A method for screening time-domain extreme value of ice load and evaluating structural strength of a polar floating structure

Abstract

The present application relates to the field of ship and ocean engineering technology, in particular to a polar floating structure ice load time domain extreme value screening and structure strength evaluation method, comprising: a numerical model of interaction between sea ice and floating structure is established based on the discrete element method, in the numerical model: the whole process of extrusion, bending and crushing of sea ice is simulated by using parallel bonding model and tensile-shear partition fracture criterion, ice condition parameters and micro-mechanical parameters of sea ice in the target sea area are input, dynamic simulation is carried out on the numerical model, and complete time curve of ice load is output; the ice load time curve is analyzed, and the dynamic design extreme value is obtained according to the dynamic characteristic parameters; the corresponding action position and direction of the dynamic design extreme value in the discrete element simulation are found out, the action position and direction are taken as the boundary conditions of static load and applied to the whole ship finite element model, the stress distribution of the whole ship finite element model is calculated, and the strength is checked according to the material yield strength and safety factor. The present application improves the evaluation accuracy.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding and marine engineering technology, specifically to a method for screening time-domain extreme values ​​of ice loads and evaluating the structural strength of polar floating structures. Background Technology

[0002] Polar floating structures face complex dynamic ice loads when operating in ice-covered areas, making ice resistance assessment a crucial technical aspect for ensuring structural safety. In current engineering practice, a strong coupling relationship exists between the time-varying characteristics of ice loads and the dynamic response of the structure. Physical processes such as ice breaking, compression, and bending generate significant impact effects. This dynamic interaction directly affects stress concentration and fatigue damage accumulation in local structural regions, and traditional static equivalent methods are insufficient to accurately characterize such nonlinear mechanical behavior. With the development of computer simulation technology, numerical tools such as the discrete element method can simulate the complete time history of ice-structure interaction, providing a new data foundation for refined strength assessment.

[0003] Existing technologies for assessing the ice resistance of polar floating structures suffer from the following main technical shortcomings: First, the empirical formula method recommended by current standards simplifies dynamic ice loads to static equivalent loads, failing to reflect the transient impact characteristics and periodic loading features of actual ice loads. This simplification leads to a fundamental difference between the load input and physical reality, potentially distorting the structural strength assessment. Second, the existing assessment process is fragmented, lacking a systematic connection between ice load calculation and structural response analysis, and manual intervention in intermediate steps introduces additional errors. Third, for time-domain ice load data obtained from numerical simulations, there is a lack of scientific extreme value screening criteria, and conventional global maximum or statistical averaging methods are insufficient to capture the most destructive load characteristics. These limitations mean that existing assessment methods may underestimate the instantaneous destructive potential of ice loads or lead to redundant structural design due to excessive conservatism, making it difficult to achieve a reasonable balance between safety and economy. Summary of the Invention

[0004] The aforementioned simplification of ice load to a static equivalent static ice force fails to accurately reflect the dynamic impact effects and time-varying characteristics of ice-structure interaction, leading to inaccurate strength assessments or overly conservative designs for polar floating structures. This invention addresses the technical problem of using time-domain extreme value screening for ice loads and assessing structural strength for polar floating structures. The invention primarily employs the discrete element method (DEM) to accurately reproduce the time-domain impact characteristics of ice loads. It extracts the most engineering-hazardous design extreme values ​​from the complex load time history based on physical characteristics and precisely maps them to the structural finite element model for static strength verification, thereby achieving a refined and high-confidence assessment of the ice resistance strength of polar floating structures.

[0005] The technical means employed in this invention are as follows:

[0006] A method for screening time-domain extreme values ​​of ice loads and evaluating the structural strength of polar floating structures includes the following steps: A numerical model of the interaction between sea ice and floating structures is established based on the discrete element method. In the numerical model, the parallel bonding model and the tension-shear partition fracture criterion are used to simulate the entire process of sea ice compression, bending and breaking. The target sea area ice condition parameters and sea ice micromechanical parameters are input, and the numerical model is subjected to dynamic simulation to output the complete time history curve of ice load. The ice load time history curve is analyzed, and the dynamic design extreme value is obtained by screening based on the dynamic characteristic parameters. The dynamic characteristic parameters include the load peak value, the load rise rate, the duration of the load exceeding the threshold, and the time interval between adjacent significant peak values. Find the corresponding action position and direction of the dynamic design extremum in the discrete element simulation, apply the action position and direction as static load boundary conditions to the whole ship finite element model, calculate the stress distribution and maximum equivalent stress of the whole ship finite element model, and perform strength verification based on the material yield strength and safety factor.

[0007] Furthermore, the micromechanical parameters of the sea ice include elastic modulus, compressive strength, bonding strength, and coefficient of friction, while the ice condition parameters include ice thickness, ice velocity, and ice density.

