KR20150021249A - Method for longitudinal strength analysis of ships subjected to lateral pressure - Google Patents

Abstract

The present invention relates to a method for analyzing the longitudinal strength of a vessel with water pressure and, more specifically, to a method for analyzing the final longitudinal strength of the vessel applying water pressure (hydrostatic pressure) which is applied when the vessel stays a port and water pressure (hydrostatic pressure + hydrodynamic pressure) generated by a wave load or the like. The method for analyzing the longitudinal strength of the vessel with the water pressure calculates the hydrostatic pressure in a full load condition and a ballast condition and the hydrodynamic pressure of the wave load based on the sea gauge of the full load condition and the ballast condition; calculates total water pressure distribution by performing linear summation based on the hydrostatic pressure and the hydrodynamic pressure; analyzes the final longitudinal strength by considering initial imperfection after determining the optimal analyzing method and an analysis order for analyzing the final longitudinal strength of the vessel according to the total water pressure distribution and applying the water pressure and vertical bending moment to the vessel; and deducting a diagram by setting a horizontal axis as a curvature and setting a vertical axis as the relation of the final bending moment.

Description

[0001] The present invention relates to a method of longitudinal strength analysis of a ship,

The present invention relates to a longitudinal strength analysis method of a ship in consideration of hydraulic pressure, and more particularly, to a method of analyzing a longitudinal strength of a ship in consideration of hydraulic pressure (hydrostatic pressure and hydrostatic pressure) And the final longitudinal strength analysis method of the ship.

Ship and offshore structures should be designed and built safely for specific design life.

For example, the design life of a general ship is 20 years, the design life of a ship to which a common structural rule is applied is 25 years for oil tankers and bulk carriers, and 30 years for LNG carriers.

Ship and offshore structures are inevitably and continuously subjected to hydrostatic loads during the above design life.

This water pressure affects the strength of ships and offshore structures and affects ultimate longitudinal strength or ultimate hull girder strength, mainly for ship-type structures.

However, there are not many studies to clarify the effect of such water pressure on the final strength of the ship, and there is not much information about the method and the result.

In addition, in the common structural rule, the influence of hydraulic pressure is not taken into account in the final longitudinal strength analysis, and the analysis through the nonlinear finite element method is not carried out due to computer calculation time and difficulty in modeling .

Therefore, it is necessary to analyze the final longitudinal strength behavior of ship structures subjected to hydraulic pressure through nonlinear finite element method.

Korean Patent No. 10-2013-0082550 (July 22, 2013)

The present invention has been devised in view of the above-mentioned need, and it is an object of the present invention to provide a method for evaluating the ultimate strength performance of a ship-like structure exposed to a hydraulic load during a design life, The purpose of this study is to provide a longitudinal strength analysis method of a ship considering the hydraulic pressure which can clearly analyze the influence of the hydraulic pressure through the method.

According to an aspect of the present invention, there is provided a method of analyzing a longitudinal strength of a ship, the method comprising: (a) calculating drafts of a ballast condition and a full condition from the main dimensions and specifications of the ship;

(b) calculating the hydrostatic pressure due to the hydrostatic pressure and the wave load in the full state and the ballast state based on the draft;

(c) calculating a total water pressure distribution by linear summation of the hydrostatic pressure and the hydrostatic pressure;

(d) calculating an initial defect of the ship;

(e) determining an optimal analysis method and an analysis sequence for analyzing the final longitudinal strength of the ship according to the total water pressure distribution; And

(f) The hydrostatic pressure and the vertical bending moment are applied to the ship in accordance with the determined analytical procedure, and the final longitudinal strength is analyzed in consideration of the calculated initial defects by the determined optimal analysis method. The abscissa is the curvature, and the ordinate is the relation of the final bending moment The method comprising: .

In addition, the hydrostatic pressure and hydrostatic pressure of each part of the ship in the step (b) are characterized by being a guide relating to the water pressure information provided by the International Classification Society (IACS).

Also, in the step (d), the initial defects are initial deflections.

The calculation of the initial deflection is also applied to the plate and the stiffener.

의 수학식의 의해 산정되는 것을 특징으로 한다. Also, the initial deflection

, And the following formula is calculated.

