References

Task

The deposition of active pharmaceutical ingredients on skin or mucosa surfaces or their migration into biological tissue, respectively, can be enhanced by the application of a driving electric field. This process is known as "Iontophoresis".
The efficiency of an iontophoretic application with respect to various regions of biological surface had to be studied for Braun GmbH, a well-known supplier of consumer products and small appliances.

Solution

The migration of ions of the active ingredient through the carrier substance and the tissue follows the electric current density vector field.
However, biological tissue is not just an electric ion conductor but shows significant dielectric permittivity, too. Therefore a surface charge builds up at the boundary between tissue and carrier substance. In case of a pulsed driving voltage the electric current density will contain components required for charging and discharging.
Within the ANSYS FEM-model both properties, i.e. conductivity and dielectric permittivity, are defined for each material in one and the same simulation. The transient simulation returns the time-dependent current density vector field including the components required for boundary (dis-)charging.
The effective ion flow impacting the 3D skin surface is finally obtained by time-averaging the current density at each point of the boundary.

Customer Benefit

The simulation results reveal optimum operating parameters for moving the active ingredient to the desired location in the tissue:

• Evaluating the migration rate especially into pores of different size
• Understanding the effect of various dynamic signal parameters like signal shape and frequency on the migration rate;
  optimization of the driving signal
• Optimizing the shape and size of the active electrode

Task

BMW uses simulation tools to ensure a first-class quality of its cars. The VirtualPaintShop (VPS/DRY) is an integral part of the BMW production process. VPS/DRY is used to simulate the drying process of car bodies after painting. For that reason a VPS/DRY model of the drying oven is required (oven model).

Solution

The simulation of car body drying processes requires a reliable model of the drying oven. The VPS/DRY oven model takes into account the heat transfer by conduction, convection and by radiation. Furthermore, measurement data, drawings and technical descriptions are considered.
Temperature-time graphs at 39 measurement points of the BMW roadster Z4 were checked in order to obtain a high-quality oven model. A very good agreement between measurement and simulation was achieved, as shown as an example at the speaker bracket.
Additional measurements on other car bodies confirmed that the transfer of the once-determined oven data to these car bodies show good results.

Benefit for the customer

VPS/DRY simulations give an insight in the curing of paint, adhesives, bake-hardening steels and aluminium alloys in early development stages. Also mechanical deformations and stresses can be analysed, due to the transient temperature profile in the oven.
The results are used to optimize the production, reduce prototypes and increase paint quality.
The portability of the results is important to simulate model variations within a short response time (over night).

Topic

Sometimes engineers need to have their own element within the ANSYS Mechanical environment. Examples can be found in the bearing industry where long term experience is available in the stiffness description of roller bearings. Sometimes this information is available based on empirical formulas, sometimes the information about the nonlinear stiffness is available just in simple tables. The question is now how to implement this information in ANSYS using the stiffness behavior as an element.

Solution

The User-Programmable-Feature-Interface (UPF) allows us to implement own commands, own material laws and also complete new elements. Within the users element description it is possible to define an individual stiffness, mass and damping matrix that can be also depending on the underlying deformation of the structure. Since this element is fully integrated in the Newton-Raphson scheme for the solution of nonlinear problems it is also possible to implement nonlinear elements in this way.
The code itself has to be provided in the Fortran77 format. The integration of this code is done by compilation of the code fragments and linking it to the remaining ANSYS libraries. The element can also be used within the ANSYS Workbench environment by means of command snippets.

Task

The company Pfisterer Sefag develops and manufactures insulators and fittings for worldwide use in power supply networks. In the design process of new silicon insulators for high power transmission lines, achieving a low enough electric field on the insulator surface is crucial in order to avoid damage due to corona discharges. Following a non-standard request from a customer who wanted to guarantee a lower electrical field than usually accepted, an optimization of the geometrical dimensions of conducting corona rings placed at the end of the insulator was required.

