CN1424229A - Precisive smoothing methdd for shell moulding - Google Patents

Abstract

A precise fairing method for lofting ship hull includes such steps as creating a cubic spline function according to the values of several offset points on contour of ship hull, finding out the spline coefficient and shear saltus of each offset point, judging the positive or negative sign of the shear saltuses for two adjacent offset points, regulating their values until it is not greater than 3 mm, repeating above steps until there is no excessive flex point, and repeating above steps until there is no excessive concave-convex shape. Its advantages are high automatization level, and short period.

Description

The accurate method for fairing of shell setting-out

Technical field

The present invention relates to a kind of method of building shell, particularly a kind of accurate method for fairing of shell setting-out.

Background technology

The hull design data provide without setting-out, only swollen flat phenomenon can appear in the shell external form of producing according to these data, consequently partly its outward appearance is quite ugly at the water surface, underwater portion then running resistance increases, carry out fairing so will set up the function batten to each bar shell molded lines such as waterline, buttock line, station track etc., the shell external form of producing according to the data after the fairing is stream line pattern, realizes that it is specious, the purpose that running resistance is little.

The shell setting out method is to set up math modeling according to designing requirement at present, as function cubic spline, parametric cubic batten, non-uniform rational B-spline etc., use several different methods, carry out fairing processing as method of least square, circle rate serial method etc., its defective is that the effect of fairing is undesirable, sometimes need manually to adjust repeatedly, and the efficient of fairing is low, the shell fairing time of a ship is 1～3 month.

Summary of the invention

A kind of accurate method for fairing of shell setting-out is included in the value that shell treats to get on the molded lines of fairing n data point, and the first derivative values at place, two ends, and the precise light of this molded lines is along adopting following steps:

A) set up cubic spline function, this function is expressed a curve of crossing n data point and the satisfied end points first derivative of giving, tries to achieve the spline coefficients at each data point place by cubic spline function, and a given n data point is (x _i, y _i), set 1≤i≤n, x _i＜x _I+1, 1≤i≤n-1, and the first derivative of two-end-point is y ₁' and y _n', then the expression formula of cubic spline function y (x) is: $y\left(x\right)=y_i+\frac{y_{i+1}-y_i}{x_{i+1}-x_i}(x-x_i)-\frac{(x-x_i)(x_{i+1}-x)}{x_{i+1}-x_i}[c_i({2x}_{i+1}-x-x_i)+c_{i+1}(x_{i+1}-x-{2x}_i)]$

X in the formula _i≤ x≤x _I+1, c _iBe spline coefficients, 1≤i≤n, and try to achieve the shearing jerk e at each data point place _i, its expression formula is $e_i=\frac{c_{i+1}-c_i}{x_{i+1}-x_i}-\frac{c_i-c_{i-1}}{x_i-x_{i-1}},$ 2≤i in the formula≤n-1 judges the adjacent two shearing jerk product e of data point place one by one _I-1E _i, e _iE _I+1, e _I+1E _I+2Sign, adjust the value of these data points repeatedly, till adjustment amount is not more than 3mm;

B) according to the value of n the data point that obtains after the steps A fairing just, set up the cubic spline function curve again, when this curve has unnecessary flex point to exist, make the interval at unnecessary flex point place, press from left to right, for continuous spline coefficients symbol more than 3 and 3 occur+-+,-+-and+--+,-++-,+-...-+,-+... +-, adjust the value of each data point repeatedly, adhere to specification and till the total flex point number of curve is less than or equal to design flex point number up to the symbol of the spline coefficients at two-end-point place;

C) according to the value of each data point that obtains after the fairing among steps A fairing just and the B, set up the cubic spline function curve again, by end points and normal flex point SPL is divided into m segment, each segment is made the interval at the flat place of unnecessary distension, press from left to right, when contrary sign being arranged, then adjust the value of described interval data point repeatedly, till the symbol of shearing jerk reaches continuous at least 5 jack per lines for the symbol of the shearing jerk that is not more than 5 data points continuously.

The fairing that above-mentioned steps A, B, C carry out is called fairing just, middle fairing, with nothing left suitable, and each step is calculated adjustment amount by the formula of this programme, adjusts, and these calculating and being adjusted under the control of fairing criterion software are finished automatically by computing machine.Advantage of the present invention is to have realized shell setting-out automation, and the setting-out cycle is short, and the shell of a ship of setting-out only needs a week, and can reach the suitable effect of precise light.