Where a is the spacing of transverse frames, b is the spacing of longitudinal stiffeners, h _w is the height of the stiffener, w _opl is the plate initial deflection, w _ow is the initial deflection of the stiffener web, w _oc is the column initial deflection of the stiffener, _os is the sideways shear foundation load of the stiffener.

The method of determining the analysis order in the step (e) is as follows. First, the water pressure is firstly applied to the ship, the preceding analysis is performed, and then the second vertical bending moment is applied to the ship subjected to the water pressure- And a method of performing an analysis by applying a water pressure and a vertical bending moment (hogging moment or sagging moment) to a ship at the same time.

In the step (f), the model of the ship may be a wire model, a cargo hold model, a 2-cargo hold model, a 1-cargo hold model, a 2-bay sliced hull section model, bay sliced) hull section model to analyze the final longitudinal strength.

The final longitudinal strength analysis in the step (f) is characterized by using a nonlinear finite element method (NLFEM).

In the final longitudinal strength analysis in the step (f), the planes at both ends of the ship are rotated in a planar state and rotate together as they rotate around the neutral axis due to the vertical bending moment applied to the plane .

In addition, the nodes at both ends of the ship generate a node to apply a vertical bending moment to a node located on a neutral axis of the ship through Multi-Point Constraint (MPC), and perform analysis.

In the step (f), the final longitudinal strength analysis is performed by simultaneously applying a water pressure to the ship and a vertical bending moment of two kinds (hogging moment or sagging moment).

And (g) evaluating whether or not the performance of the final longitudinal strength analyzed by the step (f) is safe as compared with the external force to be applied.

According to the means for solving the above-mentioned problems, an analytical method relating to the final longitudinal strength evaluation of a ship-like structure to which a hydraulic pressure is applied is developed, and the influence of the hydraulic pressure on the structure is accurately analyzed, You can provide / present a diagram to perform the evaluation.

In addition, the final longitudinal strength performance evaluation method for hydrostatic pressure vessels is applicable to various ship types (ships other than oil tankers and bulk carriers) for which the hydraulic pressure guideline is not clear, and can be applied to various ship type structures.

FIG. 1 is a flow chart according to an analysis method of longitudinal strength of a ship in consideration of water pressure in accordance with an embodiment of the present invention.
Fig. 2 is an enlarged view showing a section and an initial deflection of a double hull oil tanker to which a common structural rule is applied.
Fig. 3 is a view showing a range for carrying out the final longitudinal strength analysis of the ship-like structure.
FIG. 4 is a view showing analysis boundary conditions of various models among the analysis ranges mentioned in FIG. 3. FIG.
FIG. 5 is a graph comparing the analysis results of different analysis methods using the results of the final longitudinal strength test and the nonlinear finite element method, the large finite element method, the idealized structural element method, and other design formula methods.
FIG. 6 is a graph showing curvature-to-neutral axis change of a structure summarized by the analysis methods shown in FIG.
7 is a graph showing the hydrostatic pressure distribution in the full state obtained by the embodiment of FIG.
8 is a graph showing the dynamic pressure distribution at full load obtained by the embodiment of FIG.
9 is a graph showing a linear distribution of hydrostatic pressure and hydrostatic pressure in a full state obtained by the embodiment of FIG.
10 is a graph showing the hydrostatic pressure distribution during the ballast condition obtained by the embodiment of FIG.
11 is a graph showing the hydrodynamic pressure distribution in the ballast state obtained by the embodiment of FIG.
12 is a graph showing a distribution obtained by linearly summing hydrostatic pressure and hydrostatic pressure in the ballast state obtained by the embodiment of FIG.
FIG. 13 is a graph showing the final longitudinal strength analysis result in the ballast state obtained by the embodiment of FIG. 1; FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

It is to be noted that the same components of the drawings are denoted by the same reference numerals and symbols as possible even if they are shown in different drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Also, when a part is referred to as "including " an element, it does not exclude other elements unless specifically stated otherwise.

FIG. 1 is a flow chart according to an analysis method of longitudinal strength of a ship in consideration of water pressure in accordance with an embodiment of the present invention.

The following explains the example of a Suez Max-class double hull oil tanker with common structural rules, which can be applied to other ships.

