Testing and characterization of second-order differential microphones

The focus of this thesis is the testing and characterizing of directional microphones, designed based on the ear of the fly Ormia ochracea. The response of these microphones is modeled as a linear combination of the gradients of the sound field. A least squares approach is employed in order to determine the transfer functions between the response and these gradients. Knowledge of these complex transfer functions is crucial in understanding the nature and quality of the response of these microphones. Once determined, these transfer functions are used to simulate the plane wave response of differential microphones. This process is invaluable to acoustic research groups that do not have access to an anechoic chamber because the plane wave response is a standard by which acoustic devices are measured. This process was validated by comparing the true plane wave response of an industry standard differential microphone with its simulated plane wave response

Rotor Blade Modeling in a Helicopter Multi Body Simulation Based on the Floating Frame of Reference Formulation

The Floating Frame of Reference formulation was chosen to include the Beam Advanced Model in DLR’s Versatile Aeromechanics Simulation Tool. During the development and concurrent testing of the model in the field of helicopter rotor dynamics, some particular shortcomings have become apparent. These mainly – but not exclusively – concern inertial loads affecting the flexible motion of beams. This paper treats the related physical phenomena, and proposes enhancements to the model which remedy the deficiencies of the baseline method. Particular attention is given to the introduction of rotational shape functions to account e.g. for the propeller moment and the consideration of an accelerated Floating Frame of Reference to address the blade attachment’s radial offset from the rotor center in the centrifugal field. Furthermore, the application of external loads (e.g. airloads) away from the beam’s nodes or off the beam axis is addressed as a prerequisite for independent structural and aerodynamic discretization. Finally, the modal reduction under centrifugal loading is considered. The individual model upgrades are verified based on analytical reference results of appropriate rotor dynamics test cases. The enhancements are necessary for simulating flexible helicopter rotor blades within a Multi Body System – a feature required for sophisticated simulation scenarios in which the limitations of conventional rotor models (e.g. constant rotational hub speed) are exceeded

Testing and characterization of second-order differential microphones

The focus of this thesis is the testing and characterizing of directional microphones, designed based on the ear of the fly Ormia ochracea. The response of these microphones is modeled as a linear combination of the gradients of the sound field. A least squares approach is employed in order to determine the transfer functions between the response and these gradients. Knowledge of these complex transfer functions is crucial in understanding the nature and quality of the response of these microphones. Once determined, these transfer functions are used to simulate the plane wave response of differential microphones. This process is invaluable to acoustic research groups that do not have access to an anechoic chamber because the plane wave response is a standard by which acoustic devices are measured. This process was validated by comparing the true plane wave response of an industry standard differential microphone with its simulated plane wave response

Beam Modeling in a Floating Frame of Reference for Torsion Dynamics of Helicopter Rotor Blades

In the ongoing development of DLRs Versatile Aeromechanics Simulation Tool, an elastic beam model is integrated into the Multibody System based on the Floating Frame of Reference formulation. Although the application of this formulation for one dimensional beam models has already been addressed in the literature, the challenge remains to properly model the torsion dynamics of rotor blades - especially under high centrifugal loads. To this aim, this work suggests the consideration of rotational shape functions in the inertia shape integrals and in the application of gravitational, inertial, and external loads. This modified approach is validated based on the structural analysis of a rotor blade with complex geometrical properties

Modeling the Friction Boundary Layer of an Entire Brake Pad with an Abstract Cellular Automaton

The principle energy exchange of a brake system occurs in the tribological boundary layer between the pad and the disc. The associated phenomena are primarily responsible for the dynamics of brake systems. The wear debris forms flat contact structures, or “patches,” which carry the majority of the normal load in the system and are highly influential on the friction behavior of the system. A new simulation tool is presented, which is capable of rapidly performing simulations of the contact between an entire brake pad and disc. The “Abstract Cellular Automaton” simulations accurately model the patch coverage state of a brake pad surface based on the system’s load history. This can be used to simulate the complex dissipation phenomena within the tribological contact of the entire pad, including time-dependent local friction coefficients, wear and wear debris transport, and vibrational effects on highly differing scales