CN114638180A - Hydrodynamic-based method for monitoring stress of net cage and netting - Google Patents

Hydrodynamic-based method for monitoring stress of net cage and netting Download PDF

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CN114638180A
CN114638180A CN202210535935.4A CN202210535935A CN114638180A CN 114638180 A CN114638180 A CN 114638180A CN 202210535935 A CN202210535935 A CN 202210535935A CN 114638180 A CN114638180 A CN 114638180A
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netting
mass body
mass
force
net cage
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CN114638180B (en
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白晔斐
魏笑然
刘英男
支泓欢
刘紫薇
房欣
刘金伟
周一帆
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Hainan Institute of Zhejiang University
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Abstract

The invention discloses a hydrodynamic-based method for monitoring the stress of a net cage, which comprises the following steps: s1: acquiring and identifying basic characteristic information of the netting, and constructing an initial form of the complete netting; s2: acquiring and recording environmental characteristics and dynamic changes of an external ocean flow field in real time; s3: realizing simulation calculation of netting deformation based on a hydrodynamic model; s4: according to the calculation result, drawing the deformation and stress conditions of the netting under the influence of the external flow field environment; s5: and calculating the internal force borne by the netting unit structure, identifying the part of the netting material with the internal force exceeding the maximum endurance and highlighting the part, and further judging the vulnerable part of the netting of the marine aquaculture net cage. The invention can be used for the deformation and stress analysis of the net cage under complex sea conditions and the monitoring of vulnerable parts. The deformation process and the characteristics of the netting can be reasonably analyzed, the weak and easily damaged area of the netting is analyzed, prior reference is provided for replacement, arrangement, knitting modes and material selection of the netting, and the manufacturing and replacing cost of the net cage netting is effectively reduced.

Description

Hydrodynamic-based net cage and netting stress monitoring method
Technical Field
The invention relates to the field of aquaculture engineering and marine informatization services, in particular to a method for monitoring the stress of a net cage and a netting based on hydrodynamics.
Background
The netting is an important component of the deep-sea net cage, and plays a key role in ensuring smooth exchange between the deep-sea cage body and an external water environment, maintaining a fish growth environment, preventing fish from escaping and being invaded by natural enemies and the like.
However, the soft characteristic of the netting makes the netting easy to move and deform under the action of external load, and the volume loss of the net cage can be increased when the flow velocity is high, so that the normal growth of cultured fishes is influenced. Therefore, the study of the movement deformation of the netting under the action of water flow has important practical significance for deeply knowing the flow resistance characteristic of the net cage and taking the selection of the setting area of the net cage as a reference.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a hydrodynamic force-based net cage stress monitoring method, which can realize deformation monitoring and stress analysis of the net cage under different marine environments, thereby saving the actual application cost and providing a basis for the shape, structural design and position arrangement of the net cage.
In order to achieve the purpose, the invention discloses a method for monitoring the stress of a net cage and a netting based on hydrodynamics, which comprises the following steps:
s1: acquiring and identifying basic characteristic information of the netting, and constructing an initial form of the complete netting;
s2: acquiring and recording environmental characteristics and dynamic changes of an external ocean flow field in real time;
s3: realizing simulation calculation of netting deformation based on a hydrodynamic model;
wherein, under the space coordinate system, any mass body in the netting is aligned
Figure 678609DEST_PATH_IMAGE001
The stress is as follows:
Figure 808239DEST_PATH_IMAGE002
Figure 809562DEST_PATH_IMAGE003
is a mass body
Figure 38549DEST_PATH_IMAGE001
The mass of (c);
Figure 725489DEST_PATH_IMAGE004
is a mass body
Figure 393231DEST_PATH_IMAGE001
Additional mass coefficients of (a);
Figure 530951DEST_PATH_IMAGE005
is a mass body
Figure 508003DEST_PATH_IMAGE001
Acceleration of (2);
Figure 200016DEST_PATH_IMAGE006
is a mass body
Figure 405869DEST_PATH_IMAGE001
The force of gravity is applied to the steel plate,
Figure 352091DEST_PATH_IMAGE007
is a mass body
Figure 250777DEST_PATH_IMAGE001
The buoyancy force is applied to the steel plate,
Figure 226823DEST_PATH_IMAGE008
is a mass body
Figure 220056DEST_PATH_IMAGE001
The tension force is applied to the steel wire rope,
Figure 535630DEST_PATH_IMAGE009
is a mass body
Figure 605218DEST_PATH_IMAGE001
Is subjected to fluid resistance; it is written in matrix form as follows:
Figure 759905DEST_PATH_IMAGE010
Figure 307561DEST_PATH_IMAGE003
is a mass body
Figure 539959DEST_PATH_IMAGE001
The mass of (c);
Figure 29715DEST_PATH_IMAGE004
is a mass body
Figure 652458DEST_PATH_IMAGE001
The additional mass coefficient of (2);
Figure 269384DEST_PATH_IMAGE011
is a mass body
Figure 44704DEST_PATH_IMAGE001
Acceleration in three directions;
Figure 456094DEST_PATH_IMAGE006
is a mass body
Figure 628449DEST_PATH_IMAGE001
The force of gravity is applied to the steel plate,
Figure 767175DEST_PATH_IMAGE007
is a mass body
Figure 708587DEST_PATH_IMAGE001
The buoyancy force is applied to the steel plate,
Figure 759719DEST_PATH_IMAGE012
is a mass body
Figure 104857DEST_PATH_IMAGE001
The component of the applied pulling force in three directions,
Figure 63585DEST_PATH_IMAGE013
is a mass body
Figure 593924DEST_PATH_IMAGE001
Is subjected to components of fluid force resistance in three directions;
the forces between the interconnected masses are:
Figure 596384DEST_PATH_IMAGE014
Figure 681014DEST_PATH_IMAGE015
Figure 443434DEST_PATH_IMAGE016
is a mass body
Figure 47853DEST_PATH_IMAGE001
The number of other masses connected to the mass,
Figure 971947DEST_PATH_IMAGE017
display and mass body
Figure 793141DEST_PATH_IMAGE001
Connected mass body
Figure 828093DEST_PATH_IMAGE018
The force applied to it is such that,
Figure 598603DEST_PATH_IMAGE019
is a mass body
Figure 693598DEST_PATH_IMAGE001
And
Figure 783781DEST_PATH_IMAGE018
the distance between them;
Figure 622424DEST_PATH_IMAGE020
is a mass body
Figure 981861DEST_PATH_IMAGE001
And
Figure 497025DEST_PATH_IMAGE018
when the distance exceeds the critical length, i.e.
