Common use of Computational fluid dynamics Clause in Contracts

Computational fluid dynamics. The development of CFD methods, which can be included in the daily work of an ENT surgeon, is one of the most promising and challenging tasks for the future of upper and lower airway diagnosis. The analysis is based on CT- or MR-imaging data (48). As such, this method requires patient exposure to radiation, unless CT has been performed for other indications. ▇▇▇▇▇ et al. reported on the middle nasal cavity area as a key space with a high correlation for subjective nasal obstruction measured by VAS and nasal obstruction symptom evaluation score (NOSE) (49). By means of extraction algorithms the three-dimensional surface of the airway, i.e., the interface between air and tissue, is reconstructed from the corresponding CT data (50). This surface consists of a set of triangles forming a watertight volume of the region of interest. It serves as a basis to construct a computatio- nal mesh for the simulation. This mesh is necessary to approxi- mately solve the governing equations of fluid mechanics, i.e., the Navier-▇▇▇▇▇▇ equations (conservation of mass, momentum, and energy), in their discrete form on computers. Lattice- Boltzmann methods (LBM) operating on hierarchical Cartesian meshes (51) have shown to be efficient for the computation of the flow in the nasal cavity (5, 48, 50, 52-54). They allow for effective paral- lelization, easy boundary treatment, and accurate simulation of respiratory flows. The application of adaptive outflow conditi- ons at geometry outlets placed at the pharynx at inspiration in conjuction with second-order accurate no-slip wall-boundary conditions and Saint-Venant-Wanzel inflow conditions at the nostrils allows an in-solve adjustment of the ▇▇▇▇▇▇▇▇ number (50), or in other words, an adaptation of the ratio on inertial to viscous forces. ▇▇▇▇▇ et al. (50) and ▇▇▇▇▇▇▇▇▇▇ et al. (5, 52, 53) have shown detailed studies of the nasal airflow using this method and classify nasal cavities by the total pressure loss, wall-shear stress, heating capability, and heat transfer. While the feasibility of CFD methods is obvious, the transfer to daily practice is closely related to the development of high- performance small computers and standard programs allowing the use of CFD at a reasonable price. That is, accuracy, which is defined by the mesh resolution and the simulation and modelling method, comes at a defined computational cost. High resolution simulations are currently only viable by employing high-performance computing (HPC) hardware. For this reason, many approaches follow a model such as The ▇▇▇▇▇▇▇▇-averaging ▇▇▇▇▇▇-▇▇▇▇▇▇ (RANS) approach. Such RANS computations are computationally cheaper than directly solving the Navier-▇▇▇▇▇▇ equations without using any model- ling approach. However, the error introduced by such models is not easily quantifiable and their application stays questionable since the assumption of turbulent flow, a prerequisite of turbu- lence models, is not necessarily true for nasal cavity flows. In the end it needs to be stated that to the best of the author’s knowledge, no simulation tool has made its way into daily clinical practice so far, at least any which is capable of finding a reasonable balance between computational costs, high ac- curacy, and user-friendlyness. Two further tests should be mentioned as suitable for limited indications: