CN114896836A - Submarine cable anchor falling impact test method based on anchor falling-submarine cable-soil model - Google Patents
Submarine cable anchor falling impact test method based on anchor falling-submarine cable-soil model Download PDFInfo
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Abstract
The submarine cable anchor falling impact test method based on the anchor falling-submarine cable-soil model is used for constructing the anchor falling-submarine cable-soil model and simulating the anchor falling to impact submarine cables in soil; establishing a stress-strain relation model of the submarine cable based on the nonlinear material attribute of the submarine cable; establishing a molar coulomb model of soil; setting an analysis step length and starting a finite element software power display part; considering the interaction of anchor falling, submarine cable and soil in the model and setting contact conditions; applying an initial speed to anchor falling and setting a boundary condition; constructing a finite element grid model of the submarine cable, and locally and gradually refining the grid of the soil region at the anchor falling impact position; and (3) importing the model into finite element software, combining the set condition parameters to obtain a numerical analysis model of the submarine cable, and solving the model to obtain the sinking depth of the submarine cable at the impact position and the sinking depth of the submarine cable in the soil. The method can reduce the simulation error of the anchor drop impact submarine cable and improve the authenticity of the simulation of the anchor drop impact submarine cable.
Description
Technical Field
The invention relates to the technical field of submarine cable anchor damage assessment, in particular to a submarine cable anchor falling impact test method based on an anchor falling-submarine cable-soil model.
Background
With the rapid development of large-scale and high-speed ships, the number of ships is increasing, so that the traffic density of water areas and the loading capacity of dangerous goods are also increasing. Along with the rapid development of shipping industry in China, fishery is rapidly developed, and meanwhile, with frequent operation of fishing boats, the out-of-order work of operation boats happens occasionally, and the submarine cable pipeline is damaged by external force, so that power transmission and information transmission are seriously threatened. In addition, the submarine cable is impacted by ocean currents, so that the pipeline of the submarine cable is not deep enough or is exposed and suspended, and the probability of damage accidents caused by anchoring of the submarine cable is increased. The external force damage caused by the falling anchor impacting the submarine cable seriously threatens the safe operation of the submarine cable. Therefore, an effective defense technical means must be established, so that the submarine cable is in a controlled state in real time, the pipeline information and state are mastered in time, the corresponding treatment is effectively carried out aiming at the occurrence situation of anchor damage, and the damage caused by the collision of the falling anchor to the submarine cable is reduced.
The damage experiment of the submarine cable is difficult to realize due to anchor dropping impact, and the damage condition of the submarine cable under different conditions is evaluated by a finite element simulation method. In the prior art, a finite element model with a submarine cable-anchor falling part as a main body is basically constructed in submarine cable anchor damage simulation, soil conditions need to be considered for more reasonably simulating real conditions, anchor damage research can be carried out by changing environmental parameters, embedding depth and other conditions of soil, damage conditions of the submarine cable impacted by the anchor falling can be more comprehensively simulated, and then prejudgment is carried out through research results. However, the method is still based on finite element simulation, and the simulation of related parameters cannot be completely similar to real data.
Disclosure of Invention
The invention provides a submarine cable anchor falling impact test method based on an anchor falling-submarine cable-soil model, which combines soil parameters on the basis of conventional anchor falling-submarine cable finite element simulation and can change soil environment parameters to consider the anchor damage condition of a submarine cable. The method can reduce the simulation error of the anchor drop impact submarine cable and improve the authenticity of the simulation of the anchor drop impact submarine cable.
The technical scheme adopted by the invention is as follows:
the submarine cable anchor falling impact test method based on the anchor falling-submarine cable-soil model comprises the following steps:
the method comprises the following steps: constructing a falling anchor-submarine cable-soil model, and simulating the falling anchor to impact a submarine cable in soil;
step two: establishing a stress-strain relation model of the submarine cable based on the nonlinear material attribute of the submarine cable; establishing a molar coulomb model of the soil, and equating the falling anchor to a rigid body;
step three: setting analysis step length and starting a finite element software power display part;
step four: considering the interaction of anchor falling, submarine cable and soil in the model, and setting contact conditions;
step five: applying an initial speed to anchor falling, and setting a boundary condition;
step six: constructing a finite element grid model of the submarine cable, and locally and gradually refining the grid of the soil region at the anchor falling impact position;
step seven: and (4) importing the models in the first step and the second step into finite element software, combining the condition parameters set in the third step and the fifth step to obtain a numerical analysis model of the submarine cable, and solving the model to obtain the sinking depth of the submarine cable at the impact position and the sinking depth of the submarine cable in the soil.