Solution

An electrostatic assumption was used with adapted maximum voltages. Since Electrostatic analyses are not included in the Mechanical module of Workbench, a 3D thermal static analysis was used with adapted units and material properties in order to calculate the electric field in the air and in the structure.
The geometrical dimensions of the corona rings were parameterized and an iterative optimization procedure allowed a decrease of the maximum electric field value to a satisfying level.

Customer Benefit

Following this study Pfisterer Sefag has gained;

• A useful design to start experimental validation and production without extensive iterative prototyping.
• Increased knowledge about the influence of geometrical parameters on the electric field
• A private training based on this consulting work with a knowledge transfer that will allow engineers at Pfisterer Sefag to perform similar analyses themselves on future new designs using the intuitive Workbench Mechanical interface.

Task

In today’s era of high-power electronics, all classes of electronics equipment like desktop computers, servers, telecom and avionics enclosures tend to pack in more power in the least amount of space possible. This presents enormous challenges to the thermal management of these systems and subsequently, the need to develop new methodologies in thermal analysis of such systems. The foremost among such needs is how to cope with the geometrical complexities that have become common features in electronics equipment. The thermal analyst has to perform flow and heat transfer analysis on a complex system consisting of components of various sizes in a geometrically complex space.

Solution

For simulation of the complete control unit, a simplified cover model has been created manually from polygonal blocks. The CAD information was employed to set up the vertices of the polygonal blocks. The transformation of PCBs and components was made automatically in ANSYS Icepro. Most of components have been represented in simplified fashion using rectangular blocks but the heat sinks have been imported with all the details. Non-conformal meshing has been employed to reduce the number of nodes in the final mesh. The forced convection from the fan in the control unit, free convection over the device, heat conductivity and radiation have been considered during solution with ANSYS Icepak.

Customer Benefit

Nowadays it is possible to start with a CAD model and then convert it to a simplified form appropriate for a CFD simulation. This allows us to evaluate the temperature distribution and predict the components temperatures. This improves design performance, reduces the need for physical prototyping, and cuts time-to-market.

Task

Door slam analysis is a task typically performed with explicit FE solvers due to higher requirements of solver resources for transient analyses of large models observed with implicit FE solvers.
CMS allows us to overcome this limitation with its divide and conquer methodology. The complete model will be divided into smaller parts and these parts will be reduced to a single element leaving only its few interface nodes as degree of freedom.
Some additional advantages using this method are a higher result quality in comparison to explicit solvers through local mesh refinement without reducing the time step size down to an unpractical magnitude and a significantly reduced computing time in comparison to standard implicit scheme.

Solution

Since CMS is available in ANSYS Mechanical but not yet in ANSYS Workbench, APDL macros were programmed to integrate this capability directly into ANSYS Workbench.
All the necessary CMS steps covering generation, use and expansion passes are automated by the macros.
“Named-Selection” and “Joints” are used to feed the macros with the relevant information.
The expanded results of the parts, which were initially separated, will be merged automatically for a direct post processing in ANSYS Workbench.
The so called super element created during the generation pass is also reusable for subsequent dynamic load cases.

Benefit for the customer

The CMS integration in ANSYS Workbench has brought the following advantages to the customer:

• Reduce Pre-Processing time since the model used for the door slam analysis is almost identical to the existing model for static loads.
• Minimal learning curve for experienced Workbench user.
• Seamless workflow for static and dynamic simulations in one platform.

ViTAL is a software tool created by CADFEM on behalf of AIRBUS for the fast generation and fully nonlinear analysis of fuselage skin panel within the FE solver ANSYS. The generation process is fully parametric using the ANSYS Parametric design language APDL. A comprehensive graphical user interface has been created including many advanced modelling features.

The behavior until failure of stiffened fuselage panels is crucial in the design procedure of aircrafts. Extensive experimental testing is performed to study the mechanical behavior and determine the allowable loads under different loading conditions. Simulation is used to reduce the number of necessary tests, perform parametric studies and get additional information on loaded structures which are inaccessible to measuring devices.

