CN110282073A - Ship hydrodynamics prediction technique and system based on hull Wet surface grid in wave - Google Patents
Ship hydrodynamics prediction technique and system based on hull Wet surface grid in wave Download PDFInfo
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Abstract
The present disclosure discloses ship hydrodynamics prediction techniques and system based on hull Wet surface grid in wave, read the data point of ship；According to the data point on each waterline, the cubic B-spline expression formula of inverse waterline；Cubic B-spline expression formula based on waterline calculates the broad sense cross section curve of hull lines；It determines the type of wave and the expression formula on corrugated, according to the type of wave and the expression formula on corrugated, finds the intersection point of broad sense cross section curve and instantaneous corrugated, and then obtain hull Wet surface grid in wave；Based on hull Wet surface grid in wave, hydrodynamic force suffered by ship in wave is predicted.
Description
Technical Field
The present disclosure relates to the field of marine engineering and ocean engineering technologies, and in particular, to the division of a hull wet surface mesh in waves and the prediction of ship hydrodynamic force.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In the course of implementing the present disclosure, the inventors found that the following technical problems exist in the prior art:
surface element methods are often used to predict the hydrodynamic performance of ships during the ship design process. The division of the hull wet surface mesh is the first step in the binning calculation. A set of reasonably divided grids not only influences the accuracy of a calculation result, but also sometimes even directly relates to the success or failure of calculation. At present, two main types of methods for binning the wet surface of a ship body exist. The first method is to adopt the existing computer aided design software to pre-establish a geometric model of the hull surface and then to obtain the hull surface mesh by dispersing the model. The method has the advantages that the distribution condition of the grids on the surface of the ship body can be intuitively obtained, but the method has the defects that the work of establishing a geometric model of the surface of the ship body is time-consuming and labor-consuming, the obtained grid data can be output only through a limited number of data formats, and the method has great limitation in application.
The second type of method uses spline functions (typically B-splines or non-uniform rational B-splines) to fit the surface of the hull. The method can flexibly establish a mathematical model of the surface of the ship hull, and is convenient for outputting the ship hull grid data for a subsequent calculation program. However, two general problems exist in the related research at present, the first is that the model value points of the ship body need to be preprocessed before the surface of the ship body is fitted by adopting a spline function (for example, the surface curved sheet of the ship body is divided, the model value points are encrypted, and the like), and the process is often complicated; another problem the methods reported so far tend to be directed only to still water conditions, i.e. the wet surface area of the vessel is constant. For a ship wet surface with transient changes in waves, ideal meshing conditions are often difficult to give by applying the existing methods.
The technical problem to be solved in the prior art is how to divide the wet surface grids of the ship body so as to predict the hydrodynamic performance of the ship.
Disclosure of Invention
In order to solve the deficiencies of the prior art, the present disclosure provides a ship hydrodynamic prediction method and system based on a hull wet surface grid in waves. The method is realized based on a spline function, can directly perform grid division on the ship wet surface which instantaneously changes in waves according to the known ship type value point, and does not need to perform pretreatment on the type value point of a ship body. With the wet surface mesh generated, a prediction of the vessel hydrodynamic force can be made.
In a first aspect, the present disclosure provides a method for predicting ship hydrodynamic force based on a wet surface grid of a hull in waves;
the ship hydrodynamic prediction method based on the ship body wet surface grid in the waves comprises the following steps:
reading a model value point of a ship;
according to the type value points on each waterline, inversely calculating a cubic B spline expression of the waterline;
calculating a generalized section curve of the hull shape based on a cubic B spline expression of a waterline;
determining the type of the wave and the expression of the wave surface, and searching an intersection point of the generalized cross-section curve and the instantaneous wave surface according to the type of the wave and the expression of the wave surface so as to obtain a hull wet surface grid in the wave;
and predicting the hydrodynamic force of the ship in the waves based on the ship body wet surface grid in the waves.
In a second aspect, the present disclosure also provides a vessel hydrodynamic prediction system based on a hull wet surface mesh in waves;
ship hydrodynamic prediction system based on ship body wet surface grid in waves comprises:
a type point reading module configured to: reading a model value point of a ship;
a back-calculation module configured to: according to the type value points on each waterline, inversely calculating a cubic B spline expression of the waterline;
a generalized cross-sectional curve computation module configured to: calculating a generalized section curve of the hull shape based on a cubic B spline expression of a waterline;
an in-wave hull wet surface grid acquisition module configured to: determining the type of the wave and the expression of the wave surface, and searching an intersection point of the generalized cross-section curve and the instantaneous wave surface according to the type of the wave and the expression of the wave surface so as to obtain a hull wet surface grid in the wave;
a hydrodynamic prediction module configured to: and predicting the hydrodynamic force of the ship in the waves based on the ship body wet surface grid in the waves.
