Method for evaluating wind wave resistance of kelp leaves and application

Abstract

The invention relates to an evaluation method of wind wave resistance of kelp leaves and application, and belongs to the technical field of seawater algae culture, the method comprises the following steps: 1) preparing kelp test samples, and dividing each kelp sample into at least two groups of test samples; 2) applying a tensile load to one group of test samples until the test samples are damaged to obtain a stress-strain curve; 3) performing a stress relaxation test on the other group of test samples to obtain a stress relaxation curve; and 4) performing principal component analysis on the obtained mechanical characteristic parameters of the test sample so as to comprehensively evaluate the wind wave resistance of the kelp leaves. Based on the comprehensive score, the wind wave resistance of the leaves of different kelp strains is evaluated, and a theoretical basis is provided for breeding of wind wave resistant kelp varieties.

Description

Technical Field

[0001] The invention belongs to the technical field of seawater algae cultivation, and specifically relates to an evaluation method for the wind and wave resistance of kelp leaves and an application thereof. Background Art

[0003] Offshore kelp farming has both advantages and challenges. The water flow exchange rate in offshore deep waters is fast, which is conducive to metabolic processes such as photosynthesis, thereby increasing the yield of kelp. However, offshore aquaculture areas often encounter high sea conditions of level 3-4 (up to level 5 during storm surges), with wave heights of up to 0.5-2.5m and flow rates of 0.3-1.5m / s. The strong currents generated by such high sea conditions not only pose a challenge to the safety of aquaculture facilities, but also produce strong mechanical stress on the kelp (such as stretching, bending, and twisting), which can easily cause the kelp to fall off or break off. The proportion of kelp falling off or being damaged at the edge of some offshore aquaculture areas can be as high as more than 50%. Therefore, cultivating new varieties of kelp that are resistant to wind and waves is of great significance to promoting the development of the offshore kelp farming industry. The ability of kelp to resist wind and waves mainly depends on the mechanical strength and flexibility of its algal tissue, but there is currently a lack of scientific and objective evaluation methods, which seriously restricts the cultivation of wind and wave-resistant seaweed varieties. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a method for evaluating the wind and wave resistance of kelp leaves and its application. The method sets parameters such as the shape and size of the kelp leaf samples, the loading rate, the algae position, the constant strain and the relaxation time, and carries out tests on the tensile performance and relaxation performance of the kelp leaves under tensile force, so as to obtain relevant parameter indicators reflecting the mechanical strength and flexibility of the kelp algae, and then performs principal component analysis on these parameters, and evaluates the wind and wave resistance of the leaves of different kelp strains based on the comprehensive scores, thereby providing a theoretical basis for the breeding of wind and wave resistant kelp varieties.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for evaluating the wind and wave resistance of kelp leaves, the method comprising the following steps: 1) preparing kelp test samples, each kelp sample is divided into two groups of samples; 2) applying a tensile load to one group of samples until the sample is destroyed, and obtaining a stress-strain curve; 3) performing a stress relaxation test on the other group of samples, that is, after applying a tensile load to the sample to reach a set displacement, maintaining the displacement (constant strain) for a certain period of time, and obtaining a stress relaxation curve; 4) performing principal component analysis on the obtained mechanical characteristic parameters of the samples, so as to comprehensively evaluate the wind and wave resistance of the kelp leaves.

[0007] Furthermore, the step 1) prepares the kelp test sample: the kelp leaves are made into dumbbell-shaped specimens to ensure that the specimen breaks in the middle during the tensile test and provide sufficient clamping force at the clamping end;

[0008] The narrow part of the sample is the test site, and the gauge length is preferably set to 25-30 mm and the width is 4-6 mm; 5 points are randomly selected within the gauge length range, their thickness is measured, and the average value is taken as the sample thickness; the kelp leaf samples of different strains must meet the following conditions: they are collected at the same growth stage and taken from the same tissue part of the algae, and at least two groups of test samples are prepared for each kelp, which are used to complete the tensile load test and the stress relaxation test respectively.

