CN113947002B - Method for calculating convection heat transfer coefficient of spectrum beam combination semiconductor laser - Google Patents

Method for calculating convection heat transfer coefficient of spectrum beam combination semiconductor laser Download PDF

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CN113947002B
CN113947002B CN202111549463.XA CN202111549463A CN113947002B CN 113947002 B CN113947002 B CN 113947002B CN 202111549463 A CN202111549463 A CN 202111549463A CN 113947002 B CN113947002 B CN 113947002B
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heat transfer
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transfer coefficient
semiconductor laser
temperature
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杨军红
孙涛
刘浩
王家赞
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Guangdong Zhuojie Laser Technology Co ltd
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Guangdong Guangdong Hong Kong Macao Dawan District Hard Science And Technology Innovation Research Institute
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Abstract

The application relates to the technical field of lasers, and provides a method for calculating a convection heat transfer coefficient of a spectrum beam combination semiconductor laser, which comprises the following steps: establishing a semiconductor laser light-thermal field coupling numerical model; and setting initial conditions and boundary conditions of the optical-thermal field; setting a convection heat transfer coefficient parameter between the optical element and the environmental fluid, setting a time step parameter, and solving to obtain the optical field distribution and the temperature field distribution of the optical element under different convection heat transfer coefficients at different moments; deriving temperature data of selected points on the grating with different convective heat transfer coefficients at different moments, preprocessing the data, and inputting the preprocessed data into an LSTM network for training; after the network training is finished, inputting untrained temperature data segments, and verifying the accuracy of the network prediction convection heat transfer coefficient. The calculation method provided by the application does not need multiple iterations, is not only limited to be suitable for a steady-state heat transfer model, but also is not limited in application range and short in calculation time.

Description

Method for calculating convection heat transfer coefficient of spectrum beam combination semiconductor laser
Technical Field
The application belongs to the technical field of lasers, and particularly relates to a method for calculating a convection heat transfer coefficient of a spectrum beam combination semiconductor laser.
Background
When the spectrum beam combination semiconductor laser works, an optical element in the laser is influenced by a photothermal effect, the temperature distribution of the optical element is changed, and meanwhile, fluids such as air in the external environment and the like and the surface of the optical element generate convection heat to limit the temperature rise of the optical element in the laser. When the laser is operated, the convective heat transfer coefficient between the fluid in the external environment and the optical element is an important parameter for the temperature field distribution of the optical element. And (3) calculating a correct convection heat transfer coefficient, and establishing an accurate temperature field distribution model of the optical element in the laser so as to monitor the thermal distribution of the optical element when the laser works.
The coupled simulation software based on finite element method is widely used in the numerical solving of multiple physical fields.
At present, aiming at the defects of the calculation method of the convection heat transfer coefficient of the optical element in the laser and the calculation method of the convection heat transfer coefficient of other thermal scenes, the traditional method generally establishes a finite element heat transfer numerical model for the object to be measured, continuously adjusts the convection heat transfer coefficient through an iterative algorithm to ensure that the error between the temperature of the numerical model and the temperature of an actual model is smaller than a preset range, and outputs the convection heat transfer coefficient.
However, the above calculation method needs multiple iterations and is only suitable for the steady-state heat transfer model, the application range is limited, and the calculation time is long.
Disclosure of Invention
The embodiment of the application aims to provide a method for calculating a convection heat transfer coefficient of a spectrum beam combination semiconductor laser, so as to solve the technical problems that a common calculation method in the prior art needs multiple iterations, is only suitable for a steady-state heat transfer model, and has a limited application range and long calculation time.
In order to achieve the purpose, the technical scheme adopted by the application is as follows: the method for calculating the convection heat transfer coefficient of the spectrum beam combination semiconductor laser comprises the following steps:
establishing a geometric model of a laser in multi-physical-field coupling simulation software according to an optical element in the spectrum beam combination semiconductor laser, and establishing a light-heat field coupling numerical model of the spectrum beam combination semiconductor laser according to a geometric optical propagation equation, a photo-thermal effect equation and a solid thermal heat transfer equation;
setting material parameters of each optical element of the geometric model and setting initial conditions and boundary conditions of an optical-thermal field according to geometric parameters of optical elements in the spectrum beam combination semiconductor laser based on multi-physical-field coupling simulation software;
setting a convection heat transfer coefficient parameter between the optical element and the environmental fluid, setting a time step parameter, calculating the optical-thermal field coupling numerical model of the spectral beam combining semiconductor laser established in the step one, and solving to obtain the optical field distribution and the temperature field distribution of the optical element under different convection heat transfer coefficients at different moments;
step four, deriving temperature data of selected points on the grating with different convective heat transfer coefficients at different moments, preprocessing the data, and inputting the preprocessed data into an LSTM network for training;
and fifthly, inputting untrained temperature data segments after the network training is finished, and verifying the accuracy of the network prediction convection heat transfer coefficient.
