Method for applying torsional vibration alternating load to shaft system of reciprocating compressor

Abstract

The invention discloses a method for applying torsional vibration alternating load of a reciprocating compressor shaft system, which comprises the following steps of: applying radial displacement constraint at each bearing of the reciprocating compressor shaft system according to the bearing load characteristic of a shaft system main shaft; considering the characteristic that a reciprocating compressor shaft system adopts a structural dynamics analysis method to carry out torsional vibration calculation, alternating connecting rod force acting on all rows of crank pins is decomposed into tangential force and normal force, the tangential force and the normal force are applied to all rows of crank pins of the shaft system, the driving force of a motor is simplified into constant reverse torque, and the torsional vibration of the reciprocating compressor shaft system is calculated. The tangential force is applied to the outer ring of the motor rotor for loading, and the loading method is implemented by using ANSYS finite element calculation software APDL language, so that the working efficiency of applying the shafting alternating load is improved, the operation process of applying the shafting alternating load is further simplified, the calculation amount is reduced, and the analysis efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of applying alternating loads to a shaft system of a reciprocating compressor, and in particular to a method for applying torsional vibration alternating loads to a shaft system of a reciprocating compressor. Background Art

[0002] When a reciprocating compressor is working, as the crankshaft rotates at high speed, the entire shaft system is subjected to periodic alternating loads. This periodic alternating load causes the shaft system to produce various forms of vibration, such as bending, torsion, and bending-torsion combination. In the calculation process of shaft system torsional vibration, radial constraints must be applied to the main bearing supports of the shaft system. In the harmonic response, transient response and static analysis of the shaft system, connecting rod forces need to be applied to the crank pins of each column of the shaft system, and driving torque and fixed constraints need to be applied to the motor rotor. It can be seen that applying shaft system alternation is a very complex process, and the method of applying connecting rod forces is even more complex. According to the three elements of force, the magnitude and direction of the connecting rod force acting on each column of crank pins change with the change of the compressor rotation angle. Therefore, when applying the compressor connecting rod force, dozens of local coordinate systems need to be set to cope with the change in the direction of the connecting rod force. This complex method of applying shaft system alternating loads greatly affects the analysis efficiency of shaft system torsional vibration, and also increases the error rate of the calculation process of reciprocating compressor shaft system torsional vibration.

[0003] Therefore, the prior art still needs to be improved and enhanced. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a method for applying torsional vibration alternating loads on a reciprocating compressor shaft system, aiming to solve the problems of complex analysis process and low analysis efficiency of the alternating loads on the reciprocating compressor shaft system in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, a method for applying torsional vibration alternating load to a shaft system of a reciprocating compressor comprises:

[0007] Step 1: Use ANSYS finite element analysis software to define displacement constraints, applied forces or torques and other loads at different positions of the shaft system. Considering the characteristics of the reciprocating compressor shaft system using the structural dynamics analysis method for torsional vibration calculation, the node coordinate system at the main bearing support is transformed and constraints are applied. The alternating connecting rod force acting on each row of crank pins is decomposed into tangential force and normal force. The tangential force and normal force are applied to the crank pins of each row of the shaft system. The driving force of the motor is simplified into a constant reverse torque, and a tangential force is applied to the outer ring of the motor rotor.

[0008] Step 2: Based on the load spectrum of the time history, on the ANSYS software platform, the loading method in step 1 is converted into a command flow language and applied to each corresponding combined unit body to achieve the application of torsional vibration alternating loads on the reciprocating compressor shaft system.

[0009] Furthermore, in step 1, transforming the node coordinate system at the main bearing support and applying constraints includes:

[0010] The bearing support parts of the crankshaft system are simplified into rigid constraints, and the free rotation of each main bearing support of the shaft system is defined in the ANSYS classic environment, which is achieved by defining the displacement of the nodes there. Considering that these nodes are allowed to move freely in the tangential and axial directions along the main journals, the cylindrical coordinate system is activated, and all the nodes associated with the surfaces of each column of the main journals are rotated to the cylindrical coordinate system, so that these nodes can realize the definition of bearing constraints by defining UX=0.

[0011] Furthermore, in step 1, the alternating connecting rod force acting on each row of crank pins is decomposed into tangential force and normal force, and the tangential force and normal force applied to each row of crank pins of the shaft system include:

[0012] The magnitude and direction of the connecting rod force acting on the crank pin change with the change of the compressor rotation angle. If the connecting rod force is decomposed into a tangential force perpendicular to the crankshaft rotation radius and a normal force consistent with the rotation radius, in the local Cartesian coordinate system used to draw the crank pin, only the magnitude of the tangential force and the normal force will change when time changes; considering the tangential and normal forces in the local Cartesian coordinate system applied to these nodes, activate the creation of the local Cartesian coordinate system of each column of crank pins, and rotate all the nodes associated with the surface of each column of crank pins to the local coordinate system, so that these nodes can realize the application of alternating connecting rod loads by defining the tangential force FX and the normal force FY.

