Quantitative assessment method for toughness of semi-submersible platform under local mooring failure

Abstract

The present invention relates to a quantitative assessment method for the toughness of a semi-submersible platform under local mooring failure, comprising: constructing a performance level curve of the semi-submersible platform from before and after local mooring failure to the entire recovery process based on the response process of the semi-submersible platform in three stages: absorbing damage, adapting to damage, and recovering after damage, and quantifying the toughness of the semi-submersible platform into three parts: absorption toughness, adaptation toughness, and recovery toughness; collecting statistical data on the structural response before and after local mooring failure of the semi-submersible platform and data required for recovery operation, and processing the initial data to obtain calculated data values; conducting a safety inspection on the semi-submersible platform; taking the toughness of the semi-submersible platform as an overall index, and absorption toughness, adaptation toughness, and recovery toughness as primary indexes, constructing secondary toughness indexes under the three types of toughness respectively, to obtain a three-layer index system for the toughness assessment of the semi-submersible platform; and obtaining three types of toughness weight values ​​and a toughness value of the semi-submersible platform.

Description

Technical Field

[0001] The present application relates to the technical field of toughness assessment of marine engineering structures, and in particular to a method for quantitatively assessing the toughness of a semi-submersible platform based on local mooring failure. Background Art

[0002] In recent years, disaster prevention and mitigation have received significant attention in major national projects, and the safety assessment of engineering systems and structures has become increasingly crucial. Resilience refers to a structure's ability to maintain, restore, and optimize its safety state when subjected to external disturbances. Compared to traditional disaster prevention and mitigation, resilience focuses more on a system's ability to resist, absorb, and adapt to destructive events such as natural disasters, and to rapidly recover after damage. Therefore, resilience assessments of marine engineering structures are of great significance.

[0003] Semi-submersible platforms are one of the important equipment for marine development. During long-term operation, their mooring systems may be subject to external extreme disasters or corrosion fatigue aging, which may cause the mooring lines to break, thereby damaging the platform structure system and threatening the safety of personnel, equipment and property.

[0004] At present, domestic and foreign scholars have conducted a lot of research on resilience assessment in the field of engineering structures, mainly focusing on infrastructure such as earthquakes, urban and rural communities, medical and power systems, and interrelated system network structures. However, in the field of marine engineering, safety assessment of marine structures has hardly involved relevant research on resilience, and the existing resilience system and indicators are not suitable for resilience assessment of offshore platforms. Summary of the Invention

[0005] This embodiment of the application provides a quantitative assessment method for the toughness of a semi-submersible platform under local mooring failure, which is conducive to further optimizing the design and safe operation of large-scale marine structural systems. The technical solution is as follows:

[0006] A quantitative assessment method for the toughness of a semi-submersible platform under local mooring failure includes:

[0007] (1) Based on the three-stage response process of a semi-submersible platform, namely, absorbing damage, adapting to damage, and recovering after damage, a performance level curve of the semi-submersible platform from the time of partial mooring failure to the entire recovery process is constructed, and the toughness of the semi-submersible platform is quantified into three parts: absorption toughness, adaptation toughness, and recovery toughness.

[0008] Absorption resilience refers to the ability of a semi-submersible platform to absorb damage and reduce its impact on itself, and is measured by the transient response of the semi-submersible platform's movement; Adaptation resilience refers to the ability of a semi-submersible platform to adapt to damage and its impact after being damaged so that the post-damage steady state is close to the original steady state, and is measured by the steady-state response of the semi-submersible platform's movement; Recovery resilience refers to the ability of a semi-submersible platform to quickly recover from damage and maintain normal operation, and is measured by the time and cost for the semi-submersible platform to return to normal;

[0009] (2) Collect the structural response data of the semi-submersible platform before and after the partial mooring failure and the data required for the recovery operation, and process the initial data to obtain the calculated data value;

[0010] The required data include the horizontal displacement, angular displacement, mooring line tension, recovery time and cost of the semi-submersible platform before and after partial mooring failure under different working conditions;

[0011] The method for obtaining the calculated data values ​​of various types of data is as follows: select the most dangerous state of each different working condition, that is, take the maximum response value of all initial data under the selected working condition, and take the absolute value;

