Bulk cargo ship head and tail peak tank arrangement bending moment optimization method for sampling large and small tank capacity grids
By constructing a three-dimensional ship model and sampling two-dimensional parameter meshes, and combining the numerical difference method to calculate sensitivity, the problems of accuracy and floating state constraints in the optimization of longitudinal bending moment in the arrangement of the bow and stern peaks of bulk carriers were solved, and high-precision optimization design was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-03-17
AI Technical Summary
Existing technologies rely on empirical design and limited scheme verification in optimizing the layout of the fore and stern peaks and the overall longitudinal bending moment of bulk carriers, making it difficult to achieve accurate optimization. Furthermore, they fail to effectively incorporate floating constraints, resulting in insufficient optimization accuracy and poor engineering applicability.
A three-dimensional ship model including the basic structure of the bow and stern conning towers was constructed. A two-dimensional parametric mesh sampling method was used, and the sensitivity was calculated by numerical difference method. The model was then optimized in combination with the floating state requirements to determine the optimal compartment combination.
It achieves precise control of the overall longitudinal bending moment, improves optimization accuracy, meets the requirements of ship floating state specifications, and has strong engineering applicability.
Smart Images
Figure CN121671815A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of shipbuilding technology, and in particular to a method for optimizing the bending moment of the bow and stern pointed holds of a bulk carrier by sampling the grid size of the hold volume. Background Technology
[0002] With the development of the global shipping industry, bulk carriers are trending towards larger sizes (such as 210,000-ton large bulk carriers) and more complex shipping conditions. Ships need to adapt to different routes (such as coastal and ocean-going), different cargo types (such as iron ore and coal), different loading conditions (such as full load, ballast, and compartment loading), and extreme sea states (such as storms). This places higher demands on the optimization of the longitudinal bending moment. At the same time, the International Maritime Organization (IMO) and various national classification societies (such as LR, CCS, and ABS) are imposing increasingly stringent requirements on ship floatability (draft, trim) and stability (initial metacentric height, stability curves), further requiring that the optimization of the longitudinal bending moment be simultaneously satisfied with floatability constraints to ensure the engineering applicability of the design scheme.
[0003] Against this backdrop, the relationship between the volume of the fore and stern peak holds and the overall longitudinal bending moment has become an important research direction in bulk carrier design. How to achieve precise optimization of the overall longitudinal bending moment by scientifically adjusting the hold volume, while simultaneously meeting the requirements of buoyancy and stability, has become a technical problem that the industry urgently needs to solve.
[0004] Currently, in the field of optimizing the layout of the fore and stern peak holds and the overall longitudinal bending moment of bulk carriers, the closest existing technologies mainly rely on a combination of traditional empirical design and finite scheme verification, as detailed below:
[0005] 1. Empirical values for cabin capacity parameters
[0006] In existing technologies, the initial setting of the fore and aft peak hold capacity often relies on engineers' design experience or comparative data from similar ship types. For example, designers typically refer to the fore and aft peak hold capacity ranges of bulk carriers of the same tonnage (e.g., the fore peak hold accounts for 3%-5% of the total capacity, and the aft peak hold accounts for 2%-4%), and directly determine 2-3 fixed capacity schemes (e.g., 3000m² for the fore peak hold). 3 Aft tip compartment 2000m 3 ; Foremost cabin 3500m 3 Aft tip compartment 1800m 3 (etc.), lacking a systematic analysis of cabin capacity parameters.
[0007] 2. Finite scheme verification of total longitudinal bending moment
[0008] After determining the fixed cargo hold scheme, existing technologies use ship structural mechanics software (such as NAPA) to calculate the total longitudinal bending moment of each scheme under typical operating conditions (such as full-load departure and ballast arrival). The bending moment results of different schemes are compared, and the scheme with the smaller bending moment is selected as the preliminary design scheme. During the verification process, the bending moment calculation is mainly based on the principles of ship statics, deriving the total longitudinal bending moment through a simplified load-buoyancy balance model, without establishing a quantitative correlation model between cargo hold capacity and bending moment.
[0009] In summary, existing technologies, characterized by experiential approaches, limited solutions, and independent verification, are ill-suited to the precise optimization requirements of the longitudinal bending moment under complex operating conditions of large bulk carriers. This is the closest existing technology to which this invention is aimed.
[0010] The existing technology has the following drawbacks:
[0011] Insufficient optimization accuracy: Traditional design methods rely on experience to determine the volume of the fore and aft peak compartments, and only use a limited number of fixed schemes by engineers to perform bending moment verification. With limited schemes to compare, it is difficult to accurately capture the pattern of longitudinal bending moment change with the volume of the compartments, resulting in low accuracy of longitudinal bending moment control.
[0012] Lack of systematic optimization mechanism: Existing technologies have not established a systematic sampling and optimization mechanism for cabin volume, a core parameter affecting the overall longitudinal bending moment. It is impossible to accurately analyze the degree of influence of cabin volume changes on the overall longitudinal bending moment (i.e., sensitivity), making it difficult to carry out targeted optimization design based on sensitivity results, resulting in a large degree of blindness in the optimization process.
[0013] Ineffective integration of floating constraints: When optimizing the longitudinal bending moment, existing technologies often fail to fully consider the floating requirements of the ship and cannot simultaneously verify floating parameters such as draft difference and stability height during the cabin adjustment process. This may result in the optimized scheme reducing the longitudinal bending moment but failing to meet the floating requirements of the ship's actual navigation and lacking engineering applicability. Summary of the Invention
[0014] To overcome the aforementioned deficiencies in the existing technology, this invention provides a method for optimizing the bending moment of the bow and stern pointed holds of a bulk carrier by sampling the grid of hold size.
[0015] The present invention solves the above-mentioned technical problems through the following technical solution:
[0016] A method for optimizing the bending moment of the fore and stern peak holds of a bulk carrier using grid sampling of hold size includes:
[0017] Step 1: Based on the ship's compartment distribution and hull shape, construct a three-dimensional ship model including the basic structure of the bow and stern peaks;
[0018] Step 2: Construct a two-dimensional parametric mesh using the cabin volumes of the fore and aft peaks as the core parameters;
[0019] Step 3: Select key optimization conditions that have a significant impact on the total longitudinal bending moment;
[0020] Step 4: For each node in the mesh, calculate the total longitudinal bending moment under the selected working condition;
[0021] Step 5: Based on the bending moment calculation results of the mesh nodes, the sensitivity is calculated using the numerical difference method;
[0022] Step 6: Combine the sensitivity analysis results with the ship's floating state requirements to define the optimization feasible region.
[0023] Furthermore, in step 1, the model needs to define the geometric boundary constraints of the fore and stern hulls and integrate the overall longitudinal bending moment calculation module.
[0024] Furthermore, in step 2, the range of values for the cabin volume of the forepeak compartment is set to [V1]. min V1 max The aft tip compartment volume ranges from [V2]. min V2 max Discretization is performed according to preset step sizes ΔV1 and ΔV2 to generate a set of grid nodes {(V1 i V2 j )|i=1,2,...,n;j=1,2,...,m}, where n and m are the number of nodes in the capacity grid of the forepeak and sternpeak modules, respectively.
[0025] Furthermore, the grid step size is adjusted according to the optimization accuracy and computation time requirements; the higher the accuracy requirement, the smaller the step size.
[0026] Furthermore, in step 3, the full-load condition, ballast arrival condition, extreme storm ballast condition, compartment loading condition, and strength condition that meets the requirements of the common specifications are selected as the calculation conditions.
[0027] Furthermore, in step 4, for each node in the mesh, the cabin model of the fore and stern peaks is adjusted in the ship model, and the total longitudinal bending moment calculation module is called to calculate the total longitudinal bending moment under the selected working condition.
[0028] Furthermore, the ship's floating state parameters and stability need to be recorded simultaneously during the calculation process to ensure that the basic floating state and stability constraints are met.
[0029] Further, in step 5, the cabin capacity sensitivity S1 of the forepeaker is defined as the ratio of the change in total longitudinal bending moment ΔM to the change in cabin capacity ΔV1 of the forepeaker, and the cabin capacity sensitivity S1 = ΔM / ΔV1; the cabin capacity sensitivity S2 of the forepeaker is defined as the ratio of the change in total longitudinal bending moment ΔM to the change in cabin capacity ΔV2 of the stern, and the cabin capacity sensitivity S2 = ΔM / ΔV2; by plotting the sensitivity, the distribution characteristics of S1 and S2 in different cabin capacity intervals are displayed intuitively, and the cabin capacity sensitive area with the most significant impact on bending moment is determined.