[0013] Furthermore, in step 1, the driving force of the motor is simplified into a constant reverse torque, and the tangential force applied to the outer ring of the motor rotor includes:

[0014] During the shaft harmonic response analysis and transient response analysis, the driving torque on the motor rotor is applied in the tangential direction of the outermost node of the motor rotor. The coordinate system of the outer node of the motor rotor is rotated to the cylindrical coordinate system so that these nodes can realize the application of the motor driving torque load by defining the tangential force FX.

[0015] Furthermore, in step 2, the shaft system load mainly includes the connecting rod force F of each column on the crank pin. L , driving torque M acting on the motor rotor Z , connecting rod force F L Decomposed into tangential force F T and radial force FR , where the radial force F R , driving torque M on the motor rotor Z Obtained directly from the thermo-dynamic calculation, the radial force F T Calculated by the following formula:

[0016] F T =2MD / s

[0017] Where, MD—represents the torque borne by the crank pin, which is directly obtained from the thermal-dynamic calculation;

[0018] s—indicates the stroke of the compressor.

[0019] Furthermore, in step 2, before applying the time history load, the tangential force and radial force of the node on the crank pin and the tangential force on the node of the outer ring of the motor rotor also need to be calculated:

[0020] Tangential force on the crankpin node:

[0021]

[0022] In the formula, — represents the tangential force acting on the node compressor rotation angle i on the jth row crank pin, in N;

[0023] — represents the torque MD at the crank pin of the jth row at the moment of compressor rotation angle i, in kN·m;

[0024] Radial force on the crankpin node:

[0025]

[0026] In the formula, — represents the radial force acting on the node compressor rotation angle i on the jth row crank pin, in N;

[0027] — represents the radial force F-RAD acting on the crank pin of the jth row at the moment of compressor rotation angle i, in kN;

[0028] — represents the centrifugal force of the equivalent mass of the jth column, in N;

[0029] Tangential force on the nodes of the motor rotor outer ring:

[0030] F yi =2MZ·10 6 / (D26·sumnode2)(i=1~72)

[0031] In the formula, F yi— represents the tangential force acting on the node of the outer ring of the motor rotor at time i, in N;

[0032] MZ—indicates the actual torque of the compressor, in kN·m.

[0033] Furthermore, the comprehensive load acting on the shaft system in step 2 includes the tangential force on the crankpin nodes of each row and radial force Tangential force F on the motor rotor node yi ; On the ANSYS software platform, applying these time history loads is achieved using multiple load steps:

[0034] The compressor crankshaft starts from the rotation angle of 0°, and every 5° rotation becomes a load step. The crankshaft rotates one cycle for a total of 72 load steps, that is, all loads at the crankshaft angle θ and time t together constitute 1 load step; when the duration of the shaft system transient response calculation is set to 1 revolution, 72 load steps will be generated at equal time intervals. When the calculation duration ZS is set to an integer ≥ 2, the above 72 groups of loads will be repeated ZS times, and finally ZS×72 load steps will be generated for the final solution; for the convenience of loading, it is necessary to define a multidimensional array in the ANSYS software to store the torque borne by each crank pin in one cycle and radial force Then, the loop statements in the APDL parametric language are used to complete the application of different load steps in multiple cycles.

[0035] The technical solution adopted by the present invention has the following beneficial effects:

[0036] In the present invention, radial displacement constraints are applied to each bearing of the reciprocating compressor shaft system according to the characteristics of the load on the main shaft bearing of the shaft system; considering the characteristics of the reciprocating compressor shaft system using a structural dynamics analysis method for torsional vibration calculation, the alternating connecting rod force acting on each row of crank pins is decomposed into a tangential force and a normal force, and the tangential force and the normal force are applied to each row of crank pins of the shaft system, and the driving force of the motor is simplified into a constant reverse torque, and loading is performed by applying a tangential force to the outer ring of the motor rotor, and the loading method is implemented using the APDL language of the ANSYS finite element calculation software, thereby improving the work efficiency of applying the shaft system alternating load, further simplifying the operation process of applying the shaft system alternating load, reducing the amount of calculation, and improving the analysis efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a shaft system finite element model for applying constraints and loads in a method for applying torsional vibration alternating loads to a shaft system of a reciprocating compressor provided by the present invention;

[0038] Figure 2A schematic diagram of the node direction after the node coordinate system is transformed in a method for applying torsional vibration alternating loads on a reciprocating compressor shaft system provided by the present invention;

[0039] Figure 3 A schematic structural diagram of a method for applying torsional vibration alternating loads to a reciprocating compressor shaft system provided by the present invention;

[0040] Figure 4 A schematic structural diagram of a method for applying torsional vibration alternating loads to a reciprocating compressor shaft system provided by the present invention;

[0041] Figure 5 A schematic structural diagram of a method for applying torsional vibration alternating loads to a reciprocating compressor shaft system provided by the present invention;

[0042] Figure 6 A schematic diagram of crank force for a method of applying torsional vibration alternating loads to a reciprocating compressor shaft system provided by the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] In this embodiment, a method for applying torsional vibration alternating load to a reciprocating compressor shaft system includes:

[0045] Step 1: According to the characteristics of the materials of each part of the reciprocating compressor shaft system, a shaft system finite element model is established, and the unit types of the crank pin, flywheel, motor rotor and other combination units are divided according to the combination unit body;

