CN102270254B - Fatigue design method for deep water riser - Google Patents

Abstract

The invention belongs to the technical field of ocean oil and gas equipment, in particular relates to a fatigue design method for a deep water riser. In the method, while the fatigue damage of the deep water riser is considered, a coupling effect of a floating platform vortex-induced motion and riser vortex-induced vibration, influence of the fatigue damage caused by short-term flow on the fatigue damage accumulation of the deep water riser, influence of the fatigue damage caused by floating platform vortex-induced motion and the short-term flow on the fatigue damage of the riser, and influence of the fatigue damage caused by extreme wave load on the fatigue damage of the riser are considered. The fatigue design method for the deep water riser more accords with the actual fatigue damage accumulation nature of the deep water riser, the well-known Miner's linear damage accumulation standard, and current environment load variation tendency and characteristics, and is more scientific, more reasonable, and more safe and reliable in a design result.

Description

A kind of Fatigue Design Methods of Deepwater Risers

Technical field

The invention belongs to marine oil and gas equipment Design technology, be specifically related to a kind of Fatigue Design Methods of Deepwater Risers.

Background technology

Ocean deepwater standpipe is one of important component part in modern marine engineering structure system, is also one of member of weak rapid wear simultaneously.Ocean deepwater riser interiors generally has the former oil and gas of High Temperature High Pressure to pass through, and the effect of wave, ocean current load is born in outside, and due to the complicacy of the residing marine environment of Deepwater Risers, its affected factor of institute is also many.Fatigue damage is the main damage form of Deepwater Risers, and therefore, the fatigue design of Deepwater Risers is the key of Deepwater Risers design.

Existing Deepwater Risers Fatigue Design Methods mainly adopts S-N curve method, and the method is mainly based on linear cumulative damage criterion (known method):

$D=\underset{i}{\overset{m}{\mathrm{\Σ}}}\frac{n_i}{N_i}\≤\frac{1}{f}---\left(1\right)$

In above formula: D is the fatigue damage summation that various long-range circumstances loads (comprising wave, stream and platform motion) cause; n _ifor the cycle index of a certain stress amplitude, by calculating; N _ifor this stress amplitude causes the cycle index that fatigure failure is required, from the curve of fatigue (different materials, different structure and varying environment condition have different S-N curves for S-N curve, known curve) of vertical tube structure material; M is the number that causes the different stress amplitudes of fatigue damage; F is design fatigue safety coefficient.

For the fatigue design of Deepwater Risers, above formula can specifically be expressed as:

$D=(D_{\mathrm{wave}}+D_{\mathrm{LTVIV}}+D_{\mathrm{LTVIM}})\≤\frac{1}{f}---\left(2\right)$

In formula: D _wavethe fatigue damage causing for wave load; D _lTVIVfor the fatigue damage that stream vortex-induced vibration causes for a long time; D _lTVIMfor swashing kinetic standpipe fatigue damage in floating platform whirlpool under long-term stream effect.

Due to the statistics Yi Nianwei unit of long-range circumstances load (stormy waves stream), be that probability of happening, action direction and the intensity of load normally be take year as reoccurrence period statistics, so the standpipe fatigue damage D that formula (2) calculates is annual damage ratio.Therefore, design can be calculated by following formula (known method) fatigue lifetime:

If the fatigue damage that different loads cause adopts different design safety factor (DSF)s, formula (3) can be expressed as (known method):

In formula: f _wavedesign fatigue safety coefficient for wave load; f _lTVIVdesign fatigue safety coefficient for long-term stream vortex-induced vibration; f _lTVIMfor considering that under long-term stream effect, the design fatigue safety coefficient that motion causes standpipe fatigue damage is swashed in floating platform whirlpool.