In a third aspect, the present disclosure also provides an electronic device comprising a memory and a processor, and computer instructions stored on the memory and executed on the processor, wherein the computer instructions, when executed by the processor, perform the steps of the method of the first aspect.
In a fourth aspect, the present disclosure also provides a computer-readable storage medium for storing computer instructions which, when executed by a processor, perform the steps of the method of the first aspect.
Compared with the prior art, the beneficial effect of this disclosure is:
the ship body modeling can be directly carried out according to the known ship model value points, the model value points of the ship body do not need to be preprocessed, and meshing can be carried out on the ship wet surface which changes instantaneously in waves. With the wet surface mesh generated, a prediction of the vessel hydrodynamic force can be made.
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The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a schematic diagram of a typical value point, wherein white open circles represent known typical value points;
FIG. 2 is a cubic B-spline curve for each waterline built from the type points;
FIG. 3 is a diagram showing a data point diagram obtained by dividing each water line by equal parameters. Black dots in the figure represent segmentation points obtained after segmentation of parameters such as a waterline and the like, and artificially increased section curve zero points;
FIG. 4 is a schematic diagram of a generalized cross-sectional curve back calculated from the data points in FIG. 3;
FIG. 5 is a schematic illustration of a hull wet surface cross-sectional curve cut at a transient wave front;
FIG. 6 is a cross-sectional curve under the instantaneous wet surface divided equally according to parameters to finally obtain a hull surface grid map under the instantaneous wet surface.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Description of the terms:
parameterization curve: each coordinate component of a point on the curve is represented as an explicit function of an independent parameter in the form of
Here u is a so-called parameter. A typical parametric curve, such as a circular arc in the first quadrant, can be expressed in parametric form:
as another example, A, B bars in space are assumed to have respective coordinates of (X)a，Ya) And (X)b，Yb) The coordinate (X) of any point C on the AB linec，Yc) Can be represented by the parameter u:
the parameter u is the ratio of the distance from point C to point A to the distance from point B to point A. When u is 0, a is C; when u is 1, C is B. Any point on the segment AB has a unique parameter associated with it.
Cubic B-spline curve:
a B-spline curve is a parametric curve represented in a piecewise polynomial form. The definition of the P-th B-spline curve is:
wherein p is the number of times of the curve,in order to control the rows of vertices,is defined in a non-uniform node vector(m +1 nodes in total, and the relationship between m and n satisfies n-m-p-1) as a B-spline basis function of degree p:
the B-spline curve is determined by the control vertices and the node vectors. And each point on the curve has a unique parameter u corresponding to it. The parameter u can be used in various ways, and typically, for example, the parameter u can be regarded as the arc length from a point on the curve to the start of the curve. Different parameterization methods will produce different curve shapes. The parameterization method of the accumulated chord length without the cause is used for solving the parameterization problem aiming at the appearance characteristics of the ship.
And (3) positive calculation and negative calculation of the B spline curve:
the positive calculation of the B-spline curve refers to the control vertex and node vector of the known B-spline curve, and the coordinates of each point on the curve are calculated. The inverse operation refers to the coordinate of a plurality of points in a known space, and the B spline expression passing through the points is obtained, and comprises two parts of the sum node vector of the control vertex.
Boat shape value table: the physical dimensions of a ship hull are often expressed in coordinate values of points at specific positions on a 'model surface', and the coordinate values are called model values. The profile value table is a table for recording the profile value of each profile intersection on the profile map, and is composed of a height value (height from the base line) and a half-width value (distance from the centerline plane).
Waterline: is the section line of the plane parallel to the horizontal plane and the surface of the ship body.
Equal parameter segmentation: the B-spline curve is used as a parameter curve, and the upper points of the B-spline curve have unique parameters corresponding to the parameters. For the present method, the curves used all use standardized parameter intervals (i.e., [0,1] interval, where parameter 0 corresponds to the start of the curve and parameter 1 corresponds to the end of the curve). The equal parameter division is to divide the [0,1] interval according to equal intervals, and the obtained parameter value is substituted into a curve expression to obtain each corresponding point on the curve.
Instantaneous wave surface: the wave surface of the wave is time-varying. The instantaneous surface here refers to the shape of the wave surface at any time.
Instantaneous wet surface: since the waves are time varying, the wet surface (i.e. the type surface below the wave surface) of a vessel when it is sailing in the waves is also time varying. The instantaneous wet surface here refers to a vessel-type surface below the wave surface at any time.
Dimensionless cumulative chord length parameterization is shown in formulas (12) and (13).
Bisection method: i.e. a binary search method. The searching process starts from the middle element of the array, and if the middle element is exactly the element to be searched, the searching process is ended; if a particular element is larger or smaller than the intermediate element, then the search is made in the half of the array that is larger or smaller than the intermediate element and the comparison is started from the intermediate element as was done at the beginning. If at some step the array is empty, the delegate cannot be found. Each comparison of this search algorithm reduces the search range by half.
