1. A method for determining optimal stress and sample distribution in an accelerated life test of a nuclear power valve comprises the following steps:

step 1: the specific stress type applied to the nuclear power valve is selected as temperature stress, the service life distribution of the valve is determined to obey Weibull distribution, the shape parameter of the Weibull distribution is m, and the scale parameter is mEta; then, the service life distribution parameter sigma is 1/m, and mu is ln eta, and the linear relation mu of the stress x and the service life distribution parameter mu of the nuclear power valve is determined₀+γ₁x and satisfies the Allen equation eta ═ exp (gamma) between the characteristic life and the test temperature₀+γ₁x)，γ₀，γ₁And σ is a model parameter obtained from the prior data;

step 2: establishing an optimization objective function, which comprises the following specific steps:

step 2.1: in the optimization design of the nuclear power valve accelerated life test scheme, the variance factor V is usually adopted when the stress level number under a linear-extreme model is M_MTo optimize the objective function, the optimal stress level and sample distribution ratio are solved.

Step 2.2: the objective function is established as follows:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

wherein, V_MDenotes the variance factor, x, at a stress level of M₀Representing normal stress level, n representing total number of samples, z_pRepresenting the P-order quantile of the distribution of the standard extremum, g (i) representing the temperature stress constraint, h (i) representing the sample constraint, T_iDenotes the temperature stress, p_iRepresenting the sample distribution ratio, M representing the number of stress levels, and F representing the variance factor with respect to the stress level x_iAnd sample distribution ratio p_iThe information matrix of (2);

and step 3: aiming at the optimization design problem of the nuclear power valve accelerated life test scheme, the constraint problem of test optimization is processed by adopting an internal penalty function method, and an objective function is solved to obtain the optimal temperature stress level x_iAnd sample distribution ratio p_i。

2. The method for determining the optimal stress and sample distribution in the accelerated life test of the nuclear power valve as claimed in claim 1, wherein the specific method in the step 3 is as follows:

step 3.1: introducing a penalty function to the optimized objective function, and constraining the function by an inequality:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

conversion to a new objective function:

wherein r is^(k)Indicating taking a penalty factor, r^(k+1)＝C·r^(k)C is a penalty factor reduction coefficient;

step 3.2: and calculating the stress level and the optimal sample distribution number when the target function is at the minimum value.

3. The method for determining the optimal stress and sample distribution in the accelerated life test of the nuclear power valve as claimed in claim 1, wherein the calculation method in the step 3.2 is as follows:

step 3.2.1: determining an objective function f (x) assuming the objective function has a plurality of decision variables, i.e. x ═ x₁,x₂,...,x_n)；

Step 3.2.2: determining iteration number N, initial step length lambda and initial value x of optimization variable before optimization₀And control accuracy xi, where xi > 0;

step 3.2.3: and judging whether the set iteration number is reached, namely whether k is less than N and k is 1.

Step 3.2.4: if k is 1 for the first iteration, n-dimensional vectors μ are randomly generated between (- σ, σ)_i＝(μ_i1,μ_i2,...,μ_in) Where σ ═ x_max-x_minThen mu is measured_iIs transformed to obtainLet x_i＝x+σμ'_iTo obtain { x₁,x₂,...,x_nSubstituting the solution into the objective function value to calculate to obtain a group of solutions which enable the objective function value to be minimum, and finishing the first iteration;

step 3.2.5: converting the target function with constraint into an unconstrained target function, then calculating the target function, and if the condition f is met₁(x₁)＜f₁(x) Then a better point than the starting value is found, so that k equals 1 and x equals x₁Returning to step 3.2.3, if the condition is not satisfied, k is k +1, r^(k+1)＝C·r^(k)Returning to the step 3.2.4;

step 3.2.6: if the iteration number meets the condition and the optimal value is not found yet, outputting the current solution but not the optimal solution; when the end condition is reached, namely sigma < xi, the algorithm is cut; and if the cutoff condition is not met, continuing the iteration.