Figure 777965DEST_PATH_IMAGE021
When the elastic force exists, the elastic force exists between the two, otherwise, the elastic force does not exist;
Figure 420299DEST_PATH_IMAGE022
is a mass body
Figure 650554DEST_PATH_IMAGE018
A projected area along the stretching direction;
Figure 556193DEST_PATH_IMAGE023
and
Figure 386746DEST_PATH_IMAGE024
as elastic deformation parameter of mass body；
Under the space coordinate system, when the mass body
Figure 816459DEST_PATH_IMAGE001
When the distances between the mass bodies connected with the mass bodies exceed respective critical lengths, the components of the tensile force borne by the mass bodies along three coordinate axes are as follows:
Figure 353751DEST_PATH_IMAGE025
wherein
Figure 961450DEST_PATH_IMAGE026
Are respectively and first
Figure 27101DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 948921DEST_PATH_IMAGE018
The tension of the mass body to the mass body
Figure 668615DEST_PATH_IMAGE027
A component in direction;
Figure 696483DEST_PATH_IMAGE028
is as follows
Figure 439311DEST_PATH_IMAGE001
The position of the individual mass body is,
Figure 961559DEST_PATH_IMAGE029
is as follows
Figure 286492DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 439256DEST_PATH_IMAGE018
The position of the individual mass;
the fluid resistance includes velocity forces and inertial forces, expressed as:
Figure 466118DEST_PATH_IMAGE030
Figure 41325DEST_PATH_IMAGE009
is as follows
Figure 407715DEST_PATH_IMAGE001
The fluid resistance experienced by the individual mass,
Figure 528118DEST_PATH_IMAGE031
and
Figure 61517DEST_PATH_IMAGE032
respectively the velocity force and the inertia force experienced,
Figure 925568DEST_PATH_IMAGE033
and
Figure 412044DEST_PATH_IMAGE034
are respectively a mass body
Figure 218195DEST_PATH_IMAGE001
Velocity and acceleration of (d);
Figure 157332DEST_PATH_IMAGE035
is a mass body
Figure 825074DEST_PATH_IMAGE001
Projected area along the water flow velocity;
Figure 447947DEST_PATH_IMAGE036
is an additional mass coefficient;
Figure 441311DEST_PATH_IMAGE037
is the fluid density;
Figure 867744DEST_PATH_IMAGE038
is the fluid velocity;
Figure 588444DEST_PATH_IMAGE039
is the velocity force coefficient;
under the space coordinate system, the mass body
Figure 252775DEST_PATH_IMAGE001
The components of the fluid resistance experienced along the three axes are:
Figure 899264DEST_PATH_IMAGE040
wherein
Figure 609731DEST_PATH_IMAGE041
Are respectively the first to
Figure 822537DEST_PATH_IMAGE001
Fluid resistance, projected area, velocity and acceleration experienced by individual masses
Figure 449697DEST_PATH_IMAGE027
A component in direction;
Figure 456967DEST_PATH_IMAGE042
is the fluid velocity edge
Figure 654730DEST_PATH_IMAGE027
The component in the direction of the light beam,
Figure 953119DEST_PATH_IMAGE043
is a mass body
Figure 919938DEST_PATH_IMAGE001
The volume of (a);
and (3) simultaneously connecting the control equations of all the mass bodies to obtain the motion equation of the netting:
Figure 160426DEST_PATH_IMAGE044
；
wherein
Figure 298015DEST_PATH_IMAGE045
For the mass of each mass body,
Figure 914941DEST_PATH_IMAGE046
as for the gravity of each mass body,
Figure 939529DEST_PATH_IMAGE047
as to the buoyancy of each of the mass bodies,
Figure 92862DEST_PATH_IMAGE048
the acceleration in three directions for each mass,
Figure 999638DEST_PATH_IMAGE049
the components of the tensile force to which each mass body is subjected in three directions,
Figure 889097DEST_PATH_IMAGE050
the component of the fluid force experienced by each mass in three directions;
the motion equation of the netting is linearized and solved by a Newmark-beta algorithm, wherein the expression of the algorithm is as follows:
Figure 96087DEST_PATH_IMAGE051
wherein the content of the first and second substances,
Figure 865329DEST_PATH_IMAGE052
，
Figure 524981DEST_PATH_IMAGE053
and
Figure 218130DEST_PATH_IMAGE054
the position, velocity and acceleration at the next moment,
Figure 764780DEST_PATH_IMAGE055
，
Figure 721235DEST_PATH_IMAGE056
and
Figure 602603DEST_PATH_IMAGE057
the position, velocity and acceleration at the current time,
Figure 348711DEST_PATH_IMAGE058
in order to be a step of time,
Figure 671239DEST_PATH_IMAGE059
and
Figure 343136DEST_PATH_IMAGE060
is a specified parameter;
equations (2-9) are converted to incremental equations:
Figure 977379DEST_PATH_IMAGE061
wherein, the first and the second end of the pipe are connected with each other,
Figure 12331DEST_PATH_IMAGE062
the position, speed and acceleration increment from the current moment to the next moment; (2-2) is arranged into the following form:
Figure 517262DEST_PATH_IMAGE063
wherein the content of the first and second substances,
Figure 861525DEST_PATH_IMAGE064
is a mass body in the nonlinear power system
Figure 609163DEST_PATH_IMAGE001
Is expressed by the equation
Figure 447806DEST_PATH_IMAGE065
And (3) performing Taylor expansion at the moment, and then performing a linearization equation:
Figure 72823DEST_PATH_IMAGE066
wherein:
Figure 338719DEST_PATH_IMAGE067
Figure 868926DEST_PATH_IMAGE068
Figure 776839DEST_PATH_IMAGE069
wherein the content of the first and second substances,
Figure 256362DEST_PATH_IMAGE070
are respectively a mass body
Figure 650084DEST_PATH_IMAGE001
Acceleration, velocity and displacement increment from the current moment to the next moment;
Figure 480637DEST_PATH_IMAGE071
are respectively an equation
Figure 395503DEST_PATH_IMAGE072
In that
Figure 244379DEST_PATH_IMAGE065
Derivatives of acceleration, velocity and displacement in three directions at time;
Figure 55341DEST_PATH_IMAGE073
is powered by water
Figure 327184DEST_PATH_IMAGE065
For speed in three directions at any timeThe derivative(s) of the signal(s),
Figure 45742DEST_PATH_IMAGE074
respectively, the three components of the pulling force are
Figure 499857DEST_PATH_IMAGE065
Time division pair
Figure 544036DEST_PATH_IMAGE075
Derivative of displacement in direction;
after the parameters are calculated, substituting the parameters into a formula (2-13), and combining the formula (2-13) and the formula (2-11) to obtain a linear equation set;
s4: according to the calculation result, drawing the deformation and stress conditions of the netting under the influence of the external flow field environment;
s5: and calculating the internal force borne by the netting unit structure, identifying the part of the netting material with the internal force exceeding the maximum endurance and highlighting the part, and further judging the vulnerable part of the netting of the marine aquaculture net cage.
