. 2 、Opening area of the second cargo hold hatch: 800m 2 、Opening area of the third cargo hold hatch: 500m 2 ). See Table 7 for details.

[0125]

[0126] It can be seen from the above table that the most unfavorable wave direction is the bow oblique wave, and the maximum hourly water inflow height of the open cargo hold is 240mm / h.

[0127] 2.4 Additional tests

[0128] 2.4.1 The additional test is to measure the amount of water entering each open cargo hold of the ship model under the additional test conditions and to determine the maximum hourly flooding height of the open cargo hold.

[0129] 2.4.2 If additional trim loading is required in accordance with the provisions of 1.2.2.3, the ship model should be adjusted to loading plan A003 in 1.2.2.5. Containers should be arranged similarly and the test conducted in the most unfavorable wave direction obtained from the basic test. The requirements for the additional test are consistent with those for the basic test. Subsequently, the ship model should be adjusted to loading plan A004 in 1.2.2.5 and the test conducted similarly.

[0130] The additional test conditions are shown in Table 8.

[0131]

[0132] 3 Evaluation of Test Results

[0133] The evaluation includes: comparison with the evaluation criteria and the countermeasures to be taken when the evaluation criteria are exceeded.

[0134] 3.1 Evaluation Criteria

[0135] 3.1.1 Evaluation Criteria for the Overwash Quantity Test of Open Cargo Holds

[0136] The overwash quantity per hour of the open cargo hold = the open area of the hatch × the water ingress height per hour.

[0137] The evaluation criterion is that the maximum water ingress height per hour measured for any open cargo hold in the test should not exceed the maximum allowable value specified for each navigation area.

[0138] The maximum allowable value of the water ingress height per hour for open cargo holds in each navigation area is shown in Table 9.

[0139]

[0140] 3.2 Evaluation of the Rationality of the Model Test Results of the Overwash Quantity of Open Cargo Holds

[0141] 3.2.1 For a ship model that meets the following requirements, the model test results are reasonable:

[0142] In the basic test conditions and the additional test conditions (if any), the maximum water ingress height per hour measured for any open cargo hold does not exceed the maximum allowable value specified for each navigation area.

[0143] That is:

[0144] When there are no additional test conditions, in the basic test conditions, the maximum water ingress height per hour measured for any open cargo hold does not exceed the maximum allowable value specified for each navigation area;

[0145] When there are additional test conditions, in the basic test conditions and the additional test conditions, the maximum water ingress height per hour measured for any open cargo hold does not exceed the maximum allowable value specified for each navigation area;

[0146] 3.2.2 Reasonably arrange the order of test conditions, and give priority to the more adverse wave direction conditions. For test conditions that exceed the evaluation criteria, promptly adopt reasonable countermeasures, including adding simulated hatch covers stacked on the hatch coaming of the cargo hold or on the open deck as an additional measure to reduce water ingress into the empty cargo hold; repeat the tests in "2.3" and "2.4", including the basic test conditions and additional test conditions (if any). In this case, impose corresponding restrictions during the operation of the actual ship in the open state.

[0147] The method for completely simulating the test object in the present invention can truly construct the structural characteristics of the actual ship and accurately reflect the seakeeping characteristics of the actual ship; the debugging method of the ship model loading plan corresponding to each test condition can fully evaluate the trim and center of gravity range of the actual ship operation; the container layout plan for each test condition determined by the test method is closer to the actual ship operation while considering the most unfavorable situation; the method for determining the minimum maneuvering speed in the special cases of stern quartering waves and following waves can avoid the problem of excessive water ingress into the open cargo hold caused by resonant rolling and prevent the damage of the ship model or even the failure of the test; the method for determining each test condition evaluates the influence of the superposition of the most unfavorable wave direction, the most unfavorable wave direction and the most unfavorable ship model loading, simplifies the number of conditions, and ensures the test accuracy and improves the efficiency.

[0148] The present invention method establishes the loading methods of the ship model under the preliminary test, basic test, and additional test conditions, and gives the determination methods of parameters such as draft, trim, metacentric height, longitudinal moment of inertia and transverse moment of inertia, roll natural period, and decay coefficient.

[0149] The paper "Influence of DNV•GL New Specification on the General Design of Open Multi-purpose Ships and Measures to Reduce Green Water" (authors He Xinyu et al., Shipbuilding of China, No. 3, 2021, Serial No. 192) proposes that "in all wave directions, the GM value of the ship is selected as the GM value corresponding to the resonance of the roll period and the spectral peak period in beam seas. If the GM value corresponding to the resonance exceeds the maximum value of the ship's limit GM curve, the maximum value of the limit GM curve can be selected. For the 3 wave directions with relatively poor results, the maximum value of the limit GM curve is taken again", while the present invention adopts the technical feature that "GM1 is the metacentric height value corresponding to the deepest draft of the open ship on the limit curve of metacentric height; GM2 is the metacentric height value corresponding to the resonance of the actual ship's roll period and the spectral peak period; if the resonance metacentric height value is greater than the maximum metacentric height value GM3 on the limit curve of metacentric height or the maximum metacentric height value GM4 corresponding to the deepest draft loading condition of the actual ship in the open state, then select one of GM3 and GM4 as GM2". GM1 and GM4 fully consider the change range of the metacentric height of the actual ship operation when loading light and heavy goods, overcome the problem that the test results are on the safe side caused by the existing metacentric height value selection method, and ensure the test accuracy.

