CN109145467A - A kind of bed ripples migration prediction technique suitable for typhoon region - Google Patents

A kind of bed ripples migration prediction technique suitable for typhoon region Download PDF

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CN109145467A
CN109145467A CN201810989946.3A CN201810989946A CN109145467A CN 109145467 A CN109145467 A CN 109145467A CN 201810989946 A CN201810989946 A CN 201810989946A CN 109145467 A CN109145467 A CN 109145467A
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wave
typhoon
bed ripples
migration
formula
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CN109145467B (en
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曹高辉
林缅
江文滨
姬莉莉
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Institute of Mechanics of CAS
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Abstract

The bed ripples that the present invention provides a kind of suitable for typhoon region prediction technique of migrating based on statistics, physics and practical three angles proposes the average migration velocity of spectral energy, and prediction result is stable and accurate.It is different from existing scalar form, it calculates typhoon migration process and acts on vector, and influence when to different typhoon different locations is overlapped, it is big according to short time some typhoon influences, but the reason of typhoon influence is cancelled out each other in Long time scale, migration caused by conventional current and wave combined flow is calculated, and predicts long duration waveform with it.The bed ripples waveform that the model of this paper can accurately be fitted typhoon zone has the advantages that high-efficiency high-accuracy compared with existing other methods, the bottom Evolution Forecast that can be used in 10~20 years.

Description

A kind of bed ripples migration prediction technique suitable for typhoon region
Technical field
It is comprehensive when migrating more particularly to the bed ripples of influence area that detects a typhoon a kind of the present invention relates to ocean engineering field The method for closing Nonlinear spectral analysis and wave sediment transport theory.
Background technique
Seabed is richly stored with mineral resources and petroleum resources.It is increasingly withered for the resource that utilizes with land It exhausts, the mankind start more to develop and utilize marine resources.The fast development of marine oil and gas industry in recent years, offshore oil increasingly at For the main source of crude oil in China increment.Seabed sand waves are a kind of very common offshore submarine geomorphies, and vertical profile is in fluctuating Shape.Under the hydrodynamism of ocean, the form of bed ripples and position all change in (year) at any time, belong to unstable landforms class Type.Bed ripples migration may cause the hanging of submarine pipeline (line), or even the weight such as generation fracture, ocean platform are collapsed, channel accretion Big harm.The migration of Accurate Prediction bed ripples can reduce economic loss, and serve the addressing design of ocean engineering structure.
Currently used bed ripples migration Predicting Technique mainly include the following types:
Field measurement: using multi-beam measurement method to more all previous measured knot after the multiple depth of water investigation of bed ripples area progress Fruit determines bed ripples migration direction and migration rate.Apparent this method is costly, and control time by meteorological condition and The restriction of sea situation, interval, at all can not real-time monitoring and prediction bed ripples migrations generally all at 1 year or more.It is predictable not Come, the time of observation and spatial resolution and length are still extremely limited.
Empirical equation calculates: researcher it is believed that under normal circumstances the flowing of nearly bottom be the major impetus of bed ripples migration, Bed ripples migration rate depends primarily on flow velocity size, and migration direction should be consistent with flow velocity direction.Correlative study proposes a system Arrange different bed ripples migration rate calculation formula.These formula are in accordance with the parameters such as bed load discharge, bed ripples wave height to count Bed ripples migration rate is calculated, wherein Sediment Transport rule is sheared flow velocity or mean flow rate calculating by bottom and obtained.These formula are general It is used by engineering circles and mechanics circle, in early days for predicting the bed ripples migration velocity in river.Also have using in Yu Haiyang later The simulation of bed ripples migration, but the bed ripples under the influence of reversing current is migrated and is not suitable for.
Dynamics calculation: its from the formation of the bed ripples in the angle research tide race area that sandy seabed and ocean current interact with Migration.Current coastal waters common in the world and region ocean numerical model include POM, ECOM, ROMS, FVCOM etc., their quilts It is widely used in simulating oceanic tide, flow field and thermohaline field etc..However method haves the characteristics that calculating consumption is big.
Spectral analysis method: bed ripples is regarded as a series of superposition of cosine waves by this method, using bispectral analysis and considers sand Wave it is non-linear, and bed ripples is divided into free wave and forced wave, wherein forced wave is nonlinear terms, describes that asymmetric (spike is flat Bottom or zigzag) bed ripples.But the prediction result of simple spectral analysis method is unstable, and is not suitable for typhoon influence region.
Summary of the invention
When migrating the invention aims to provide a kind of bed ripples of influence area that detects a typhoon, comprehensive Nonlinear spectral analysis With the method for wave sediment transport theory.
Particularly, the present invention provides a kind of bed ripples migration prediction technique suitable for typhoon region, includes the following steps:
Step 100, a period as unit of year is set, takes the sand of Seabed same position two periods of head and the tail Wave image；
Step 200, using spectral analysis method, bed ripples is regarded as to a series of superposition of cosine waves, is obtained by parameter Estimation The linear velocity and order transfer function of wave spectrum, free wave that free wave Fourier transformation obtains calculate the average speed of spectral energy Spend and obtain total migration of bed ripples in the period；
Step 300, the wave height for synthesizing wave in the period in single typhoon and period are calculated first, are recycled non-linear defeated Husky formula calculates its caused Sediment Transport, then Sediment Transport caused by all typhoons of superposition calculation, to obtain the period The migration of typhoon caused by interior all typhoons；
Step 400, typhoon migration is subtracted using total migration to obtain the conventional migration under no typhoon factor, with conventional migration Conventional migration velocity of the bed ripples within the unit time is obtained divided by the period；
It step 500, is that the bed ripples in purpose time can be predicted to cut open according to wave spectrum, order transfer function and conventional migration velocity Face.
In an embodiment of the invention, as follows using spectral analysis method process in the step 200:
Bed ripples is divided into free wave and forced wave, first obtains the bed ripples shape under bed ripples not migration state:
B (x)=a (x)+β a2(x) (1)
Wherein a (x) is a series of input of the superposition formation of cosine waves, and b (x) is output, and β is order transfer function；Li It is characteristic wavelength；Fourier transformation is done simultaneously to formula (1) both sides to obtain:
B (k) is the Fourier transformation of b (x), and A (k) is the Fourier transformation of a (x), carries out diagonal item to above formula and simplifies:
Deformation obtains:
B (k)=H(1)(k)A(k)+J(2)(k)F{a2(x)} (5)
H(1)It (k) is linear first-order transfer function, J(2)It (k) is a square order transfer function, F { } indicates that Fourier becomes It changes, and F-1{ } indicates inverse Fourier transform；
Add time t indicates come the free wave that Seabed develops when obtaining bed ripples migration:
Enable H(1)(k)=1, J(2)(k)=β (k), forced wave is described using order transfer function β (k), by free wave It is superimposed to obtain output waveform with forced wave are as follows:
B (x, t)=a (x, t)+F-1{β(k)F{a2(x,t)}} (7)
So far, the line of non-linear bed ripples is obtained by free wave a (x) or its Fourier transformation wave spectrum A (k), free wave Speed v (k) and order transfer function β (k) realizes description.
In an embodiment of the invention, in the step 200, free wave Fourier is obtained by parameter Estimation and is become The linear velocity of the wave spectrum, free wave got in return and the process of order transfer function are as follows；
Step 210, the spectrum of initial waveform is divided into free wave and forced wave, when primary iteration, it is assumed that free wave is located at spectrum Near spike number, and forced wave obtains free wave wave spectrum A (k) near two times of spectral peak wave number；
Step 211, the output waveform b (x, t) of initial waveform is calculated by formula (6) and formula (7), actual measurement is obtained To waveform diagram be set as targeted graphical z (x, t), targeted graphical z (x, the t) difference for subtracting output waveform b (x, t) is regarded as A series of superposition of cosine waves is simultaneously calculated, and the corresponding obtained wave spectrum of difference is added on the wave spectrum A (k) of initial waveform；
Step 212, it after obtaining new wave spectrum A (k), calculates again, the output waveform b (x, t) for getting back new, according to precision It needs, iterates, until being restrained after achieving the goal.
