Mech 232
Mech 232
                                                            Structural Optimization
                                                           Theory | Objectives & Constraints | General
                                                           Considerations | Application Examples
Q&A
An Overview
    Ansys’ up-front simulation tool allowing you to design    Ansys’ flagship tool for detailed structural analysis to
    (CAD) and explore ideas, iterate and innovate quickly    solve complex structural engineering problems utilizing
    across multiple physics using fast GPU-based solvers.      implicit, explicit solvers and advanced meshing tech.
Mechanical LS-DYNA
Mechanical LS-DYNA
                                                                                                      Physical Prototyping
                                         Manufacturing & Processing                              → Expensive and time-consuming
                                                                                                      Validation
     Simulation Driven Design
                                         Material                                    Virtual          Physical
               Concept                                    CAD Model                                                     Testing    Production
                                         Selection                                 Prototyping        Prototype
                                                                                                                                                Cost and time
                                                                               Virtual                                                            savings
                                                                             Prototyping                 Physical Prototyping
                                          Manufacturing & Processing         Verification
                                                                            → Cheaper and
                                                                            faster process
                                                                      manage                            increase
                                                                      complexity                        quality
                         1                   2                                3
                                                                  “Finite Elements” used as
       CAD model imported         Geometry divided into         variables in physics equations,
                                    “Finite Elements”             Software computes results
Telescoping Truss Model “Mesh” created for Truss Model Deformation Results
          Solid Mechanics
      e.g. bracket
                                                    Physical principles                                           System of algebraic
                                                                                                                       equations
                                                    Governing equations
                                                                                                                   FEA approximate
                                     SM                             FM                           TA
           Fluid Mechanics
                             Euler-Bernoulli beam           Navier-Stokes motion        Fourier’s law of heat                SM
      e.g. pipe                   deflection                  of viscous fluids               transfer
                                                       2           2𝑤
                               d2
                                   𝐸𝐼
                                      d2 𝑢
                                           =𝑞
                                                     d
                                                     𝜕u         d
                                                            ⋅ ∇ u − 𝜈∇2 u ==
                                                        + u 𝐸𝐼
                                                                              1
                                                                            − 𝑞∇𝑝 + 𝑔       𝑞𝑥 = −𝑘
                                                                                                       𝑑𝑇             𝑲 𝐮 = 𝐅
                              d𝑥 2    d𝑥 2           𝜕𝑡                       𝜌                        𝑑𝑥
                                                    d𝑥 2         d𝑥 2
                                                                                                                Stiffness   Nodal     Force
                                                                                                                 matrix     vector    vector
         Thermal Analysis                           Boundary conditions                                                     (disp.)
      e.g. heat sink
                                    SM                           FM                               TA
                                                                                                                            ⇒
                                  Fixed end                   Parallel flow               Insulation at x=0
                                   𝜕𝑢                   2
                                                       d 𝑢                                      𝑑𝑇
                                                                                                                    𝐮 = ሾ𝐊ሿ−1 𝐅
                              θ 0 = ቤ     =0                = −1; 𝑢 0 = 𝑢 1 = 0            −𝑘      ቤ   =0
                                   𝜕𝑥 𝑥=0              d𝑦 2                                     𝑑𝑥 𝑥=0
                       …
            Solid Mechanics
        e.g. bracket
                                                                    Physical principles                                                      System of algebraic
                                                                                                                                                  equations
                                               Governing equations                                Boundary conditions
                                                 Euler-Bernoulli beam                        Fixed end                Free end                FEA approximate
                                                      deflection
                                                   d2     d2 𝑢                         𝜕𝑢                             d2 𝑢            𝐹
                                                                                                                                                        SM
 Simplification                                        𝐸𝐼      =𝑞                 θ 0 = ቤ     =0                 𝜏 0 = 2อ          =−
                                                  d𝑥 2    d𝑥 2                         𝜕𝑥 𝑥=0                         d𝑥              𝐸𝐼
                                                                                                                             𝑥=𝐿
                                                                                                                                                 𝑲 𝐮 = 𝐅
                              Discretization
                                                                                      𝑞
                                                                 1 Element 1 2   Element 2   3   Element 3   4                             Stiffness   Nodal     Force
                                                                                                                                            matrix     vector    vector
                                                                                                                                                       (disp.)
