CN111597506A - Prediction method for near-shore wave breaking parameters and wave height - Google Patents
Prediction method for near-shore wave breaking parameters and wave height Download PDFInfo
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Abstract
The invention discloses a method for predicting near-shore wave breaking parameters and wave height, in particular to a method for calculating wave breaking parameters by applying a new breaking index formula in a parameterized wave prediction model, simulating and forecasting the wave height based on a wave energy conservation equation. The method has higher prediction precision, and the root mean square percentage error is 7 to 13 percent. Compared with other wave prediction model results of the same type, the prediction precision is improved by 10% -24% (the average improvement is 19%). Especially under the condition of normal waves (the incident wave steepness is less than 0.025), the prediction accuracy is remarkably improved.
Description
Technical Field
The invention belongs to the technical field of simulation and prediction of near-shore waves, and particularly relates to a method for predicting near-shore wave breaking parameters and wave height.
Background
The wave is one of main driving forces of the coast physical process, and the accurate prediction of the wave height has very important significance on the simulation of the evolution of the coast morphology, the design of coast wave-resistant buildings and the planning of the development of marine fishery. In shallow water areas, wave breaking is the dominant process of controlling wave height distribution on the seabed, and also influences the nonlinear form, wave currents, sediment movement and seabed landform evolution of waves.
The parameterized wave prediction model based on time averaging is widely used for the simulation and forecast of the near-shore waves due to high calculation efficiency and calculation accuracy. Such models are based on the conservation equation of wave energy, which considers that the attenuation of wave energy during the propagation of waves from deep sea to shallow water is caused by wave breakup. Therefore, the accuracy of the calculation of the wave energy dissipation caused by wave breaking is a key factor affecting the reliability of the wave forecasting model. Existing models tend to refer to a probabilistic distribution of random wave heights and calculate the wave energy loss beyond the critical wave height. The accuracy of this method of calculating wave energy loss depends on a key parameter in the model, the fragmentation index. However, it is difficult to satisfy the high-precision prediction of the near-shore wave height by using the existing fragmentation index formula, and particularly, the prediction precision needs to be improved under the condition of the normal waves.
Reference documents:
[1]Ruessink,B.G.,Walstra,D.J.R.,and Southgate,H.N.Calibration andverification of a parametric wave model on barred beaches.CoastalEngineering,2003,48:139–149.
[2]Apotsos,A.,Raubenheimer,B.,Elgar,S.,and Guza,R.T.Testing andcalibrating parametric wave ransformation models on natural beaches.CoastalEngineering,2008,55:224–235.
[3]Thornton,E.B.,and Guza,R.T.Transformation of wave heightdistribution.Journal of Geophysical research:Oceans,1983,88(C10):5925–5938.
[4]Janssen,T.T.,and Battjes,J.A.A note on wave energy dissipationover steep beaches.Coastal Engineering,2007,54(9):711–716.
[5]Baldock,T.E.,Holmes,P.,Bunker,S.,and van Weert,P.Cross-shorehydrodynamics within an unsaturated surf zone.Coastal Engineering,1998,34:173–196.
[6]Battjes,J.A,and Janssen,J.P.F.M.Energy loss and set-up due tobreaking of random waves.Proceedings of the 16th International Conference onCoastal Engineering,1978,pp.569–587.
[7]Salmon,J.E.,Holthuijsen,L.H.,Zijlema,M.,van Vledder,G.P.,andPietrzak,J.D.Scaling depth-induced wave-breaking in two-dimensional spectralwave models.Ocean Modelling,2015,600 87:30–47.
[8]Lin,S.,and Sheng J.Assessing the performance of wave breakingparameterizations in shallow waters in spectral wave models.Ocean Modelling,2017,120:41–59.
disclosure of Invention
The purpose of the invention is as follows: aiming at the defects in the prior art, the invention provides a method for predicting the near-shore wave breaking parameters and the wave height, which applies a new breaking index formula in a parameterized wave prediction model to calculate the wave breaking parameters and predict the near-shore wave height, thereby improving the accuracy of wave height prediction.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a method for predicting near-shore wave breaking parameters and wave heights comprises the following steps:
step 3, sequentially calculating the fragmentation index, the fragmentation wave height and the wave energy dissipation of each grid point from the second grid point, and sequentially calculating the wave energy flow of each grid point according to an energy conservation equation;
step 4, calculating the root mean square wave height of each grid point according to the wave energy flow of each grid point obtained in the step 3;
and 5, acquiring measured wave height data in the calculated water area, carrying out error analysis on the measured wave height data and the wave height data obtained in the step 4, and evaluating the accuracy of wave height prediction according to error evaluation indexes.
