A method for calculating the liquid level height of a tank in a liquid cargo ship stowage instrument

Abstract

The present invention discloses a method for calculating the liquid level height of a cabin in a liquid cargo ship stowage instrument, comprising the following steps: obtaining three-dimensional data of the liquid tank; calculating tank capacity parameters; and calculating the actual liquid level height of the cabin by a successive linearization method. The present invention obtains three-dimensional data of the liquid tank by equidistantly cutting the inner surface data of the liquid tank along the length of the ship. Based on the three-dimensional data of the liquid tank, the liquid level height is calculated when the volume, heel angle, and pitch angle of the liquid cargo are known. The following conclusions are drawn from the experiment: 1) It is feasible to determine the liquid level height of the liquid cargo using the three-dimensional data of the cabin and the heel and pitch angles of the ship, and the calculation accuracy is high; 2) The present invention has good real-time performance while ensuring the calculation accuracy, and generally requires 3 to 5 iterations to converge, which can better meet the calculation requirements of the righting arm curve in the liquid cargo ship stowage instrument.

Description

Technical Field

[0001] The invention relates to a method for calculating the liquid level height of a ship's cabin, in particular to a method for calculating the liquid level height of a cabin under arbitrary transverse and longitudinal inclinations of the ship in a liquid cargo ship stowage instrument. Background Art

[0002] Taking into account that the heel and trim of a liquid cargo ship will cause the equal volume free flow of liquid in a partially filled tank, which will cause changes in related parameters such as the center of gravity of the liquid cargo and the moment of inertia of the free liquid surface, when calculating the buoyancy and stability of a liquid cargo ship, it is necessary to redetermine the free liquid surface of the partially filled tank based on the current heel and trim of the ship, so as to calculate the parameters of the loaded liquid.

[0003] At present, the methods for re-determining the liquid level of the loading liquid mainly include measurement correction method and off-line interpolation method. Reference 1 corrects the measured liquid level height and interpolates the tank capacity curve to obtain the liquid cargo volume under the corresponding transverse and longitudinal inclinations; Reference 2 calculates the relationship curve between the inclined liquid surface position and volume under different transverse inclination angles, and then performs the interpolation calculation, and the real-time performance of the calculation is good; Reference 3 calculates the tilting moment generated by the movement of liquid under a certain load according to the shape of the liquid tank, thereby realizing the free liquid surface correction calculation under any load condition; Reference 4 analyzes the cause of the error in tank capacity calculation according to IMO specifications, and proposes an accurate free liquid surface calculation method based on three-dimensional NURBS expression; Reference 5 establishes a liquid tank mathematical model based on the measurement data of the total station, and calculates the liquid cargo volume under different floating states using the liquid level height of the sounding tube; Reference 6 calculates the liquid level height of each station when the sounding tube position, reading and ship trim are known, and obtains the tank capacity by integrating the tank capacity simulation curve; Reference 7 integrates the liquid surface area under different liquid level heights based on the liquid tank mathematical model to obtain the liquid cargo volume, and the calculation result is relatively accurate, but the influence of the ship's transverse and longitudinal inclination is not considered.

[0004] When the measurement plus correction method is used to calculate the free liquid surface of liquid cargo, the calculation accuracy mainly depends on the accuracy of the established liquid tank mathematical model and the accuracy of the measured liquid surface, which is easy to cause large errors in actual operation; by establishing a relationship curve between the inclined liquid surface position and the liquid cargo volume, the real-time performance of offline difference calculation is better, but the calculation error is large when there is a longitudinal tilt effect.

[0005] The references involved in the present invention are as follows:

[0006] [1] Ma Kun, Li Zuozhi, Yang Yang. “Research on real-time calculation method of intact stability of ships[J]”, Journal of Dalian University of Technology, 2007, 47(03): 383-386.

[0007] [2][2] Ma Kun, Chen Dezhi. “Corrected calculation method of free surface stability at large inclination angles[J]”, China Shipbuilding, 2005(01): 3-9.

[0008] [3] Ma Kun, Dong Xiaoxia, and Yang Fan. “Real-time calculation of ship free surface correction for stability curves[J]”, Chinese Journal of Ship Research, 2006, 1(01): 54-57+80.

