LS-DYNA常見問題集錦3

2016-09-25 by:CAE仿真在線來源:互聯(lián)網(wǎng)

23液面晃動(dòng)

液面晃動(dòng)(sloshing)問題的研究在實(shí)際工程中有重要的意義,比如在石化工業(yè)中廣泛應(yīng)用的大型儲(chǔ)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(dòng)情況如何,是否存在安全隱患,都需要進(jìn)行數(shù)值模擬研究。下面就ANSYS/LS-DYNA軟件在這方面的應(yīng)用。

眾所周知,ANSYS/LS-DYNA在顯式計(jì)算領(lǐng)域占據(jù)主導(dǎo)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(yōu)勢(shì)。針對(duì)液面晃動(dòng)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(jì)算流體和結(jié)構(gòu)間相互作用的最常用的方法,包括單物質(zhì)+空材料和多物質(zhì)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(shí)質(zhì)上此處二者沒有區(qū)別,只是因?yàn)榧嫒菪赃M(jìn)行的設(shè)置;兩種精度供選擇-單精度、雙精度。
*section_solid_ale
對(duì)單物質(zhì)+空材料為12號(hào)算法,對(duì)多物質(zhì)耦合為11號(hào)算法。
*ale_multi-material_group
進(jìn)行多物質(zhì)的定義,最多可以定義20種材料。可以根據(jù)物質(zhì)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(zhì)的算法(Euler或Ale),或是在運(yùn)算過程中切換使用兩種算法,并可對(duì)流體物質(zhì)進(jìn)行自由度約束。該命令多與下列三個(gè)命令結(jié)合使用:
* ale_multi-material_system_curve
定義ale系統(tǒng)的運(yùn)動(dòng)曲線。
* ale_multi-material_system_node
通過一系列節(jié)點(diǎn)定義ale的運(yùn)動(dòng)參考坐標(biāo)系統(tǒng)。
* ale_multi-material_system_switch
定義euler和ale參考系統(tǒng)的切換。
上述命令是流體物質(zhì)涉及的關(guān)鍵字,而我們知道,結(jié)構(gòu)采用Lagrange單元來離散,二者之間的耦合通過下列命令來實(shí)現(xiàn):
*constrained_lagrange_in_solid
耦合算法分為兩種:罰耦合和運(yùn)動(dòng)約束。前者遵循能量守恒,后者遵循動(dòng)量守恒。一般令結(jié)構(gòu)網(wǎng)格較流體網(wǎng)格密以保證界面不出現(xiàn)滲透,否則可以增大NQUAD參數(shù)值來增加耦合點(diǎn),如設(shè)置該值為4或5。在970中,此命令第三行又增加了一個(gè)控制字ILEAK-0,1或2,一般可設(shè)置為1。
最后給出一個(gè)典型算例-水箱跌落的部分關(guān)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(wǎng)格(meshfree)算法,在連續(xù)體的破碎或分離分析中得到了廣泛的關(guān)注和應(yīng)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(yōu)勢(shì),可以說無網(wǎng)格算法正在成為數(shù)值分析領(lǐng)域的研究熱點(diǎn),具有很好的發(fā)展前景。
我們知道傳統(tǒng)的有限單元法中,單元的形狀對(duì)結(jié)果的精度影響很大,如果單元因?yàn)樽冃芜^大可能造成矩陣奇異,使得精度降低甚至無法計(jì)算下去。而SPH算法則是把每個(gè)粒子作為一個(gè)物質(zhì)的插值點(diǎn),各個(gè)粒子間通過規(guī)則的內(nèi)插函數(shù)計(jì)算全部質(zhì)點(diǎn)即可得到整個(gè)問題的解。
主要的關(guān)鍵字如下:
*section_sph
提供算法選擇,以及sph粒子的滑順長(zhǎng)度的定義;
*control_sph
提供sph算法的控制,如粒子排序后的循環(huán)次數(shù)、計(jì)算空間、中止時(shí)間以及維數(shù);
處理sph粒子與其它結(jié)構(gòu)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(dòng)幅度較小時(shí)可以采用此種方法進(jìn)行分析,流體用ALE算法描述,結(jié)構(gòu)采用Lagrange算法;需要注意的一點(diǎn):對(duì)ALE網(wǎng)格要進(jìn)行滑順處理,以控制網(wǎng)格形態(tài),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(dòng)采用上述方法,LS-DYNA求解器在下一個(gè)版本LS970中在MESHFREE功能上增加了更為穩(wěn)定和高效的EFG技術(shù),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。