[0009] The step 2) applies a tensile load to a group of samples in the kelp test samples prepared in step 1 until the samples are broken, and obtains a stress-strain curve; specifically, the wide parts at both ends of the samples are wrapped with flexible materials, fixed on the fixture of the tensile testing machine, stretched at a stretching rate of 20-50mm / min until broken, and the changes in the tensile force F and the elongation △L are recorded to generate an F~△L curve, i.e., a stress-strain curve, and calculate the tensile elastic modulus, tensile strength, maximum tensile force, and elongation at break; the samples that break within the gauge range (the narrow part of the dumbbell-shaped sample) are valid samples, and the samples that break outside the gauge range (generally in the transition zone from the dumbbell neck to the head) are invalid samples; at least 10 parallel measurement data of valid samples are required for each kelp, and there is no significant difference in the thickness of the valid samples between different strains.

[0010] The step 3) is to conduct a stress relaxation test on another group of sample samples, that is, after applying a tensile load to the sample to reach a set displacement, maintain the displacement (constant strain) for a certain time to obtain a stress relaxation curve, including: wrapping the wide parts of the two ends of the sample with flexible materials and fixing them on the fixture of the testing machine. Enter the gauge length, width and thickness of the sample in the software. The number and thickness of the samples must meet the following requirements: each kelp must have at least 10 parallel samples, and there is no significant difference in the thickness of different samples; using the program control function, the sample is stretched to a constant strain at a stretching rate of 20-50mm / min, and the constant strain time (i.e., relaxation time) is set to 240-360 seconds. The value range of constant strain is 10%-12% of the sample gauge length. The software system automatically records the stress reduction value over time to obtain a "force-time" stress relaxation curve. The stress relaxation curve is fitted using the Maxwell three-element model to obtain stress relaxation parameters such as the equilibrium elastic modulus, attenuated elastic modulus and viscosity coefficient of the sample. The Maxwell three-element model formula is: F(t) = D × E 0 +D×E 1 ×exp(-t / T). In the formula, F(t) is the load on the material (N); D is the constant strain; E0 is the equilibrium elastic modulus (or instantaneous elastic modulus) (N·mm -1 ), E 1 is the attenuation elastic modulus (or elastic coefficient) of the Maxwell body (N·mm -1 );T is the relaxation time of the Maxwell body model element, t is the set relaxation time (s). Viscosity coefficient η=E 1 T (Unit: Ns mm -1 ).

[0011] The step 4) performs principal component analysis on the obtained mechanical characteristic parameters of the sample to comprehensively evaluate the wind and wave resistance of the kelp leaves; specifically, (1) the average values ​​of the obtained mechanical strength index and flexibility index of each strain are sorted into a matrix form, with the sample number as the row and the characteristic parameter as the column; the mechanical strength index includes tensile strength and maximum tensile force, and the flexibility index includes tensile elastic modulus, elongation at break, equilibrium elastic modulus, attenuation elastic modulus and viscosity coefficient;

[0012] (2) First, perform Z-score standardization on the data;

[0013] (3) Using the standardized data matrix, perform “dimensionality reduction-factor analysis-principal component analysis” in the statistical analysis software to determine the number of principal components and select the principal components with a cumulative variance explanation rate of more than 90%. Use the variance explanation rate value to calculate the weight of each indicator. Based on the principal component score, calculate the comprehensive score and ranking of each strain to comprehensively evaluate the wind and wave resistance of kelp leaves.

[0014] The present invention also provides a method for breeding kelp varieties resistant to wind and waves using the evaluation method. The method uses the evaluation method to evaluate the wind and wave resistance of kelp individuals, arranges them from large to small according to the comprehensive scores, and selects the individuals ranked at the top as breeding parents. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of a dumbbell specimen of a kelp leaf, where the gauge length is the length of the narrow part of the specimen;

[0016] Figure 2 Example diagram of the names of various tissue parts of kelp;

[0017] Figure 3 An example of a kelp specimen breaking after stretching, where √ represents a valid sample and × represents an invalid sample. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further explained below by examples, but the protection scope of the present invention is not limited in any form by the examples.

[0019] Example:

[0020] 1) Preparation of kelp test samples

[0021] In mid-May, three strains of each of the six kelp strains (named A, B, C, D, E, and F) were collected from the Rongcheng Sea. The base and mid-belt tissue of each kelp leaf were cut off. The names of the various parts of the kelp leaf are as follows: Figure 2 As shown in the figure, 30 dumbbell-shaped specimens were prepared using a dumbbell-shaped cutter. Figure 1 As shown. The total length of each sample is 75mm, the length of the test part is 25mm (gauge length), and the width is 4mm. Five points are randomly selected within the gauge length range for thickness measurement, and the sample thickness range is between 3.14-3.58mm. The dumbbell-shaped samples made from each kelp are divided into two groups.