The fatigue damage causing for short-term stream vortex-induced vibration, existing technology is not accumulated in the fatigue damage (formula (2)) that long-range circumstances load causes, but employing formula (5) and formula (6) are calculated separately:

$D_{\mathrm{STVIV},L}\≤\frac{1}{f_{\mathrm{STVIV},L}}---\left(5\right)$

$D_{\mathrm{STVIV},S}\≤\frac{1}{f_{\mathrm{STVIV},S}}---\left(6\right)$

In formula: D _{sTVIV, L}and f _{sTVIV, L}be within 100 years one, to meet vortex-induced vibration fatigue damage and the design fatigue safety coefficient thereof that circulation causes; D _{sTVIV, S}and f _{sTVIV, S}be within 100 years one, to meet vortex-induced vibration fatigue damage and the design fatigue safety coefficient thereof that undercurrent causes.

Prior art is not calculated short-term stream (meet circulation for 100 years one or meet undercurrent for 100 years one) the lower floating platform of effect whirlpool and is swashed kinetic standpipe fatigue damage, do not calculate the fatigue damage that Mechanics of Extreme Wave (10 years one chances, 50 years chance or 100 years one chances) causes, because the probability of happening of past short-term stream and Mechanics of Extreme Wave is smaller yet.

There are following four obvious deficiencies in prior art:

1. floating platform whirlpool is swashed to fatigue damage that vortex-induced vibration that the vertical fatigue damage of kinetic deep water and standpipe produce under ocean current direct effect causes independent calculating respectively, then the two is carried out to linear superposition and calculate the fatigue damage that long-term stream causes, this is a large shortcoming of prior art.Because, standpipe is that (tubular platform passes through guide ring by certain connected mode, tension leg platform (TLP) passes through stretcher) flexibly connect with floating platform, and the vortex-induced vibration of the sharp motion in the whirlpool of floating platform and standpipe produces under ocean current acts on simultaneously, because the diameter (18～28m) of floating platform is far longer than the diameter (0.3～0.5m) of standpipe, therefore, while being subject to the action of ocean current of identical flow velocity simultaneously, act on floating platform all different with whirlpool induced lift force size (relevant from cylinder diameter) and frequency (relevant with cylinder diameter) on standpipe, thereby motion is swashed in the whirlpool of floating platform, (floating platform rigidity is large, do not occur bending and deformation, belong to rigid motion, therefore, be called whirlpool and swash " motion ", but still be reciprocal vibration, rather than the motion as boats and ships.) all different with vortex-induced vibration (reciprocal elastic bending deflection) frequency of standpipe and amplitude, and the two move through to connect and interact, be that a kind of coupling fortune (shaking) is moving.Because vibration (vibration) frequency of the two is different with amplitude, therefore, between the vibration of floating platform and the vibration of standpipe, have phase differential, and this phase differential is constantly to change.This coupled relation that swash between motion and riser vortex excited vibration in floating platform whirlpool can not calculate by the two simple linear superposition, and only, when the phase differential of the two is zero, simple linear superposition is only feasible.Therefore, prior art adopt the method calculate respectively again linear superposition to calculate floating platform whirlpool to swash the standpipe fatigue damage that motion and ocean current cause be inaccurate.

2. the fatigue damage that pair short-term stream vortex-induced vibration causes is independently calculated check, does not consider the impact on standpipe accumulation of fatigue damage of fatigue damage that short-term stream vortex-induced vibration causes, and this is the another shortcoming of prior art.The fatigue damage of structure is a kind of cumulative effect, and within the military service phase of structure, the fatigue damage that any type of load causes all will be accumulated in the damage of structure, will never be because of the disappearance of load " healing ".Therefore, whether the load of which kind of form no matter when occurring in the structure military service phase and this load occur repeatedly, and its fatigue damage once causing all will be accumulated in the damage of structure, thereby the degree of injury of structure is increased.Although short-term stream is not etesian, if the short-term stream that occurred of standpipe military service initial stage, the fatigue damage accumulation that the fatigue damage that it causes so must cause with follow-up any form load and affect the safety of standpipe.Therefore, prior art does not consider that the fatigue damage that short-term stream vortex-induced vibration causes is irrational to the cumulative effect of standpipe fatigue damage.