In the first step, a 35kV three-core composite submarine cable is selected as a research object, a submarine cable structure model is built by utilizing SolidWorks, and clockwise spiral in a three-core conductor and anticlockwise spiral outside a galvanized steel armored steel wire are truly simulated; the submarine cable is complex in structure, and the shielding layer, the water blocking tape and other parts with lower mechanical strength are omitted, so that a three-dimensional submarine cable geometric model is established; then establishing a soil and anchor model; and (4) taking the actual engineering condition into consideration, embedding the submarine cable into the soil to form a falling anchor-submarine cable-soil model, and simulating the falling anchor to impact the submarine cable in the soil.
In the first step, specific parameters of the three-core composite submarine cable are determined, and models of a copper conductor, an insulating layer, a lead sheath, a filling layer, an optical unit, optical unit inner and outer steel wires, an optical unit sheath, an armor layer and an outer sheath are established, wherein the specific process comprises the following steps:
s1.1: firstly, determining the outer diameters of a conductor, an insulating layer and a lead sheath, then determining optical units, inner and outer steel wires of the optical units and the outer diameters of the optical unit sheaths to meet the requirement that three-core conductor parts are 120-degree symmetrical, respectively positioning the two optical units at the middle positions of two adjacent conductor parts, taking only one optical unit for simplifying calculation, drawing a plain sketch on SolidWorks, stretching a boss of one conductor part, carrying out array processing on the part to ensure that a three-phase conductor is 120 degrees, then stretching the optical unit parts, and finally bending and twisting the conductor parts and the optical units;
s1.3: and (3) reconstructing a filling part: determining the outer diameter of a lead sheath and the outer diameter of an optical unit outer sheath, constructing conductor parts and optical unit torsion according to the previous operation, confirming the filling outer diameter on the basis, stretching the conductor parts and the optical unit torsion into a cylinder, and finally performing module subtraction combination to obtain a filling module;
3) then, an armor part is constructed, and the number of armor steel wires on the outer layer of the three-core composite submarine cable is calculated according to the number of wound steel wires and the pitch to obtain:
in the above formula: r is the radius of the cylinder in the armor layer, unit: mm; r is the radius of the armor wire, unit: mm; and n is the number of the armored steel balls.
Drawing a single armor steel wire layer plane sketch according to the armor steel wire radius obtained by the formula, stretching to the same height, then carrying out array treatment to ensure that the armor steel wires are tangentially arranged to be round and stretched, and finally carrying out anticlockwise spiral treatment on the armor steel wires, wherein the spiral angle is
Wherein the helix angle and the winding angle α satisfy the following relationship:
4) and finally, constructing an outer sheath part, making a plan sketch after confirming the outer diameter of the outer sheath, stretching the outer sheath to the same height, and finally forming an assembly body by the parts to obtain the three-core composite submarine cable geometric model.
In the first step, the soil model is a cuboid module, the anchor falling model is replaced by an object with the same bottom surface shape, the object is simplified in a bullet shape, the submarine cable geometric model is embedded into the soil model, the submarine cable geometric model is buried by a certain depth h, and the anchor falling is opposite to the middle of the submarine cable and tangent to the surface of the soil model.
In the second step, the submarine cable has a complex structure, shows obvious nonlinear material properties, and does not satisfy the linear relationship between the stress and the strain. When the material is in an elastic stage, good elastic properties are shown, and the stress-strain relationship of the submarine cable meets Hooke's law:
σ＝Eε；
wherein: e (E ═ tan α) is the elastic modulus, σ denotes stress, and ∈ denotes strain.
When the deformation of the load-unloading material can be completely recovered, when the material enters a yielding stage, the material begins to lose the deformation resistance and reaches a yielding state; after the yield stage, the material is in a strengthening stage, and the material recovers the deformation resistance; when the stress exceeds the strength limit, the material breaks and completely fails.
The soil adopts a molar coulomb model, and a friction angle, an expansion angle and a cohesive force yield stress are specified.
Classical moore's law
c is the yield stress of the cohesive force,
is the angle of friction and τ is the shear strength
The falling anchor is regarded as a rigid body, and the elastic modulus is larger.