Further, the gravity and the buoyancy of the mass body are only related to the density, the volume and the seawater density of the mass body, and the expression is as follows:
Figure 536132DEST_PATH_IMAGE076
wherein the content of the first and second substances,
Figure 527221DEST_PATH_IMAGE077
is a mass body
Figure 849225DEST_PATH_IMAGE001
The density of (a), the value of which is related to the material selection;
Figure 798726DEST_PATH_IMAGE078
is the volume of the mass;
Figure 763271DEST_PATH_IMAGE079
is the acceleration of gravity;
Figure 338478DEST_PATH_IMAGE037
is the density of seawater.
Further, the basic characteristic information of the netting in the step S1 includes: the number and the attributes of the basic unit structures, the topological relation among the basic unit structures and the special basic units.
Further, the basic unit structure includes: the tubercles and the legs of the eyes; the number of basic unit structures includes: the number of nodes and mesh feet possessed by the netting; the properties of the basic unit structure comprise the position, the speed and the density of the node and the ocular foot, the diameter of the node, the diameter and the length of the ocular foot, the additional mass coefficient of the node and the ocular foot, the hydrodynamic coefficient, the elastic coefficient of the ocular foot and the critical length.
Further, the topological relation among the basic unit structures is specifically as follows: each of the nodes of the netting is linked to a mesh foot, each mesh foot being connected to only two nodes, thereby forming a topology between the basic unit structures.
Further, the special basic unit is specifically: during deformation of the netting there are fixed nodes, whose positions remain unchanged and are not affected by water flushes or by the pulling of other nodes, which are called special basic units.
Further, in step S3, the calculation result includes: the positions, speeds, accelerations and stress conditions of the eyes and the nodules at different moments; topological relation between the ocular legs and the nodes; the calculation result is stored in mat, txt or dat format.
Further, in step S4, the drawing the content includes: selecting the deformation condition of the net cage netting under the influence of the external flow field environment at the moment of carving; selecting the stress condition of the net cage under the influence of the external flow field environment at the moment of carving; the pull force of any node and foot of the netting and the change condition of the water flow force along with time.
Further, in step S4, a picture drawing result at a single moment, an animation drawing result for a period of time, or a complete process is formed in a three-dimensional view or a two-dimensional projection view.
Further, in step S5, the vulnerable portion of the net is determined by calculating the pulling force applied to the mesh and the knot of the net.
The invention can be used for the deformation and stress analysis of the net cage under complex sea conditions and the monitoring of vulnerable parts. The deformation process and characteristics of the netting can be reasonably analyzed, the weak and easily damaged area of the netting is analyzed, and a prior reference is provided for replacement, arrangement, knitting modes and material selection of the netting, so that the manufacturing and replacement cost of the net cage netting is effectively reduced.
Drawings
FIG. 1 is a schematic flow diagram of the present invention;
FIG. 2 is a schematic view of a nodule and a foot;
FIG. 3 is a schematic view of the initial configuration of the net cage according to the embodiment of the present invention;
FIG. 4 is a Y-axis projection of the deformation result of the 50 th second netting in the embodiment;
FIG. 5 is a three-dimensional diagram illustrating the force distribution of the 50 th second net in the example;
FIG. 6 is a timing chart of the pulling force of the fixed knot at the lower right corner in the example;
FIG. 7 is a timing chart of the pulling force of the top right fixed knot in the example.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The invention relates to a hydrodynamic-based net cage stress monitoring method, which analyzes the deformation characteristics and stress conditions of a net cage under different marine environments based on a hydrodynamic model and various numerical monitoring methods, and the analysis result can be used for quickly identifying the vulnerable area of the net cage. Firstly, fishing net information to be monitored and external flow field information are input, the system can automatically acquire and identify basic characteristics of the netting, record environmental characteristics and dynamic changes of an external ocean flow field in real time, and then solve the motion process of the netting. In the solving process, all attributes of the basic units of the netting at the current moment are counted firstly, then the variation of the netting attributes at the next moment is calculated by the selected numerical solving method, meanwhile, all calculation results can be stored and a netting deformation and stress analysis graph can be drawn, and finally, the easily damaged parts of the netting are analyzed according to the stress condition.
Fig. 1 shows an overall process of a method for monitoring the stress of a net cage based on hydrodynamics in an embodiment of the invention. In the construction stage, the system constructs a complete initial form of the netting by acquiring and identifying basic characteristic information of the netting, and simultaneously acquires external marine environment characteristics and records the dynamic change of a marine flow field. And then the system carries out simulation solving on the deformation process of the net cage according to the input information, the net cage deformation and stress results can be stored in different formats or displayed through pictures or videos, and finally, the vulnerable parts of the net cage are detected.
The invention relates to a method for monitoring the stress of a net cage and a netting based on hydrodynamics, which comprises the following steps:
s1: acquiring and identifying basic characteristic information of the netting, and constructing an initial form of the complete netting;
s2: acquiring and recording environmental characteristics and dynamic changes of an external ocean flow field in real time;
s3: realizing simulation calculation of netting deformation based on a hydrodynamic model;
s4: according to the calculation result, drawing the deformation and stress conditions of the netting under the influence of the external flow field environment;
s5: and calculating the internal force borne by the netting unit structure, identifying the part of the netting material with the internal force exceeding the maximum endurance and highlighting the part, and further judging the vulnerable part of the netting of the marine aquaculture net cage.
As shown in fig. 2, which is a schematic view of a knot and a mesh foot, the knot of the netting is called a knot, and the mesh line between two adjacent knots is called a mesh foot. According to the lumped mass method, the nodes and the legs are considered to be connected by a no-mass spring. Thereby discretizing the netting into a plurality of sets of nodules and mesh feet mass points. To simplify the model operation, assume the nodule is a sphere and the ocular foot is a cylinder.
In step S1, the netting to be monitored is input, the basic characteristic information of the netting is automatically identified, and the initial form of the complete netting is constructed.
The basic characteristic information of the netting comprises: the number and the attributes of the basic unit structures, the topological relation among the basic unit structures and the special basic units. The basic unit structure includes: the tubercles and the legs of the eyes; the number of basic unit structures includes: the number of nodes and mesh feet possessed by the netting; the properties of the basic unit structure comprise the position, the speed and the density of the node and the ocular foot, the diameter of the node, the diameter and the length of the ocular foot, the additional mass coefficient of the node and the ocular foot, the hydrodynamic coefficient, the elastic coefficient of the ocular foot and the critical length.
The topological relation among the basic unit structures refers to that: each knot of the garment is linked to a pin, each knot possibly being connected to a different number of pins, but each pin must be connected to only two knots, thereby forming a topology between elementary cells.
