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Top News:

Shape Optimization of Wheel Spokes to Survive Wheel Impact Test
2018-03-07
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Shape optimization with non-linear quasi-static analysis of wheel impact test
using five shape basis vectors (SBV) results in significant reduction of plastic strains.

For the homologation of alloy wheels, a number of standard tests have to be performed before such wheels are allowed to be used in cars. Such tests are bending fatigue test, radial fatigue test, and impact test. The latter test represents the inclined collision of a wheel and a curb at low speed, where the spokes are not allowed to crack. To pass this test at the first time successfully, previous numerical simulation and optimization can avoid late re-design and late start of production.

The impact test conditions describe a low speed impact on the rim, which can be handled as quasi-static analysis case. An elastic-plastic contact analysis is easily applied to compute effective plastic strains, where the results are taken after the potential energy of the falling mass is consumed by elastic and plastic deformations of the test rig with the wheel. The point of failure is defined, when the effective plastic strain exceeds the ultimate plastic strain of the material used.

When failure occurs, a shape optimization can be applied to reduce the plastic strain at the critical points. In addition, a special condition has to be fulfilled, which does not allow to make shape changes of the front view, because this is exclusively defined by the stylist. This is a very special manufacturing constraint for the optimization.

The attached picture shows the shape optimization of a wheel to survive the impact test. The initial model shows high plastic strains on the reverse side of the spokes with 11.9% and 4.9%. A parametric shape optimization of the reverse side of the spokes is performed taking the fivefold cyclic symmetry of the wheel into account. Three Shape Basis Vectors (SBV) are used for the outer radius of the spokes and two additional SBV are used for the inner radius of the spokes. The weight is used as objective and the effective plastic strain is used as constraint limited to 3.4% for the two highly strained locations on the spokes' reverse side. Convergence is achieved after three iterations with six loops each, which are used to calculate the derivatives for all five SBV for this non-linear optimization task. To reduce the plastic strains, the weight of the wheel has to be increased by 3.2%.

The set-up of the shape optimization is supported by the Shape Wizard in VisPER. Here, the SBV are specified and prepared for the later optimization with PERMAS. VisPER is also used for the result evaluation, where the history plots for constraints and objective are generated and the shape changes and resulting stress and strain fields are visualized. Additional history plots show the influence of the single SBV on the shape change.

Two animations about change of effective plastic strain and the coordinates on the reverse side of the spokes give a more detailed impression.

More details of shape optimization are described here and in the PERMAS Product Description.

PERMAS® is making realistic simulations practical. PERMAS® supports advanced product designs through effective and rapid optimization of complex situations. PERMAS® is an integrated FE analysis software combining thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

Comparison of experimental modal analysis (EMA) with dynamic eigenvalue analysis
2018-02-06
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Example of a ladder frame with measured and computed natural frequencies and mode shapes.
The MAC matrix at top right side shows strong correlation for five modes.

For structures under dynamic loads, simulations and experiments are frequently used side by side. This leads to mutual benefits. On the one hand, simulation provides a means to identify preferred points to measure. On the other hand, experimental results can be used to identify differences between experimental and simulation model, which provide a basis for model updating to fit the test results by simulation.

One important comparison between experimental modal analysis (EMA) and Dynamic EigenValue analysis (PERMAS module DEV) is between measured and computed natural frequencies and between measured and computed mode shapes. While the natural frequencies can be compared directly, the comparison of mode shapes is usually made using MAC matrices (MAC - Modal Assurance criterion). To this end, each mode shape of the experiment is compared with each computed mode shape and vice versa. The values of a MAC matrix is between Zero and One. Values near One indicate a strong similarity of the mode shapes, while small values indicate different mode shapes.

PERMAS is capable to read model and results (from a Universal File) and to use them subsequently to generate and export directly the MAC matrix with the computed mode shapes.