[0008] Furthermore, in the numerical model, sea ice is discretized into spherical particle units, which are connected by a parallel bonding model. Seawater drag and buoyancy are introduced to simulate the continuous fracture and fragment flow process of sea ice under structural compression.

[0009] Furthermore, the stress distribution is calculated under the combined condition of hydrostatic load and selected ice force extreme values. Three-point rigid boundary conditions are applied in the whole ship finite element model to eliminate rigid body displacement, and the equivalent stress distribution of the structure is solved by the static finite element method.

[0010] Furthermore, the whole ship finite element model includes a whole ship model, a side local model, a bow rib model, and a liquid tank coupling model.

[0011] Furthermore, the screening step for the dynamic design extrema includes: The ice load time history curve is filtered and denoised, and the sliding window method is used to identify all local load peaks in the time history. The occurrence time, load amplitude and corresponding location of each load peak are recorded. For each local load peak, the rate of increase is calculated. Peaks with a rate of increase lower than a preset threshold are discarded, and the remaining peaks are the first candidate peaks. The formula for calculating the rate of increase is:

[0012] in, For the rate of increase, The peak load amplitude, The load value at the starting point. The duration from the starting point to the peak value; Calculate the duration for which each first candidate peak exceeds a preset time threshold, and remove peaks whose duration is less than the preset time threshold to obtain second candidate peaks; Calculate the time interval between adjacent candidate peaks in the second candidate peak. If the time interval is less than the preset lower limit of the breaking cycle, it is determined that the two belong to the same ice breaking event, and the one with the larger load amplitude is retained. If the time interval is greater than the preset lower limit of the breaking cycle, it is determined that they are two independent events, and both are retained. The dynamic design extreme value is obtained.

[0013] Furthermore, the maximum equivalent stress of the structure is compared with the allowable stress of the material, and the formula for calculating the allowable stress is:

[0014] in, For allowable stress, For the material's yield strength, As a safety factor, the strength test is qualified when the maximum equivalent stress of the structure is less than or equal to the allowable stress; the strength test is unqualified when the maximum equivalent stress of the structure is greater than the allowable stress.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention uses the Discrete Element Method (DEM) to perform high-fidelity time-domain ice load simulation, which realistically reproduces the periodic dynamic impact process of sea ice. It fundamentally overcomes the inherent limitation of the traditional empirical formula method that simplifies ice load to static force, making the load input for structural strength assessment closer to physical reality, and the assessment results more accurate and reliable.

[0016] 2. This invention, by scientifically screening design extrema based on dynamic characteristics, focuses on typical hazardous events with strong impact and high destructive force in ice loads, rather than using potentially overly conservative standard static ice forces or statistical averages. This avoids safety hazards caused by underestimating dynamic impact effects and prevents structural redundancy and increased construction costs due to overly conservative designs, providing a precise basis for optimized design. 3. The process of this invention is clear and repeatable, and it seamlessly connects the traditionally disconnected ice load prediction with structural analysis, overcoming the drawbacks of relying on isolated and empirical steps, and greatly improving the standardization of the assessment and the efficiency of engineering applications.

[0017] 4. This invention is particularly suitable for evaluating the strength performance of single-point moored floating structures (such as FPSOs) under slow, continuous compression conditions such as flat ice. It can accurately reveal the key weak areas of the structure in this specific hazardous scenario, thereby providing direct and effective technical guidance for the safety verification of mooring systems, the design of anti-icing bow structures, and the establishment of operational safety boundaries.

[0018] Based on the above reasons, this invention can be widely applied in fields such as shipbuilding and marine engineering. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to the present invention.

[0021] Figure 2 This is a schematic diagram of the discrete element parallel bonding model used in this invention.

[0022] Figure 3 This is a schematic diagram of high-fidelity time-domain ice load simulation using the discrete element method (DEM) employed in this invention.

[0023] Figure 4 This is the original ice load time history curve for the dynamic extreme value screening of this invention.

[0024] Figure 5 This is a time history curve of ice load for complex ice conditions according to the present invention.

[0025] Figure 6 This is a schematic diagram of the ice load application scenario and the evaluation object of the present invention.

[0026] Figure 7 This is a schematic diagram of the multi-scale finite element model used in this invention for direct calculation of structural strength.

[0027] Figure 8 This is a cloud map showing the results of the refined strength assessment of the key structural regions based on dynamic ice force extreme values ​​in this invention.

[0028] Figure 9 This diagram represents the quantitative evaluation and verification of the structural strength safety margin under extreme ice load conditions according to the present invention.

[0029] Figure 10This invention provides a structural stress distribution diagram under static water load as a benchmark for load influence analysis.