As shown in FIG. 1, in the first step (S10), the main dimensions and other specifications of a ship to be analyzed by using a computer are grasped and an odd number is calculated to calculate a hydraulic pressure applied to the ship.

Here, the draft is the vertical distance from the water surface to the lowest part of the water-immersed vessel when the ship is floating.

At this time, the draft and ballast condition (full load condition) and ballast condition (ballast condition, loading and unloading of the ballast water and maintaining the stability of the ship) Is to be calculated accurately.

In the second step S20, based on the draft information calculated in the first step S10, the hydrostatic pressure is calculated in two cases, that is, in the full state and the ballast state.

In the third step S30, similar to the second step S20, the hydrostatic pressure is calculated for two cases and is calculated based on the guideline of the common structure rule.

In the fourth step S40, the total hydrostatic pressure is calculated by linearly summing the hydrostatic pressure and the hydrostatic pressure calculated in the second step S20 and the third step S30.

In the fifth step S50, the initial defects of the selected ship-like structure, that is, the initial deflection and the welding residual stress, are calculated.

Here, the welding residual stress is ignored in the case of the longitudinal strength analysis in the common structure rule, and the initial deflection is expressed by Equation (1) described later.

In the sixth step S60, the analysis range of the selected ship-like structure is calculated.

In the seventh step (S70), various methods are analyzed and the analysis order is determined in order to calculate an optimal method for final longitudinal strength analysis.

In the eighth step S80, final strength analysis is performed under hogging and sagging loads in consideration of initial defects, and the relationship is expressed as a relationship between the curvature (transverse axis) and the longitudinal strength (longitudinal axis).

In the ninth step (S90), the safety factor is calculated and evaluated by comparing the structural strength performance (final longitudinal strength performance) with the external force applied to the structure.

<Examples>

In the present embodiment, a Suexmax class double hull oil tanker with a hydraulic pressure is selected as a target vessel, and the characteristics of the final longitudinal strength of the ship considering the influence of hydraulic pressure are analyzed using a computer.

First, in the first step (S10), the main dimensions and other specifications of the Suez Max-class double hull oil tanker are grasped and the odd number is calculated to estimate the hydraulic pressure applied to the ship.

Table 1 below shows the main dimensions of the ship structure.

As shown in Table 1, the main dimensions include weight, length between perpendiculars, scantling length, width, length, odd number, and square block coefficient.

Table 2 below shows other specifications of the ship structure.

Other specifications include hull cross-sectional area, moment of inertia, section modulus of deck (deck) and bottom, and neutral axis position as shown in Table 2.

In the second step S20, based on the draft information calculated in the first step S10 (the odd number shown in Table 1), the static sea pressure is calculated in two cases, that is, the full state and the ballast state .

The draft at full load is 17 m and the draft at ballast is 7.7 m.

When the hydrostatic pressure in the full state is applied, it is calculated as shown in Fig. 7, and when the hydrostatic pressure in the ballast state is applied, as shown in Fig.

In the third step S30, based on the draft information calculated in the first step S10 (the odd number shown in Table 1), the dynamic sea pressure is calculated in two cases, namely, the full state and the ballast state .

At this time, the draft at the full condition is 17 m and the draft at the ballast condition is 7.7 m.

When the hydrostatic pressure in full condition is applied, it is calculated as shown in Fig. 8, and when hydrostatic pressure in the ballast condition is applied, as shown in Fig.

The load component information of each part of the ship to which the hydrostatic pressure or hydrostatic pressure is applied in the second step (S20) and the third step (S30) is related to the hydraulic pressure information provided by the International Association of Classification Society (IACS) Based on the guidelines.

In the fourth step (S40), the total pressure distribution applied in a linear summation of hydrostatic pressure and hydrostatic pressure is calculated and detailed.

The results of linear summation and detailing in the full state are expressed as shown in FIG. 9, and the linear sum and detail in the ballast state can be represented as FIG.

In the fifth step (S50), the initial defects of the Suez Max-class double hull oil tanker are calculated.

In this case, the initial residual stress caused by the initial deflection and welding is considered, and the welding residual stress is neglected in the case of the longitudinal strength analysis in the common structure rule. Therefore, only the influence of the initial deflection is considered in this embodiment.

