System-Level Modeling Approach to Improve Mechanical Ventilation

Towards a system level modeling approach to improve mechanical ventilation

This pandemic COVID-19 outbreak has called for all possible acceleration in medical innovation to improve immunity and to stay prepared to treat the adversity on health grounds. Besides the in vivo and in vitro approaches, the in-silico ways would complement this mission. Such advanced adoption of computational modeling offers many advantages starting with patient safety going on to personalized treatments, bringing down the invasive routes of drug administration to make it more painless. The focused work on Novel Drug Delivery Systems (NDDS), a 505 (b) (2), or a Paragraph 4 filing would benefit by better optimization when the right set of simulations are devised to pave the way on.

Ethical concerns on animal testing have also been spinning off lately to grab more attention into the in-silico adoption. Digitalization and simulation put up to the right use, there’s more data generated and that would come from more candidates analyzed by a larger sample on the Design of Experiments (DOE).

The outputs derived from simulations can be better quality inputs for the PBPK/PD models to work with. So, the modeling studies actually can be ranging from a 3D component level to a system level. System-level simulations or the Reduced Order Models (ROM) derived from a detailed 3D model simulation can present quicker ways of analyzing even biological units to for necessary responses or stimuli in a virtual environment.

Even the fields as niche as tissue culture, genetics can benefit very much from computational modeling with a focus to virtually study the sensitivity of the cells to the imposed bio-environment. What if scenarios on the impeller speed, fill level and the positioning of the scaffold, etc.., can be virtually studied to find the right answers before going to be physical. Forensic science as well seeks to use simulations to discover the root cause of the victim’s damage, such as explaining the angle of attack of a bullet based on the sort of wound it plunged in the body.

As mentioned, while 3D simulations are always there to cater to the finest details needed, developing system-level models is also equally important to be quick at attending to treatments for patients requiring personalized therapies. As of today, even surgeons with a very limited mathematical background can leverage computational modeling successfully to plan and execute critical, life-sustaining surgeries proving to be a bliss to the enrolled patients.

In the case of a life-sustaining mechanical ventilator, the focus is to use patient-specific operational conditions for the pressure applied based on the flow rate of the ventilation. This is to avoid any Ventilator Induced Lung Injury (VILI) which can be either acute possibility or unless for Severe Acute Respiratory Syndrome (SARS) such as COVID-19. The below-shown representation is a system-level network built with Ansys Twin builder by mechanical & electrical elements to represent the reaction of an artificial lung connected to an input waveform from a mechanical ventilator.

Figure 1: Simulation Model in ANSYS Twin Builder

The model input is a pressure wave supplied to the lung (cylinder with piston) through the trachea (pipe). A flow sensor is used as an en-route to measure the flow rate. Mechanical spring and damping are used to represent resistance and compliance. We can see the conversion from cmH2o to Pascal & Liter’s to m3 in the above expressions to match the medical unit system for the mechanical Spring and damping coefficients.

The below representation is the simulation result as the lung volume and flow rate as a reaction to the fed pressure waveform

Figure 2: Lung Pressure, Volume and flow rate

In addition to the system modeling, a 3D simulation is performed using the Ansys CFD tools on a lung airway model. A real-time breathing cycle is used as an input to such simulation.

Figure 3: The applied breathing cycle and the velocity in the lung air way as a 3D Simulation output

An initial pursuit has been set up to conceive a simulator which can offer an easily accessible platform to test and monitor a pressure signal and other parameters during artificial ventilation. Besides the deployment for regular medical care, this simulator is intended for academic learning and training as well. The outlook is about simulating a 3D Computational Fluid Dynamics (CFD) model and building a Reduced Order Model (ROM) of the breathing cycle in Ansys Fluent. Such ROM shall then be integrated with Twin Builder to develop a holistic response system.