3. do not consider that floating platform whirlpool that short-term stream causes swashs the impact on Deepwater Risers fatigue damage of fatigue damage that motion causes, this is the 3rd shortcoming of prior art.The intensity of short-term stream is large, and it will cause that floating platform significantly swashs motion (resonance) in whirlpool, therefore, should not ignore the standpipe fatigue damage that it causes.This is only one, and it two is that the probability of happening of short-term stream increases gradually, and the definition that tradition is met for 100 years by the phenomenon that Return period is even met for a year is at present negated.Even if the standpipe that the next year after short-term stream occurs installs, also may occur for the second time in its military service phase in 20 years and for the third time.So, do not consider that the sharp fatigue damage causing of moving in floating platform whirlpool that short-term stream causes will directly cause unsafe fatigue design to the impact of Deepwater Risers fatigue damage.Therefore, prior art does not consider that the sharp standpipe fatigue damage causing of moving in floating platform whirlpool that short-term stream causes does not meet engineering reality.

4. do not consider the impact on Deepwater Risers fatigue damage of fatigue damage that Mechanics of Extreme Wave load causes, this is the 4th shortcoming of prior art.Because even if the probability of happening of Mechanics of Extreme Wave load is low, but still may occur in the military service phase of 20 years at standpipe.The definition of meeting for 50 years one is not to occur once for every 50 years, therefore, even met the standpipe of the next year installation after wave occurs at 50 years one, within its military service phase in 20 years, also may there is once again to meet for 50 years one the wave load of even meeting for 100 years, moreover the actual military service phase of standpipe tends to extend because of the needs of oil-field development.And in recent years due to reasons such as climate changes, the Frequency of extreme environmental conditions is more and more higher, the wave load of meeting for 50 years one or meet for 100 years of past definition has been gradually become the disaster of " taking place frequently " by original " accidental " phenomenon.So, for the such important structure thing of Deepwater Risers (say its important be because, once have an accident, the economic loss causing and political fallout will be huge) do not consider that the fatigue damage that Mechanics of Extreme Wave load causes is inaccurate on the impact of Deepwater Risers fatigue damage.

Summary of the invention

The object of the invention is to the defect on Deepwater Risers fatigue design for prior art, a kind of more rationally and more Deepwater Risers Fatigue Design Methods of science is provided.

Technical scheme of the present invention is as follows: a kind of Fatigue Design Methods of Deepwater Risers, comprising:

The standpipe fatigue damage rate that the calculation of design parameters Long-Term Wave load of the wave speckle pattern based on Deepwater Risers design object marine site, corresponding S-N curve and floating platform and standpipe causes unit is 1/ year, wherein, and n1 _ithe cycle index of i the stress amplitude causing for Long-Term Wave load, N1 _ifor the required cycle index of fatigure failure occurs under this stress amplitude effect, S1 is the number of the different stress amplitudes of the standpipe that causes of annual Long-Term Wave load;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the long-term stream of calculation of design parameters of the ocean current data based on Deepwater Risers design object marine site, corresponding S-N curve and floating platform and standpipe causes and riser vortex excited vibration cause unit is 1/ year, wherein, and n2 _ifor the cycle index of i the stress amplitude that under long-term stream effect, the sharp motion in floating platform whirlpool and riser vortex excited vibration cause, N2 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S2 is for swashing the number of the motion different stress amplitudes of standpipe that excited vibration causes with riser vortex in floating platform whirlpool under annual long-term stream effect;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting circulation data, corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and the vortex-induced vibration of standpipe cause unit is 1/ time, wherein, and n3 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that motion and riser vortex excited vibration cause swashed in floating platform whirlpool under circulation effect, N3 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S3 is the number of meeting the sharp motion in the floating platform whirlpool different stress amplitudes of standpipe that excited vibration causes with riser vortex under circulation effect for each 100 years;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting undercurrent data, corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and the vortex-induced vibration of standpipe cause unit is 1/ time, wherein, and n4 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that motion and riser vortex excited vibration cause swashed in floating platform whirlpool under undercurrent effect, N4 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S4 is the number of meeting the sharp motion in the floating platform whirlpool different stress amplitudes of standpipe that excited vibration causes with riser vortex under undercurrent effect for each 100 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 10 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n5 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 10 years, N5 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S5 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 10 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 50 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n6 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 50 years, N6 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S6 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 50 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 100 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n7 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 100 years, N7 _ifor the required cycle index of fatigure failure that this stress amplitude causes, S7 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 100 years;

