MESHING CAPABILITIES IN ABAQUS CAE

It is a well-known fact in the CAE community that the efficiency and accuracy of finite element models are directly dependent on the quality of the underlying meshes in the model. The various quality parameters associated with elements are element size, aspect ratio, skew angle, jacobian, warp, and many more. Yet another parameter of concern is element topology, which means triangular/quadrilateral elements in case of shell meshes and tetrahedral/hexahedral elements in case of solid meshes. Each of these element topologies has its own advantages and disadvantages; for example, tetrahedral elements are easy to create on complex geometries but they have slower convergence, while hexahedral elements are very much desired in computational expensive simulations such as crash due to better convergence and accuracy but cannot be created easily.

Due to specific meshing requirements arising from the increasing complexity of part geometries, meshing techniques are becoming more important across all industry verticals. Transportation & mobility is primarily concerned with hexahedral meshes of pre-defined quality for very complex geometries. This industry has more focus on using Hypermesh and Ansa as a dedicated meshing tools. However these tools are primarily known for good meshing capabilities only. When there is a need to create input decks for advanced non-linear simulations such as with Nastran solution sequences 600/700 or for Abaqus multiphysics or acoustics, many of the solver features are not supported by Hypermesh or Ansa and have to be entered manually into the deck. Aerospace industry has almost always a requirement for composites modeling. They prefer a user interface that can either create or import composite plies and layups. The need for high quality meshes on complex geometries is rather rare. Due to these reasons Aerospace industry has been relying on MSC Patran since many years due to its composites modeling capabilities. However industry is now looking at alternate tools as Patran is losing its competitive edge on CAD import, CAD repair as well as meshing techniques. The CAD repair features are very minimal, there is no CAD associative interface to propagate design changes on FE side and meshing techniques offered are still at very basic level as well.

The objective of this blog is to highlight the meshing techniques in Abaqus CAE that makes CAE a tool of choice in situations where a decent quality mesh, tight integration with multiple CAD platforms as well as tight integration with Abaqus solver are topics of concern for the analyst. It’s worth mentioning for Aerospace industry audience that Abaqus CAE has basic composite modeling capabilities. For advanced composite modeling and visualization capabilities, there is an add on module called composite modeler for Abaqus CAE and there is tight integration between CATIA composites workbench and Abaqus CAE for transfer of FE meshes as well as ply layup information.

THE MESHING TECHNIQUES

 There are primarily four meshing techniques available in Abaqus CAE, both for solid meshes as well as for shell meshes.

Free meshing: This is the easiest of all the techniques as it almost always works with a single click. It primarily generates quadrilateral or triangular elements on surfaces and tetrahedral elements on solids, even on very complex geometries. The downside is that user has very minimal control on elements quality except controlling the mesh density using global and local seeding options.

Sweep meshing: This technique is useful when hexahedral elements are needed on solids with minimal geometry editing though this technique is applicable on surfaces as well. The meshing algorithm automatically identifies a source side and a target side on the geometry, it creates a quadrilateral shell mesh on the source side and sweeps those elements to the target side thereby converting them to hexahedral or bricks. The underlying shell mesh is automatically deleted. The downside is some geometry restrictions with respect to source and target side.

Structured meshing: This meshing techniques is useful when high quality hexahedral or near to perfect shell elements are required on solids or surfaces. This technique offers a better mesh control to the user compared to sweep meshing technique. It works by partitioning the complex solids into smaller six or eight sided parametric solids that can be brick meshed. The nodes at the boundaries are automatically fused to ensure connectivity.

Bottom’s up meshing: This is the last approach when all the other meshing techniques fails. It works on the concept of divide and rule. To some extent it resembles sweep meshing but the underlying geometry restrictions are removed.

THE COLOR CODING FEATURE

This is one feature that sets Abaqus CAE apart from other meshing tools available in the market. While doing meshing, user can see either entire part or regions associated with part (in case of partitions) in pre-defined colors. These colors helps in determining which region of the part would be meshed with which meshing technique if the mesh algorithm is executed. The color cold is as follows:

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The process is quite interactive. The orange color is most undesirable as these regions are non-meshable and require further partitions. Once the region is correctly partitioned and subdivided regions become meshable, the color code is updated instantly. What the user needs to see is the combination of greens, yellows and pinks with peach at certain times before executing meshing operation. During meshing, user has option to either mesh one region at a time or the entire part having multiple regions. In case of interfaces having different element topologies on each side such as green with pink or yellow with pink, tie constraints are automatically created at the boundary to ensure mesh connectivity.