[0046] Step 2: Use ANSYS finite element analysis software to define displacement constraints, applied forces or torques and other loads at different positions of the shaft system. Considering the characteristics of the reciprocating compressor shaft system using the structural dynamics analysis method for torsional vibration calculation, the node coordinate system at the main bearing support is transformed and constrained, and the alternating connecting rod force acting on each row of crank pins is decomposed into tangential force and normal force. Tangential force and normal force are applied to the crank pins of each row of the shaft system, the driving force of the motor is simplified into a constant reverse torque, and a tangential force is applied to the outer ring of the motor rotor;

[0047] Among them, the finite element analysis model is composed of several units and nodes, and each unit and node has its own coordinate system. The same is true for the construction of the finite element analysis model in Chapter 3. The current shaft system units and nodes still maintain the overall Cartesian coordinate system when they are created. When using ANSYS finite element analysis software to define displacement constraints, apply forces or torques and other loads at different positions of the shaft system, they are usually applied directly to the nodes at different positions. In the calculation process of the torsional vibration of the shaft system, displacement constraints must be applied to the main bearing supports of the shaft system. In the harmonic response, transient response and static analysis of the shaft system, connecting rod forces need to be applied to the crank pins of each column of the shaft system, and driving torque and fixed constraints need to be applied to the motor rotor. According to the characteristics of the node directions required by various constraints and forces, the node coordinate systems of these parts need to be transformed respectively to meet the necessary conditions for applying loads and displacement constraints. Figure 1 The figure shows the finite element model of the shaft system with bearing displacement constraints, connecting rod load on the crank pin, and driving torque on the motor rotor. Figure 4-2 Shown is the node direction after the node coordinate system is transformed. Figure 1 ①~⑧ are radial displacement constraints imposed on the shaft system. The node directions are as follows: Figure 2 (a) Figure 1 Ⅰ~VI are connecting rod forces applied at the crank pin positions of each column of the shaft system (connecting rod forces are decomposed into X and Y directions, X direction is tangential force, Y direction is normal force), and the node directions are as follows: Figure 2 (b) Figure 1 The "driving torque" is the driving torque applied to the motor rotor in the harmonic response analysis or transient response analysis. The node direction is as follows: Figure 2 (c) as shown.

[0048] (1) Transformation of the node coordinate system at each main bearing support and definition of bearing constraints

[0049] Reciprocating compressors and their matching motors for large process flows usually use sliding bearings made of babbitt alloy as main shaft bearings. According to the relationship between the compression working speed and the natural frequency of the shaft system, the influence of the oil film oscillation at the compressor bearing on the torsional vibration of the system can be ignored. Therefore, the bearing support part of the crankshaft shaft system can be simplified into a rigid constraint, that is, the crankshaft shaft system can rotate freely at each main bearing support. Engineering experience shows that this simplified method can meet the needs of engineering design. In the ANSYS classic environment, the free rotation of each main bearing support of the shaft system can be defined by defining the displacement of the node at that location. Considering that these nodes allow free movement along the tangential and axial directions of the main journal, the cylindrical coordinate system can be activated, and all nodes associated with the surface of each column of the main journal can be rotated to the cylindrical coordinate system so that these nodes can meet the conditions for defining the bearing constraints. The command flow for transforming the node coordinate system at each main bearing support is shown in (M4-1) to (M4-3), where command flow (M4-1) activates the cylindrical coordinate system, command flow (M4-2) is a custom module (corresponding to the file DU6M_BD.mac), whose function is to select all the nodes at each main bearing support, and command flow (M4-3) is to rotate the coordinate system of the selected node into the cylindrical coordinate system. The command flow in the custom module DU6M_BD.mac can be Figure 3 The three-step GUI operation (Utility Menu / Select / Entities) generates: First, select 32 faces at the bearing constraints of the shaft system, such as Figure 3 As shown in (a), select Areas and By Num / Pick in the Select Entities① frame, click OK to pop up the Select Areas② frame, select all faces in turn with the mouse, click OK to pop up the Select Entities③ frame and generate the command flow (M4-5) and the subsequent 26 lines; the second is to associate all the nodes on the 32 faces, such as Figure 3 As shown in (a), select Nodes and Atached to in the Select Entities③ frame, and click OK to generate the command flow (M4-6); third, list all the nodes on the 32 faces, such as Figure 3 As shown in (b), clicking Pick All in the Rotate Nodes into CS box generates a command stream (M4-7) and the subsequent 102 lines in the log file, and also generates a command stream (M4-3).