                                                                                       𝑢1   𝐹1                   𝑁𝑜𝑑𝑒 1: 𝑢1−3 = 0
                                                                                                                                                       ⇒
                                                                                       𝑢2 = 𝐹2
                                                                                                                 𝑁𝑜𝑑𝑒 4: 𝐹1 ≠ 0
                                                                                       𝑢3   𝐹3
                                                                                                                                               𝐮 = ሾ𝐊ሿ−1 𝐅
                                                                        𝑲              𝐮 = 𝐅
            Analytical
            Solid Mechanics
        e.g. bracket
                                                               Physical principles                      System of algebraic
                                                                                                             equations
                                               Governing equations          Boundary conditions
                                                                                                         FEA approximate
                                                                                                                  ⇒
                                                    • Galerkin Method of Weighted Residuals
                                                                                                          𝐮 = ሾ𝐊ሿ−1 𝐅
            Analytical
          Internal stresses and must be                             The constitutive material                Apart from cracks in a structure,
            in equilibrium everywhere                              behavior (stress-strain and                 displacements/strains must
            which presupposes a local                                  strain-displacement                    continuous if the structure is
          equilibrium (i.e. the sum of all                       relationship) must be satisfied.                      continuous.
                  forces is zero).
                             Body and
                              surface                                                                                     Displacements
                               forces
                                                                                  *
                                                           Stresses                            Strains
                                                                   𝑆𝑡𝑟𝑒𝑠𝑠 𝝈
         designers and engineers discuss structural problems                                Plastic
                                                                                 Elastic
                                                                                            regime
                                                                                                                                 × true
         or test results; however, these are not always                          regime
         accurately reflecting the stresses and strains a part                                              × UTS
                                                                                                                                FS
         experiences.                                                                                                            × engineering
                                                                                   𝜎
     •   Engineering stresses and strains are accurate if a part              𝐸=
         is only elastically deformed.                                             𝜀
                                                                 F    A
                                                                                    Conservation of volume:
     𝑆𝑡𝑟𝑒𝑠𝑠 𝝈
                                      true
                                                                                     𝐴0 × 𝐿0 = 𝐴 × 𝐿
                                              𝐹              L
                                    𝜎𝑡𝑟𝑢𝑒   =                                       Strain:
                                              𝐴                                                ∆𝐿       𝐿−𝐿0       𝐿
                                                       ×                            𝜀𝑒𝑛𝑔 =          =          =        −1
                                                                                               𝐿0        𝐿0        𝐿0
                                                                 F   A0
                                                       ×
                              engineering               L0                                          𝐹   𝐹×𝐿
                                                                                         𝜎𝑡𝑟𝑢𝑒 =      =
                                             𝐹                                                      𝐴 𝐴0 × 𝐿0
                                    𝜎𝑒𝑛𝑔 =
                                             𝐴0
                                                                                    𝐹
                                                  𝑆𝑡𝑟𝑎𝑖𝑛 𝜺                𝜎𝑡𝑟𝑢𝑒 =        × (1 + 𝜀𝑒𝑛𝑔 ) = 𝜎𝑒𝑛𝑔 × (1 + 𝜀𝑒𝑛𝑔 )
                                                                                    𝐴0
Tension Compression
     21
Structural Analysis – Equivalent (von Mises) Stress
     • The state of stress in 3D space can be described by a 3 × 3 tensor. Every stress component could be visualised
       and analysed individually, however, sometimes it might be more convenient to investigate just one plot,
       encompassing a single scalar value, the so called equivalent (von Mises) stress, which serves as an indicator for
       failure:
         𝜎𝑥𝑥        𝜎𝑥𝑦       𝜎𝑥𝑧                                         2                         2                       2        2     2     2
                                                         𝜎𝑥𝑥 − 𝜎𝑦𝑦            + 𝜎𝑦𝑦 − 𝜎𝑧𝑧               + 𝜎𝑧𝑧 − 𝜎𝑥𝑥             + 6 𝜎𝑥𝑦 + 𝜎𝑦𝑧 + 𝜎𝑧𝑥
         𝜎𝑦𝑥        𝜎𝑦𝑦       𝜎𝑦𝑧 ⇒ 𝜎𝑣 =
         𝜎𝑧𝑥        𝜎𝑧𝑦       𝜎𝑧𝑧                                                                          2
                                                                                                                                                                 𝝈𝒛𝒛
     • This so called von Mises yield criterion constitutes a means for determining the                                                                                𝝈𝒛𝒚
       onset of material yielding and is the most widely used criterion. Other popular
       criteria are for yielding in isotropic material are the Tresca criteria as well as the                                                                          𝝈𝒛𝒙
                                                                                                                                                           𝝈𝒚𝒛               𝝈𝒙𝒛
       Hill criteria for anisotropic behaviour.