The attached picture shows an example, which kindly has been made available by Prof. Dr.-Ing. Jörg Bienert of Ingolstadt University of Applied Sciences. He has determined the experimental results for the ladder frame structure, while the simulation and the comparison have been made by INTES. The location of the sensors does not fit to nodes of the FE mesh. So, interpolation regions were used to connect the sensor locations with the neighboured nodes of the FE mesh. By doing so, the computed results are available at the same points as the measured results and the comparison can be performed directly by generating the corresponding MAC matrix.

For the first three modes, the computed and measured natural frequencies and mode shapes are shown. We see from the MAC matrix that the modes four to seven were not available in the experimental results. The experiment used one-dimensional sensors, which perfectly detect displacements normal to the ladder frame. But the computed modes four to seven show displacements in the plane of the ladder frame, which are not detectable by the used sensors.

More information is available about the capabilites of PERMAS to perform eigenvalue analysis, either real eigenvalue analysis, or modal condensation and complex eigenvalue analysis, or real eigenvalue analysis by Multi-Level Dynamic Reduction.

PERMAS® is making realistic simulations practical. PERMAS® supports advanced product designs through effective and rapid optimization of complex situations. PERMAS® is an integrated FE analysis software combining thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

Graphic-Based Process for Frequency Response Analysis
2017-12-18
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Model description, mode shape visualization, PERMAS job submission,
and evaluation of frequency response results with VisPER.

Frequency response analysis (FRA) as a forced vibration analysis under harmonic loading is available with PERMAS since many years. In case of a modal FRA, the eigenmodes and eigenfrequencies are calculated first and the FRA is performed in a second step. It is a frequently proven procedure to check the eigenmodes first before starting the FRA. Beside the mode shapes, strain and kinetic energy distributions and effective masses are also important to check.

In an action to facilitate the use of FRA, the application process is now supported by VisPER, the graphical user interface of PERMAS. The steps of the FRA process for a given structure are as follows:

  1. The eigenmodes and eigenfrequencies are computed and exported to the binary HDF5 formatted result file of PERMAS.
  2. VisPER is used to read and visualize the modes and frequencies.
  3. All FRA related input like damping, harmonic loads, excitation frequencies, nodes for response evaluation can be easily specified in VisPER.
  4. The PERMAS FRA job is set up in VisPER and started from within VisPER. The modes and frequencies need not to be re-calculated. Hence, the computation time is reduced accordingly.
  5. The FRA results are read and post-processed with VisPER.

Model data, mode shapes, FRA results, and generated pictures and animations can be collected in a PowerPoint, Word, or Excel file using a provided template, which can be tuned to specific requirements.

When the user checks the eigenmodes and eigenfrequencies in a post-processing step, it is quite logical to proceed with the definition of the FRA specifications in the same software. Subsequently, the FRA job can be started and FRA results can be imported in VisPER after the PERMAS job is finished. After result evaluation of the FRA, modifications of the dynamic model are supported and the FRA can be repeated in the same way.

The attached picture shows two overlapping bonded sheets with harmonic concentrated load and a node set for response results. The first two mode shapes are shown (for bending and torsion). After specifying the additional FRA input, the PERMAS frequency response analysis is started from within VisPER (screen shown bottom left). Then, the FRA results are postprocessed with VisPER (screen shown bottom right).

VisPER is the Graphical User Interface (GUI) of PERMAS. VisPER integrates pre- and post-processing functions and it allows to start PERMAS executions. Moreover a reporting facility supports the creation of reports containing model information and analysis results by pictures and animations.

PERMAS® is making realistic simulations practical. PERMAS® supports advanced product designs through effective and rapid optimization of complex situations. PERMAS® is an integrated FE analysis software combining thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

Multimodal Optimization to Design and Position Vibration Absorbers
2017-09-09
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Simply supported beam subject to harmonic pressure load

Vibration absorbers are mainly used in civil engineering, e.g. for high-rise structures and bridges. But also mechanical engineering benefits from vibration absorbers, e.g. in machine/building interaction or insulation of vibrating structures. Moreover, in case of vibrations tending to instabilities, vibration absorbers are always an important topic, e.g. brake squealing, blisk vibrations in jet engines.

