CN116127806A - Method and device for evaluating critical strain capacity of bent pipe combined section - Google Patents

Abstract

The invention relates to the technical field of pipeline stress analysis, in particular to an evaluation method and device for critical strain capacity of a bent pipe combined section. Fitting a Ramberg-Osgood constitutive model according to the size and material parameters of a pipeline to obtain a stress-strain curve of the pipeline; constructing a finite element model of the pipeline according to the stress-strain curve, and applying a combined load; obtaining a load-displacement curve of the pipeline, and determining the load of the bent pipe section reaching a critical buckling state; extracting axial direction strain of the strain stabilizing sections of the first section of straight pipe and the second section of straight pipe in a critical buckling state; an average of the strain in the axial direction of the strain plateau is calculated as the critical strain of the pipe. By the embodiment, the critical strain capacity of the bending pipe combined section under the action of complex load is calculated when the bending pipe combined section is in local buckling failure, and the reliability of the structural stability assessment technology of the on-site bending pipe combined section is improved.

Description

Method and device for evaluating critical strain capacity of bent pipe combined section

Technical Field

The invention relates to the technical field of pipeline stress analysis, in particular to an evaluation method and device for critical strain capacity of a bent pipe combined section.

Background

Pipeline transportation is one of the main transportation modes of petroleum and natural gas, and in order to meet the high requirements of different areas on hydrocarbon, pipelines are inevitably laid under complex geological conditions. In the prior art, the stress state of the pipeline can be calculated according to the stress distribution of the axial load and the internal pressure, but because of complex topography conditions, the trend and the direction of the pipeline are required to be changed through the bent pipe so as to achieve the conveying purpose, the pipeline is affected by the bending curvature of the bent pipe, the local stress distribution at the bent pipe is uneven under the internal pressure effect, and when the combined load acts near the bent pipe, the pipeline instability risk is greatly increased.

The method for evaluating the critical strain capacity of the bent pipe combined section is needed at present, so that the critical strain capacity of the bent pipe combined section when the local buckling failure of the bent pipe combined section is calculated under the action of complex load, and the reliability of the structural stability evaluation technology of the on-site bent pipe combined section is improved.

Disclosure of Invention

In order to solve the problem that the critical strain capacity of the bent pipe combined section cannot be determined due to the fact that the local stress state of the bent pipe cannot be calculated in the prior art, the embodiment of the invention provides an evaluation method and an evaluation device for the critical strain capacity of the bent pipe combined section, which realize safety evaluation of a bent pipe when the bent pipe section is subjected to combined load, improve the reliability of a structural stability evaluation technology of the on-site bent pipe combined section, and solve the problem that the critical strain capacity of the bent pipe combined section cannot be evaluated when the local bending failure of the bent pipe combined section is caused under the complex load.

In order to solve the technical problems, the specific technical scheme is as follows:

in one aspect, embodiments herein provide a method of evaluating critical strain capacity of a composite section of an elbow, comprising,

according to the size and material parameters of the pipeline, a stress-strain curve of the pipeline is obtained through Ramberg-Osgood constitutive model fitting, wherein the pipeline comprises three pipe sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

constructing a finite element model of the pipeline according to the stress-strain curve, and applying a combined load;

obtaining a load-displacement curve of the pipeline according to the applied combined load, and determining the load of the bent pipe section reaching a critical buckling state;

extracting axial direction strain of the strain stabilizing sections of the first section of straight pipe and the second section of straight pipe in a critical buckling state;

an average of the strain in the axial direction of the strain plateau is calculated as the critical strain of the pipe.

Further as one embodiment of the present description, obtaining the conduit dimensions and material parameters further includes,

pipe diameter, wall thickness, steel grade, elastic modulus E, poisson's ratio v, yield strength sigma _y And ultimate tensile strength sigma _u 。

Further as one embodiment of the present specification, the Ramberg-Osgood constitutive model further includes a Ramberg-Osgood constitutive model expressed as

Wherein epsilon is the true strain; sigma is the true stress; e is the elastic modulus; sigma (sigma) _y Is the yield strength; alpha is the material hardening coefficient and n is the material hardening index.

Further as one embodiment of the present specification, constructing a finite element model from the stress-strain curve further comprises,

selecting the unit type of the pipe section and adding material parameters;

grid division is carried out on three pipe sections of the pipeline;

setting the boundary conditions of the grid and applying a combined load on the pipe.

Further as one embodiment of the present description, the combined loading and applying a combined load further includes,

the combined load comprises pipeline internal pressure, axial load generated by eccentric axial compression displacement and bending moment load; the application of the combined load includes applying the internal pipeline pressure to the inner pipeline surface, and applying the axial load generated by the eccentric axial compression displacement and the bending moment load to the end surface of the pipeline.