[0012] (3) Conducting a safety inspection on the semi-submersible platform by: calculating the tension value of the remaining mooring line under each local mooring failure condition and calculating the safety factor, setting a safety factor threshold, and if the safety factor is greater than the set safety factor threshold, the semi-submersible platform is considered to be in a safe state; otherwise, continuous failure will occur, and the semi-submersible platform is determined to be in a failure state, wherein the safety factor is the ratio of the breaking strength of the mooring line to the maximum tension it is subjected to;

[0013] (4) Taking the resilience of the semi-submersible platform as the overall index, absorption resilience, adaptation resilience, and recovery resilience as the first-level indicators, the second-level resilience indicators are constructed under the three types of resilience, and a three-level index system for the resilience assessment of the semi-submersible platform is obtained. The method is as follows:

[0014] 1) The secondary indicator under absorption toughness is the transient angular displacement R of the semi-submersible platform θ,TS , the transient angular displacement R θ,TS Including three kinds of data: transient roll, pitch and heading angular displacement; transient angular displacement R θ,TS It is defined as the ratio of the maximum original steady-state rocking angle of the semi-submersible platform to the maximum transient rocking angle after local mooring failure:

[0015]

[0016] Among them, θ OS is the maximum value of the original steady-state shaking angle; θ TS is the maximum instantaneous shaking angle of the semi-submersible platform after partial mooring failure;

[0017] 2) The secondary indicators under adaptive resilience are the steady-state horizontal displacement, steady-state angular displacement and steady-state tension response of the semi-submersible platform. The steady-state horizontal displacement includes two types of data: sway and surge, and the steady-state angular displacement includes three types of data: roll, pitch and bow. For the steady-state horizontal displacement resilience measurement index, and the steady-state angular displacement toughness index R θ,SS , defined as the ratio of the original steady-state response value to the new steady-state response value compared to the original steady-state response value:

[0018]

[0019] in, and θ OS are the maximum response values ​​of horizontal displacement and angular displacement in the original steady state, respectively; and θ DS are the maximum response values ​​of horizontal displacement and angular displacement in the new steady state after local mooring failure;

[0020] For the steady-state tension toughness measure, it is expressed as the average change, which is defined as the average of the ratios of the increase in the mooring cable tension in the new steady state compared to the original steady state to the original steady state tension:

[0021]

[0022] Among them, T k,DS is the maximum value of the kth group of mooring line tension in the new steady state; T k,OS is the maximum value of the tension of the kth mooring line group in the original steady state; N is the number of mooring line groups;

[0023] 3) The recovery operation in recovery resilience is to replace the mooring line, that is, recovery resilience is measured by recovery time and recovery cost;

[0024] The secondary indicator under recovery toughness is the relative cable replacement time R of the semi-submersible platform. t and the relative cable replacement cost R c ; For the relative cable replacement time R t , defined as the ratio of the time from the moment the semi-submersible platform is damaged to the moment the recovery process begins to the time the semi-submersible platform recovers:

[0025]

[0026] Among them, t0 is the moment when the semi-submersible platform is damaged; t2 is the moment when the recovery starts; t3 is the moment when the recovery is completed; t r =t3-t2, the duration of the recovery phase;

[0027] For the relative cable replacement cost R c, defined as the ratio of the difference between the cost of the recovery phase to the power of 1 / 4 and the number of failed mooring lines to itself:

[0028]

[0029] Among them, c r Refers to the cost of the recovery phase, i.e. the cost of replacing the mooring line; n f Refers to the number of mooring lines that failed;

[0030] The damage coefficient of the semi-submersible platform is defined to estimate the degree to which the semi-submersible platform deviates from the normal operating state under different failure conditions. Based on engineering experience, the benchmark recovery time t and benchmark recovery cost c when a single cable breaks under ideal conditions are determined, that is, the fastest cable replacement time and the minimum cost required under ideal conditions. The actual recovery time and recovery cost when a single cable breaks are:

[0031] t r =(1+μ i )t,c r =(1+μ i )c

[0032] Among them, μ i is the damage coefficient of the semi-submersible platform under failure condition i, which indicates the degree of deviation between the new steady state and the original steady state and is defined as 1 minus the mean ratio of the calculated data values ​​under the two steady states;

[0033] (5) The CRITIC method is used to assign weights to the indicators, and the values ​​of each indicator and its weight are weighted to obtain three types of resilience weight values ​​and the resilience value of the semi-submersible platform.