Although time dependent processes are often responsible for amplifying vibration amplitudes, broad-band damping is still of great interest, because the critical frequencies are not known in advance. Therefore, we focus here on deterministic harmonic loads.

The classical means for vibration absorption are tuned mass dampers, consisting of a secondary mass, a viscous damper, and an elastic spring. They are commonly attached to a primary vibrating system for suppressing undesirable vibrations. Finding closed solutions for optimal parameters of dynamic vibration absorbers is usually limited to simple academic two-degree-of-freedom systems. However, in finite element analysis of flexible structures several modes must be damped for large structural models, a broad band of excitation frequencies has to be applied, and multiple vibration absorbers should be handled simultaneously.

The solution is a multimodal optimization with a sizing approach for the parameters of each absorber and a positioning approach of the absorbers to find the optimum location. With PERMAS, a unified approach is made, where the finite element analysis and the optimization is performed in one single software using one single finite element model. In each optimization loop, a dynamic eigenvalue analysis, a modal frequency response analysis, and an optimization step is performed. This fully integrated optimization procedure enables the user to simultaneously find optimal parameters including positions of multiple dynamic vibration absorbers in the frequency domain.

The attached picture shows a simple application case, where a supported beam is subject to a harmonic pressure load at the top surface. Three mass dampers are initially applied at the mid point, at one quarter point and at three quarters point on the bottom side of the beam.

The locations in X direction beside stiffness and damping values of all three vibration absorbers are used as design variables. The absorbers solely act in load direction. The objective of the optimization is the minimum displacement amplitude in the middle of the beam bottom side in the frequency range [0, 120] Hz. The vibration absorbers at the quarter points move towards the center point during the optimization. The displacement amplitude at the fundamental eigenfrequency of the initial configuration is reduced from 92 mm to 39 mm.

More examples of absorber optimization are presented on the previously published paper. In addition, PERMAS optimization features are also described here.

PERMAS® is making realistic simulations practical. PERMAS® supports advanced product designs through effective and rapid optimization of complex situations. PERMAS® is an integrated FE analysis software combining thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

New generation at INTES
2017-07-21
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After 33 years, INTES CEO Reinhard Helfrich transferred his position to Rolf Fischer on July 1st, 2017. Reinhard Helfrich remains responsible for the development of INTES' international operations. "Our goal is to preserve our independence and to put the next generation in charge of INTES", says Reinhard Helfrich. "By this step, we are creating a new basis of confidence among our customers regarding the continuous further development of INTES."

Rolf Fischer has been the head of INTES software development for more than 20 years. "To our customers, we already provide software for the future challenges in model complexity and computing speed", Rolf Fischer underscores. "The software will become even more attractive for our international customers by future developments of functional extensions and high comfort. Here, we are putting strong emphasis on innovative solutions in close cooperation with our customers."

Ever since INTES was founded in 1984, the company has been and continues to be a privately held and independent software development enterprise. With its products PERMAS® and VisPER® for the Finite Element Analysis of parts, machines, and vehicles, INTES became an established company on the market. PERMAS® is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. VisPER® is the matching integrated pre- and post-processor with graphical user interface and comfortable modeling features and result evaluation.

PERMAS® is making realistic simulations practical. PERMAS® supports advanced product designs through effective and rapid optimization of complex situations. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

PERMAS® on new INTEL® XEON® SCALABLE PROCESSORS
2017-07-11
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The overall performance of PERMAS® always depends on the performance of both hardware and software. The close cooperation between Intel and Intes over many years ensures the ongoing adoption of new features to be at the forefront of high performance computing. As a consequence, a new processor release is always accompanied by the best adapted software. This is exactly what INTES wants to provide to its customers.

We want to target all customers who have an increasing need for high performance FE solutions. Simulation driven design fosters this trend to more accurate simulation results. A higher accuracy is possible by using larger and more complex models.