Background

The traditional accelerated life test of the nuclear power valve has the defects of long test time and large sample amount, so that an accelerated life test scheme needs to be optimally designed, a group of optimal stress levels and sample distribution proportions are searched, the precision of the life estimation value of the valve at the normal stress level is the highest, the test time is shortened, and the number of samples is reduced. Currently, the common global optimal solution methods include a lagrangian method, a linear programming method, and some artificial intelligence algorithms such as a genetic algorithm, a particle swarm algorithm, a simulated annealing algorithm, and the like. The optimization algorithm is quite popular in the fields of science and technology and mechanical engineering, but the optimization problem in reality is accompanied by various constraint conditions, so that a band constraint solving optimization method based on a genetic algorithm is derived, and the optimization difficulty is increased because the range of penalty coefficients in the traditional penalty function is difficult to determine.

Disclosure of Invention

The method overcomes the defects of the technical background in the design field of the conventional nuclear power valve accelerated life test scheme, determines the constraint condition of test optimization according to the acceleration of the test and the statistical precision requirement of test data, and adopts an internal penalty function method to process the constraint problem of the test optimization.

The technical scheme of the invention is a method for determining the optimal stress and sample distribution in an accelerated life test of a nuclear power valve, which comprises the following steps:

step 1: selecting a specific stress type applied to a nuclear power valve as temperature stress, determining that the service life distribution of the valve obeys Weibull distribution, wherein the shape parameter of the Weibull distribution is m, and the scale parameter is eta; then, the service life distribution parameter sigma is 1/m, and mu is ln eta, and the linear relation mu of the stress x and the service life distribution parameter mu of the nuclear power valve is determined₀+γ₁x and satisfies the Allen equation eta ═ exp (gamma) between the characteristic life and the test temperature₀+γ₁x)，γ₀，γ₁And σ is obtained from a priori dataThe model parameters of (1);

step 2: establishing an optimization objective function, which comprises the following specific steps:

step 2.1: in the optimization design of the nuclear power valve accelerated life test scheme, the variance factor V is usually adopted when the stress level number under a linear-extreme model is M_MTo optimize the objective function, the optimal stress level and sample distribution ratio are solved.

Step 2.2: the objective function is established as follows:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

wherein, V_MDenotes the variance factor, x, at a stress level of M₀Representing normal stress level, n representing total number of samples, z_pRepresenting the P-order quantile of the distribution of the standard extremum, g (i) representing the temperature stress constraint, h (i) representing the sample constraint, T_iDenotes the temperature stress, p_iRepresenting the sample distribution ratio, M representing the number of stress levels, and F representing the variance factor with respect to the stress level x_iAnd sample distribution ratio p_iThe information matrix of (2);

and step 3: aiming at the optimization design problem of the nuclear power valve accelerated life test scheme, the constraint problem of test optimization is processed by adopting an internal penalty function method, and an objective function is solved to obtain the optimal temperature stress level x_iAnd sample distribution ratio p_i。

Further, the specific method of step 3 is as follows:

step 3.1: introducing a penalty function to the optimized objective function, and constraining the function by an inequality:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

conversion to a new objective function:

wherein r is^(k)Represents taking a penalty factor, r: (^k+1)＝C·r(^k)C is a penalty factor reduction coefficient;

step 3.2: and calculating the stress level and the optimal sample distribution number when the target function is at the minimum value.

Further, the calculation method in step 3.2 is as follows:

step 3.2.1: determining an objective function f (x) assuming the objective function has a plurality of decision variables, i.e. x ═ x₁,x₂,...,x_n)；

Step 3.2.2: determining iteration number N, initial step length lambda and initial value x of optimization variable before optimization₀And control accuracy xi, where xi > 0;

step 3.2.3: and judging whether the set iteration number is reached, namely whether k is less than N and k is 1.