[0050] After completing the transformation of the node coordinate system at the bearing support, directly call DU6M_BD to select the node at the bearing position and define the bearing constraint. The command flow for defining the bearing constraint is shown in (M4-4). Apply the displacement constraint in the X direction to the selected node, that is, UX = 0; the GUI operation is as follows: Figure 4 As shown, the graphical display of the bearing constraint is as follows Figure 2 As shown in (a), the specific command flow operation is as follows:

[0051] CSYS,1! *Activate the cylindrical coordinate system, that is, the current coordinate system is the cylindrical coordinate system (M4-1) DU6M_BD (M4-2) NROTAT,P51X! *Transfer the cylindrical coordinate system to the node selected above (M4-3) ALLSEL,ALL! *This step cannot be omitted

[0052] DU6M_BD! *This step cannot be omitted

[0053] D,P51X,,,,,,UX,,,,,(M4-4)ALLSEL,ALL! *Select all. The following command flow is the entire contents of the DU6M_BD.mac file

[0054] FLST,5,32,5,ORDE,25(M4-5)

[0055] FITEM,5,44! *44,48,50,52 are the face numbers of the first row of bearings

[0056] FITEM,5,48

[0057] FITEM,5,50

[0058] FITEM,5,52

[0059] FITEM,5,66! *66,68,69,71 are the face numbers of the second row of bearings

[0060] FITEM,5,68

[0061] FITEM,5,-69

[0062] FITEM,5,71

[0063] FITEM,5,124! *124, 127, 128, 146 are the face numbers of the bearings in the third row

[0064] FITEM,5,127

[0065] FITEM,5,-128

[0066] FITEM,5,146

[0067] FITEM,5,163! *163,165,166,168 are the face numbers of the 4th row bearings

[0068] FITEM,5,165

[0069] FITEM,5,-166

[0070] FITEM,5,168

[0071] FITEM,5,193! *193,195,196,197 are the face numbers of the 5th row of bearings FITEM,5,195

[0072] FITEM,5,-197

[0073] FITEM,5,477! *477,478,479,480 are the face numbers of the 6th row bearings FITEM,5,-480

[0074] FITEM,5,494! *494,495,496,497 are the surface numbers of the motor bearing 1FITEM,5,-497

[0075] FITEM,5,514! *514,515,516,517 are the surface numbers of the motor bearing 2 FITEM,5,-517

[0076] ASEL,S,,,P51X

[0077] NSLA,S,1(M4-6)

[0078] FLST,2,2496,1,ORDE,102(M4-7)! *12,14, etc. 2496 nodes are all the node numbers associated with the 32 faces at the bearing mentioned above FITEM,2,12

[0079] FITEM,2,14

[0080] FITEM,2,-21

[0081] FITEM,2,59

[0082] FITEM,2,-242

[0083] FITEM,2,319

[0084] FITEM,2,-405

[0085] FITEM,2,476

[0086] FITEM,2,-482

[0087] FITEM,2,620

[0088] FITEM,2,-684 FITEM,2,18325 FITEM,2,18327 FITEM,2,-18334 FITEM,2,18371 FITEM,2,-18463 FITEM,2,18465 FITEM,2,-18472 FITEM,2,18510 FITEM,2,-18516 FITEM,2,18591 FITEM,2,-18597 FITEM,2,18634 FITEM,2,-18709 FITEM,2,18782 FITEM,2,-18856 FITEM,2,19035 FITEM,2,-19095 FITEM,2,22386 FITEM,2,22388 FITEM,2,-22395 FITEM,2,22433 FITEM,2,-22525 FITEM,2,22527 FITEM,2,-22534 FITEM,2,22554 FITEM,2,-22560 FITEM,2,22599 FITEM,2,-22605 FITEM,2,22624 FITEM,2,-22699 FITEM,2,22776 FITEM,2,-22850 FITEM,2,22997 FITEM,2,-23057 FITEM,2,41049FITEM,2,41051FITEM,2,-41058FITEM,2,41095FITEM,2,-41187FITEM,2,41189FITEM,2,-41196FITEM,2,41234FITEM,2,-41240FITEM,2,41315FITEM,2,-41321FITEM,2,41358FITEM,2,-41433FITEM,2,41506FITEM,2,-41580FITEM,2,41759FITEM,2,-41819FITEM,2,45045FITEM,2,45047FITEM,2,-45054FITEM,2,45092FITEM,2,-45184FITEM,2,45186FITEM,2,-45193FITEM,2,45213FITEM,2,-45219FITEM,2,45258FITEM,2,-45264FITEM,2,45283FITEM,2,-45358FITEM,2,45435FITEM,2,-45509FITEM,2,45656FITEM,2,-45716FITEM,2,63572FITEM,2,63574FITEM,2,-63581FITEM,2,63619FITEM,2,-63626FITEM,2,63664

[0089] FITEM,2,-63671

[0090] FITEM,2,63709

[0091] FITEM,2,-63715

[0092] FITEM,2,63752

[0093] FITEM,2,-63934

[0094] FITEM,2,63996

[0095] FITEM,2,-64132

[0096] FITEM,2,70623

[0097] FITEM,2,-70646

[0098] FITEM,2,70671

[0099] FITEM,2,-70874

[0100] FITEM,2,72109

[0101] FITEM,2,-72132

[0102] FITEM,2,72157

[0103] FITEM,2,-72180

[0104] FITEM,2,72218

[0105] FITEM,2,-72389

[0106] (2) Transformation of the node coordinate system at the crank pin of each column of the shaft system

[0107] The loads borne by each row of crank pins are quite complex. For any row of crank pins in the reciprocating compressor shaft system, the magnitude and direction of the force acting on the crank pin are changing with the change of the compressor rotation angle, which greatly increases the difficulty of applying the force on the crank pin. In engineering, the connecting rod force is usually decomposed into a tangential force perpendicular to the direction of the rotation radius and a normal force consistent with the direction of the rotation radius (such as Figure 2 (b) shows that when applying the connecting rod force, only the corresponding tangential force and normal force at different rotation angles need to be loaded, and there is no need to consider the change in the direction of the force (the direction of the force is directly determined by the direction of the combined force of the tangential force and the normal force). In order to ensure that the direction of the nodes on each row of crank pins is consistent with Figure 2 (b) is completely consistent, and all nodes on the cylindrical surface of each row of crank pins need to be rotated to the local coordinate system used to draw the crank pins. For the 1st and 2nd row of crank pins, since the geometric model drawing and the construction of the finite element model are both carried out in the global Cartesian coordinate system 0, the nodes on these two rows of crank pins do not need to be transformed in the node coordinate system. However, for the 3rd and 4th row of crank pins and the 5th and 6th row of crank pins, since these two groups of crank pins are drawn in the local coordinate systems 11 and 12 respectively (the XY plane is rotated in the opposite direction by a crank angle of 240°), which is different from the global Cartesian coordinate system 0 used when creating the nodes, the coordinate systems of these two groups of nodes need to be transformed respectively.

[0108] The transformation method of the node coordinate system at the 3rd and 4th columns and the 5th and 6th columns is exactly the same as the transformation method of the node coordinate system at each main bearing support. Considering the inconsistency of the loads applied to the crankpins in different columns, in order to maintain the consistency of the format with the subsequent loading program, the node coordinate system of the crankpins in different columns is transformed separately (in fact, the transformation of the node coordinate system at the 3rd and 4th columns or the 5th and 6th columns can be performed at the same time). The command flow for the transformation of the node coordinate system of the crankpin of the 3rd column of the shaft system is (M4-7) to (M4-9), among which the command flow (M4-8) is similar to the command flow (M4-2), and is also a custom module (corresponding to the file DU6M_FXY3.mac), and DU6M_FXY3 is used to select all nodes on the crankpin of the 3rd column. Among them, command streams (M4-10) to (M4-12) are also custom modules. DU6M_FXY4 is used to select all nodes on the 4th column crank pin. Similarly, DU6M_FXY6 is used to select all nodes on the 6th column crank pin. The specific command stream operations are as follows:

[0109] CSYS,11 ! *Activate local coordinate system 11 (M4-7) DU6M_FXY3 (M4-8) NROTAT,P51X! *Rotate the 3rd row crankpin node to coordinate system 11 (M4-9) ALLSEL,ALL! *Select all

[0110] DU6M_FXY4 (M4-10) NROTAT,P51X! *Rotate 4-column crankpin nodes to coordinate system 11 ALLSEL,ALL! *Select all

[0111] CSYS,12 ! *Activate local coordinate system 12

[0112] DU6M_FXY5(M4-11)NROTAT,P51X! *Rotate the 5th column crankpin node to coordinate system 12 ALLSEL,ALL! *Select all

[0113] DU6M_FXY6 (M4-12) NROTAT,P51X! *Rotate 6-column crankpin nodes to coordinate system 12 ALLSEL,ALL! *Select all The following command flow is the entire contents of the DU6M_FXY3.mac file

[0114] FLST,5,4,5,ORDE,4

[0115] FITEM,5,97! *97,101,103,105 are the 4 face numbers at the 3rd row crank pin FITEM,5,101

[0116] FITEM,5,103

[0117] FITEM,5,105

[0118] ASEL,S,,,P51X

[0119] NSLA,S,1

[0120] FLST,2,344,1,ORDE,17

[0121] ! *27957, 27959 and other 344 nodes are all the node numbers associated with the 4 faces of the 3rd row crank pin FITEM,2,27957

[0122] FITEM,2,27959

[0123] FITEM,2,-27968

[0124] FITEM,2,28016

[0125] FITEM,2,-28108

[0126] FITEM,2,28110

[0127] FITEM,2,-28119

[0128] FITEM,2,28158

[0129] FITEM,2,-28166

[0130] FITEM,2,28243

[0131] FITEM,2,-28251

[0132] FITEM,2,28289

[0133] FITEM,2,-28364

[0134] FITEM,2,28457

[0135] FITEM,2,-28531

[0136] FITEM,2,28746

[0137] FITEM,2,-28806

[0138] (3) Transformation of the motor rotor node coordinate system

[0139] During the analysis of the shaft harmonic response and transient response, the driving torque on the motor rotor is applied in the tangential direction of the node on the outermost circle of the motor rotor. The direction of the node force is as follows: Figure 2 (c) Therefore, the motor rotor outer ring node coordinate system also needs to be rotated to the cylindrical coordinate system. The command flow is shown in (M4-13) to (M4-15), where the command flow (M4-14) is also a custom module (corresponding to the file DU6M_FXY9.mac), and DU6M_FXY9 is used to select all nodes on the outermost ring of the motor rotor.