The new INTEL® XEON® SCALABLE PROCESSORS are supported by PERMAS® from the very beginning. On these processors, PERMAS® shows excellent performance as documented on a joint flyer.
There is up to 56% higher 4-socket performance than in a previous-generation server.

The leap in performance on this new INTEL® XEON® SCALABLE PROCESSORS is mainly due to the AVX 512 instruction set, because it perfectly supports the high level matrix operations in PERMAS®. Increased memory bandwidth helps to better exploit the speed of the processors.

Large simulation models are mostly running out-of-core. A high speed storage device like Intel’s NVMe SSD drives are directly addressed by PERMAS® without the need to use an I/O controller resulting in very efficient I/O and short overall run times. In particular, short access times combined with a direct I/O scheme in PERMAS® provides high data transfer to optimally feed the processors. An additional increase of data transfer can be obtained by striped SSD drives.

Processor systems with several sockets are very suitable to increase throughput for multiple jobs, particularly in combination with high performance SSD drives.

How INTES implemented PERMAS® on this new generation of INTEL® XEON®; SCALABLE PROCESSORS is shown in an instructive movie.

PERMAS® is making realistic simulations practical. PERMAS® provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS® supports better product designs through effective and rapid optimization of complex situations. PERMAS® is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS®, a Short Description is available. More detailed information may be obtained from the Product Description.

PERMAS computes vehicles' stressed wire harness
2017-07-05
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Model of wire harness between car body and door.
Stress results and contact pressure at a door opening of 70 degrees.

Covers and openings of vehicles usually contain electric drives and functions like adjustable and heatable exterior mirrors, window lifters, speakers, and lighting in doors. These functions need power which is supplied by wires from the battery. The wires have to allow for a wide opening of doors. This leads to high stresses in the wires which can lead to wire breakage. So, a stress analysis of wires during door opening is essential to prove a wire harness design.

The picture to the left shows an industrial example of a typical wire harness between a car body and a door. The wire consists of thirteen conductors of various diameters. A bellow is applied to protect the wire from water. While the upper end of bellow and wire are fixed at the car body, the lower ends have to follow a prescribed opening of the door by 70 degrees. The rotational axis is shown which corresponds to the hinges of the door.

The stress analysis of this wire harness mainly depends on contact:

  1. Contact between the conductors of the wire.
  2. Contact between the convolutions of the bellow at the outer side and at the inner side of the bellow.
  3. Contact between wire and the inner surface of the bellow.
The first two contacts are characterized by a greater number of bodies with potential contact between conductors and convolutions, where the real contact zones cannot be predicted easily. The most effective way of modeling these contacts is by self-contact, where the software itself looks for the current contacts between the bodies and updates the contacts as appropriate. In addition, large displacements and large rotations are taken into account, while the material is still elastic.

The lower left picture shows the nodal von Mises stresses in the wire after the rotation of 70 degrees. For the same rotation, the lower right picture shows the contact between wire and bellow by solid areas on a transparent bellow, where the solid areas show the contact pressure as a result.

Two animations about motion and stresses of the wire harness are more enlightening.

More details on contact analysis are collected in the PERMAS Product description, pp. 72 to 77.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information may be obtained from the Product Description here.

Topology Optimization with Contact
2017-06-23
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Comparison of shapes found by topology optimization in PERMAS for different
coupling conditions between a block with quadratic bore and a bent beam.

It is a question raised often what to do with contact in topology optimization. Is it possible? Is contact as a nonlinear feature managed properly at all? What is the influence of contact on the results? Contact is the most frequently used nonlinearity and an important boundary condition. So, there is the good message that contact can be used in a standard way by topology optimization in PERMAS.

The picture to the left shows a simple example, where a block with a hole is supporting a bent beam. It is a fully solid model with contact between the beam and block hole. The initial gap between both bodies is zero. The objective of the topology optimization is the compliance and the weight constraint is to save 60 percent of the design space.