Optionally, the first step specifically includes:
when high-power laser beams are emitted into the optical element, the laser intensity is gradually reduced along with the increase of the depth of the incident medium according to the Lambert law
Figure 465345DEST_PATH_IMAGE001
And the calculation formula I between the intensity of the laser on the grating is as follows:
Figure 832873DEST_PATH_IMAGE002
laser beam with power
Figure 746602DEST_PATH_IMAGE003
The calculation formula of the incident light power P after transmitting through the optical element is two:
Figure 224988DEST_PATH_IMAGE004
in the formula one and the formula two,
Figure 304677DEST_PATH_IMAGE005
is the absorption coefficient of the material, and the expression is as follows:
Figure 515210DEST_PATH_IMAGE006
n is the refractive index of the material,
Figure 181814DEST_PATH_IMAGE007
is a measure of the attenuation coefficient of the material,
Figure 696847DEST_PATH_IMAGE008
the number of waves in the vacuum is shown,
Figure 132508DEST_PATH_IMAGE009
，
Figure 576259DEST_PATH_IMAGE010
which is the wavelength in the vacuum, is,
Figure 730159DEST_PATH_IMAGE011
the distance traveled by the laser beam in the optical element;
according to the principle of heat transfer, the increment of total energy of a control body is equal to the work done by mass force and surface force in unit time, net heat entering the control body and heating of an internal heat source in the control body, after a laser beam passes through an optical element, a part of light is absorbed and converted into internal energy of the material by the material, the internal energy is transmitted from a high-temperature area to a low-temperature area while the temperature of a light transmission area is increased, when the internal energy is transmitted to the surface of the optical element, the original thermal balance between the surface of the optical element and external air is destroyed, convective heat transmission occurs on the surface of the optical element, the temperature distribution of the optical element can be calculated according to an energy balance equation and boundary conditions, and the specific calculation formula III is as follows:
Figure 48883DEST_PATH_IMAGE012
wherein the content of the first and second substances,
Figure 276733DEST_PATH_IMAGE013
is the temperature at a certain point on the optical element at a certain time,
Figure 156964DEST_PATH_IMAGE014
as a matter of time, the time is,
Figure 31117DEST_PATH_IMAGE015
is the density of the material and is,
Figure 389417DEST_PATH_IMAGE016
the specific heat capacity is defined, k is the thermal conductivity, and when k takes a positive value, it indicates that the heat of the target optical element flows from a high temperature region to a low temperature region,
Figure 799670DEST_PATH_IMAGE017
is an internal heat source and is used as a heat source,
Figure 585224DEST_PATH_IMAGE018
for the laplacian operator, the calculation formula four is:
Figure 884356DEST_PATH_IMAGE019
in the formula three and the formula four, the first,
Figure 46347DEST_PATH_IMAGE020
calculating signs for partial derivatives;
the calculation formula five of the convection heat transfer process between the surface of the optical element and the environmental fluid is as follows:
Figure 311106DEST_PATH_IMAGE021
wherein the content of the first and second substances,
Figure 31675DEST_PATH_IMAGE022
h is the convective heat transfer coefficient, T is the surface temperature of the optical element,
Figure 381885DEST_PATH_IMAGE023
is the ambient fluid temperature.
Optionally, in the first step, the geometric model includes a semiconductor laser bar array, a conversion lens, a diffraction grating, and an output coupling mirror, and a bar light emitting area is disposed on the semiconductor laser bar array.
Optionally, in the second step, the glass material parameters of the coupling simulation material K9 of the spectral beam combining semiconductor laser include refractive index, attenuation coefficient of the material, density, thermal conductivity and specific heat capacity; the semiconductor laser bar array parameters comprise output light wavelength, power and beam diameter; the parameters of the conversion lens include a focal length; the parameters of the diffraction grating include the grating period; the parameters of the output coupling mirror include the focal length.
Optionally, wherein the refractive index n of the glass material of the coupling simulation material K9 is 1.51, the attenuation coefficient of the material
Figure 81988DEST_PATH_IMAGE024
Is composed of
Figure 201253DEST_PATH_IMAGE025
Density of
Figure 30407DEST_PATH_IMAGE026
Is composed of
Figure 867913DEST_PATH_IMAGE027
The thermal conductivity k is 1.38W/(m.K), and the specific heat capacity
Figure 371706DEST_PATH_IMAGE028
703J/(kg.k); wherein the wavelength range of output light of the semiconductor laser bar array is 967.4-975.4nm, the average power P is 47W, and the diameter of a light beam is 2 mm; the focal length of the conversion lens is 200mm, the grating period of the diffraction grating is 1600 lines/mm, and the focal length of the output coupling mirror is 200 mm.
Optionally, in step three, the convective heat transfer coefficient between the optical element and the ambient fluid is minimized
Figure 867451DEST_PATH_IMAGE029
Is 2
Figure 431288DEST_PATH_IMAGE030
Maximum convective heat transfer coefficient between optical element and ambient fluid
Figure 756090DEST_PATH_IMAGE031
Is 20
Figure 797995DEST_PATH_IMAGE032
Step length of
Figure 328072DEST_PATH_IMAGE033
Is 0.1
Figure 62809DEST_PATH_IMAGE034
(ii) a Step of time
Figure 609328DEST_PATH_IMAGE035
Is 2s, total duration
Figure 219039DEST_PATH_IMAGE036
It is 15 min.
Optionally, the step four specifically includes:
deriving temperature T data of different convective heat transfer coefficients at different time points on the optical element;
utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of n + 1;
preprocessing the segment with the length of n +1 to obtain temperature data with the length of n
Figure 167403DEST_PATH_IMAGE037
And rate of change of temperature with time data
Figure 73043DEST_PATH_IMAGE038
The concrete calculation formula six is:
Figure 543076DEST_PATH_IMAGE039
wherein the content of the first and second substances,
Figure 926784DEST_PATH_IMAGE040
the value of k is a natural number between 1 and n;
obtained temperature data
Figure 995234DEST_PATH_IMAGE041
And rate of temperature change data
Figure 71774DEST_PATH_IMAGE038
As input to the LSTM network, i.e.