Further as one embodiment of the present description, the in-line pressure further includes,

by P/P _y Representation, where P _y To induce an internal pressure at which the hoop stress reaches the material yield stress, the calculation formula is as follows:

wherein t is the wall thickness of the pipeline, D is the outer diameter of the pipeline, and sigma _y Is the yield strength.

Further as one embodiment of the present description, the eccentric axial compression displacement generating the axial load and bending moment load further includes,

the axial load and bending moment load expressions are as follows:

wherein u is ₀ Representing uniformly distributed load coefficients; u (u) ₁ Is an alternating load coefficient; i is the ith node of the end face of the straight pipe, and the value interval is [1, n ]]The method comprises the steps of carrying out a first treatment on the surface of the n is the number of end face loading points; a is the load eccentricity coefficient.

Further as one embodiment of the present specification, the critical buckling state further includes a buckling state when the load is at a maximum in the load-displacement curve, and the load is characterized by increasing and decreasing as the displacement increases.

Further as one embodiment of the present description, the strain plateau further comprises,

the strain stabilizing section is a region with gentle strain change of the first section of straight pipe and the second section of straight pipe; the axial direction strain is the axial strain of the strain plateau and the axial direction is- (a x 180), where a is the eccentric load coefficient.

Further as one embodiment of the present description, the critical strain is the average strain of the strain plateau further includes,

the average strain calculation formula for the strain plateau is as follows:

wherein ε _i Axial compressive strain for the ith node of the strain stabilizing section of the pipeline; i is a node in the axial direction, and the value range is [1, n]The method comprises the steps of carrying out a first treatment on the surface of the n is the total number of nodes of the strain stabilizing segment.

On the other hand, the embodiment also provides an evaluation device for critical strain capacity of the bent pipe combined section, which comprises,

the stress-strain curve acquisition unit is used for obtaining a stress-strain curve of the pipeline through Ramberg-Osgood constitutive model fitting according to the size and material parameters of the pipeline, wherein the pipeline comprises three pipeline sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

establishing a finite element model unit, which is used for constructing a finite element model of the pipeline according to the stress-strain curve and applying a combined load;

determining a critical buckling unit, which is used for obtaining a load-displacement curve of the pipeline according to the applied combined load and determining the load of the bent pipe section reaching the critical buckling state;

the critical strain extraction unit is used for extracting the axial directional strain of the strain stabilizing section of the first section of straight pipe and the second section of straight pipe in a critical buckling state;

and a critical strain calculating unit for calculating an average value of the strain in the axial direction of the strain plateau as the critical strain of the pipe.

In another aspect, embodiments herein also provide a computer device comprising a memory, a processor, and a computer program stored on the memory.

In another aspect, embodiments herein also provide a computer storage medium having a computer program stored thereon. By utilizing the embodiment, the critical strain capacity of the bending pipe combined section under the action of complex load is calculated when the bending pipe combined section is in local buckling failure, and the reliability of the structural stability evaluation technology of the on-site bending pipe combined section is improved. According to the size of the pipeline, the material parameters and the curvature radius of the elbow, a Ramberg-Osgood constitutive model is used for fitting to obtain a stress-strain curve of the material, the problem of uneven stress distribution of an elbow region is considered, the local buckling fold form of the on-site pipeline is reduced, a finite element model of an elbow combination section is constructed, a combination load is applied, an axial strain of the pipeline in a critical buckling state is obtained by a method for constructing the finite element model of the elbow combination section, and the average strain of a strain stable section is used as the critical strain of the pipeline section, so that the critical strain capacity of the pipeline section is obtained, and an accurate basis can be provided for evaluating the structural stability of the elbow combination section in a pipeline system. The method solves the problem that in the prior art, when the bending pipe combination section fails in local buckling under the action of complex load, the critical strain capacity is evaluated.

Drawings

In order to more clearly illustrate the embodiments herein or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments herein and that other drawings may be obtained according to these drawings without inventive effort to a person skilled in the art.

FIG. 1 is a schematic diagram of an embodiment of a method for evaluating critical strain capacity of a combined section of an elbow according to the present disclosure;

FIG. 2 is a flow chart illustrating a method for evaluating critical strain capacity of a combined section of an elbow in accordance with an embodiment of the present disclosure;

FIG. 3 shows a stress-strain curve of a material;

FIG. 4 illustrates a process for constructing a finite element model from stress-strain curves;

the finite element model of the bent pipe combined section shown in fig. 5;

FIG. 6 shows a load-displacement curve;

FIG. 7 shows an evaluation device for critical strain capacity of a combined section of an elbow;

fig. 8 is a schematic structural diagram of a computer device according to an embodiment of the present disclosure.