The special basic units are: during deformation of the netting, there may be fixed nodes, the positions of which remain unchanged and are not affected by water scouring or other node pulling, etc. Such nodules are called special elementary units and need to be recorded separately.
In step S2, acquiring and recording the environmental characteristics and dynamic changes of the external flow field in real time; and recording the change condition of the external flow field to be monitored for subsequent simulation monitoring.
The external marine flow field environmental characteristics include: flow field flow rate, flow field direction, fluid density, gravitational acceleration, total monitoring duration, and monitoring time interval. The dynamic change means that: the flow field velocity, direction, density may vary with position and time.
Step S3 includes the following steps:
s31, selecting a relevant solving algorithm and a solving mode according to actual problem requirements;
s32, automatically combining basic characteristic information of the netting and external smooth environment characteristics by the system, and carrying out simulation monitoring based on the selected solving algorithm;
and S33, storing the monitoring result.
A computation and solving method for simulation of netting deformation based on a hydrodynamic model comprises a four-order Runge Kutta method and a Newmark-beta method, and serial versions and parallel versions of the four-order Runge Kutta method and the Newmark-beta method can be selected. If the solving algorithm is an explicit four-order Runge-Kutta numerical method, directly calculating the positions, the speeds and the topological relations of all basic unit structures of the netting at the next moment according to the hydrodynamic model; if the solving algorithm is an implicit Newmark-beta numerical method, a control equation set of the netting system is calculated, and the position, speed and topological relation of all basic unit structures of the netting at the next moment is obtained through the solving equation set.
After the system is combined with basic characteristic information of the netting and external smooth environment characteristics, the monitoring process is carried out based on the selected solving algorithm, and the method comprises the following steps:
s321, initializing netting input;
s322, counting the positions, the speeds and the topological relations of all basic unit structures of the netting at the current moment;
s323, calculating the stress conditions of all basic unit structures of the netting at the current moment;
s324, based on the selected solving algorithm, if the solving algorithm is an explicit four-order Runge Kutta numerical method, directly calculating the positions, the speeds and the topological relations of all basic unit structures of the netting at the next moment according to a hydrodynamic model; if the solving algorithm is an implicit Newmark-beta numerical method, calculating a control equation set of the netting system, and obtaining the position, speed and topological relation of all basic unit structures of the netting at the next moment by solving the equation set;
and S325, repeating S321-S324 until the monitoring time is over, and storing the intermediate calculation result.
Wherein, under the space coordinate system, any mass body in the netting is aligned
Figure 767185DEST_PATH_IMAGE001
The stress is as follows:
Figure 90850DEST_PATH_IMAGE080
Figure 621320DEST_PATH_IMAGE003
is a mass body
Figure 485371DEST_PATH_IMAGE001
The mass of (c);
Figure 706268DEST_PATH_IMAGE004
is a mass body
Figure 512419DEST_PATH_IMAGE001
The additional mass coefficient of (2);
Figure 513873DEST_PATH_IMAGE005
is a mass body
Figure 119298DEST_PATH_IMAGE001
Acceleration of (2);
Figure 287978DEST_PATH_IMAGE006
is a mass body
Figure 15762DEST_PATH_IMAGE001
The force of gravity is applied to the steel plate,
Figure 973354DEST_PATH_IMAGE007
is a mass body
Figure 897317DEST_PATH_IMAGE001
The buoyancy force is applied to the steel plate so as to ensure that the steel plate is floated,
Figure 889543DEST_PATH_IMAGE008
is a mass body
Figure 788229DEST_PATH_IMAGE001
The tension force is applied to the steel wire rope,
Figure 498696DEST_PATH_IMAGE009
is a mass body
Figure 462235DEST_PATH_IMAGE001
Is subject to fluid resistance. It is written in matrix form as follows:
Figure 308969DEST_PATH_IMAGE081
Figure 644135DEST_PATH_IMAGE003
is a mass body
Figure 825587DEST_PATH_IMAGE001
The mass of (c);
Figure 842084DEST_PATH_IMAGE004
is a mass body
Figure 25547DEST_PATH_IMAGE001
The additional mass coefficient of (2);
Figure 266036DEST_PATH_IMAGE005
is a mass body
Figure 951095DEST_PATH_IMAGE001
Acceleration of (2);
Figure 754972DEST_PATH_IMAGE006
is a mass body
Figure 576297DEST_PATH_IMAGE001
The force of the gravity to which the utility model is subjected,
Figure 722108DEST_PATH_IMAGE007
is a mass body
Figure 894463DEST_PATH_IMAGE001
The buoyancy force is applied to the steel plate,
Figure 3496DEST_PATH_IMAGE008
is a mass body
Figure 944907DEST_PATH_IMAGE001
The tension force is applied to the steel wire rope,
Figure 979728DEST_PATH_IMAGE009
is a mass body
Figure 373800DEST_PATH_IMAGE001
Is subjected to fluid resistance;
the pulling force applied to the mass is equal to the sum of the forces applied to the connected masses, thus acting on the masses
Figure 66950DEST_PATH_IMAGE001
Comprises the following steps:
Figure 862868DEST_PATH_IMAGE082
Figure 635301DEST_PATH_IMAGE083
wherein, the first and the second end of the pipe are connected with each other,
Figure 454353DEST_PATH_IMAGE016
is a mass body
Figure 216772DEST_PATH_IMAGE001
The number of other masses connected to the mass,
Figure 116464DEST_PATH_IMAGE017
display and mass body
Figure 243820DEST_PATH_IMAGE001
Connected mass body
Figure 612485DEST_PATH_IMAGE018
The acting force is applied to the elastic force, and the expression of the acting force is shown as (2-3);
Figure 867011DEST_PATH_IMAGE019
is a mass body
Figure 637520DEST_PATH_IMAGE001
And
Figure 185045DEST_PATH_IMAGE018
the distance between them;
Figure 41006DEST_PATH_IMAGE020
is a mass body
Figure 348490DEST_PATH_IMAGE001
And
Figure 190151DEST_PATH_IMAGE018
critical length of (2) whenThe distance exceeding a critical length, i.e.
Figure 642998DEST_PATH_IMAGE021
If so, the elastic force is considered to exist between the two, otherwise, the elastic force is not considered.
Figure 923938DEST_PATH_IMAGE022
Is a mass body
Figure 520267DEST_PATH_IMAGE018
A projected area along a stretching direction;
Figure 468631DEST_PATH_IMAGE023
and
Figure 905429DEST_PATH_IMAGE024
is the elastic deformation parameter of the mass body, and the value of the elastic deformation parameter is related to the material of the netting.