ViTAL provides boundary conditions to simulate shear pressure tests and frame bending tests performed at AIRBUS. Special „aircraft-like“ boundary conditions are an approach to the environmental deformation constraints of the panel as part of the fuselage and enable variable panel sizes.

The modeling accounts for joint technologies like riveting, welding, bonding and splices, many nonlinear material models and stacked materials (AL-GFRP, CFRP), force and displacement con-trolled loading. Structural Components can be imported from CAD-Systems via ANSYS Design-Modeler.

Task

Sandwich structures of compression resistant porous core material laminated by tensile resistant CFRP allow structures for very low weight at extremely high stiffness. But regions with bonding failures tend to grow progressive if a threshold of the structural load is reached: The whole structure collapses and often causes further irreversible problems.

Needs:

• A reliable method to simulate the behaviour of debonded regions and its impact on the affected structure.
• A prediction of the limit load at which the progressive debonding starts.

Solution

By fitting on experimental data parameters the debonding toughness of laminate and core will be determined. A routine was written to generate debonded regions in a sandwich model and set up the cohesive zone element definition. A continuous damage criterion was developed to predict the progressive debonding load threshold. A load step control was established to minimize the solution time. Enhanced post processing was developed to generate contour plots of all relevant cohesive results, mainly the Fracture Energy Release Rate distribution and a damage growth rate.

Benefit for the customer

• Practicable FE model set up and solution times for simulation of problems covering very complex physics.
• The limit load at which the progressive debonding and collapsing of the sandwich structure starts can be predicted for arbitrary debonded region shapes and structural load.

Task

If gas volumes are enclosed in parts that undergo large deformation, the compressed gas significantly influences the deformation behaviour, reaction forces and stress distribution (for example in tires, gaskets, balls, PET bottles, …).
But in general, enclosed gas volumes are not regarded by structural FE-Analyses.

Solution

CADFEM developed an easy to use approach to solve problems like this:
An APDL command block must be added into the ANSYS Workbench tree of a current model.

The APDL module then

• Tracks the enclosed gas volume
• Applies the pressure caused by the gas
• Iterates the pressure via a chosen gas law (isothermal, adiabatic, …) until gas equilibrium
• Returns the final result back to the Workbench environment.

No mesh of the enclosed gas volume is needed. Hence, there are much fewer restrictions in deformation. Even collapsing to a small final volume with then high inside pressure and temperature is possible!

Benefit for the customer

• Easy application and problem set up.
• No additional software features needed.
• Relevance of enclosed gas volumes can be determined:
  Changing reaction forces, deformation, stress, pressure and temperature

Task

The Calibration Target is installed inside an antenna of the ALMA (Atacama Large Millimeter/submillimeter Array) project. Because of a HVAC system (heating, ventilation and air conditioning) turbulent air flow is predicted. But for the absolute accuracy of the astronomical observations a specified operating temperature of the structure and its stability is essential.
Different load cases were performed to simulate the environmental air conditions with its influence on the operating structure.

Solution

The air flow velocity is low in the inner regions of the Calibration target. Therefore the air is heated up significantly by the hot walls of the target. But the turbulent flow around the Calibration Target causes a cooling effect of the housing structure. To resolve this influence on the temperature gradients on the solid structure a conjugated heat transfer analysis was performed. For the foil heaters a specified heat generation was considered.
Both, fluid volume and the solid structure had to be modeled and meshed. Because of symmetry a half model was adequate.

Benefit for the customer

Usually only an vague estimated heat exchange with the environment (e.g. convection coefficients) is used as boundary condition for the thermal structure model.
Simulating the interaction between the flow field and the temperature directly within one coupled analysis may save costs for additional simulation loops and leads to more reliable results.

Task

The aim of this analysis is to estimate the stationary temperature distribution in an IGBT module. The module is attached to a heat sink, which has one cooling channel. A power loss occurs in 2 chips at the top of the module.