[0030] Figure 11 This is a comparison diagram of structural stress distribution under wave load conditions obtained by the traditional long-term forecasting method in this invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] like Figure 1 As shown, this invention provides a method for screening time-domain extreme values ​​of ice loads and evaluating the structural strength of polar floating structures, comprising the following steps: S1. A numerical model of the interaction between sea ice and floating structure is established based on the discrete element method. In the numerical model, the parallel bonding model and the tension-shear partition fracture criterion are used to simulate the entire process of sea ice compression, bending and breaking. The target sea area ice condition parameters and sea ice micromechanical parameters are input, and the numerical model is subjected to long-term dynamic simulation to output the complete time history curve of ice load.

[0034] The micromechanical parameters of sea ice include elastic modulus, compressive strength, bond strength and coefficient of friction, while ice condition parameters include ice thickness, ice velocity and ice density.

[0035] In the numerical model, sea ice is discretized into spherical particle units, which are connected by a parallel bonding model. Seawater drag and buoyancy are introduced to simulate the continuous fracture and fragment flow process of sea ice under structural compression.

[0036] Figure 2The diagram clearly demonstrates the core micromechanical model upon which the patented method relies for high-fidelity time-domain numerical simulation of ice loads—a parallel bonded contact model between two spherical particles. Specifically, it illustrates the mechanical relationship between particle A and particle B at the contact point, clearly marking the key internal force components acting on the bond. It intuitively defines how forces and torques are transmitted between the microscopic units (particles) of sea ice discretized in the discrete element method, and simulates their bonding and fracture behavior. The mechanical relationships shown in the diagram form the physical basis for subsequently setting macroscopic mechanical parameters of sea ice and conducting large-scale time-domain simulations. This model ensures that the simulation can realistically reflect the compression, bending, and breakage processes of sea ice, thereby generating physically meaningful dynamic ice load time-history curves, serving as the theoretical cornerstone and data source of the entire evaluation process.

[0037] Figure 3 The left side of the image shows a schematic diagram of the discrete element method (DEM) numerical simulation scenario of the interaction between a polar FPSO and flat ice. The right side shows the time history curve of the corresponding ice load (F_X) as a function of time (t), clearly indicating the key parameters of the simulation condition: ice thickness 1.5 m, ice velocity 0.4 m / s, and the average ice load of 12133 kN over this time period. The time history curve on the right clearly presents the periodic dynamic impact process of the ice load, which is crucial information that traditional static empirical formula methods cannot obtain. This provides original, high-fidelity data input for the subsequent extreme value screening step based on dynamic characteristics. The simulation scenario on the left and the physically meaningful time history curve on the right together demonstrate that the adopted DEM numerical simulation method can effectively reproduce the complex physical process of ice-structure interaction, ensuring the reliability and accuracy of the first step (S1) of the patented method. The specific working parameters (1.5m ice thickness, 0.4m / s ice velocity) and load data (average force 12133kN) marked in the figure are an instance of the application of this patented method to a specific design condition, proving the feasibility of the method.

[0038] S2. Analyze the ice load time history curve and select the dynamic design extreme values ​​based on the dynamic characteristic parameters. The dynamic characteristic parameters include the load peak value, load rise rate, duration of load exceeding the threshold, and time interval between adjacent significant peak values.

[0039] Figure 4The image shows the complete time history curves of ice loads experienced by an FPSO under four typical flat ice conditions. Specifically, it consists of four sub-plots: (a) LC2 condition (ice thickness 1.0 m, ice velocity 0.4 m / s), (b) LC4 condition (ice thickness 1.0 m, ice velocity 0.8 m / s), (c) LC6 condition (ice thickness 1.5 m, ice velocity 0.4 m / s), and (d) LC8 condition (ice thickness 2.0 m, ice velocity 0.4 m / s). These four sets of time history curves together form a complete dynamic database of ice loads. Each curve exhibits a significant, periodic impact process, with dynamic characteristics such as peak height, impact frequency, and load rise rate showing regular differences with variations in ice thickness and ice velocity (e.g., LC8 condition has the highest peak value and the longest impact period). These curves are the core inputs for the simulation-to-screening method of this patent, and are the direct objects of the screening logic. The complex fluctuation characteristics of the curves indicate that ice loads cannot be fully characterized by a static equivalent value. The impact peaks marked in the graph, especially the representative peaks generated by the complete sea ice breaking cycle, are the key load events that pose a momentary threat to the structure. This is from a data visualization perspective. Each sub-graph corresponds to a specific load condition (such as LC2, LC4, LC6, LC8), which allows the screening operation to be tailored to specific design environments. The screening module is based on these specific curves, using algorithms to identify and extract the most engineering-hazardous dynamic extreme points, and outputs them as deterministic load inputs for subsequent direct calculations of structural strength.