Below is an example of a part that has been partitioned to create certain sweep meshable yellow regions where brick elements are needed. The other region is pink with tetrahedral elements associated to it.

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EFFECTIVE PARTITIONING

Transition of orange region to either yellow, green or peach requires intelligent partitioning of surfaces or solids. While there are many such partitioning tools available, achieving desired results with minimum partitions requires some practice in using these tools. Let’s highlight few of these partitioning methods:

Solid partitions:  Six options are available.

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VIRTUAL TOPOLOGY

This is an optional process that may be needed before partitioning and prior to meshing. This is a way to fix bad CAD data. Many times CAD data has more details than needed by the meshing algorithm. This includes very short edges and very small surfaces. Virtual topology offers certain tools to combine such small faces and edges. There is also an option to suppress these small features so that meshing algorithm does not recognize them.

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There was a day when it was unlikely that a company would buy a 3D CAD system without extensively evaluating it.  They required demos, trials, benchmarks, pilot projects and extensive financial ROI analysis.  Are those days gone?  Early in my career, I made a living by simply being able to demonstrate relatively new 3D CAD technology.  These days, a demo is rarely required for purchases of 3D CAD.  Decisions about a company’s core 3D CAD package have generally been previously made, or are now based on data formats of customers or suppliers.

It seems that 3D CAD is simply now an expected part of product development processes and an integral part of PLM in general.  The specific version of 3D CAD doesn’t seem to be nearly as critical as companies previously expected them to be.  Most can now get the job done in small to mid-size companies, with minor differences depending on the specific situation.

There does still seem to be a “pecking order” for the various CAD systems in the manufacturing sector.  The large companies with the broadest set of requirements (and the deepest pockets) generally define the standard.  This includes the Automotive and Aerospace OEMs as an example.  Once they settle on a primary CAD system, many other suppliers base their CAD requirements upon the OEM’s decision.  This doesn’t automatically mean the suppliers choose the same CAD system; just that the supplier needs to be able to communicate and exchange data with the OEM in an efficient manner.  Often times, an automotive supplier will obtain a license or two of the OEM’s chosen CAD software, but it will not be deployed across their entire environment.  The “Top-Tier” CAD that the OEM decided upon may only be used to translate and communicate directly with the OEM, while the bulk of their CAD users might be using a “Mid-Tier” CAD system that is perfectly capable of meeting the supplier’s design requirements.  A host of emerging cloud based CAD technology is also available.

 

So what does this mean to the industry?  Focus on the next thing.  Maybe that is a fully electronic PLM environment, or updated NC or additive manufacturing software.  It could be the adoption of up-front simulation technology to accelerate the design cycle.  There are a lot of things from a technology continuity perspective that can still be addressed once the CAD platform has been settled upon.  Just don’t lose sight of other opportunities for continuous improvement once your CAD house is in order.

With Teamcenter Active Workspace, Siemens PLM purposely chose to focus on specific use case/role support versus just duplicating every functionality of the Teamcenter Rich client.  The initial emphasis has been to provide a zero install client to the broader, and often less frequent users, in the enterprise.  These users require a zero install client that is easy to learn.

With every release of Active Workspace, Siemens PLM continues to broaden the use cases and roles supported in it.  The graphic from left to right shows the usecases/roles already delivered with complete use case support to the ones which are under the works to enable richer application exposure for authoring capabilities. Siemens has also exposed some administration capabilities in Active Workspace such as for user management and a new XRT editor, right inside of the Active Workspace user interface.  Again all with no client install.

Active Workspace User Experience
It’s all about the content .  Active Workspace shifts the focus from the Application to the Content – the User’s data is the most important thing.  The User Interface (UI) is simple, clean, light, and fast. Subdued colors let the user’s creation be the star of the show.