Figure 91421DEST_PATH_IMAGE042
Is prepared from (a)
Figure 278820DEST_PATH_IMAGE041
，
Figure 201776DEST_PATH_IMAGE043
) The corresponding convection heat transfer coefficient h is taken as the output of the LSTM network;
the LSTM network unit structure comprises an input gate i, a forgetting gate f, a control gate c and an output gate o, and the working process expression of the LSTM network unit is as follows:
the formula seven is calculated by the calculation method,
Figure 449218DEST_PATH_IMAGE044
wherein the sigm is a sigmoid function,
Figure 893843DEST_PATH_IMAGE045
the input gate for the k time step,
Figure 884933DEST_PATH_IMAGE046
is the weight matrix of the input gate i associated with the input value x,
Figure 662396DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 579275DEST_PATH_IMAGE048
is an AND output value
Figure 809399DEST_PATH_IMAGE049
The associated input gate i weight matrix,
Figure 604179DEST_PATH_IMAGE049
is the output value of the last LSTM network element, and
Figure 236149DEST_PATH_IMAGE049
an initial value is set to be a value,
Figure 261612DEST_PATH_IMAGE050
is the weight offset of input gate i;
the calculation formula eight is shown in the figure,
Figure 244611DEST_PATH_IMAGE051
wherein the sigm is a sigmoid function,
Figure 577503DEST_PATH_IMAGE052
is a forgetting gate of the k time step,
Figure 562515DEST_PATH_IMAGE053
for the forgetting gate f weight matrix associated with the input value x,
Figure 588240DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 730639DEST_PATH_IMAGE054
is an AND output value
Figure 100178DEST_PATH_IMAGE049
The associated forgetting gate f weight matrix,
Figure 706740DEST_PATH_IMAGE049
the output value of the last LSTM network element,
Figure 903366DEST_PATH_IMAGE055
weight bias for forget gate f;
the calculation formula is nine, and the calculation formula is,
Figure 329799DEST_PATH_IMAGE056
wherein the sigm is a sigmoid function,
Figure 768609DEST_PATH_IMAGE057
is an output gate for the k time step,
Figure 229677DEST_PATH_IMAGE058
for the output gate o weight matrix associated with the input value x,
Figure 269308DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 947152DEST_PATH_IMAGE059
is an AND output value
Figure 159959DEST_PATH_IMAGE049
The associated output gate o weight matrix,
Figure 741113DEST_PATH_IMAGE049
the output value of the last LSTM network element,
Figure 279542DEST_PATH_IMAGE060
is the weight offset of the output gate o;
the formula ten is calculated by the following method,
Figure 179102DEST_PATH_IMAGE061
wherein tanh is a hyperbolic tangent function,
Figure 461179DEST_PATH_IMAGE062
is a control gate for the k time step,
Figure 834523DEST_PATH_IMAGE063
for the weight matrix of the control gate c associated with the input value x,
Figure 776809DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 665130DEST_PATH_IMAGE064
is an AND output value
Figure 750898DEST_PATH_IMAGE049
The associated weight matrix of the control gates c,
Figure 775486DEST_PATH_IMAGE049
the output value of the last LSTM network element,
Figure 154252DEST_PATH_IMAGE065
weight bias for control gate c;
the calculation formula eleven is calculated,
Figure 529870DEST_PATH_IMAGE066
the formula twelve is calculated and the formula twelve,
Figure 91432DEST_PATH_IMAGE067
wherein the content of the first and second substances,
Figure 469062DEST_PATH_IMAGE068
for the output of the k time step concealment layer,
Figure 520194DEST_PATH_IMAGE069
determining the information to be updated, forgotten and output of the unit memory from a formula seven to a formula ten for the state of a k time step unit, updating the state of the unit and outputting the state of a hidden layer through a formula one and a formula two, and finally merging the full-connection FCN network
Figure 648687DEST_PATH_IMAGE070
And outputting the predicted convection heat transfer coefficient h through a sigmoid function.
Optionally, in step four, the first step,
making n =5, and utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of 6;
preprocessing the segment with the length of 6 to obtain the temperature data with the length of 5
Figure 545099DEST_PATH_IMAGE071
And temperatureTime rate of change of degree data
Figure 597410DEST_PATH_IMAGE072
I.e. by
Figure 553865DEST_PATH_IMAGE073
Is composed of
Figure 841758DEST_PATH_IMAGE074
。
Optionally, in step five, the relative error between the predicted value and the true value is used as the evaluation criterion of the prediction accuracy, and the relative error is
Figure 40396DEST_PATH_IMAGE075
The calculation formula (c) is:
Figure 159662DEST_PATH_IMAGE076
in the formula (I), the compound is shown in the specification,
Figure 552597DEST_PATH_IMAGE077
in order to predict the value of the network,
Figure 390103DEST_PATH_IMAGE078
and if the maximum relative error of the network predicted convection heat transfer coefficient is less than 1% after the test set temperature data is input into the network, the convection heat transfer coefficient of the finite element model at the moment is considered to be the convection heat transfer coefficient of the actual object and the environment.
Optionally, the multi-physics coupled simulation software is embodied as COMSOL Multiphysics simulation software.
In summary, the present application includes at least one of the following beneficial effects:
1. the modeling of multiple physical fields of the spectrum beam combining laser is realized, the influence of the high-power laser beam on the temperature distribution of the optical element due to the photo-thermal effect is simulated, the LSTM network is trained according to the temperature data of a certain point on the optical element at different moments and under different convection heat transfer coefficients, and the network can realize the accurate prediction of the convection heat transfer coefficient through testing;
2. the method is favorable for calculating the convection heat transfer coefficient of the spectrum beam combination semiconductor laser, provides a necessary theoretical basis for monitoring the thermal distribution of an optical element when the laser works, does not need multiple iterations, is not only limited to be suitable for a steady-state heat transfer model, but also is not limited in application range and short in calculation time.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic flow chart of a method for calculating a convective heat transfer coefficient of a spectral beam combining semiconductor laser according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of an internal structure of a simulated spectral beam combining semiconductor laser in an embodiment of the invention.
Fig. 3 is a power cloud of an optical path of a simulated spectral beam combining semiconductor laser in an embodiment of the invention.
Fig. 4 is a cloud diagram of the temperature field distribution of the optical element of the simulated spectral beam combining semiconductor laser in the embodiment of the invention.