[0034] The present invention has at least the following beneficial effects:

[0035] 1) A performance level curve from the platform before and after partial mooring failure to the entire recovery process was constructed, and the platform resilience was quantified into three parts: absorption resilience, adaptation resilience, and recovery resilience;

[0036] 2) A resilience assessment method suitable for offshore floating platforms is proposed. By constructing a three-tiered index system for the resilience assessment of semi-submersible platforms, it can provide a reference for the resilience assessment of other marine engineering structures.

[0037] 3) Conducting a resilience assessment of the semi-submersible platform from the perspective of the overall structure allows for preventive and recovery measures to be taken in advance for conditions with lower resilience, which will be beneficial for further optimizing the design and safe operation of large-scale marine structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1 A flow chart of a method for quantitatively evaluating the toughness of a semi-submersible platform under local mooring failure is provided for an embodiment of the present application;

[0040] Figure 2 A schematic diagram of a semi-submersible platform performance level curve is provided for an embodiment of the present application;

[0041] Figure 3 A schematic diagram of a semi-submersible platform resilience assessment indicator framework provided in an embodiment of the present application;

[0042] Figure 4 A schematic diagram of the mooring system layout and mooring line numbering and failure combination is provided for the embodiment of the present application;

[0043] Figure 5 A semi-submersible platform resilience assessment index system and an index weight diagram are provided for the embodiment of the present application. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] The terms "comprises," "comprising," and "having," and any variations thereof, as used in the specification and claims of this application, are intended to cover non-exclusive inclusions. For example, a process or method comprising a series of steps is not limited to the listed steps but may optionally include steps not listed, or other steps inherent to such process or method.

[0046] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0047] See also Figure 1 , Figure 1 The present invention provides a flow chart of a method for quantitatively evaluating the toughness of a semi-submersible platform under local mooring failure. Figure 1 As shown in Figure 2, the quantitative assessment method for the toughness of a semi-submersible platform under local mooring failure includes:

[0048] (1) Based on the three-stage response process of the platform, namely, absorbing damage, adapting to damage, and recovering after damage, a performance level curve of the platform from before and after local mooring failure to the entire recovery process is constructed, and the platform resilience is quantified into three parts: absorption resilience, adaptation resilience, and recovery resilience.

[0049] Definition of semi-submersible platform resilience: It is the ability of a semi-submersible platform to absorb and adapt to damage and quickly recover to normal mooring levels and maintain normal mooring operations after suffering internal or external damage resulting in local mooring failure.

[0050] Based on the three-stage response process of the platform, namely, absorbing damage, adapting to damage, and recovering after damage, a performance level curve of the platform from before and after local mooring failure to the entire recovery process is constructed.

[0051] like Figure 2 As shown in Figure 1, assuming that the performance level of the platform is 100% when it is operating normally, the platform response process is divided into three stages.

[0052] 1) The period from t0 to t1 is the absorption phase, reflecting the platform's ability to absorb damage. At t0, the platform suffers mooring failure, causing a sharp decline in functionality. At t1, the transient response reaches its maximum value. The magnitude of the transient response directly reflects the platform's ability to absorb damage.

[0053] 2) The period from t1 to t2 is the adaptation phase, reflecting the platform's ability to adapt to the disruption. After t1, the platform gradually adapts to the disruption until it reaches a new stable state. The degree of deviation between the two stable states reflects the platform's adaptability.

[0054] 3) t2-t3 is the recovery phase, reflecting the platform's ability to recover from damage. Recovery begins at t1 and is complete at t2. The resources, time, and cost used during the recovery process reflect the platform's recovery capabilities.

[0055] Therefore, the platform resilience is quantified into three parts: absorption resilience, adaptation resilience, and recovery resilience.

[0056] Absorption resilience refers to the ability of a semi-submersible platform to absorb damage and reduce the impact on itself, and is measured by the transient response of the platform's movement; adaptive resilience refers to the ability of a semi-submersible platform to adapt to damage and its impact after suffering damage so that the post-damage steady state is close to the original steady state, and is measured by the steady-state response of the platform's movement; recovery resilience refers to the ability of a semi-submersible platform to quickly recover from damage and maintain normal operation, and is measured by the recovery time and cost for the platform to return to normal.