[0009] [4] Lu Conghong, Lin Yan, Ji Zhuoshang, “Accurate free surface correction based on NURBS expression[J]”, China Shipbuilding, 2007, 48(01): 30-38.

[0010] [5] Xiang Yong, Hu Yong. “Measurement and correction of ship liquid cargo tank capacity”, Naval Architecture and Marine Engineering, 2011, 40(02): 40-44.

[0011] [6] Xiao Buqiao, “A simple and easy method for calculating tank capacity[J]”, China Ship Repair, 2001(03):34-36.

[0012] [7] Chen Binkang, Zhao Chengbi, “Precise calculation method of ship cargo tank volume”, Journal of Wuhan Water Transport Engineering Institute, 1994, 18(01): 26-33.

[0013] [8] Liu Chunlei, Yin Yong, Sun Xiaofeng, et al., “Calculation of ship geometric characteristics based on STL model[J]”, Journal of System Simulation, 2015, 27(10): 2264-2271.

[0014] [9] Zhao Xiaofei and Lin Yan, “Matrix method for solving ship floating problems[J]”, China Shipbuilding, 1985(03):57-66.

[0015]

[10] Liu Chunlei. Research and Implementation of Intelligent Loading Instrument for Bulk Carriers. Dalian: Dalian Maritime University, 2013.

[0016]

[11] Germanischer Lloyd S E.Rules for Classification and Construction[S].2013. Summary of the invention

[0017] In order to solve the above problems existing in the prior art, the present invention designs a method for calculating the liquid level height of the cabin in the liquid cargo ship stowage instrument to solve the problems of low calculation accuracy of the free liquid surface of the liquid cargo in the liquid cargo ship stowage instrument, poor real-time performance and difficulty in calculation under the influence of longitudinal inclination.

[0018] In order to achieve the above object, the technical solution of the present invention is as follows: A method for calculating the liquid level height of a tank in a liquid cargo ship stowage instrument comprises the following steps:

[0019] A. Obtaining three-dimensional data of the tank

[0020] The three-dimensional data of the inner surface of the tank is used as the data source for calculation. In order to conveniently describe the relative position of the liquid cargo in the tank, the reference coordinate system EX is introduced. 0 Y 0 Z 0 , this coordinate system is a left-hand rectangular coordinate system, where point E is the intersection of the mid-transverse section, mid-longitudinal section and base plane of the ship, EX 0 The axis is horizontal and points to the bow, which is positive. 0 The axis is vertically upward, EY 0 Axis perpendicular to EX 0 The axis is horizontal to the right and positive. Check the loading manual to get the coordinates of the cabin volume center point P, and use the projection point O of point P on the cabin base plane as the origin to establish the cabin rectangular coordinate system OXYZ, where the OXY plane coincides with the cabin base plane, and the OX axis is parallel to EX 0 The axis is positive when it points to the bow direction, the OZ axis is perpendicular to the OXY plane and points upward, and the OY axis is perpendicular to the OXZ plane and points to the right. All calculations are based on the cabin rectangular coordinate system.

[0021] The cabin is cut along the length of the ship at a fixed interval δ to obtain the tank line polygon at each cross section and obtain the three-dimensional data of the cabin inner surface. The interval δ is 0.10±0.01m.

[0022] B. Calculation of tank capacity parameters

[0023] Since the ship will inevitably produce heel and pitch during operation, the liquid in the tank will flow freely with the ship's heel and pitch to reach a state of equilibrium. When calculating the ship's floating state and stability, it is necessary to redetermine the liquid level to calculate the free surface moment of inertia of the cabin and make a free surface correction. Based on the three-dimensional data of the cabin interior surface, the successive linearization method is used to determine the liquid level in the tank when the ship's heel angle, pitch angle and liquid cargo volume are known, so that the cabin volume at the calculated liquid level is equal to the initial liquid cargo volume. During the rolling and pitching process of the ship, the total volume of the ship remains unchanged. The ship's heel angle θ and pitch angle φ are known, and the cabin liquid level h needs to be calculated:

[0024] The liquid cargo parameter equation is:

[0025] V 0 -V=0 (1)

[0026] Implicitly expressed as:

[0027] f(h)=0 (2)

[0028] Where V 0 is the initial liquid cargo volume of the tank, and V is the liquid cargo volume under given parameters θ, φ, and h.

[0029] C. Calculate the actual tank liquid level using the successive linearization method

[0030] The basic idea of ​​the successive linearization method is to use the difference between the calculated liquid cargo volume and the actual liquid cargo volume and the current liquid surface area to continuously correct the liquid surface height so that the calculated volume gradually approaches the actual volume until the final liquid surface height is determined. First, query the flat draft tank capacity table in the loading manual, and use the known liquid cargo volume to interpolate to obtain the liquid surface height in the tank when the ship is flat draft, and set the initial value of the liquid surface height h to this height. Given φ, θ, and h, the liquid cargo volume V under the liquid surface is obtained by integration, and V and V are used to calculate the liquid surface height. 0 The difference between the waterline area S and the current liquid level height is corrected by h to obtain the final result.

[0031] The linearization equation is obtained by successive linearization method as follows:

[0032] df(h k )(hh k )+f(h k )=V 0 k=0,1,2,… (3)

[0033] In the formula, h k is the liquid level height at the kth calculation, f(h) is the liquid cargo volume when the liquid level is h, df(h k ) is the value of f(h) at h k The partial derivative at . According to the principle of statics:

[0034]

[0035] Where S is the waterline area of ​​the compartment at the liquid level h.

[0036] In the kth calculation, formula (3) is written as follows:

[0037] S.dh k +f(h k )=V 0 (5)

[0038] The calculation parameters for the k+1th time are shown in the following formula:

[0039] h k+1 =h k +dh k (6)

[0040] The calculation process of the successive linearization method is as follows:

[0041] C1, let i = 1, give h the initial value of the first iteration h 1

[0042] C2. Calculate the liquid level h using the trapezoidal integration method1 The volume V 1 ,

[0043]

[0044] Where L is the length of the cabin, A 1 is the area of ​​the cross section at the cabin direction x.

[0045] C3. Determine whether the termination condition is met

[0046] f(h)=|V 0 -V 1 |<ε (8)

[0047] If it is satisfied, output the current liquid level h and end; if it is not satisfied, set i=2 and go to step C4.

[0048] C4. Perform the i-th iteration and calculate the new liquid level h i+1

[0049]

[0050] Where V i 、s i The liquid level is h i Liquid cargo volume and liquid surface area.

[0051] C5. Determine whether the termination condition is met:

[0052] f(h i )=|V 0 -V i |<ε (10)

[0053] If it is satisfied, output the current liquid level h and end; if it is not satisfied, set i=i+1 and go to step C4.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention obtains three-dimensional data of the liquid tank by performing equidistant cutting of the inner surface data of the liquid tank along the length direction. Based on the three-dimensional data of the liquid tank, the liquid level height is calculated when the liquid cargo volume, heel angle and pitch angle are known. The experiment draws the following conclusions:

[0056] 1) It is feasible to determine the liquid level of liquid cargo using the three-dimensional data of the cabin and the ship's heel angle, and the calculation accuracy is high;

[0057] 2) The present invention has good real-time performance while ensuring the calculation accuracy. Generally, 3 to 5 iterations are required to converge, which can better meet the calculation requirements of the righting arm curve in the liquid cargo ship stowage instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the change in liquid level under cabin heel and pitch.

[0059] Figure 2 It is a three-dimensional slice diagram of liquid cargo tank R1.01P.

[0060] Figure 3 It is a flow chart of the present invention.

[0061] Figure 4 Schematic diagram of the calculation cabin.

[0062] Figure 5 It is the comparison curve of the righting arm under DAM1.

[0063] Figure 6 It is the comparison curve of the righting arm under DAM2.

[0064] Figure 7 It is the comparison curve of the righting arm under DAM3. DETAILED DESCRIPTION

[0065] The present invention will be further described below in conjunction with the accompanying drawings.