After obtaining the linear velocity v (k) and order transfer function β (k) of wave spectrum A (k), free wave, spectral energy is average Speed is calculate by the following formula:
U is spectral energy average speed in formula, v (k) and A (k) respectively represent wave number be the corresponding speed of the free wave of k with Spectrum value size；
Bed ripples in calculation interval is always migrated Ls=Utt；ttFor the time interval of initial time and last moment.
In an embodiment of the invention, it in the step 300, calculates and synthesizes wave in the period in single typhoon Wave height and the process in period it is as follows:
Typhoon Wind Field is calculated using Holland pressure model, is described using center of typhoon as the air pressure of the arbitrary section of starting point Distribution calculates are as follows:
In formula, r is distance；P is the air pressure at center of typhoon r；P0For center of typhoon barometric minimum；Δ P=Pn-P0 For center of typhoon air pressure drop, PnFor typhoon peripheral environment air pressure；A and B is typhoon form parameter；
If RmaxFor maximum wind speed radius, Rmax=A1/B, do not consider coriolis force, the wind of typhoon obtained by geostrophic wind equation Fast section:
In formula, VrFor the circulation of typhoon wind speed at center of typhoon r, VRmaxFor circulation maximum wind velocity；
The wave height surged with total wave is first calculated using Qi Chen's gift empirical equation, and the wave height of stormy waves is obtained according to principle of stacking, And then find out wave height and the period of synthesis wave:
H in formularTo synthesize unrestrained wave height, TrFor the superposition of wind wave and swell period；HrfFor stormy waves wave height, TrfFor wind wave periods；HruTo surge Wave height, TruFor the period of surging.
In an embodiment of the invention, in the step 300, Sediment Transport process caused by single typhoon is calculated It is as follows:
The net silt discharge of wave in a cycle in single typhoon is calculated using Watanabe formula:
Q in formulab,netIt is the net silt discharge of single width by volume, d is sediment grain size；ω is silt-settling velocity, ψ Shields Number, wherein critical Shields number ψc=0.11, τbmFor bottom shear stress maximum value, ρ is the density of water, ρsFor silt density, g For acceleration of gravity, fwFor bottom friction coefficient；Bottom level path velocity maximum valueH is the wave of wave Height, T are the period of wave, and k is wave number, and h is the depth of water；
Bottom friction coefficient fwBy calculating with the relational expression of Reynolds number and opposite roughness, process is as follows:
Reynolds number in formulaBottom water particle motion amplitudeksFor bottom roughness height, k is takens =2d90；
The migration rate of bed ripples in single typhoon can be calculated by Rubin formula again:
U in formulagFor bed ripples migration rate, HsFor Sand wave height, γ is deposit bulk density, qsRate is transported for bed-sit.
In an embodiment of the invention, in the step 400, conventional migration velocity V is obtainedcFormula it is as follows:
In formula, ttFor bed ripples migration time, LsAlways to migrate in the period, LtFor the migration of bed ripples caused by the typhoon in the period.
The present invention is based on statistics, physics and practical three angles, propose the average migration velocity of spectral energy, prediction result Stablize and accurate.It is different from existing scalar form, it calculates typhoon migration process and acts on vector, and to different typhoon differences position Influence when setting is overlapped, big according to short time some typhoon influences, but typhoon influence is cancelled out each other in Long time scale Reason calculates migration caused by conventional current and wave combined flow, and predicts long duration waveform with it.The model of this paper can accurately be intended The bed ripples waveform for closing typhoon zone has the advantages that high-efficiency high-accuracy compared with existing other methods, can be used in 10~20 years Bottom Evolution Forecast.
Detailed description of the invention
Fig. 1 is the prediction technique flow diagram of one embodiment of the present invention；
Fig. 2 is northern bay landforms and research area's bottom relief map and diagrammatic cross-section；
Fig. 3 is 2004 and 2007 in Fig. 2 waveform measured values and calculated value schematic diagram；Wherein initial waveform is 2004 The waveform of measurement, target waveform are the waveform of 2007 measurements；
The schematic diagram of stormy waves and superposition of surging when Fig. 4 is typhoon in one embodiment of the present invention；
Fig. 5 is typhoon " Da Wei " movement routine and the wind field schematic diagram that Holland model calculates；
Fig. 6 is that the wave height schematic diagram that area is distinguished and admirable, surges and synthesizes wave is studied caused by typhoon " Da Wei "；
Fig. 7 is that the period schematic diagram that area is distinguished and admirable, surges and synthesizes wave is studied caused by typhoon " Da Wei "；
Fig. 8 is the migration schematic diagram of bed ripples caused by typhoon；
Fig. 9 is that schematic diagram is offset in typhoon interaction；
Figure 10 is bed ripples waveform diagram of the one embodiment of the present invention according to the parameter prediction the year two thousand twenty being calculated.