Solution

For the described task, a thermal Finite Element Model was set up in ANSYS.
The module and the heat sink were meshed with volume elements. The cooling channel was meshed with FLUID116 elements.
FLUID116 is a line element with pressure and temperature degrees of freedom, which can transport heat and mass in a channel system. In the present case only the temperature degree of freedom was adapted. (Keyopt(1)=1).
The inside of the channel was meshed with SURF152 elements and convection was accounted for by setting the Keyopt(2)=2. The temperature and flow dependant heat transfer coefficients were evaluated through Nusselt numbers.
The flow rate in the channel was given and the inlet flow temperature was prescribed to 20°C. At all other boundaries natural convection with a film coefficient of 5 W/(m²K) to surrounding air 20°C was assumed.

Benefits with FLUID116

The use of FLUID116 elements in ANSYS offers a wide range of possibilities within thermal analyses involving channel systems and presents an accurate and “easy to use” alternative to more costly and complex CFD-approaches.

Task

GALACSI is an adaptive optic system housing several wave front sensor cameras, relay optics, electronics and required mechanical systems.
The complete structure is mounted to one of the VLT Telescopes of the Paranal Observatory in Chile.
Flexures of the optical system (mirrors/lenses) due to environmental conditions (gravity, earthquake, temperature changes) may deteriorate the performance of the system significantly.
Aiming to ensure the reliability of the sensitive structure GALACSI's stiffness behavior was determined using ANSYS® Workbench™.

Solution

A finite element model of the support structure based on solid elements was created. Optical components or sub systems were idealized at the position of their optical points using point-masses attached to the respective mounting locations. Third parties' components (e.g. drives) were simplified using their data sheet's stiffness values.
Flexures and eigenfrequencies were calculated for various configurations possible. The optical point displacements and rotations were exported with respect to optical path's alignments.

Benefit for the customer

By means of these results and the customer's sensitivity matrix the image stability of the system has been evaluated by the customer.
Introducing the required optical coordinate systems in the FE environment allows an efficient postprocessing of the system's behaviour.

Task

In the swiftly growing offshore wind industry, sound emission especially under water is a growing concern. In order to determine the peak sound pressure at certain locations in advance a detailed numerical simulation of the transient driving impact and the related hydroacoustics is necessary.

As an example a large monopole with conical shape (total length 50m, diameters 3m - 4,75m, wall thickness 50mm) was investigated which was installed with the hydraulic MENCK hammer MHU 800S. The impact energy is 820kJ which generates an impact force of 85MN. The final penetra-tion depth of the pile is 20m and the water depth is 22m.

Solution

Using the ANSYS® Workbench™ environment, a flexible dynamics model was set up to assess the underwater noise emission from hammer impact, through the pile and into the surrounding area.

FE model:

• Nonlinear contacts.
• ANSYS acoustic elements simulate water environment.
• Two-way algorithm (strong, matrix coupling) simultaneously calculates the interaction of Fluid & Structure (FSI) for structural displacement and sound pressure values.

Results:

• Axial displacement produces radial bending vibration in the pile. Sound vibration within the pile is responsible for sound emission.
• A snapshot fixed point-in-time to show the sound pressure wave from hammer impact down through to seabed is shown at right.
• Also shown at right are the three simulated microphone signals.

Customer benefit

High noise levels are easily assessed through this simulation. Hence appropriate noise protection systems can be developed such enclosing the pile in a "bubble curtain" or an auxiliary pile with air cambers, treatment of the pile surface or other solutions.

Task

A plan sifter is a device where granular media for food industry are separated by oscillating motions. These low-frequency motions raise suspicion to excite large vibration amplitudes in the glass walls or doors of a mill. The task is to identify this potential transfer mechanism by FEM and to take action for vibration reduction.

Solution

A finite element mesh for the room cavity is generated. The three cutouts in the mesh on the right show the idealization of the sifter geometry. First an acoustic modal analysis is performed assuming rigid walls. As a result the 1st resonance frequency is identified together with its mode shape. The typical half wave resonance is approved, as expected, by analytics for this rectangular cavity. So far no amplitude information can be obtained from those results. In order to compute the vibration amplitudes of the large elastic glass windows a harmonic analysis is performed that takes into account fluid-structure interaction at the sifter walls and at the glass windows. ANSYS FLUID30 elements have both pressure and displacement degrees of freedom and thus allow the excitation of the cavity by given sifter motions. The acoustic cavity vibration will then give rise to structural vibrations. As an example a vibration pattern of the glass front (left wall of Fig. 3) is presented in Fig. 4.