Based on Fatigue Design Criterion, by following formula, carry out the fatigue design of standpipe and check:

D＝(D _wave×f _wave+D _LTVIM+LTVIV×f _LTVIM+LTVIV)×n _life+(D _{STVIM，L+STVIV，L}×n _loop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV+(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave≤1

Can be calculated as follows the designed life of standpipe:

n _life＝[1-(D _{STVIM，L+STVIV，L}×n _loop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV-(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave]/(D _wave×f _wave+D _LTVIM+LTVIV×f _LTVIM+LTVIV)

In above formula, f _wavefor the design fatigue safety coefficient of Long-Term Wave load, f _lTVIM+LTVIVfor the design fatigue safety coefficient of long-term stream load, f _sTVIM+STVIVfor the design fatigue safety coefficient of short-term stream load, f _extremewavefor the design fatigue safety coefficient of Mechanics of Extreme Wave load, n _lifefor standpipe designed life, n _loopfor within 100 years one, meeting the prediction frequency of circulation, n in phase designed life _subfor within 100 years one, meeting the prediction frequency of undercurrent, n in phase designed life _{wave, 10}for within 10 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 50}for within 50 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 100}for within 100 years one, meeting the prediction frequency of wave load in phase designed life.

Beneficial effect of the present invention is as follows: Deepwater Risers Fatigue Design Methods provided by the present invention has been considered the coupling effect of the sharp motion in floating platform whirlpool and riser vortex excited vibration, considered the impact on Deepwater Risers accumulation of fatigue damage of fatigue damage that short-term stream causes, considered that floating platform whirlpool that short-term stream causes swashs the impact on standpipe fatigue damage of fatigue damage that motion causes, considered the impact on standpipe fatigue damage of fatigue damage that Mechanics of Extreme Wave load causes, the simple linear stack of calculating than the non-coupling of existing method is more scientific, more meet the natural law, and more meet the Fatigue Damage Process of structure.

Embodiment

Below in conjunction with embodiment, describe the present invention.

Short-term stream is the high current field of a kind of " accidental ", but owing to not being etesian environmental phenomenon, therefore, existing Deepwater Risers Fatigue Design Methods is in the design of calculating standpipe during fatigue lifetime, do not consider the fatigue damage that short-term stream vortex-induced vibration causes, that is while, calculating accumulation of fatigue damage, do not comprise the fatigue damage that short-term stream causes.But due to the intensity large (flow velocity is large) of short-term stream, the fatigue damage that existing Deepwater Risers fatigue design causes short-term stream is calculated individually.This is obviously irrational, because the fatigue damage that short-term stream causes is not by with the disappearance of short-term stream " healing ", it will be present among standpipe and with original fatigue damage and follow-up fatigue damage accumulation, with total accumulation of fatigue damage effect Damage Structure safety, rather than be independent of the independent Damage Structure safety of fatigue damage of other form.Therefore, the fatigue design of Deepwater Risers should be considered the impact of short-term stream vortex-induced vibration fatigue.

Mechanics of Extreme Wave load referred within longer a period of time may only there is wave load once, as 50 years or 100 years one chances, is all far longer than its wave height and period of wave the wave load of meeting for a year.Existing Deepwater Risers Fatigue Design Methods is not considered the impact on standpipe fatigue damage of fatigue damage that such " accidental " property Mechanics of Extreme Wave load causes, reason is to be generally 20 years the designed life of Deepwater Risers, therefore, within the standpipe military service phase, such wave load may not can occur, even if occur, also only continue several days, its caused fatigue damage is minimum to the fatigue damage contribution of standpipe, can ignore.But since entering 21 century, extreme marine environment takes place frequently, and the hurricane in the Gulfian is no longer 50 years chances, and is almost 1 year chance.The typhoon of China's southeastern coast also almost all can occur every year, and according to National Bureau of Oceanography's statistics, the wave of meeting for 50 years was the annual generation of Bohai Offshore 26 days.This shows, Mechanics of Extreme Wave load has been no longer the accidental phenomenon of Return period, and becomes the environmental load of meeting for a year.Therefore,, when carrying out Deepwater Risers fatigue design, should consider the contribution to standpipe fatigue damage of fatigue damage that Mechanics of Extreme Wave load causes.