[0057] (2) Collect the structural response data of the platform before and after local mooring failure and the data required for recovery operations, and process the initial data to obtain the calculated data value;

[0058] The required initial data include the horizontal displacement, angular displacement, mooring line tension, recovery time, and recovery cost of the semi-submersible platform before and after partial mooring failure under different working conditions;

[0059] The method for obtaining the calculated data values ​​of various types of data is as follows: select the most dangerous state of each different working condition, that is, take the maximum response value of all initial data under the selected working condition, and take the absolute value;

[0060] (3) Conduct safety inspection on the platform by calculating the tension value of the remaining mooring line under each local mooring failure condition and calculating the safety factor. If the minimum safety factor is greater than 1.25, the platform is considered to be in a safe state; otherwise, continuous failure will occur, and the platform is considered to be in a failed state. The safety factor is the ratio of the breaking strength of the mooring line to the maximum tension it is subjected to.

[0061] (4) Taking platform resilience as the overall index, absorption resilience, adaptation resilience and recovery resilience as the first-level indicators, the second-level resilience indicators are constructed under the three types of resilience, and a three-level index system for semi-submersible platform resilience assessment is obtained, as follows: Figure 3 As shown, all indicator values ​​are dimensionless values, and the method is as follows:

[0062] 1) The secondary indicator under absorption toughness is the transient angular displacement R of the platform θ,TS , the transient angular displacement R θ,TS Including three kinds of data: transient roll, pitch and heading angular displacement; transient angular displacement R θ,TS It is defined as the ratio of the maximum original steady-state rocking angle of the platform to the maximum transient rocking angle after local mooring failure:

[0063]

[0064] Among them, θ OS is the maximum value of the original steady-state shaking angle; θ TS is the maximum value of the transient shaking angle after the local mooring failure of the platform;

[0065] 2) The secondary indicators under adaptive resilience are the three types of indicators of the platform's steady-state horizontal displacement, steady-state angular displacement and steady-state tension response. The steady-state horizontal displacement includes two types of data: sway and surge, and the steady-state angular displacement includes three types of data: roll, pitch and bow. For the steady-state horizontal displacement resilience measurement indicator, and the steady-state angular displacement toughness index R θ,SS , defined as the ratio of the original steady-state response value to the new steady-state response value compared to the original steady-state response value:

[0066]

[0067] in, and θ OS are the maximum response values ​​of horizontal displacement and angular displacement in the original steady state, respectively; and θ DS are the maximum response values ​​of horizontal displacement and angular displacement in the new steady state after local mooring failure.

[0068] For the steady-state tension toughness measure, it is expressed as the average change, which is defined as the average of the ratios of the increase in the mooring cable tension in the new steady state compared to the original steady state to the original steady state tension:

[0069]

[0070] Among them, T k,DS is the maximum value of the kth group of mooring line tension in the new steady state; T k,OS is the maximum value of the tension of the kth group of mooring lines in the original steady state; N is the number of mooring line groups.

[0071] 3) The recovery operation in recovery resilience is to replace the mooring line, that is, recovery resilience is measured by recovery time and recovery cost.

[0072] The secondary indicator under recovery toughness is the relative cable replacement time R of the platform. t and the relative cable replacement cost R c For the relative cable replacement time R t , defined as the ratio of the duration from the moment the platform is damaged to the moment the recovery process begins to the duration of the platform recovery phase:

[0073]

[0074] Among them, t0 is the time when the platform is damaged; t2 is the time when recovery starts; t3 is the time when recovery is completed; t r =t3-t2, which is the duration of the recovery phase.

[0075] For the relative cable replacement cost R c, defined as the ratio of the difference between the cost of the recovery phase to the power of 1 / 4 and the number of failed mooring lines to itself:

[0076]

[0077] Among them, c r Refers to the cost of the recovery phase, i.e. the cost of replacing the mooring line; n f Refers to the number of failed mooring lines.

[0078] The platform damage coefficient μ is defined to estimate the degree to which the platform deviates from the normal operating state under different failure conditions.

[0079] Based on engineering experience, the ideal benchmark recovery time t = 12 hours and the benchmark recovery cost c = 756,000 yuan for a single cable break are determined, which are the fastest cable replacement time and the minimum cost required under ideal conditions. The actual recovery time and recovery cost for a single cable break are:

[0080] t r =(1+μ i )t,c r =(1+μ i )c

[0081] Where, t = 12; c = 75.6; μ i is the platform damage coefficient under failure condition i, which indicates the degree of deviation between the new steady state and the original steady state. It is defined as 1 minus the mean ratio of the calculated data values ​​under the two steady states:

[0082]

[0083] Among them, x ij,OS is the calculated data value under the original steady state; x ij,DS is the calculated data value under the new steady state.