Benefit for the customer

• Based on this model the customer can check the influence of different parameters, e.g.
• adding acoustic damping layers to walls,
• adding another room wall to increase the 1st acoustic cavity mode,
• checking for the benefit of shifted excitation phase angles for the three sifters,
• testing the influence of slightly out-of-tune frequencies for the shifter excitation.

This way the physical background of the problem and the sensitive parameters can be identified by a rather simple simulation model and promising measures can be proposed without the need for expensive on-site experiments.

Task / Motivation

In ANSYS, the User Programmable Features (UPF) are a very powerful tool for customizing and extending the program behavior. Besides UserFunctions, UserElements and a lot more, the programming of own material models is the most popular application. As an example, the implementation of a model for soft biological tissues is shown on the right side.

Task

The driving mechanism of an automotive device respectively the driving moment has to be designed such that vibration amplitudes of 5g are achieved. An electric motor gives a short moment impulse (blue arrow on the top figure) to an eccentric. The rotation is transformed into a translational motion by an elastic beam and the vibrating device is suspended to ground by a spring-damper mechanism. After switching off the moment the free vibration amplitude shall be 5g at the beginning.

Solution

The vibration behavior is dominated by the coil spring. The elastic modes of the device itself are assumed to be considerably higher. For that reason a rigid transient analysis for the multibody system (MBS) is set up in ANSYS (see feature tree in the figure). After importing the CAD model to ANSYS DesignModeler rigid assemblies are grouped together and rigid parts are connected via joints. Different kind of joint elements (spherical, translational, universal, …) can be configured by imposing appropriate kinematic constraints on any, or some, of the six relative degrees of freedom of two components. After loading the revolute joint of the eccentric by a transient moment signal (blue curve) the desired acceleration response of the device can be computed (red curve).
Modeling a part's flexibility can be moderately important, or it can be critically important. In this case the long slender driving beam was suspected of having some impact on the final result. Within the same GUI ANSYS allows switching between rigid and flexible bodies. In this case the beam has been tagged to be flexible resulting in a FE meshed part (see top figure). A modal analysis gives the first desired mode of the vibrating spring-mass system at 60Hz followed by the first elastic beam mode at 800Hz (bottom figure). This large frequency gap is a first indicator that the assumption of neglecting flexibility for the rigid transient solution has been qualified. Running a flexible transient analysis within ANSYS gives a final confirmation because the displacement results are almost identical compared to the rigid case.

Conclusion

A complex assembly can be efficiently investigated due to the option of having both rigid and flexible multibody dynamics within a unique, comfortable GUI of ANSYS workbench.

Task

Modern engine development needs to combine economical aspects with high technological standards. Aiming for consistent life durability, while achieving a more efficient design, weight reduction directly increases the economical efficiency in engine development. Durability analyses based on static and cyclic stresses considering the combustion cycle and its thermo-mechanical influence on the durability as well as static loads resulting from press fittings or pretension are performed to ensure the endurance strength of the engine.

Finite Element Analyses determine reliable thermo-mechanical stresses due to the compression process of the airfuel mixture, combustion, exhaust outlet and the air fuel mixture inlet. Here the analysis considers the engine's cooling process in combination with the combustion cycle as well as the thermal interaction between fluid and structure within the cylinder head.

Solution

A CFD analysis by ANSYS CFX covering the cooling and combustion process determines the thermal behavior within the engine and provides the basis used for a subsequent stress analysis. This mechanical analysis implies several load cases describing the combustion cycle as well as temperature dependent material properties and nonlinear contacts in a comprehensive finite element model (3,200,000 nodes and 60 nonlinear contact regions). Thermo-mechanical stresses within critical regions of the engine are determined for a subsequent durability analysis in a non-linear ANSYS FE simulation. Further results focus on the contact behavior and the deformation of specific parts and the entire model. The complex analysis of the engine behavior provides information about the contact pressure and possible gaps occurring within the combustion cycle. This information is used to rule out undesired effects on the thermo-mechanical behavior of the engine and its several parts already in the design phase.