[0030] Furthermore, in step 6, within the sensitive area, the cabin adjustment direction that reduces the overall longitudinal bending moment is selected first; after bending moment optimization, the optimal cabin combination is finally output.
[0031] Furthermore, the direction of cabin volume adjustment to reduce the overall longitudinal bending moment includes: if S1 is positive, then reduce the cabin volume of the bow tip within the allowable range of the floating state; if S2 is negative, then increase the cabin volume of the stern tip.
[0032] The beneficial effects of this invention are as follows: This invention can accurately capture the pattern of longitudinal bending moment variation with cabin volume, thus greatly improving the control accuracy of longitudinal bending moment. This invention establishes a systematic sampling and optimization mechanism for cabin volume, a core parameter affecting longitudinal bending moment, accurately analyzing the degree of influence (i.e., sensitivity) of cabin volume changes on longitudinal bending moment. Based on the sensitivity results, targeted optimization design is carried out, realizing a systematic optimization mechanism. When optimizing longitudinal bending moment, this invention can fully consider the ship's floating state requirements, and can simultaneously verify floating state parameters such as draft difference and stability height during cabin volume adjustment. This ensures that the optimized solution not only reduces longitudinal bending moment but also meets the floating state specifications for actual ship navigation, demonstrating strong engineering applicability. Attached Figure Description
[0033] Figure 1 This is a schematic diagram of the cabin capacity parameter grid of a preferred embodiment of the present invention.
[0034] Figure 2 This is a sensitivity analysis diagram of the bow tip of the ship when the present invention is used as an example of a 210,000-ton bulk carrier.
[0035] Figure 3 This is a sensitivity analysis diagram of the stern tip compartment when using a 210,000-ton bulk carrier as an example. Detailed Implementation
[0036] The present invention will be described more clearly and completely below with reference to a preferred embodiment and the accompanying drawings.
[0037] A method for optimizing the bending moment of the fore and stern peak holds of a bulk carrier using grid sampling of hold size includes:
[0038] Step 1: Based on the ship's compartment distribution and hull shape, construct a three-dimensional ship model including the basic structure of the bow and stern peaks;
[0039] Step 2: Construct a two-dimensional parametric mesh using the cabin volumes of the fore and aft peaks as the core parameters;
[0040] Step 3: Select key optimization conditions that have a significant impact on the total longitudinal bending moment;
[0041] Step 4: For each node in the mesh, calculate the total longitudinal bending moment under the selected working condition;
[0042] Step 5: Based on the bending moment calculation results of the mesh nodes, the sensitivity is calculated using the numerical difference method;
[0043] Step 6: Combine the sensitivity analysis results with the ship's floating state requirements to define the optimization feasible region.
[0044] Specifically, the method in this embodiment also includes the following specific steps.
[0045] 1. Establish a benchmark ship model.
[0046] Based on the ship's compartment distribution and hull form, a three-dimensional ship model is constructed, including the basic structures of the bow and stern peaks. The model needs to clearly define the geometric boundary constraints of the bow and stern peaks, i.e., the limiting positions of the bow and stern peak boundaries, and integrate a longitudinal bending moment calculation module that can automatically update the ship's load conditions and buoyancy distribution model based on the input bow and stern peak volume parameters.
[0047] 2. Construction of cabin capacity parameter grid.
[0048] A two-dimensional parametric mesh is constructed using the capacities of the fore and aft peaks as the core parameters. The capacities of the fore and aft peaks are set to a range of [V1]. min V1 max The aft tip compartment volume ranges from [V2]. min V2 max Discretization is performed according to preset step sizes ΔV1 and ΔV2 to generate a set of grid nodes {(V1 i V2 j Let |i = 1, 2, ..., n; j = 1, 2, ..., m}, where n and m are the number of nodes in the forward and aft tip compartment mesh, respectively. The mesh step size can be adjusted according to the optimization accuracy and computation time requirements; the higher the accuracy requirement, the smaller the step size.