[0150] The paper "Research on Deck Wave Assessment Method for Determining the Freeboard of Open Container Ships" (authors Sun Anlin et al., China Shipbuilding, Vol. 60, No. 3 (No. 231 in total)) proposes that "the remaining five open cargo holds should be covered with flexible waterproof materials to collect water caused by incoming waves." The present invention adopts the technical feature of "obtaining the most unfavorable cargo holds for each of the five wave directions of head waves, bow waves, transom waves, stern waves, and following waves through preliminary tests, and dynamically adjusting the container layout in each test condition and each open cargo hold according to changes in wave direction." This method of container layout in open cargo holds fully considers the loading needs of the actual operation of the ship, overcomes the problem of conservative simulation of test objects in the existing technology, and improves the economy of the ship.

[0151] The paper "The Impact of DNV•GL's New Standards on the Overall Design of Open Multipurpose Ships and Measures to Reduce Waves" (author He Xinyu et al., Ships, Issue 3, 2021, Issue 192) proposes "measurement of wave water inflow in all wave directions, 1 hour for each condition, and then repeated measurement in the three wave directions with poor results. Additional longitudinal tilt values need to be added to the open seakeeping model test." The present invention adopts the technical feature of "the basic test conditions are first tested in all wave directions and then in transverse waves, and the additional test conditions are tested in the most unfavorable wave direction obtained in the basic test." The 6 basic test conditions and 2 additional test conditions fully assess the effects of the most unfavorable wave direction, the most unfavorable wave direction and the most unfavorable ship model loading, overcoming the problems of the existing technology of 8 horizontal longitudinal tilt test conditions and the long test time caused by the superposition of 8 additional longitudinal tilt test conditions, ensuring the accuracy of the test while improving the test efficiency.

[0152] The method of the present invention provides countermeasures to be taken when the wave load on the open cargo hold of a ship is assessed to be unreasonable, thereby ensuring smooth completion of the test.

[0153] The present invention has the following advantages:

[0154] (1) The method of the present invention can simulate complex wave phenomena and accurately capture dynamic changes;

[0155] (2) The method of the present invention has a wide range of applications and can be applied to open container ships in all navigation areas. It can simulate the ship motion response in various sea conditions in various navigation areas, and the test results are highly accurate.

[0156] (3) The method of the present invention can avoid the high technical risks of marine ship testing, prevent the threat to the safety of ships, personnel and equipment caused by severe sea conditions, and reduce costs.

[0157] (4)The method of the present invention accurately simulates environmental conditions such as sea waves and ship speed, truly constructs the structural characteristics of a real ship, determines the container layout plan for each test condition by experimental methods, fully examines the trim and center of gravity ranges during actual ship operation, scientifically and reasonably designs the test process, provides countermeasures to be taken when the assessment of the green water volume on the open cargo hold of the ship is unreasonable, ensuring the accuracy and reliability of the test; avoiding being overly conservative in the test objects and condition simulation, which may affect the ship's economy; providing reasonable countermeasures for various special situations during the test to ensure the smooth completion of the test.

[0158] The present invention innovatively constructs a model test method for the green water volume on the open cargo hold of an open-top container ship in waves, fills the gaps in the existing specifications in terms of details and depth, provides a more comprehensive implementation basis and guiding criteria, and provides a guarantee for the safe navigation of ships in complex sea conditions.