The picture shows three optimizations with three different boundary conditions:

  1. Block and beam are coupled at the common interface. So, no contact is applied.
  2. The surface of the block hole is not changed and the first layer of elements at the block hole is not changeable by the topology optimization.
  3. The surface of the block hole is changeable and the surface can be reduced where no contact is active.
All pictures are generated after a fully converged topology optimization with a clear separation of filled and void elements and a subsequent smoothing of the finally achieved surface.

The first column shows a perspective view of the topology optimization result, where the initial block size is shown in transparency. The second column shows a cut through the mid plane of the topology optimization result. The third column shows the contact status at the block hole (for cases two and three only). The contact status perfectly reflects the different shape.

The example model was inspired by the following publication: Ahmad, Z., Sultan, T., Zoppi, M., Abid, M., Park, G. J. (2016) ‘Nonlinear response topology optimization using equivalent static loads—case studies’, Engineering Optimization.

The set-up of a topology optimization with contact is very easy and particularly tailored for PERMAS by its pre- and post-processor VisPER. Contacts are defined as for every contact analysis (by using the contact wizard). Objective and constraints for the topology optimization are also defined (by using the topology optimization wizard). The final smoothed surface shape can be exported during post-processing of the results as an FE mesh or by STL format to process the result of the topology optimization further (e.g. new meshing).

More details of topology optimization are presented on the flyer published previously. It is illustrated by an industrial example. In addition, topology optimization is also described here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information may be obtained from the Product Description here.

PERMAS saves weight and improves endurance
2017-04-24 (Freeform Optimization)
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Freeform optimization is a method for shape optimization of Finite Element (FE) models, where the geometry of the model surface is modified while the element topology remains unchanged.

Freeform optimization is not a mathematical shape optimization method but it uses optimality criteria. They describe the relationship between a geometry change and its influence on a certain result quantity. Mainly, the relationship between a geometry change and equivalent stresses in the material is of great importance. This means that a high stress can be reduced by adding material (i.e. increase of part thickness) at the position of the high stress. The same holds for the inverse, i.e. a stress increases when part thickness is reduced.

Beside equivalent stresses all stress-like quantities like principal stresses, stress differences between different load cases, effective strains or safety factors can be used. Typical optimization solutions are stress homogenizations under weight conditions or a weight optimization under stress limits. The method is well suited for large models with many load cases and is mainly used to optimize the shape of models with free surface geometry like cast parts for housings of transmissions and engines. Applicable analysis methods are among others linear and non-linear static analysis including contact as well as frequency response analysis in dynamics.

The implementation of the method in PERMAS has now been extended by a combination with mathematical optimization methods in case of certain additional constraints, which are best represented by sensitivities. For example, this allows the limitation of displacements at bearings or an additional constraint on the compliance of the optimized structure. In dynamics, vibration amplitudes of selected nodes can also be restraint. Also, a third party software for endurance calculations can be invoked from within PERMAS in order to take its results as constraint or even objective function in a freeform optimization. By combining parametric and non-parametric optimization methods, many realistic requirements can be considered in one single optimization.

The set-up of an optimization model for freeform optimization is very easy and particularly tailored for PERMAS by its pre- and post-processor VisPER. A surface node set has to be selected only to sufficiently define the design space for freeform optimization. The related design elements are selected automatically. Stress and weight constraints as well as other constraints are very easily defined.

PERMAS freeform optimization targets to save weight and improve endurance in one single optimization. The time for development of structural parts can be significantly shortened while the structural behavior is improved by optimization.

The details of a freeform optimization is presented on the attached flyer. It is illustrated by an industrial example. More information on optimization can be found here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available. More detailed information is available from the Product Description.

Topology Optimization in Dynamics
2017-03-29
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Comparison of frequency response of en engine bracket after an all static optimization (left)
and an optimization with both static and dynamic excitation (right).

