CN111274743B - Medical rolling pump flow field simulation modeling method - Google Patents
Medical rolling pump flow field simulation modeling method Download PDFInfo
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- CN111274743B CN111274743B CN202010061280.2A CN202010061280A CN111274743B CN 111274743 B CN111274743 B CN 111274743B CN 202010061280 A CN202010061280 A CN 202010061280A CN 111274743 B CN111274743 B CN 111274743B
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Abstract
The invention discloses a simulation modeling method of a medical rolling pump flow field; simulating deformation caused by extrusion of a rolling pump hose by utilizing three sections of smooth curves, and establishing a parameterized two-dimensional model according to the hose diameter, the fixed wall diameter, the roller radius, the extrusion arc radius, the roller pendulum length, the roller number and the blocking angle of the pump; meshing the model, importing CFD software, simulating roller motion by using a dynamic meshing method of the software, and providing a calculation process of a real-time boundary position; the simulation method provided by the invention has higher precision and calculation efficiency, can be used for researching the influence of structural parameters such as the size, the rotating speed, the blocking angle and the like of the rolling pump roller on the hemolysis rate, and can also be used for further parameter optimization design.
Description
Technical Field
The invention relates to a simulation construction method technology of a medical rolling pump flow field, and belongs to the technical field of rolling pumps.
Background
The rolling pump is widely used in ventricular assist, hemodialysis and extracorporeal circulation because of its advantages of convenient manufacture, reliable flow rate, low pollution to blood, etc. However, the roller presses the hose during operation of the roller pump to cause a large mechanical shearing stress, which easily causes massive destruction (hemolysis) of blood cells, and threatens the health of patients. Therefore, the optimization design for reducing the mechanical stress of the rolling pump is of great importance.
Because the mechanical stress is difficult to intuitively measure through experiments, the time consumed by directly carrying out the hemolysis experiment is relatively long, and the influence of the parameters of the rolling pump on the hemolysis rate is difficult to obtain, so that the flow field simulation is carried out on the fluid machinery such as a pump and a fan by adopting fluid mechanics analysis software, and the prediction of the parameters including the speed, the pressure and the shearing stress is a common and convenient means.
Compared with rotary pumps such as centrifugal pumps and axial flow pumps, the deformation generated when the rolling pump is extruded is difficult to describe, so that the simulation research on the rolling pump by using Computational Fluid Dynamics (CFD) technology is more difficult. The extrusion deformation of the rolling pump can be simulated by utilizing the fluid-solid coupling technology, but the calculation amount is huge due to the factors of combined calculation of fluid analysis software and mechanical analysis software, large-scale deformation of a hose and the like, the calculation period is overlong, and the practical application of engineering is not facilitated. Therefore, it is necessary to design a simulation method for the medical rolling pump, which has reliable results and high efficiency.
Disclosure of Invention
Technical problems:
in performing CFD calculations, the accuracy and efficiency of the calculations need to be considered simultaneously. The first problem to be solved is therefore how to accurately describe the operation of the rolling pump, in particular the compression deformation of its hose, using a simplified model. Since its nonlinear deformation is difficult to express by a definite analytical relation, it must be simplified. Secondly, how to define the real-time shape of the dynamic boundary is needed to be considered, and as the hose consists of an arc part and a linear part and two conditions of single-roller extrusion and double-roller extrusion can occur in the operation process, the shape definition of the dynamic boundary must be combined with the operation characteristics of the rolling pump, and an effective and simple method is designed.
The technical scheme is as follows:
the invention discloses a medical rolling pump flow field simulation method based on a two-dimensional CFD technology, which mainly comprises the following steps:
a two-dimensional model of the rolling pump is built, the model comprising a fixed boundary, a dynamic boundary and an internal flow field. The boundaries here are both made up of linear and circular arc portions. The fixed boundary remains stationary during the simulation and the shape of the moving boundary is updated over time steps. The deformation of the roller extrusion was simulated with three smooth circular curves. This model then has the following structural parameter determination: hose diameter, fixed wall diameter, roller radius, arc radius, roller pendulum length, number of rollers, and blockage angle δ. The choking angle is the maximum roll angle of the roller at full compression and is equal to the arcuate inner wall opening angle of the pump.
