LS-DYNA常見問題集錦3

2016-09-25 by:CAE仿真在線來源:互聯網

23液面晃動

液面晃動(sloshing)問題的研究在實際工程中有重要的意義,比如在石化工業中廣泛應用的大型儲罐,一般直徑在幾十米,甚至上百米。在地震或其他意外條件下液面的波動情況如何,是否存在安全隱患,都需要進行數值模擬研究。下面就ANSYS/LS-DYNA軟件在這方面的應用。

眾所周知,ANSYS/LS-DYNA在顯式計算領域占據主導地位,隨著各種新的算法的不斷采用,在求解的廣度、精度以及效率上,ANSYS/LS-DYNA具有同類軟件所無法比擬的優勢。針對液面晃動問題,ANSYS/LS-DYNA提供以下三種方法:
1、流固耦合
流固耦合是ANSYS/LS-DYNA計算流體和結構間相互作用的最常用的方法,包括單物質+空材料和多物質耦合兩大類,流體單元有Euler和ALE兩種。其涉及的主要命令如下:
*control_ale
算法選擇有兩種2、3,分別為Euler和ale實質上此處二者沒有區別,只是因為兼容性進行的設置;兩種精度供選擇-單精度、雙精度。
*section_solid_ale
對單物質+空材料為12號算法,對多物質耦合為11號算法。
*ale_multi-material_group
進行多物質的定義,最多可以定義20種材料。可以根據物質間能否混合將各種材料定義在不同的材料組ID中。
* ale_multi-material_system_group
該命令決定流體物質的算法(Euler或Ale),或是在運算過程中切換使用兩種算法,并可對流體物質進行自由度約束。該命令多與下列三個命令結合使用:
* ale_multi-material_system_curve
定義ale系統的運動曲線。
* ale_multi-material_system_node
通過一系列節點定義ale的運動參考坐標系統。
* ale_multi-material_system_switch
定義euler和ale參考系統的切換。
上述命令是流體物質涉及的關鍵字,而我們知道,結構采用Lagrange單元來離散,二者之間的耦合通過下列命令來實現:
*constrained_lagrange_in_solid
耦合算法分為兩種:罰耦合和運動約束。前者遵循能量守恒,后者遵循動量守恒。一般令結構網格較流體網格密以保證界面不出現滲透,否則可以增大NQUAD參數值來增加耦合點,如設置該值為4或5。在970中,此命令第三行又增加了一個控制字ILEAK-0,1或2,一般可設置為1。
最后給出一個典型算例-水箱跌落的部分關鍵字:
*KEYWORD
*TITLE
boxwater2.k: dropping a water box onto a rigid platform
$========================================================================
$ [1] EXECUTION CONTROLS
$========================================================================
*CONTROL_TERMINATION
$ ENDTIM ENDCYC DTMIN ENDENG ENDMAS
0.0500000 0 0.0000000 0 0.0000000
*CONTROL_TIMESTEP
$ DTINIT TSSFAC ISDO TSLIMT DT2MS LCTM ERODE MS1ST
0.0000000 0.2000000 0 0.0000000 0.0000000 0 0 0
*CONTROL_ENERGY
$ HGEN RWEN SLNTEN RYLEN
2 2 2 2
$========================================================================
$ [3] OUTPUT CONTROLS
$========================================================================
*DATABASE_BINARY_D3PLOT
$ DT CYCL LCDT BEAM
0.0005000 0
*DATABASE_GLSTAT
0.0001000
$========================================================================
$ [5] |SECTIONS|PARTS| DEFs
$========================================================================
*PART
water in the box
$ PID SECID MID EOSID HGID GRAV ADPOPT TMID
1 1 1 1 0 0 0 0
*SECTION_SOLID_ALE
$ SECID ELFORM AET
1 12
$ AFAC BFAC CFAC DFAC START END AAFAC
0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
$-------------------------------------------------------------------------------
*MAT_NULL
$ MID RHO PC MU TEROD CEROD YM PR
1 1000.0000 -1.000+10 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
*EOS_LINEAR_POLYNOMIAL
$ EOSID C0 C1 C2 C3 C4 C5 C6
1 0.0000000 1.50000+9 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
$ E0 V0
0.0000000 1.0000000
$========================================================================
*PART
void portion in the box
2 1 1 1 0 0 0 0
*INITIAL_VOID_PART
2
$========================================================================
*PART
rigid box containing water
$ PID SECID MID EOSID HGID GRAV ADPOPT TMID
3 3 3 0 0 0 0 0
*SECTION_SOLID
$ SECID ELFORM AET
3 0
*MAT_RIGID
3 2000.0000 1.00000+8 0.0000000 0.0000000 0.0000000 0.0000000
0.0000000 0.0000000 0.0000000
0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
$========================================================================
*PART
rigid super-heavy platform
$ PID SECID MID EOSID HGID GRAV ADPOPT TMID
4 4 4
*SECTION_SHELL
$ SID ELFORM SHRF NIP PROPT QR/IRID ICOMP
4 0
$ T1 T2 T3 T4 NLOC
0.011 0.011 0.011 0.011
*MAT_ELASTIC
$ MID RHO E PR DA DB K
4 1000000.0 1.0000+14
$========================================================================
$ [8] BC's + IC's + BODY LOADS + FORCE FIELDS
$========================================================================
*INITIAL_VELOCITY
$ NSID NSIDEX BOXID
0
$ VX VY VZ VXR VYR VZR
0.0 -20.0 0.0
$-------------------------------------------------------------------------------
*LOAD_BODY_Y
$ LCID SF LCIDDR XC YC ZC
1 1.00
*DEFINE_CURVE
$ LCID SIDR SFO OFFA OFFO DATTYP
1
$ X=abcissa Y=ordinate
0.0 981.0
1.0 981.0
$========================================================================
$ [9] LAGRANGIAN CONTACTS CONSTRAINTS, ...
$========================================================================
$ SFS = scale fact on dflt SLAVE penal stifns (see CONTROLL_CONTACT)
$ SFM = scale fact on dflt MASTER penal stifns (see CONTROLL_CONTACT)
*CONTACT_AUTOMATIC_NODES_TO_SURFACE
$ SSID MSID SSTYP MSTYP SBOXID MBOXID SPR MPR
3 4 3 3
$ FS FD DC VC VDC PENCHK BT DT