[0049] Figure 1 This is a schematic diagram of the cabin capacity parameter grid. The horizontal axis represents the cabin capacity V1 of the bow tip cabin, and the vertical axis represents the cabin capacity V2 of the stern tip cabin. The grid nodes represent the sampled cabin capacity combinations, and the size and color intensity of the nodes reflect the magnitude of the total longitudinal bending moment.
[0050] 3. Optimize operating condition screening.
[0051] Based on bulk carrier design and operation experience, key optimization conditions that significantly affect the overall longitudinal bending moment are selected. To reduce the computational workload and improve efficiency, the full-load condition, ballast arrival condition, extreme storm ballast condition, compartment loading condition, and strength condition that meets common specification requirements are prioritized as calculation conditions. Five to eight core conditions, including those mentioned above, can be selected as calculation conditions.
[0052] Each of the aforementioned preferred operating conditions has its own characteristics. Under full load conditions, cargo is evenly distributed. Under ballast arrival conditions, there is a significant difference in draft between the bow and stern. Under extreme storm ballast conditions, the ship encounters extreme forces under severe sea conditions. Under compartment loading conditions, heavy cargo holds are loaded with cargo, while light cargo holds are empty.
[0053] 4. Batch calculation of total longitudinal bending moment
[0054] For each node in the mesh (V1) i V2 j In the ship model, adjust the cabin models of the fore and aft peaks, and call the overall longitudinal bending moment calculation module to calculate the overall longitudinal bending moment M under the selected working conditions. ij The selectable operating conditions include fully loaded departure, fully loaded arrival, ballast departure, and ballast arrival. During the calculation process, the ship's float parameters and stability must be recorded simultaneously to ensure that basic float and stability constraints are met. Ship float parameters include draft and trim.
[0055] 5. Capacity-bending moment sensitivity analysis.
[0056] Based on the bending moment calculation results from the mesh nodes, the sensitivity is calculated using the numerical difference method. The cabin volume sensitivity S1 of the forepeak compartment is defined as the ratio of the change in total longitudinal bending moment ΔM to the change in cabin volume ΔV1 of the forepeak compartment, i.e., S1 = ΔM / ΔV1; the cabin volume sensitivity S2 of the aft peak compartment is defined as the ratio of the change in total longitudinal bending moment ΔM to the change in cabin volume ΔV2 of the forepeak compartment, i.e., S2 = ΔM / ΔV2. By plotting the sensitivity, the distribution characteristics of S1 and S2 within different cabin volume ranges are visually displayed, identifying the cabin volume sensitive areas that have the most significant impact on bending moment.
[0057] 6. Moment optimization based on floating state and stability constraints.
[0058] Based on the sensitivity analysis results and the ship's floating state requirements, an optimization feasible region is defined. Within the sensitive region, the direction of cargo hold adjustment that reduces the overall longitudinal bending moment is prioritized: if S1 is positive (i.e., increased cargo hold volume leads to increased bending moment), the cargo hold volume of the forepeak tank is reduced within the allowable range of floating state; if S2 is negative (i.e., increased cargo hold volume leads to decreased bending moment), the cargo hold volume of the aft peak tank is appropriately increased. During the optimization process, the parameters must be verified using floating state check formulas to ensure compliance with specifications. These parameters include draft difference, stability, etc. After bending moment optimization, the optimal cargo hold combination (V1_opt, V2_opt) is finally output.
[0059] Taking a 210,000-ton bulk carrier as an example, the specific implementation steps are as follows:
[0060] Baseline model establishment: A baseline model of all ship compartments is established using ship design software, with the top of the forepeak and the fore-end bulkhead of the sternpeak as variables to control the cargo hold capacity.
[0061] Capacity grid settings: The capacity of the forepeak compartment is set to 100–4000 m. 3 The tail tip compartment volume is set at 650–2500 m³. 3 The forward tip cabin has 15 nodes and the aft tip cabin has 10 nodes, forming 150 grid spaces.
[0062] Batch calculation of bending moment: For 81 cabin combinations, calculate the total longitudinal bending moment (sag in still water, camber in still water, sagging in damage, and camber in damage) under the selected working conditions.
[0063] Sensitivity analysis: Based on the calculation results, the sensitivity of each bending moment relative to the cabin volume was calculated using the finite difference method; among them, the sagging moment and the arching moment at the point of failure are not affected by the cabin volume of the fore and stern peaks, and their results are not listed.