Topology optimization is a standard method for shape finding under given boundary conditions and loads. Often, static load cases are used for topology optimization, because it is easy to apply and gives a good first impression of the best shape. For dynamically loaded structures, it is obvious that a topology optimization should include a dynamic analysis, too. To this end, the topology optimization method has to be extended for dynamic analysis. This extension has been developed in PERMAS to enable topology optimization to be used simultaneously for static and modal frequency response analysis.

The example of an engine bracket as shown in the picture to the left is used to show the effect of a concurrent use of static and dynamic loading in topology optimization. At the top of the picture, the design space and its boundary conditions are shown. So-called frozen regions are applied for the fixations of the part, which are not allowed to be modified during topology optimization. Release directions are also taken into account.

Below, the left column shows the optimized shape for a static load only, and the right column shows the optimized shape for a static load combined with a harmonic (sine or cosine) excitation. The weight of the optimized part is the same for both cases. The found designs are both fully converged results with a zero-one distribution of skipped (i.e. a filling ratio near zero) and remaining elements (i.e. a filling ratio near one).

The bottom of the picture compares the frequency response of the loading point for both cases. The shape found by static loading only shows a much higher amplitude when a harmonic excitation is applied compared to the other case, where the harmonic excitation has been taken into account during optimization. It can be concluded that a topology optimization under harmonic excitation urgently requires an optimizer, which can properly handle static and modal frequency response analysis simultaneously.

An animation of both optimizations over all iterations is shown here.

A paper is available on the engine bracket optimization, too.

Why you should use PERMAS for Topology Optimization in Dynamics? Although the need for a topology optimization with harmonic excitation is obvious, such a feature is not sufficiently supported in many other optimizers. The reason lies in the very nonlinear relation between small changes of structural stiffness and mass and the resulting change of frequency responses. This nonlinearity becomes very critical in case of plastics, because parts of this material show more eigenfrequencies in a typical frequency range than metal parts. Moreover, it is not sufficient to monitor the response just for one frequency, but a monitoring over the complete frequency range is required. PERMAS handles all these cases properly and provides the right means for topology optimization under harmonic excitations. PERMAS delivers a fully converged shape of the optimized parts, which is very close to the final design or can be directly used for production. By using PERMAS, dynamically loaded parts can be successfully optimized and high costs for testing and re-design of parts can be significantly reduced.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

New software PCGen to model fluid tanks for PERMAS
2017-02-01
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Tank modelling with PCGen

Fluid tanks are applied in a wide range from space flight in launchers and satellites to storage tanks in refineries and power plants. Such tanks are usually almost rotationally symmetric, i.e. they have a few deviations like longitudinal ribs or bolted flanges. It is also characteristic for these models that the structure mainly consists of shell elements. In addition, the fluid is also modeled to calculate the dynamic coupling between structure and fluid. For a highly efficient modeling of fluid tanks, PCGen (PERMAS Component Generator) has been developed as extension to VisPER (Visual PERMAS), which combines the modeling of geometry, structure, fluid, and meshing in one single tool.

The new apporach of PCGen can be described as follows:

  • A library of parametric geometrical models is available for all typical parts of a tank.
  • These parts are piled up from the bottom until the tank is completed. Subsequently the parameters are updated to the required values.
  • Thicknesses of the shell elements and possibly the filling level of the fluid are added.
  • Material properties of structure and fluid are defined.
  • Finally, the model is compatibly meshed after some settings for the mesh size, and it is stored for subsequent computations with PERMAS.
  • Completed!

In order to take the vibrations of the fluid surface into account, PCGen generates wave elements on the fluid surface. The frequencies of the surface waves are computed and shown by PCGen under the simplifying assumption of a rigid structure. After a coupled vibration analysis with PERMAS, these surface eigenfrequencies can be compared with the FEA results.

In the adjacent picture, some of the modeling phases are shown for a perfectly rotationally symmetric storage tank. The total time to model the fluid tank is about 6 minutes.

A film about the complete modeling of the tank is shown here. An additional flyer shows the most important details about PCGen.