There is a simple top-down, left-to-right flow of information: Who I am and my role is first .What I’m working on is clear and obvious . Data brings with it the right capability for the context – Viewer, Where Used, Attachments, History etc.  One need not know how to open tools – just read the tabs to figure out what’s available. Each tab of content brings the right capability

This part has 3D content and so it has a viewer tab. That tab brings the right viewing commands to work with it. The user focuses on “What” he needs to work on, not the “Tools” to do work. Commands and tabs are smart – they don’t appear when they don’t work or don’t have content. This eliminates the visual clutter .

Active Workspace Framework
The Active Workspace Framework enables consistency and efficiency, both for the end user and the developer. It has established patterns that control where content and features go in the UI. Common elements and modules keep the UI consistent and simplify development. Users learn interaction patterns and see them behave consistently in new areas. 

The display is data driven – what you open to work on controls what information is presented. A jet engine has a 3D Viewer and Trace Links, but a Shampoo bottle has Trade Items and Vendors. The underlying data may be technically the same, but is always presented in terms appropriate for that industry, data, and even the user.

The Abaqus user community knows that computational fluid dynamics module was deprecated in 2017 release of Abaqus CAE. It means that within Abaqus CAE or through standalone Abaqus, it is not possible to perform CFD simulations beyond 2016 release. This has been a subject of criticism among few users. However, its worth mentioning that CFD is still available in Abaqus through 3D Experience platform fluid mechanics analyst (FLA) role. Dassault Systemes has decided to migrate the functionality from standalone products to the platform but it is still in existence. The FLA role is available both on premise as well as on cloud. So what are the value adds of performing CFD through 3DExperience platform!!

No need to create fluid domain 😊

This is a BIG BONANZA because every analyst knows how tough it is to create fluid domain for complex 3D Models. The 3DExperience platform offers a technique called hybrid meshing that has two main advantages. Firstly, it does not require a fluid CAD. The user needs to provide minimum information in terms of geometric features such as faces, planes, face normal etc. so that application can well predict fluid location and boundaries in given part of assembly geometry. Once it is will predicted, it gets well meshed also. Take a simple example: flow between two intersecting pipes. User just need to provide surface normal to two pipes in correct direction as well as three planes for inlet and outlet. With this information FLA user interface can create a bounded region internally on its own. The fluid domain tool helps in selecting respective geometries for parts, regions, openings and boundaries. Just this much information is good enough to proceed with the meshing operation.

 

Good quality hexahedral meshes with perfect boundary layer control 😉

FLA offers hex dominant meshing technique that operates on fluid domain created above. It has two outstanding offerings. First it gives maximum number of hexahedral elements. Yes, hexahedral elements and that too without any partitioning. Second, it is possible to define (and achieve) boundary layer as per user specified criteria. User can define number of layers as well as thickness of layers. Even in transition regions such as location where pipes intersect and geometry abruptly changes, the boundary layer specification is well respected.

 

Lastly, FLA role is the center of attraction of SIMULIA R&D for further enhancements. Dassault Systemes recently acquired two CFD companies named XFlow and Exa. The CFD solver offerings from these two companies work on Lattice Boltzmann principles while the traditional Abaqus CFD solver in 3DExperience work on Navier-Stokes principles. The Lattice Boltzmann based solver is suitable for external and unbounded, high speed transient and compressible flows that has many applications in aerodynamic computations in T&M and A&D industry verticals. These solvers will be integrated in future releases of FLA role or will be available as a new role in 3DExperience platform.

If you have been using Autodesk Inventor for a while you may already know this, but there is a process for migrating Inventor’s “Content Center” libraries.  This should be done to ensure you don’t end up with duplicate parts (file names) for the same fastener, pin or other common part.  When libraries are migrated, it allows the new software version and its updated libraries to recognize that a particular existing component is being placed.  The existing model will be utilized in this case.  If the libraries are not migrated, a whole new set of model files will get created when you start placing component from Content Center in a new version of Inventor.

Here is the general procedure:

  1. Determine where your current style library is located.  It may be in the default location for individual users, or may be in a common location.
  2. Launch the “Autodesk Inventor Style Library Manager”.  This is a separate program in Windows that isn’t started from within Inventor.
  3. In the “Style Library 1” area browse to your old style library that you located in step 1.  It should say that “some style collections need migration”.
  4. Select the Migrate button at the bottom

I also recommend backing up an previous style libraries before migrating them.  There have been various accounts of libraries failing to migrate and becoming corrupted.  Making a backup and testing the migration is imperative if you have extensive modifications in your existing style library.