Specific embodiment
This programme is analyzed with typhoon weather data normal certain time limit, then goes to predict according to obtaining result The bed ripples migration in specified year.Treatment process is as follows: firstly, according at the beginning of the Seabed altitude information of acquisition given two periods Beginning waveform and last moment waveform, such as 2004 to 2007；The total displacement of bed ripples is obtained by spectrum analysis, then, considers typhoon The change of position in migration calculates single platform wind action, and typhoon influences all in the period are superimposed, are just obtained caused by typhoon Total displacement finds in calculating process, although single typhoon may cause the big displacement of bed ripples, in Long time scale not on the same stage Wind effect is cancelled out each other；It is displaced finally, total displacement is subtracted the total typhoon of typhoon, obtains displacement caused by conventional Action of Wave Current, Conventional migration velocity is calculated, i.e., following bed ripples waveform is predicted using the routine migration velocity.
As shown in Figure 1, the disclosed bed ripples migration prediction technique suitable for typhoon region of one embodiment of the invention is general Include the following steps:
Step 100, a period as unit of year is set, takes the sand of Seabed same position two periods of head and the tail Wave image；
Here period can be any one period before prediction year, generally take 3-5.Such as Fig. 2 institute Show, such as takes this period of 04-07, (there are six sections here, i.e., for research area's bottom relief maps in 2004 and profile position P1~P6).WGS84 earth coordinates and Mercator projection (UTM) method are chosen, measurement is obtained into the conversion of longitude and latitude elevation coordinate For XYZ coordinate, and import Surfer software.Multiple sections are intercepted in the apparent region of bed ripples, obtain the position of the whole story point of section Set the bottom height of each point on coordinate and section.Since survey region is far from seashore, so outputting and inputting there is no silt, Only consider the oscillating part that bed surface rises and falls, which is considered the main movable part in corresponding time range.Profile control Dispersed elevation is 0, obtains the waveform in section each year.
Step 200, using spectral analysis method, bed ripples is regarded as to a series of superposition of cosine waves, is obtained by parameter Estimation The linear velocity and order transfer function of wave spectrum, free wave that free wave Fourier transformation obtains；Calculate the average speed of spectral energy Spend and obtain total migration of bed ripples in the period；
When bed ripples to be regarded as to a series of superposition of cosine waves, consider the non-linear of bed ripples, by bed ripples be divided into free wave and Forced wave.
(1) when not considering bed ripples migration, if bed ripples shape is represented by
B (x)=a (x)+β a2(x) (1)
Wherein a (x) is input, and b (x) is output, and β is order transfer function.The a (x) of input is a series of cosine waves Superposition, LiIt is characteristic wavelength.Fourier transformation is done simultaneously to formula (1) both sides to obtain:
B (k) is the Fourier transformation of b (x), and A (k) is the Fourier transformation of a (x), estimates two-parameter secondary transmission letter Number H(2)(k1, k2) a large amount of time is needed, diagonal item is carried out to above formula and is simplified:
Deformation obtains:
B (k)=H(1)(k)A(k)+J(2)(k)F{a2(x)} (5)
H(1)It (k) is linear (single order) transmission function, J(2)It (k) is square (second order) transmission function.F { } indicates Fourier Transformation, and F-1{ } indicates inverse Fourier transform.
According to aforementioned derivation process, it can derive that parameter when bed ripples migration calculates basis.
(2) consider bed ripples migration, time t be added, the linear segment (free wave) that bottom develops indicates are as follows:
Enable H(1)(k)=1, J(2)(k)=β (k), non-linear partial (forced wave) are retouched using order transfer function β (k) It states, is superimposed free wave and forced wave to obtain output waveform are as follows:
B (x, t)=a (x, t)+F-1{β(k)F{a2(x,t)}} (7)
The wave spectrum A (k) that non-linear bed ripples can be obtained by free wave a (x) or its Fourier transformation, the linear velocity of free wave V (k) and order transfer function β (k) are described.