[0040] Figure 5 The figure shows the ice load (in kN) on the FPSO under (a) LC15 and (b) LC31 conditions as a function of time (in seconds). The horizontal axis represents time, and the vertical axis represents ice load. The curves are drawn in black against a white background, with clear layout. The core function of this figure is to demonstrate that the patented high-fidelity time-domain simulation method is not only applicable to smooth ice but can also effectively simulate the interaction between ice fragments and structures. Ice fragment loads exhibit different dynamic characteristics than smooth ice: more frequent load impacts, more random peak distribution, more dramatic curve fluctuations, and no obvious long-period pattern. This proves that the evaluation method of this invention has broad applicability and can cover the main types of ice loads in the polar regions. The two curves in the figure are the direct inputs for the dynamic extreme value screening step under the ice fragment condition. The screening module needs to intelligently identify those impact peaks with significant amplitudes that pose an instantaneous threat to the structure from this highly random and discontinuous time-history signal. For example, it needs to screen out high-load events that occur in a short period of time and may represent large ice fragment collisions. This further highlights the necessity of the present invention based on dynamic feature screening, because simple statistical averaging is more difficult to characterize the extreme effects of ice crushing load.

[0041] Figure 6The diagram illustrates the basic stress model of a floating structure (FPSO) in polar waters subjected to sea ice compression. Specifically, it depicts a floating structure with typical upper modules and single-point mooring characteristics, where the area below the waterline at the bow is subjected to a horizontal force from the left, clearly marked with a blue arrow and the words "ice load." This diagram visually defines the engineering problem that the patented method aims to solve—the structural response and strength assessment of a polar floating structure under horizontal ice loads. The ice load is concentrated at the bow of the floating structure, and the areas of maximum and high stress under ice loads are concentrated there. Therefore, this diagram, from both geometric and stress perspectives, pre-identifies the structural components that require key attention throughout the assessment process.

[0042] The steps for screening extreme values ​​in dynamic design include: The first step is to filter and denoise the ice load time history curve, and use the sliding window method to identify all local load peaks in the time history, and record the occurrence time, load amplitude and corresponding location of each load peak.

[0043] The second step is to calculate the rate of increase for each local load peak, remove peaks with a rate of increase lower than a preset threshold, and retain the first candidate peaks. The formula for calculating the rate of increase is:

[0044] in, For the rate of increase, The peak load amplitude, The load value at the starting point. The duration from the starting point to the peak value.

[0045] The third step is to calculate the duration of each first candidate peak exceeding a preset time threshold, and then remove peaks whose duration is lower than the preset time threshold to obtain the second candidate peak.

[0046] Step 4: Calculate the time interval between adjacent candidate peaks in the second candidate peak. If the time interval is less than the preset lower limit of the crushing cycle, it is determined that the two belong to the same ice crushing event, and the one with the larger load amplitude is retained. If the time interval is greater than the preset lower limit of the crushing cycle, it is determined that they are two independent events, and both are retained. The dynamic design extreme value is obtained.

[0047] S3. Locate the location and direction of the dynamic design extremum in the discrete element simulation, apply the location and direction as static load boundary conditions to the whole ship finite element model, calculate the stress distribution and maximum equivalent stress of the whole ship finite element model, and perform strength verification based on the material yield strength and safety factor.

[0048] The stress distribution is calculated under the combined condition of hydrostatic load and the selected extreme ice force. Three-point rigid boundary conditions are applied in the global finite element model of the ship to eliminate rigid body displacement, and the static finite element method is used to solve the equivalent stress distribution of the structure.

[0049] The global finite element model of the ship includes the global ship model, the side local model, the bow floor model and the liquid tank coupling model.

[0050] The maximum equivalent stress of the structure is compared with the allowable stress of the material. The calculation formula for the allowable stress is:

[0051] where, is the allowable stress, is the yield strength of the material, is the safety factor. When the maximum equivalent stress of the structure is less than or equal to the allowable stress, the strength check is qualified; when the maximum equivalent stress of the structure is greater than the allowable stress, the strength check is unqualified.

[0052] Figure 7This is a multi-scale finite element model system for polar FPSOs. It consists of four sub-models of different scales and functions: (a) Full-ship finite element model: This model fully presents the discretized mesh of the overall structure of the target FPSO (with forecastle and superstructure), serving as the basis for assessing the longitudinal strength and overall deformation of the hull beams. (b) Port side finite element model: This model focuses on the local structure on the port side of the hull, clearly displaying the mesh of longitudinal stiffeners, transverse bulkheads, and other components. It is used to analyze the transverse strength and local deformation response of the side structure under asymmetric ice loads or local compression. (c) Rib plate finite element model: This model further scales up to the key transverse strong frame or rib plate structure, showcasing the refined mesh of plates and stiffeners. It is specifically used to assess the local plate strength, stiffener stability, and stress concentration phenomena in areas directly affected by ice loads. (d) Finite element model of liquid tanks near the midships: Transparent rendering is used to show the double-shell structure and internal liquid domain of the cargo oil tanks or ballast tanks. This is used to couple the evaluation of the dynamic pressure load of liquid cargo sloshing on the bulkhead structure under ship motion, reflecting a comprehensive consideration of complex load conditions. This figure shows that the strength evaluation of this patent does not use a simplified model of a single scale, but constructs a multi-level, multi-scale finite element model system from the whole ship to the side local, and then to key components, while taking into account the coupling effect of liquid tanks. This ensures that the evaluation can capture the overall load path and accurately analyze the stress state of local danger points, which is the geometric and discretization basis for refined and high-confidence evaluation. The "dynamic design extreme values" selected in the second step of the patent will be mapped and applied to the corresponding finite element models in this figure according to their location of action. For example, the ice force acting on the bow is mainly loaded on the relevant nodes of (a) the whole ship model and (c) the rib plate model; while the large ship motion (such as pitching) caused by ice load may excite the sloshing load of the liquid tank model in (d). These models are the ultimate solvers for calculating the structural stress response under the combined effects of hydrostatic pressure, ice load, and sloshing load.

[0053] Figure 8The diagram consists of four stress cloud maps: (a) outer shell, (b) inner shell, (c) truss, and (d) bulkhead. A color gradient from blue (low stress) to red (high stress) visually represents the magnitude and concentration of stress. This diagram represents the decisive assessment conclusion obtained after completing the entire process. The high-stress areas (yellow to red) clearly shown in the diagram are not uniformly distributed, but highly concentrated at the leading edges of the bow outer and inner shells, as well as specific bulkhead areas. This quantitatively and visually demonstrates that the dynamic ice force extrema selected by the method of this invention can accurately identify the potential weak points most likely to fail under real ice load impact. It shows that the selected extrema are not random data, but carry load characteristics that lead to critical structural responses, thus refuting the engineering necessity and scientific validity of the core step of dynamic feature-based selection from the results. This represents the endpoint of the patented method's transformation from processing time-dimensional signals (ice load time history) to analyzing spatial-dimensional responses (structural stress field). It transforms abstract, time-varying impact loads into concrete, quantifiable, and locatable spatialized safety information. The specific stress values ​​and locations marked in the diagram allow engineers to directly determine where and by how much stress exceeds allowable standards under the most representative dynamic load impacts selected from a pool of data. This achieves a closed loop from load analysis to actionable engineering decisions, demonstrating the ultimate practical value of this patented method. The stress concentration patterns revealed in the diagram provide precise targets for ice-resistant structure optimization. Designers can then target specific areas for reinforcement, rather than implementing generalized, conservative reinforcement across the entire ship. Therefore, this diagram is not only a conclusion of safety verification but also an input for efficient optimization design. It enables structural reinforcement measures to directly respond to the actual mechanical behavior revealed by dynamic ice loads, thereby improving safety while avoiding unnecessary weight and cost increases, achieving a balance between safety and economy through a data-driven approach. This diagram is crucial visual and quantitative evidence supporting the transformation of the entire patented method from theoretical processes to practical engineering value.