Under the space coordinate system, when the mass body
Figure 719670DEST_PATH_IMAGE001
When the distances between the mass bodies connected with the mass bodies exceed respective critical lengths, the components of the tensile force borne by the mass bodies along three coordinate axes are as follows:
Figure 165694DEST_PATH_IMAGE084
wherein
Figure 765303DEST_PATH_IMAGE026
Are respectively the first to
Figure 318208DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 573740DEST_PATH_IMAGE018
The tension of the mass body to the mass body
Figure 541564DEST_PATH_IMAGE027
A component in the direction.
Figure 464521DEST_PATH_IMAGE028
Is as follows
Figure 462695DEST_PATH_IMAGE001
The position of the individual mass body is,
Figure 736682DEST_PATH_IMAGE029
is as follows
Figure 462192DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 285661DEST_PATH_IMAGE018
The position of the individual mass.
The fluid resistance includes two components, velocity force and inertia force. For the mass body
Figure 438424DEST_PATH_IMAGE001
The expression is as follows:
Figure 681931DEST_PATH_IMAGE030
Figure 742290DEST_PATH_IMAGE009
is as follows
Figure 436577DEST_PATH_IMAGE001
The fluid resistance experienced by the individual mass body,
Figure 9510DEST_PATH_IMAGE031
and
Figure 258088DEST_PATH_IMAGE032
respectively the velocity force and the inertia force experienced,
Figure 387718DEST_PATH_IMAGE033
and
Figure 624927DEST_PATH_IMAGE034
are respectively a mass body
Figure 181810DEST_PATH_IMAGE001
Velocity and acceleration of (d);
Figure 120947DEST_PATH_IMAGE035
is a mass body
Figure 37957DEST_PATH_IMAGE001
Projected area along the water flow velocity;
Figure 441256DEST_PATH_IMAGE036
is an additional mass coefficient;
Figure 903462DEST_PATH_IMAGE037
is the fluid density;
Figure 83557DEST_PATH_IMAGE038
is the fluid velocity;
Figure 820569DEST_PATH_IMAGE039
is the velocity force coefficient;
under the space coordinate system, the mass body
Figure 16058DEST_PATH_IMAGE001
The component of the fluid resistance along three axes is:
Figure 898432DEST_PATH_IMAGE085
wherein
Figure 608899DEST_PATH_IMAGE041
Are respectively the first to
Figure 884023DEST_PATH_IMAGE001
Fluid resistance, projected area, velocity and acceleration experienced by individual masses
Figure 684751DEST_PATH_IMAGE027
A component in the direction.
Figure 19917DEST_PATH_IMAGE042
Is the fluid velocity edge
Figure 155363DEST_PATH_IMAGE027
The component in the direction of the light beam,
Figure 217866DEST_PATH_IMAGE043
is a mass body
Figure 919106DEST_PATH_IMAGE001
Of the cell membrane.
The gravity and the buoyancy of the mass body are only related to the density, the volume and the seawater density of the mass body, and the expression is as follows:
Figure 425174DEST_PATH_IMAGE086
wherein the content of the first and second substances,
Figure 61298DEST_PATH_IMAGE077
is a mass body
Figure 615907DEST_PATH_IMAGE001
The density of (a), the value of which is related to the material selection;
Figure 702812DEST_PATH_IMAGE078
is the volume of the mass;
Figure 363469DEST_PATH_IMAGE079
is the acceleration of gravity;
Figure 473508DEST_PATH_IMAGE037
is the density of seawater.
And (3) simultaneously establishing the control equations of all the mass bodies to obtain the motion equation of the netting system:
Figure 628546DEST_PATH_IMAGE087
；
wherein
Figure 55110DEST_PATH_IMAGE045
For the mass of each mass body,
Figure 902980DEST_PATH_IMAGE046
as for the gravity of each mass body,
Figure 500315DEST_PATH_IMAGE047
as to the buoyancy of each of the mass bodies,
Figure 708311DEST_PATH_IMAGE048
the acceleration in three directions for each mass,
Figure 504229DEST_PATH_IMAGE049
the components of the tensile force to which each mass body is subjected in three directions,
Figure 195104DEST_PATH_IMAGE050
the fluid force experienced by each mass has components in three directions.
For each mass, the resultant force to which it is subjected is related not only to its own position and velocity, but also to the positions of other connected masses, so the system of equations (2-8) is highly non-linear and not easily solved directly.
Since the system of equations (2-8) has strong non-linearity and the number of equations increases with the number of quality points, it is not easy to directly solve. Firstly, the method is linearized and then solved by utilizing a Newmark-beta algorithm. The Newmark-beta algorithm belongs to an implicit solving algorithm, and the algorithm expression is as follows:
Figure 919933DEST_PATH_IMAGE088
。
wherein
Figure 416773DEST_PATH_IMAGE052
，
Figure 536039DEST_PATH_IMAGE053
And
Figure 709400DEST_PATH_IMAGE054
the position, velocity and acceleration at the next moment,
Figure 281327DEST_PATH_IMAGE055
，
Figure 739115DEST_PATH_IMAGE056
and
Figure 978467DEST_PATH_IMAGE057
the position, velocity and acceleration at the current time,
Figure 525992DEST_PATH_IMAGE058
in order to be a step of time,
Figure 67438DEST_PATH_IMAGE059
and
Figure 171660DEST_PATH_IMAGE060
the parameters can be selected according to actual conditions. The specific application method is as follows:
equation (2-9) is first converted to an incremental equation:
Figure 999939DEST_PATH_IMAGE089
wherein
Figure 780682DEST_PATH_IMAGE062
The position, velocity and acceleration increments from the current time to the next time. Arranging (2-2) into the following form:
Figure 61622DEST_PATH_IMAGE090
wherein
Figure 703956DEST_PATH_IMAGE064
Is a mass body in the nonlinear power system
Figure 403053DEST_PATH_IMAGE001
Is expressed by the equation
Figure 43112DEST_PATH_IMAGE065
And (3) performing Taylor expansion at the moment, and neglecting high-order terms, then performing a linearization equation:
Figure 122933DEST_PATH_IMAGE091
wherein:
Figure 506641DEST_PATH_IMAGE092
Figure 840670DEST_PATH_IMAGE093
Figure 467610DEST_PATH_IMAGE094
wherein
Figure 723142DEST_PATH_IMAGE070
Are respectively a mass body
Figure 972858DEST_PATH_IMAGE001
Acceleration, velocity and displacement increments from the current time to the next time.
Figure 410661DEST_PATH_IMAGE071
Are respectively an equation
Figure 392524DEST_PATH_IMAGE072
In that
Figure 932090DEST_PATH_IMAGE065
Derivatives in time of acceleration, velocity and displacement in three directions.