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Interpretation & Importance of Mass Participation in Modal Analysis

We often come across the dynamics or vibration problems in most of the product development across all industries.  We have gained enough knowledge through the degree of Bachelors or Masters, with an example of the famous engineer disastrous design of “Tacoma Narrows Bridge-1940”, that considering the dynamics effects in design is quite critical.  Generally, a dynamics problem is categorized into linear or nonlinear dynamics. This blog is related to the linear dynamics and nonlinear dynamics will be discussed in length in another blog. The most commonly heard terminology which we stumble upon in the design of such vibrating products is “natural frequencies“, “resonance“, “eigenmodes” etc. We have many linear dynamics simulation techniques such as “Harmonic Analysis“, “Random Vibration“, “Response Spectrum“, “Transient Analysis“, “Acoustic Analysis“, etc based on the loading it undergoes and also on the output we are interested in. But all these dynamics simulations start with the first step called “Modal Analysis“.

Modal Analysis

What makes something unique is an identity of its own, right? What if I say natural frequency is the identity of a body? Let’s see why. Assume you are imparting energy (striking) to a body. What will happen is obvious, the body will start to vibrate. But the vibrational frequency will be in its natural frequencies. It doesn’t matter how much or where you give the energy it will always vibrate in its natural frequencies, period.  This is why the base of any dynamic analysis is said to be modal analysis as it shows its identity or behavior.

The modal analysis calculates natural frequencies and mode shapes of the designed model. It’s the only analysis that doesn’t require any input excitation or loads, which also makes sense, as mentioned before natural frequencies are independent of the excitation loads. Natural frequency depends only on two things mass and stiffness.

Why do we need to do the modal analysis?

Yes, we can find natural frequencies, and mode shapes through modal analysis but why to do it? Let me explain that through an example, when you ride a motorcycle, sometimes you might have experienced vibration in your handle. Some bikes have too much vibration that, you can’t even use your rear mirror. This is because the handle’s natural frequency is matching with engines RPM.

Structure borne noise: A structure makes peak noise when it’s vibrating in its natural frequency.

Whirling of shafts: To find the critical RPM of a shaft so that, crossing the critical speed will be done with precautions to avoid resonance.

Avoiding resonance is always preferred, thus shifting or modifying natural frequency can help to control, above mentioned issue. Natural frequency depends on only two parameters, modifying them will help to design a dynamic body part.

As an engineer, I always go in search of the physical meaning rather than proving by an equation. But at times equations are unavoidable.

Now let us see how we can get the natural frequency of a system.

Excitation force Equation of any dynamic system can be represented as

Every natural frequency is associated with each mode shape and mode shape represents the displacement behavior. There is enough material on the internet which explains mode shape. Right now, let’s concentrate on the “Mass Participation Factor” other important information from modal analysis, which would assist us in the simulation of other linear dynamic simulations.  What is mass participation in general? Consider a 3 massed system as shown below.

The figure shown above is a mode of the system. Here masses participating in the X direction are M1 and M2  and thus total mass participation is M1 +M2.  The only difference in FEA is that instead of lumped masses, the system will be discretized by elements.

Now let’s see ANSYS modal Analysis. Here I’m taking a cantilever beam, with 0.8478 kg. Having a cross-section of 3*60*600.

As you can see from the participation factor calculation. I have solved the first 12 natural frequencies. In this table, ANSYS solver calculates only frequency and Participation factor ie 1st and 4th column. Every other column is calculated from these two values. Let’s look at the most important column one by one.

As you can see this ratio is in direct comparison with total mass, which gives a better clarity on how much of the total mass participation is extracted. In other words, the sum of the effective masses in each direction should equal the total mass of the structure. But clearly, this depends on the number of extracted modes.

The same logic is for rotational mass participation. But here you might get ratios bigger than 1. Then, there can be confusion as mass participating is more than the total mass of the system? The answer is, participation factors for rotational DOFs are calculated about the global origin (0,0,0). The calculated effective mass essentially contains a moment arm (effective mass multiplied by the distance from centroid). Thus, the effective mass for the rotational DOFs can be greater than the actual mass and the participation factors can be greater than 1.0.