Deepwater Risers is that (tubular platform passes through guide ring by certain connected mode, tension leg platform (TLP) passes through stretcher) flexibly connect with floating platform, and the vortex-induced vibration of the sharp motion in the whirlpool of floating platform and standpipe produces under ocean current acts on simultaneously, because the diameter (18～28m) of floating platform is far longer than the diameter (0.3～0.5m) of standpipe, therefore, while being subject to the action of ocean current of identical flow velocity simultaneously, act on floating platform all different with whirlpool induced lift force size (relevant from cylinder diameter) and frequency (relevant with cylinder diameter) on standpipe, thereby motion is swashed in the whirlpool of floating platform, (floating platform rigidity is large, do not occur bending and deformation, belong to rigid motion, therefore, be called whirlpool and swash " motion ", but still be reciprocal vibration, rather than the motion as boats and ships) all different with amplitude with the vortex-induced vibration of standpipe (reciprocal elastic bending deflection) frequency, and moving through of the two connects interaction, that a kind of coupling fortune (shaking) is moving.Because vibration (vibration) frequency of the two is different with amplitude, therefore, between the vibration of floating platform and the vibration of standpipe, have phase differential, and this phase differential is constantly to change.This coupled relation that swash between motion and riser vortex excited vibration in floating platform whirlpool can not calculate by the two simple linear superposition, and only, when the phase differential of the two is zero, simple linear superposition is only feasible.Therefore, prior art adopt the method calculate respectively again linear superposition to calculate floating platform whirlpool to swash the fatigue damage that motion and riser vortex excited vibration cause be inaccurate.

For these reasons, the present invention proposes a kind of Fatigue Design Methods of Deepwater Risers, comprise the calculating content of following several respects:

1. the standpipe fatigue damage rate that Long-Term Wave load causes

The standpipe fatigue damage rate that the calculation of design parameters Long-Term Wave load of the wave speckle pattern based on Deepwater Risers design object marine site (the wave probability of happening of different wave height and different wave direction in a year), corresponding S-N curve and floating platform and standpipe causes unit is 1/ year, wherein, and n1 _ithe cycle index of i the stress amplitude causing for Long-Term Wave load, N1 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S1 is the number of the different stress amplitudes that cause of Long-Term Wave load.The cycle index n1 of i the stress amplitude that Long-Term Wave load causes _ican adopt floating platform and standpipe model of coupling or block mold and adopt time history analysis method and rain flow method calculating, i stress amplitude causes the cycle index N1 that fatigure failure is required _ican be checked in by corresponding S-N curve.These calculation and analysis methods are all known technologies, and those skilled in the art can realize completely.

2. the fatigue damage rate that the sharp motion in floating platform whirlpool that long-term stream causes and riser vortex excited vibration cause

The fatigue damage rate that the sharp motion in floating platform whirlpool that the long-term stream of calculation of design parameters of the ocean current data based on Deepwater Risers design object marine site (the ocean current probability of happening of the flow velocity of different water depth and different directions in a year), corresponding S-N curve and floating platform and standpipe causes and riser vortex excited vibration cause unit is 1/ year, wherein, and n2 _ifor the cycle index of i the stress amplitude that under long-term stream effect, the sharp motion in floating platform whirlpool and riser vortex excited vibration cause, N2 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S2 is the number that under long-term stream effect, the different stress amplitudes that motion and riser vortex excited vibration cause are swashed in floating platform whirlpool.N2 _i, N2 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

3. the fatigue damage rate that the sharp motion in floating platform whirlpool that in short-term stream, circulation causes and riser vortex excited vibration cause

