Peristaltic pump FSI simulation for safer dialysis
- Alvaro Filho
- 12 hours ago
- 5 min read
“Hardware is hard,” goes a saying in Silicon Valley. One might add: life-saving hardware is even harder. Despite all the advanced medical technology invented by humanity, to this day the kidney remains the only organ that has been permanently replaced by a machine. And although hemodialysis is a remarkable and life-saving achievement, each session lasts up to four hours, three times a week, for many years—placing a significant burden on the lives and safety of patients.
That said, the new structural modeling capabilities available through Simcenter STAR-CCM+ have been explored to help improve the design of blood pumps, making dialysis machines safer and treatments less stressful for every patient. Below, see how some of the features of Simcenter STAR-CCM+, along with its best-in-class fluid-structure interaction (FSI) simulation tools, contributed to achieving this goal.
Improving Hemodialysis
Approximately 3 million people worldwide receive hemodialysis treatment, resulting in about 1.3 million sessions per day. While generally considered safe, the malfunction or improper handling of dialysis machines can cause serious harm to patients, posing a constant and lasting risk to their health.
Many injuries or complications are related to improper blood flow, where too much or too little blood is extracted from the patient, making the treatment ineffective or causing pain or even fainting during the session.
The blood flow rate is specifically tailored to each patient’s needs, taking into account factors like weight, size, blood pressure and viscosity, and overall health.
The patient’s blood circulation to the dialyzer is managed by a roller pump, a type of peristaltic pump that uses rollers to compress and release a flexible tube to move blood through it. The blood flow generated by the pump varies depending on the material, length, and size of the tube, as well as the quality and type of vascular access. Proper occlusion, ensuring the tube is fully compressed by the rollers, is also essential for moving the correct blood volume without slippage. It's crucial to consider all these factors in the pump design process and validate it across a wide range of scenarios to ensure optimal blood mass flow and safety for every patient.
Dialysis Machine. Source: NAGWA
From a technical perspective, a fluid-structure coupled simulation setup is considered the ideal tool to manage this complex mix of mechanical, physical, and patient-specific factors and ensure the design performs well in any situation.
FSI Simulation with a Peristaltic Pump for Safer Dialysis
Capturing fluid-structure interaction (FSI) with accurate contact modeling is fundamental for robust and precise simulations. By faithfully modeling the complexity of the system, FSI simulations can help design safe and effective blood pumps.
The Challenges of FSI Simulation in Peristaltic Pumps
Simulating peristaltic pumps, including both the fluid and solid domains in a single setup, offers significant advantages. This integrated approach enables not only visualization of how changes in tube thickness affect tube deformation but also how these changes, in turn, influence blood pressure and mass flow.
However, simulating peristaltic pumps is more complex than it appears. The significant fluid-structure interaction (FSI) means that the deformation of the tubing impacts fluid flow and vice versa. This requires a tight two-way coupling of fluid dynamics and structural mechanics. The flexible tubing exhibits non-linear behavior due to large deformations and contact.
The peristaltic motion involves continuously moving boundaries as the rollers compress and release the tubing. Accurately capturing these moving boundaries in simulations is challenging and requires advanced mesh evolution techniques and dynamic stabilization methods. The pumping action relies on the rollers pinching the tube against the casing, making accurate modeling of the contact between the roller, casing, and flexible tube crucial. Incorrect contact modeling can lead to inaccurate predictions of the tube’s cross-sections, pump pressures, and flow rates.
Fortunately, Simcenter provides all the tools needed to perform high-fidelity two-way coupled FSI simulations and predict the behavior of peristaltic pumps in various scenarios. And with the mechanical technology incorporated into the latest Simcenter STAR-CCM+ versions, contact modeling has become easier and more accurate, even for the most complex applications.
Mesh evolution through mesh morphing and dynamic remeshing
Difficulties of contact modelling
Contact modelling is essential in structural mechanics, but no algorithm exists that efficiently solves all types of contact problems. The optimal solution depends on the type of contact and the required accuracy and robustness.
The structural solver uses the Penalty Method for contact enforcement. This method relies heavily on a user-defined penalty parameter, which controls the contact stiffness, or the pressure generated by contact penetration. While a high penalty parameter can yield precise contact resolution, it also decreases the simulation’s robustness and speed.
Selecting an optimal penalty parameter is particularly difficult for dynamic problems with significant contact changes, such as in this peristaltic pump simulation. The interactions between the blood, the flexible tubing and the rollers that repeatedly go in and out of contact, lead to dynamic changes in contact forces and fluid pressure. A static penalty parameter will cause varying penetration between the tube and the rotor, affecting the fluid cross-section and flow rate. This variability results in inaccurate predictions of the pump’s outlet mass flow rate and poses a challenge to straight-forward peristaltic pump FSI simulation.
The image below shows how different penalty parameters cause variations in the penetration, altering the occlusion of the flexible tube. The graph underneath shows the outlet mass flows resulting from the variations in occlusion and gives an idea of how important correct contact modelling is for the correct simulation of a peristaltic pump.
Cross section of pinched tube for different penalty parameters
Outlet mass flows resulting from different penalty parameters
Advanced contact modelling with the Uzawa algorithm
To address the limitations of the Penalty Method, the structural solver now introduces a new contact modeling approach that combines the benefits of the Penalty Method and the very exact but computationally costly Lagrange Multiplier method. This approach is based on the iterative solution of the Augmented Lagrange Method (ALM) using the Uzawa algorithm.
ALM includes an additional augmentation loop in each iteration, updating the contact pressure until the specified contact constraint accuracy is achieved. While the convergence speed of each augmentation still depends on the chosen penalty parameter, the final contact constraint accuracy does not, making it easier for users to control the allowed contact penetration precisely.
Outlet mass flows and contact penetration differences between Penalty and Uzawa Method
With the Uzawa algorithm, contact penetration can be limited to a specific value, ensuring the desired accuracy. The figure above demonstrates how this method effectively maintains contact penetration below levels achieved with a high penalty value, further improving the accuracy of mass flow predictions. This approach eliminates the need for extensive fine-tuning of the penalty parameter and at the same time decreases simulation time by 6%, saving both time and computational resources.
Beyond hemodialysis
With the new advanced contact modelling methods in the structural solver, together with the best-in-class fluid-structure-interaction simulation capabilities of Simcenter STAR-CCM+, designing reliable and efficient peristaltic pumps has never been more achievable.
These simulations help ensure that all aspects of a pump’s performance are optimized, resulting in safer, more effective treatments for patients. In addition to hemodialysis, peristaltic pumps play a crucial role in a variety of other applications, from chemical processing to food and beverage manufacturing, where fluid flow is essential.
Want to develop safer, more efficient medical devices while reducing risk and accelerating innovation? Schedule a meeting with CAEXPERTS and learn how advanced simulations with Simcenter STAR-CCM+ can transform your peristaltic pump designs and more—with accuracy, time savings, and patient safety at the forefront.
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E-mail: contato@caexperts.com.br
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