Task

Optical instruments for astronomic observations are required to be very accurate and stiff, in an unfriendly environment (thermal variations, earthquakes …). Typical optical sensors are very sensitive to possible deformations of their mechanical support structures. The structure under investigation has been the support of the GRAAL adaptive optics system for the cryogenic wide-field imager HAWK-I on ESO's VLT (Very Large Telescope).

Solution

The stiffness behavior has been analyzed with respect to different load scenarios. Both gravitational loads and thermal deflection due to different thermal expansion have been of interest.
The structural finite element model has been prepared by means of ANSYS Workbench. Thin plate like parts could be meshed with solid like shell elements in order to get an accurate stiffness behavior with reduced modeling effort. Many attached subsystems like sensor systems could be idealized by means of single mass points. The complicated bearing systems have been idealized in different ways. Depending on the size of it the degree of idealization is different. Small compact bearings have been idealized by just a spring connection with corresponding stiffness whereas large roller bearings are considered in a more detailed manner.

Results

The deflection of the structure at different sensor position points showed the quality of the design with respect to their global stiffness.

Task

The Atacama Large Millimeter Array (ALMA), located in the Atacama Desert in northern Chile, is an astronomical interferometer, which consists of 66 single radio-telescopes ("antenna") of 12 m and 7 m diameter. The antenna foundation base plates are embedded in concrete. The antenna itself is mounted on the three base plates by ridges, consisting of a flat lower part and a half-cylindrical upper part. The antenna feet have a recess to rest on the ridges. The assembly is kept together by M52 bolts. There are high tolerances of planarity in all contact areas between the parts. Given the number of foundations to be realized (more than 200 antenna stations), these tolerances should be relaxed to reduce manufacturing costs. Therefore the influence of the tolerance of planarity on the stiffness of the antenna foundation has to be investigated.
To simulate inaccuracies caused by manufacturing, convex and concave deformations of these contact areas are generated by moving the x-coordinate of the surface nodes according to a sine function with respect to the z-coordinate.

Solution method

Nonlinear contact analyses with very high resolution of contact stiffness (penetration) have been performed. The contact penetration had to be an order of magnitude below the tolerance of planarity of 20 µm (typical edge length: about 300 mm). The bolt loads and the antenna mass have been applied to the model. A linear-elastic material model with small deformations has been assumed for this analysis.

Three different solution models had to be compared:

• the unmodified geometry without manufacturing tolerances,
• the model with concave modifications of the contact areas
• and the model with convex modifications of the contact areas.

Results and Conclusions

The deformation of the structure is dominated by the applied bolt pretension. The stiffness during that first load step is different for all three models. But as soon as the contact regions are closed, the stiffness of the structure is the same for all three model variants. Therefore the influence of the tolerance of planarity on the stiffness of the antenna foundation is negligible for the manufacturing tolerances investigated.

Task

Self-excited friction induced oscillations occur in different engineering applications. Prominent examples are annoying noise problems like squealing breaks, squealing railway wheels or squeaking door hinges. Moreover, the same mechanism may even lead to functional failure due to the inherent instability of the vibrations. For instance an electric sliding contact (Fig. 1) must rely on a steady sliding contact state without vibration instabilities. That means the steady sliding state has to be stable with respect to small perturbations for the given set of friction parameters.

Solution by means of ANSYS

After having solved the initial stationary friction state in a nonlinear static contact analysis, some of the most important friction instability phenomena have been investigated:

• mode coupling instability: two originally separated modes coincide with increasing friction, exchanging energy so that one mode is damped and the other is excited. This is done by means of a complex modal analysis accounting for the unsymmetric stiffness matrix.
• stick-slip effect: an alternation of sticking and sliding phases leads to typical saw-tooth response (Fig. 2). A nonlinear transient analysis with adequate contact settings and a proper time step strategy is required.
• Negative damping for some modes due to the decreasing velocity dependent friction law (Fig. 4). A nonlinear transient analysis yields increasing harmonic response (Fig. 3).