Ideally, the ratio of effective mass to total mass can be useful for determining whether or not a sufficient number of modes have been extracted for the “Mode Superposition” for further analysis. Modal superposition is a solution technique for all linear dynamic analyses. Any dynamic response can be calculated as the sum of the mode shapes, that are weighted with some scaling factor (modal coefficient). Also, the time step of the transient simulation is calculated based on the most influential mode in the modal analysis.

Modal analysis is usually done without considering any force or working environment. This assumption is taken by considering mass and stiffness to be constant. But at times this doesn’t work, like a pressurized vessel or pipe. As compressive or tensile force changes the stiffness. In such cases, we have to do a prestressed Modal Analysis.

In some cases, like rotating shafts with motors, turbines, the natural frequency will not match with the working condition. This is because, for different RPM, stiffness also changes,(Centrifugal force changes). In these cases, we need to consider the rotational speed of the shaft. In ANSYS Modal Analysis (Rotodynamic Analysis) rotational speed with Coriolis effect can be directly given to find the critical speed of the shaft.

Modal analysis is a prerequisite for all linear dynamics analyses like Harmonic, Random vibration, and Response spectrum analysis. Hence Modal Analysis plays a huge role wherever you are trying to find out vibration characteristics of a design. Thereby it is relevant for most industries like Rotating machines, construction, automobile, Machine tool, agricultural equipment, and Mining.

Engineering Simulation opens up a huge range of possibilities. Since CAEsimulation requires more than just software, we at CADFEM help our customers to adopt simulation for success in every phase of product development, thereby enabling them to realize their product promise.

Please click here to understand more about NextGen Engineering Simulation Possibilities.

Please feel free to connect with us at marketing@cadfem.in or +91-9849998435, for a quick Demo on this Product.

Author Bio:

Mr. Vineesh Vijayan, Application Engineer

CADFEM India

Mr. Vineesh Vijayan has done his Master of Technology in Machine Design. With good expertise in Structural Simulation currently, he is contributing his efforts to CADFEM India as an Application Engineer.

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Open the Door to Material Optimization

Introduction:

The world is evolving at a quantum speed with transforming technology. The human life cycle has enriched to tend towards advancement in every sector. Businesses have adopted the transformation & obtained the benefits of technology involved in their mainframe process to become multi-billion companies. Making the product a hero in every story, Engineering the product or designing a physical product demands focus on four major factors; Design, Analysis, Manufacturing, and Materials. Though the first three factors are digitally transformed, the materials field is still lagging. This article exclusively focuses on optimizing your right material choices.

Let’s start with an example of a company facing a similar conundrum.

Background:

Referring to the case of an OEM, that manufactures an industry renowned product.

Due to the stringent industry standards and to stay ahead of the competition, the company decided to optimize their existing product and its performance. Following the advancement, they relied on simulation results for quick feedback from different design iterations. Furthermore, parametric optimization yielded them even better results compared to the manual design iterations. Overall, they were able to achieve a 9% Reduction in Weight and a 5 % Increase in Efficiency through Design Optimization.

Much to the Team’s surprise, the product manager wasn’t satisfied with this result. Hence, he assembled his team to initiate an experiment with different material types. 

The broader idea of this activity was to understand how he could improve his product and cut down costs to the company, thereby naming this activity as Material optimization.

Optimized Product = Design Optimization + Material optimization

Following the superior’s directive, the team started dedicating their efforts to bring the best out of current results, in terms of cutting costs, reducing development time & raising standards of performance. Four of his team members heading the R & D were investigating the case study with different ideas as below. 

The first member tried to use the existing available material data with him to see if he can get the best possible combination;

The second member tried to use the materials preferred by his company to avoid supply chain issues;

The third member tried to reach out to suppliers/consultants for a piece of advice on material choices; and

The fourth member tried to browse on the internet for material data.

However, none of the above approaches answered the below questions

  1. Which material to choose?
  2. Is there a better material choice available?
  3. Is there a cheaper solution? 
  4. Is the chosen data, reliable?
Capture

This is where companies need a tool like, Granta Selector which does answer the above questions.