[ reference numerals description ]:

101. a terminal;

102. a server;

501. a finite element model of the pipeline;

502. a first section of straight pipe;

503. a second section of straight pipe;

504. bending the pipe;

701. a stress-strain curve acquisition unit;

702. establishing a finite element model unit;

703. determining a critical buckling unit;

704. extracting a critical strain unit;

705. calculating a critical strain unit;

802. a computer device;

804. a processing device;

806. storing the resource;

808. a driving mechanism;

810. an input/output module;

812. an input device;

814. an output device;

816. a presentation device;

818. a graphical user interface;

820. a network interface;

822. a communication link;

824. a communication bus.

Detailed Description

The following description of the embodiments of the present disclosure will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the disclosure. All other embodiments, based on the embodiments herein, which a person of ordinary skill in the art would obtain without undue burden, are within the scope of protection herein.

It should be noted that the terms "first," "second," and the like in the description and claims herein and in the foregoing figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments described herein may be capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or device that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed or inherent to such process, method, article, or device.

Fig. 1 is a schematic diagram of an evaluation system for critical strain capacity of a bent pipe combined section according to an embodiment of the present invention, which may include a terminal 101 and a server 102, where a communication connection is established between the terminal 101 and the server 102, so as to enable data interaction. The terminal 101 may input the pipeline size and pipeline parameters to the server 102, obtain a stress-strain curve of the pipeline by fitting the constitutive model, construct a finite element model, apply a combined load to the finite element model by the terminal 101, analyze the stress-strain state of the finite element model by the server 102, obtain critical strain of the pipeline, and send the verification result to the terminal 101 for display or storage.

In this embodiment of the present disclosure, the server 102 may be an independent physical server, or may be a server cluster or a distributed system formed by a plurality of physical servers, or may be a cloud server that provides cloud services, a cloud database, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, and basic cloud computing services such as big data and an artificial intelligence platform.

In an alternative embodiment, terminal 101 may include, but is not limited to, a smart phone, a desktop computer, a tablet computer, a notebook computer, a digital assistant, and the like type of electronic device. Alternatively, the operating system running on the electronic device may include, but is not limited to, an android system, an IOS system, linux, windows, and the like.

It should be noted that, fig. 1 is only one application environment provided by the present disclosure, and in practical application, other application environments may also be included, which is not limited in the embodiment of the present invention.

In addition, it should be noted that, in practical application, the application environment shown in fig. 1 may be applied to a petroleum and natural gas pipeline transportation scenario, an on-site pipeline stability evaluation scenario, etc., which is not limited in this specification.

In order to solve the problems existing in the prior art. The embodiment of the invention provides an evaluation method and device for critical strain capacity of a bent pipe combined section. The method has the advantages that when the bent pipe section is subjected to combined load, safety evaluation is carried out on the bent pipe, the reliability of the structural stability evaluation technology of the on-site bent pipe combined section is improved, and the critical strain capacity when the local buckling failure of the bent pipe combined section cannot be evaluated under the complex load is solved. Fig. 2 is a schematic flow chart of an evaluation method for critical strain capacity of a bent pipe combined section according to an embodiment of the present disclosure, in which a process for calculating critical strain capacity of a pipe is described. The order of steps recited in the embodiments is merely one way of performing the order of steps and does not represent a unique order of execution. In actual computing or system execution, the processes may be performed sequentially or in parallel as shown in the embodiments or figures. As shown in fig. 2 in particular, the method may be performed by the server 102, and may include:

step 201: according to the size and material parameters of the pipeline, a stress-strain curve of the pipeline is obtained through Ramberg-Osgood constitutive model fitting, wherein the pipeline comprises three pipe sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

step 202: constructing a finite element model of the pipeline according to the stress-strain curve, and applying a combined load;

step 203: obtaining a load-displacement curve of the pipeline according to the applied combined load, and determining the load of the bent pipe section reaching a critical buckling state;

step 204: extracting axial direction strain of the strain stabilizing sections of the first section of straight pipe and the second section of straight pipe in a critical buckling state;

step 205: an average of the strain in the axial direction of the strain plateau is calculated as the critical strain of the pipe.