Description of the performed task

The so called drop test is one of the most severe load cases for testing the structural integrity of electronic handheld structures. Typical failure modes can be:

• Loss of connection between plastic cover parts
• Cracks within the plastic cover parts
• Damage within electronic parts at the PCB
• Failure at the solder joints between electronic parts and PCB

The simulation of such a test scenario by means of FEM is widely accepted and established in industry. LS-DYNA and ANSYS are approved software packages for simulations in this field. Typically different mathematical algorithms for the transient solution of an impact loading are implemented in those codes. Normally highly transient analyses are solved efficiently by explicit codes like LS-DYNA. However, due to the time step criterion and the related mesh size requirements for explicit methods, ANSYS as an implicit code is necessary to resolve local stress fields.

The typical failure modes shown above can be classified into different scales - the macro scale considering global structural parts and the micro scale with possible failure mechanisms within the electronic parts. Because of the different constraints for the different integration methods it isn't either reasonable to use a pure explicit nor to use a pure implicit solver to calculate the structural response both for the global model and the very detailed electronic components. The solution of this contradiction is a combination of both the explicit method for simulation of the global structure with a very coarse description of the critical parts and the implicit method for simulation of a submodel with the specific components. In this case the load time histories of the global analysis are used simply as the boundary condition for the submodel.

This coupling allows the combination of the advantages of explicit and implicit time integration without caring about non convergence or too small time steps. Short simulation times and very detailed results for further assessment of the structure are possible.

Simulation Task

Unfortunately it is common for consumer products to be subjected to mechanical shock loading, particularly those ones associated with being dropped during transportation or delivery. The ability to withstand such loading situation is crucial for the design of a successful product like those of Bosch-Siemens-Hausgeräte. In that view, a properly designed package can mitigate the potentially damaging vibration input, filtering its effects from the product protected within. In order to pack and seal goods, foam based materials are typically used in addition with plastic shrink wrap in many industries. In the design of a successful product it is not only important to know how the design of components is affecting the packaging system but also vice versa. Pre-stressing due to the plastic shrink wrap (thermal shrinkage) is also very important and has to be taken into account before a numerical drop test is done.

Solution Method and Result

The present work deals with the numerical simulation of a drop test of a cooker including packaging foam and plastic foil wrapping. Additionally the pre-stressing of cooker and packaging due to thermal shrinkage of the plastic foil has been taken into account in the numerical investigation. For this, a thermal pre-stressing simulation of the plastic wrapping has been included before the actual drop test of the whole assembly has been conducted. The permanent deformations of the cooker nearby the impacted edge as well as the deformation of package foam in the vicinity of the impacted edge were the primary areas of interest and compared with experimental data. LS-DYNA was used to perform the drop test simulation of the cooker as well as the thermal pre-stress simulation of the plastic wrapping. The simulation results are in good agreement with the experimental drop test results. The foundation for an optimized procedure for product/package design has been achieved.

Task

A seismic analysis is frequently required for large buildings or other tall structures particularly at locations in seismic active regions. For that purpose FE analysis is applied to proof the integrity of the structure during an earthquake. Here, the 12m ALMA (Atacama Large Millimeter Array) telescope (Fig. 1) has been analyzed.

Solution by means of ANSYS

A response spectrum for the given earthquake location is defined e.g. by government authorities (Fig. 2). Now, the analyst's task is to do a modal analysis first to get the eigenfrequencies and mode shapes of the structure. After that the mode shapes are scaled according to the given response spectrum. A mode combination method like SRSS or CQC is applied to get the final result, for instance in terms of maximum displacement (Fig. 3). This way a response spectrum analysis does not compute the whole transient time history of the earthquake excitation. Rather it is a simplified method to get the maximum response. Large models with more some million degrees of freedom can be analyzed this way. A special filtering technique may be used in order to suppress negligible modes. Usually a certain percentage of the overall structural mass is required to participate in oscillation. For that purpose modal participation factors and modal effective mass output from ANSYS may be used.