Users of Dassault Systemes must have seen the following image multiple times in last few years. In this article, I am talking about what this image means from simulation perspective.

 

The image above is the brand logo of Dassault Systemes next generation innovation called 3D Experience platform. This image is called 3D Compass and its four quadrants symbolizes four major offerings  available in an integrated fashion with the platform. The north quadrant symbolizes collaboration, the east quadrant symbolizes 6W Tags, the west quadrant symbolizes designer applications and the south quadrant symbolizes our favorite simulation applications. The idea behind its introduction is very clear from simulation environment.

“BREAK THE SILOS”

The word silos may seem unpleasant to hear at times but that’s exactly how FEA or MBD simulation community has been since many years. These are small departments of very specialized people in large organizations that mostly work in isolation. The reason of working in isolation has been simple and justified till now. The complexity of products these specialists use has been an overwhelming task for other departments such as design, production, marketing, procurement, IT etc. that are a part of overall product lifecycle management. Moreover simulation forms a process of product lifecycle only when a new concept design is launched that has to be virtually tested either to save cost, reduce time or meet certain requirements imposed by regulatory boards such as NHTSA, FAA, FDA etc. This is not always the case.

The 3D Experience platform integrates and brings together all the departments involved in product lifecycle including simulation experts. The integration happens at base level by a data management and collaboration server called ENOVIA that allows users with different roles to create, modify, share, manage or propagate data from one person to other without using share drives, emails or any sort of data migration. In terms of T&M and A&D companies these roles might be product designers, design engineers, manufacturing engineers, FEA specialists, material experts, method developers etc. The platform offers roles for users. Each role is a collection of apps just like we see in our mobile phones. However, in case of 3D Experience platform, these roles are divided in four different categories based on four corners of the 3D Compass. These are 3D Modeling apps, Social and Collaborative apps, information intelligence apps and simulation apps. Few of these apps serve as pre-requisites to any user who wish to be a part of platform. But others such as simulation apps are assigned only to those users who wish to perform simulation.

 

With the 3D Experience platform, a simulation expert works on the same data that is created by a designer to perform simulation without any manual data transfer. No more specialized product formats such as Abaqus CAE, Tosca, fe-safe that have their own file architecture not compatible with designer products such as CATIA, Creo, Solidworks etc. Once the simulation is complete, results are stored in the same database that can be instantly viewed by engineering managers, product designers, R&D head or any user who is not actively using simulation. So no more specialized output file formats such as odb, conf, ldf, stlx etc. A simulation role armored with simulation apps allows a specialist to get into the platform, access the data created by designer, create simulation model in same environment, perform the analysis on user machine or on cluster and publish and share the results. Simple it is! Once the silos are broken, there is yet another aspect of 3D Experience platform that makes it unique in the way it works.

“ELIMINATE FILE BASED FOLDERS FROM THE SYSTEM”

Everything created or imported in the platform is saved within the ENOVIA collaboration server. The data can reside either on-premise or on-cloud based on chosen architecture. The user can search or access the data using advanced 6W Tags search criteria based on questions such as who, what, when, where, which etc. In case of cloud based architecture, this data can be assessed and modified from anywhere using devices such as smart phones or ipads. Can your smart phone read Abaqus odb files! The answer is perhaps no but yet it is possible to access Abaqus output data on smart phones using 3D experience platform.

Typically when new software releases come out, there are always a few really key improvements that really stand out.  Many times, it is a cool new modeling feature, or maybe an entirely new approach to design.  In Inventor, this might be like the addition of Freeform Modeling or Direct Editing as examples.  Unfortunately these are features or techniques that might not be applicable to many users.

If you are using both Autodesk Inventor and Vault together however, you should probably pay attention to this one:  The Vault status icons in the “recently used” area.  These icons now clearly identify the current Vault status of one of your recent files when in the Inventor “Open” dialog box.  Is the file checked out?  Is the file checked in, and up to date in my workspace? Has someone else modified the file since I last worked on it?  Have I checked in my latest development ideas or new parts yet?  All of these can be determined simply by noticing the Vault status bubbles in the “Open” dialog box.