By the method of the embodiment, the evaluation of critical strain capacity when the bending pipe combined section is locally bent and fails under the action of complex load is realized, wherein the bending pipe combined section is generally constructed by three parts and comprises two straight pipes and one bent pipe, and the connection sequence is two straight pipes and one bent pipe; in order to improve the accuracy of the pipeline stress analysis, the pipeline size and material parameters are collected, including the pipeline diameter, the wall thickness, the steel grade, the elastic modulus, the poisson ratio, the yield strength and the ultimate tensile strength, and the pipeline diameter can be 660mm-1016mm, the wall thickness can be 7.1mm-9.7mm, and the steel grade is divided into X60, X65 and X80; according to the obtained data parameters, calculating by utilizing a Ramberg-Osgood constitutive model, and fitting to obtain a stress-strain curve of the pipeline, wherein the Ramberg-Osgood constitutive model expression is as follows:

wherein epsilon is the true strain; sigma is the true stress; e is the elastic modulus; sigma (sigma) _y Is the yield strength; alpha is the material hardening coefficient and n is the material hardening index.

In the embodiment, firstly, the relation between the stress and the strain of the pipeline is obtained, and the stress-strain curve of the pipeline is drawn by recording the deformation of the pipeline under different axial loads, bending loads and internal pressure loads, wherein the abscissa of the stress-strain curve is the strain of the pipeline, and the ordinate is the stress of the pipeline corresponding to the different strains; the shape of the curve reflects various deformation processes such as buckling fold, axial deformation, bending deformation and the like of the pipeline under the action of external force; since the steel used in the pipeline has elastic deformability, if the steel is loaded continuously after exceeding the buckling strength, local buckling failure can be caused, and the pipeline can be plastically deformed until being destroyed, and the process is represented by a stress strain curve.

In embodiments herein, the types of pipelines may include petroleum transportation pipelines, natural gas transportation pipelines, and embodiments herein are not limited. The types of external forces may include, but are not limited to, earthquake, landslide, ground subsidence, permafrost thawing, or soil liquefaction. In the embodiment, the pipeline can be a transportation pipeline which is already laid and put into use, or the pipeline which is not yet laid is subjected to simulation analysis, so that in order to improve the structural stability evaluation efficiency, the axial strain of the pipeline in the critical buckling state is obtained by using the finite element method in the embodiment, and then the critical strain capacity of the pipeline section is obtained, so that an accurate basis can be provided for evaluating the structural stability of the bent pipe combined section in the pipeline system.

Illustratively, according to one embodiment herein, pipe dimensions and material parameters are obtained, wherein the pipe dimensions comprise a pipe diameter of 660mm and a pipe wall thickness of 7.1mm; the material parameters comprise steel grade X65, elastic modulus 208GPa, poisson's ratio alpha as the hardening coefficient of the material, and taking 0.3%; n is a material hardening index, 22.83 is taken, yield strength and tensile strength are 497.25MPa and 578.83MPa respectively, and the calculation is carried out according to a Ramberg-Osgood constitutive model expression:

the stress-strain curve of the material is fitted as shown in figure 3.

According to one embodiment herein, to calculate the strain capacity of a bent-tube assembly under complex loading, a finite element model of the pipeline needs to be constructed for finite element analysis; as shown in fig. 4, constructing a finite element model from the stress-strain curve further includes,

step 401: selecting the unit type of the pipe section and adding material parameters;

step 402: grid division is carried out on three pipe sections of the pipeline;

step 403: setting the boundary conditions of the grid and applying a combined load on the pipe.

In embodiments herein, establishing a finite element model requires approximate regularity of pipe dimensions, material parameters, stress and strain; establishing a geometric model according to the pipeline size, wherein the representation form of the geometric model in a computer comprises a solid model, a curved surface model and a wire frame model, and when the geometric model is established, the shape and the size of the pipeline are required to be necessarily simplified, changed and processed according to the specific characteristics of the pipeline so as to adapt to the characteristics of finite element analysis; determining the type of the adopted unit, wherein the unit selection needs to be comprehensively considered according to the type, shape characteristics, stress and strain curves of the pipeline structure; and the cell type further includes a set of internal characteristic data required for calculation to define the material parameters, modulus of elasticity, yield strength, cross-sectional shape and size of the pipe; in step 402, grid division is the core work of building a finite element model, and node and unit data are defined by a grid assembly generated by grid division; on the basis of the geometric model, automatically dividing grids by a computer through certain manual control; after the grid model is subjected to necessary inspection and corresponding processing, step 403 is performed to set the boundary condition of the grid, wherein the boundary condition reflects the complex load born by the pipeline and is the expression form of the actual stress state on the finite element model; two links are generally needed for establishing boundary conditions, namely, the actual stress state is quantized firstly, namely, the stress state is expressed as a definable mathematical form on a geometric model, such as determining a distribution rule of surface pressure and internal pressure distribution of a pipeline, test data are needed, and then the quantized stress state is defined as boundary conditions on the model, such as axial movement or lateral constraint, compression load, bending load and internal pressure; after reasonable grid forms are divided and correct boundary conditions are defined, a complete finite element model is built, and then a corresponding analysis program can be called to calculate the model, and then calculation results are displayed, processed and studied.