[0140] CSYS,1! *Activate the cylindrical coordinate system, that is, the current coordinate system is the cylindrical coordinate system (M4-13) DU6M_FXY9 (M4-14) NROTAT,P51X! *Transfer the cylindrical coordinate system to the above selected node (M4-15)

[0141] ALLSEL,ALL! *Select all The following command flow is the entire contents of the DU6M_FXY9.mac file

[0142] FLST,5,8,5,ORDE,4

[0143] FITEM,5,505! *505-508,510-513 are the 8 face numbers of the outer ring of the motor rotor

[0144] FITEM,5,-508

[0145] FITEM,5,510

[0146] FITEM,5,-513

[0147] ASEL,S,,,P51X

[0148] NSLA,S,1

[0149] FLST,2,816,1,ORDE,8

[0150] ! *80896-80975, 82656-82943 and other 816 nodes are all the node numbers of the motor rotor outer ring

[0151] FITEM,2,80896

[0152] FITEM,2,-80975

[0153] FITEM,2,81240

[0154] FITEM,2,-81607

[0155] FITEM,2,82376

[0156] FITEM,2,-82455

[0157] FITEM,2,82656

[0158] FITEM,2,-82943

[0159] Step 2: Based on the load spectrum of the time history, on the ANSYS software platform, the loading method in step 1 is converted into a command flow language and applied to each corresponding combined unit body to achieve the application of torsional vibration alternating load on the shaft system of the reciprocating compressor;

[0160] During the operation of the reciprocating compressor, the shaft system is always subjected to a variety of complex loads, mainly including the connecting rod force acting on the crank pin (decomposed into tangential force and radial force), the driving torque acting on the motor rotor, etc. L like Figure 5 As shown, the radial force F R It can be directly obtained from the thermodynamic calculation, the tangential force F T It can be calculated by formula (5-5):

[0161] F T =2MD / s (5-5)

[0162] Where, MD—represents the torque borne by the crank pin, which is directly obtained from the thermal-dynamic calculation;

[0163] s—indicates the stroke of the compressor.

[0164] Similar to the application of shaft loads in the harmonic response analysis of the shaft system, the transient response analysis of the shaft system also applies loads on various nodes. Therefore, before applying the time history load, it is also necessary to calculate the tangential force and radial force on the nodes on the crank pin and the tangential force on the nodes on the outer ring of the motor rotor.

[0165] (1) Tangential force on the crankpin node

[0166]

[0167] In the formula, — represents the tangential force acting on the node compressor rotation angle i on the jth row crank pin, in N.

[0168] — represents the torque MD at the jth crankpin at the moment of compressor rotation angle i, in kN·m.

[0169] (2) Radial force on the crankpin node

[0170]

[0171] In the formula, — represents the radial force acting on the node compressor rotation angle i at the jth row crank pin, unit N

[0172] —Represents the radial force F-RAD acting on the jth crank pin at the moment of compressor rotation angle i, in kN.

[0173] — represents the centrifugal force of the equivalent mass of the jth column, in N.

[0174] (3) Tangential force on the nodes of the outer ring of the motor rotor (the nodes are in the cylindrical coordinate system)

[0175] F yi =2MZ·10 6 / (D26·sumnode2) (i=1~72) (5-8)

[0176] In the formula, F yi —Represents the tangential force acting on the node of the outer ring of the motor rotor at time i, in N.

[0177] MZ—indicates the actual torque of the compressor, in kN·m.

[0178] In this embodiment, the application of the time history load is introduced in detail by taking the application of the shaft system comprehensive load as an example. In the transient response analysis of the shaft system, whether the general alternating load, static load or simple harmonic load is applied to the shaft system, these load forms must be the load spectrum of the time history. The comprehensive load acting on the shaft system includes the tangential force on each row of crankpin nodes and radial force Tangential force F on the motor rotor node yi . On the ANSYS software platform, the application of these time history loads must be implemented using multiple load steps: the compressor crankshaft starts from an angle of 0°, and every 5° rotation becomes a load step. The crankshaft rotates one circle for a total of 72 load steps, that is, all loads when the crankshaft angle is at an angle θ (i.e., time t) together constitute 1 load step. When the duration of the shaft system transient response calculation is set to 1 revolution (this embodiment is timed by the compressor operating speed ZS), 72 load steps will be generated at equal time intervals. When the calculation duration ZS is set to an integer ≥ 2, the application of the above 72 groups of loads will be repeated ZS times, and finally ZS×72 load steps will be generated for the final solution. For the convenience of loading, it is necessary to define a multidimensional array in the ANSYS software to store the torque borne by each column of crank pins within one cycle. and radial force Then, the loop statement in APDL parametric language is used to complete the application of different load steps in multiple cycles. The command flow for applying the time history load is as follows:

[0179] *DIM,loadvalue,ARRAY,72,2,6,,, (M5-48)

[0180] Par6Mload (M5-49)

[0181] *SET,PI,3.1415926

[0182] *SET,Flx1,(CM1 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0183] ! * Centrifugal force generated by the equivalent mass of column 1

[0184] *SET,Flx2,(CM2 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0185] *SET,Flx3,(CM3 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0186] *SET,Flx4,(CM4 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0187] *SET,Flx5,(CM5 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0188] *SET,Flx6,(CM6 / 2+CRRM)*(pi*n / 30)*(pi*n / 30)*(R*1e-3)

[0189] ! *Centrifugal force generated by the equivalent mass of column 6

[0190] DU6M_fxy1! *Select all nodes on the crank pin cylindrical surface

[0191] *GET,sumnode,NODE,,COUNT,,,,! *Sum the number of nodes selected by "DU6M_fxy1"