FIG. 5 is a graph showing temperature changes at selected points on a grating for different heat transfer coefficients in an embodiment of the present invention.
Fig. 6 is a diagram of an LSTM network element architecture in an embodiment of the invention.
Fig. 7 is a diagram of the overall framework of the LSTM network in the embodiment of the present invention.
FIG. 8 is a test set relative error curve in an embodiment of the present invention.
Wherein, in the figures, the respective reference numerals:
1. a semiconductor laser bar array; 2. a bar light emitting area; 3. a conversion lens; 4. a diffraction grating; 5. an output coupling mirror; 6. temperature data collection point.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.
It will be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, as used herein, refer to an orientation or positional relationship indicated in the drawings that is solely for the purpose of facilitating the description and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be considered as limiting the present application.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.
Referring to fig. 1 to 8, a method for calculating a convective heat transfer coefficient of a spectral beam combining semiconductor laser according to an embodiment of the present application will be described.
The embodiment of the present application provides a method for calculating a convective heat transfer coefficient of a spectrum beam combination semiconductor laser, please refer to fig. 1, which includes the following steps:
the method comprises the steps of firstly, establishing a geometric model of the laser in multi-physical-field coupling simulation software according to optical elements in the spectrum beam combination semiconductor laser, wherein the multi-physical-field coupling simulation software is COMSOL Multiphysics simulation software, and establishing a light-heat field coupling numerical model of the spectrum beam combination semiconductor laser according to a geometric optical propagation equation, a photo-thermal effect equation and a solid thermal heat transfer equation.
When high-power laser beams are emitted into the optical element, the laser intensity is gradually reduced along with the increase of the depth of the incident medium according to the Lambert law
Figure 658011DEST_PATH_IMAGE001
And the calculation formula I between the intensity of the laser on the grating is as follows:
Figure 366204DEST_PATH_IMAGE002
laser beam with power
Figure 867724DEST_PATH_IMAGE003
The calculation formula of the incident light power P after transmitting through the optical element is two:
Figure 425482DEST_PATH_IMAGE004
in the formula one and the formula two,
Figure 732966DEST_PATH_IMAGE005
is the absorption coefficient of the material, and the expression is as follows:
Figure 764507DEST_PATH_IMAGE079
n is the refractive index of the material,
Figure 997780DEST_PATH_IMAGE007
is a measure of the attenuation coefficient of the material,
Figure 544299DEST_PATH_IMAGE080
the number of waves in the vacuum is shown,
Figure 389895DEST_PATH_IMAGE009
，
Figure 338260DEST_PATH_IMAGE010
which is the wavelength in the vacuum, is,
Figure 742434DEST_PATH_IMAGE011
the distance traveled by the laser beam in the optical element;
according to the principle of heat transfer, the increment of total energy of a control body is equal to the work done by mass force and surface force in unit time, net heat entering the control body and heating of an internal heat source in the control body, after a laser beam passes through an optical element, a part of light is absorbed and converted into internal energy of the material by the material, the internal energy is transmitted from a high-temperature area to a low-temperature area while the temperature of a light transmission area is increased, when the internal energy is transmitted to the surface of the optical element, the original thermal balance between the surface of the optical element and external air is destroyed, convective heat transmission occurs on the surface of the optical element, the temperature distribution of the optical element can be calculated according to an energy balance equation and boundary conditions, and the specific calculation formula III is as follows:
Figure 776249DEST_PATH_IMAGE081
wherein the content of the first and second substances,
Figure 425536DEST_PATH_IMAGE082
is the temperature at a certain point on the optical element at a certain time,
Figure 930205DEST_PATH_IMAGE014
as a matter of time, the time is,
Figure 6745DEST_PATH_IMAGE015
is the density of the material and is,
Figure 262277DEST_PATH_IMAGE016
when k is a positive value, it indicates that the heat of the target optical element is directed from a high temperature region to a low temperature regionThe flow of the mixture is controlled by the flow controller,
Figure 715255DEST_PATH_IMAGE017
is an internal heat source and is used as a heat source,
Figure 136747DEST_PATH_IMAGE018
for the laplacian operator, the calculation formula four is:
Figure 384189DEST_PATH_IMAGE083
in the formula three and the formula four, the first,
Figure 127017DEST_PATH_IMAGE084
calculating signs for partial derivatives;
the calculation formula five of the convection heat transfer process between the surface of the optical element and the environmental fluid is as follows:
Figure 554325DEST_PATH_IMAGE021
wherein the content of the first and second substances,
Figure 331788DEST_PATH_IMAGE022
h is the convective heat transfer coefficient, T is the surface temperature of the optical element,
Figure 750131DEST_PATH_IMAGE085
is the ambient fluid temperature.
Referring to fig. 2, the geometric model includes a semiconductor laser bar array 1, a conversion lens 3, a diffraction grating 4 and an output coupling mirror 5, and a bar light emitting area 2 is disposed on the semiconductor laser bar array 1.
And secondly, setting material parameters of each optical element of the geometric model and setting initial conditions and boundary conditions of an optical-thermal field according to geometric parameters of optical elements in the spectrum beam combination semiconductor laser based on multi-physical-field coupling simulation software.
Parameters of a coupling simulation material K9 glass material of the spectrum beam combination semiconductor laser comprise refractive index, attenuation coefficient of the material, density, thermal conductivity and specific heat capacity; the semiconductor laser bar array parameters comprise output light wavelength, power and beam diameter; the parameters of the conversion lens include a focal length; the parameters of the diffraction grating include the grating period; the parameters of the output coupling mirror include the focal length.