The estimation of parameter A (k), v (k) and β (k) therein, is obtained using following iterative method:
Step1: being divided into free wave and forced wave for the spectrum of initial waveform (such as: the waveform at t=2004 moment), initial to change Dai Shi, it is assumed that free wave is located near spectral peak wave number, and forced wave obtains free wave wave spectrum near two times of spectral peak wave number A(k)；
Step2: b (x, t) is calculated by formula (6) and formula (7)；
Step3: targeted graphical (such as: the waveform at t=2007s moment) is z (x, t), z (x, t)-b (x, t) i.e. targeted graphical With the difference for calculating figure as, difference is regarded to a series of superposition of cosine waves；Here targeted graphical is that actual measurement obtains Waveform diagram z (x, t), calculating waveform is the b (x, t) being calculated with formula (7).
Step4: z (x, t)-b (x, t) is remaining that this part cosine wave calculates, then the initial free wave group that is added to On point, (z (x, t)-b (x, t) is the difference of measured value and calculated value, this partial difference carries out inverse Fourier and changes, and obtains difference Then corresponding wave spectrum is then added to A (k) in step1 above；
Step5: obtaining new free wave spectrum A (k), calculate again, has thus obtained the b (x, t) of second step；
Step6: according to precision needs, iterating, until convergence.
The free wave linear velocity unstable result that result above obtains considers, speed responsing cosine wave phase from statistics angle The change of position, small amplitude wave speed have little significance；Consider from physical angle, bed ripples migration
Based on being translated with bed load, big change will not occur for waveform；Consider from practical term, utilizes energy average speed Error of fitting difference very little, but different periods data prediction result is accurate.From the aspect of above three, and square of amplitude Energy is represented, introduces spectral energy average speed processing spectrum analysis as a result, as follows:
U is spectral energy average speed in formula, v (k) and A (k) respectively represent wave number be the corresponding speed of the free wave of k with Spectrum value size (i.e. free wave amplitude).Bed ripples in calculation interval is always migrated Ls=Utt；ttFor initial time and last moment Time interval.As shown in figure 3, by taking one of profile P 1 as an example: 2004 and 2007 waveform measured values and calculating For value as schemed, initial waveform is the waveform of 2004 measurements, and target waveform is the waveform of 2007 measurements.
Step 300, the wave height for synthesizing wave in the period in single typhoon and period are calculated first, are recycled non-linear defeated Husky formula calculates its caused Sediment Transport, then Sediment Transport caused by all typhoons of superposition calculation, to obtain the period The migration of typhoon caused by interior all typhoons；
Here by taking maximum typhoon " Da Wei " in 2005 as an example, displacement caused by single typhoon is first calculated.
(1) stormy waves and the wave height surged and period during calculating typhoon, and calculate wave height and the period of synthesis wave.
Wave height is larger during typhoon, and comparatively trend effect is small, only considers wave action when so calculating typhoon effect Under bed ripples migration.Consider wave nonlinearity, calculate net silt discharge caused by the asymmetry of wave particle movement, selects Watanabe formula obtains the functional relation of dimensionless silt discharge Yu dimensionless shear stress.Silt-settling velocity uses Rubey formula meter It calculates.
Typhoon Wind Field is calculated using Holland pressure model, is described using center of typhoon as the air pressure of the arbitrary section of starting point Distribution, it is writeable are as follows:
In formula, r is distance；P is the air pressure at center of typhoon r；P0For center of typhoon barometric minimum；Δ P=Pn-P0 For center of typhoon air pressure drop, PnFor typhoon peripheral environment air pressure；A and B is typhoon form parameter, RmaxFor maximum wind speed radius, Rmax=A1/B。
Do not consider coriolis force, by geostrophic wind equation, the wind profile of typhoon can be obtained:
In formula, VrFor the circulation of typhoon wind speed at center of typhoon r, VRmaxFor circulation maximum wind velocity.
In the symmetrical wind field of circle, stormy waves and the synthesis wave direction surged are reduced to as shown in Figure 4.