In order to improve the calculation speed and ensure that the topological relation is unchanged when the grid is updated, a quadrilateral grid and a mapping surface method are adopted to divide the two-dimensional model. The boundary conditions of the speed inlet and the pressure outlet are adopted, the inlet speed is taken as the average speed obtained by measurement or calculation, and the outlet pressure is set to be 0. And introducing the movable grid into the CFD model, adjusting the internal grid according to the shape of the movable boundary at each moment, and performing flow field calculation.
The calculation method for determining the dynamic boundary shape at each time is as follows:
in a first step, assuming that a certain roller is a characteristic roller, its initial position angle can be obtained from an initial geometric model, and its instantaneous position angle can be calculated from time t and the rotational speed ω of the pump. Accordingly, the instantaneous position angle of each roller can be calculated from the spacing between the rollers.
In a second step, three critical positions of the roller are determined, including a linear portion of the roller that is about to contact the hose, a circular arc portion of the hose that is about to contact the roller, and a circular arc portion of the hose that is about to be fully in contact with the roller. The three critical positions are utilized to divide the position relationship between the roller and the hose into four conditions, wherein the four conditions comprise that the roller is not contacted with the hose, the roller only presses the linear part of the hose, the roller simultaneously presses the linear part and the circular arc part of the hose, and the roller only presses the circular arc part.
And thirdly, except for the first extrusion condition, calculating control angles of starting points of three sections of arc curves under the other three conditions, classifying all points on a dynamic boundary by using the control angles, and determining the curve sections to which the points belong.
The control angle refers to the position angle of four endpoints of three continuous arcs at the extruded part on the dynamic boundary.
And fourthly, calculating the coordinates of each point on the dynamic boundary at the current moment. The position of the point of the part which is not extruded is unchanged, and the position of the point of the extruded part is calculated according to the relation between each section of circular arc and the rotation center point of the pump.
The above-described program for determining the boundary shape is programmed using a computer language and loaded into CFD software. After each time step update, the positions of all points on the dynamic boundary are determined, thereby obtaining the real-time dynamic boundary shape. And solving the flow field by the CFD software according to the current boundary and the grid, and entering the next time step after meeting the convergence condition until meeting the set total time. And storing the result of each time step to obtain the transient flow field result of the rolling pump.
The beneficial effects are that:
the invention establishes a medical rolling pump flow field simulation method based on a two-dimensional CFD technology, utilizes a fully parameterized two-dimensional model as a simulation initial model, utilizes three smooth arc curves to simulate the deformation of an extruded hose, and provides a calculation method of the real-time shape of the boundary. The two-dimensional model established contains substantially all the structural parameters of the medical roll pump, and introduces an important parameter of the occlusion angle which is ignored by engineers. Through operation discovery, the program calculation speed is higher, and the calculated result can basically reflect the change condition of the rolling pump flow field. Because of the complete parameterized modeling process and higher precision and calculation efficiency, the method can be used for researching the influence of structural parameters such as the size, the rotating speed, the blocking angle and the like of the rolling pump roller on the hemolysis rate, and can also be used for further parameter optimization design.
Drawings
FIG. 1 is a schematic diagram of the present invention;
FIG. 2 is a two-dimensional model diagram of a medical rolling pump;
FIG. 3 is a schematic view of the critical position of the roller about to contact the linear portion of the hose;
FIG. 4 is a schematic view of the critical position of the roller in the immediate contact with the circular arc portion of the hose;
FIG. 5 is a schematic view of the roller about to be fully in the critical position of the circular arc portion of the hose;
FIG. 6 is a schematic diagram of solving control angles for a third extrusion scenario.