First embodiment, the present embodiment provides a ship hydrodynamic prediction method based on a hull wet surface grid in waves. Taking S-175 container ship as an example, assume that its U-line model points are known (U is 13 in this embodiment). The determination of the ship model value point depends on a coordinate system, and usually a right-hand rectangular coordinate system is taken, wherein an X axis is forward directed to a ship bow, a Y axis is forward directed to a port, and a Z axis is forward and vertically upward. The longitudinal position of the origin of coordinates is positioned at the vertical line of the stern of the ship, and the vertical position of the origin of coordinates is positioned at the base line.
The method provided by the invention has no special requirement on the coordinate system, and only needs to be consistent with the coordinate system defined by the model value point.
The ship hydrodynamic prediction method based on the ship body wet surface grid in the waves comprises the following steps:
s1, reading a model value point of the ship;
s2, according to the type value points on each waterline, the cubic B spline expression of the waterline is reversely calculated;
s3, calculating a generalized section curve of the hull shape based on a cubic B spline expression of a waterline;
s4, determining the type of the wave and the expression of the wave surface, and searching the intersection point of the generalized cross-section curve and the instantaneous wave surface according to the type of the wave and the expression of the wave surface, so as to obtain a hull wet surface grid in the wave;
and S5, predicting the hydrodynamic force of the ship in the waves based on the wet surface grid of the ship body in the waves.
As one or more embodiments, S1, reading the model value point of the ship, as shown in the figure1, first receiving an input known type value point, which is recorded asWherein i represents a waterline mark number of a model value point, the ship base line is 0, the forward direction is increased progressively along the Z axis, and the forward direction of the Z axis is vertically upward; j represents the position of the type value point on the waterline, the first point of the stern is taken as 0, the forward direction of the stern is increased progressively along the X axis, and the forward direction of the X axis points to the bow;
for one or more embodiments, S2 is to inverse compute the B-spline expression of the waterline by using the method of specifying two-end directors according to the type value point on each waterline.
For one or more embodiments, S2, as shown in FIG. 2, inverse-computing the B-spline expression of the waterline based on the type points on each waterline;
the method for acquiring the cubic B spline expression of the ith waterline comprises the following steps:
s21, parameterization of shape point: assuming that the ith water line contains n +1 type value points, the type value points on the ith water lineThe value range of the middle j is 0,1, …, n; parameterizing n +1 type value points according to an accumulated chord length method; let diThe total chord length of the ith waterline
Wherein,represents the jth type value point on the ith waterline,representing the j-1 th type value point on the ith waterline;
parameter value corresponding to jth type value point on ith waterlineExpressed as:
wherein,representing the parameter value corresponding to the j-1 model value point on the ith waterline;
constructing node vectorsWherein,
ui,0＝…＝ui,3＝0， (3-1)
ui,n+3＝…＝ui,n+6＝1， (3-2)
wherein u isi,0,ui,1,ui,2,…,ui,n+6And (n + 7) elements of node vectors required for defining the ith waterline cubic B-spline expression.
S22, determination of guide vectors: let the ith waterline first guide vector beThe tail director isTo calculateAndlet the coordinates of two model value points on the ith waterline closest to the stern be
Wherein,representing the nearest type value point coordinate on the ith waterline from the stern;the second nearest type value point coordinate from the stern on the ith waterline is represented;
similarly, let the coordinates of the two model points on the ith waterline closest to the bow be:
wherein,representing the nearest type value point coordinate to the bow on the ith waterline;a model point coordinate representing a second closest to the bow;
computingAnd
s23, solving an equation set (8) by adopting cubic B splines according to a back calculation algorithm of given two-end director to obtain the ith waterline control vertex to be solved
Wherein,the 1 st control point coordinate of the cubic B-spline expression representing the ith waterline,the 2 nd control point coordinate of the cubic B-spline expression representing the ith waterline, and so on,the (n + 3) control point coordinate of the cubic B-spline expression for the ith waterline (i.e., the last control point).Represents the 1 st type point coordinate on the ith waterline,represents the 2 nd type point coordinate on the ith waterline, and so on,the (n + 1) th type value point (namely the last type value point) coordinate of the ith waterline;is defined in a non-uniform node vectorThe cubic B-spline basis function above, defined as:
wherein u isi,kTo representThe k-th element of (1), ui,k+1To representThe (k + 1) th element in (1), p represents the number of times of the B-spline basis function; u is a variable of the parameter curve, and k is an intermediate variable;
control vertex solved according to equation (8)Coordinated node vectorAnd obtaining a cubic B spline expression of the ith waterline, and recording the cubic B spline expression as:
wherein,obtaining cubic B spline expression of the ith waterline,is defined in a non-uniform node vectorCubic B-spline basis functions above.