Figure 205070DEST_PATH_IMAGE073
Is powered by water
Figure 779271DEST_PATH_IMAGE065
The derivatives of the velocity in three directions at a time,
Figure 932035DEST_PATH_IMAGE074
respectively, three components of the pulling force are
Figure 677006DEST_PATH_IMAGE065
Time division lower pair
Figure 688431DEST_PATH_IMAGE075
Derivative of the displacement in the direction.
After the relevant parameters are calculated, the relevant parameters are substituted into (2-13), and (2-13) and (2-11) are combined to obtain a linear equation set which can be solved by software MATLAB.
In step S3, after the simulation calculation, the calculation results to be saved include: the positions, speeds, accelerations and stress conditions of the eyes and the nodules at different moments; topological relation between the ocular foot and the nodule. The calculation result can be stored in a mat format, a txt format and a dat format; the storage form is as follows: txt, mat, dat formats.
In step S4, the renderable content includes: selecting the deformation condition of the net cage netting under the influence of the external flow field environment at the moment of carving; selecting the stress condition of the net cage netting under the influence of the external flow field environment at the moment of carving; the pull force of any node and foot of the netting and the change condition of the water flow force along with time. And selecting the deformation condition of the net cage under the influence of the external flow field environment at any moment, wherein the deformation condition comprises a three-dimensional visual angle and a two-dimensional projection visual angle. The drawing content can be in a picture format or a video format.
S41, reading the history item or directly using the storage result of the current item;
s42, optionally, according to actual needs, drawing deformation conditions of the net cage under the influence of the external flow field environment according to positions of nodules and legs at different moments in the stored result; wherein, the deformation condition can be used for drawing a three-dimensional visual angle and also drawing a two-dimensional projection visual angle so as to observe the detail change in the deformation process.
And S43, optionally, according to actual needs, calculating the internal force applied to the netting unit structure according to the topological relation between the nodules and the eyes and feet at different moments in the stored result, wherein the values of the internal force are presented by different colors.
And S44, optionally, drawing the pulling force of any nodule and foot according to the stored result and the change of water flow force along with time according to actual needs.
S45, optionally, according to actual needs, the drawing result of the picture at a single moment may be obtained and saved, or the drawing result of the animation of a period of time or a complete process may be obtained and saved.
Finally, the vulnerable parts of the netting are judged by comparing the basic properties of the netting according to the calculated pulling force on the mesh feet and the nodes of the netting.
In the specific application, the width of the net is 1.5 m, the depth of the net is 1 m, the flow field water flow is 0.5m/s uniform flow, and the direction is along the positive direction of an X axis. Six parts at the two sides of the top end and the bottom of the netting are fixed nodes. The mesh opening size is 2.5 cm, which is schematically shown in fig. 3. The parameters of the tubercle and the foot are shown in the following table.
Figure 54821DEST_PATH_IMAGE095
In order to ensure the convergence of the monitoring result, the time step is set to be 0.01 second, and the total time length is set to be 50 seconds. The Y-axis projection view of the 50 th second web deformation is shown in FIG. 4.
Because the top has only 2 fixed nodes, and the bottom has 6 fixed nodes, so the power that each fixed node of top shared is bigger on the atress, and consequently the top is tensile more obvious. And because the density of the netting is smaller than that of the seawater as a whole, the netting is in an upward floating state as seen from a side view.
Through calculation, when the netting system is stable, the values of the tension borne by the fixed nodes on the left side and the right side of the top are 0.1709N, and the fixed nodes are the most stressed nodes. Therefore, the system analyzes that the part is most prone to aging, and the vulnerable part needs extra attention.
We show the calculation process with the nodes in the middle of the uppermost layer of the netting as an example:
at the initial time, the coordinates of the nodule
Figure 440803DEST_PATH_IMAGE096
Is (0,0.75,1), speed
Figure 204229DEST_PATH_IMAGE097
And acceleration
Figure 537121DEST_PATH_IMAGE098
All are 0, according to the material, the nodes
Figure 820335DEST_PATH_IMAGE099
. In addition, the diameter, density and elasticity parameters of the nodules
Figure 65634DEST_PATH_IMAGE100
And
Figure 801508DEST_PATH_IMAGE101
as already given in the table. The flow velocity of the water flow is 5m/s, the direction is along the positive direction of the X axis, and the density of the fluid is
Figure 187359DEST_PATH_IMAGE102
Acceleration of gravity of
Figure 590659DEST_PATH_IMAGE103
And a total of 4 mesh legs connected to the nodule, none of which exceed the critical length. Therefore, at this time, based on the above parameters, the following formula (2-4)The tensile force of the nodule can be calculated to be 0N; from equations (2-5), the water flow force can be calculated as: 4.89e-04N, from equations (2-7), the gravity and buoyancy can be calculated to be 0.0017N and 0.0018N, respectively. The acceleration at the current time is thus determined as: the next time coordinate is calculated as (9.34e-05,0.75,1) by substituting into Newmark-beta method, i.e. (2-9).
The monitoring results of the tension are given in fig. 5, 6 and 7. According to the three-dimensional view for drawing the stress condition of the netting at the 50 th second, fig. 5 is the distribution condition of the tensile force among the nodes at the 50 th second, and it can be seen that the tensile force is the largest at the fixed nodes, and the tensile force is smaller as the fixed nodes are farther away. Fig. 6 and 7 are timing charts of the tensile force of the fixed knot at the lower right corner and the upper right corner of the netting, respectively, and it can be seen that the tensile force is continuously increased in the first 10 seconds and gradually becomes stable at about the 10 th second under the influence of water flow impact. In the steady state, the upper right corner pull force is 50% greater than the lower right corner pull force, which is also consistent with previous analysis.
The invention has the advantages and positive effects that:
1. the invention can be used for the deformation and stress analysis of the net cage under complex sea conditions and the monitoring of vulnerable parts. The deformation process and characteristics of the netting can be reasonably analyzed, the weak and easily damaged area of the netting is analyzed, and a prior reference is provided for replacement, arrangement, knitting modes and material selection of the netting, so that the manufacturing and replacement cost of the net cage netting is effectively reduced.
2. The invention has high flexibility and expansibility in programming. The invention fully considers the particularity and complexity in the process of applying to practical problems, designs an explicit solving algorithm and an implicit solving algorithm respectively in the monitoring process, and simultaneously provides serial and parallel versions respectively, so that the monitoring process can be well adjusted according to the practical requirements.