Wherein the refractive index n of the glass material of the coupling simulation material K9 is 1.51, and the attenuation coefficient of the material
Figure 245834DEST_PATH_IMAGE024
Is composed of
Figure 273571DEST_PATH_IMAGE025
Density of
Figure 171120DEST_PATH_IMAGE086
Is composed of
Figure 760364DEST_PATH_IMAGE027
The thermal conductivity k is 1.38W/(m.K), and the specific heat capacity
Figure 477784DEST_PATH_IMAGE087
703J/(kg.k); wherein the wavelength range of output light of the semiconductor laser bar array is 967.4-975.4nm, the average power P is 47W, and the diameter of a light beam is 2 mm; the focal length of the conversion lens is 200mm, the grating period of the diffraction grating is 1600 lines/mm, and the focal length of the output coupling mirror is 200 mm.
Setting a convection heat transfer coefficient parameter between the optical element and the environmental fluid, setting a time step parameter, calculating the optical-thermal field coupling numerical model of the spectral beam combining semiconductor laser established in the step one, and solving to obtain the optical field distribution and the temperature field distribution of the optical element under different convection heat transfer coefficients at different moments.
Minimum convective heat transfer coefficient between optical element and ambient fluid
Figure 246895DEST_PATH_IMAGE088
Is 2
Figure 998950DEST_PATH_IMAGE089
Maximum convective heat transfer coefficient between optical element and ambient fluid
Figure 759096DEST_PATH_IMAGE090
Is 20
Figure 462348DEST_PATH_IMAGE091
Step length of
Figure 598931DEST_PATH_IMAGE092
Is 0.1
Figure 205493DEST_PATH_IMAGE093
(ii) a Step of time
Figure 572758DEST_PATH_IMAGE094
Is 2s, total duration
Figure 264770DEST_PATH_IMAGE095
It is 15 min.
The power cloud of the optical field of the optical element at different times and different convective heat transfer coefficients is shown in fig. 3, and the temperature field distribution cloud of the optical element at different times and different convective heat transfer coefficients is shown in fig. 4.
And step four, deriving temperature data of selected points on the grating with different convective heat transfer coefficients at different moments, preprocessing the data, and inputting the preprocessed data into an LSTM network for training.
Deriving temperature T data of different convective heat transfer coefficients at different time points on the optical element;
utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of n + 1;
preprocessing the segment with the length of n +1 to obtain temperature data with the length of n
Figure 205045DEST_PATH_IMAGE037
And rate of change of temperature with time data
Figure 666113DEST_PATH_IMAGE038
Concrete calculation ofThe formula six is:
Figure 266596DEST_PATH_IMAGE039
wherein the content of the first and second substances,
Figure 445905DEST_PATH_IMAGE040
the value of k is a natural number between 1 and n;
obtained temperature data
Figure 924291DEST_PATH_IMAGE041
And rate of temperature change data
Figure 676084DEST_PATH_IMAGE038
As input to the LSTM network, i.e.
Figure 214512DEST_PATH_IMAGE042
Is prepared from (a)
Figure 615538DEST_PATH_IMAGE041
，
Figure 897615DEST_PATH_IMAGE043
) The corresponding convection heat transfer coefficient h is taken as the output of the LSTM network;
the LSTM network unit structure comprises an input gate i, a forgetting gate f, a control gate c and an output gate o, and the working process expression of the LSTM network unit is as follows:
the formula seven is calculated by the calculation method,
Figure 566231DEST_PATH_IMAGE044
wherein the sigm is a sigmoid function,
Figure 275561DEST_PATH_IMAGE045
the input gate for the k time step,
Figure 163883DEST_PATH_IMAGE046
is the weight matrix of the input gate i associated with the input value x,
Figure 443727DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 733894DEST_PATH_IMAGE048
is an AND output value
Figure 614125DEST_PATH_IMAGE049
The associated input gate i weight matrix,
Figure 989743DEST_PATH_IMAGE049
is the output value of the last LSTM network element, and
Figure 112158DEST_PATH_IMAGE049
an initial value is set to be a value,
Figure 256831DEST_PATH_IMAGE050
is the weight offset of input gate i;
the calculation formula eight is shown in the figure,
Figure 307964DEST_PATH_IMAGE051
wherein the sigm is a sigmoid function,
Figure 607096DEST_PATH_IMAGE052
is a forgetting gate of the k time step,
Figure 769087DEST_PATH_IMAGE053
for the forgetting gate f weight matrix associated with the input value x,
Figure 33846DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 990301DEST_PATH_IMAGE054
is an AND output value
Figure 839046DEST_PATH_IMAGE049
Correlated forgetting gate f weight matrix，
Figure 804728DEST_PATH_IMAGE049
The output value of the last LSTM network element,
Figure 923994DEST_PATH_IMAGE055
weight bias for forget gate f;
the calculation formula is nine, and the calculation formula is,
Figure 316929DEST_PATH_IMAGE056
wherein the sigm is a sigmoid function,
Figure 325074DEST_PATH_IMAGE057
is an output gate for the k time step,
Figure 828867DEST_PATH_IMAGE058
for the output gate o weight matrix associated with the input value x,
Figure 68219DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 130591DEST_PATH_IMAGE059
is an AND output value
Figure 189813DEST_PATH_IMAGE049
The associated output gate o weight matrix,
Figure 497298DEST_PATH_IMAGE049
the output value of the last LSTM network element,
Figure 591156DEST_PATH_IMAGE060
is the weight offset of the output gate o;
the formula ten is calculated by the following method,
Figure 762112DEST_PATH_IMAGE061
wherein tanh is a hyperbolic tangent function,
Figure 308631DEST_PATH_IMAGE062
is a control gate for the k time step,
Figure 154227DEST_PATH_IMAGE063
for the weight matrix of the control gate c associated with the input value x,
Figure 601127DEST_PATH_IMAGE047
is the input value for the k time step,
Figure 506766DEST_PATH_IMAGE064
is an AND output value
Figure 540581DEST_PATH_IMAGE049
The associated weight matrix of the control gates c,
Figure 189868DEST_PATH_IMAGE049
the output value of the last LSTM network element,
Figure 491274DEST_PATH_IMAGE065
weight bias for control gate c;
the calculation formula eleven is calculated,
Figure 505498DEST_PATH_IMAGE066
the formula twelve is calculated and the formula twelve,
Figure 26609DEST_PATH_IMAGE096
wherein the content of the first and second substances,
Figure 978122DEST_PATH_IMAGE068
for the output of the k time step concealment layer,
Figure 635500DEST_PATH_IMAGE069
for the state of the k time step unit, determining the information to be updated, forgotten and output of the unit memory from the seventh calculation formula to the tenth calculation formula, and updating the state of the unit memory by the eleventh calculation formula and the twelfth calculation formulaAnd hidden layer output, and finally, full-connection FCN network merging
Figure 882941DEST_PATH_IMAGE070
And outputting the predicted convection heat transfer coefficient h through a sigmoid function.