Further, in step 2, the wave energy flow expression is as follows:
in the formula, FwRepresenting wave energy flow, HrmsIs root mean square wave height, cgThe wave group velocity is shown, theta is a wave direction angle, and rho and g respectively represent the density and the gravity acceleration of the water body; the subscript (n) denotes the nth grid point. The wave group velocity is obtained by linear wave theory calculation, and the root mean square wave height and wave direction angle data of the first grid point are from the wave buoy.
Further, in step 3, the expression of the fragmentation index of the grid point is as follows:
wherein γ is a fragmentation index, s0The subscript (n) represents the nth grid point, n is more than or equal to 2.
Further, in step 3, the expression of the fragmentation wave height of the grid point is:
the wave energy dissipation expression at the grid points is:
according to the energy conservation equation, the wave energy flow expression of the grid point is as follows:
Fw(n)=Fw(n-1)-Db(n)
in the formula, HbThe breaking wave height is determined, gamma is a breaking index, k is a wave number, and h is water depth; dbIs the wave breaking energy dissipation value, α is the coefficient controlling the breaking strength, fpThe frequency of the spectrum peak is shown as rho and g respectively representing the density and the gravity acceleration of the water body, HrmsIs root mean square wave height;FwRepresenting wave energy flow; the subscripts (n) and (n-1) indicate the nth, (n-1) th grid point, n.gtoreq.2.
Further, in the step 4, from the second grid point, the wave group velocity of each grid point is obtained through the linear wave theory calculation, and the wave direction angle of each grid point is calculated by adopting the law of refraction; and (3) substituting the wave energy flow, the wave group velocity and the wave direction angle of each grid point into the formula (1), and calculating to obtain the root mean square wave height of each grid point.
Further, in the step 5, a Root Mean Square Percentage Error (RMSPE) is used as an error evaluation index, and an expression of the error evaluation index is as follows:
in the formula, RMSPE is the root mean square percentage error, N is the total number of grid points, N is the serial number of the grid points, and M and O respectively represent the wave height obtained by the simulation calculation of the grid points and the actually measured wave height. The smaller the RMSPE, the higher the accuracy of the forecast.
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the invention applies a new fragmentation index formula in a parameterized wave prediction model, can obtain high-precision wave height prediction, and has a percentage root mean square error of 7-13%. Compared with the conventional wave prediction model of the same type, the wave height prediction method can improve the overall accuracy of wave height prediction by 10-24%. In addition, the wave height prediction method in the invention can be used for remarkably improving under the condition of normal waves (when the incident wave is steep).
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a graph of the predicted wave height versus the measured wave height for the method of the present invention;
FIG. 3 is a graph comparing the wave height prediction error of the method of the present invention with the error of other wave prediction models;
FIG. 4 is a schematic diagram showing the relationship between the error improvement of the wave height predicted by the method of the present invention and incident wave elements.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
The flow of the method for predicting the near-shore wave breaking parameters and the wave height is shown in figure 1, and the method specifically comprises the following steps:
the wave energy flow expression is:
in the formula, FwRepresenting wave energy flow (unit: kilo-gram per square second), HrmsIs root mean square wave height (unit: meter), cgThe wave group velocity (unit: meter per second), theta is the wave direction angle (radian system), and rho and g respectively represent the density and the gravity acceleration of the water body; the subscript (n) denotes the nth grid point. The wave group velocity is obtained by linear wave theory calculation, and the root mean square wave height and wave direction angle data of the first grid point are from the wave buoy.