According to Qi Chen's gift empirical equation of wind (gushing) unrestrained wave height and period, wave height and the period of synthesis wave are calculated, due to wind Field is symmetrical approximate using circle, and the wave height surged with total wave is first calculated using empirical equation, obtains the wave of stormy waves according to principle of stacking Height, and then find out wind, period for surging and synthesis cycle:
H in formularTo synthesize unrestrained wave height, TrFor the superposition of wind wave and swell period；HrfFor stormy waves wave height, TrfFor wind wave periods；HruTo surge Wave height, TruFor the period of surging.
The wind field signal that the above results can be found in typhoon shown in fig. 5 " Da Wei " movement routine and Holland model calculates； The wave height signal that research area is distinguished and admirable caused by typhoon " Da Wei " shown in fig. 6, surges and synthesizes wave；Typhoon shown in Fig. 7 " reaches The period signal that research area is distinguished and admirable caused by dimension ", surges and synthesizes wave.
(2) Sediment Transport caused by single typhoon is calculated；Calculating work is carried out with aforementioned obtained synthesis wave wave height and period With displacement, it is then converted to the direction of section.
Consider net sediment transport caused by wave particle movement asymmetry, calculates wave a cycle using Watanabe formula Interior net silt discharge:
Q in formulab,netIt is the net silt discharge of single width by volume, d is sediment grain size, and ω is silt-settling velocity, with Rubey public affairs Formula calculates, and studying sediment grain size in area is 0.2mm, and ψ is Shields number, wherein critical Shields number ψc=0.11, τbmThe bottom of for Portion's shear stress maximum value, ρ are the density of water, ρsFor silt density, g is acceleration of gravity, bottom level path velocity maximum valueH is the wave height of wave, and T is the period of wave, and k is wave number, and h is the depth of water.
Bottom friction coefficient fwBy being calculated with the relational expression of Reynolds number and opposite roughness:
Reynolds number in formulaBottom water particle motion amplitudeksThe bottom of for Bed roughness height, takes ks=2d90。
The migration rate of bed ripples is calculated using Rubin formula:
U in formulagFor bed ripples migration rate, H is Sand wave height, and γ is deposit bulk density, qsRate is transported (with weight for bed-sit Meter).
Typhoon is typhoon to bed ripples action direction in survey region synthesis wave direction, and approximation takes the heart channel of Hang-Shaoyin in survey region Latitude calculates single typhoon to the effect displacement vector F of bed ripples section as positiont.For different actual measurement bed ripples sections, The size of typhoon effect is related with the difference of its wave height and the depth of water, and the effect that typhoon migrates for bed ripples is effect displacement vector Ft Projection on profile direction.
(3) bed ripples migration L caused by multiple typhoons between calculating 2004-2007t.It is as shown in Figure 8: 04-07 total 85 A typhoon first calculates effect migration vector caused by single typhoon, then will influence to be superimposed caused by typhoons all in the period.By The typhoon effect of Fig. 9 offsets schematic diagram it is found that from 2 past two typhoons of typhoon track 1 and typhoon track, produces conjunction respectively It is opposite for the action direction in bed ripples fortune region at the synthesis wave (i.e. stormy waves+surge) of direction 1 and compound direction 2.
On only a few typhoon that bed ripples generation migration influences, these typhoon wind speed are big and operating path is close is studied All typhoons of 04-07 are calculated to the effect displacement vector F of P1 in regiontFor [- 2.0, -0.7] m, platform wind action is indicated General direction is southwest.By FtProfile direction is projected to, the displacement of section bed ripples generation, 04-07 bed ripples migration-are obtained 0.8m.And it is recognized that while single typhoon may cause the big displacement of bed ripples, but different typhoons act on phase in Long time scale Mutually offset.So typhoon influence displacement can be subtracted in total displacement, displacement caused by conventional Action of Wave Current is obtained, is done with this pre- It surveys.
Step 400, typhoon migration is subtracted using total migration to obtain the conventional migration under no typhoon factor, with conventional migration Conventional migration velocity of the bed ripples within the unit time is obtained divided by the period；
Conventional migration velocityIn formula, ttFor bed ripples migration time, LsAlways to migrate in the period, LtFor the period The migration of bed ripples caused by interior typhoon.