In the third step, the step length is set, the time length, namely the total time of the impact process, is generally in the ms level, the power display part of the finite element software ABAQUS is started, because the specific action time is not known, the time can be set to be increased conservatively, the impact time length is judged by observing the energy, stress and speed curves in the calculation process, and then the proper time length is adjusted. And then creating a field output variable, setting required parameters such as stress, strain, displacement and the like, finally creating a process output variable, and setting energy parameters of the anchor.
In the fourth step, before the contact condition is set, in order to save the operation time, a set is created for all soil surfaces, because each layer of submarine cable has a complex structure and the surfaces are not continuous, the submarine cable is set to be universal contact, the contact type is automatically identified through finite element software ABAQUS, and the method comprises the steps of setting a friction formula of tangential behavior as a penalty function, defining a friction coefficient, and setting pressure interference of normal behavior as hard contact; setting the falling anchor as a rigid body and endowing the gravity center with the falling anchor; and finally, placing the whole submarine cable in the soil.
The fifth step is as follows:
the initial speed of falling the anchor is considered at first, the anchor sinks in the water, when the sea water depth is enough, the sinking speed of the anchor reaches the constant after falling for a period of time, and is the sinking limit speed, the gravity, the drainage volume and the flow resistance of the anchor at the moment meet the energy conservation, and the stress balance equation of the anchor at the moment is as follows:
the anchor with mass m freely falls in the seawater, the contact with the surface of the seabed is large speed, the initial speed of the anchor is considered, and the simplified calculation is as follows:
the initial energy of anchor falling has additional hydrodynamic energy besides kinetic energy, and the actual initial impact energy is as follows:
m a ＝ρ water (I) C a V
Wherein: m represents the mass of the anchor, in units: kg;
m a denotes the added mass, in units: kg;
v represents the volume of the anchor, in units: m is 3 ；
g represents the acceleration of gravity, unit: m/s 2 ；
ρ Anchor Density of the anchors, unit: kg/m 3 ；
A represents the area of the anchor projection in the sinking direction, in units: m is 2 ；
v T Represents the anchor bottoming velocity, in units: m/s;
C d representing the resistance coefficient of the anchor, and taking 0.8;
C a the additional mass coefficient of the anchor is represented, 1.5 is taken, and the value of the additional mass coefficient can refer to the table 1;
TABLE 1 drag resistance coefficient and additional mass coefficient for differently shaped objects
V obtained by calculation T After input, setting boundary conditions, applying full constraint to the cable, and completely limiting six degrees of freedom at the head end and the tail end; and then boundary constraint is applied to the soil, four parallel surfaces of YX and XZ are all fixed in the extending direction, and the XY plane of the bottom surface is completely fixed in all directions.
In the sixth step, the finite element mesh model of the submarine cable is an anchor-submarine cable-soil model after meshing. The finite element mesh model of the submarine cable is shown in a front view in fig. 8(a) and in a top view in fig. 8 (b).
In the sixth step, the sub-components of the assembly body module are subjected to grid division. In all the grid division modes, structured grids, namely hexahedron division, are preferentially adopted, and then other forms of division are adopted.
For anchor drop, defined as rigid body, the mesh subdivision form will not affect the accuracy of analysis and computation time, then use the simplest C3D4 four-node linear tetrahedron coarse mesh division technique;
for submarine cables, wherein the columnar structures such as the armor layer and the outer sheath do not support structured grids, a C3D8R grid division technology is adopted, integral reduction and hourglass control are achieved, wherein the subdivision of the armor layer is thinner than that of the armor layer, the armor layer mainly bears a mechanical structure, and mechanical performance is more complex due to torsion, so that the overall seeds of the armor layer are small, and accurate analysis results are convenient to obtain;
for soil, the soil is of a cuboid structure, a structured grid is adopted perfectly, C3D8R grid division is adopted, integral is reduced, and hourglass control is carried out.
And seventhly, the numerical analysis model of the submarine cable is the anchor-submarine cable-soil model after the display power solution is carried out.
And seventhly, finishing the input of the preprocessing from the first step to the sixth step, in the editing operation, in order to improve the operation speed, performing parallel computation by using a plurality of processors, wherein the default processor is 2, and according to different computer conditions, the number of the processors for modulating the computer core number is reduced by two, so that the computation is facilitated. After the input data is written, data check is performed first to ensure that the calculation can be submitted after the check is error-free. And finally, extracting the sinking depth and sinking depth of the three-core composite submarine cable under the impact of different anchor falling states.