As one or more embodiments, S3, based on the cubic B-spline expression of the waterline, calculating the generalized cross-sectional curve of the hull shape by using a method that does not specify the two-end director;
as one or more embodiments, S3, based on the cubic B-spline expression of the waterline, calculates a generalized cross-sectional curve of the hull form.
As shown in fig. 3, each obtained waterline is divided according to equal parameters;
assuming that M grids are used in the ship length direction (M is selected according to the accuracy of hydrodynamic calculation and the complexity of the ship profile, and M is 30 in fig. 3), the parameter interval [0, 1%]Performing M equal division to obtain a parameter vJJ/M (λ 0,1 …, M); v is to beJTaking a cubic B spline expression into the waterline to obtain discrete points uniformly distributed according to parameters on the waterline, and recording the discrete points as
Wherein i represents a vertical index of discrete points, and points on the ship baseline are 0 and are positively increased along the Z axis.
J represents that the discrete point horizontal index takes the first point of the stern as 0 and increases along the X axis in the positive direction, and U is the number of waterlines.
Usually, the ship hull is bilaterally symmetrical, only half of the ship hull needs to be divided when grid division is carried out, and the other half of the ship hull can be obtained by adopting a symmetrical method. As the 0 waterline on the model value table of the ship body is given according to the base line, and the base line is not the boundary of the half ship body, when each section curve is inversely calculated, a zero point is artificially added to each other section curve besides the head and tail contour lines.
Artificially adding a zero point to each other section curve, and adopting the following marking method to mark points on the head and tail contour lines of the ship:
whereinRepresenting a discrete point column directly obtained from a waterline and used for back-computing the head and tail contour lines of the ship;and the modified discrete point rows are shown and used for back-computing the head and tail contour lines of the ship.
For points on other cross-sectional curves:
whereinThe discrete point column used to back-calculate the J-th section curve is shown after the artificial zero point is added.Representing an initial row of points obtained by the waterline; x is the number of0,J,x1,J,x2,JAre respectively a pointX coordinate of (a), y1,J,y2,JAre respectively a pointY coordinate of (a).
To obtainAfter that, the parameters are correspondingly equalAnd (3) carrying out B-spline back calculation again for three times along the vertical direction on the points (namely the points with the same subscript J), and naming the obtained curve as a generalized section curve.
Compared with the conventional two-dimensional hull section curve in the ship engineering, the generalized section curve is a three-dimensional curve, so that the curvature change condition of the hull surface can be better described.
As one or more embodiments, obtainingAfter that, the parameters are correspondingly equalB-spline back calculation is carried out again for three times along the vertical direction on the points (namely the points with the same subscript J), and the obtained curve is named as a generalized section curve; the method comprises the following specific steps:
as shown in fig. 4. The method for parameterizing dimensionless accumulated chord length is used, and then a B-spline which does not specify guide vectors at two ends is used for back calculation to calculate the generalized section curve, and the method comprises the following steps:
(1)parameterization of (2). Selecting a group of identical subscripts JPoint, let its coordinate be (x)i,j,yi,j,zi,j) The value range of i is 0,1, …, S. J ranges from J to 0,1, …, M. Wherein
U is the number of waterlines, and M is the number of grids in the length direction of the ship
Set of identical subscripts JThe points are parameterized. Order to
Wherein d'JIs the section chord length after dimensionless, L is the ship length, B is the ship width, and T is the draft.
Parameter value corresponding to ith point on J-th generalized cross-sectional curveIs shown as
Wherein the definition of each parameter is the same as that in (11) and (12).
Accordingly, a node vector is constructed
u′0,J＝…＝u′3,J＝0，u′S+1,J＝…＝u′S+4,J＝1，
U 'here'0,j,u′1,j,…,u′S+4,jEach element (S +5 in total) of the node vector required for the cubic B-spline expression representing the J-th section curve,the value of the parameter corresponding to the ith data point on the J-th section curve is determined according to the formula (13).
(2) Solving an equation set (15) according to a reverse calculation method without assigned guide vectors to obtain a control vertex of the J-th section curve to be solvedWherein I ═ 0,1, …, S;
is defined in a non-uniform node vectorCubic B-spline basis functions above.And representing the parameter value corresponding to the ith data point on the section curve to be obtained.
Resulting control verticesCoordinated node vectorAnd obtaining a cubic B spline expression of the J-th generalized section curve, and recording the cubic B spline expression as:
wherein,the control vertexes of the J-th section curve (S +1 in total, I is 0,1, …, S),is defined in a non-uniform node vectorCubic B-spline basis functions above.