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting circulation data (flow velocity of different water depth, the flow direction and duration), corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and riser vortex excited vibration cause unit is 1/ time, wherein, and n3 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that the vortex-induced vibration of motion and standpipe causes swashed in floating platform whirlpool under circulation effect, N3 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S3 meets the number that the different stress amplitudes that motion and riser vortex excited vibration cause are swashed in floating platform whirlpool under circulation effect for 100 years one.N3 _i, N3 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

4. the fatigue damage rate that the sharp motion in floating platform whirlpool that in short-term stream, undercurrent causes and riser vortex excited vibration cause

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting undercurrent data (flow velocity of different water depth, the flow direction and duration), corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and riser vortex excited vibration cause unit is 1/ time, wherein, and n4 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that the vortex-induced vibration of motion and standpipe causes swashed in floating platform whirlpool under undercurrent effect, N4 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S4 meets the number that the different stress amplitudes that motion and riser vortex excited vibration cause are swashed in floating platform whirlpool under undercurrent effect for 100 years one.N4 _i, N4 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

Within 5.10 one, meet the fatigue damage rate that Mechanics of Extreme Wave load causes

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data (wave height, wave direction, period of wave and duration), corresponding S-N curve and floating platform and standpipe for 10 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n5 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 10 years, N5 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S5 is the number of meeting the different stress amplitudes that wave loads cause for 10 years.N5 _i, N5 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

Within 6.50 one, meet the fatigue damage rate that Mechanics of Extreme Wave load causes

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data (wave height, wave direction, period of wave and duration), corresponding S-N curve and floating platform and standpipe for 50 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n6 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 50 years, N6 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S6 is the number of meeting the different stress amplitudes that wave loads cause for 50 years.N6 _i, N6 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

Within 7.100 one, meet the fatigue damage rate that Mechanics of Extreme Wave load causes

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data (wave height, wave direction, period of wave and duration), corresponding S-N curve and floating platform and standpipe for 100 years based on Deepwater Risers design object marine site causes unit is 1/ time, wherein, and n7 _ibe the cycle index of meeting i the stress amplitude that Mechanics of Extreme Wave loads cause for 100 years, N7 _ifor the required cycle index of fatigure failure that this stress amplitude causes, S7 is the number of meeting the different stress amplitudes that wave loads cause for 100 years.N7 _i, N7 _icalculating also can adopt above-mentioned identical method, as time history analysis method and rain flow method, S-N curve.

8. the fatigue damage of standpipe and the designed life of standpipe

By D _wavebe multiplied by the design fatigue safety coefficient f of Long-Term Wave load _wavewith n designed life _life; D _lTVIM+LTVIVbe multiplied by the design fatigue safety coefficient f of long-term stream load _lTVIM+LTVIVwith n designed life _life; D _{sTVIM, L+STVIV, L}be multiplied by the design fatigue safety coefficient f of short-term stream load _sTVIM+STVIVprediction frequency n with 100 years one chance circulation in phase designed life _loop; D _{sTVIM, S+STVIV, S}be multiplied by the design fatigue safety coefficient f of short-term stream load _sTVIM+STVIVprediction frequency n with 100 years one chance undercurrents in phase designed life _sub; D _{wave, 10}be multiplied by the design fatigue safety coefficient f of Mechanics of Extreme Wave load _extremewaveprediction frequency n with 10 years one chance wave loads in phase designed life _{wave, 10}; D _{wave, 50}be multiplied by the design fatigue safety coefficient f of Mechanics of Extreme Wave load _extremewaveprediction frequency n with 50 years one chance wave loads in phase designed life _{wave, 50}; D _{wave, 100}be multiplied by the design fatigue safety coefficient f of Mechanics of Extreme Wave load _extremewaveprediction frequency n with 100 years one chance wave loads in phase designed life _{wave, 100}, and based on Fatigue Design Criterion (known criterion):

$D=\underset{i}{\overset{m}{\mathrm{\Σ}}}\frac{n_i}{N_i}\×f_i\≤1$

By following formula, carrying out the fatigue design of standpipe checks:

D＝(D _wave×f _wave+D _LTVIM+LTVIV×f _LTVIM+LTVIV)×n _life+(D _{STVIM，L+STVIV，L}×n _loop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV+(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave≤1