The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A method for monitoring the stress of a net cage and a net jacket based on hydrodynamics is characterized by comprising the following steps:
s1: acquiring and identifying basic characteristic information of the netting, and constructing an initial form of the complete netting;
s2: acquiring and recording environmental characteristics and dynamic changes of an external ocean flow field in real time;
s3: realizing simulation calculation of netting deformation based on a hydrodynamic model;
wherein, under the space coordinate system, any mass body in the netting is aligned
Figure 897201DEST_PATH_IMAGE001
The stress is as follows:
Figure 657347DEST_PATH_IMAGE002
Figure 908068DEST_PATH_IMAGE003
is a mass body
Figure 310231DEST_PATH_IMAGE001
The mass of (c);
Figure 447951DEST_PATH_IMAGE004
is a mass body
Figure 129730DEST_PATH_IMAGE001
The additional mass coefficient of (2);
Figure 556164DEST_PATH_IMAGE005
is a mass body
Figure 293175DEST_PATH_IMAGE001
Acceleration of (2);
Figure 534670DEST_PATH_IMAGE006
is a mass body
Figure 371039DEST_PATH_IMAGE001
The force of the gravity to which the utility model is subjected,
Figure 298150DEST_PATH_IMAGE007
is a mass body
Figure 307694DEST_PATH_IMAGE001
The buoyancy force is applied to the steel plate,
Figure 154428DEST_PATH_IMAGE008
is a mass body
Figure 942124DEST_PATH_IMAGE009
The tension force is applied to the steel wire rope,
Figure 139887DEST_PATH_IMAGE010
is a mass body
Figure 953122DEST_PATH_IMAGE001
Is subjected to fluid resistance; the matrix form is:
Figure 919941DEST_PATH_IMAGE011
Figure 848845DEST_PATH_IMAGE003
is a mass body
Figure 799484DEST_PATH_IMAGE001
The mass of (c);
Figure 603361DEST_PATH_IMAGE004
is a mass body
Figure 690265DEST_PATH_IMAGE001
The additional mass coefficient of (2);
Figure 39338DEST_PATH_IMAGE005
is a mass body
Figure 699776DEST_PATH_IMAGE012
Acceleration of (2);
Figure 854814DEST_PATH_IMAGE006
is a mass body
Figure 999488DEST_PATH_IMAGE001
The force of gravity is applied to the steel plate,
Figure 96626DEST_PATH_IMAGE007
is a mass body
Figure 693960DEST_PATH_IMAGE013
The buoyancy force is applied to the steel plate,
Figure 387110DEST_PATH_IMAGE008
is a mass body
Figure 933760DEST_PATH_IMAGE014
The tension force is applied to the steel wire rope,
Figure 686952DEST_PATH_IMAGE010
is a mass body
Figure 568321DEST_PATH_IMAGE001
Is subjected to fluid resistance;
the forces between the interconnected masses are:
Figure 517691DEST_PATH_IMAGE015
Figure 636957DEST_PATH_IMAGE016
Figure 826630DEST_PATH_IMAGE017
is a mass body
Figure 943097DEST_PATH_IMAGE001
The number of other masses connected to the mass,
Figure 978049DEST_PATH_IMAGE018
display and mass body
Figure 686242DEST_PATH_IMAGE001
Connected mass body
Figure 296084DEST_PATH_IMAGE019
The force applied to it is such that,
Figure 355306DEST_PATH_IMAGE020
is a mass body
Figure 193949DEST_PATH_IMAGE001
And
Figure 569698DEST_PATH_IMAGE019
the distance between them;
Figure 835595DEST_PATH_IMAGE021
is a mass body
Figure 116534DEST_PATH_IMAGE001
And
Figure 8136DEST_PATH_IMAGE019
when the distance exceeds the critical length, i.e.
Figure 690921DEST_PATH_IMAGE022
When the elastic force exists, the elastic force exists between the two, otherwise, the elastic force does not exist;
Figure 393298DEST_PATH_IMAGE023
is a mass body
Figure 700215DEST_PATH_IMAGE019
A projected area along the stretching direction;
Figure 880660DEST_PATH_IMAGE024
and
Figure 480269DEST_PATH_IMAGE025
the elastic deformation parameter of the mass body;
under the space coordinate system, when the mass body
Figure 806077DEST_PATH_IMAGE001
When the distances between the mass bodies connected with the mass bodies exceed respective critical lengths, the components of the tensile force borne by the mass bodies along three coordinate axes are as follows:
Figure 61609DEST_PATH_IMAGE026
wherein
Figure 999740DEST_PATH_IMAGE027
Are respectively the first to
Figure 453855DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 232455DEST_PATH_IMAGE019
The tension of the mass body to the mass body
Figure 772021DEST_PATH_IMAGE028
A component in direction;
Figure 12378DEST_PATH_IMAGE029
is as follows
Figure 740907DEST_PATH_IMAGE001
The position of the individual mass body is,
Figure 955987DEST_PATH_IMAGE030
is as follows
Figure 982849DEST_PATH_IMAGE001
The mass bodies being connected to the first
Figure 43209DEST_PATH_IMAGE019
The position of the individual mass;
the fluid resistance includes velocity forces and inertial forces, expressed as:
Figure 721184DEST_PATH_IMAGE031
Figure 310428DEST_PATH_IMAGE010
is as follows
Figure 513002DEST_PATH_IMAGE001
The fluid resistance experienced by the individual mass body,
Figure 377053DEST_PATH_IMAGE032
and
Figure 660266DEST_PATH_IMAGE033
respectively the velocity force and the inertia force experienced,
Figure 951570DEST_PATH_IMAGE034
and
Figure 202292DEST_PATH_IMAGE035
are respectively a mass body
Figure 870034DEST_PATH_IMAGE001
Velocity and acceleration of (d);
Figure 433520DEST_PATH_IMAGE036
is a mass body
Figure 364567DEST_PATH_IMAGE001
Projected area along the water flow velocity;
Figure 587738DEST_PATH_IMAGE037
is an additional mass coefficient;
Figure 308438DEST_PATH_IMAGE038
is the fluid density;
Figure 300665DEST_PATH_IMAGE039
is the fluid velocity;
Figure 199351DEST_PATH_IMAGE040
is the velocity force coefficient;
under the space coordinate system, the mass body
Figure 863813DEST_PATH_IMAGE001
The component of the fluid resistance along three axes is:
Figure 138936DEST_PATH_IMAGE041
wherein, the first and the second end of the pipe are connected with each other,
Figure 985669DEST_PATH_IMAGE042
are respectively the first to
Figure 55256DEST_PATH_IMAGE001
Fluid resistance, projected area, velocity and acceleration experienced by individual masses
Figure 236708DEST_PATH_IMAGE028
A component in direction;
Figure 253206DEST_PATH_IMAGE043
is the fluid velocity edge
Figure 436669DEST_PATH_IMAGE028
A component in the direction;
Figure 880420DEST_PATH_IMAGE044
is a mass body
Figure 565479DEST_PATH_IMAGE001
The volume of (a);
and (3) simultaneously connecting the control equations of all the mass bodies to obtain the motion equation of the netting:
Figure 166093DEST_PATH_IMAGE045
；
wherein the content of the first and second substances,
Figure 987419DEST_PATH_IMAGE046
for the mass of each mass body,
Figure 398809DEST_PATH_IMAGE047
as for the gravity of each mass body,
Figure 728421DEST_PATH_IMAGE048
as to the buoyancy of each of the mass bodies,
Figure 352300DEST_PATH_IMAGE049
the acceleration in three directions for each mass,
Figure 277400DEST_PATH_IMAGE050
the components of the tensile force to which each mass body is subjected in three directions,
Figure 859691DEST_PATH_IMAGE051
the component in three directions of the fluid force experienced by each mass;