Vault Status Icons

This is a further  followup to my previous articles on digital twins, focusing on the Feedback Loop pillar

Smart Factory loop
The feedback loop starts with the Smart Factory. This is a fully digitalized factory model of a production system connected via sensors, SCADA systems, PLCs or other automation devices to the main product lifecycle management (PLM) data repository. In the Smart Factory, all events on the physical shop floor during production are recorded and directly pushed back to the PLM system or through the cloud. Artificial intelligence (AI) technology is used to study and analyze this information, and the main findings are sent back to either product development
in manufacturing planning or facility planning.
Why is this important? Production facilities and the manufacturing processes tends to change immediately after start of production. New ideas will be implemented, new working methods will be deployed and new suppliers might be selected; all requiring changes to the production system or process. Since these modifications will certainly impact the future, updating them in the system at this stage is becoming a must. Production systems outlive the product lifecycle, and many companies use their production systems to make multiple products. These factors contribute to the increasing need to regularly capture these changes in the PLM system, which can later be used to distribute this information to all parties. The information collected during production can also serve as the basis for improving the maintainability of manufacturing resources. With this information, we can enable much better (sensor) condition-based maintenance, and thus increase uptime and productivity.

Smart product loop
Almost every product made today is a smart product. Many companies are looking for ways to improve the connection with their smart products while they are being used by their customers. Monitoring product use can provide a lot of knowledge for improving products. More than that, connecting to these smart products can generate a new type of business model that may result in more competitive offerings.

PLM Challenge

These feedback loops and the data it generate is a challenge for PLM too. In the short term, the PLM issue for digital twins is how IoT-gathered data can best be put to work—extrapolated, parsed, and redirected? To where? At whose direction? The quick and easy solutions are analytics running on the cloud, machine-to-machine (M2M), and analyses based on Artificial Intelligence (AI). Such questions are expected as digital twins emerge as the next revolution in both data management and lifecycle management.
Ultimately, the use of PLM will allow us to bring digital twins into close correspondence—in sync—with their physical equivalents in the real world. When this comes to pass, we can expect problems to be uncovered more quickly, products to be supported. Products with digital twins will be more reliable with less downtime while operating more efficiently and at lower cost. PLM-powered digital twins will boost user and owner confidence in their physical products. Ultimately, digital twins reflect what users and owners expect to receive when they sign a contract or purchase order.

A classic deployment of a digital twin includes three pillars: product design, manufacturing process planning and feedback loops.

  1. Product design

A digital twin includes all design elements of a product, namely:

  • 3D models using computer-aided design (CAD) systems
  • System models (using systems engineering product development solutions, such as systems-driven product development)
  • Bill-of-materials (BOM)
  • 1D, 2D and 3D analysis models using computer-aided engineering (CAE) systems such as Simcenter™ software
  • Digital software design and testing using application lifecycle management (ALM) systems such as Polarion ALM software
  • Electronics design using systems developed by Mentor Graphics

Using these elements results in a comprehensive computerized model of the product, enabling almost 100 percent of virtual validation and testing of the product under design. All of this eliminates the need for prototypes, reduces the amount of time needed for development, improves the quality of the final manufactured product and enables faster iterations in response to customer feedback.

  1. Manufacturing process planning

The Siemens solutions available today enable the development of three models critical to any manufacturer:

  • Manufacturing process model – the how – resulting in an accurate description of how this product will be produced
  • Production facility model – the where – providing a full digital representation of the production and assembly lines needed to make the product
  • Production facility automation model – Describing how the automation system, including supervisory control and data acquisition (SCADA) systems, programmable logic controller (PLC) hardware and software, human-machine interface (HMI) hardware and software, etc., will support the production system

The value of the digital twin in manufacturing offers a unique opportunity to virtually simulate, validate and optimize the entire production system. It also lets you test how the product, with all its primary parts and subassemblies, will be built using manufacturing processes, production lines and automation.

  1. Feedback loops

When it comes to the feedback loops of the Digital Twins pillars , there are two kinds that have a significant impact on most manufacturers

  • The Smart Factory Loop and
  • The Smart Product Loop.

“Product Design” and “Manufacturing process planning” pillars were in existence for  a while but the “Feedback loops” is a newer one. I will discuss elaborately on it in my next blog .