Can be calculated as follows the designed life of standpipe:

n _life＝[1-(D _{STVIM，L+STVIV，L}×nloop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV-(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave]/(D _wave×f _wave+D _LTVIM+LTVIV×f _LTVIM+LTVIV)

In above formula, f _wavefor the design fatigue safety coefficient of Long-Term Wave load, f _lTVIM+LTVIVfor the design fatigue safety coefficient of long-term stream load, f _sTVIM+STVIVfor the design fatigue safety coefficient of short-term stream load, f _extremewavefor the design fatigue safety coefficient of Mechanics of Extreme Wave load, n _lifefor standpipe designed life, n _loopfor within 100 years one, meeting the prediction frequency of circulation, n in phase designed life _subfor within 100 years one, meeting the prediction frequency of undercurrent, n in phase designed life _{wave, 10}for within 10 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 50}for within 50 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 100}for within 100 years one, meeting the prediction frequency of wave load in phase designed life.

Design fatigue safety coefficient f _wave, f _lTVIM+LTVIV, f _sTVIM+STVIV, f _extremewavevalue be to be checked in by design specifications according to the safe class of platform, design fatigue safety coefficient f _wave, f _lTVIM+LTVIV, f _sTVIM+STVIVand f _extremewavedesirable identical value, also can get different value according to the character of load.Load uncertainties is large, and its design fatigue safety coefficient is got higher value, and vice versa.

Deepwater Risers Fatigue Design Methods proposed by the invention has been considered the coupling effect of the sharp motion in floating platform whirlpool and riser vortex excited vibration, considered the impact on Deepwater Risers accumulation of fatigue damage of fatigue damage that short-term stream causes, considered that floating platform whirlpool that short-term stream causes swashs the impact on standpipe fatigue damage of fatigue damage that motion causes, considered the impact on standpipe fatigue damage of fatigue damage that Mechanics of Extreme Wave load causes, the simple linear stack of calculating than the non-coupling of existing method is more scientific, more meet the natural law, and, the Fatigue Damage Process that more meets structure than existing method.The present invention more meets the fatigue damage accumulation essence of Deepwater Risers reality, more meets known Miner ' s linear damage accumulation criterion, more meets current environmental load variation tendency and feature, more scientific, more reasonable, design result safety and reliability.

Obviously, those skilled in the art can carry out various changes and modification and not depart from the spirit and scope of the present invention the present invention.Like this, if of the present invention these are revised and within modification belongs to the scope of the claims in the present invention and equivalent technology thereof, the present invention is also intended to comprise these changes and modification interior.

Claims (6)

1. a Fatigue Design Methods for Deepwater Risers, comprising:

The standpipe fatigue damage rate that the calculation of design parameters Long-Term Wave load of the wave speckle pattern based on Deepwater Risers design object marine site, corresponding S-N curve and floating platform and standpipe causes wherein, n1 _ithe cycle index of i the stress amplitude causing for Long-Term Wave load, N1 _ifor the required cycle index of fatigure failure occurs under this stress amplitude effect, S1 is the number of the different stress amplitudes of the standpipe that causes of annual Long-Term Wave load;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the long-term stream of calculation of design parameters of the ocean current data based on Deepwater Risers design object marine site, corresponding S-N curve and floating platform and standpipe causes and riser vortex excited vibration cause wherein, n2 _ifor the cycle index of i the stress amplitude that under long-term stream effect, the sharp motion in floating platform whirlpool and riser vortex excited vibration cause, N2 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S2 is for swashing the number of the motion different stress amplitudes of standpipe that excited vibration causes with riser vortex in floating platform whirlpool under annual long-term stream effect;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting circulation data, corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and the vortex-induced vibration of standpipe cause wherein, n3 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that motion and riser vortex excited vibration cause swashed in floating platform whirlpool under circulation effect, N3 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S3 is the number of meeting the sharp motion in the floating platform whirlpool different stress amplitudes of standpipe that excited vibration causes with riser vortex under circulation effect for each 100 years;

The fatigue damage rate that the sharp motion in floating platform whirlpool that the calculation of design parameters short-term stream of meeting undercurrent data, corresponding S-N curve and floating platform and standpipe for 100 years one based on Deepwater Risers design object marine site causes and the vortex-induced vibration of standpipe cause wherein, n4 _ibe within 100 years one, to meet the cycle index that i the stress amplitude that motion and riser vortex excited vibration cause swashed in floating platform whirlpool under undercurrent effect, N4 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S4 is the number of meeting the sharp motion in the floating platform whirlpool different stress amplitudes of standpipe that excited vibration causes with riser vortex under undercurrent effect for each 100 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 10 years based on Deepwater Risers design object marine site causes wherein, n5 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 10 years, N5 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S5 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 10 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 50 years based on Deepwater Risers design object marine site causes wherein, n6 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 50 years, N6 _ifor this stress amplitude causes the cycle index that fatigure failure is required, S6 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 50 years;

The fatigue damage rate that the calculation of design parameters Mechanics of Extreme Wave load of meeting Wave Data, corresponding S-N curve and floating platform and standpipe for 100 years based on Deepwater Risers design object marine site causes wherein, n7 _ibe the cycle index of meeting i the stress amplitude that wave loads cause for 100 years, N7 _ifor the required cycle index of fatigure failure that this stress amplitude causes, S7 is the number of meeting the different stress amplitudes of standpipe that wave causes for each 100 years;

Based on Fatigue Design Criterion, by following formula, carry out the fatigue design of standpipe and check:

D＝(D _wave×f _wave+D _LTVIM+LTVIV×f _LTVIM+LTVIV）×n _life+(D _{STVIM，L+STVIV，L}×n _loop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV+(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave≤1

Can be calculated as follows the designed life of standpipe:

n _life＝[1-(D _{SIVIM，L+STVIV，L}×n _loop+D _{STVIM，S+STVIV，S}×n _sub)×f _STVIM+STVIV-(D _wave，10×n _wave，10+D _wave，50×n _wave，50+D _wave，100×n _wave，100)×f _extremewave]/(D _wavef _wave×D _LTVIM×f _LTVIM+LTVIV)

In above formula, f _wavefor the design fatigue safety coefficient of Long-Term Wave load, f _lTVIM+LTVIVfor the design fatigue safety coefficient of long-term stream load, f _sTVIM+STVIVfor the design fatigue safety coefficient of short-term stream load, f _extremewavefor the design fatigue safety coefficient of Mechanics of Extreme Wave load, n _lifefor standpipe designed life, n _loopfor within 100 years one, meeting the prediction frequency of circulation, n in phase designed life _subfor within 100 years one, meeting the prediction frequency of undercurrent, n in phase designed life _{wave, 10}for within 10 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 50}for within 50 years one, meeting the prediction frequency of wave load, n in phase designed life _{wave, 100}for within 100 years one, meeting the prediction frequency of wave load in phase designed life.

2. the Fatigue Design Methods of Deepwater Risers as claimed in claim 1, is characterized in that: the wave speckle pattern in described Deepwater Risers design object marine site is represented is the wave probability of happening of different wave height and different wave direction in a year.

3. the Fatigue Design Methods of the Deepwater Risers as described in claim l, is characterized in that: the ocean current data in described Deepwater Risers design object marine site refer to that the probability of happening of different in flow rate and different directions ocean current in a year and flow velocity thereof are along the distribution of the depth of water.

4. the Fatigue Design Methods of the Deepwater Risers as described in claim l, is characterized in that: within 100 years one of described Deepwater Risers design object marine site, meet circulation flow velocity, the flow direction and the duration that circulation data refer to different water depth.

5. the Fatigue Design Methods of Deepwater Risers as claimed in claim 1, is characterized in that: within 100 years one of described Deepwater Risers design object marine site, meet undercurrent flow velocity, the flow direction and the duration that undercurrent data refer to different water depth.

6. the Fatigue Design Methods of Deepwater Risers as claimed in claim 1, is characterized in that: within 10 years, 50 years of described Deepwater Risers design object marine site, 100 years one, meet wave height, wave direction, period of wave and the duration that Wave Datas refer to wave.