The invention relates to a submarine cable anchor falling impact test method based on an anchor falling-submarine cable-soil model, which has the following technical effects:
1) compared with the prior art, the invention adds the soil environment factors, and can simulate the damage condition of anchor damage to the submarine cable under the soil bodies in different states by changing the relevant parameters of the soil.
2) The invention simplifies the complex internal structure in submarine cable simulation and effectively improves the calculation speed on the premise of ensuring the accuracy of the result.
3) The method directly judges the local damage condition of the submarine cable in the impact process through the stress-strain cloud picture.
4) The method is based on conventional anchor dropping-submarine cable finite element simulation, and combines soil parameters, reduces the simulation error of anchor dropping impact submarine cables, can improve the authenticity of the anchor dropping impact submarine cable simulation, and can change the soil environment parameters to consider the damage condition of the submarine cables caused by anchor damage.
Drawings
Fig. 1 is a flow chart of the method for simulating the anchor falling impact three-core composite submarine cable considering soil according to the present invention.
Fig. 2 is a schematic view of a simplified geometric cross section of a three-core composite submarine cable.
FIG. 3(a) is a schematic view of an internal spiral structure with a conductor as a main body;
FIG. 3(b) is a schematic view of the filling section;
FIG. 3(c) shows a schematic view of a portion of the armor;
fig. 3(d) shows the outer sheath structure.
Fig. 4 is a grid section view under the anchor drop-submarine cable-soil body assembly.
FIG. 5(a) is a first cloud of the sea cable subjected to impact stress;
FIG. 5(b) is a cloud chart II of the sea cable subjected to impact stress;
FIG. 5(c) is a cloud chart III of the sea cable subjected to impact stress;
fig. 5(d) is a cloud chart of the sea cable subjected to the impact stress.
Fig. 6 is a schematic view of a soil module.
Fig. 7 is a schematic view of an anchor dropping module.
FIG. 8(a) is a schematic view showing the anchor bottom tangent to the soil surface and the buried depth h as the height of the soil surface from the bottom of the submarine cable;
fig. 8(b) is a schematic view showing the position where the anchor strikes the middle of the submarine cable.
FIG. 9(a) is a schematic diagram of cable application full restraint;
FIG. 9(b) is a schematic diagram of the application of boundary constraints to the soil.
Detailed Description
The submarine cable anchor falling impact test method based on the anchor falling-submarine cable-soil model comprises the steps of constructing the anchor falling-submarine cable-soil body model according to the anchor falling impact condition of the actual three-core composite submarine cable, considering a three-dimensional dual nonlinear finite element model, adding a complex three-core conductor and an optical fiber to be mutually spiral, considering armor steel wire torsion, carrying out contact setting on the complex condition, utilizing ABAQUS to construct display dynamic analysis, and analyzing the influence of anchor damage by calculating the sunken depth and the sunken soil depth of the submarine cable. The method flow of the invention is shown in figure 1 and comprises the following steps:
the method comprises the following steps: selecting a 35kV three-core composite submarine cable as a research object,
the specific models are as follows: YJQF 41-26/35-3X 500+ 2X 36C submarine cable containing 72-core optical cables;
a structural model is built by utilizing SolidWorks, clockwise spiral in a three-core conductor and anticlockwise spiral outside a galvanized steel armored steel wire are simulated really, the submarine cable is complex in structure, a shielding layer, a water blocking tape and other parts with lower mechanical strength are omitted, and a three-dimensional submarine cable geometric model is built. Then, a soil and anchor dropping model is established, the submarine cable is embedded into the soil in consideration of the actual engineering condition to form an anchor dropping-submarine cable-soil body model, and the anchor dropping is simulated to impact the submarine cable in the soil;
step two: constructing an elastic-plastic material numerical model of the submarine cable based on the nonlinear stress-strain relationship of the composite material, wherein the soil adopts a Mokolun model, the basic yield stress, the friction angle and the cohesive force yield stress are considered, and the drop anchor is equivalent to a rigid body;
step three: setting analysis step length and adopting ABAQUS power display function;
step four: constructing the interaction of a three-core composite submarine cable model by considering the falling anchor impact of soil, and setting contact conditions;
step five: constructing an initial condition that the anchor falling of the soil impacts the three-core composite submarine cable, applying an initial speed to the anchor falling according to energy conservation, and setting a boundary condition;
step six: constructing a finite element grid model of the anchor drop impact three-core composite submarine cable considering soil, locally and gradually refining the grid of the soil area aiming at the anchor drop impact position, and establishing a fine grid in a preset depth area of the finite element simulation process in order to ensure the solution precision of impact response in the finite element simulation process;
step seven: and (4) introducing the model in the first step and the model in the second step into the ABAQUS, combining with the condition parameters constructed in the third step and the fifth step to obtain a numerical analysis model of the anchor drop impact three-core composite submarine cable considering soil, and solving to obtain the sinking depth of the submarine cable at the impact position and the sinking depth of the submarine cable in the soil.