According to one embodiment herein, the elbow composite section finite element model requires unit type selection, meshing, boundary condition setting, and load application of the pipe section; the finite element model is constructed by three parts, and comprises two sections of straight pipes and a section of bent pipe, wherein the bent pipe is connected behind the first section of straight pipe and the second section of straight pipe, the length of the first section of straight pipe is 0.35m, the length of the second section of straight pipe is 0.7m, and the angle of the bent pipe section is 30 degrees; the wall thickness of the first section of straight pipe is required to exceed the wall thickness of the second section of straight pipe and the wall thickness of the bent pipe, and the exceeding range is 0.5mm-1mm; establishing a geometric model according to the set pipeline size and the material parameters obtained in the step 201; because the dimensional characteristics, shape and size of the geometric model are not required to be completely the same as those of the original structure, the specific characteristics of the pipeline, such as shape and size, can be necessarily simplified, changed and processed; performing unit selection of a finite element model of the pipeline according to the type, shape characteristics, stress-strain curve, elastic modulus and yield strength of the structure of the pipeline; because the pipeline is of a thin-wall structure, the pipeline body can adopt a 4-node shell unit with three layers of thickness, the end face of the pipeline is used as a loading face, and a secondary unit is selected to connect the center point of the end face with the end face; dividing grids by adopting an automatic or semi-automatic grid dividing method, wherein the grid size of the first straight pipe section and the third bent pipe section is 25 multiplied by 43mm, and the grid size of the second straight pipe section is 15 multiplied by 43mm; the grid model is subjected to necessary inspection, and boundary conditions are defined after corresponding processing; in the boundary condition, the section of the first part of straight pipe connected with the second part of straight pipe needs to be provided with annular rigid constraint so as to ensure that the section of the pipe section is not deformed, and the bent pipe constrains the translation and rotation of the pipe section.

In the embodiment, after a complete finite element model is constructed, calculating the model by calling a corresponding analysis program, applying a combined load, then obtaining a load-displacement curve of a pipeline, calculating, and displaying, processing and researching a calculation result; the combined load comprises pipeline internal pressure, axial load and bending moment load, wherein the pipeline internal pressure can be pressure from the inside of a pipeline for transporting hydrocarbon such as petroleum and natural gas, and the axial load and the bending moment load can be external stretching or bending force applied to the pipeline under complex geological conditions due to foundation movement caused by earthquake, landslide, permafrost thawing and the like; the combined load is loaded separately by two times according to the constructed finite element model,

the first step is to apply the internal pressure of the pipe by selecting the inner surface of the pipe;

and secondly, selecting the end face of the pipeline to load axial load and bending moment load.

In embodiments herein, the internal pressure of the pipe is through P/P _y Representation, where P _y The internal pressure when the hoop stress reaches the material yield stress is caused, and the calculation formula is shown as follows:

wherein t is the wall thickness of the pipeline, and D is the outer diameter of the pipeline. The internal pressure of the pipeline is within the range of 0-0.8P _y 。

The axial load and bending moment load u are generated by the application of an eccentric axial compression displacement, the load expression is as follows:

wherein u is ₀ Representing uniformly distributed load coefficients; u (u) ₁ Is an alternating load coefficient; i is the ith node of the end face of the straight pipe, and the value interval is [1, n ]]The method comprises the steps of carrying out a first treatment on the surface of the n is the number of end face loading points; a is the load eccentricity coefficient;

wherein the load coefficient u is uniformly distributed ₀ Alternating load coefficient u ₁ The number n of the end face loading points and the load eccentric coefficient a have different value ranges according to different steel grades selected by the pipeline；

The uniformly distributed load coefficient u ₀ When the steel grade is X60, u ₀ The value interval is [0,40 ]]The method comprises the steps of carrying out a first treatment on the surface of the When the steel grade is X65, u ₀ The value interval is [0,50 ]]The method comprises the steps of carrying out a first treatment on the surface of the When the steel grade is X80, u ₀ The value interval is [0,60 ]]。

The alternating load coefficient u ₁ When the steel grade is X60, u ₁ The value interval is [0,60 ]]The method comprises the steps of carrying out a first treatment on the surface of the When the steel grade is X65, u ₁ The value interval is [0,70 ]]The method comprises the steps of carrying out a first treatment on the surface of the When the steel grade is X80, u ₁ The value interval is [0,80 ]]。

The number of the end face loading points n is 45-50 when the steel grade is X60; when the steel grade is X65, the value of n is 48-53; when the steel grade is X80, the value of n is 50-55.