It step 500, is that the bed ripples in purpose time can be predicted to cut open according to wave spectrum, order transfer function and conventional migration velocity Face.
It the wave spectrum that is obtained using step 200, order transfer function and is predicted with routine migration velocity obtained in step 400 The bed ripples section in purpose time.Effect is as shown in Figure 10.
The present invention is based on statistics, physics and practical three angles, propose the average migration velocity of spectral energy, prediction result Stablize and accurate；It is different from existing scalar form, it calculates typhoon migration process and acts on vector, and to different typhoon differences position Influence when setting is overlapped；It was found that short time some typhoon influences are big, but typhoon influence is cancelled out each other in Long time scale, meter Migration caused by conventional current and wave combined flow is calculated, and predicts long duration waveform with it.The model of this paper can accurately be fitted typhoon The bed ripples waveform in area has the advantages that high-efficiency high-accuracy compared with existing other methods, and the bottom that can be used in 10~20 years is drilled Become prediction.
So far, although those skilled in the art will appreciate that present invention has been shown and described in detail herein multiple shows Example property embodiment still without departing from the spirit and scope of the present invention, still can according to the present disclosure directly Determine or deduce out many other variations or modifications consistent with the principles of the invention.Therefore, the scope of the present invention is understood that and recognizes It is set to and covers all such other variations or modifications.

Claims (6)

  1. The prediction technique 1. a kind of bed ripples suitable for typhoon region is migrated, which comprises the steps of:
    Step 100, a period as unit of year is set, takes the bed ripples figure of Seabed same position two periods of head and the tail Picture；
    Step 200, using spectral analysis method as, bed ripples is regarded to a series of superposition of cosine waves, freedom is obtained by parameter Estimation The linear velocity and order transfer function of wave spectrum, free wave that wave Fourier transformation obtains calculate spectral energy average speed simultaneously Obtain total migration of bed ripples in the period；
    Step 300, the wave height for synthesizing wave in the period in single typhoon and period are calculated first, recycle non-linear sediment transport public Formula calculates its caused Sediment Transport, then Sediment Transport caused by all typhoons of superposition calculation, to obtain institute in the period There is the migration of typhoon caused by typhoon；
    Step 400, subtract typhoon migration using total migration with obtain under no typhoon factor it is conventional migrate, with conventional migration divided by The period obtains conventional migration velocity of the bed ripples within the unit time；
    It step 500, is the bed ripples section in predictable purpose time according to wave spectrum, order transfer function and conventional migration velocity.
  2. The prediction technique 2. bed ripples according to claim 1 is migrated, which is characterized in that
    It is as follows using spectral analysis method process in the step 200:
    Bed ripples is divided into free wave and forced wave, first obtains the bed ripples shape under bed ripples not migration state:
    B (x)=a (x)+β a2(x) (1)
    Wherein a (x) is a series of input of the superposition formation of cosine waves, and b (x) is output, and β is order transfer function；LiIt is feature Wavelength；Fourier transformation is done simultaneously to formula (1) both sides to obtain:
    B (k) is the Fourier transformation of b (x), and A (k) is the Fourier transformation of a (x), carries out diagonal item to above formula and simplifies:
    Deformation obtains:
    B (k)=H(1)(k)A(k)+J(2)(k)F{a2(x)} (5)
    H(1)It (k) is linear first-order transfer function, J(2)It (k) is a square order transfer function, F { } indicates Fourier transformation, and F-1{ } indicates inverse Fourier transform；
    Add time t indicates come the free wave that Seabed develops when obtaining bed ripples migration:
    Enable H(1)(k)=1, J(2)(k)=β (k), forced wave is described using order transfer function β (k), by free wave and beam Wave is tied up to be superimposed to obtain output waveform are as follows:
    B (x, t)=a (x, t)+F-1{β(k)F{a2(x,t)}} (7)
    So far, the linear velocity v of non-linear bed ripples is obtained by free wave a (x) or its Fourier transformation wave spectrum A (k), free wave (k) and order transfer function β (k) realizes description.
