Aina za uchanganuzi¶

FrontISTR hutoa aina mbalimbali za uchanganuzi kwa fizikia ya muundo na joto, kuanzia usawa tuli hadi mabadiliko kwa muda, hali thabiti ya mzunguko, na uchimbaji wa sifa za asili za mfumo. Ukurasa huu unaonyesha jambo linalolengwa na kila aina ya uchanganuzi, eneo lake la matumizi, na jinsi ya kuchagua. Kwa syntax ya input file tazama keyword reference; kwa maelezo ya kihisabati ya formulation tazama theory manual.

Muhtasari wa vipengele¶

Aina za uchanganuzi za FrontISTR zinaweza kutambulishwa kwa mchanganyiko wa mihimili mitatu ifuatayo.

• Fizikia inayolengwa: muundo (displacement na stress), joto (temperature na heat flux), au coupling kati yake
• Utunzaji wa mwendo: kama inertia term inajumuishwa na kama mabadiliko kwa muda yanafuatiliwa. Hii ni mihimili miwili huru
  • Hakuna inertia na hakuna ufuatiliaji wa muda → static equilibrium
  • Hakuna inertia lakini muda unafuatiliwa → quasi-static (viscoelasticity, creep, n.k.)
  • Inertia inajumuishwa na muda unafuatiliwa → transient dynamic response
  • Hushughulikiwa katika frequency domain kama periodic steady state → harmonic response
  • Hakuna external force; sifa za mfumo wenyewe hutolewa → intrinsic characteristics
• Linearity: linear (small deformation na linear material) au nonlinear (large deformation, nonlinear material, contact)

Mchanganyiko uliotekelezwa wa sifa hizi unalingana na aina za uchanganuzi zilizoelezwa hapa chini. Kwenye input, !SOLUTION huchagua kategoria kuu ya uchanganuzi, huku !DYNAMIC, !EIGEN, !HEAT, n.k. zikibainisha sifa zinazohusiana. Step size na increments kwa uchanganuzi unaobadilika kwa muda hudhibitiwa na !STEP.

Jinsi ya kuchagua aina ya uchanganuzi¶

Anza kuchagua aina ya uchanganuzi kwa kufafanua jambo linalochunguzwa na matokeo unayotaka. Hata kwa kitu kilekile, aina inayofaa hubadilika kulingana na kile unachotaka kujua. Kuchunguza vipengele vifuatavyo kwa mpangilio husaidia kufikia aina inayofaa.

1. Unataka kupata nini? — Displacement na stress, temperature distribution, vibration modes, au frequency response. Kiasi kinachotakiwa huamua mfumo mkuu wa aina ya uchanganuzi
2. Je, inertia lazima izingatiwe? — Chagua dynamic analysis ikiwa load hubadilika haraka kiasi kwamba acceleration huathiri response. Ikiwa mabadiliko ni ya polepole na inertia inaweza kupuuzwa, static analysis inatosha
3. Je, mabadiliko kwa muda lazima yafuatiliwe? — Hata inertia ikiwa inaweza kupuuzwa, time-dependent material response kama viscoelasticity au creep hutatuliwa ndani ya static-analysis framework kwa kugawa muda katika steps (quasi-static analysis)
4. Je, dhana ya linearity inatumika? — Linear analysis inatosha kwa small deformation na linear material. Ikiwa large deformation, nonlinear material, au contact ipo, chagua nonlinear analysis

Jedwali lifuatalo linaonyesha uhusiano kati ya matatizo ya kawaida na aina za uchanganuzi.

Static analysis¶

Static analysis hutatua equilibrium equation bila inertia term. Framework hii haijumuishi tu steady equilibrium isiyofuata muda, bali pia quasi-static analysis inayofuatilia equilibrium kwa kila wakati kwa mfululizo wakati wa kushughulikia time-dependent material response kama viscoelasticity na creep au nonlinear behavior yenye history. Tofauti na dynamic analysis ni kuwepo kwa inertia term, si kuwepo kwa mabadiliko kwa muda.

Linear static analysis hudhani small deformation na linear material na hutatua equilibrium equation kwa linear-system solve moja. Ina gharama ndogo zaidi ya computation na hutumika kwa stress evaluation na uchunguzi wa awali wa design.

Nonlinear static analysis hutumika ikiwa tatizo lina large deformation (geometric nonlinearity), nonlinear material (elastoplasticity, hyperelasticity, viscoelasticity, creep), contact, au mchanganyiko wake. Kwa kuwa equilibrium equation ni nonlinear, load hugawanywa katika increments na kutumika hatua kwa hatua, huku Newton-Raphson iterations zikitatua kila increment. Kwa time-dependent materials kama viscoelasticity na creep, increments na iterations hizo hizo hufanywa huku equilibrium ya kila wakati ikifuatiliwa mfululizo.

Kwenye input, weka !SOLUTION, TYPE=STATIC; ongeza parameter NONLINEAR ikiwa nonlinearity inatumika. Time stepping, increment control, na convergence criteria huwekwa kwa !STEP. Tazama Step control kwa maelezo ya increment control.

Dynamic analysis¶

Dynamic analysis hutatua equation of motion yenye inertia term kama mabadiliko kwa muda na kupata time-history response kwa history ya external force. Inalenga matukio ambapo acceleration ya mfumo huathiri sana response, kama impact loads, earthquake response, na wave propagation.

Time-integration schemes zimegawanywa kwa ujumla katika implicit na explicit methods. Uchaguzi hutegemea time scale ya jambo, ukubwa wa tatizo, na stability requirement ya time step. Implicit method inafaa pale low-frequency components zinapotawala na time step kubwa kiasi inahitajika; explicit method inafaa kwa high-frequency phenomena kama impact na wave propagation ambazo tayari zinahitaji time steps ndogo.

Implicit method¶

Implicit method (Newmark-β) hutatua simultaneous equations katika kila time step ili kupata displacement, velocity, na acceleration za wakati unaofuata. Haina stability restriction ya time step, hivyo kwa structural response inayotawaliwa na low-frequency components (kama earthquake response na mechanical vibration) inaweza kutumia time steps kubwa na kupunguza idadi ya steps. Kwa upande mwingine, simultaneous-equation solve inahitajika kila step, hivyo haifai sana kwa phenomena zinazohitaji idadi kubwa sana ya steps.

Explicit method¶

Explicit method (central-difference method) huhesabu state ya wakati unaofuata moja kwa moja kutoka taarifa za step iliyopita pekee. Gharama kwa step ni ndogo kwa sababu simultaneous equations hazitatuliwi, lakini time step hupunguzwa na condition inayotokana na smallest natural period ya mfumo (CFL condition). Hii ni faida kwa impact, wave propagation, na high-speed contact, ambako time step ndogo tayari inahitajika.

Kwenye input, weka !SOLUTION, TYPE=DYNAMIC na uchague method pamoja na integration parameters kama za Newmark-β kupitia !DYNAMIC. Tumia !STEP kubadilisha boundary-condition/load groups katika steps nyingi au kuweka increment control kwa kila step. Katika implicit nonlinear dynamic analysis, automatic increment na cutback kulingana na convergence pia zinapatikana.

Modal analysis¶

Modal analysis hutatua generalized eigenvalue problem ya mass matrix na stiffness matrix bila external force ili kutoa natural frequencies na natural mode shapes za mfumo wenyewe. Hutumika kutathmini vibration characteristics za structure, kutambua resonance points, na kama hatua ya awali ya frequency-response analysis inayotumia modal superposition.

Lanczos method hutumika kutoa kwa ufanisi idadi iliyotajwa ya low-order modes. Lumped mass matrix hutumika kama mass matrix.