The load eccentric coefficient a is the value of a when the steel grade is X60

When the steel grade is X65, the value of a is

When the steel grade is X80, a takes the value of +.>

And obtaining the value range of each coefficient in the load expression according to the value range and the material parameters obtained in the step 201, and calculating the load born by the pipeline.

Illustratively, according to one embodiment herein, as shown in FIG. 5, a finite element model of a composite section of an elbow is created where 501 is a finite element model of a pipe, 660mm in diameter, 7.1mm in pipe wall thickness, and 26.4m in radius of curvature of the elbow. The steel grade is X65, the elastic modulus is 208GPa, the Poisson ratio is 0.3, and the yield strength and the tensile strength are 497.25MPa and 578.83MPa respectively; wherein the length of the first straight pipe 502 is 0.35m, the curvature radius of the bent pipe 504 is 26.4m, the grid size of the first straight pipe and the bent pipe is 25 multiplied by 43mm, the length of the second straight pipe 503 is 0.7m, and the grid size is 15 multiplied by 43mm; the internal pressure is set to be 6.3MPa, the steel grade is set to be X65, and the load is set to be 6.3MPaThe expression is according to the above value range, the cloth load coefficient u ₀ The value interval is [0,50 ]]The method comprises the steps of carrying out a first treatment on the surface of the Alternating load coefficient u ₁ The value interval is [0,70 ]]The method comprises the steps of carrying out a first treatment on the surface of the The number of the end face loading points is 48-53; the value of the load eccentric coefficient a is

The obtained load expression is +.>

In the embodiment, a load-displacement curve is drawn according to the change of the load and displacement of the loading surface of the finite element model, and the load-displacement curve is used for determining the critical moment when the pipeline is in buckling failure; as shown in fig. 6, the load shows a tendency of increasing and then decreasing with increasing displacement, and is the critical buckling state of the pipeline when the load reaches the maximum point; when the load born by the bent pipe combined section reaches a maximum load point c, the displacement born by the pipeline is the maximum axial load and bending moment load born by the pipeline, and the displacement is a limit load state when the pipeline is bent; when the load reaches a peak value, the pipeline material is hardened due to the continuous development of buckling, the load is reduced due to the fact that the displacement is increased continuously, and meanwhile, the buckling deformation of the pipeline section can be observed at the stage.

Extracting axial direction strain of the strain stabilizing sections of the first section of straight pipe and the second section of straight pipe in a critical buckling state; the circumferential direction of the axis is- (a x 180), wherein a is the eccentric load coefficient; the strain stationary section is a central position which is far away from the pipe section and generates local buckling, and the strain change is relatively gentle; extracting axial strain along the axial direction of the first section of straight pipe and the second section of straight pipe in the critical buckling state of the pipeline, so that strain tends to be gentle when the distance from the buckling area is 0.21D, and the length of the pipeline in the gentle section is 0.3D; thus when the pipe reaches a critical buckling state, node strain from the strain plateau at a buckling center distance of 0.21D occurs; taking the buckling center as a starting point, taking the axial direction of the pipeline as a positive direction, and selecting nodes from the starting point with the distance of 0.21D, wherein one node is selected every 10 mm; the length of the selected pipe section is 0.3D; the region is 0.15D-0.25D from the local buckling center position, and the length of the strain plateau is 0.3D-0.5D; the average strain of the whole strain plateau region needs to be calculated as follows:

wherein ε _i Axial compressive strain for the ith node of the strain stabilizing section of the pipeline; i is a node in the axial direction, and the value range is [1, n]The method comprises the steps of carrying out a first treatment on the surface of the n is the total number of nodes of the strain stabilizing section; when critical buckling occurs to the bent pipe section, the average strain of the whole strain stable area is equal to the critical strain capacity; at a distance of 0.21D from the buckling center, the average strain value of the pipeline strain plateau reaches epsilon _c When the pipeline reaches critical buckling state, once epsilon is exceeded _c Buckling failure occurs.

Illustratively, according to one embodiment herein, as shown in table 1, the axial strain of the tube segment in the strain plateau region in the critical buckling state is selected starting from the buckling center as a starting point and along the axial direction of the tube as a positive direction, wherein the distance from the starting point is 0.21D, one node is selected every 10mm, 10 nodes are selected in total, and the length of the selected tube segment is 0.3D; the axial compressive strain of the pipe was measured at each node, and the average axial compressive strain was calculated as the critical buckling state of the pipe using a formula from the 11 axial compressive strains obtained by the measurement.