A paper is available, which also shows details about bolted joints of fluid tanks.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

One-stop FSI analysis for liquid sloshing in an earthquake
2016-12-22
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Fluid-structure coupled modal time-history analysis for simulation
of storage tanks in an earthquake

Liquid storage tanks with critical content (like oil) in an earthquake have to withstand the structural loads and, in addition, the maximum filling level has to be restricted to avoid spill-over of the liquid. Many national standards provide corresponding requirements, e.g. in ASCE 4-98 or GB50191-93 for the nuclear field.

Because the large liquid mass implies high loading of the tank structure due to rapid movements in an earthquake, the simulation is best done using fluid-structure interaction (FSI) analysis, or more precisely, fluid-structure coupled (FSC) analysis. In this way, the stresses in the structure and the wave height at the free liquid surface can be determined in one single simulation.

To this end, beside the structural model PERMAS provides fluid elements and their coupling to the structure as well as special wave elements for the free liquid surface to determine wave heights. A time signal of horizontal excitation of the tank baseplate due to an earthquake is a possible load case. The simulation is then performed by a modal time-history analysis, where the coupled vibration modes are calculated first and used afterwards to compute the coupled response behavior of the tank.

The adjoining example shows at the top the tank model with the first vibration mode, where the displacements show the structural mode and pressure distribution shows the coupled fluid mode. Below, the acceleration signal of the earthquake is shown over a period of 20 seconds. The next row contains the surface wave at certain point in time on the left and two stress distributions of the tank walls at different points in time on the right. At the bottom, a comparison is given between the requirements of the mentioned standards and the simulation results. The requirements following the American and Chinese Standard for Seismic Analysis of Safety-Related Nuclear Structures are cited from Zhang Liqiang, Tang Qionghui, Fluid Structure Interaction Analysis of Liquid Sloshing Phenomenon in Storage Tank, 18th National Conference on Structural Mechanics of Reactors, October 2014, Chengdu.

For this tank, the fundamental eigenfrequency of the surface wave is met very well. For wave height and overturning moment, the simulation results are between the values of the two standards.

Now, which run time has to be spend to solve the coupled analysis task? Less than 10 minutes!

Animations over time for surface waves and structural stresses are available here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

PERMAS uses production processes in optimizing sheet metal parts
2016-12-01
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Rolling, blanking, and beading to achieve the stiffest sheet metal
under given weight.

In the development of sheet metal parts various production processes like rolling (to get thickness variations), blanking (to cut out the final sheet), and beading (to generate beads for higher stiffness) are very important. In order to optimize sheet metal parts for weight and stiffness, these production processes have to be represented by suitable model modifications. The integration of this optimization in Finite Element (FE) analysis facilitates the direct identification of the necessary production steps.

To this end, the rolling is implemented by the optimization method called free sizing to achieve variable sheet thicknesses. This method works like topology optimization and modifies the thickness of shell elements in a wide range to get the desired part properties.

The blanking process is implemented by topology optimization, where an unambiguous selection of required elements is generated.

For the stiffening of the sheet metal part, bead generation by shape optimization is available, where the nodes of the shell mesh are moved normal to the sheet to get the stiffening effect.

By applying the Multi-Modal Optimization (MMO) approach in PERMAS, all these previously mentioned methods can be combined in one single optimization.

The adjoining example of a simple shell model under torsional loading shows the effect of the three combined optimization methods. The stiffest structure under a given weight and symmetry conditions is the corresponding objective. The results of the different production steps and the final result of the optimization are shown.

An animation of the shape changes over all iterations of the optimization is available here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

PERMAS to explore buckling load factors and mode shapes
2016-10-27
image

Three samples of rib height with different buckling mode shapes.

For many structures, buckling is an important design constraint and has to be checked by buckling analysis beside other types of analysis. Mainly beam- and shell-like structures are typically subject to buckling. To check the buckling performance a linear buckling analysis to calculate buckling load factors and buckling mode shapes is used.