[0054] Figure 9Using a visualization approach that emphasizes both dual operating conditions, time history, and statistical values, the significant improvement in ice resistance performance achieved by the ship type optimized using the method of this patent was quantitatively verified. Specifically, this is presented through two parallel sub-figures (a) and (b): a comparison of operating conditions with different ice thicknesses, a comparison of core data, and an analysis of fluctuation characteristics. This figure employs refined finite element stress cloud map visualization technology to systematically present the quantitative distribution of equivalent stress in key components of the FPSO bow section under the extreme smooth ice condition (ice thickness 2.0m, ice velocity 0.4m / s) selected according to the method of this invention. Specifically, it consists of four stress cloud maps: (a) bow outer shell, (b) bow inner shell, (c) bow girder, and (d) bow bulkhead. A color gradient from blue (low stress) to red (high stress) visually and quantitatively displays the magnitude of stress and spatial concentration. The LC8 operating condition corresponding to this figure is one of the most stringent smooth ice scenarios set in this invention. The figure clearly shows that under these external conditions, the maximum equivalent stresses of the bow outer shell and inner shell reached approximately 301.1 MPa and 284.2 MPa, respectively. These values ​​are extremely close to but do not exceed the allowable stress of material NV-36 (322.7 MPa). This quantitative result has dual significance: First, it irrefutably proves that under extreme ice conditions, the structural safety margin is significantly compressed, and the ice load is the controlling load of the design, highlighting the necessity of using the method of this invention for accurate evaluation; second, the conclusion that the stress did not exceed the limit is itself direct evidence that the design has been verified using this patented method, demonstrating the applicability and reliability of the method in engineering judgment. The ice load time history curve for the LC8 condition has an impact peak with extremely high amplitude. The maximum ice force value selected from this time history by this invention was used in this calculation. Figure 9The high-intensity, high-concentration stress distribution pattern presented is precisely the inevitable structural response caused by the dynamic impact load. This strongly proves that the extreme values ​​selected by this invention are not mathematically random points, but loads that can accurately induce and quantify the mechanical behavior of the structure under extreme conditions. Using overly conservative static empirical values ​​may overestimate the stress, leading to over-design; using average values ​​may underestimate the risk. The results in this figure are precisely near the safety boundary, verifying the accuracy and superiority of the core step of dynamic feature-based screening in balancing safety and economy from an engineering consequence perspective. This figure visualizes the stress spectrum of the structure near the safety red line. The stress concentration areas in the figure (such as the red and yellow areas in specific parts of the shell) are the most vulnerable hotspots under extreme ice loads. This provides designers with precise targeted reinforcement targets, allowing for targeted reinforcement of local areas rather than the whole structure, achieving optimal cost. At the same time, the specific maximum stress value of 301.1 MPa provides a quantitative benchmark for setting monitoring-based safety warning thresholds during the operation phase. Therefore, this figure is not only an evaluation conclusion, but also a key data interface connecting design and operation and guiding the efficient allocation of resources, reflecting the closed-loop value of the method of this invention from analysis to in-depth engineering application.

[0055] Figure 10 Employing multi-component refined finite element stress cloud visualization technology, this system reveals the inherent stress transmission patterns and baseline stress levels of the target floating structure (FPSO) under the baseline condition of basic hydrostatic load. Specifically, it consists of four stress cloud maps: (a) outer shell, (b) inner shell, (c) ribs and vertical girder, and (d) longitudinal and horizontal girder. Using a color gradient from blue (low stress) to red (high stress), it quantitatively and regionally displays the initial mechanical state of the structure under load-free conditions. This figure accurately quantifies the structural response caused solely by the hydrostatic load in the combined load condition. The figure shows that under hydrostatic pressure, the stress distribution mainly follows the overall bending of the hull beams and the local water pressure distribution patterns. For example, the outer shell experiences relatively uniform stress, while stress concentration occurs at the connection nodes and intersections between the inner shell and the longitudinal and transverse girder. This provides an indispensable reference for accurately identifying and isolating additional stresses purely caused by the dynamic extreme values ​​of ice load. Without this reference, the independent contribution of ice load cannot be clearly defined. The high-stress areas revealed in this diagram are locations that require attention in traditional wave load design for ship structures. Furthermore, comparing this diagram with... Figure 8 , Figure 9A comparison clearly reveals that ice loads induce entirely new high-stress concentration zones in areas such as the bow hull front and waterline region, which are absent or minimally significant under static water loads. This comparison intuitively and quantitatively demonstrates the existence of unique, ice-load-dominated sensitive areas in polar floating structures. The dynamic extreme value screening and direct calculation proposed in this patented method are precisely designed to address this specific threat, thus achieving a leap from "strength assessment to ice-resistant specific strength assessment" in engineering design. Using the benchmark established in this figure, engineers can quantitatively analyze the load contribution decomposition capability under combined working conditions, determining the proportion of total stress originating from static water and the proportion from ice loads, making design decisions more scientific. For example, nodes with already high static water background stress pose a greater risk after the addition of ice loads and require priority reinforcement; while high-stress zones newly induced by ice loads require specialized research into their ice-resistant structures. Therefore, this figure is not only the result of a single working condition but also a key analytical tool and comparative basis supporting the patented method in achieving refined and differentiated strength assessment and optimization decisions, reflecting the systematic and rigorous nature of the invention.