Determining specific parameters of a YJQF41-26/35-3 × 500+2 × 36C three-core composite submarine cable, establishing a copper conductor, an insulating layer, a lead sheath, a filling layer, an optical unit inner and outer steel wire, an optical unit sheath, an armor layer and an outer sheath model for the simplified three-core composite submarine cable with the specific process as follows:
1) firstly, an inner spiral part taking a conductor as a main body is determined: fig. 3(a) shows a schematic view of an internal spiral structure with a conductor as a main body. Determining the outer diameters of a conductor, an insulating layer and a lead sheath, then confirming the outer diameters of an optical unit, an inner steel wire and an outer steel wire of the optical unit and the outer diameter of the sheath of the optical unit, wherein the three-core conductor part is 120-degree symmetrical, the two optical units are respectively positioned at the middle positions of two adjacent conductor parts, only one optical unit is taken for simplifying calculation, a plain sketch is drawn on SolidWorks, a boss of one conductor part is stretched, the part is subjected to array processing, the three-phase conductor is 120-degree, then the optical unit part is stretched, and finally the conductor part and the optical units are bent and twisted;
2) and (3) reconstructing a filling part: fig. 3(b) is a schematic view of the filling part. Determining the outer diameter of a lead sheath and the outer diameter of an optical unit outer sheath, constructing conductor parts and optical unit torsion according to the previous operation, confirming the filling outer diameter on the basis, stretching the conductor parts and the optical unit torsion into a cylinder, and finally performing module subtraction combination to obtain a filling module;
3) then, constructing an armor part: FIG. 3(c) shows a schematic of a portion of the armor. The number of the armored steel wires on the outer layer of the three-core composite submarine cable is calculated according to the number of the wound steel wires and the pitch:
in the above formula: r is the radius of the cylinder in the armor layer, unit: mm; r is the radius of the armor wire, unit: mm.
Drawing a single armor steel wire layer plane sketch according to the armor steel wire radius obtained by the formula, stretching to the same height, performing array treatment to ensure that the armor steel wires are tangentially arranged to be round and stretched, and finally performing anticlockwise spiral treatment to the armor steel wires, wherein the spiral angle is
Wherein the helix angle and the winding angle α satisfy the following relationship:
4) then, constructing an outer sheath part: fig. 3(d) shows the outer sheath structure. And drawing a plan sketch after confirming the outer diameter of the outer sheath, stretching the same height, and finally forming an assembly body on the parts to obtain the three-core composite submarine cable.
The soil module is a cuboid, as shown in fig. 6, and must be much larger than the submarine cable module to ensure the authenticity of the submarine cable buried in the soil.
The anchor falling module is replaced by an object with the same bottom surface shape, the simplified bullet shape is realized, as shown in fig. 7, the shape of the bottom surface of the anchor is basically a curved surface, and therefore the bullet shape with a simple structure is selected.
And finally, embedding the submarine cable into soil, burying the submarine cable at a certain depth h, wherein the falling anchor is opposite to the middle of the submarine cable and is tangent to the surface of the soil.
The soil module, the anchor falling module, the depth h and the anchor falling are opposite to the middle of the submarine cable and tangent to the soil surface. As shown in fig. 8(a), the bottom surface of the anchor is tangent to the soil surface, and the burying depth h is the height from the soil upper surface to the bottom of the submarine cable; as shown in fig. 8(b), the anchor strikes the mid-sea cable.
The submarine cable has a complex structure, shows obvious nonlinear material properties, and has a stress-strain relationship which does not satisfy a linear relationship. When the material is in the elastic phase, good elastic properties are shown, and the stress-strain relationship satisfies hooke's law:
σ＝Eε；
wherein: and E (E ═ tan alpha) is the elastic modulus, when the load-unloading material deforms, the material can be completely recovered, when the material enters a yielding stage, the material begins to lose the deformation resistance and reaches a yielding state, after the yielding stage, the material is in a strengthening stage, the material recovers the deformation resistance, and when the stress exceeds the strength limit, the material breaks and completely fails. The soil adopts a molar coulomb model, and a friction angle, an expansion angle and a cohesive force yield stress are specified. The falling anchor is regarded as a rigid body, and the modulus is larger.