Step 3, sequentially calculating the fragmentation index, the fragmentation wave height and the wave energy dissipation of each grid point from the second grid point, and sequentially calculating the wave energy flow of each grid point according to an energy conservation equation;
the crushing index expression of the grid points is as follows:
wherein γ is a fragmentation index, s0The incident wave is steep, the incident wave is obtained through a wave buoy, k is wave number, the wave number is obtained by solving a dispersion equation, h is water depth (unit: meter), subscript (n) represents an nth grid point, and n is more than or equal to 2;
the expression of the height of the fragmentation wave at the grid point is as follows:
the wave energy dissipation expression at the grid points is:
according to the energy conservation equation, the wave energy flow expression of the grid point is as follows:
Fw(n)=Fw(n-1)-Db(n)
in the formula, HbThe breaking wave height is determined, gamma is a breaking index, k is a wave number, and h is water depth; dbIs the wave breaking energy dissipation value, α is the coefficient for controlling the breaking strength, the value is 1, fpThe frequency of the spectrum peak is shown as rho and g respectively representing the density and the gravity acceleration of the water body, HrmsRoot mean square wave height; fwRepresenting wave energy flow; the subscripts (n) and (n-1) indicate the nth, (n-1) th grid point, n.gtoreq.2.
Step 4, calculating the root mean square wave height of each grid point according to the wave energy flow of each grid point obtained in the step 3; the method specifically comprises the following steps:
calculating the wave group velocity of each grid point from the second grid point through a linear wave theory, and calculating the wave direction angle of each grid point by adopting a refraction law; and (3) substituting the wave energy flow, the wave group velocity and the wave direction angle of each grid point into the formula (1), and calculating to obtain the root mean square wave height of each grid point.
And 5, acquiring measured wave height data in the calculated water area, carrying out error analysis on the measured wave height data and the wave height data obtained in the step 4, and evaluating the accuracy of wave height prediction according to error evaluation indexes. In this embodiment, the measured wave height distribution along the way is calculated by downloading the data of the pressure sensor along the way. The comparison of the wave height predicted using the method of the present invention with the measured wave height is shown in figure 2.
The Root Mean Square Percentage Error (RMSPE) is used as an error evaluation index, and the expression is as follows:
in the formula, RMSPE is the root mean square percentage error, N is the total number of grid points, N is the serial number of the grid points, and M and O respectively represent the wave height obtained by the simulation calculation of the grid points and the actually measured wave height. The smaller the RMSPE, the higher the accuracy of the forecast.
In this embodiment, the existing wave prediction models of the same type for comparing the prediction effects include: r2003 model (literature [1 ]); TG1983_ t model (documents [2], [3 ]); JB2007_ t models (documents [2] and [4 ]); b1998_ t model (documents [2], [5 ]); BJ1978_ t model (literature [2], [6 ]); the Sal2015 model (reference [7 ]); l2017 model (document [8 ]).
FIG. 3 shows the root mean square percentage error of predicted wave heights using the method of the present invention compared to the wave prediction model error described above. The errors of the method of the invention on the Duck coast, the Egmond coast and the Terschelling coast are respectively 7%, 13% and 12%, the prediction precision is improved by 22% compared with the R2003 model, the prediction precision is improved by 10% compared with the TG1983_ t model, the prediction precision is improved by 15% compared with the JB2007_ t model, the prediction precision is improved by 17% compared with the B1998_ t model, the prediction precision is improved by 20% compared with the BJ1978_ t model, the prediction precision is improved by 23% compared with the Sal2015 model, and the prediction precision is improved by 24% compared with the L2017 model.
In the embodiment, BSS (Brier Skill score) indexes are introduced to quantitatively evaluate the prediction results of the method and the conventional wave prediction model of the same type, so that the improvement of the accuracy of the wave prediction by using the method is verified.
The BSS index expression is as follows:
wherein, RMSPE(a)Indicating the prediction of wave height using the method of the invention, RMSPE(b)Representing the prediction of wave height using the existing same type of wave prediction model. A BSS value greater than 0 indicates that the accuracy of predicting the wave height using the method of the present invention is higher than using the existing same type of wave prediction model. Conversely, a BSS value less than 0 indicates that the accuracy of the wave height predicted by the method is lower than that of the existing wave prediction model of the same type. The closer the BSS value is to 1, the more remarkable the improvement of the prediction precision is.