Step 3.2.4: if k is 1 for the first iteration, n-dimensional vectors μ are randomly generated between (- σ, σ)_i＝(μ_i1,μ_i2,...,μ_in) Where σ ═ x_max-x_minThen mu is measured_iIs transformed to obtainLet x_i＝x+σμ′_iTo obtain { x₁,x₂,...,x_nSubstituting the solution into the objective function value to calculate to obtain a group of solutions which enable the objective function value to be minimum, and finishing the first iteration;

step 3.2.5: converting the target function with constraint into an unconstrained target function, then calculating the target function, and if the condition f is met₁(x₁)＜f₁(x) Then a better point than the starting value is found, so that k equals 1 and x equals x₁Returning to step 3.2.3, if the condition is not satisfied, k is k +1, r^(k+1)＝C·r^(k)Returning to the step 3.2.4;

step 3.2.6: if the iteration number meets the condition and the optimal value is not found yet, outputting the current solution but not the optimal solution; when the end condition is reached, namely sigma < xi, the algorithm is cut; and if the cutoff condition is not met, continuing the iteration.

The invention has the beneficial effects that: through experimental analysis, when the accelerated life test optimization design of the nuclear power valve is carried out, the random walk optimization algorithm and the penalty function method are combined to effectively solve the optimization solving problem with constraint, a set of optimal stress level and sample distribution proportion are found, the penalty factor is determined more accurately and simply while the optimal value of the variable is solved, and a new thought is provided for solving the constraint problem of other optimization algorithms.

Drawings

FIG. 1 is a flow chart of a solution for random tape-walking constraint optimization

FIG. 2 is a flow chart of an improved random walk optimization algorithm

Detailed Description

Step 1: the specific stress type applied to the nuclear power valve is selected as temperature stress, the service life distribution of the valve is determined to obey Weibull distribution, the shape parameter of the Weibull distribution is m, and the scale parameter is eta. Then, the service life distribution parameter sigma is 1/m, and mu is ln eta, and the linear relation mu of the stress x and the service life distribution parameter mu of the nuclear power valve is determined₀+γ₁x and satisfies the Allen equation eta ═ exp (gamma) between the characteristic life and the test temperature₀+γ₁x)，γ₀，γ₁And σ is a model parameter obtained from the prior data;

step 2: establishing an optimization objective function, which comprises the following specific steps:

step 2.1: variance factor V of stress level M is generally used in optimization design of nuclear power valve accelerated life test scheme_MTo optimize the objective function, the optimal stress level and sample distribution ratio are solved.

Step 2.2: the objective function is established as follows:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

wherein, V_MDenotes the variance factor, x, at a stress level of M₀Representing normal stress level, n representing total number of samples, z_pRepresenting the P-order quantile of the distribution of the standard extremum, g (i) representing the temperature stress constraint, h (i) representing the sample constraint, T_iDenotes the temperature stress, p_iRepresenting the sample distribution ratio, M representing the number of stress levels, and F representing the variance factor with respect to the stress level x_iAnd sample distribution ratio p_iThe information matrix of (2);

and step 3: aiming at the optimization design problem of the nuclear power valve accelerated life test scheme, the constraint problem of test optimization is processed by adopting an internal penalty function method, and an objective function is solved to obtain the optimal stress level x_iAnd sample distribution ratio p_i。

Further, the specific method of step 3 is as follows:

step 3.1: introducing a penalty function to the optimized objective function, and constraining the function by an inequality:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2,...,M)

conversion to a new objective function:

wherein r is^(k)Indicating taking a penalty factor, r^(k+1)＝C·r(^k)C is a penalty factor reduction coefficient;

step 3.2: and calculating the stress level and the optimal sample distribution number when the target function is at the minimum value.

Further, the calculation method in step 3.2 is as follows:

step 3.2.1: determining an objective function f (x) assuming the objective function has a plurality of decision variables, i.e. x ═ x₁,x₂,...,x_n)；

Step 3.2.2: determining iteration number N, initial step length lambda and initial value x of optimization variable before optimization₀And control accuracy xi, where xi > 0;

step 3.2.3: and judging whether the set iteration number is reached, namely whether k is less than N and k is 1.