[0192] Give sumnode

[0193] allsel,all

[0194] DU6M_FXY9! *Select all nodes on the outer ring of the motor rotor

[0195] *GET,sumnode2,NODE,,COUNT,,,,

[0196] allsel,all

[0197] *do,k,1,ZS

[0198] *do,i,1,72

[0199] *do,j,1,7

[0200] *if,j,eq,1,then! *Apply the load on the first crankpin

[0201] DU6M_fxy1

[0202] f,p51x,fx,-(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0203] ! *Load (M5-50) of applied formula (5-6)

[0204] DU6M_fxy1

[0205] f,p51x,fy,-(loadvalue(i,2,j)*1e3+Flx1) / sumnode! *Apply the load of formula (5-7)

[0206] allsel,all

[0207] *endif

[0208] *if,j,eq,2,then! *Apply the load on the second crankpin

[0209] DU6M_fxy2

[0210] f,p51x,fx,(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0211] allsel,all

[0212] DU6M_fxy2

[0213] f,p51x,fy,(loadvalue(i,2,j)*1e3+Flx2) / sumnode

[0214] allsel,all

[0215] *endif

[0216] *if,j,eq,3,then! *Apply the load on the 3rd crankpin

[0217] DU6M_fxy3

[0218] f,p51x,fx,-(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0219] allsel,all

[0220] DU6M_fxy3

[0221] f,p51x,fy,-(loadvalue(i,2,j)*1e3+Flx3) / sumnode allsel,all

[0222] *endif

[0223] *if,j,eq,4,then! *Apply the load on the 4th crankpin DU6M_fxy4

[0224] f,p51x,fx,(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0225] allsel,all

[0226] DU6M_fxy4

[0227] f,p51x,fy,(loadvalue(i,2,j)*1e3+Flx4) / sumnode allsel,all

[0228] *endif

[0229] *if,j,eq,5,then! *Apply the load DU6M_fxy5 on the 5th crank pin

[0230] f,p51x,fx,-(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0231] allsel,all

[0232] DU6M_fxy5

[0233] f,p51x,fy,-(loadvalue(i,2,j)*1e3+Flx5) / sumnode allsel,all

[0234] *endif

[0235] *if,j,eq,6,then! *Apply the load DU6M_fxy6 on the 6th crank pin

[0236] f,p51x,fx,(loadvalue(i,1,j)*1e6) / (sumnode*r)

[0237] allsel,all

[0238] DU6M_fxy6

[0239] f,p51x,fy,(loadvalue(i,2,j)*1e3+Flx6) / sumnode

[0240] allsel,all

[0241] *endif

[0242] *if,j,eq,7,then! *Apply the load on the motor rotor

[0243] DU6M_FXY9 (M5-51)

[0244] f,p51x,fy,MZ*1e6 / (sumnode2*D26 / 2)

[0245] ! *Load (M5-52) of applied formula (5-8)

[0246] allsel,all

[0247] *endif

[0248] *enddo

[0249] t=(60 / (72*n))*((i-1+(k-1)*72))

[0250] ! *Calculate the time point of the current load step (M5-53)

[0251] time,t(M5-54)

[0252] outpr,basic,last! *Set the calculation result printout option to "basic output"

[0253] outres,basic,last! *Set the output option for writing calculation results to the database to "basic output"

[0254] lvscale,n / ne! *n / ne represents the scaling factor of inertial load (M5-55)

[0255] lswrite,(i+(k-1)*72)! *Write all currently defined parameters into the payload file

[0256] *enddo

[0257] *enddo

[0258] LSSOLVE,1,72*ZS,1,(M5-56)

[0259] save

[0260] FINISH

[0261] The above command stream (M5-48) defines a 72x2x6 multidimensional array named loadvalue(72,2,6). The column torque MD at the i-th compressor rotation angle of the j-th crank pin is stored at the loadvalue(i,1,j) position of the array, and the radial force F-RAD at the i-th compressor rotation angle of the j-th crank pin is stored at the loadvalue(i,2,j) position of the array. The command stream (M5-49) reads the relevant data of the "time history load". The command stream (M5-50) applies the tangential force at the node on the first crank pin at the i-th moment. (i=1~72). In GUI operation, enter "-(loadvalue(i,1,j)*1e6) / (sumnode*r)" in VALUE Force / moment value. In addition, each load step must have a time point defined for it. The command stream (M5-54) is the definition of the time point of the load step. The GUI operation is as follows: Figure 6 As shown; the time point t is calculated based on the crankshaft speed n, the current load step number i and the current crankshaft circle number k, and the command flow is shown in (5-53). During the transient response analysis of the shaft system, the actual calculated speed may be inconsistent with the speed defined in the modal calculation. Therefore, ANSYS software provides a command to scale the load vector. The command flow is shown in (M5-55), where n is the speed defined in the transient response analysis, and ne is the speed defined in the modal analysis.

[0262] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the schemes disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed in this disclosure. The description and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the claims.