The step size is set and the power display portion is activated, the impact process typically being in the order of ms. Because the action time of the prop body is unknown, the time can be set to be increased conservatively, the impact duration is judged by observing energy, stress and speed curves in the calculation process, and then the appropriate time length is adjusted.
Before setting the contacts, to save operating time, sets are created for each side first. Because the structures of all layers of the submarine cable are complex and the surface is not continuous, the submarine cable is set to be universal contact, and the contact type is automatically identified through software. And setting the falling anchor as a rigid body, giving a gravity center, and finally setting the whole submarine cable and the soil boundary as a built-in structure.
In order to consider the initial speed of anchor dropping, the anchor dropping sinks in water, when the depth of seawater is enough, the sinking speed of the anchor after the anchor drops for a period of time reaches a constant value, and is a sinking limit speed, the gravity, the drainage volume and the flow resistance of the anchor dropping at the moment meet the energy conservation, and the stress balance equation of the anchor at the moment is as follows:
the anchor with mass m falls freely in the sea water, and its contact with the seabed surface is made a large velocity, which is also the considered initial velocity of the falling anchor, and the simplified calculation is:
the initial energy of the anchor is additional hydrodynamic energy besides kinetic energy, and the actual initial impact energy is as follows:
m a ＝ρ water (W) C a V
Wherein: m represents the mass of the anchor, in units: kg;
m a denotes the added mass, in units: kg;
v represents the volume of the anchor, in units: m is 3 ；
g represents the acceleration of gravity, unit: m/s 2 ；
A represents the area of the anchor projection in the sinking direction, in units: m is 2 ；
v T Represents the anchor bottoming velocity, in units: m/s;
C d representing the resistance coefficient of the anchor, taking: 0.8;
C a the additional mass coefficient of the anchor is 1.5, and the value of the additional mass coefficient can be referred to table 1.
TABLE 1 drag resistance coefficient and additional mass coefficient for differently shaped objects
V obtained by calculation T After inputting, boundary conditions are set, full constraint is applied to the cable, and six degrees of freedom at the head end and the tail end are completely limited, as shown in fig. 9 (a). Then, boundary constraint is applied to the soil, four parallel surfaces YZ and XZ are all fixed in the extending direction, and the bottom surface XY plane is completely fixed in all directions, as shown in FIG. 9 (b).
For the assembly body module, the sub-components are divided into grids, and fig. 4 is a grid division diagram under the assembly body of the anchor drop-submarine cable-soil body. In all the grid division modes, structured grids, namely hexahedron division, are preferentially adopted, and then other forms of division are adopted. For anchor drop, defined as a rigid body, the mesh subdivision form does not affect the accuracy of analysis and the computation time, and then the simplest C3D4 four-node linear tetrahedron rough-division mesh technology is adopted. For the submarine cable, the columnar structures such as the armor layer and the outer sheath do not support the structured grids, a C3D8R grid division technology is adopted, integral reduction and hourglass control are achieved, the subdivision of the armor layer is thinner than the subdivision of the armor layer, the armor layer mainly bears a mechanical structure, mechanical performance is more complex due to torsion, therefore the overall seeds of the armor layer are small, and accurate analysis results are convenient to obtain. For soil, the soil is of a cuboid structure, a structured grid is adopted perfectly, C3D8R grid division is adopted, integral is reduced, and hourglass control is carried out.
After the preprocessing input is finished, in the editing operation, in order to improve the operation speed, a plurality of processors are used for performing calculation in parallel, the default processor is 2, and the number of the processor-number-modulation computer cores is reduced by two according to different computer conditions, so that the calculation is facilitated. After the input data is written, data check is performed first to ensure that the calculation can be submitted after the check is error-free. And finally, extracting the stress-strain change condition, the sinking depth and the sinking depth of the three-core composite submarine cable under the impact of different anchor falling states. Fig. 5(a) -5 (d) are cloud charts of the impact stress applied to the submarine cable.