                                                                                                                                                                                   𝝈𝒙𝒚
     • The von Mises stress can also be calculated from the principal stresses:
                                                                                                                                                                                   𝝈𝒙𝒙
          𝜎1      0          0                                                                                                                                   𝝈𝒚𝒙
                                                    𝜎1 − 𝜎2      2   + 𝜎2 − 𝜎3         2   + 𝜎3 − 𝜎1        2                                          𝝈𝒚𝒚
          0       𝜎2         0 ⇒ 𝜎𝑣 =
          0       0          𝜎3                                           2
Note: Recall that the two expressions (original and principal coordinate axis) provide the same equivalent stress value for a given stress condition.
                     1          2               2               2
        𝜎𝑣 =           𝜎 − 𝜎2       + 𝜎2 − 𝜎3       + 𝜎3 − 𝜎1
                     2 1
                                                                                                𝜎3
                                                                                    𝜎2                           𝜎2
23       ©2025 ANSYS, Inc.
Structural Analysis – Linear and Nonlinear FEM
     •   All phenomena we see in nature have some degree of nonlinearity. To simplify various physical problems, it is common to
         assume linear relationships and present a solution that is sufficiently accurate, but still an approximation.
     •   In the underlying system of equations in the linear analyses, it is possible to observe the relation between the force and the
         displacement, in which the stiffness matrix is constant. However, outside the material’s linear elastic region, for large
         deformations, the stiffness matrix is no longer constant, and the linear assumption cannot be applied.
                                                                                                                               𝑲 𝐮 = 𝐅
     •   Since the stiffness matrix is a function of its geometry and material properties, it is possible to
                                                                                                                        Stiffness     Nodal       Force
         highlight three main sources of non-linearity.
                                                                                                                         matrix       vector      vector
                                                                                                                                      (disp.)
     •   It is possible that the nonlinearities present in the model are a result of a combination of factors, not just one alone. Thus, it
         is important to analyse what is the main source of nonlinearity and think carefully, according to the wanted application, if it is
         possible to simplify the model to a linear comportment.
                                                                                                       Introduction to nonlinearities – Ansys Innovation Course
Linear approximation
                                                                                Structured x Unstructured
      Hexahedral                                      Tetrahedral
                              Element Size
                                 0.005m
                                             What is convergence?        The process of convergence consists in decreasing the element size and analyzing its impact in the
                                                                         solution of the underlying partial differential equations.
                                                                           …when it is possible to obtain the converged solution after which mesh refinement does not
                                             A mesh is independent…
                                                                           change the result anymore.
                          Garbage-In                                                               Garbage-Out
                                                              Think critically about what
                                                             assumptions you are making
                                                                       and why!
Simulation Tool
     Truck Water Wading Simulation     Wall impacting a battery pack      Hydroplaning with Flexible Tires
                                      (Current density + temperature)
               Fuel Tank Integrity   Coupling w. DEM to simulate mud    Drive Side Airbag Folding and Deploy
                                     or snow deposition
34    ©2025 ANSYS, Inc.
Manufacturing
           Sheet Winding        Roll Forming      Sheet Metal       Press Hemming       Rubber Forming
                                                    Forming
                                                                     Helmet Design
36    ©2025 ANSYS, Inc.
Beating Heart                                                                                  Automatic generation of the Purkinje network (top)
                                                                                                          and muscle fibers (bottom)
                                                                                                                                                                               LS-DYNA model
     Challenge
     •   Provide a high-fidelity multi-physics evaluation tool for beating human heart simulation.                                     User input:
     •   Accelerate device or clinical app development by testing implanted device performance,                                        • geometry
         e.g. pacemakers, stent meshes, prosthetic valves, etc.                                                                        • physics
                                                                                                                                       • database
     •   Develop coupled physics-based tool for patient-specific risk assessment.
     •   Reduce animal testing, time for device development and failed clinical interventions.
                                                                                                                  Unified pre-processing, execution, and post-processing for electro-physiology,
     Solution                                                                                                                  fluids and structures, incl. relevant physical coupling.