Frequently, high load factors are desired and ribs are a successful means to increase load factors for shell structures. Besides, buckling mode shapes are also of importance, because mode shapes change with rib design. In order to make a rib design with highest load factor and a desired mode pattern, a design exploration is very useful.

The simple adjoining example shows the influence of the rib height not only on the buckling load factor but also on the mode shape. To explore this behavior, an automatic sampling process is performed, which scans a range of rib heights to get the related load factors and the heights when mode shapes change.

This sampling process is performed by PERMAS in an integrated manner, i.e. sampling is part of one solver run only and no other software is needed. The required pre-processing steps to define the sampled variable and its values is supported by VisPER, the graphical model editor of PERMAS.

A movie showing the history of changing rib heights is available here. An extended abstract is available from here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

INTES released Multi-Modal Optimization in PERMAS
2016-09-09
image

A multi-modal optimization of a cylindrical shell
with simultaneous topology and shape optimization.

For many years, topology optimization and shape optimization were used independently and successively to optimize structural parts or assemblies using Finite Element (FE) models. Now, INTES released PERMAS Version 16, where both types of optimization were unified to allow an simultaneous optimization of shape and topology.

This combination of different optimization methods is named 'Multi-Modal Optimization'.

On the attached image the multi-modal optimization of a cylindrical shell under a concentrated load is shown, where the shape of the shell and the element topology of required and neglectible elements is optimized by both a simultaneous use of topology and shape optimization. The stiffness of the structure is maximized under a given weight. The topology shows a converged result, where the great majority of the elements show a clear assignment to the required or to the neglectible element sets. The shape is modified due to a few shape basis vectors. The idea for this example is taken from the paper DOI 10.1007/s00158-013-0894-9.

The Multi-Modal Optimization opens a new class of optimization problems, which could not been solved so far.

Pre- and post-processing of optimization models is fully supported by VisPER, the PERMAS Graphical User Interface. The definition of design space, shape basis vectors, and all other optimization parameters is supported by using wizards as guided model description features, which make the optimization of topology and shape an easy task for the analyst.

A movie showing the iteration history during optimization is available here.

PERMAS is making realistic simulations practical. PERMAS provides extremely fast and accurate solutions for realistic simulations of large models and complex situations in time. PERMAS supports better product designs through effective and rapid optimization of complex situations. PERMAS is an integrated FE analysis software. It combines thermo-mechanics, vibro-acoustics, and design optimization. For more information on PERMAS, a Short Description is available here. More detailed information is available from the Product Description here.

PERMAS to calculate bolt loosening
2016-08-16
image

Model set-up (top), contact pressure under bolt head and
in the thread (middle), and the bolt head rotation
due to bolt loosening (bottom)

In mechanical engineering, bolt connections are used very frequently for part connections. Beside other design conditions, the most frequently asked question is about the self-loosening of such bolt connections under operational loads. Can this self-loosening be calculated using FE analysis?

From an analysis point of view, it requires a nonlinear static analysis including frictional contact and a cyclic loading based on realistic operation of the structure. Friction needs to be applied in the thread and at the bolt head. Moreover, large rotations and an update of the contact geometry during rotation is also required. PERMAS integrates all these functions to facilitate this kind of analysis.

The paper “Experimental and numerical studies of bolted joints subjected to axial excitation” by J. Liu, H. Ouyang, J. Peng, C. Zhang, P. Zhou, L. Ma, M. Zhu, published 2016 in Wear, describes a experimental set-up to detect the pretension loss in case of axial loading of a bolt, which is called relaxation. In cooperation with the authors, we got their FEA model of the set-up to use it for calculation with PERMAS. Beside relaxation, the model could also be used to demonstrate self-loosening of the bolt due to shear forces on the bolt connection.

The appendant picture shows the model set-up at the top, the contact pressure in the thread and under the bolt head in the middle, and the rotation of the bolt head due to self-loosening at the bottom. Movies to these pictures are also available from here. An extended abstract in German is available from here.