Step 3.2.4: if k is 1 for the first iteration, n-dimensional vectors μ are randomly generated between (- σ, σ)_i＝(μ_i1,μ_i2,...,μ_in) Where σ ═ x_max-x_minThen mu is measured_iIs transformed to obtainLet x_i＝x+σμ′_iTo obtain { x₁,x₂,...,x_nSubstituting the solution into the objective function value to calculate to obtain a group of solutions which enable the objective function value to be minimum, and finishing the first iteration;

step 3.2.5: converting the target function with constraint into an unconstrained target function, then calculating the target function, and if the condition f is met₁(x₁)＜f₁(x)，Then a better point than the starting value is found, so that k equals 1 and x equals x₁Returning to step 3.2.3, if the condition is not satisfied, k is k +1, r^(k+1)＝C·r^(k)Returning to the step 3.2.4;

step 3.2.6: if the iteration number meets the condition and the optimal value is not found yet, outputting the current solution but not the optimal solution; when the end condition is reached, namely sigma < xi, the algorithm is cut; and if the cutoff condition is not met, continuing the iteration.

The optimization algorithm provided by the invention comprises the following calculation steps:

step 1: in the optimization design of the accelerated life test of the valve, the accelerated test is assumed to have a temperature level T of 2₁＜T₂Determining the distribution ratio and the ultimate stress level of the sample in the test to satisfy p₁+p₂＝1。V_MRepresenting the variance factor when the stress level is M, and g (i) and h (i) are practical value range constraints of the experimental variable.

The objective function is:

s.t.g(i)＝T_i-1-T_i＜0,(i＝1,2)

step 2: the estimated value of the model parameter can be obtained according to the experiment of touching the bottomz_p0.5; according to the test conditions, the normal working stress level T of the product can be known₀At 85 ℃, the transformation stress is x₀＝1000/(273.15+T₀) Ultimate operating stress level, T_max140 ℃ with a transformation stress ofGiven a confidence of 60%, K_γ0.84162, then the confidence interval width is 2W 0.4, according to the formula n V_M(K_γσ/W)²Calculating the sample size, introducing a penalty function to obtain a new target function as follows:

the temperature stress level and the sample proportion are used as decision variables in the formula, x: t is₁,T₂,p₁,p₂；r⁽¹⁾＞r⁽²⁾＞r⁽³⁾＞...＞r^(k)For the penalty factor, a positive number is typically taken,

to construct a sequence of decreasing penalty factors, then

r^(k+1)＝Cr^(k)

In the formula, C ∈ (0,1) is a penalty factor reduction coefficient. In general, a penalty factor r is taken⁽¹⁾And (4) setting the penalty factor reduction coefficient C to be 1 and setting the penalty factor reduction coefficient C to be 0.5-0.7.

And step 3: and calculating the temperature stress level value at the minimum value of the objective function and the optimal sample distribution ratio.

Further, the calculation method in step 3 is as follows:

step 3.1.1: determining an objective function f (x), assuming that the objective function has a plurality of decision variables, i.e. x: t is₁,T₂,p₁,p₂；

Step 3.1.2: before optimization, the iteration number N is 1000, the initial step length lambda is 0.5, and the initial value x of the optimization variable is determined₀:[2.793,2.421,0,1,1]And the control precision xi is 0.00001 (wherein xi is more than 0, and the value is generally very small);

step 3.1.3: and judging whether the set iteration number is reached, namely whether k is less than N and k is 1.

Step 3.1.4: if k is 1, the first iteration is carried out at ([ -0.372, -1)],[0.372,1]) Between random generation10 vectors mu_i＝(μ_i1,μ_i2,...,μ_in) Then mu is measured_iIs transformed to obtainLet x_i＝x+σμ′_iTo obtain { x₁,x₂,...,x₁₀Substituting the solution into the objective function value to calculate to obtain a group of solutions which enable the objective function value to be minimum, and finishing the first iteration.

Step 3.1.5: converting the target function with constraint into an unconstrained target function, then calculating the target function, and if the condition f is met₁(x₁)＜f₁(x) Then a better point than the starting value is found, so that k equals 1 and x equals x₁Returning to step 3.1.3, if the condition is not satisfied, k is k +1, r^(k+1)＝Cr^(k)If C is 0.5-0.7, returning to the step 3.1.4;

step 3.1.6: if the iteration number meets the condition and the optimal value is not found yet, the current solution is output but the optimal solution is not. When the end condition is reached, namely sigma < xi, the algorithm is cut; and if the cutoff condition is not met, continuing the iteration.

TABLE 1 comparison of conventional random walk and modified random walk results