     •   A complete ecosystem for fast pre- and post-processing, optimization and a
         full suite of design and analysis tools. (SpaceClaim, Discovery, Workbench Meshing)
     •   Accuracy: Implicit time integration solution for nonlinear material models for valves,                                       Transmembrane
                                                                                                                   Bundle of
         implants and surrounding soft tissues.                                                                                          Potential
                                                                                                                   Bachmann
     •   Robustness: Strongly coupled fluid-structure interaction (FSI) provides stable
         solutions for coupled mechanical and hemodynamic simulations.                         Aortic valve
     Benefits
     •   Strongly coupled multi-physics capability on a single code platform
         enabling the solution of complex problems in a single run.
     •   Predict physiological response to device or intervention in silico.                                  Mitral valve
                                                                                                                                                  Action
     •   Reduce the cost of physical testing.
                                                                                                                                                  Potential
                                                                                                          Bundle of His
An Introduction
                                                                                                                           A process that
                                                                                                                           uses a physics
                                                                                                                           driven approach
                                                         / Size Optimization
                                                         •   Domain of the design is known a priori and
                                                             remains fixed
                                                         •   Typical parametric optimization
                                                / Shape Optimization
                                                •   Goal: find the optimal shape of the domain
                                                •   Boundary manipulation
                                        / Topology Optimization
                                        •   The number, location, shape and size the of holes
                                            and the connectivity of the domain are unknown
                                            a priori
                                        •   Improves specific performance
/ Shape Opt.
                                 / Topology Opt.
                                 •   Density-Based (SIMP)
                                 •   Level Set
                                 •   Mixable-Density
/ Topography Opt.
/ Lattice Opt.
     Design Space:
              i) Convex                                                        Convex                                 Non-Convex
              ii) non-convex
     Search mechanism:
             i) Deterministic vs Stochastic
             ii) Gradient vs Non-gradient (e.g.      Det. Gradient Descent Stoch. Gradient Descent                 Non-gradient*
             heuristic)                                                 Particle swarm optimization - Wikipedia
46       ©2025 ANSYS, Inc.
Topology Optimization – General Formulation
                                                                                                              Finding the “optimal” design within the
        • The purpose of topology optimization is                                                                         available scope
          to find the optimal lay-out of a structure                                                    1.    What is our objective for “optimal” design?
          within a specified region.                                                                    2.    What are the available options & constraints?
                                                                                                        3.    How do we describe different designs?
        • The only known quantities in the
          problem are the applied loads, the
          possible support conditions, the volume
          of the structure to be constructed and                                                                  Design Variable                      State Variable
          possibly     some     additional    design                                                   Objective function         min → 𝑓 𝐬, 𝐮(𝐬)
                                                                                                                                  𝐬∈ℝn
          restrictions such as the location and size
                                                                                                       Inequality constraints     s. d.   ℎ𝑖 𝐬, 𝐮(𝐬) ≤ 0    𝑤𝑖𝑡ℎ 𝑖 = 1, … , 𝑛ℎ
          of prescribed holes or solid areas.
                                                                                                       Equality constraints               𝑔𝑗 𝐬, 𝐮(𝐬) = 0 with 𝑗 = 1, … , 𝑛 𝑔
        • In this problem the physical size and the                                                    Equality constraints               𝐬𝑚𝑖𝑛 ≤ 𝐬 ≤ 𝐬max
          shape and connectivity of the structure
          are unknown.
     Martin P. Bendsøe, Ole Sigmund, Topology Optimization Theory, Methods, and Applications (2004).
                                         Unconstraints                                                      Constraints
                 12                                                             12
                 10                                                             10
                                                                                                                              𝑓 𝐬, 𝐮(𝐬)
                  8                                 𝑓 𝐬, 𝐮(𝐬)                    8              ℎ 𝐬, 𝐮(𝐬)
                  6                                                              6
4 4
                  2                                                              2                                                𝑔 𝐬, 𝐮(𝐬)
                  0                                                              0
                      0       1   2          3          4       5         6          0      1          2         3        4         5         6
𝑔𝑗 𝐬, 𝐮(𝐬) = 0 with 𝑗 = 1, … , 𝑛 𝑔
𝐬𝑚𝑖𝑛 ≤ 𝐬 ≤ 𝐬max
                                                                                                         Surface
                                          Level set function
     Evolution equation
                                          discretised with grid-
     (Hamilton-Jacobi)
                                          points (centre of element)
53        ©2025 ANSYS, Inc.   Structural and Multidisciplinary Optimization (2014), 51(5): 1159-1172
Lightweighting Strategies in Additive Manufacturing
                                                        Generative
                                                        Design
                                                        Real-time
                                                        decisions
                                                        Explore
                                                        possibilities
                                                                                         prediction confidence
                                                                                                                                                   95%
     Challenge
     •   Coming up with new jet engine bracket designs as quickly as                                                                                      Displacement
         possible that meet structure requirements and constraints.