In the case of the initial residual stresses due to welding, it is generally considered to reduce the yield strength of the material by 15%. In the analysis of the final longitudinal strength of the ship, it is required to comply with the International Society of Classification Societies (IACS) It is not considered in the guidelines.

The initial deflection consists of plate deflection, web deflection of the stiffener, column type deflection and sideways deflection, which is expressed as Equation (1).

Where a is the spacing of the transverse frame, b is the longitudinal spacing of the reinforcing material, h _w is a reinforcement height, w _opl will plate the initial deflection, w _ow the reinforcing web initial deflection, w _oc is the column type initial deflection, w _os is a reinforcing material of reinforcing material The side-by-side second is the foundation load.

FIG. 2 shows a Suez-Max class double-hull oil tanker considering the influence of the initial deflection considered in the fifth step (S50). The deck portion is enlarged to show more clearly the effect of initial deflection.

The fifth step (S50) is for the purpose of making the structure of the actual ship in the later analysis of the ship.

In the sixth step S60, an operation of calculating a main analysis range of the selected ship structure is performed.

The range to be applied for the final longitudinal strength analysis of ship-type structures can be distinguished by the six models shown in FIG.

4A is a view showing a cargo hold model, FIG. 4C is a 2-cargo hold model, FIG. 4D is a 1-cargo hold model and FIG. 4E is a 2-bay sliced hull section model And FIG. 4F shows a 1 bay sliced hull section model.

In this embodiment, an analysis is performed by applying a 1 bay sliced hull section model as shown in FIG. 4f to reduce computer analysis cost (analysis efficiency) and time.

Here, a bay means a section sliced by a plurality of frames partitioning one cargo hold.

In the seventh step (S70), the optimal method for the final longitudinal strength analysis is selected and the analysis order is determined.

The final longitudinal strength analysis of FIG. 5 and the neutral axis of the ship structure shown in FIG. 6 are also compared and analyzed.

Based on the experimental results (Test result by Dow), nonlinear finite element method (NLFEM, in this embodiment, using ANSYS simulation code), large finite element method (ISFEM, , The idealized structural unit method (ISUM), the CSR method in this embodiment), the modified Paik-Mansour formula method, and the simple bean theory method (using the ALPS / HULL simulation code) ) To find the most efficient interpretation method.

In this embodiment, the analysis is carried out through the nonlinear finite element method (NFLEM), which provides the finest solution.

As a method of determining the analytical order, there is a method of performing a preliminary analysis by applying hydraulic pressure first to the first structure, performing an analysis by applying a second vertical bending moment to the structure deformed by hydraulic pressure through a geometric update method , And second, applying the hydraulic and vertical bending moments at the same time.

In this embodiment, hydraulic pressure and two kinds of vertical bending moments (hogging moment or sagging moment) are simultaneously applied to the ship structure to perform analysis.

Accordingly, in step S80, hydraulic pressure and two kinds of vertical bending moments (hogging moment sagging moment) are applied to the ship structure at the same time, and the hogging and sagging loads are applied, (NFLEM). The result of the analysis is derived from the relationship between the curvature (transverse axis) and the final longitudinal strength (longitudinal axis).

As shown in FIG. 3, in the analysis of the final longitudinal strength, planes at both ends are rotated about the neutral axis (NA) due to the vertical bending moment applied to the plane, And rotate together.

In addition, the nodes at both ends generate a node to apply the vertical bending moment to a node located on the neutral axis of the structure through Multi-Point Constraint (MPC) and perform analysis.

As a result, the final longitudinal strength analysis results in the ballast state as shown in FIG. 13 can be obtained.

The multi-point constraint technique is a numerical technique that is used to simulate a finite element analysis of a problem where the behavior of an object is constrained to other objects that are fixed or moving around.

Finally, in the ninth step (S90), it is evaluated whether or not the final longitudinal strength performance of the Suez-Marx class double hull oil tanker carried out considering the influence of hydraulic pressure is safe as compared with the external force applied.

The external force applied is calculated as the sum of the bending moments (Ms) and the wave induced bending moments (Mt) in the still water as shown in Table 3 below, and is expressed in hogging and sagging.