  3. The prediction technique 3. bed ripples according to claim 2 is migrated, which is characterized in that
    In the step 200, by parameter Estimation obtain the linear velocity of wave spectrum, free wave that free wave Fourier transformation obtains with And the process of order transfer function is as follows；
    Step 210, the spectrum of initial waveform is divided into free wave and forced wave, when primary iteration, it is assumed that free wave is located at spectral peak wave Near number, and forced wave obtains free wave wave spectrum A (k) near two times of spectral peak wave number；
    Step 211, the output waveform b (x, t) of initial waveform is calculated by formula (6) and formula (7), actual measurement is obtained Waveform diagram is set as targeted graphical z (x, t), regards targeted graphical z (x, the t) difference for subtracting output waveform b (x, t) as a series of The superposition of cosine wave is simultaneously calculated, and the corresponding obtained wave spectrum of difference is added on the wave spectrum A (k) of initial waveform；
    Step 212, it after obtaining new wave spectrum A (k), calculates again, the output waveform b (x, t) for getting back new, according to precision need It wants, iterates, until being restrained after achieving the goal.
    After obtaining the linear velocity v (k) and order transfer function β (k) of wave spectrum A (k), free wave, spectral energy average speed It is calculate by the following formula:
    U is spectral energy average speed in formula, and v (k) and A (k) respectively represent wave number as the corresponding speed of the free wave of k and frequency spectrum It is worth size；
    Bed ripples in calculation interval is always migrated Ls=Utt；ttFor the time interval of initial time and last moment.
  4. The prediction technique 4. bed ripples according to claim 3 is migrated, which is characterized in that
    In the step 300, calculates the wave height for synthesizing wave in the period in single typhoon and the process in period is as follows:
    Typhoon Wind Field is calculated using Holland pressure model, is described using center of typhoon as the gas pressure distribution of the arbitrary section of starting point, It calculates are as follows:
    In formula, r is distance；P is the air pressure at center of typhoon r；P0For center of typhoon barometric minimum；Δ P=Pn-P0For platform Wind central gas pressure drop, PnFor typhoon peripheral environment air pressure；A and B is typhoon form parameter；
    If RmaxFor maximum wind speed radius, Rmax=A1/B, do not consider coriolis force, cutd open by the wind speed that geostrophic wind equation obtains typhoon Face:
    In formula, VrFor the circulation of typhoon wind speed at center of typhoon r, VRmaxFor circulation maximum wind velocity；
    The wave height surged with total wave is first calculated using Qi Chen's gift empirical equation, the wave height of stormy waves is obtained according to principle of stacking, in turn Find out wave height and the period of synthesis wave:
    H in formularTo synthesize unrestrained wave height, TrFor the superposition of wind wave and swell period；HrfFor stormy waves wave height, TrfFor wind wave periods；HruFor wave height of surging, TruFor the period of surging.
  5. The prediction technique 5. bed ripples according to claim 4 is migrated, which is characterized in that
    In the step 300, it is as follows to calculate Sediment Transport process caused by single typhoon:
    The net silt discharge of wave in a cycle in single typhoon is calculated using Watanabe formula:
    Q in formulab,netIt is the net silt discharge of single width by volume, d is sediment grain size；ω is silt-settling velocity, and ψ is Shields number, In critical Shields number ψc=0.11, τbmFor bottom shear stress maximum value, ρ is the density of water, ρsFor silt density, g is gravity Acceleration, fwFor bottom friction coefficient；Bottom level path velocity maximum valueH is the wave height of wave, and T is The period of wave, k are wave number, and h is the depth of water；
    Bottom friction coefficient fwBy calculating with the relational expression of Reynolds number and opposite roughness, process is as follows:
    Reynolds number in formulaBottom water particle motion amplitudeksFor bottom roughness height, k is takens= 2d90；
    The migration rate of bed ripples in single typhoon can be calculated by Rubin formula again:
    U in formulagFor bed ripples migration rate, HsFor Sand wave height, γ is deposit bulk density, qsRate is transported for bed-sit.
  6. The prediction technique 6. bed ripples according to claim 5 is migrated, which is characterized in that
    In the step 400, conventional migration velocity V is obtainedcFormula it is as follows:
    In formula, ttFor bed ripples migration time, LsAlways to migrate in the period, LtFor the migration of bed ripples caused by the typhoon in the period.
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