                                                                                                                                                          Von Mises stress
     •   Moreover, it is important to make use of existing designs that have
         accumulated over years, retaining the knowledge from previous
                                                                                                                     50         100          250
         projects.
                                                                                                                          training samples
                                                                                                                                                            Discovery          SimAI
     Solution
     •   Up to 250 training samples, with different and topologically diverse bracket
         designs, were run to build a global AI model. (SimAI, optiSLang, Discovery)
     •   Based on knowledge from previous projects and simulations, optiSLang can                                  Unseen Shape Verification
                                                                                                                                                                             Displacement
         predict a new shape, while SimAI shows you its physical behavior in less than
         a few seconds. The AI model can be extended and retrained with new designs
         at any time to capture additional physical behavior. (optiSLang, SimAI)                                 Discovery                                    SimAI
     Benefits
     •   0 scraps, use all the designs you have from the past to move forward,
         even a bad design is a source of knowledge.
     •   Reduce your current workflow by 90%, go directly from CAD to physics.
     •   Use 100% of your team and let AI guide them with new ideas, no deep
         knowledge of physics required.
                                                                                                                                               Von Mises stress
Pattern repetition
Housing
[1]
[1] - Carter, W.T., Erno, D.J., Abbott, D.H., Bruck, C.E., Wilson, G.H., Wolfe, J.B., Finkhousen, D.M., Tepper, A., Stevens, R.G.: The GE Aircraft Engine Bracket Challenge:
An Experiment in Crowdsourcing for Mechanical Design Concepts
  63              ©2025 ANSYS, Inc.
GE-Bracket Challenge – Structural Optimization
Load Case 2
                                                                                           CAD
                                      …
Load Case 2
MASS
No Manufacturing Constraints
No Housing Constraint
                                                                   Member Size Minimum        Member Size Maximum   Member Size Gap Size
         No Extrusion Constraint
                                   Tech Tips
                                L-Bracket Example
L-Bracket Example
vs
L-Bracket Example
Plastic Steel
L-Bracket Example
Plastic Steel
vs
                                                                                                                      𝑬
                                                                                                              𝑮=
                                                                                                                   𝟐(𝟏 + 𝝂)
0 𝝂 0.5
L-Bracket Example
vs vs
L-Bracket Example
                                                  Manufacturing
                                                    Constraint:
                                                 Table Direction (Y)
                                                  Ensure realistic
                                                  constraints are
                                                 applied → Sanity
                                                       Check
Y-Direction
vs
                                   vs
              2                                1
                                                           Unsp
                                                               rung
                                                                    &   Rot
                                                                           atio
                                                                                nal
                                                                                    Ma
                                                                                       ss
                                                                                            
                                                                             -45% Weight
                                                                                                      <1 kg
         Developing a Hybrid CFRP Wheel With Ansys Software
                                     -71% Stress
                                      From plastic to elastic
                                12x Stiffness
93   ©2025 ANSYS, Inc.
At a Glance – Structural Optimization Application
         / Shape Optimization
         •    Easy setup
         •    Only meshing parts
         •    Program Controlled Settings
         •    Best practice post-processing of
              TO-Solution                           -32% Stress
                                                    From plastic to
                                                    elastic
< 15 min
                     / Lattice Optimization
                     •   Easy & fast validation
                     •   Automatic generated & applied variables on
                         initial geometry
                     •   Solid material is substitute by beams
                     •   Outer shape doesn’t change                      -52% Weight
                     •   Knockdown factors are a fast approach for       Maintain Max
                         validation, properties of lattices are mapped   Displacement
                         onto solid elements
                                                                             < 2 min
Structural Optimization
                                                                         Additive Suite
                                         Ansys Motion
Learning and community platform designed for students, educators and engineering professionals to enhance their
                             engineering knowledge with free learning resources
/ And more!
Setup
Fine-Tuning Efficiency
 Predator Cycling Optimizes the Cycling Experience With   Ansys Topology Optimization | Lightweighting & Shape
 Simulation (ansys.com)                                   Optimization