[0066] The present invention takes the cargo hold and ballast tank of the liquid cargo ship "JIN ZHOU WAN" with a length of 138m, a width of 22.6m and a displacement of 19847.2t as an example, calculates and determines the liquid level height when the heel angle is 0°, 10°, 20° to 50° and the liquid cargo volume accounts for 10%, 50% and 90% of the total tank volume, and compares it with the NAPA calculated value. Since the cargo hold and ballast tank of this liquid cargo ship are symmetrical about the longitudinal section of the ship, this embodiment is based on Figure 3 The process shown in the figure calculates the cargo hold and ballast tank located on the right side of the longitudinal section of the ship (such as Figure 4 shown), Figure 1 The figure shows the change of liquid level after the heel and pitch of a cabin change. Figure 2 Shown is a 3D slice diagram of a cabin R1.01P.

[0067] NAPA software is an internationally renowned ship CAD software developed by NAPA of Finland. Germanischer Lloyd and Det Norske Veritas regard NAPA's calculation results as accurate values ​​and compare them with the calculation results of the loading instrument submitted for inspection to determine whether the loading instrument submitted for inspection meets the certification requirements.

[0068] On the VS2013 platform under the Windows 7 operating system, the successive linearization method calculation program was written using C++ language. 3When the calculated liquid level is compared with the NAPA calculation result, it is found that all three methods can obtain high calculation accuracy, but the time required to achieve the accuracy requirement is slightly different. The liquid level heights under different compartments with cargo volumes accounting for 10%, 50% and 90% of the full compartment volume and heel angles of 0°, 10° to 50° are calculated. Because the calculation generates a lot of data, in order to reduce the length, this embodiment only gives the comparison results of the calculation results under the successive linearization method with the NAPA calculation values, that is, the error of each calculation, see Tables 1 to 3. All the calculation results are statistically analyzed, and the statistical results of the average error, maximum error, average number of iterations, and maximum number of iterations for each calculation are shown in Table 4.

[0069] Table 1 Calculation results of the successive linearization method when the loading volume accounts for 10%

[0070]

[0071] Table 2 Calculation results of the successive linearization method when the loading volume accounts for 50%

[0072]

[0073]

[0074] Table 3 Calculation results of the successive linearization method when the loading volume accounts for 90%

[0075]

[0076] Table 4 Calculation results analysis

[0077]

[0078] The calculation results are analyzed and the maximum absolute error is 7.5 cm, which meets the classification society's error requirement of 50 cm. The maximum number of iterations is 4, and the convergence speed is fast.

[0079] Based on the research results of this invention, the Navigation Research Institute of Dalian Maritime University successfully completed the floating and stability calculation module in the liquid cargo ship stowage instrument, and applied it to the liquid cargo ship stowage instrument SMART LOAD jointly developed with the Shanghai Ship Design and Research Institute. At present, the stowage instrument has passed the certification of the six major international classification societies, CCS, ABS, DNV, NK, BV and LR, and has been successfully loaded on more than 100 ships.

[0080] The algorithm of the present invention and the NAPA loading instrument are used to calculate the righting arm curve of the liquid cargo ship JIN ZHOU WAN under partial damage conditions, and the calculation results of the two are compared. The ship loading state and damaged compartment under the selected damage conditions are shown in Table 5.

[0081] Table 5 Ship loading conditions and damaged compartments

[0082]

[0083] The calculation data of SMART LOAD and NAPA can be found in Figures 5 to 7 .

[0084] The error analysis of the calculation results is shown in Table 6.

[0085] Table 6 Error analysis

[0086] Tab 6 Error analysis

[0087]

[0088] Germanischer Lloyd's Register requires that the stability calculation error in the bulk carrier stowage instrument based on three-dimensional design data should meet 5 cm or 5%. The actual effect of the present invention meets the accuracy requirements of the classification society and achieves a very high accuracy.