Claims

1. A method for applying torsional vibration alternating load to a reciprocating compressor shaft system, characterized in that: include: Step 1: Use ANSYS finite element analysis software to define displacement constraints, apply forces or torque loads at different positions of the shaft system. Considering the characteristics of the reciprocating compressor shaft system using the structural dynamics analysis method for torsional vibration calculation, the node coordinate system at the main bearing support is transformed and constraints are applied. The alternating connecting rod force acting on each row of crank pins is decomposed into tangential force and normal force. Tangential force and normal force are applied to the crank pins of each row of the shaft system. The driving force of the motor is simplified into a constant reverse torque, and a tangential force is applied to the outer ring of the motor rotor. Step 2: Based on the load spectrum of the time history, on the ANSYS software platform, the loading method in step 1 is converted into a command flow language and applied to each corresponding combined unit body to achieve the application of torsional vibration alternating loads on the reciprocating compressor shaft system.

2. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: In step 1, the node coordinate system at the main bearing support is transformed and constraints are imposed, including: The bearing support parts of the crankshaft system are simplified into rigid constraints, and the free rotation of each main bearing support of the shaft system is defined in the ANSYS classic environment, which is achieved by defining the displacement of the nodes there. Considering that these nodes are allowed to move freely in the tangential and axial directions along the main journals, the cylindrical coordinate system is activated, and all the nodes associated with the surfaces of each column of the main journals are rotated to the cylindrical coordinate system, so that these nodes can realize the definition of bearing constraints by defining UX=0.

3. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: In step 1, the alternating connecting rod force acting on each row of crank pins is decomposed into tangential force and normal force. The tangential force and normal force applied to each row of crank pins of the shaft system include: The magnitude and direction of the connecting rod force acting on the crank pin change with the change of the compressor rotation angle. If the connecting rod force is decomposed into a tangential force perpendicular to the crankshaft rotation radius and a normal force consistent with the rotation radius, in the local Cartesian coordinate system used to draw the crank pin, only the magnitude of the tangential force and the normal force will change when time changes; considering the tangential and normal forces in the local Cartesian coordinate system applied to these nodes, activate the creation of the local Cartesian coordinate system of each column of crank pins, and rotate all the nodes associated with the surface of each column of crank pins to the local coordinate system, so that these nodes can realize the application of alternating connecting rod loads by defining the tangential force FX and the normal force FY.

4. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: In step 1, the driving force of the motor is simplified into a constant reverse torque, and the tangential force applied to the outer ring of the motor rotor includes: During the shaft harmonic response analysis and transient response analysis, the driving torque on the motor rotor is applied in the tangential direction of the outermost node of the motor rotor. The coordinate system of the outer node of the motor rotor is rotated to the cylindrical coordinate system so that these nodes can realize the application of the motor driving torque load by defining the tangential force FX.

5. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: In step 2, the shaft system load mainly includes the connecting rod force F on the crank pin. L , the driving torque M acting on the motor rotor Z , connecting rod force F L Decomposed into tangential force F T and radial force F R , where the radial force F R , driving torque M on the motor rotor Z Obtained directly from the thermo-dynamic calculation, the radial force F T Calculated by the following formula: F T =2MD / s Where, MD—represents the torque borne by the crank pin, which is directly obtained from the thermal-dynamic calculation; s—indicates the stroke of the compressor.

6. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: In step 2, before applying the time history load, it is also necessary to calculate the tangential force and radial force of the node on the crank pin and the tangential force on the node of the outer ring of the motor rotor: Tangential force on the crankpin node: In the formula, — represents the tangential force acting on the node compressor rotation angle i on the jth row crank pin, in N; — represents the torque MD at the crank pin of the jth row at the moment of compressor rotation angle i, in kN·m; Radial force on the crankpin node: In the formula, — represents the radial force acting on the node compressor rotation angle i on the jth row crank pin, in N; — represents the radial force F-RAD acting on the crank pin of the jth row at the moment of compressor rotation angle i, in kN; — represents the centrifugal force of the equivalent mass of the jth column, in N; Tangential force on the nodes of the motor rotor outer ring: F yi =2MZ·10 6 / (D26·sumnode2)(i=1~72) In the formula, F yi — represents the tangential force acting on the node of the outer ring of the motor rotor at time i, in N; MZ—indicates the actual torque of the compressor, in kN·m.

7. The method for applying torsional vibration alternating load to a reciprocating compressor shaft system according to claim 1, characterized in that: The comprehensive load acting on the shaft system in step 2 includes the tangential force on the crankpin nodes of each row. and radial force Tangential force F on the motor rotor node yi ; On the ANSYS software platform, applying these time history loads is achieved using multiple load steps: The compressor crankshaft starts from the rotation angle of 0°, and every 5° rotation becomes a load step. The crankshaft rotates one cycle for a total of 72 load steps, that is, all loads at the crankshaft angle θ and time t together constitute 1 load step; when the duration of the shaft system transient response calculation is set to 1 revolution, 72 load steps will be generated at equal time intervals. When the calculation duration ZS is set to an integer ≥ 2, the above 72 groups of loads will be repeated ZS times, and finally ZS×72 load steps will be generated for the final solution; for the convenience of loading, it is necessary to define a multidimensional array in the ANSYS software to store the torque borne by each crank pin in one cycle and radial force Then, the loop statements in the APDL parametric language are used to complete the application of different load steps in multiple cycles.

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