carrying out linearization processing on the motion equation of the netting, and solving by utilizing a Newmark-beta algorithm, wherein the algorithm expression is as follows:
Figure 253763DEST_PATH_IMAGE052
wherein, the first and the second end of the pipe are connected with each other,
Figure 212492DEST_PATH_IMAGE053
，
Figure 445894DEST_PATH_IMAGE054
and
Figure 199087DEST_PATH_IMAGE055
the position, velocity and acceleration at the next moment,
Figure 532985DEST_PATH_IMAGE056
，
Figure 295405DEST_PATH_IMAGE057
and
Figure 165403DEST_PATH_IMAGE058
the position, velocity and acceleration at the current time,
Figure 558338DEST_PATH_IMAGE059
in order to be a step of time,
Figure 379532DEST_PATH_IMAGE060
and
Figure 414485DEST_PATH_IMAGE061
is a specified parameter;
equations (2-9) are converted to incremental equations:
Figure 604901DEST_PATH_IMAGE062
wherein the content of the first and second substances,
Figure 168738DEST_PATH_IMAGE063
the position, speed and acceleration increment from the current moment to the next moment; arranging (2-2) into the following form:
Figure 477228DEST_PATH_IMAGE064
wherein the content of the first and second substances,
Figure 581450DEST_PATH_IMAGE065
is a mass body in the nonlinear power system
Figure 409729DEST_PATH_IMAGE001
Is expressed by the equation
Figure 895199DEST_PATH_IMAGE066
And (3) performing Taylor expansion at the moment, and then performing a linearization equation:
Figure 441718DEST_PATH_IMAGE067
wherein:
Figure 333320DEST_PATH_IMAGE068
Figure 812843DEST_PATH_IMAGE069
Figure 452902DEST_PATH_IMAGE070
wherein the content of the first and second substances,
Figure 240380DEST_PATH_IMAGE071
are respectively a mass body
Figure 889667DEST_PATH_IMAGE001
Acceleration, velocity and displacement increment from the current moment to the next moment;
Figure 941805DEST_PATH_IMAGE072
are respectively an equation
Figure 549504DEST_PATH_IMAGE073
In that
Figure 867353DEST_PATH_IMAGE066
Derivatives of acceleration, velocity and displacement in three directions at time;
Figure 71064DEST_PATH_IMAGE074
is powered by water
Figure 728441DEST_PATH_IMAGE066
The derivatives of the velocity in three directions at a time,
Figure 959571DEST_PATH_IMAGE075
respectively, three components of the pulling force are
Figure 967978DEST_PATH_IMAGE066
Time division lower pair
Figure 706871DEST_PATH_IMAGE076
Derivatives of displacement in direction;
after the parameters are calculated, substituting the parameters into a formula (2-13), and combining the formula (2-13) and the formula (2-11) to obtain a linear equation set;
s4: according to the calculation result, drawing the deformation and stress conditions of the netting under the influence of the external flow field environment;
s5: and calculating the internal force borne by the netting unit structure, identifying the part of the netting material with the internal force exceeding the maximum endurance and highlighting the part, and further judging the vulnerable part of the netting of the marine aquaculture net cage.
2. A method as claimed in claim 1, wherein the gravity and buoyancy of the mass body are related to the density, volume and sea water density of the mass body, and the expression is:
Figure 484334DEST_PATH_IMAGE077
wherein the content of the first and second substances,
Figure 151945DEST_PATH_IMAGE078
is a mass body
Figure 444386DEST_PATH_IMAGE001
(ii) a density of (d);
Figure 458740DEST_PATH_IMAGE079
is the volume of the mass;
Figure 621868DEST_PATH_IMAGE080
is the acceleration of gravity;
Figure 476692DEST_PATH_IMAGE038
is the density of seawater.
3. The method for monitoring the stress of the net cover of the net cage based on hydrodynamics as claimed in claim 1, wherein the basic characteristic information of the net cover in the step S1 includes: the number and the attributes of the basic unit structures, the topological relation among the basic unit structures and the special basic units.
4. A method as set forth in claim 3, wherein said basic unit structure comprises: the tubercles and the legs of the eyes; the number of basic unit structures includes: the number of the nodes and the mesh feet of the netting; the properties of the basic unit structure comprise the position, the speed and the density of the node and the ocular foot, the diameter of the node, the diameter and the length of the ocular foot, the additional mass coefficient of the node and the ocular foot, the hydrodynamic coefficient, the elastic coefficient of the ocular foot and the critical length.
5. A hydrodynamic force-based method for monitoring the stress on the net of a net cage according to claim 3, wherein the topological relationship between the basic unit structures is as follows: each node of the netting is linked to a mesh foot, each mesh foot being connected to only two nodes, thereby forming a topology between the basic unit structures.
6. The method for monitoring the stress on the netting of a net cage based on hydrodynamics as claimed in claim 3, wherein the special basic units are specifically: during deformation of the netting there are fixed nodes, whose positions remain unchanged and are not affected by water flushes or by the pulling of other nodes, which are called special basic units.
7. The method for monitoring the stress on the net of the net cage based on hydrodynamics as claimed in claim 1, wherein the calculation result in step S3 includes: the positions, speeds, accelerations and stress conditions of the eyes and the nodules at different moments; topological relation between the ocular legs and the nodes; the calculation result is stored in mat, txt or dat format.
8. The method for monitoring the stress on the net of the net cage based on hydrodynamics as claimed in claim 1, wherein the step S4 of plotting the content includes: selecting the deformation condition of the net cage under the influence of the external flow field environment at the moment of carving; selecting the stress condition of the net cage netting under the influence of the external flow field environment at the moment of carving; the pull force of any node and foot of the netting and the change condition of the water flow force along with time.
9. The method for monitoring the stress on the net of a net cage based on hydrodynamics as claimed in claim 8, wherein in step S4, a three-dimensional view or a two-dimensional projection view is used to form a single-time picture drawing result, a time-period animation drawing result or a complete-process animation drawing result.
10. The method for monitoring the stress on the net of the net cage based on hydrodynamics as claimed in claim 1, wherein in step S5, the vulnerable portion of the net is determined according to the calculated pulling force on the mesh and the knot of the net.
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