Node	Axial compressive Strain/%
		1	0.587
2	0.540
		3	0.525
4	0.517
		5	0.512
6	0.507
		7	0.504
8	0.504
		9	0.511
10	0.529
		11	0.560

TABLE 1 axial Strain of tube sections in regions of strain plateau in critical buckling conditions

According to the formula

The axial compressive strain at 11 nodes obtained in the table was summed and calculatedAverage value, obtained result was 0.527%, and critical strain value was 0.527%; the final calculated data of 0.527% is the ultimate strain at which the critical buckling of the pipeline occurs, equal to the critical strain capacity; when the average strain value of 0.3D for the pipe strain plateau reaches 0.527% at a distance of 0.21D from the buckling center, the pipe reaches a critical buckling state, and buckling failure occurs once it exceeds 0.527%.

The embodiment also provides an evaluation device for critical strain capacity of the bent pipe combined section, as shown in fig. 7, comprising,

the stress-strain curve obtaining unit 701 is configured to obtain a stress-strain curve of a pipeline by fitting a Ramberg-Osgood constitutive model according to a pipeline size and a material parameter, where the pipeline includes three pipe sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

a finite element model unit 702 is established for constructing a finite element model of the pipeline according to the stress-strain curve and applying a combined load;

a critical buckling unit 703, configured to obtain a load-displacement curve of the pipe according to the applied combined load, and determine a load of the bent pipe section reaching a critical buckling state;

an extraction critical strain unit 704 for extracting the axial direction strain of the strain plateau of the first and second straight pipes in a critical buckling state

A critical strain calculation unit 705 for calculating an average value of the axial direction strain of the strain plateau as the critical strain of the pipe. Since the principle of the device for solving the problem is similar to that of the method, the implementation of the device can be referred to the implementation of the method, and the repetition is omitted.

Fig. 8 is a schematic structural diagram of a computer device according to an embodiment of the present invention, where the apparatus may be the computer device in this embodiment, and perform the method described above. The computer device 802 may include one or more processing devices 804, such as one or more Central Processing Units (CPUs), each of which may implement one or more hardware threads. The computer device 802 may also include any storage resources 806 for storing any kind of information, such as code, settings, data, etc. For example, and without limitation, storage resources 806 may include any one or more of the following combinations: any type of RAM, any type of ROM, flash memory devices, hard disks, optical disks, etc. More generally, any storage resource may store information using any technology. Further, any storage resource may provide volatile or non-volatile retention of information. Further, any storage resources may represent fixed or removable components of computer device 802. In one case, the computer device 802 may perform any of the operations of the associated instructions when the processing device 804 executes the associated instructions stored in any storage resource or combination of storage resources. The computer device 802 also includes one or more drive mechanisms 808, such as a hard disk drive mechanism, an optical disk drive mechanism, and the like, for interacting with any storage resources.

The computer device 802 may also include an input/output module 810 (I/O) for receiving various inputs (via an input device 812) and for providing various outputs (via an output device 814). One particular output mechanism may include a presentation device 816 and an associated Graphical User Interface (GUI) 818. In other embodiments, input/output module 810 (I/O), input device 812, and output device 814 may not be included, but merely as a computer device in a network. The computer device 802 may also include one or more network interfaces 820 for exchanging data with other devices via one or more communication links 822. One or more communications buses 824 couple the above-described components together.

The communication link 822 may be implemented in any manner, such as, for example, through a local area network, a wide area network (e.g., the internet), a point-to-point connection, etc., or any combination thereof. Communication link 822 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

Corresponding to the method in fig. 2 to 6, embodiments herein also provide a computer readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the method described above.

Embodiments herein also provide a computer readable instruction wherein the program therein causes the processor to perform the method as shown in fig. 2 to 6 when the processor executes the instruction.

It should be understood that, in the various embodiments herein, the sequence number of each process described above does not mean the sequence of execution, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments herein.

It should also be understood that in embodiments herein, the term "and/or" is merely one relationship that describes an associated object, meaning that three relationships may exist. For example, a and/or B may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

Those of ordinary skill in the art will appreciate that the elements and algorithm steps described in connection with the embodiments disclosed herein may be embodied in electronic hardware, in computer software, or in a combination of the two, and that the elements and steps of the examples have been generally described in terms of function in the foregoing description to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

It will be clear to those skilled in the art that, for convenience and brevity of description, specific working procedures of the above-described systems, apparatuses and units may refer to corresponding procedures in the foregoing method embodiments, and are not repeated herein.

In the several embodiments provided herein, it should be understood that the disclosed systems, devices, and methods may be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative, e.g., the division of the units is merely a logical function division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. In addition, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices, or elements, or may be an electrical, mechanical, or other form of connection.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the elements may be selected according to actual needs to achieve the objectives of the embodiments herein.

In addition, each functional unit in the embodiments herein may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.