Making n =5, and utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of 6;
preprocessing the segment with the length of 6 to obtain the temperature data with the length of 5
Figure 891349DEST_PATH_IMAGE071
And rate of change of temperature with time data
Figure 318657DEST_PATH_IMAGE072
I.e. by
Figure 96120DEST_PATH_IMAGE073
Is composed of
Figure 514463DEST_PATH_IMAGE074
。
The temperature variation curves of the selected points on the different convective heat transfer coefficient gratings at different times are shown in fig. 5, the structure diagram of the LSTM network elements is shown in fig. 6, and the general framework diagram of the LSTM network is shown in fig. 7.
And fifthly, inputting untrained temperature data segments after the network training is finished, and verifying the accuracy of the network prediction convection heat transfer coefficient.
In other thermal fields, the criteria for judging whether the convective heat transfer coefficient calculation method meets the conditions are as follows: and after the convection heat transfer coefficient h is iterated for multiple times, when the relative error between the reference point temperature of the finite element model and the reference point temperature of the actual object is less than 1%, the convection heat transfer coefficient of the finite element model at the moment is considered to be the convection heat transfer coefficient between the actual object and the environment. According to the above criteria, the present embodiment uses the relative error between the predicted value and the true value as the evaluation criterion of the prediction accuracy, and the relative error
Figure 508701DEST_PATH_IMAGE075
The calculation formula (c) is:
Figure 37903DEST_PATH_IMAGE076
in the formula (I), the compound is shown in the specification,
Figure 607556DEST_PATH_IMAGE077
in order to predict the value of the network,
Figure 960914DEST_PATH_IMAGE078
and if the maximum relative error of the network predicted convection heat transfer coefficient is less than 1% after the test set temperature data is input into the network, the convection heat transfer coefficient of the finite element model at the moment is considered to be the convection heat transfer coefficient of the actual object and the environment.
The test set data versus error curve is shown in fig. 8. The maximum relative error of the network prediction convection heat transfer coefficient is less than 1%, the reliability of the method for calculating the convection heat transfer coefficient of the spectrum beam combination semiconductor laser is proved, and meanwhile, the reasonability of a finite element model and the method for calculating the convection heat transfer coefficient of the LSTM network is also proved.
Compared with the prior art, the spectrum beam combination semiconductor laser convection heat transfer coefficient calculation method has the advantages that the spectrum beam combination laser multi-physical-field modeling is achieved, the influence of high-power laser beams on the temperature distribution of an optical element due to the photo-thermal effect is simulated when the high-power laser beams pass through the optical element, an LSTM network is trained according to temperature data of a certain point on the optical element under different convection heat transfer coefficients at different moments, and the network can achieve accurate prediction of the convection heat transfer coefficients through testing; the method is favorable for calculating the convection heat transfer coefficient of the spectrum beam combination semiconductor laser, and provides a necessary theoretical basis for monitoring the thermal distribution of optical elements when the laser works; and multiple iterations are not needed, the method is not only limited to be applied to a steady-state heat transfer model, but also the application range is not limited, and the calculation time is short.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (9)

1. A method for calculating a convection heat transfer coefficient of a spectrum beam combination semiconductor laser is characterized by comprising the following steps of:
establishing a geometric model of a laser in multi-physical-field coupling simulation software according to an optical element in the spectrum beam combination semiconductor laser, and establishing a light-heat field coupling numerical model of the spectrum beam combination semiconductor laser according to a geometric optical propagation equation, a photo-thermal effect equation and a solid thermal heat transfer equation;
setting material parameters of each optical element of the geometric model and setting initial conditions and boundary conditions of an optical-thermal field according to geometric parameters of optical elements in the spectrum beam combination semiconductor laser based on multi-physical-field coupling simulation software;
setting a convection heat transfer coefficient parameter between the optical element and the environmental fluid, setting a time step parameter, calculating the optical-thermal field coupling numerical model of the spectral beam combining semiconductor laser established in the step one, and solving to obtain the optical field distribution and the temperature field distribution of the optical element under different convection heat transfer coefficients at different moments;
step four, deriving temperature data of selected points on the grating with different convective heat transfer coefficients at different moments, preprocessing the data, inputting the preprocessed data into an LSTM network for training, and deriving temperature T data of different convective heat transfer coefficients at different moments of a certain point on the optical element;
utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of n + 1;
preprocessing the segment with the length of n +1 to obtain temperature data with the length of n
Figure 145758DEST_PATH_IMAGE001
And rate of change of temperature with time data
Figure 701546DEST_PATH_IMAGE002
Tool for measuringThe volume calculation formula six is:
Figure 350833DEST_PATH_IMAGE003
wherein the content of the first and second substances,
Figure 216021DEST_PATH_IMAGE004
the value of k is a natural number between 1 and n;
obtained temperature data
Figure 230245DEST_PATH_IMAGE005
And rate of temperature change data
Figure 249891DEST_PATH_IMAGE002
As input to the LSTM network, i.e.
