Michal Bezdek

A coupled finite-element, boundary-integral method for simulating ultrasonic flowmeters

Todays most popular technology of ultrasonic flow measurement is based on the transit-time principle. In this paper, a numerical simulation technique applicable to the analysis of transit-time flowmeters is presented. A flowmeter represents a large simulation problem that also requires computation of acoustic fields in moving media. For this purpose, a novel boundary integral method, the Helmholtz integral-ray tracing method (HIRM), is derived and validated. HIRM is applicable to acoustic radiation problems in arbitrary mean flows at low Mach numbers and significantly reduces the memory demands in comparison with the finite-element method (FEM). It relies on an approximate free-space Greens function which makes use of the ray tracing technique. For simulation of practical acoustic devices, a hybrid simulation scheme consisting of FEM and HIRM is proposed. The coupling of FEM and HIRM is facilitated by means of absorbing boundaries in combination with a new, reflection-free, acoustic-source formulation. Using the coupled FEM-HIRM scheme, a full three-dimensional (3-D) simulation of a complete transit-time flowmeter is performed for the first time. The obtained simulation results are in good agreement with measurements both at zero flow and under flow conditions

A novel numerical method for simulating wave propagation in moving media

A novel boundary integral method for simulating acoustic wave propagation in nonuniformly moving media is introduced. It is based on a generalized free-space Greens function which utilizes parameters obtained by solving the ray-tracing equations. Inserted into the Helmholtz integral, this approximate Greens function allows prediction of acoustic fields in moving media at low Mach numbers using the given boundary data. In order to validate the method, the acoustic field generated by a vibrating piston in a nonuniform shear flow is computed and compared with the results of a FEM simulation. Furthermore, an application of the method to simulation of wave propagation across a 2D cylindrical duct is presented.

A novel boundary integral formulation for acoustic radiation in a nonuniform flow: coupling to FEM and applications

A realistic 3D simulation of a complete transit time ultrasonic flowmeter is presented here for the first time. The applied simulation scheme is based on the novel boundary integral method for acoustic radiation in a nonuniform flow (the Helmholtz-Integral-Raytracing Method, HIRM) introduced in (1). In this paper, the coupling of HIRM and FEM is discussed in detail. For the FEM-HIRM interface, a new type of reflection- free acoustic source is formulated. The coupled FEM-HIRM scheme is verified by means of an experimental setup in which both fluid-borne and structure-borne ultrasound contribute to the received electrical signals. Finally, the simulation tool is applied to an ultrasonic flowmeter of diameter 100 mm and operational frequency 500 kHz. The obtained simulation results exhibit a very good agreement with the measurements. In this manner, the applicability of HIRM to modeling of complex acoustic systems involving moving media is demonstrated.