Kwenye input, weka !SOLUTION, TYPE=EIGEN na uweke idadi ya modes za kutoa, shift value, n.k. kwa !EIGEN.

Frequency-response analysis¶

Frequency-response analysis hupata periodic steady-state response ya mfumo chini ya harmonic (sinusoidal) external force huku excitation frequency ikibadilishwa. Tofauti na time-history dynamic analysis, hutatua moja kwa moja katika frequency domain, hivyo inafaa kwa kutathmini resonance characteristics na kubuni steady vibration.

Suluhisho linategemea modal superposition: response hujengwa kwa kujumlisha natural modes zilizopatikana mapema kwa modal analysis. Kwa hiyo modal analysis ya mfumo huo huo lazima ifanywe kabla ya frequency-response analysis. Linear models pekee zinatumika; haiwezi kutekelezwa ikiwa geometric au material nonlinearity imewashwa.

Kwenye input, hushughulikiwa kama aina ya dynamic analysis: weka !SOLUTION, TYPE=DYNAMIC, kisha bainisha frequency response kwa subparameters za !DYNAMIC. Excitation condition huwekwa kwa !FLOAD.

Heat-conduction analysis¶

Heat-conduction analysis hutatua heat-conduction equation ili kupata temperature distribution na heat flux. Hutumia finite-element mesh ileile kama structural analysis, lakini kila node ina temperature DOF moja tu, na material properties zinazohusika ni thermal conductivity, specific heat, na density. Boundary conditions pia ni tofauti na structural analysis: prescribed temperature, heat flux, convection, na radiation.

Kwa sifa za muda, kuna steady-state heat conduction inayotafuta equilibrium isiyobadilika kwa muda na transient heat conduction inayofuatilia mabadiliko ya temperature field. Uchaguzi hutegemea kama unataka final equilibrium temperature au jinsi temperature inavyobadilika kwa muda.

Kwenye input, weka !SOLUTION, TYPE=HEAT na utaje steady au transient pamoja na time step kupitia !HEAT.

Coupled thermal-stress analysis¶

Coupled thermal-stress analysis hutumia temperature distribution kutoka heat-conduction analysis kama thermal-strain load katika structural analysis ili kupata stress na deformation zinazotokana na temperature field. Matumizi ya kawaida ya FrontISTR ni one-way coupling: thermal analysis na structural analysis hutekelezwa tofauti, na temperature field hupitishwa upande mmoja kupitia result file.

Utaratibu ni kufanya kwanza heat-conduction analysis na kupata result file ya temperature distribution. Kisha, wakati wa structural analysis, soma temperature field hiyo kama temperature load kwa !TEMPERATURE, READRESULT. Structural-analysis framework yenyewe ni sawa na static au dynamic analysis ya kawaida; hakuna haja ya kutaja aina mpya maalumu ya uchanganuzi kwa coupling.

Two-way coupling ambapo structural deformation huathiri heat conduction (kwa mfano mabadiliko ya thermal boundary conditions kutokana na deformation) haijumuishwi katika toleo hili la nyaraka.

Mada zinazohusiana¶

• Maktaba ya elementi — Aina za elementi zinazopatikana kwa kila aina ya uchanganuzi
• Material data — Material models zinazoweza kutumiwa katika kila aina ya uchanganuzi
• Nonlinear iteration na time integration — Newton-Raphson iterations, contact iterations, na time-integration schemes
• Step control — Time increments, convergence criteria, na load increment control
• Linear elastic static analysis (theory/appendix) — Formulation ya linear static analysis
• Tangent stiffness matrix (theory) — Tangent stiffness ya nonlinear static analysis
• Newton-Raphson method (theory) — Iterative solution method
• Dynamic analysis methods (theory) — Formulation ya dynamic analysis
• Modal analysis (theory) — Formulation ya eigenvalue problem
• Frequency-response analysis (theory) — Formulation ya frequency response
• Transient heat-conduction analysis (theory) — Formulation ya heat-conduction analysis