[0089] The present invention is not limited to this embodiment, and any equivalent concepts or changes within the technical scope disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A method for calculating the liquid level height of a tank in a liquid cargo ship stowage instrument, characterized in that: The following steps are involved: A. Obtaining three-dimensional data of the tank The three-dimensional data of the inner surface of the liquid tank is used as the data source for calculation; in order to conveniently describe the relative position of the liquid cargo in the tank, the reference coordinate system EX0Y0Z0 is introduced. This coordinate system is a left-hand rectangular coordinate system, in which point E is the intersection of the mid-transverse section, mid-longitudinal section and base plane of the ship, the EX0 axis is horizontally pointing to the bow, the EZ0 axis is vertically upward, and the EY0 axis is perpendicular to the EX0 axis and horizontally to the right. The coordinates of point P, the center of the cabin volume, are obtained by consulting the loading manual, and the cabin rectangular coordinate system OXYZ is established with the projection point O of point P on the cabin base plane as the origin, in which the OXY plane coincides with the cabin base plane, the OX axis is parallel to the EX0 axis, pointing to the bow direction is positive, the OZ axis is perpendicular to the OXY plane and upward is positive, and the OY axis is perpendicular to the OXZ plane and right is positive. All calculations are based on the cabin rectangular coordinate system; The cabin is cut along the length of the ship at a fixed interval δ to obtain the tank line polygon at each cross section and obtain the three-dimensional data of the cabin interior surface; the interval δ is 0.10±0.01m; B. Calculation of tank capacity parameters Since the ship will inevitably produce heel and pitch during operation, the liquid in the tank will flow freely with the ship's heel and pitch to reach a balanced state. When calculating the ship's floating state and stability, it is necessary to re-determine the liquid level to calculate the inertia moment of the free liquid surface in the cabin and make a free liquid surface correction. Based on the three-dimensional data of the cabin interior surface, the successive linearization method is used to determine the liquid level in the tank when the ship's heel angle, trim angle and liquid cargo volume are known, so that the cabin volume under the calculated liquid level is equal to the initial liquid cargo volume. During the rolling and trimming process of the ship, the total volume of the ship remains unchanged. The ship's heel angle θ and trim angle φ are known, and the cabin liquid level h needs to be calculated: The liquid cargo parameter equation is: V0-V=0(1) Implicitly expressed as: f(h)=0(2) Where V0 is the initial liquid cargo volume of the tank, and V is the liquid cargo volume under given parameters of θ, φ, and h; C. Calculate the actual tank liquid level using the successive linearization method The basic idea of ​​the successive linearization method is to use the difference between the calculated liquid cargo volume and the actual liquid cargo volume and the current liquid surface area to continuously correct the liquid surface height, so that the calculated volume gradually approaches the actual volume until the final liquid surface height is determined; first, query the flat draft tank capacity table in the loading manual, and use the known liquid cargo volume to interpolate to obtain the liquid surface height in the tank when the ship is flat draft, and set the initial value of the liquid surface height h to this height; given φ, θ, and h, the liquid cargo volume V under the liquid surface is obtained by integration, and h is corrected by using the difference between V and V0 and the waterline area S under the current liquid surface height to obtain the final result; The linearization equation is obtained by successive linearization method as follows: df(h k )(h-h k )+f(h k )=V0 k=0,1,2,…(3) In the formula, h k is the liquid level height at the kth calculation, f(h k ) is the liquid level height h k Liquid cargo volume at time, df(h k ) is the value of f(h) at h k The partial derivative at ; According to the principle of statics: Where S is the waterline area of ​​the compartment at the liquid level h; In the kth calculation, formula (3) is written as follows: S·dh k +f(h k )=V0(5) The calculation parameters for the k+1th time are shown in the following formula: h k+1 =h k +dh k (6) The calculation process of the successive linearization method is as follows: C1, let i = 1, give h the initial value of the first iteration h1 C2. Use the trapezoidal integration method to calculate the volume V1 under the liquid level h1. Where L is the length of the cabin, A1 is the area of ​​the cross section at x in the cabin direction; C3. Determine whether the termination condition is met f(h)=|V0-V1|<ε(8) If satisfied, output the current liquid level h1 and end; if not satisfied, set i=2 and go to step C4; C4. Perform the i-th iteration and calculate the new liquid level h i In the formula, h i-1 is the liquid level height of the i-1th iteration, V i-1 、s i-1 The liquid level is h i-1 The volume and surface area of ​​the liquid cargo; C5. Calculate the liquid level as h i Liquid cargo volume V i , determine whether the termination condition is met: f(h i )=|V0-V i |<ε(10) If satisfied, output the current liquid level h i , end; if not satisfied, set i=i+1 and go to step C4.

Images