$ SFS SFM SST MST SFST SFMT FSF VSF
100. 100.
$========================================================================
$ [10] EULERIAN & ALE CONTACTS CONSTRAINTS, ...
$========================================================================
*CONTROL_ALE
$ DCT NADV METH AFAC BFAC CFAC DFAC EFAC
2 1 4-1.0000000 0.0000000 0.0000000 0.0000000
$ START END AAFAC VFACT VLIMIT EBC
0.0000000 0.0000000 0.0000000 0.0
*ALE_REFERENCE_SYSTEM_GROUP
$ SID STYPE PRTYP PRID BCTRAN BCEXP BCROT ICOORD
1 0 5 1
$ XC YC ZC EXPLIM

*SET_PART_LIST
$ SID DA1 DA2 DA3 DA4
1
$ PID1 PID2 PID3 PID4 PID5 PID6 PID7 PID8
1 2
*ALE_REFERENCE_SYSTEM_NODE
$ NSID
1
$ N1 N2 N3 N4 N5 N6 N7 N8
5 6 7

2、 SPH算法
SPH算法作為DYNA中第一種無網格(meshfree)算法,在連續體的破碎或分離分析中得到了廣泛的關注和應用。在解決極度變形和破壞類型的問題上SPH有著其他方法無法比擬的優勢,可以說無網格算法正在成為數值分析領域的研究熱點,具有很好的發展前景。
我們知道傳統的有限單元法中,單元的形狀對結果的精度影響很大,如果單元因為變形過大可能造成矩陣奇異,使得精度降低甚至無法計算下去。而SPH算法則是把每個粒子作為一個物質的插值點,各個粒子間通過規則的內插函數計算全部質點即可得到整個問題的解。
主要的關鍵字如下:
*section_sph
提供算法選擇,以及sph粒子的滑順長度的定義;
*control_sph
提供sph算法的控制,如粒子排序后的循環次數、計算空間、中止時間以及維數;
處理sph粒子與其它結構的相互作用采用接觸算法。
下面給出某一算例的部分命令流:
*KEYWORD
*TITLE
sph test
$
*DATABASE_FORMAT
0
$units:cm,gm,us
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ CONTROL OPTIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*CONTROL_PARALLEL
1
*CONTROL_ENERGY
2 2 2 2
*CONTROL_SHELL
20.0 1 -1 1 2 2 1
*CONTROL_TIMESTEP
0.0000 0.9000 0 0.00 0.00
*CONTROL_TERMINATION
$1000.0000 0 0.00000 0.00000 0.00000
0.800E+05 0 0.00000 0.00000 0.00000
*CONTROL_SPH
2 0
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ TIME HISTORY $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*DATABASE_BINARY_D3PLOT
200.0E+00
$0.500E+00
*DATABASE_BINARY_D3THDT
0.8000E+02
*DATABASE_EXTENT_BINARY
0 0 3 1 0 0 0 0
0 0 4 0 0 0
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ SECTION DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*SECTION_SOLID
2 1
*SECTION_SPH
1
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ MATERIAL DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*MAT_RIGID
2 7.80 2.10 0.300000 0.0 0.0 0.0
1.00 7.00 7.00

*MAT_RIGID
3 7.80 2.10 0.300000 0.0 0.0 0.0
1.00 6.00 7.00

*MAT_RIGID
4 7.80 2.10 0.300000 0.0 0.0 0.0
1.00 6.00 7.00

*MAT_NULL
1 1.00
*EOS_GRUNEISEN
1 .1484000 1.9790000 .0000000 .0000000 .1100000 3.0000000 .0000000
.0000000
$
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ PARTS DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
$
*PART
Part 1 for Mat 4 and Elem Type 1
1 1 1 1 0 0 0
$
*PART
Part 2 for Mat 2 and Elem Type 1
2 2 2 0 0 0 0
$
*PART
Part 3 for Mat 3 and Elem Type 1
3 2 3 0 0 0 0
*PART
Part 3 for Mat 3 and Elem Type 1
4 2 4 0 0 0 0
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ RIGID BOUNDRIES $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*LOAD_BODY_Y
2,1.0
*DEFINE_CURVE
2
0.0,9.8E-10
1.0,9.8E-10
$
*DEFINE_CURVE
1 0 1.000 1.000 0.000 0.000
0.000000000000E+00 1.000000000000E-04
1.000000000000E+05 1.000000000000E-04
*BOUNDARY_PRESCRIBED_MOTION_RIGID
3 2 0 1 -1.00 0 0.000 0.000
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ NODE DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*CONTACT_AUTOMATIC_NODES_TO_SURFACE
1 1 3 2 0 0 0 0
0.000 0.000 0.000 0.000 0.000 0 0.000 0.0000E+08
0.000 0.000 0.100 0.000 0.000 0.000 0.000 0.000
1 0.1000000 3
*SET_PART_LIST
1
2,3,4
*INCLUDE
mesh.k
*END
3、ALE(接觸算法)
采用接觸算法分析流固耦合問題也是一種選擇,在液面波動幅度較小時可以采用此種方法進行分析,流體用ALE算法描述,結構采用Lagrange算法;需要注意的一點:對ALE網格要進行滑順處理,以控制網格形態,保證求解精度。
下面是某算例的部分命令流:

*KEYWORD
*TITLE
ALE
$
*DATABASE_FORMAT
0
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ CONTROL OPTIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*CONTROL_PARALLEL
1
*CONTROL_ENERGY
2 2 2 2
*CONTROL_ALE
3 1 2 1.0000000 1.0000000 0.000000 1.0000000
1.0000e+9 0.000000 0.000000 2
*CONTROL_TIMESTEP
0.0000 0.9000 0 0.00 0.00
*CONTROL_CONTACT
0.0000000 0.0000000 1 0 2 0 0
0 0 0 0
*CONTROL_TERMINATION
0.100E+05 0 0.00000 0.00000 0.00000
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ TIME HISTORY $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*DATABASE_BINARY_D3PLOT
0.1000E+03
*DATABASE_BINARY_D3THDT
0.1000E+02
*DATABASE_EXTENT_BINARY
0 0 3 1 0 0 0 0
0 0 4 0 0 0
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ SECTION DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*SECTION_SOLID
2 1
*SECTION_SOLID_ALE
1 5
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ MATERIAL DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*MAT_RIGID
2 7.80 2.10 0.280000 0.0 0.0 0.0
1.00 7.00 7.00

*MAT_RIGID
3 7.80 2.10 0.280000 0.0 0.0 0.0
1.00 6.00 7.00

*MAT_RIGID
4 7.80 2.10 0.280000 0.0 0.0 0.0
1.00 6.00 7.00

*MAT_NULL
1 1.0000000 0.0000000 1.00000-8 0.0000000 0.0000000 0.0000000 0.0000000
*EOS_LINEAR_POLYNOMIAL
1 1.00000-6 1.92100-3 0.0000000 0.0000000 0.4000000 0.4000000 0.0000000
0.0000000 0.0000000
$
$
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ PARTS DEFINITIONS $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
$
*PART
Part 1 for Mat 4 and Elem Type 1
1 1 1 1 0 0 0
$
*PART
Part 2 for Mat 2 and Elem Type 1
2 2 2 0 0 0 0
$
*PART
Part 3 for Mat 3 and Elem Type 1
3 2 3 0 0 0 0
*PART
Part 3 for Mat 3 and Elem Type 1
4 2 4 0 0 0 0
$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$ RIGID BOUNDRIES $
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$
*CONTACT_SURFACE_TO_SURFACE
1 2 3 3 0 0 0 0
0.0000 0.0000 0.0000 0.0000 0.0000 0 0.00000.1000E+08
1.0000 0.0001 0.0000 0.0000 1.0000 1.0000 1.0000 1.0000
*CONTACT_SURFACE_TO_SURFACE
1 3 3 3 0 0 0 0
0.0000 0.0000 0.0000 0.0000 0.0000 0 0.00000.1000E+08
1.0000 0.0001 0.0000 0.0000 1.0000 1.0000 1.0000 1.0000
*CONTACT_SURFACE_TO_SURFACE
1 4 3 3 0 0 0 0
0.0000 0.0000 0.0000 0.0000 0.0000 0 0.00000.1000E+08
1.0000 0.0001 0.0000 0.0000 1.0000 1.0000 1.0000 1.0000
$
*DEFINE_CURVE
1 0 1.000 1.000 0.000 0.000
0.000000000000E+00 1.000000000000E-04
1.000000000000E+05 1.000000000000E-04
*BOUNDARY_PRESCRIBED_MOTION_RIGID
3 2 0 1 -1.00 0 0.000 5.00e3
*BOUNDARY_PRESCRIBED_MOTION_RIGID
4 2 0 1 -1.00 0 5.00e3 0.000
$
通常我們處理液面晃動采用上述方法,LS-DYNA求解器在下一個版本LS970中在MESHFREE功能上增加了更為穩定和高效的EFG技術,在解決此類問題上將給予我們更大的靈活性和更多的選擇。