[0022] 2) Stretch the blade until it breaks and obtain the stress-strain curve

[0023] For one of the two groups of samples of each kelp, the wide parts at both ends were wrapped with double gauze and fixed on the fixture of a microcomputer-controlled electronic universal material testing machine. After the gauge length, width and thickness of the sample were input into the software system of the testing machine, the sample was stretched at a stretching rate of 20 mm / min until it broke, and the stress-strain curve was obtained, from which the tensile elastic modulus (E m ), tensile strength (TS), maximum tensile strength (F m ), elongation at break (E b ). Among them, the tensile elastic modulus refers to the proportional coefficient of stress and strain of the sample in the elastic deformation stage (initial stretching), which can measure the ease of elastic deformation of the material; the tensile strength refers to the maximum ability of the sample to resist damage under tension, that is, the ratio of the maximum force the sample withstands when it breaks to its original cross-sectional area. The sample that breaks within the gauge range (the narrow part of the dumbbell-shaped sample) is a valid sample, and the sample that breaks outside the gauge range (generally in the transition zone from the dumbbell neck to the head) is an invalid sample, such as Figure 3 In this example, at least 10 valid samples of each kelp were measured in parallel, and there was no significant difference in thickness among different valid samples (the average thickness ranged from 3.26 to 3.35 mm).

[0024] 3) Perform a stress relaxation test on the blade to obtain a stress relaxation curve, that is, after applying a tensile load to the sample to reach a set displacement, maintain the displacement (constant strain) for a certain period of time to obtain a stress relaxation curve.

[0025] For the other group of samples in the two groups of samples of each kelp, the wide parts at both ends were wrapped with double-layer gauze and fixed on the fixture of the microcomputer-controlled electronic universal material testing machine. The gauge length, width and thickness of the sample were entered in the software. The average thickness of this group of samples ranged from 3.24 to 3.32 mm (there was no significant difference between the groups). Using the program control function of the testing machine software, the stretching rate was set to 20 mm / min, the constant strain was set to 2.5 mm, and the relaxation time was set to 300 seconds. The software system automatically records the decrease in stress over time to obtain the "force-time" stress relaxation curve: in the initial stage of maintaining a constant strain, the internal stress of the material decreases sharply with the increase of time, while in the later stage the internal stress slowly decays with time and finally stabilizes. The Maxwell three-element model was used to fit the stress relaxation curve to obtain the equilibrium elastic modulus (E 0 ), attenuation elastic modulus (E 1 ) and viscosity coefficient (η) and other stress relaxation parameters. Among them, the elastic modulus reflects the strength of elastic deformation ability. The smaller its value, the stronger the elastic deformation ability of the sample and the better the softness of the internal organization; the viscosity coefficient reflects the strength of the sample's viscous resistance to deformation. The smaller its value, the weaker the sample's viscous resistance to deformation and the better the fluidity of the internal organization structure. The formula of Maxwell's three-component model is: F(t) = D×E 0 +D×E 1 ×exp(-t / T). In the formula, F(t) is the load on the material (N); D is the constant strain; E 0 is the equilibrium elastic modulus (or instantaneous elastic modulus) (N·mm -1 ), E 1 is the attenuation elastic modulus (or elastic coefficient) of the Maxwell body (N·mm -1 );T is the relaxation time of the Maxwell body model element, t is the set relaxation time (s). Viscosity coefficient η=E 1 T (Unit: Ns mm -1 ).

[0026] 4) Conduct principal component analysis on the mechanical characteristic parameters of the obtained samples to comprehensively evaluate the wind and wave resistance of kelp leaves

[0027] (1) Data preparation

[0028] The mechanical strength indexes (TS, F m ) and flexibility index (E m 、E b 、E 0 、E 1 The average values ​​of , n) are organized into a matrix form, with sample numbers as rows and characteristic parameters as columns, as shown in Table 1;

[0029] Table 1 Mechanical characteristics data of kelp samples

[0030]

[0031]

[0032] Note: "-1", "-2" and "-3" represent 3 samples of each strain, such as A-1, A-2 and A-3 represent 3 samples of strain A.