Any complete FEA solution has at-least three mandatory components: Pre-Processor, solver and post-processor. If you compare it with an automobile, solver is the engine that has all the steps/solution sequences to solve the discretized model. It can be regarded as the main power source of a CAE system. The pre-processor is a graphical user interface that allows user to define all the inputs into the model such as geometry, material, loads and boundary scenarios etc. In our automobile analogy, pre-processor can be regarded as the ignition key without which it is not possible to utilize the engine (solver) efficiently. The post-processor is a visualization tool to make certain conclusion from requested output: either text or binary. A good CAE workflow is regarded as one that offers closed loop CAD to CAD data transfer.

The above workflow is not closed so there is no scope of model update. Any changes in design requires all the rework. This has been the traditional workflow in organizations that have completely disconnected design and analysis departments. Designers send the CAD data to analysts who perform FEA in specialized tools and submit the product virtual performance report back to designers. If a change is mandatory, FEA is performed manually all over again. Let’s look at a better workflow.

In this workflow, if the initial design does not meet the design requirements, it is updated and sent to the solver, not to the pre-processor. It means that all the pre-processing steps are mapped from old design to new design without any manual intervention. This is an effort to bridge the gap between design and analysis departments that has been embraced by the industry so far. The extent to which the GAP can be bridged depends on the chosen workflow but to some extent, almost every CAE company has taken an initiative to introduce products that bridge this GAP. Let’s discuss in context of Dassault Systemes and Siemens.

Dassault Systemes: After acquiring Abaqus Inc in 2005, Dassault Systemes rebranded it as SIMULIA with the objective of giving users access to simulation capabilities without requiring the steep learning curve of disparate, traditional simulation tools. They have been introducing new tools to meet this objective.

  • The first one in series was Associative interfaces for CATIA, Pro-E and Solidworks which is a plug-in to Abaqus CAE. With this plug-in it is possible to automatically transfer the updated data from above mentioned CAD platforms to Abaqus CAE with a single click. All the CAE parameters in Abaqus CAE are mapped from old design to updated design. It’s a nice way to reduce re-work but design and simulation teams are still separate in this workflow.
  • Next initiative was SIMULIA V5 in which Abaqus was introduced in CATIA V5 as a separate workbench. This workbench includes additional toolbars to define Abaqus model and generate Abaqus input file from within CATIA. Introduce Knowledge ware, and user has all the nice features to perform DOE’s and parametric studies. This approach brings designers and analysts with CATIA experience under one roof.
  • Next Dassault Systemes introduced SIMULIA on 3D Experience platform allowing analysts to utilize data management, process management and collaboration tools with Abaqus in the form of simulation apps and roles. The solution is now in a mature stage with incorporation of process optimization, light weight optimization, durability and advanced CFD tools. By merging SIMULIA with BIOVIA we are also talking about multi scale simulation from system to molecular level. It is further possible to perform the simulation and store the data on public or private cloud.

Siemens PLM solutions: Siemens traditional CAE tools include FEMAP user interface and NX Nastran solver. Both have been specialized tools primarily meant for analysts with little or no connectivity to CAD. More specialized and domain specific tools were added with the acquisition of LMS and Mentor Graphics.

  • In 2016 Siemens introduced its new Simulation solutions portfolio called as Simcenter that includes all Siemens simulation capabilities that can be integrated with NX environment. The popular pre-processor in Simcenter series is NX CAE that has bi-directional associativity with NX CAD. Though meant for specialists, NX CAE offers a closed loop workflow between NX CAD and NX Nastran thus making easier to evaluate re-designs and perform DOE’s.
  • Siemens also offers NX CAE add-on environments for Abaqus and Ansys thereby allowing analysis to efficiently incorporate these solvers in their NX design environment.
  • It is further possible to use Simcenter solutions with Siemens well known PLM solution Teamcenter for enterprise wide deployment of Siemens simulation tools.

This shift in approach is not limited to Dassault Systemes and Siemens. Every organization in this space be it Ansys, Autodesk or Altair are introducing such closed form solutions. One reason may be the recent acquisition of many CAE companies by bigger organizations such as Dassault, Siemens and Autodesk. Nevertheless, the change has been triggered and it will continue.

 

 

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