Granta Selector is a tool that can help optimize your material choices, which not only has material properties of metals, plastics, polymers, ceramics and various other classes of materials but also has features like search, plot and compare your choice of materials as shown in the pic.

Apart from the features mentioned above, Granta selector has:

  • FE export tool to export simulation ready material data to most of the FE platforms
  • synthesizer tool to estimate material and process cost 
  • Eco Audit tool to estimate the environmental impact of the selected material at the early stage of the design.

To use how to use above-mentioned tools, click here to understand how Tecumseh, a global leader of commercial refrigeration compressors used Granta Selector to reduce development time by three-fold and saved millions of euros of cost savings from making the right materials decisions.

please click here for more information on Material optimization.

Please feel free to connect with us at marketing@cadfem.in or +91-9849998435, for a quick Demo on this Product.

Author Bio:

Mr. Gokul Pulikallu, Technical Lead-South

CADFEM India

Mr. Gokul Pulikallu has done his Bachelor of Technology  & he is carrying 9 years of experience in the field of structural Mechanics simulation and optimization. His main focus is Design Optimization & Material Optimization and helps customers adopt these technologies efficiently.

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Robustness Evaluation – Why Bother?

This article will explain how ANSYS optiSLang can be used for robustness evaluation in virtual product development.

A successful product. Isn’t that the goal for every product company? It begins right from the step where engineers come up with world class product innovations to getting the right marketing mix that brings commercial success. Is every product successful? No. Is every product with a great design successful? Maybe.

The Symptom

Robustness Evaluation - Why Bother?
Courtesy: Android Authority

More often than not, we find market leaders stumble with product failures. The infamous Samsung’s Note 7 will come to your mind instantly. Hundreds of users were at the forefront of dangerous incidents where phones caught fire due to short-circuiting. Samsung conducted severe internal testing and several independent investigations. They found that, in certain extreme situations, electrodes inside each battery crimped, weakened the separator between the electrodes, and caused short circuiting. In some other cases, batteries had thin separators in general, which increased the risks of separator damage and short circuiting. Economics-wise, the incident caused Samsung to recall 2.5 million devices, lose over $5 billion and damaged its reputation.

Faulty Takata airbags’ inflators contained a defect that cause some of them to explode and project shrapnel into drivers and passengers. 50+ people worldwide lost their lives due to this design failure. 70 million Takata airbag inflaters were to be recalled at a cost of $9 billion to its automaker customers. For a Tier-I supplier, this liability was so huge that they filed for bankruptcy.

Such glaring errors after product launch, with severe economic implications, aren’t limited to Samsung and Takata alone. Honda, Michelin and many more companies have been involved in product recalls due to design failures.

Obviously, such design flaws need to be mitigated. Isn’t it?

The Probable Solution

To preempt design failures, today’s engineers use state-of-the-art engineering technology. Traditionally, product development teams used extensive prototyping and testing to validate design variants during the design life cycle. Of course, this is cumbersome, expensive and time-consuming.

Over the past few decades, engineering simulations have opened up a whole new range of possibilities for the design engineers. ANSYS, Inc., the market leader for engineering simulations, provides state-of-the-art technology to simulate systems involving mechanical, fluid, electrical, electronic and semiconductor components. With added insight, design engineers are able to test a lot more design variants on a virtual platform using this technology.

Consequently, the benefits – innovation, lowered cost of product development, higher product profitability and faster time-to-market. The staggering economic benefits and tremendous value on the offer have prompted several product companies to introduce simulations upfront using a Simulation-Driven Product Development approach.

Companies like Samsung and Takata were power users of engineering simulations. They used technology extensively in their design phase and perform virtual tests to validate designs. Only validated designs were put through production, QA and then sent off to the market. Despite simulating and validating designs, these companies witnessed monumental product failure in the market that caused loss of life, led to economic losses and damage to their reputation.

If they used simulation-driven product development, what went wrong?

The Cause

While the probable solution can mitigate and even eliminate design failures, there are other forces at play that you will need evaluate carefully. Hence it is imperative to understand the root cause for occurrence of design failures despite conducting extensive state-of-the-art simulations.