[0084] (5) The CRITIC (Criteria Importance Through Intercrieria Correlation) method is used to assign weights to the indicators. The values ​​of each indicator and its weight are weighted to obtain three types of resilience weight values ​​and the platform resilience value.

[0085] The empowerment process of the CRITIC Act is as follows:

[0086] Assuming there are m calculation conditions and n evaluation indicators, the original indicator data matrix is ​​formed:

[0087]

[0088] Among them, y ij(i=1,2,...m,j=1,2...n) represents the jth evaluation index value in the i-th working condition.

[0089] 1) Dimensionless processing

[0090] For positive indicators:

[0091]

[0092] For contrarian indicators:

[0093]

[0094] 2) Calculate indicator variability

[0095]

[0096] in, S j are the mean and standard deviation of the j-th indicator respectively.

[0097] 3) Calculation indicator conflict

[0098]

[0099] Among them, r ij It represents the correlation coefficient between the evaluation indicators.

[0100] 4) Calculate the amount of information of indicators

[0101] C j =S j ×R j

[0102] 5) Calculate the weight. The objective weight of the jth indicator is

[0103]

[0104] Three primary toughness index values ​​y ij (Ι) The calculation formula is:

[0105]

[0106] Where y ij (ΙΙ) is the value of the jth secondary index under the i-th working condition, including R θ,TS 、 R θ,SS 、R T 、R t and R c ; is the weight of each secondary indicator.

[0107] Similarly, the platform resilience value can be obtained

[0108]

[0109] Where, is the weight of the first-level resilience index.

[0110] The calculated toughness value can be used to assess the resilience of a semisubmersible platform under different mooring failure conditions. A higher toughness value indicates a better ability for the platform to absorb and adapt to damage, as well as a faster recovery from damage. At the same time, for conditions with lower toughness, preventive and recovery measures should be implemented in advance.

[0111] In this example, a performance level curve was constructed for the entire process from the failure of a local mooring failure to recovery, quantifying the platform's resilience into three components: absorption resilience, adaptation resilience, and recovery resilience. The structural response data before and after the failure of the local mooring failure and the data required for recovery operations were collected, and the initial data was processed to obtain calculated data values. The platform was then safety inspected. Using platform resilience as the overall indicator, secondary resilience indicators were constructed under each of the three types of resilience, resulting in a three-tiered indicator system for assessing the resilience of a semi-submersible platform. The CRITIC method was used to weight the indicators, and the values ​​of each indicator and their respective weights were weighted to obtain the three resilience weights and the semi-submersible platform's resilience value. Assessing the resilience of a semi-submersible platform from a holistic structural perspective allows for the implementation of preventive and recovery measures in advance for conditions with low resilience, which is conducive to further optimizing the design and safe operation of large-scale marine structures.

[0112] In one possible embodiment, the present application also provides a specific method for quantitatively evaluating the toughness of a semi-submersible platform under local mooring failure, as follows:

[0113] The mooring system consists of 12 cables, divided into four groups, and symmetrically arranged on the outside of the four columns. A single cable is a three-section combination of anchor chain, polyester cable, and anchor chain. The wave is a regular wave with a wave height of 16m, a period of 12s, and an incident angle of 0°. The mooring system plan and cable number and group number are attached. Figure 4 shown.

[0114] Due to the symmetry of the mooring, it is easy to know that the tension of the two groups of cables 2 and 3 in the wave-facing direction is greater than the tension of the two groups of cables 1 and 4 in the wave-back direction. After calculation and analysis, it is known that the impact on the platform is relatively small when one mooring cable breaks, so only the case of two mooring cables breaking will be studied in the subsequent study.

[0115] Analysis shows that when the mooring system is intact, the tension in M6 and M7 in the wave direction is the largest, and failure is most likely to occur. Therefore, this paper studies four failure conditions, namely M3&M6, M3&M7, M5&M6 and M6&M7. The different failure combinations and descriptions are as follows: Figure 4 As shown in Table 1:

[0116] Table 1 Description of mooring line failure combinations

[0117]

[0118] Under full mooring conditions, when waves are incident at 0°, the platform's six degrees of freedom (DOF) responses are significant in surge and pitch, while the other DOF responses are minimal. Because asymmetric failure of the mooring lines can cause significant sway, roll, and pitch, these factors are also taken into account when calculating the resilience index.

[0119] The platform's structural response data, including transient and steady-state responses, were collected before and after failure under the four aforementioned operating conditions. For the tension response, the tension values ​​of the cable with the highest tension in each cable group were calculated before and after failure. The platform's transient response, steady-state response, and maximum tension response under the four failure conditions are shown in Tables 3 and 4.

[0120] Table 3 Maximum transient response of platform angular displacement under different failure conditions

[0121]

[0122]

[0123] Table 4 Platform motion response and maximum mooring cable tension under different failure conditions

[0124]

[0125] A safety inspection of the platform was carried out, namely, the safety factors of the remaining mooring cables under four failure conditions were tested. Calculations showed that the safety factors under the four conditions were all much greater than 1.25, indicating that the platform was considered to be in a safe state.

[0126] The heave response of the platform remains almost unchanged before and after local mooring failure and is not used as a measure of toughness.

[0127] Assuming the platform is operating 150 kilometers offshore, starting from the moment t0 when the mooring line breaks, an operating engineering vessel and three tugboats depart from the shore at an average speed of 12 knots. The time required to reach the platform is 6.75 hours, that is, t2-t0=6.75 hours.

[0128] The recovery operation is set as replacing the mooring line. The platform damage coefficients under the four failure conditions of M3&M6, M3&M7, M5&M6 and M6&M7 are calculated to be 0.582, 0.576, 0.768 and 0.431 respectively;

[0129] Based on engineering experience, the benchmark recovery time t = 12 hours and the benchmark recovery cost c = 756,000 yuan when a single cable breaks. The actual recovery time and recovery cost when two cables break are shown in Table 5.

[0130] Table 5 Platform recovery time and recovery cost under different failure conditions

[0131]

[0132] Substituting the calculated data values ​​in Table 3, Table 4 and Table 5 into the constructed index calculation formula, the secondary index values ​​y of the three toughness can be obtained. ij (ΙΙ) , as shown in Table 6. Then, the CRITIC method is used to calculate and weight the secondary and primary indicators under three working conditions, and the weight of each indicator can be obtained, as shown in Table 6. Figure 5 shown.

[0133] Table 6 Secondary toughness index values ​​under different failure conditions

[0134]

[0135]

[0136] The platform toughness values ​​under different working conditions can be obtained by performing weighted calculation on the first-level toughness index values ​​and their weights under different working conditions, as shown in Table 7.

[0137] Table 7 Platform toughness values ​​under different failure conditions

[0138]

[0139] It can be seen that under the three operating conditions, the platform's resilience is greatest when M6&M7 fails, followed by M3&M7, then M3&M6, and least when M5&M6 fails. It can be seen that compared to a unilateral failure of the mooring line, the platform's resilience is greater when the mooring line fails symmetrically about the platform. The platform's resilience is lowest when M5&M6 fails. In this case, all degrees of freedom of the platform exhibit a large response, the platform's absorption and adaptability are low, and recovery is more difficult. Therefore, in practical engineering, M5&M6 failures should be avoided as much as possible to prevent continuous failures.