[0056] Figure 11 Using a traditional evaluation process combining long-term forecasting and design wave method with finite element analysis, the system presents the equivalent stress background distribution of the target FPSO structure under the CLC1 characteristic wave load, representing an extreme sea state. Specifically, it consists of four stress cloud maps: (a) outer shell, (b) inner shell, (c) ribs and vertical girder, and (d) longitudinal and horizontal girder. Color gradients quantitatively display the stress field under wave-induced overall bending and local loads on the hull beams. The innovation and necessity of this invention are demonstrated from the opposite perspective: this figure represents the mainstream and mature method for strength assessment of floating structures in current standards. The high-stress areas revealed in the figure (such as the connection between the longitudinal girder and the bulkhead, and specific parts of the inner shell) are classic danger zones dominated by wave loads. However, comparing this figure with the method of this invention... Figure 8 , Figure 9 A direct comparison of the stress cloud diagrams (under extreme ice loads) reveals significant differences and even spatial separation between the key stress regions induced by wave loads and ice loads on the structure. The high-stress areas caused by wave loads (in this figure) are mostly concentrated at strong structural member nodes near the midships, while those caused by ice loads (…) Figure 8 , Figure 9This will induce unique, highly concentrated stress in the bow region. This visual comparison irrefutably proves that relying solely on traditional wave-based design wave methods cannot effectively identify and assess the unique strength risks of polar floating structures caused by ice loads. Therefore, this figure strongly supports the necessity and urgency of proposing an independent time-domain extreme value screening and direct calculation method for ice loads from the perspective of the limitations of existing technology. This figure quantitatively presents the stress level of the structure in non-ice extreme environments, which constitutes the conventional safety baseline for design. What this invention focuses on and addresses is the incremental risk and specific failure modes caused by the superposition or induction of ice loads above this baseline. As can be seen from the comparison, in the bow region, the stress generated by traditional wave loads is often low, while ice loads can cause its stress to increase sharply. This clearly defines the technical mission and application scenario of the patented method of this invention: it is not intended to replace traditional wave strength assessment, but rather to serve as a specialized, parallel assessment module for polar-specific loads, filling the gaps or deficiencies of traditional methods in ice resistance strength assessment. This positioning positions the patented method as complementary to existing technologies, rather than a simple replacement, highlighting its innovative uniqueness and technological acceptability. (This figure and...) Figure 8 , Figure 9 Together, these constitute a complete strength spectrum for polar floating structures under the two dominant environmental loads of waves and ice. This enables designers to conduct risk-based differentiated designs: traditional methods are used to optimize wave-sensitive areas, while the methods of this invention are applied to specifically design and strengthen ice-sensitive areas (such as the bow). Ultimately, only by comprehensively evaluating these two sets of results can true global optimization and safety under all operating conditions be achieved. Therefore, this figure is not only a demonstration of traditional methods but also a key component of the more complete and advanced wave-ice integrated strength assessment system constructed by this invention. It demonstrates that the methods of this invention can work collaboratively with traditional processes to jointly improve the overall scientific level and safety assurance capabilities of polar structure design.

[0057] As a preferred embodiment of the present invention, the main hull of the polar floating structure (including side plating, deck, and bottom plating) is made of high-strength marine steel plates that meet the requirements of polar navigation, such as NV-36 grade steel plates with a standard yield strength of 355 MPa. This material is a conventional and typical choice for polar vessels and marine engineering structures to meet basic strength and low-temperature toughness requirements. The mooring system of the structure, especially the anchor chain, uses high-strength alloy steel of the corresponding design grade, such as RAMNAS FL-4 grade or similar high-strength cast steel, to withstand the huge dynamic tension caused by ice loads. In critical areas where the structure is in direct contact with ice, where stress is concentrated, or where special protection is required (such as near the bow waterline, sides, etc.), steel of the same or higher grade as the main structure can be used, and ice resistance requirements can be met by increasing plate thickness and optimizing the arrangement of aggregates (i.e., structural reinforcement). One of the core objectives of the evaluation method of the present invention is to provide accurate load basis and optimization guidance for the structural reinforcement design of such areas. The anti-corrosion and anti-icing coatings for the structure can employ high-performance epoxy coatings or anti-icing coating systems suitable for polar low-temperature environments. These functional coatings protect the main steel structure from seawater corrosion and physical wear caused by sea ice adhesion. Their selection is common knowledge in the field, and their specific materials and properties do not affect the implementation and effectiveness of the evaluation method of this invention.

[0058] This invention also includes a system for screening time-domain extreme values ​​of ice loads and evaluating structural strength of polar floating structures, comprising: The ice load time-domain high-fidelity simulation module consists of a discrete element method (DEM) solver, a sea ice micro-parameter library, a particle contact model library, a boundary condition applicator, and a data output interface.

[0059] The dynamic design extreme value intelligent screening module consists of a time history data processor, a dynamic feature parameter (rise rate, period, peak value) recognizer, and a screening logic controller.

[0060] The structural strength direct calculation and evaluation module consists of a static finite element (FEM) solver, load mapping and application elements, a result post-processor, and a strength checker.

[0061] The high-fidelity ice load time-domain simulation technology of this invention is based on the discrete element method (DEM), which discretizes sea ice into a large number of spherical particle units that follow a specific contact model. The particles are connected by a parallel bonding model. By defining microscopic parameters such as bonding strength and friction coefficient, and introducing seawater drag and buoyancy, it can simulate complex fluid-structure interaction processes such as continuous fracture and debris flow around sea ice under structural compression with high fidelity. This results in a dynamic ice load time history with clear physical meaning, fundamentally overcoming the static limitations of empirical formula methods.