[0033] The greater the elongation at break, the greater the ductility that the algae can withstand when stretched, and the higher the flexibility; the greater the tensile strength and maximum tensile force, the higher the mechanical strength. m ), equilibrium elastic modulus (E 0 ), attenuation elastic modulus (E 1 The smaller the values ​​of flexibility indicators such as E and viscosity coefficient (η), the easier it is for the sample to produce elastic deformation and the weaker the viscous resistance to deformation, and the higher the flexibility. m 、E 0 、E 1 and η are adjusted to negative values, and the results in Table 2 are obtained;

[0034] Table 2 Adjusted mechanical characteristics data of kelp samples

[0035]

[0036] (2) Data standardization

[0037] The adjusted data were normalized by Z-score to eliminate the dimensional differences between different mechanical characteristic parameters. The normalization method is to subtract the mean (μ j ), and then divided by its standard deviation (σ j ), so that the data are within the same dimension range and dimensionless units, the calculation formula is: Z ij =(X ij -μ j ) / σ j Among them, Z ij is the standardized data, X ij is the original data, μ j is the mean value of the jth characteristic parameter, σ j is the standard deviation of the jth characteristic parameter. The standardized data matrix is ​​shown in Table 3;

[0038] Table 3 Data matrix after standardization of mechanical characteristics test values ​​of kelp samples

[0039]

[0040] (3) Principal component analysis

[0041] Using the standardized data matrix, "dimensionality reduction-factor analysis-principal component analysis" was performed in the statistical analysis software to select the principal components with a cumulative variance explanation rate of more than 90%. This embodiment extracts 3 principal components, of which the variance explanation rates of principal component 1, principal component 2 and principal component 3 are 79.21%, 10.33% and 4.84% respectively, and the cumulative variance explanation rate of these 3 principal components is 94.37%, as shown in Table 4. The weight coefficients (variance explanation rate / cumulative variance explanation rate 94.37%) of principal component 1, principal component 2 and principal component 3 calculated using the variance explanation rate values ​​are 83.93%, 10.95% and 5.13% respectively, as shown in Table 5;

[0042] Table 4 Variance Explanation

[0043] Element Variance explained (%) Cumulative variance explained (%) 1 79.21 79.21 2 10.33 89.53 3 4.84 94.37 4 2.70 97.07 5 1.91 98.98 6 0.84 99.82 7 0.18 100.00

[0044] Table 5 Weight coefficients of principal components

[0045] name Variance explained (%) Cumulative variance explained (%) Weight (%) Principal component 1 79.21 79.21 83.93 Principal component 2 10.33 89.53 10.95 Principal component 3 4.84 94.37 5.13 .

[0046] Using the standardized data matrix (Table 3), the weight coefficient of the principal component (Table 5) and the component score coefficient matrix (Table 6), the principal component score, comprehensive score and ranking of each sample (Table 7) were calculated, thereby obtaining the comprehensive score (the average of the comprehensive scores of 3 parallel samples) and ranking (Table 8) of each strain. The final analysis showed that the wind and wave resistance of kelp leaves of different strains ranked as follows: strain D> strain E> strain C> strain B> strain F> strain A. The deep-water aquaculture test verified that the leaf breakage rate of kelp strains D and E was significantly lower, further confirming that the evaluation results of this method have high reliability;

[0047] Table 6 Component score coefficient matrix

[0048] name Principal component 1 Principal component 2 Principal component 3 Maximum tensile strength 0.160 0.401 -0.212 tensile strength 0.128 0.892 0.668 Elongation at break 0.166 0.158 -0.96 Elastic modulus 0.170 -0.327 -0.253 Balanced elastic modulus 0.173 -0.222 -0.381 Decayed elastic modulus 0.168 -0.288 0.254 Viscosity coefficient 0.155 -0.403 1.126

[0049] Table 7 Principal component scores, comprehensive scores and rankings of kelp samples

[0050]

[0051]

[0052] Table 8 Comprehensive scores and rankings of kelp strains

[0053] Ranking strain Comprehensive score 1 D 1.02 2 E 0.75 3 C 0.22 4 B -0.11 5 F -0.42 6 A -1.45

Claims

1. A method for evaluating the wind and wave resistance of kelp leaves, characterized in that: The method comprises the following steps: 1) preparing kelp test samples, wherein each kelp sample is divided into at least two groups of test samples; 2) applying a tensile load to one group of test samples until the test sample is destroyed, thereby obtaining a stress-strain curve; 3) performing a stress relaxation test on another group of test samples, thereby obtaining a stress relaxation curve; and 4) performing a principal component analysis on the obtained mechanical characteristic parameters of the test samples, thereby comprehensively evaluating the wind and wave resistance of the kelp leaves.