Description of drawings

Fig. 1 is the original curvature figure of a first post line.

Fig. 2 is the same first post line curvature chart after fairing just and middle fairing again.

Fig. 3 be same first post line through with nothing left along after curvature chart.

Fig. 4 is that single molded lines precise light is along program flow diagram.

The specific embodiment

A kind of accurate method for fairing of shell setting-out, fairing with the first post line of certain shell is an example, the original curvature of this head post line is shown in Fig. 1, and the first post line curvature in steps A fairing just and B after the fairing is shown in Fig. 2, again through step C with nothing left along after first post line curvature be shown in Fig. 3.Its flex point number of first post line after steps A, B, C fairing, shearing jerk symbol, swollen flat degree all satisfy the requirement of industrial applicibility.

Its single molded lines program flow diagram of the shell setting-out of above-mentioned steps as shown in Figure 4, from beginning P1, through input data P2, set up set of equations, ask splines FACTOR P 3, the unit's of asking spline coefficients and shearing jerk P4, enter and judge whether fairing P5 just, fairing P7 during if whether fairing then directly enters at the beginning of need not, be that fairing just is then by first fairing P6, fairing P7 in then judging whether, if whether fairing then directly enters with nothing left along P9 in need not, being whether middle fairing is then with nothing left along P9 by going unnecessary flex point P8 to enter, if need not the with nothing left suitable end of run P11 that then declares, is with nothing left suitable then through removing the flat P10 end of run of unnecessary distension P11.

List of references Su Buqing Liu Ding unit's work " computational geometry ", Shanghai science tech publishing house (Shanghai), 1980;

Claims (1)

1. the accurate method for fairing of a shell setting-out is included in the value that shell treats to get on the molded lines of fairing n data point, and the first derivative values at place, two ends, and the precise light of this molded lines is along adopting following steps:

A) set up cubic spline function, this function is expressed a curve of crossing n data point and the satisfied end points first derivative of giving, tries to achieve the spline coefficients at each data point place by cubic spline function, and a given n data point is (x _i, y _i), set 1≤i≤n, x _i＜x _I+1, 1≤i≤n-1, and the first derivative of two-end-point is y ₁' and y _n', then the expression formula of cubic spline function y (x) is: $y\left(x\right)=y_i+\frac{y_{i+1}-y_i}{x_{i+1}-x_i}(x-x_i)-\frac{(x-x_i)(x_{i+1}-x)}{x_{i+1}-x_i}[c_i({2x}_{i+1}-x-x_i)+c_{i+1}(x_{i+1}-x-{2x}_i)]$

X in the formula _i≤ x≤x _I+1, c _iBe spline coefficients, 1≤i≤n, and try to achieve the shearing jerk e at each data point place _i, its expression formula is $e_i=\frac{c_{i+1}-c_i}{x_{i+1}-x_i}-\frac{c_i-c_{i-1}}{x_i-x_{i-1}},$ 2≤i in the formula≤n-1 judges the adjacent two shearing jerk product e of data point place one by one _I-1E _i, e _iE _I+1, e _I+1E _I+2Sign, adjust the value of these data points repeatedly, till each adjustment amount is not more than 3mm;

B) according to the value of n the data point that obtains after the steps A fairing just, set up the cubic spline function curve again, when this curve has unnecessary flex point to exist, make the interval at unnecessary flex point place, press from left to right, for continuous spline coefficients symbol more than 3 and 3 occur+-+,-+-and+--+,-++-,+-...-+,-+... +-, adjust the value of each data point repeatedly, adhere to specification and till the total flex point number of curve is less than or equal to design flex point number up to the symbol of the spline coefficients at two-end-point place;

C) according to the value of each data point that obtains after the fairing among steps A fairing just and the B, set up the cubic spline function curve again, by end points and normal flex point SPL is divided into m segment, each segment is made the interval at the flat place of unnecessary distension, press from left to right, when contrary sign being arranged, then adjust the value of described interval data point repeatedly, till the symbol of shearing jerk reaches continuous at least 5 jack per lines for the symbol of the shearing jerk that is not more than 5 data points continuously.

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