FIG. 4 shows the error improvement (compared to the R2003 model) versus incident wave element for the Duck coast for predicting wave height using the method of the present invention. The zero point of the abscissa time corresponds to 12 points on 21/1994-9 (eastern time of the united states). It can be seen from the figure that the BSS value is greater than 1 when the incident wave steepness is less than 0.025. The method provided by the invention has the advantages that the error of predicting the wave height is obviously improved under the condition of normal waves.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiments according to the technical spirit of the present invention are within the scope of the present invention.
Claims (6)
1. A method for predicting near-shore wave breaking parameters and wave heights is characterized by comprising the following steps: the method comprises the following steps:
step 1, acquiring forecast water depth data of a coast and wave data collected by a wave buoy;
step 2, taking the water area between the wave buoy and the shore as a calculation range, dividing the calculation range into grids at equal intervals, enabling the starting point of each grid to be located at the wave buoy, and calculating the wave energy flow of a first grid point according to the collected data of the wave buoy;
step 3, sequentially calculating the fragmentation index, the fragmentation wave height and the wave energy dissipation of each grid point from the second grid point, and sequentially calculating the wave energy flow of each grid point according to an energy conservation equation;
step 4, calculating the root mean square wave height of each grid point according to the wave energy flow of each grid point obtained in the step 3;
and 5, acquiring measured wave height data in the calculated water area, carrying out error analysis on the measured wave height data and the wave height data obtained in the step 4, and evaluating the accuracy of wave height prediction according to error evaluation indexes.
2. The method of predicting near-shore wave breaking parameters and wave heights of claim 1, wherein: in the step 2, the wave energy flow expression is as follows:
in the formula, FwRepresenting wave energy flow, HrmsIs root mean square wave height, cgThe wave group velocity is shown, theta is a wave direction angle, and rho and g respectively represent the density and the gravity acceleration of the water body; the subscript (n) denotes the nth grid point.
3. The method of predicting near-shore wave breaking parameters and wave heights of claim 2, wherein: in step 3, the expression of the fragmentation index of the grid point is as follows:
wherein γ is a fragmentation index, s0The subscript (n) represents the nth grid point, n is more than or equal to 2.
4. The method of predicting near-shore wave breaking parameters and wave heights of claim 3, wherein: in step 3, the expression of the height of the fragmentation wave at the grid point is as follows:
the wave energy dissipation expression at the grid points is:
according to the energy conservation equation, the wave energy flow expression of the grid point is as follows:
Fw(n)=Fw(n-1)-Db(n)
in the formula, HbThe breaking wave height is determined, gamma is a breaking index, k is a wave number, and h is water depth; dbIs the wave breaking energy dissipation value, α is the coefficient controlling the breaking strength, fpThe frequency of the spectrum peak is shown as rho and g respectively representing the density and the gravity acceleration of the water body, HrmsRoot mean square wave height; fwRepresenting wave energy flow; the subscripts (n) and (n-1) indicate the nth, (n-1) th grid point, n.gtoreq.2.
5. The method of predicting near-shore wave breaking parameters and wave height of any of claims 2-4, wherein: step 4, from the second grid point, calculating by a linear wave theory to obtain the wave group velocity of each grid point, and calculating the wave direction angle of each grid point by adopting a refraction law; and (3) substituting the wave energy flow, the wave group velocity and the wave direction angle of each grid point into the formula (1), and calculating to obtain the root mean square wave height of each grid point.
6. The method of predicting near-shore wave breaking parameters and wave heights of claim 1, wherein: in the step 5, the root mean square percentage error is used as an error evaluation index, and the expression is as follows:
in the formula, RMSPE is the root mean square percentage error, N is the total number of grid points, N is the serial number of the grid points, and M and O respectively represent the wave height obtained by the simulation calculation of the grid points and the actually measured wave height.
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
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CN113408179A (en) * | 2021-07-15 | 2021-09-17 | 天津大学 | Dynamic simulation method for calculating real-time wave breaking-caused mixing |
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