[0064] Figure 2 Sensitivity analysis diagram of the foremost cabin; Figure 3 This is a sensitivity analysis diagram of the tail tip compartment.
[0065] Optimization Implementation: Analysis of the results shows that the sensitivity of the longitudinal center camber and center sag moments relative to the bow and stern peaks is positive. This means that the center camber moment increases with the increase of the bow and stern peak volume. Conversely, since the center sag moment is negative, it decreases with the increase of the bow and stern peak volume. Furthermore, the sensitivity value of the stern peak volume is greater than that of the bow peak volume. Considering the combined effects of buoyancy and stability, the optimization scheme for the original ship is shown in Table 1.
[0066] Table 1 Optimization Scheme
[0067] Bending moment type Bending moment change (%) Arch in still water -2.1 still water drop -13.5 Water arch 0 Water inlet vertical 0
[0068] This invention has the following characteristics:
[0069] 1. Parametric technology for benchmark ship models: Construct a three-dimensional ship model that includes geometric boundary models of the bow and stern hulls and a module for calculating the overall longitudinal bending moment. This model supports the automatic updating and calculation of hull capacity parameters sampled through traversing the mesh, providing basic support for the entire optimization process.
[0070] 2. Parametric mesh sampling method for bow and stern tip compartment volumes: Using the bow tip compartment volumes [V1min, V1max] and stern tip compartment volumes [V2min, V2max] as core parameters, a two-dimensional discrete mesh node set {(V1i, V2i, V1max]} is constructed according to preset step sizes ΔV1 and ΔV2. j This enables systematic and comprehensive sampling of cabin capacity parameters, breaking through the limitations of traditional fixed solutions.
[0071] 3. Batch calculation mechanism for longitudinal bending moment under multiple working conditions: For 5-8 selected key working conditions (such as full load, ballast, extreme storm ballast, etc.), the longitudinal bending moment calculation module is automatically called for the hull volume combination of each grid node, and the floating state (draft, trim) and stability parameters are recorded simultaneously to establish a correlation database between hull volume and bending moment.
[0072] 4. Numerical difference analysis method for cabin volume-bending moment sensitivity: Based on batch calculation results, the sensitivity of the forepeak cabin S1=ΔM / ΔV1 and the sensitivity of the stern cabin S2=ΔM / ΔV2 are defined by numerical difference method to quantify the degree of influence of cabin volume change on the total longitudinal bending moment and accurately locate the sensitive optimization area.
[0073] 5. Directional optimization strategy under floating state and stability constraints: Based on the sensitivity analysis results, within the constraints of the floating state specifications (draft difference, stability height, etc.), the direction of cabin capacity adjustment is determined according to the positive and negative values of S1 and S2 (e.g., if S1 is positive, the cabin capacity of the forepeak cabin is reduced), and the optimal cabin capacity combination (V1_opt, V2_opt) is finally output.
[0074] This invention provides a process and method for optimizing the bending moment of the bow and stern peak holds of bulk carriers based on grid sampling of hold size.
[0075] The present invention has the following advantages:
[0076] 1. This invention can accurately capture the pattern of longitudinal bending moment change with cabin volume, thus greatly improving the control accuracy of longitudinal bending moment.
[0077] 2. This invention establishes a systematic sampling and optimization mechanism for the core parameter of cabin volume that affects the overall longitudinal bending moment, accurately analyzes the degree of influence of cabin volume changes on the overall longitudinal bending moment (i.e., sensitivity), and performs targeted optimization design based on the sensitivity results, thus realizing a systematic optimization mechanism.
[0078] 3. When optimizing the longitudinal bending moment, this invention can fully consider the floating state requirements of the ship and can simultaneously verify floating state parameters such as draft difference and stability height during the cabin adjustment process. This makes the optimized solution reduce the longitudinal bending moment and meet the floating state specifications for actual ship navigation, thus having strong engineering applicability.
[0079] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.