The task

Imagine the sunrise at the foothills of Chile's Andes mountains. The wind blows slowly through the dry Atacama desert…
This scenario isn't based on the fantasy of a lonely adventurer but the given thermal load case for the design of one of the telescopes of the ALMA (Atacama Large Millimeter Array) project. In corporation with VERTEX Antennentechnik GmbH a complex thermal analysis has been performed by CADFEM Consulting.

Due to the given specifications the antenna had to be analyzed considering sun radiation, outgoing radiation and of course the convective heat transfer to the environment. Taking into account the heat transfer effects

• heat conduction
• heat convection
• heat radiation

it was possible to determine the temperature field of the antenna. Both steady state and transient analysis gives valuable information about the resulting thermal loads to the structure. Special care had to be taken into account for the laminated CFRP structure. By idealization of the CFRP material properties many simplifications could be done. As a special challenge the thermal analysis of the convective heat transfer part to the environment has been combined with a CFD analysis. Therefore also the wind influence onto the temperature field of the antenna has been computed.
The resulting temperature field can be used for subsequent structural analyses to determine thermal deformation or critical thermal stress zones.

Postprocessing of Random Vibration Analyses

Over the past few decades, the aerospace indus-try has established random vibration tests as a standard test scenario for dynamically excited structures. This method has currently become extremely interesting for the automotive industry too, owing to the highly efficient testing of fatigue properties. Electronic subcomponents in particular are subjected to the so-called shaker tests.

The corresponding analysis type in ANSYS is the Random Vibration (PSD) analysis. The results ob-tained are normally only RMS responses of struc-tural displacements or stress components, as well as PSD response spectra at single points. The CADFEM consulting division has developed the RANfat add-on module to enhance post-processing with respect to fatigue analysis based on random vibration results.

The following list provides an overview of the currently implemented post-processing methods:

• Fast, efficient fatigue analysis for complete large finite element models in the general postprocessor /post1
• fatigue analysis based on the 1σ stress results using the following approaches
  - Rayleigh
  - Dirlik
  - Zhao-Baker
  - Steinberg
• contour plots of accumulated damage and additional statistical results
• fatigue analysis using time history post-processor/post26
• probability density and cumulative damage functions of the approximated stress am-plitudes
• further statistical evaluations based on response spectra

Task

Frequency response analysis is a standard analysis task in the development of vibrating structures. It determines both the amplitude distribution of the displacements, represented as a contour plot at a specific frequency, and the corresponding frequency response at one or several result nodes of the model. Neither kind of representation, however, provides a complete picture of the acoustic behavior of a given structure. Well-established methods and analysis programs, e.g. boundary element techniques or ANSYS FLUID30/FLUID130 acoustic finite elements, are available for analyzing radiated air-borne noise, permitting the in-depth assessment of sound pressure and power. In many cases, however, during the early design stages, it is sufficient to assess acoustic behavior quickly and inexpensively without carrying out any additional analyses.

Solution

SBSound analyzes structure-borne rather than air-borne sound, as described in relevant machine acoustics literature. Said analyzes based on the modal superposition method can be carried out quickly and efficiently – normally taking just a couple of minutes.

ANSYS/SBSOUND computes the following results:

• frequency response function (FRF) of structure-borne sound power;
• the mean square velocity (surface average);
• optionally both quantities represented in terms of level [dB];
• contribution of distinct modes and/or selected panels for the quantities above presented as FRF (bottom right figure) to determine acoustic “hot spots” quickly;
• contribution of distinct modes and/or selected panels at a fixed frequency presented as a bar chart;
• contour plots of the surface normal velocity for discrete frequencies (top right figure).

Further developments are available on request, including:

• taking a weighted average of the results in third and octave bands;
• A-weigthed levels [dB(A)];