Figure 702869DEST_PATH_IMAGE006
Is prepared from (a)
Figure 360246DEST_PATH_IMAGE005
，
Figure 607688DEST_PATH_IMAGE007
) The corresponding convection heat transfer coefficient h is taken as the output of the LSTM network;
the LSTM network unit structure comprises an input gate i, a forgetting gate f, a control gate c and an output gate o, and the working process expression of the LSTM network unit is as follows:
the formula seven is calculated by the calculation method,
Figure 114631DEST_PATH_IMAGE008
wherein the sigm is a sigmoid function,
Figure 105720DEST_PATH_IMAGE009
the input gate for the k time step,
Figure 820867DEST_PATH_IMAGE010
is the weight matrix of the input gate i associated with the input value x,
Figure 737745DEST_PATH_IMAGE006
is the input value for the k time step,
Figure 233448DEST_PATH_IMAGE011
is an AND output value
Figure 762650DEST_PATH_IMAGE012
The associated input gate i weight matrix,
Figure 394619DEST_PATH_IMAGE012
is the output value of the last LSTM network element, and
Figure 747978DEST_PATH_IMAGE012
an initial value is set to be a value,
Figure 403081DEST_PATH_IMAGE013
is the weight offset of input gate i;
the calculation formula eight is shown in the figure,
Figure 735974DEST_PATH_IMAGE014
wherein the sigm is a sigmoid function,
Figure 986564DEST_PATH_IMAGE015
is a forgetting gate of the k time step,
Figure 746710DEST_PATH_IMAGE016
for the forgetting gate f weight matrix associated with the input value x,
Figure 951426DEST_PATH_IMAGE006
is the input value for the k time step,
Figure 88009DEST_PATH_IMAGE017
is an AND output value
Figure 193106DEST_PATH_IMAGE012
The associated forgetting gate f weight matrix,
Figure 61836DEST_PATH_IMAGE012
the output value of the last LSTM network element,
Figure 753849DEST_PATH_IMAGE018
weight bias for forget gate f;
the calculation formula is nine, and the calculation formula is,
Figure 927079DEST_PATH_IMAGE019
wherein the sigm is a sigmoid function,
Figure 388147DEST_PATH_IMAGE020
is an output gate for the k time step,
Figure 755675DEST_PATH_IMAGE021
for the output gate o weight matrix associated with the input value x,
Figure 934983DEST_PATH_IMAGE006
is the input value for the k time step,
Figure 646325DEST_PATH_IMAGE022
is an AND output value
Figure 165162DEST_PATH_IMAGE012
The associated output gate o weight matrix,
Figure 438012DEST_PATH_IMAGE012
the output value of the last LSTM network element,
Figure 603152DEST_PATH_IMAGE023
is the weight offset of the output gate o;
the formula ten is calculated by the following method,
Figure 619649DEST_PATH_IMAGE024
wherein tanh is a hyperbolic tangent function,
Figure 55310DEST_PATH_IMAGE025
is a control gate for the k time step,
Figure 764640DEST_PATH_IMAGE026
for the weight matrix of the control gate c associated with the input value x,
Figure 89180DEST_PATH_IMAGE027
is the input value for the k time step,
Figure 909368DEST_PATH_IMAGE028
is an AND output value
Figure 199535DEST_PATH_IMAGE012
The associated weight matrix of the control gates c,
Figure 578302DEST_PATH_IMAGE012
the output value of the last LSTM network element,
Figure 953919DEST_PATH_IMAGE029
weight bias for control gate c;
the calculation formula eleven is calculated,
Figure 312219DEST_PATH_IMAGE030
the formula twelve is calculated and the formula twelve,
Figure 722472DEST_PATH_IMAGE031
wherein the content of the first and second substances,
Figure 209823DEST_PATH_IMAGE032
for the output of the k time step concealment layer,
Figure 72737DEST_PATH_IMAGE033
determining the information to be updated, forgotten and output of the unit memory from a formula seven to a formula ten for the state of a k time step unit, updating the state of the unit and outputting the state of a hidden layer through a formula one and a formula two, and finally merging the full-connection FCN network
Figure 234728DEST_PATH_IMAGE034
Outputting the predicted convection heat transfer coefficient h through a sigmoid function;
and fifthly, inputting untrained temperature data segments after the network training is finished, and verifying the accuracy of the network prediction convection heat transfer coefficient.
2. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser as claimed in claim 1, wherein the first step specifically comprises:
when high-power laser beams are emitted into the optical element, the laser intensity is gradually reduced along with the increase of the depth of the incident medium according to the Lambert law
Figure 732443DEST_PATH_IMAGE035
And the calculation formula I between the intensity of the laser on the grating is as follows:
Figure 954477DEST_PATH_IMAGE036
laser beam with power
Figure 304687DEST_PATH_IMAGE037
The calculation formula of the incident light power P after transmitting through the optical element is two:
Figure 706587DEST_PATH_IMAGE038
in the formula one and the formula two,
Figure 825853DEST_PATH_IMAGE039
is the absorption coefficient of the material, and the expression is as follows:
Figure 953209DEST_PATH_IMAGE040
n is the refractive index of the material,
Figure 790715DEST_PATH_IMAGE041
is a measure of the attenuation coefficient of the material,
Figure 793044DEST_PATH_IMAGE042
the number of waves in the vacuum is shown,
Figure 32395DEST_PATH_IMAGE043
，
Figure 330652DEST_PATH_IMAGE044
which is the wavelength in the vacuum, is,
Figure 115110DEST_PATH_IMAGE045
the distance traveled by the laser beam in the optical element;
according to the principle of heat transfer, the increment of total energy of a control body is equal to the work done by mass force and surface force in unit time, net heat entering the control body and heating of an internal heat source in the control body, after a laser beam passes through an optical element, a part of light is absorbed and converted into internal energy of the material by the material, the internal energy is transmitted from a high-temperature area to a low-temperature area while the temperature of a light transmission area is increased, when the internal energy is transmitted to the surface of the optical element, the original thermal balance between the surface of the optical element and external air is destroyed, convective heat transmission occurs on the surface of the optical element, the temperature distribution of the optical element can be calculated according to an energy balance equation and boundary conditions, and the specific calculation formula III is as follows:
Figure 422595DEST_PATH_IMAGE046
wherein the content of the first and second substances,
Figure 250874DEST_PATH_IMAGE047
is the temperature at a certain point on the optical element at a certain time,
Figure 985611DEST_PATH_IMAGE048
as a matter of time, the time is,
Figure 30665DEST_PATH_IMAGE049
is the density of the material and is,
Figure 141841DEST_PATH_IMAGE050
the specific heat capacity is defined, k is the thermal conductivity, and when k takes a positive value, it indicates that the heat of the target optical element flows from a high temperature region to a low temperature region,
Figure 90205DEST_PATH_IMAGE051
is an internal heat source and is used as a heat source,
Figure 432063DEST_PATH_IMAGE052
for the laplacian operator, the calculation formula four is:
Figure 465878DEST_PATH_IMAGE053
in the formula three and the formula four, the first,
Figure 115165DEST_PATH_IMAGE054
calculating signs for partial derivatives;
the calculation formula five of the convection heat transfer process between the surface of the optical element and the environmental fluid is as follows:
Figure 918036DEST_PATH_IMAGE055
wherein the content of the first and second substances,
Figure 493111DEST_PATH_IMAGE056
h is the convective heat transfer coefficient, T is the surface temperature of the optical element,
Figure 14223DEST_PATH_IMAGE057
is the ambient fluid temperature.
3. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser according to claim 2, wherein: in the first step, the geometric model comprises a semiconductor laser bar array, a conversion lens, a diffraction grating and an output coupling mirror, wherein a bar light emitting area is arranged on the semiconductor laser bar array.
4. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser according to claim 3, wherein: in the second step, the parameters of the coupling simulation material K9 glass material of the spectrum beam combination semiconductor laser comprise refractive index, attenuation coefficient of the material, density, thermal conductivity and specific heat capacity; the semiconductor laser bar array parameters comprise output light wavelength, power and beam diameter; the parameters of the conversion lens include a focal length; the parameters of the diffraction grating include the grating period; the parameters of the output coupling mirror include the focal length.
5. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser according to claim 4, wherein: wherein the refractive index n of the glass material of the coupling simulation material K9 is 1.51, and the attenuation coefficient of the material
Figure 201622DEST_PATH_IMAGE058
Is composed of
Figure 124578DEST_PATH_IMAGE059
Density of
Figure 808238DEST_PATH_IMAGE060
Is composed of
Figure 816645DEST_PATH_IMAGE061
The thermal conductivity k is 1.38W/(m.K), and the specific heat capacity
Figure 807735DEST_PATH_IMAGE062
703J/(kg.k); wherein the wavelength range of output light of the semiconductor laser bar array is 967.4-975.4nm, the average power P is 47W, and the diameter of a light beam is 2 mm; the focal length of the conversion lens is 200mm, the grating period of the diffraction grating is 1600 lines/mm, and the focal length of the output coupling mirror is 200 mm.
6. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser according to claim 2, wherein: in step three, the convective heat transfer coefficient between the optical element and the ambient fluid is minimized
Figure 83733DEST_PATH_IMAGE063
Is 2
Figure 502077DEST_PATH_IMAGE064
Maximum convective heat transfer coefficient between optical element and ambient fluid
Figure 732201DEST_PATH_IMAGE065
Is 20
Figure 526981DEST_PATH_IMAGE066
Step length of
Figure 595169DEST_PATH_IMAGE067
Is 0.1
Figure 184414DEST_PATH_IMAGE068
(ii) a Time stepLong and long
Figure 167413DEST_PATH_IMAGE069
Is 2s, total duration
Figure 998841DEST_PATH_IMAGE070
It is 15 min.
7. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser as claimed in claim 1, wherein: in the fourth step of the method, the first step of the method,
making n =5, and utilizing MATLAB software to realize temperature data fixed-step random cutting to obtain a temperature data segment with the length of 6;
preprocessing the segment with the length of 6 to obtain the temperature data with the length of 5
Figure 485317DEST_PATH_IMAGE071
And rate of change of temperature with time data
Figure 511042DEST_PATH_IMAGE072
I.e. by
Figure 715758DEST_PATH_IMAGE073
Is composed of
Figure 288559DEST_PATH_IMAGE074
。
8. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser as claimed in claim 1, wherein: in the fifth step, the relative error between the predicted value and the true value is used as the evaluation standard of the prediction precision, and the relative error
Figure 629542DEST_PATH_IMAGE075
The calculation formula (c) is:
Figure 826168DEST_PATH_IMAGE076
in the formula (I), the compound is shown in the specification,
Figure 16716DEST_PATH_IMAGE077
in order to predict the value of the network,
Figure 691411DEST_PATH_IMAGE078
and if the maximum relative error of the network predicted convection heat transfer coefficient is less than 1% after the test set temperature data is input into the network, the convection heat transfer coefficient of the finite element model at the moment is considered to be the convection heat transfer coefficient of the actual object and the environment.
9. The method for calculating the convective heat transfer coefficient of a spectral beam combining semiconductor laser as claimed in claim 1, wherein: the multi-physical field coupling simulation software is particularly COMSOL Multiphysics simulation software.
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