[0062] The working principle of the dynamic characteristic-based extreme value screening technology of this invention lies in identifying engineering hazardous events driven by physical destruction processes in the time history curve. Sea ice destruction is periodic, with each complete crushing-fracture cycle generating a load pulse. The screening technology analyzes the load rise rate, pulse width, and cycle interval to identify typical peaks with high impact intensity and concentrated energy input, rather than accidental, unrepresentative outliers or flat averages. This ensures that the selected design load accurately reflects the dynamic impact nature of ice loads while possessing a reasonable probability of occurrence and engineering representativeness.

[0063] The working principle of this invention's ice load-structural strength direct assessment principle is to efficiently combine dynamic simulation with static verification. First, the actual load process is obtained through computationally expensive DEM time-domain simulation. Then, the most critical static load moments (extreme points) are extracted. Finally, the strength is verified using the computationally efficient static finite element method. This approach of dynamic load and static equivalence significantly reduces the computational cost of fully coupled transient dynamic finite element analysis while ensuring assessment accuracy, making it highly practical for engineering applications. This method is particularly suitable for assessing the threat posed by slow, continuous compression conditions like smooth ice to the tension of mooring systems and the strength of local bow structures, achieving a balance between targeted and efficient assessment.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures, characterized in that, Includes the following steps: A numerical model of the interaction between sea ice and floating structures is established based on the discrete element method. In the numerical model, the parallel bonding model and the tension-shear partition fracture criterion are used to simulate the entire process of sea ice compression, bending and breaking. The target sea area ice condition parameters and sea ice micromechanical parameters are input, and the numerical model is subjected to dynamic simulation to output the complete time history curve of ice load. The ice load time history curve is analyzed, and the dynamic design extreme value is obtained by screening based on the dynamic characteristic parameters. The dynamic characteristic parameters include the load peak value, the load rise rate, the duration of the load exceeding the threshold, and the time interval between adjacent significant peak values. Find the corresponding action position and direction of the dynamic design extremum in the discrete element simulation, apply the action position and direction as static load boundary conditions to the whole ship finite element model, calculate the stress distribution and maximum equivalent stress of the whole ship finite element model, and perform strength verification based on the material yield strength and safety factor.

2. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, The micromechanical parameters of the sea ice include elastic modulus, compressive strength, bonding strength and coefficient of friction, and the ice condition parameters include ice thickness, ice velocity and ice density.

3. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, In the numerical model, sea ice is discretized into spherical particle units, which are connected by a parallel bonding model. Seawater drag and buoyancy are introduced to simulate the continuous fracture and fragment flow process of sea ice under structural compression.

4. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, The stress distribution was calculated under the combined conditions of hydrostatic load and selected ice force extreme values. Three-point rigid boundary conditions were applied to the whole ship finite element model to eliminate rigid body displacement, and the equivalent stress distribution of the structure was solved by the static finite element method.

5. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, The finite element model of the entire ship includes the overall ship model, the side local model, the bow rib model, and the liquid tank coupling model.

6. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, The steps for screening the extreme values ​​in the dynamic design include: The ice load time history curve is filtered and denoised, and the sliding window method is used to identify all local load peaks in the time history. The occurrence time, load amplitude and corresponding location of each load peak are recorded. For each local load peak, the rate of increase is calculated. Peaks with a rate of increase lower than a preset threshold are discarded, and the remaining peaks are the first candidate peaks. The formula for calculating the rate of increase is: in, For the rate of increase, The peak load amplitude, The load value at the starting point. The duration from the starting point to the peak value; Calculate the duration for which each first candidate peak exceeds a preset time threshold, and remove peaks whose duration is less than the preset time threshold to obtain second candidate peaks; Calculate the time interval between adjacent candidate peaks in the second candidate peak. If the time interval is less than the preset lower limit of the breaking cycle, it is determined that the two belong to the same ice breaking event, and the one with the larger load amplitude is retained. If the time interval is greater than the preset lower limit of the breaking cycle, it is determined that they are two independent events, and both are retained. The dynamic design extreme value is obtained.

7. The method for screening time-domain extreme values ​​of ice load and evaluating structural strength of polar floating structures according to claim 1, characterized in that, The maximum equivalent stress of the structure is compared with the allowable stress of the material. The formula for calculating the allowable stress is as follows: in, For allowable stress, For the material's yield strength, As a safety factor, the strength test is qualified when the maximum equivalent stress of the structure is less than or equal to the allowable stress; the strength test is unqualified when the maximum equivalent stress of the structure is greater than the allowable stress.

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