[0159] Although the specific implementation manners of the present invention have been described above, those skilled in the art should understand that this is only an example. The protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these implementation manners, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A model test method for the overwash volume of the open cargo hold of an open box ship in waves, characterized in that It includes: Step 1: Simulate the test environment conditions and the test object. Step 2: Conduct tests, including preliminary tests and basic tests. The loading plans during the tests include the first loading plan and the second loading plan. The first loading plan includes the combination of the deepest draft T1 during open-sea navigation, the horizontal trim TR1, and the metacentric height value GM1 corresponding to the deepest draft on the metacentric height limit curve for open-sea conditions. The second loading plan includes the combination of the deepest draft T1 during open-sea navigation, the horizontal trim TR1, and the metacentric height GM2, where GM2 is the metacentric height value corresponding to the resonance between the actual ship's rolling period and the spectral peak period; if the resonance metacentric height value is greater than the maximum metacentric height value GM3 on the metacentric height limit curve or the maximum metacentric height value GM4 corresponding to the actual ship's deepest draft loading condition for open-sea, then select one of GM3 and GM4 as GM2. The preliminary tests include: Adjust the ship model to the first loading plan, do not arrange containers in the open cargo holds, establish the preliminary test conditions, measure the water inflow into each open cargo hold of the ship model for all preliminary test conditions respectively, and determine the most unfavorable cargo hold for each of the five wave directions: head sea, bow quartering sea, beam sea, stern quartering sea, and following sea. The basic tests include: Establish the basic test conditions, the container arrangement in the open cargo holds is dynamically adjusted according to the wave direction change. For any wave direction, simulate the most unfavorable cargo hold obtained from the preliminary tests for that wave direction as having no containers, and fully load the other open cargo holds with containers above the open deck. Adjust the ship model to the first loading plan and the second loading plan respectively, measure the water inflow into each open cargo hold of the ship model for all basic test conditions respectively, and determine the most unfavorable wave direction and the maximum hourly water inflow height of the open cargo hold. Step 3: Evaluate the test results.

2. The method for model test of the amount of water splashing into the open cargo hold of an open box ship in waves as claimed in claim 1, wherein, In Step 1, the simulation of the test environment conditions includes simulating the wave spectrum and the wave direction, and the simulation of the test object includes determining the ship model used to simulate the actual ship, determining the ship model loading plan corresponding to each test condition and debugging it, and determining the test speed. Determining the ship model loading plan corresponding to each test condition includes: Determining the draft, trim, metacentric height, longitudinal moment of inertia, transverse moment of inertia, natural rolling period, and damping coefficient of the loading plan corresponding to each test condition.

3. The wave overtopping volume model test method for the open cargo hold of an open box ship in waves according to claim 1, wherein In Step 1, the ship model can use a spare propeller and a spare rudder instead of the designed propeller and the designed rudder.

4. The wave overtopping quantity model test method for the open cargo hold of an open box ship in waves as claimed in claim 1, wherein, In Step 2, when the natural rolling period of the actual ship is twice the encounter period, under the conditions of following sea and quartering sea, increase the minimum maneuvering speed by 1 or 2 kn, and determine the propeller speed N corresponding to this speed in still water. S 1. Conduct tests at the propeller speed N S 1.

5. The method for model test of overtopping volume on the open cargo hold of an open box ship in waves according to claim 1, characterized in that, In Step 2, the loading plans during the tests include the third loading plan; the third loading plan includes the combination of the deepest draft T1 during open-sea navigation, the additional trim TR2, and the metacentric height value GM1 corresponding to the deepest draft on the metacentric height limit curve for open-sea conditions.

6. The method for wave impact volume model test on the open cargo hold of an open box ship in waves according to claim 5, characterized in that, In Step 2, the loading plans during the tests include the fourth loading plan; the fourth loading plan includes the combination of the deepest draft T1 during open-sea navigation, the additional trim TR2, and the metacentric height GM2, where GM2 is the metacentric height value corresponding to the resonance between the actual ship's rolling period and the spectral peak period; if the resonance metacentric height value is greater than the maximum metacentric height value GM3 on the metacentric height limit curve or the maximum metacentric height value GM4 corresponding to the actual ship's deepest draft loading condition for open-sea, then select one of GM3 and GM4 as GM2.

7. The method for conducting a model test on the amount of water boarding in the open cargo hold of a wave-exposed box ship as described in claim 6, characterized in that, In Step 2, conducting the test also includes conducting additional tests; establishing additional test conditions; when conducting the additional tests, the ship model is adjusted to the third loading plan, the containers are arranged in the same way as in the basic test, and the additional tests are carried out in the most unfavorable wave direction obtained from the basic test. The requirements for the additional tests are the same as those for the basic test; subsequently, the ship model is adjusted to the fourth loading plan and the test is carried out according to the test method under the third loading plan.

8. The method for model test of overtopping volume on the open cargo hold of an open box ship in waves as claimed in claim 1, wherein, In Step 3, the evaluation includes: comparison with the evaluation criteria and the countermeasures taken when exceeding the evaluation criteria.

9. The method for model test of the amount of water shipped on the open cargo hold of an open box ship in waves as described in claim 8, characterized in that, The evaluation criteria are that the maximum hourly water ingress height of any open cargo hold measured in the test shall not exceed the maximum allowable value specified for each navigation area.

10. The method for model test of overtopping volume on the open cargo hold of an open box ship in waves as claimed in claim 8, wherein The countermeasures taken when exceeding the evaluation criteria include: giving priority to conducting test conditions in more unfavorable wave directions. For test conditions that exceed the evaluation criteria, additional measures are taken to reduce water entering the empty cargo hold by increasing the simulated cargo covers stacked on the hatch coaming of the cargo hold or on the open deck, and Step 2 is repeated for the test.

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