Many design engineers often undermine or do not consider one important aspect due to lack of proper understanding. Variability. Just as design parameters such as thickness or physical loads can be varied to test different design variants, some parameters display inherent variability.

Let me explain it with a material parameter: Young’s Modulus. If you’re an engineer by qualification, you would’ve come across the Universal Testing Machine (UTM) in your freshman or sophomore year of college. To test the Young’s Modulus of any given material (say steel), the UTM pulls a material specimen at extreme ends to create tension. Using mathematical calculations, you’ll arrive at a number close to 210 MPa as the Young’s Modulus of mild steel. Let’s say you repeat this test for 99 other specimens of the same material. Each test result will be different and it will never be the same. Other than the odd case of a faulty UTM apparatus, there’s only one reason for that. Natural Scatter.

The Hero: Robustness Evaluation

Such variability (statistical) will lead to variability in the performance parameters of the product. Obviously this is quite important and engineers need to assess designs for variability well ahead of product launch. For variability, you have only one way to assess designs for product failure or risks: Robustness Evaluation.

Robustness Evaluation with ANSYS optiSlang

The preferred choice of tool for robustness evaluation is ANSYS optiSLang. For better understanding, there is a lot of material available in more detail. Instead of reading, you may also want to consider watching these webinars here and here.

Can you attribute lack of design robustness to any other product failures that you have witnessed? Do you have alternate views? Please let me know in the comments section.

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ANSYS 18.0 – The latest release is here!

Banner for ANSYS 18.0 software release

The day has arrived!! Most of our customers would’ve received announcement of the latest release – ANSYS 18. It’s time to rejoice and celebrate this new release.

ANSYS 18.0 ushers in the era of pervasive engineering simulation – an era where all types of engineers use simulation throughout the entire product lifecycle. While simulation was once the primary domain of experts and used mainly for verification, it is now moving upfront in the development process to quickly evaluate changes in design. At the same time, it’s also moving downstream of the product lifecycle process to analyze real-time operational data from connected machines in the industrial internet.

By incorporating simulation into all segments of a product’s lifecycle, ANSYS 18.0 adds tremendous value by spurring innovation, reducing development and operational costs, and improving time to market. Whether your field is structures, fluids, electromagnetics, semiconductors, systems, embedded software or some multiphysics combination of these areas, ANSYS 18.0 is the simulation platform to achieve your engineering and business goals.

Digital Launch Event

To learn more about pervasive engineering simulation and ANSYS 18.0, we invite you to the digital launch event on January 31. During this event, the ANSYS CEO, Ajei Gopal, and numerous technology leaders from industry will talk about this exciting new release from ANSYS. Here’s the line-up of the speakers from ANSYS:

  • Ajei Gopal, President and CEO, ANSYS, Inc.
  • Andre Bakker, Senior Director Fluids Development, ANSYS, Inc.
  • Dale Ostergaard, Senior Director Software Development, ANSYS, Inc.
  • Larry Williams, Senior Director Electronics Products, ANSYS, Inc.
  • Sergey Polstyanko, Senior Director, Research and Development, ANSYS, Inc.
  • Eric Bantegnie, Vice President and GM Systems Business Unit, ANSYS, Inc.

In addition, you can also learn more about ANSYS 18.0 by visiting the “What’s New” section of the Customer Portal.

Current Customers – Next Steps

Current customers can download ANSYS 18.0 from the Download Center on the ANSYS customer portal.

You need a license manager upgrade to run ANSYS 18.0 products. Your current license keys will continue to function with the new 18.0 license manager. Support for operating systems, graphics cards, third-party CAD products and more is available on the Platform Support page.

If you need any support, please feel free to contact us.

Together with ANSYS, we are excited to bring you this latest release. This comes as the result of countless hours of work by 1,000+ professionals in the research and development organization. We believe it will exceed your expectations and provide considerable value in your engineering processes and product lifecycle.

May the force always be with you! 🙂

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