Claims
1. A method for optimizing the bending moment of a fore and aft peak hold arrangement of a bulk carrier, which is grid-sampled for the hatchway size, characterized in that, It comprises: Step 1, based on the ship cabin distribution and line type, a three-dimensional ship model containing the bow and stern peak cabin basic structure is constructed; Step 2, taking the bow and stern peak cabin capacity as the core parameter, a two-dimensional parameter grid is constructed; Step 3, screening key optimization conditions with significant influence on the total longitudinal bending moment; Step 4, for each node in the grid, the total longitudinal bending moment under the selected working condition is calculated respectively; Step 5, based on the bending moment calculation results of the grid nodes, the numerical difference method is used to calculate the sensitivity; Step 6, combined with the sensitivity analysis results and the ship floating state requirements, the optimization feasible region is determined.
2. A method of hogging moment optimization for a fore and aft peak hold arrangement of a bulk carrier with hold capacity gridded sampling as claimed in claim 1, characterized in that, In step 1, the model needs to clearly define the geometric boundary constraints of the bow and stern peak cabins, and integrate the total longitudinal bending moment calculation module.
3. A method of hogging moment optimization for a fore and aft peak hold arrangement of a bulk carrier with hold capacity gridded sampling as claimed in claim 2, characterized in that, In step 2, the first tip tank volume is set to a value range of [V1 min ,V1 max ], the tail tip tank volume is set to a value range of [V2 min ,V2 max ], and discretization processing is performed according to preset steps ΔV1 and ΔV2 to generate a grid node set {(V1 i ,V2 j )|i=1,2,...,n;j=1,2,...,m}, wherein n and m are respectively the number of nodes of the first tip tank volume grid and the tail tip tank volume grid.
4. The method of optimizing the bending moment of a fore and aft peak tank arrangement of a bulk carrier for a given size of a cargo hold grid as claimed in claim 3, wherein, The grid step is adjusted according to the optimization accuracy and calculation time requirements. The higher the accuracy requirement, the smaller the step.
5. The method of optimizing the bending moment of a fore and aft peak tank arrangement of a bulk carrier with hold size grid sampling of a cargo ship as claimed in claim 3, wherein, In step 3, the full load condition, ballast to port condition, extreme storm ballast condition, compartment loading condition, and strength condition required by the coordinated common standard are selected as the calculation conditions.
6. The method of optimizing the bending moment of a fore and aft peak tank arrangement of a bulk carrier with hold size grid sampling of a bow, as claimed in claim 5, wherein, In step 4, for each node in the grid, the cabin model of the bow and stern peak cabins is adjusted in the ship model, the total longitudinal bending moment calculation module is called, and the total longitudinal bending moment under the selected working condition is calculated.
7. A method of hogging moment optimization for a fore and aft peak hold arrangement of a bulk carrier with hold size gridding sampling as claimed in claim 6, characterized in that, During the calculation process, the ship floating state parameters and stability need to be recorded synchronously to ensure that the basic floating state and stability constraints are met.
8. The method of optimizing the bending moment of a fore and aft peak tank arrangement of a bulk carrier with hold size gridded sampling of claim 6, wherein, In step 5, the bow peak cabin capacity sensitivity S1 is defined as the ratio of the total longitudinal bending moment change ΔM to the bow peak cabin capacity change ΔV1, S1 = ΔM / ΔV1; the bow peak cabin capacity sensitivity S2 is defined as the ratio of the total longitudinal bending moment change ΔM to the stern peak cabin capacity change ΔV2, S2 = ΔM / ΔV2; By drawing the sensitivity, the distribution characteristics of S1 and S2 in different cabin capacity intervals are intuitively displayed, and the cabin capacity sensitive area with the most significant influence on the bending moment is determined.
9. The method of optimizing the bending moment of a fore and aft peak tank arrangement of a bulk carrier with hold size gridded sampling of claim 8, wherein, In step 6, in the sensitive area, the cabin capacity adjustment direction that reduces the total longitudinal bending moment is preferred; after bending moment optimization, the optimal cabin capacity combination is finally output.
10. The method of hogging moment optimization for a fore and aft peak hold arrangement of a bulk carrier with hold capacity gridding sampling as claimed in claim 9, wherein, The cabin capacity adjustment direction that reduces the total longitudinal bending moment includes: if S1 is positive, reduce the bow peak cabin capacity within the floating state allowed range; if S2 is negative, increase the stern peak cabin capacity.