Cylindrical Coordinate Systems

Cal­cu­la­tions in LS-DY­NA are al­ways com­put­ed in a Carte­sian co­or­di­nate sys­tem. In cas­es where a cylin­dri­cal mod­el set­up is re­quired, a num­ber of lo­cal Carte­sian co­or­di­nate sys­tems may be de­fined to ef­fec­tive­ly mim­ic a cylin­dri­cal co­or­di­nate sys­tem. LS-Pre­Post can fa­cil­i­tate this process as well as dis­play most re­sults in an al­ter­na­tive lo­cal Carte­sian, cylin­dri­cal, or spher­i­cal co­or­di­nate sys­tem.

Input in a cylindrical coordinate system

Cer­tain LS-Pre­Post En­ti­ty Cre­ation tools have a Cylin­dri­cal CS op­tion to au­to­mat­i­cal­ly de­fine and ref­er­ence a set of lo­cal Carte­sian co­or­di­nate sys­tems in cas­es where a cylin­dri­cal co­or­di­nate sys­tem is re­quired.

1. *BOUND­ARY_­SPC

   • Mod­el → CreEnt → Bound­ary → Spc → Cre.
   • Se­lect the ra­dio but­ton Set or Node (see Set vs. Node/­Point se­lec­tion note be­low).
   • Se­lect the check box named Cylin­dri­cal CS.
   • Se­lect (and cre­ate if nec­es­sary) a CID and a di­rec­tion in that CID (Carte­sian X$X$, Y$Y$, or Z$Z$) that corresponds to the z$z$-axis in the cylindrical coordinate system.
   • Choose the nodes to be con­strained.
   • Se­lect Ap­ply.

2. *BOUND­ARY_­PRE­SCRIBED_­MO­TION

   • Mod­el → CreEnt → Bound­ary → Pre­scribed Mo­tion → Cre.
   • Se­lect the drop down Set or Node (see Set vs. Node/­Point se­lec­tion note be­low).
   • Se­lect the check box named Cylin­dri­cal CS.
   • Se­lect R or T to in­di­cate whether pre­scribed mo­tion is to be Ra­di­al or Tan­gen­tial.
   • Se­lect (and cre­ate if nec­es­sary) a CID and a di­rec­tion in that CID (Carte­sian X$X$, Y$Y$, or Z$Z$) that corresponds to the z$z$-axis in the cylindrical coordinate system.
   • Se­lect the check box Pick and choose the nodes to which the pre­scribed mo­tion should be ap­plied.
   • Se­lect Ap­ply.

3. *LOAD_­NODE

   • Mod­el → CreEnt → Load → Node → Cre.
   • Se­lect the ra­dio but­ton Set or Point (see Set vs. Node/­Point se­lec­tion note be­low).
   • Se­lect the check box named Cylin­dri­cal CS.
   • Se­lect (and cre­ate if nec­es­sary) a CID and a di­rec­tion in that CID (Carte­sian X$X$, Y$Y$, or Z$Z$) that corresponds to the z$z$-axis in the cylindrical coordinate system.
   • Choose the nodes to which loads should be ap­plied.
   • Se­lect Ap­ply.

 

Set vs. Node/Point selection

Choos­ing NODE when us­ing the above tools al­lows you to se­lect as many nodes as you want us­ing the se­lec­tion win­dow and each of those nodes will have a unique Carte­sian co­or­di­nate sys­tem (or unique vec­tor) cre­at­ed by LS-Pre­Post that will con­strain the nodes in the de­sired cylin­dri­cal di­rec­tions. If you choose SET in­stead of NODE when cre­at­ing the *BOUND­ARY_­SPC or *BOUND­ARY_­PRE­SCRIBED_­MO­TION, all the nodes in the set will share the same Carte­sian co­or­di­nate sys­tem (or same vec­tor).

• In ad­di­tion the the tools de­scribed above, *INI­TIAL_­VE­LOC­I­TY_­NODE (Mod­el → CreEnt → Ini­tial → Ve­loc­i­ty → Cre) and *INI­TIAL_­STRESS_­SOL­ID (Mod­el → CreEnt → Ini­tial → Stress Sol­id → Cre) have a have a Cylin­dri­cal CS op­tion.
• A video pro­vid­ed in bc_­in_­cylin­dri­cal_­coor_­sys­tem.tar demon­strates the se­quence of LS-Pre­Post op­er­a­tions nec­es­sary to cre­ate bound­ary con­di­tions in a cylin­dri­cal sys­tem.

Viewing results in an alternate coordinate system

Fringe and history plot results

LS-Pre­Post can dis­play fringe and his­to­ry plot re­sults in a lo­cal co­or­di­nate sys­tem as fol­lows:

• Set­tings → Gen­er­al Set­tings → Lo­cal Co­ord Sys­tem
• Se­lect the co­or­di­nate sys­tem type (Carte­sian/­Cylin­dri­cal/­Spher­i­cal)and then Cre­ate.
• Cre­ate the co­or­di­nate sys­tem us­ing the Cre­ate Co­or­di­nate Sys­tem di­a­logue.
• Be sure to wrap up the cre­ation of the co­or­di­nate sys­tem by click­ing Cre­ate­Co­ord and Done.
• Af­ter hav­ing cre­at­ed the sys­tem, high­light it in the list of cre­at­ed co­or­di­nate sys­tems, and then Ap­ply it.
• Sub­se­quent fringe or time his­to­ry plots of stress or nodal dis­place­ment will cor­re­spond to the lo­cal sys­tem you cre­at­ed.
• The leg­end in the up­per left cor­ner or or­di­nate la­bel should state "user lo­cal ax­es."
• To re­vert to the glob­al co­or­di­nate sys­tem, re­turn to the Gen­er­al Set­tings di­a­logue and se­lect Un­set.

ASCII time history data

Dis­play­ing ASCII time his­to­ry da­ta in an al­ter­na­tive co­or­di­nate sys­tem re­quires a slight­ly dif­fer­ent ap­proach:

• Cre­ate the al­ter­na­tive co­or­di­nate sys­tem us­ing Set­tings → Gen­er­al Set­tings → Lo­cal Co­ord Sys­tem as de­scribed above.
• Once the lo­cal sys­tem has been cre­at­ed, right click on the View Co­or­di­nate icon in the bot­tom tool­bar (the icon looks like a globe) to dis­play a list of co­or­di­nate sys­tems de­fined in the mod­el.
• Left click on the de­sired co­or­di­nate sys­tem.
• Go to Post → Ascii di­a­log to plot x$x$, y$y$, and z$z$ components of the desired ASCII time history.
• Once plot­ted, the curve leg­end will in­di­cate with name of the al­ter­nate co­or­di­nate sys­tem.

Measurements

Mea­sure­ments may be made in an al­ter­na­tive co­or­di­nate sys­tem as fol­lows:

• Ele­Tol → Mea­sure → Lo­cal Co­ord Sys­tem
• Se­lect Cre­ate Ax­es from the drop­down menu to cre­ate a new al­ter­nate co­or­di­nate sys­tem (or use Set­tings → Gen­er­al Set­tings → Lo­cal Co­ord Sys­tem).
• Left click to high­light the co­or­di­nate sys­tem to be used in the mea­sure­ment.
• Se­lect Co­or­di­nate or one of the Dist op­tions to per­form a mea­sure­ment in the high­light­ed co­or­di­nate sys­tem.