Fig. 5(a) -5 (d) illustrate the dynamic process of the submarine cable receiving anchor impact, fig. 5(a) illustrates that the submarine cable gradually generates elastic deformation, fig. 5(b) illustrates that the submarine cable armor exceeds yield stress and generates severe plastic deformation, fig. 5(c) illustrates that the submarine cable stress is gradually transmitted along the armor steel wire, the stress area is increased, fig. 5(d) illustrates that the stress is gradually reduced, the impact influence is gradually eliminated, but the armor generates unrecoverable deformation.
Claims (10)
1. The submarine cable anchor dropping impact test method based on the anchor dropping-submarine cable-soil model is characterized by comprising the following steps of:
the method comprises the following steps: constructing a falling anchor-submarine cable-soil model, and simulating the falling anchor to impact a submarine cable in soil;
step two: establishing a stress-strain relation model of the submarine cable based on the nonlinear material attribute of the submarine cable; establishing a molar coulomb model of the soil, and equating the falling anchor to a rigid body;
step three: setting analysis step length and starting a finite element software power display part;
step four: considering the interaction of anchor falling, submarine cable and soil in the model, and setting contact conditions;
step five: applying an initial speed to anchor falling, and setting a boundary condition;
step six: constructing a finite element grid model of the submarine cable, and locally and gradually refining the grid of the soil region at the anchor falling impact position;
step seven: and (4) importing the models in the first step and the second step into finite element software, combining the condition parameters set in the third step and the fifth step to obtain a numerical analysis model of the submarine cable, and solving the model to obtain the sinking depth of the submarine cable at the impact position and the sinking depth of the submarine cable in the soil.
2. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the first step, a 35kV three-core composite submarine cable is selected as a research object, a submarine cable structure model is built by utilizing SolidWorks, and clockwise spiral in a three-core conductor and anticlockwise spiral outside a galvanized steel armored steel wire are truly simulated; establishing a three-dimensional submarine cable geometric model; then establishing a soil and anchor model; and (4) taking the actual engineering condition into consideration, embedding the submarine cable into the soil to form a falling anchor-submarine cable-soil model, and simulating the falling anchor to impact the submarine cable in the soil.
3. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: the specific process of the step one comprises the following steps:
s1.1: firstly, determining the outer diameters of a conductor, an insulating layer and a lead sheath, then determining optical units, inner and outer steel wires of the optical units and the outer diameters of the optical unit sheaths to meet the requirement that three-core conductor parts are 120-degree symmetrical, respectively positioning the two optical units at the middle positions of two adjacent conductor parts, taking only one optical unit for simplifying calculation, drawing a plain sketch on SolidWorks, stretching a boss of one conductor part, carrying out array processing on the part to ensure that a three-phase conductor is 120 degrees, then stretching the optical unit parts, and finally bending and twisting the conductor parts and the optical units;
s1.2: and (3) reconstructing a filling part: determining the outer diameter of a lead sheath and the outer diameter of an optical unit outer sheath, constructing conductor parts and optical unit torsion according to the previous operation, confirming the filling outer diameter on the basis, stretching the conductor parts and the optical unit torsion into a cylinder, and finally performing module subtraction combination to obtain a filling module;
s1.3: then, an armor part is constructed, and the number of armor steel wires on the outer layer of the three-core composite submarine cable is calculated according to the number of wound steel wires and the pitch to obtain:
in the above formula: r is the radius of the cylinder in the armor layer, unit: mm; r is the radius of the armor wire, unit: mm; n is the number of the armored steel balls;
drawing a single armor steel wire layer plane sketch according to the armor steel wire radius obtained by the formula, stretching to the same height, then carrying out array treatment to ensure that the armor steel wires are tangentially arranged to be round and stretched, and finally carrying out anticlockwise spiral treatment on the armor steel wires, wherein the spiral angle is
Wherein the helix angle and the winding angle α satisfy the following relationship:
s1.4: and finally, constructing an outer sheath part, making a plan sketch after confirming the outer diameter of the outer sheath, stretching the outer sheath to the same height, and finally forming an assembly body by the parts to obtain the three-core composite submarine cable geometric model.
4. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the first step, the soil model is a cuboid module, the anchor falling model is simplified into a bullet shape, the submarine cable geometric model is embedded into the soil model and buried by a certain depth h, and the anchor falling is opposite to the middle of the submarine cable and tangent to the surface of the soil model.
5. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the second step, the stress-strain relationship of the submarine cable meets Hooke's law:
σ＝Eε；
wherein: e is the elastic modulus, sigma represents stress, and epsilon represents strain;
when the deformation of the load-unloading material can be completely recovered, when the material enters a yielding stage, the material begins to lose the deformation resistance and reaches a yielding state; after the yield stage, the material is in a strengthening stage, and the material recovers the deformation resistance; when the stress exceeds the strength limit, the material breaks and completely fails;
the method comprises the following steps that (1) a molar coulomb model is adopted for soil, and a friction angle, an expansion angle and a cohesion yield stress are specified; moore's law of coulombs
c is the yield stress of the cohesive force,
is the angle of friction and τ is the shear strength
The falling anchor is regarded as a rigid body, and the elastic modulus is large.
6. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the third step, setting the time length in the analysis step, namely the total time of the impact process, which is in the ms level, starting a finite element software ABAQUS power display part, conservatively setting the increased time, judging the impact duration by observing energy, stress and speed curves in the calculation process, and then adjusting the proper time length; and then creating a field output variable, setting parameters required by stress, strain and displacement, finally creating a process output variable, and setting energy parameters of the anchor.
7. The submarine cable anchor-falling impact test method based on the anchor-falling submarine cable-soil model according to claim 1, wherein: in the fourth step, before the contact condition is set, a set is created for all soil surfaces, because each layer of submarine cable has a complex structure and the surfaces are not continuous, the submarine cable is set to be in universal contact, the contact type is automatically identified through finite element software ABAQUS, and the method comprises the steps of setting a friction formula of tangential behavior as a penalty function, defining a friction coefficient, and setting pressure interference of normal behavior as hard contact; setting the falling anchor as a rigid body and endowing the gravity center with the falling anchor; and finally, placing the whole submarine cable in the soil.
8. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: the fifth step is as follows:
the initial speed of falling the anchor is considered at first, the anchor sinks in the water, when the sea water degree of depth is enough, the sinking speed of the anchor reaches the constant after falling for a period of time, for sinking limit speed, the gravity, the volume of water displacement and the flow resistance of the anchor that fall at this moment satisfy the conservation of energy, the stress balance equation of the anchor at this moment is:
the anchor with mass m falls freely in the sea water, the contact with the seabed surface is high speed, and the initial speed of the anchor is considered, and the simplified calculation is as follows:
the initial energy of anchor falling has additional hydrodynamic energy besides kinetic energy, and the actual initial impact energy is as follows:
m a ＝ρ water (W) C a V
Wherein: m represents the mass of the anchor, in units: kg;
m a denotes the added mass, in units: kg;
v represents the volume of the anchor, in units: m is 3 ；
g represents the acceleration of gravity, unit: m/s 2 ；
ρ Anchor Density of the anchors, unit: kg/m 3 ；
A represents the area of the anchor projection in the sinking direction, in units: m is 2 ；
v T Represents the anchor bottoming velocity, in units:m/s；
C d representing the resistance coefficient of the anchor, and taking 0.8;
C a an additional mass coefficient representing the anchor;
v obtained by calculation T After input, setting boundary conditions, applying full constraint to the cable, and completely limiting six degrees of freedom at the head end and the tail end; and then boundary constraint is applied to the soil, four parallel surfaces of YX and XZ are all fixed in the extending direction, and the XY plane of the bottom surface is completely fixed in all directions.
9. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the sixth step, the sub-components of the assembly body module are subjected to grid division; preferentially structuring the grids in all grid division modes, namely hexahedron division, and then dividing in other forms;
for anchor drop, the method is defined as a rigid body and adopts C3D4 four-node linear tetrahedron rough-division grid technology;
for a submarine cable, wherein the columnar structures such as an armor layer and an outer sheath do not support structured grids, a C3D8R grid division technology is adopted to reduce integral and control an hourglass;
for soil, C3D8R gridding is adopted, integration is reduced, and hourglass control is carried out.
10. The submarine cable anchor-falling impact test method based on the anchor-falling-submarine cable-soil model according to claim 1, wherein: in the seventh step, the preprocessing from the first step to the sixth step is input, in the editing operation, a plurality of processors are used for parallel calculation, and the number of the cores of the processors is modulated by the number of the processors to be reduced by two according to different computer conditions; after the input data is written, data inspection is performed first, and calculation is submitted after the inspection is ensured to be correct; and finally, extracting the sinking depth and sinking depth of the three-core composite submarine cable under the impact of different anchor falling states.
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