The integrated units, if implemented in the form of software functional units and sold or used as stand-alone products, may be stored in a computer readable storage medium. Based on such understanding, the technical solutions herein are essentially or portions contributing to the prior art, or all or portions of the technical solutions may be embodied in the form of a software product stored in a storage medium, including several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the embodiments herein. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

Specific examples are set forth herein to illustrate the principles and embodiments herein and are merely illustrative of the methods herein and their core ideas; also, as will be apparent to those of ordinary skill in the art in light of the teachings herein, many variations are possible in the specific embodiments and in the scope of use, and nothing in this specification should be construed as a limitation on the invention.

Claims (10)

1. A method for evaluating critical strain capacity of a bent pipe combined section is characterized by comprising the following steps of,

according to the size and material parameters of the pipeline, a stress-strain curve of the pipeline is obtained through Ramberg-Osgood constitutive model fitting, wherein the pipeline comprises three pipe sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

constructing a finite element model of the pipeline according to the stress-strain curve, and applying a combined load;

obtaining a load-displacement curve of the pipeline according to the applied combined load, and determining the load of the bent pipe section reaching a critical buckling state;

extracting axial direction strain of the strain stabilizing sections of the first section of straight pipe and the second section of straight pipe in a critical buckling state;

an average of the strain in the axial direction of the strain plateau is calculated as the critical strain of the pipe.

2. The method of claim 1, wherein the pipe dimensions comprise pipe diameter, wall thickness; the material parameters comprise steel grade, elastic modulus E, poisson ratio v and yield strength sigma _y And ultimate tensile strength sigma _u 。

3. The method of claim 1, wherein the Ramberg-Osgood constitutive model expression is as follows:

wherein epsilon is the true strain; sigma is the true stress; e is the elastic modulus; sigma (sigma) _y Is the yield strength; alpha is the material hardening coefficient and n is the material hardening index.

4. The method of claim 1, wherein constructing a finite element model from the stress-strain curve further comprises,

selecting the unit type of the pipe section and adding material parameters;

grid division is carried out on three pipe sections of the pipeline;

setting the boundary conditions of the grid and applying a combined load on the pipe.

5. The method of claim 1, wherein the combined load comprises a pipeline internal pressure, an axial load resulting from an eccentric axial compression displacement, and a bending moment load; the application of the combined load includes applying the internal pipeline pressure to the inner pipeline surface, and applying the axial load generated by the eccentric axial compression displacement and the bending moment load to the end surface of the pipeline.

6. The method of claim 5, wherein the internal pressure of the pipe is increased by P/P _y Representation, where P _y To induce an internal pressure at which the hoop stress reaches the material yield stress, the calculation formula is as follows:

wherein t is the wall thickness of the pipeline, D is the outer diameter of the pipeline, and sigma _y Is the yield strength.

7. The method of claim 5, wherein the eccentric axial compressive displacement generates the axial load and bending moment load as follows:

wherein u is ₀ Representing uniformly distributed load coefficients; u (u) ₁ Is an alternating load coefficient; i is the ith node of the end face of the straight pipe, and the value interval is [1, n ]]The method comprises the steps of carrying out a first treatment on the surface of the n is the number of end face loading points; a is the load eccentricity coefficient.

8. The method of claim 1, wherein the critical buckling state is a buckling state in which a load is at a maximum in a load-displacement curve, the load being characterized by an increase followed by a decrease as displacement increases.

9. The method of claim 1, wherein the critical strain is an average strain of the strain plateau and is calculated as follows:

wherein ε _i Axial compressive strain for the ith node of the strain stabilizing section of the pipeline; i is a node in the axial direction, and the value range is [1, n]The method comprises the steps of carrying out a first treatment on the surface of the n is the total number of nodes of the strain stabilizing segment.

10. An evaluation device for critical strain capacity of a bent pipe combined section is characterized by comprising,

the stress-strain curve acquisition unit is used for obtaining a stress-strain curve of the pipeline through Ramberg-Osgood constitutive model fitting according to the size and material parameters of the pipeline, wherein the pipeline comprises three pipeline sections including a first section of straight pipe, a bent pipe and a second section of straight pipe;

establishing a finite element model unit, which is used for constructing a finite element model of the pipeline according to the stress-strain curve and applying a combined load;

determining a critical buckling unit, which is used for obtaining a load-displacement curve of the pipeline according to the applied combined load and determining the load of the bent pipe section reaching the critical buckling state;

the critical strain extraction unit is used for extracting the axial directional strain of the strain stabilizing section of the first section of straight pipe and the second section of straight pipe in a critical buckling state;

and a critical strain calculating unit for calculating an average value of the strain in the axial direction of the strain plateau as the critical strain of the pipe.

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