As one or more embodiments, S4 first finds the value of the parameter u corresponding to the intersection point of the generalized cross-sectional curve and the instantaneous wave surface on the cross-sectional curve. By adopting a bisection method, continuously dividing the parameter interval into two parts to obtain Z coordinates of two end points of the interval, averaging the upper limit and the lower limit of the parameter interval when the difference of the Z coordinates of the two end points is smaller than a set threshold value, and obtaining an averaged result, namely a parameter value corresponding to the intersection point of the generalized cross-section curve and the still water surface;
on the basis, according to the type of the given wave and the expression of the wave surface, the corresponding parameter (marked as u) of the intersection point of the section curve and the wave surface on the section curve is further searchedend) (ii) a The method comprises the following specific steps: recording the X coordinate of the intersection point of the J-th generalized cross-section curve and the still water surface as XJUsing the wave surface equation, the vertical coordinate η of the cross-sectional curve at the intersection with the wave surface is obtainedJAgain using the dichotomy, the ordinate of the section curve is obtained to be equal to ηJThe parameter corresponding to the point of (1) is the calculated uend；
From 0 to u of the parametric domain curveendAnd N equal divisions are carried out, and the obtained parameters are substituted into the cross-sectional curve to obtain N grid points of the required instantaneous subsurface cross-sectional curve.
FIG. 5 is a schematic illustration of a hull wet surface cross-sectional curve cut at a transient wave front;
for hydrodynamic analysis of a ship, a wave having an analytic expression, such as a linear regular wave, a first-order STOKES wave, a second-order STOKES wave, etc., is generally considered, and these waves have corresponding wave surface expressions, which are well known in the art. in this example, consider a case where, in the linear regular wave, the ship has a wavelength λ and a wave height a. the wave surfaces of the waves in different propagation directions have analytic expressions, and in fig. 5, λ is equal to 0.5 times of the ship length, the wave height a is equal to 1/50 ship length, and the ship direction of the waves is along the negative direction of the X axis, at this time, the expression of the wave surface η is written as:
wherein T is the draft of the ship, omega is the wave circle frequency, T is the time, lambda is the wavelength, and A is the wave height.
In order to consider the change of the wet surface of the ship in the presence of waves, an intersection point of a generalized section curve and a hydrostatic surface is firstly searched. The section curve determined according to equation (16) adopts a normalized parameter interval, i.e., u is greater than or equal to 0 and less than or equal to 1. Therefore, the parameter corresponding to the intersection point of the section curve and the hydrostatic surface is necessarily in the (0,1) interval, and the parameter corresponding to the starting point and the ending point of the section curve is respectively corresponding to the u-0 and the u-1 on each section curve.
Adopting dichotomy, continuously dividing the parameter interval into two parts to obtain Z coordinates of two endpoints of the interval, and when the difference between the parameter values u corresponding to the two endpoints is less than 1.0 multiplied by 10-3And averaging the upper and lower limits of the interval at the moment, wherein the result obtained after averaging is the parameter value corresponding to the intersection point of the generalized section curve and the still water surface.
For example, for the J-th generalized cross-sectional curve, assume that its cubic B-spline expression (i.e., (16)) has been solved. In this case, the parameters u-0 and u-1 correspond to the start point (located on the base line) and the end point (located at the highest waterline) of the generalized cross-sectional curve, respectively. And (3) dividing the interval (0,1) into two intervals (0,0.5) and (0.5,1), comparing the Z coordinate of the point corresponding to the parameter u being 0.5 with the Z coordinate of the still water surface, and if the Z coordinate of the point corresponding to the parameter u being 0.5 is smaller than the Z coordinate of the still water surface, proving that the still water surface is positioned in the parameter interval (0.5, 1). And (0.5,1) further halving, and searching a parameter interval in which the parameter corresponding to the still water surface is located. Repeating the process until the difference between the upper and lower limits of the divided interval is less than 1.0 × 10-3In the meantime, the upper and lower limits of the interval at this time may be averaged, and the result obtained after averaging is the parameter value corresponding to the intersection point of the generalized cross-sectional curve and the still water surface.
The generalized cross-sectional curve has only one intersection point with the still water surface.
Recording the X coordinate of the intersection point of the J-th generalized cross-section curve and the still water surface as XJThis is substituted into the wave surface equation (17) to obtain the longitudinal coordinate η of the cross-sectional curve at the intersection with the wave surfaceJ。
Again using the bisection method, the cross-sectional curve is obtained with ηJCorresponding parameter uend。
From 0 to u of the parametric domain curveendN equal divisions are performed and the resulting parameters are substituted into the cross-sectional curves (i.e., each curve determined by equation (16)), resulting in N grid points of the desired instantaneous subsurface cross-sectional curve. (N may be chosen based on the accuracy of the hydrodynamic calculation and the complexity of the vessel profile, 30 in FIG. 6)
It should be noted that, since the vectors at the left and right ends of the ship at the base line are not equal, the cross-sectional curve may have a problem that the Z value is less than zero near the base line. It should be noted that after the grid points are generated, the Z coordinates of all the grid points are checked. And correcting the coordinate of the point with the Z coordinate less than zero to zero.