[0140] The above is a detailed introduction to the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, according to the idea of ​​the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A quantitative assessment method for the toughness of a semi-submersible platform under local mooring failure, comprising: (1) Based on the three-stage response process of a semi-submersible platform, namely, absorbing damage, adapting to damage, and recovering after damage, a performance level curve of the semi-submersible platform from the time of partial mooring failure to the entire recovery process is constructed, and the toughness of the semi-submersible platform is quantified into three parts: absorption toughness, adaptation toughness, and recovery toughness. Absorption resilience refers to the ability of a semi-submersible platform to absorb damage and reduce its impact on itself, and is measured by the transient response of the semi-submersible platform's movement; Adaptation resilience refers to the ability of a semi-submersible platform to adapt to damage and its impact after being damaged so that the post-damage steady state is close to the original steady state, and is measured by the steady-state response of the semi-submersible platform's movement; Recovery resilience refers to the ability of a semi-submersible platform to quickly recover from damage and maintain normal operation, and is measured by the time and cost for the semi-submersible platform to return to normal; (2) Collect the structural response data of the semi-submersible platform before and after the partial mooring failure and the data required for the recovery operation, and process the initial data to obtain the calculated data value; The required data include the horizontal displacement, angular displacement, mooring line tension, recovery time and cost of the semi-submersible platform before and after partial mooring failure under different working conditions; The method for obtaining the calculated data values ​​of various types of data is as follows: select the most dangerous state of each different working condition, that is, take the maximum response value of all initial data under the selected working condition, and take the absolute value; (3) Conducting a safety inspection on the semi-submersible platform by: calculating the tension value of the remaining mooring line under each local mooring failure condition and calculating the safety factor, setting a safety factor threshold, and if the safety factor is greater than the set safety factor threshold, the semi-submersible platform is considered to be in a safe state; otherwise, continuous failure will occur, and the semi-submersible platform is determined to be in a failure state, wherein the safety factor is the ratio of the breaking strength of the mooring line to the maximum tension it is subjected to; (4) Taking the resilience of the semi-submersible platform as the overall index, absorption resilience, adaptation resilience, and recovery resilience as the first-level indicators, the second-level resilience indicators are constructed under the three types of resilience, and a three-level index system for the resilience assessment of the semi-submersible platform is obtained. The method is as follows: 1) The secondary indicator under absorption toughness is the transient angular displacement R of the semi-submersible platform θ,TS , the transient angular displacement R θ,TS Including three kinds of data: transient roll, pitch and heading angular displacement; transient angular displacement R θ,TS It is defined as the ratio of the maximum original steady-state rocking angle of the semi-submersible platform to the maximum transient rocking angle after local mooring failure: Among them, θ OS is the maximum value of the original steady-state shaking angle; θ TS is the maximum instantaneous shaking angle of the semi-submersible platform after partial mooring failure; 2) The secondary indicators under adaptive resilience are the steady-state horizontal displacement, steady-state angular displacement and steady-state tension response of the semi-submersible platform. The steady-state horizontal displacement includes two types of data: sway and surge, and the steady-state angular displacement includes three types of data: roll, pitch and bow. For the steady-state horizontal displacement resilience measurement index, and the steady-state angular displacement toughness index R θ,SS , defined as the ratio of the original steady-state response value to the new steady-state response value compared to the original steady-state response value: in, and θ OS are the maximum response values ​​of horizontal displacement and angular displacement in the original steady state, respectively; and θ DS are the maximum response values ​​of horizontal displacement and angular displacement in the new steady state after local mooring failure; For the steady-state tension toughness measure, it is expressed as the average change, which is defined as the average of the ratios of the increase in the mooring cable tension in the new steady state compared to the original steady state to the original steady state tension: Among them, T k,DS is the maximum value of the kth group of mooring line tension in the new steady state; T k,OS is the maximum value of the tension of the kth mooring line group in the original steady state; N is the number of mooring line groups; 3) The recovery operation in recovery resilience is to replace the mooring line, that is, recovery resilience is measured by recovery time and recovery cost; The secondary indicator under recovery toughness is the relative cable replacement time R of the semi-submersible platform. t and the relative cable replacement cost R c ; For the relative cable replacement time R t , defined as the ratio of the time from the moment the semi-submersible platform is damaged to the moment the recovery process begins to the time the semi-submersible platform recovers: Among them, t0 is the moment when the semi-submersible platform is damaged; t2 is the moment when the recovery starts; t3 is the moment when the recovery is completed; t r =t3-t2, the duration of the recovery phase; For the relative cable replacement cost R c , defined as the ratio of the difference between the cost of the recovery phase to the power of 1 / 4 and the number of failed mooring lines to itself: Among them, c r Refers to the cost of the recovery phase, i.e. the cost of replacing the mooring line; n f Refers to the number of mooring lines that failed; The damage coefficient of the semi-submersible platform is defined to estimate the degree to which the semi-submersible platform deviates from the normal operating state under different failure conditions. Based on engineering experience, the benchmark recovery time t and benchmark recovery cost c when a single cable breaks under ideal conditions are determined, that is, the fastest cable replacement time and the minimum cost required under ideal conditions. The actual recovery time and recovery cost when a single cable breaks are: t r =(1+μ i )t,c r =(1+μ i )c Among them, μ i is the damage coefficient of the semi-submersible platform under failure condition i, which indicates the degree of deviation between the new steady state and the original steady state and is defined as 1 minus the mean ratio of the calculated data values ​​under the two steady states; (5) The CRITIC method is used to assign weights to the indicators, and the values ​​of each indicator and its weight are weighted to obtain three types of resilience weight values ​​and the resilience value of the semi-submersible platform.

2. The method for quantitatively evaluating the toughness of a semi-submersible platform according to claim 1, characterized in that: The safety factor threshold is 1.25.

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