Advances in Structural Simulations
HyperWorks 2017 helps engineer strong, light, efficient structures.
HyperWorks from Altair (altairhyperworks.com) is a general-purpose, computer-aided engineering (CAE) simulation program with a variety of targeted applications for modeling, linear and nonlinear analysis, structural optimization and other engineering considerations related to car designs. Many of the modules within HyperWorks have been bumped up to release in 2017, such as Radioss, a structural analysis solver; OptiStruct, a structural analysis optimization program; and MotionSolve, a graphical multibody builder for solving equations, evaluating system behavior and optimizing build performance. Here are some of the new features in these modules worth noting for vehicular structural engineering.
Radioss improvements involve composites, materials, crash and safety and metal forming. Ply and stacks are now independent objects with their own ID. Moreover, analyzing sandwich composites is better because plies can use different material laws. In practice, the regular sandwich shell property, PID11, allowed only one material type for the whole sandwich. Now, a new orthotropic composite shell property, PID51, lets each ply have multiple material LAW types per ply. PID51 also lets each ply have multiple integration points in the thickness.
Overall, PID51 more accurately captures the bending behavior of each ply. (Note: No more than 10 integration points are allowed for each ply, and the total number of plies is limited to 200.)
Radioss also has a new shell element for predicting composite failures, particularly in crash and BVID (Barely Visible Impact Damage) applications. The new shell element, PLY-XFEM, based on the standard Batoz shell element (fully integrated), requires both stack and ply inputs. It also takes in data about the additional relative interplay displacement (degrees of freedom) between each ply. XFEM also helps evaluate crack pattern propagation when the crack hits adjacent edges, as well as resolves the visualization of cracked 4-nodes shells (triangular holes).
A new way to evaluate hyper-visco-elastic behavior based on Arruda-Boyce formulation has also been added. LAW92 simplifies material characterization. Better, it is user-friendly: Test data can be used as input, thereby eliminating the need to manipulate data to determine material parameters. Three types of tests are supported: uniaxial, equibiaxial, and planar (i.e., plain stress-strain test).
Radioss has two main implicit solvers to simulate springback in metal forming: MUMPS, which is new, and the existing BCS. Company officials say MUMPS has higher scalability than BCS, and the accuracy of the results are about the same. Better, MUMPS is faster, and the displacement results after springback are more user-friendly because rigid body motion has been removed.
Regarding the module’s performance, nodal time step is now applied to the remaining parts when advanced mass scaling (AMS) is applied to a group of parts. In the previous version, say company officials, “element time step was applied at the borders of the not-AMS parts, which was either reducing AMS benefits or making it ineffective in some cases. The global time step method calculates the stable time step based on the full model, which often results in higher time step than the element or nodal-based time step.” This change potentially reduces CPU time from 24 percent to 48 percent.
In OptiStruct, finite sliding (continuous sliding) is now supported, which helps in analyzing gear interactions. Loads and friction can be time-dependent. The Ogden model is now supported for hyperelastic materials and the Puck failure criteria is supported for composite materials. For NVH analysis, brake squeal analysis is supported, complex eigenvalue analysis can be used for acoustic analysis and inertial relief analysis can be performed for models with more than six rigid body modes.
Bore deformation can be constrained during optimization, one-step transient thermal analysis can be used with optimization and both seam and spot weld fatigue constraints and Neuber stress and strain responses have been added.
MotionSolve 2017 has several new ways for designing products and enhancements for analyzing physical events. For instance, a new truck library contains truck components and subsystems, including several different leaf- and air spring-based front and rear suspension topologies, steering systems and powertrain. The library is enough to assemble a virtual truck in minutes. Users can then interactively run half- and full-vehicle events tests, view simulation reports, and modify the truck designs.
The truck library also includes new component test rigs for vehicle entities such as AutoSpring, AutoAirSpring, AutoDamper, AutoBumpStop and AutoReboundStop. The design data for the automotive components are stored in an ASCII file, which can be easily shared between software systems and design engineering teams. These test rigs produce plots of key characteristics and animations for engineers to analyze. The force in the AutoAirSpring, for example, is interpolated from a table of force versus spring height and static inflation pressure (i.e., information from air spring manufacturers).
A new leaf spring builder lets engineers graphically build a detailed model of a multi-leaf spring by specifying spring characteristics such as the leaf profile (tapered or straight leafs), location of rebound clip attachments, type of spring eyes (up-turned, down-turned and Berlin), and the inter-leaf friction and contact properties. The tool’s simulator lets engineers deflect the spring to its installation configuration, which can be exported to a vehicle design model.
The leaf builder also contains a test rig for analyzing leaf spring models as if in a lab, generating force versus deflection curves for various loads as needed.
Another new feature in MotionSolve 2017 lets engineers evaluate 2D contact between two curves exactly as they would with 3D contacts. The module’s 2D and 3D contact analysis and outputs are the same. Because 2D curves are defined as cubic splines, they are smooth and do not suffer from discretization errors. Not so incidentally, the analysis using 2D contact can be two to 10 times faster than the equivalent 3D method.
Although the term “continuous improvement” is generally associated with another company, Honda is certainly pursuing that approach, as is evidenced by the Accord, which is now in its ninth generation.
By James Gaffney, Product Engineer, Precision Grinding and Patrick D. Redington, Manager, Precision Grinding Business Unit, Norton Company (Worcester, MA)
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