As one or more embodiments, in obtaining the cubic B-spline curve for each waterline, the height of the highest waterline should be higher than the amplitude of the wave, taking into account the instantaneous wet surface of the vessel under the wave. (maximum distance from wave surface to sea level)
As one or more embodiments, S5: based on the generated hull wet surface grid, four adjacent grid points are projected to the same plane by adopting a Hess-Smith method, a hull surface element is generated, and the centroid coordinate of the surface element is obtained.
It is assumed that the resultant of the wave pressures generated by the linear regular waves (known as the friedel-crafts force) is considered. It is assumed that the dynamic pressure generated by the linear regular wave is equal in each plane element. And substituting the centroid coordinates of each surface element into an expression of linear regular fluctuation pressure, and multiplying the obtained result by the area of the corresponding surface element to obtain the resultant force of the wave pressure acted by the surface element. And summing the resultant force of the wave pressures acting on all surface elements, and recording as the wave pressure borne by the whole ship.
For other water power, the water power can be obtained by carrying out numerical calculation by using a surface element method based on the surface element of the hull. For brevity, no further description is provided herein.
The main innovation compared with the prior art is as follows:
1. in the prior art, a hull surface model is mostly established from a transverse section of a ship, and the embodiment starts from a waterline, so that a profile point does not need to be preprocessed (usually encrypted), and a relatively uniform section curve data point can be directly obtained.
2. In terms of inverse calculation of the section curve, the present embodiment uses a dimensionless cumulative chord length parameterization method. The original intention of this method is that the length of the hull surface is usually much greater than its width and depth, as with conventional parameterization methods, which is not conducive to representing variations in the hull geometry in width and depth. The dimensionless accumulated chord length parameterization method can better solve the problem.
3. In the problem of intersection points of the hull surface and waves, the bisection method is adopted in the embodiment, and after the wave surface is changed, the geometric shape of the hull under the wave surface can be updated only by newly searching the bisection method for each generalized section curve. The method is easy to realize, new parameterization of the type value point is not needed, and the efficiency is high.
4. In the production aspect of the ship body mesh, the cubic B spline curve is taken as a tool, the design and reconstruction of a curved surface are not needed, and the method is simpler and more efficient compared with the existing method.
Second, the embodiment provides a ship hydrodynamic prediction system based on a hull wet surface grid in waves;
ship hydrodynamic prediction system based on ship body wet surface grid in waves comprises:
in a third embodiment, the present embodiment further provides an electronic device, which includes a memory, a processor, and a computer instruction stored in the memory and executed on the processor, where when the computer instruction is executed by the processor, each operation in the method is completed, and for brevity, details are not described here again.
The electronic device may be a mobile terminal and a non-mobile terminal, the non-mobile terminal includes a desktop computer, and the mobile terminal includes a Smart Phone (such as an Android Phone and an IOS Phone), Smart glasses, a Smart watch, a Smart bracelet, a tablet computer, a notebook computer, a personal digital assistant, and other mobile internet devices capable of performing wireless communication.
It should be understood that in the present disclosure, the processor may be a central processing unit CPU, but may also be other general purpose processors, digital signal processors DSP, application specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory may include both read-only memory and random access memory, and may provide instructions and data to the processor, and a portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information.
In implementation, the steps of the above method may be performed by integrated logic circuits of hardware in a processor or instructions in the form of software. The steps of a method disclosed in connection with the present disclosure may be embodied directly in a hardware processor, or in a combination of the hardware and software modules within the processor. The software modules may be located in ram, flash, rom, prom, or eprom, registers, among other storage media as is well known in the art. The storage medium is located in a memory, and a processor reads information in the memory and completes the steps of the method in combination with hardware of the processor. To avoid repetition, it is not described in detail here. Those of ordinary skill in the art will appreciate that the various illustrative elements, i.e., algorithm steps, described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is merely a division of one logic function, and there may be other divisions when actually implemented, for example, a plurality of units or components may be combined or may be integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of devices or units through some interfaces, and may be in an electrical, mechanical or other form.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (10)
1. The ship hydrodynamic prediction method based on the ship body wet surface grid in the waves is characterized by comprising the following steps:
reading a model value point of a ship;
according to the type value points on each waterline, inversely calculating a cubic B spline expression of the waterline;
calculating a generalized section curve of the hull shape based on a cubic B spline expression of a waterline;
determining the type of the wave and the expression of the wave surface, and searching an intersection point of the generalized cross-section curve and the instantaneous wave surface according to the type of the wave and the expression of the wave surface so as to obtain a hull wet surface grid in the wave;
and predicting the hydrodynamic force of the ship in the waves based on the ship body wet surface grid in the waves.