As a result, the safety factors shown in Tables 4 and 5 can be obtained.

Table 4 shows the final longitudinal strength and the degree of safety according to the existence of hydraulic external force obtained by nonlinear finite element method (NFLEM) under full load condition.

Here, the value of () in the hydraulic external column indicates the safety factor as the final longitudinal strength ratio in the design external force, and the value of <> indicates the fluctuation factor of the final longitudinal strength in the simple bending state.

Table 5 is a table showing the final strength and safety according to the presence or absence of hydraulic external force obtained by the nonlinear finite element method (NFLEM) in the ballast state.

Here, the value of () in the hydraulic external column indicates the safety factor as the final longitudinal strength ratio in the design external force, and the value of <> indicates the fluctuation factor of the final longitudinal strength in the simple bending state.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

Claims (12)

(a) calculating the draft and ballast condition drafts from the ship's main dimensions and specifications;
(b) calculating the hydrostatic pressure due to the hydrostatic pressure and the wave load in the full state and the ballast state based on the draft;
(c) calculating a total water pressure distribution by linear summation of the hydrostatic pressure and the hydrostatic pressure;
(d) calculating an initial defect of the ship;
(e) determining an optimal analysis method and an analysis sequence for analyzing the final longitudinal strength of the ship according to the total water pressure distribution; And
(f) The hydrostatic pressure and the vertical bending moment are applied to the ship in accordance with the determined analytical procedure, and the final longitudinal strength is analyzed in consideration of the calculated initial defects by the determined optimal analysis method. The abscissa is the curvature, and the ordinate is the relation of the final bending moment The method comprising: Analysis of Longitudinal Strength of Ship Considering Water Pressure. The method according to claim 1,
Wherein the hydrostatic pressure and hydrostatic pressure of each part of the ship in the step (b) are guidelines related to the hydraulic pressure information provided by the International Classification Society (IACS). The method according to claim 1,
Wherein the initial defects in the step (d) are initial deflections. The method of claim 3,
Wherein said initial deflection is calculated for plates and stiffeners. 5. The method of claim 4,
The initial deflection is given by the following equation

Of the longitudinal strength of the ship in consideration of the hydraulic pressure.
Where a is the spacing of transverse frames, b is the spacing of longitudinal stiffeners, h _w is the height of the stiffener, w _opl is the plate initial deflection, w _ow is the initial deflection of the stiffener web, w _oc is the column initial deflection of the stiffener, _os is the sideways shear foundation load of the stiffener. The method according to claim 1,
In the step (e), the analytical procedure is determined by applying a hydraulic pressure to the ship first, performing a preliminary analysis, and then applying a second vertical bending moment to the ship subjected to the deformation due to hydraulic pressure through the geometric update method And a method of performing the analysis by applying the hydraulic pressure and the vertical bending moment (hogging moment or sagging moment) to the ship at the same time, which is a method of analyzing the longitudinal strength of the ship in consideration of hydraulic pressure. The method according to claim 1,
In the step (f), the model of the ship may be a wire model, a cargo hold model, a 2-cargo hold model, a 1-cargo hold model, a 2-bay sliced hull section model or a 1-bay sliced ) The longitudinal strength is analyzed by applying any one of the cross-sectional models of the ship. The method according to claim 1,
The final longitudinal strength analysis in the step (f) is performed by using an onlinear finite element method (NLFEM). The method according to claim 1,
In the analysis of the final longitudinal strength in the step (f), the planes at both ends of the ship are maintained in a planar state as they rotate around the neutral axis due to the vertical bending moment applied to the plane, and the water pressure Analysis of Longitudinal Strength of Ship Considered. 10. The method of claim 9,
Wherein the nodes at both ends of the ship generate a node to which a vertical bending moment is to be applied to a node located on a neutral axis of a ship through a multi-point constraint (MPC) technique and perform an analysis. Analysis of Longitudinal Strength of. The method according to claim 1,
Wherein the final longitudinal strength analysis is performed by simultaneously applying a hydraulic pressure to the ship and a vertical bending moment of two kinds (hogging moment or sagging moment) at the step (f). The method according to claim 1,
(g) evaluating whether or not the performance of the final longitudinal strength analyzed by the step (f) is safe as compared with the external force applied.

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