Detailed Description
Referring to fig. 2, a two-dimensional model of the rolling pump is built, including a fixed boundary, a movable boundary, and an internal flow field. The deformation of the hose where it is squeezed is represented by three tangential circular curves, see fig. 2. This model includes the following structural parameters: hose diameter D, fixed wall diameter D, roller radius R, arc radius R, roller pendulum length L, number of rollers N, and blockage angle δ. Where the occlusion angle refers to the maximum roll angle of the roller at full compression and is equal to the arcuate inner wall opening angle of the pump. The radius of the extrusion circular arc is caused by extrusion of the roller.
The two-dimensional model is imported into finite element analysis software, the model is divided into grids by adopting a four-deformation grid and mapping surface mode, and the grid precision meets the requirement of grid independence. The boundary conditions of the speed inlet and the pressure outlet are adopted, the inlet speed is taken as the average speed obtained by measurement or calculation, the outlet pressure is set to 0, and the material of the fluid is set to be blood. The rest solving settings can be conventional settings, so that the effect on the result is not great.
And introducing the movable grid into the CFD model, adjusting the internal grid according to the shape of the movable boundary at each moment, and performing flow field calculation. The following gives a computational expression for determining the shape of the dynamic boundary:
for modeling convenience, a coordinate system is established with the rotation center of the pump as an origin, the horizontal direction as the x-axis and the vertical direction as the y-axis. Assuming a certain roller as a characteristic roller, alpha 0 And alpha 1 Is the initial position angle and the instantaneous position angle of the roller. Alpha n Where 1 < n.ltoreq.N for the instantaneous position angle of the remaining rollers. The instantaneous position angle expression of each roller can then be obtained in combination with the rotational speed ω of the pump and the current time t:
there may be three critical situations depending on the location of the roller, 1) the roller is about to contact the linear portion of the hose (FIG. 3); 2) The roller is about to contact the circular arc part of the hose (figure 4); 3) The roller is entirely in the circular arc portion of the hose (fig. 5). The y-axis height of the roller in these three cases can be expressed as follows:
wherein:
thus, there may be 4 cases according to the roller squeeze hose:
1)y A ＜h 1 when the roller is not contacted with the hose;
2)h 1 ≤y A ＜h 2 the rollers press only the linear portion of the hose;
3)h 2 ≤y A ＜h 3 the roller simultaneously presses the linear part and the circular arc part of the hose;
4)y A ≥h 3 the roller presses only the circular arc portion.
For the extruded part of the hose, the three sections of circular arcsIs controlled by four angles beta 1 ，β 2 ，β 3 And beta 4 To determine that they respectively represent C 1 ，C 2 ，C 3 And C 4 Is a position angle of (a) in the plane of the optical disc. The following description will be given of the four-angle solution only in the most complicated third case, i.e., the roller simultaneously presses the linear portion and the circular arc portion of the hose, and the solution for the other cases is easy to be obtained in the same way, see fig. 6.
First, it is easy to obtain
Thus there is
Here, theAnd->The abscissa and ordinate values of the lower index point are indicated, and the following similar symbols have the same meaning.
Is easy to obtain:
thus, the first and second light sources are connected,
the following solves for beta 1 And beta 2 . Make a straight line l pass through B 1 And perpendicular to the linear portion of the hose, the distance from the roller center a to the line l is then:
in the middle of
Then
Similarly
Thus, it is possible to obtain:
only x is given here A In case of > 0, for x A A value of < 0 can be similarly obtained. The second and fourth cases can be calculated by analogy with the method described above.
Then after each time step update, the new coordinates of each point Q (ρ, θ) on the three arcs can be expressed as:
θ′＝θ
subscripts hereinR i Is the radius of the arc taking i as the center of the circle. When the point is on a connecting line segment between the origin and the center point of the circle to which the point belongs, +/-taking a negative sign; otherwise, the positive sign is given to the outside of the connection line.
The code of the above expression is programmed with programming software and loaded with UDF functionality provided by CFD software. Each time the system time is updated, the above expression is solved to obtain the position coordinates of all points on the boundary at that moment. After the shape of the dynamic boundary is determined, the grid inside the flow field is automatically updated to ensure the quality of the grid.
And solving the flow field by the CFD software according to the boundary conditions of the inlet and outlet, the material properties, the dynamic boundary shape and the grid at the moment, entering the next time step of calculation by the software after the convergence condition is reached, and repeating the process. In the calculation process, the result of calculation is stored once every other step (or multiple steps depending on the step size), and the calculation is finished when the total time reaches the set value. By checking the result file, the speed, pressure, shear stress and other information of the flow field can be obtained, so that the prediction of the flow field of the medical rolling pump is realized.
The above embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the protection scope of the present invention should be defined by the claims, including the technical equivalents of the technical features in the claims, as the protection scope, that is, the equivalent replacement and improvement within the protection scope of the present invention.
Claims (6)
1. A medical rolling pump flow field simulation modeling method is characterized by comprising the following steps:
(1) Simulating deformation caused by extrusion of a rolling pump hose by using three sections of smooth curves, and establishing a parameterized two-dimensional model according to structural parameters of the pump;
(2) Performing grid division on the two-dimensional model, and importing the two-dimensional model into CFD software for solving and setting;
(3) Dividing extrusion conditions into four types according to three critical positions of the roller, solving control angles of starting points of three sections of arc curves under each extrusion condition, and respectively solving the positions of points on each section of arc according to the control angles so as to determine the shape of the whole dynamic boundary;
(4) Writing a process of defining the dynamic boundary shape into a program language, and loading the program language into CFD software for simulation calculation;
the structural parameters of the pump in the step (1) comprise hose diameter, fixed wall diameter, roller radius, extrusion arc radius, roller swing length, roller quantity and blocking angle;
the blocking angle is the maximum rolling angle of the roller when the roller is fully compressed, and the value of the maximum rolling angle is equal to the opening angle of the arc-shaped inner wall of the pump;
in the step (3), the control angle is the position angle of four endpoints of three continuous arcs at the extruded part on the dynamic boundary;
in the step (3), the step of respectively calculating the positions of the points on each section of circular arc according to the control angle is as follows:
1) Firstly, judging which section of arc the point belongs to by utilizing the relation between the position angle and the control angle of the point;
2) Calculating the position of a point, keeping the angle position of the point unchanged, and calculating the diameter length of the point by using the geometric condition of the point on the circular arc;
3) When the point does not belong to the three extruded circular arcs, then the position need not be updated.
2. The medical rolling pump flow field simulation modeling method according to claim 1, wherein the method comprises the following steps: in the step (2), the two-dimensional model is subjected to grid division by utilizing a quadrilateral grid and a mapping surface method.
3. The medical rolling pump flow field simulation modeling method according to claim 1, wherein the method comprises the following steps: the CFD solving settings in step (2) include a setting of fluid material, a setting of inlet velocity, and a setting of outlet pressure.
4. A medical rolling pump flow field simulation modeling method according to claim 3, characterized in that: the outlet pressure was set to 0.
5. The medical rolling pump flow field simulation modeling method according to claim 1, wherein the method comprises the following steps: in the step (3), three critical positions comprise a linear part of the roller, which is about to contact the hose, a circular arc part of the roller, which is about to contact the hose, and a circular arc part of the hose, which is about to be completely positioned by the roller.
6. The medical rolling pump flow field simulation modeling method according to claim 1, wherein the method comprises the following steps: in the step (3), four extrusion conditions comprise that the roller is not contacted with the hose, the roller extrudes the linear part of the hose, the roller extrudes the linear part and the circular arc part of the hose at the same time, and the roller extrudes the circular arc part.
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