2. A method as claimed in claim 1, characterized in that the model point of the vessel is read, first of all the known model points are received as input, and are recordedWherein i represents a waterline mark number of a model value point, the ship base line is 0, the forward direction is increased progressively along the Z axis, and the forward direction of the Z axis is vertically upward; j represents the position of the type value point on the waterline, the first point of the stern is 0, the value is increased along the positive direction of the X axis, and the positive direction of the X axis points to the bow.
3. The method of claim 1, wherein the B-spline representation of the waterline is inverted based on the type point on each waterline;
the method for acquiring the cubic B spline expression of the ith waterline comprises the following steps:
s21, parameterization of shape point: assuming that the ith water line contains n +1 type value points, the type value points on the ith water lineThe value range of the middle j is 0,1, …, n; parameterizing n +1 type value points according to an accumulated chord length method; let diThe total chord length of the ith waterline
Wherein,represents the jth type value point on the ith waterline,representing the j-1 th type value point on the ith waterline;
parameter value corresponding to jth type value point on ith waterlineExpressed as:
wherein,representing the parameter value corresponding to the j-1 model value point on the ith waterline;
constructing node vectorsWherein,
ui,0＝…＝ui,3＝0， (3-1)
ui,n+3＝…＝ui,n+6＝1， (3-2)
wherein u isi,0,ui,1,ui,2,…,ui,n+6Representing each element of a node vector required by defining the cubic B spline expression of the ith waterline;
s22, determination of guide vectors: let the ith waterline first guide vector beThe tail director isTo calculateAndlet the coordinates of two model value points on the ith waterline closest to the stern be
Wherein,representing the nearest type value point coordinate on the ith waterline from the stern;the second nearest type value point coordinate from the stern on the ith waterline is represented;
similarly, let the coordinates of the two model points on the ith waterline closest to the bow be:
wherein,representing the nearest type value point coordinate to the bow on the ith waterline;representing the form value second closest to the bowPoint coordinates;
computingAnd
s23, solving an equation set (8) by adopting cubic B splines according to a back calculation algorithm of given two-end director to obtain the ith waterline control vertex to be solvedj＝0，...，n+2；
Wherein,the 1 st control point coordinate of the cubic B-spline expression representing the ith waterline,the 2 nd control point coordinate of the cubic B-spline expression representing the ith waterline, and so on,the coordinates of the (n + 3) th control point of the cubic B spline expression of the ith waterline are obtained;represents the 1 st type point coordinate on the ith waterline,represents the 2 nd type point coordinate on the ith waterline, and so on,the n +1 model value point coordinate of the ith waterline;is defined in a non-uniform node vectorThe cubic B-spline basis function above, defined as:
wherein u isi,kTo representThe k-th element of (1), ui,k+1To representThe (k + 1) th element in (1), p represents the number of times of the B-spline basis function; u is a variable of the parameter curve, and k is an intermediate variable;
control vertex solved according to equation (8)Coordinated node vectorAnd obtaining a cubic B spline expression of the ith waterline, and recording the cubic B spline expression as:
wherein,obtaining cubic B spline expression of the ith waterline,is defined in a non-uniform node vectorCubic B-spline basis functions above.
4. The method as claimed in claim 1, wherein the generalized cross-sectional curve of the hull form is calculated based on a cubic B-spline expression of the waterline; the method comprises the following specific steps:
dividing each obtained waterline according to equal parameters;
suppose that M grids are adopted in the ship length direction, and the parameter interval [0,1]]Performing M equal division to obtain a parameter vJJ/M (λ 0,1 …, M); v is to beλTaking a cubic B spline expression into the waterline to obtain discrete points uniformly distributed according to parameters on the waterline, and recording the discrete points as
Wherein i represents a vertical index of discrete points, and points on a ship base line are 0 and are positively increased along a Z axis;
j represents that the discrete point horizontal direction index takes the first point of the stern part as 0, the index is increased in the positive direction along the X axis, and U is the number of waterlines;
to obtainAfter that, the subscript J is the same asAnd performing B-spline back calculation on the points again for three times along the vertical direction, and naming the obtained curve as a generalized section curve.
5. The method as claimed in claim 1, wherein since the 0 waterline on the model value table of the hull is given by a base line, and the base line is not the boundary of the hull, when each section curve is back calculated, a zero point is artificially added to each other section curve in addition to the head and tail contour lines;
artificially adding a zero point to each other section curve, and adopting the following marking method to mark points on the head and tail contour lines of the ship:
whereinRepresenting a discrete point column directly obtained from a waterline and used for back-computing the head and tail contour lines of the ship;representing the corrected discrete point array used for back-calculating the head and tail contour lines of the ship;
for points on other cross-sectional curves:
whereinThe discrete point column is used for reversely calculating the J-th section curve after the artificial zero point is added;representing an initial row of points obtained by the waterline; x is the number of0,J,x1,J,x2,JAre respectively a pointX coordinate of (1), y1,J,y2,JAre respectively a pointThe y-coordinate of (a).
6. The method of claim 5, wherein obtaining is accomplished byAfter that, the parameters are correspondingly equalCarrying out B-spline back calculation on the points again for three times along the vertical direction, and naming the obtained curve as a generalized section curve;
the method comprises the following steps of using a dimensionless accumulated chord length parameterization method, and then using a B-spline back calculation method without specifying guide vectors at two ends to calculate a generalized section curve, wherein the method comprises the following steps:
(1)parameterization of (2); selecting a group of identical subscripts JPoint, let its coordinate be (x)i,j,yi,j,zi,j) The value range of i is 0,1, …, S; j ranges from J to 0,1, …, M; wherein,
u is the number of waterlines, and M is the number of grids in the length direction of the ship
Set of identical subscripts JParameterizing the points; order to
Wherein d'JIs the section chord length after dimensionless, L is the ship length, B is the ship width, and T is the draft;
parameter value corresponding to ith point on J-th generalized cross-sectional curveIs shown as
Accordingly, a node vector is constructed
u′0,J＝…＝u′3,J＝0，u′S+1,J＝…＝u′S+4,J＝1，
Wherein u'0,j,u′1,j,…,u′S+4,jThe elements of the node vector required for the cubic B-spline expression of the J-th section curve are represented,representing a parameter value corresponding to the ith data point on the J-th section curve, and determining according to the formula (13);
(2) solving an equation set (15) according to a reverse calculation method without assigned guide vectors to obtain a control vertex of the J-th section curve to be solvedWherein I ═ 0,1, …, S;
is defined in a non-uniform node vectorCubic B-spline basis functions above;representing a parameter value corresponding to the ith data point on the section curve to be obtained;
resulting control verticesCoordinated node vectorAnd obtaining a cubic B spline expression of the J-th generalized section curve, and recording the cubic B spline expression as:
wherein,is the control vertex of the J-th section curve,is defined in a non-uniform node vectorCubic B-spline basis functions above.
7. The method as claimed in claim 1, wherein, first, the value of the parameter u corresponding to the intersection point of the generalized cross-section curve and the instantaneous wave surface on the cross-section curve is found; by adopting a bisection method, continuously dividing the parameter interval into two parts to obtain z coordinates of two end points of the interval, averaging upper and lower limits of the parameter interval when the difference of the z coordinates of the two end points is smaller than a set threshold value, and obtaining an average result, namely a parameter value corresponding to the intersection point of the generalized section curve and the still water surface;
on the basis, according to the type of the given wave and the expression of the wave surface, the corresponding parameter of the intersection point of the section curve and the wave surface on the section curve is further searched and is marked as uend(ii) a The method comprises the following specific steps: recording the x coordinate of the intersection point of the J-th generalized cross-section curve and the still water surface as xJUsing the wave surface equation, the longitudinal coordinate η of the cross-sectional curve at the intersection with the wave surface is obtainedJAgain using the dichotomy, the ordinate of the section curve is obtained to be equal to ηJThe parameter corresponding to the point of (1) is the calculated uend；
From 0 to u of the parametric domain curveendAnd N equal divisions are carried out, and the obtained parameters are substituted into the cross-sectional curve to obtain N grid points of the required instantaneous subsurface cross-sectional curve.
8. Ship hydrodynamic prediction system based on ship body wet surface grid in waves is characterized by comprising:
a type point reading module configured to: reading a model value point of a ship;
a back-calculation module configured to: according to the type value points on each waterline, inversely calculating a cubic B spline expression of the waterline;
a generalized cross-sectional curve computation module configured to: calculating a generalized section curve of the hull shape based on a cubic B spline expression of a waterline;
an in-wave hull wet surface grid acquisition module configured to: determining the type of the wave and the expression of the wave surface, and searching an intersection point of the generalized cross-section curve and the instantaneous wave surface according to the type of the wave and the expression of the wave surface so as to obtain a hull wet surface grid in the wave;
a hydrodynamic prediction module configured to: and predicting the hydrodynamic force of the ship in the waves based on the ship body wet surface grid in the waves.
9. An electronic device comprising a memory and a processor and computer instructions stored on the memory and executable on the processor, the computer instructions when executed by the processor performing the steps of the method of any of claims 1 to 7.
10. A computer-readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the method of any one of claims 1 to 7.
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