2. The method for evaluating the wind and wave resistance of kelp leaves according to claim 1, characterized in that: Preparation of kelp test samples: make the kelp leaves into dumbbell-shaped test samples, with the narrow part as the test site, randomly select 5 points within the gauge range of the site, measure their thickness, and take the average value as the test sample thickness; kelp leaf test samples of different strains must meet the following conditions: be collected at the same growth stage and taken from the same tissue site of the algae, and prepare at least two groups of test samples for each kelp, which are used to complete the tensile load test and stress relaxation test respectively.

3. The method for evaluating the wind and wave resistance of kelp leaves according to claim 2, characterized in that: Set the gauge length to 25-30mm and the width to 4-6mm.

4. The method for evaluating the wind and wave resistance of kelp leaves according to claim 1, characterized in that: The method for obtaining the stress-strain curve is to wrap the wide parts of both ends of the test sample with flexible materials, fix them on the fixture of the tensile testing machine, stretch them at a stretching rate of 20-50 mm / min until they break, record the changes in the tensile force F and the elongation △L, generate the F~△L curve, i.e. the stress-strain curve, and calculate the tensile elastic modulus, tensile strength, maximum tensile force and elongation at break; Those that broke within the gauge length were valid test samples, and those that broke outside the gauge length were invalid test samples. At least 10 parallel measurement data of valid test samples were required for each kelp, and there was no significant difference in the thickness of valid test samples between different kelp strains.

5. The method for evaluating the wind and wave resistance of kelp leaves according to claim 1, characterized in that: The method for obtaining the stress relaxation curve is to wrap the wide parts of the two ends of the test sample with flexible materials and fix them on the fixture of the testing machine. The number and thickness of the test samples must meet the following requirements: each kelp must have at least 10 parallel test samples, and there is no significant difference in thickness between test samples of different strains; the test sample is stretched to a constant strain at a stretching rate of 20-50 mm / min, and the constant strain time is set to 240-360 seconds; the constant strain value range is 10%-12% of the test sample gauge length, and the "force-time" stress relaxation curve is obtained. The stress relaxation curve is fitted using the Maxwell three-element model, thereby obtaining the stress relaxation parameters of the test sample including the equilibrium elastic modulus, attenuated elastic modulus and viscosity coefficient.

6. The method for evaluating the wind and wave resistance of kelp leaves according to claim 1, characterized in that: The principal component analysis was performed on the mechanical characteristic parameters of the test samples to comprehensively evaluate the wind and wave resistance of the kelp leaves; specifically, (1) the average values ​​of the mechanical strength index and flexibility index of each strain were sorted into a matrix form, with the sample number as the row and the characteristic parameter as the column; the mechanical strength index included tensile strength and maximum tensile force, and the flexibility index included tensile elastic modulus, elongation at break, equilibrium elastic modulus, attenuation elastic modulus and viscosity coefficient; (2) First, perform Z-score standardization on the data; (3) Using the standardized data matrix, perform "dimensionality reduction-factor analysis-principal component analysis" in the statistical analysis software to determine the number of principal components and select the principal components with a cumulative variance explanation rate of more than 90%; The variance explanation rate value is used to calculate the weight of each indicator; The comprehensive score and ranking of each strain were calculated based on the principal component scores, and the wind and wave resistance of kelp leaves was comprehensively evaluated.

7. A method for breeding kelp varieties resistant to wind and waves using the evaluation method described in any one of claims 1 to 6, characterized in that: The method uses the evaluation method to evaluate the wind and wave resistance of kelp individuals, arranges them from large to small according to the comprehensive scores, and selects the plants ranked at the top as breeding parents.

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