Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Second order approximation of natural frequency constraints in structural synthesis

Abstract: The paper is concerned with structural optimization problems in which the constraints consist of limits imposed on the natural frequencies of the structure. Improvements in the quality of approximations for the frequency constraints are sought by considering second-order Taylor series expansions. Analysis of the second-order sensitivity of natural frequencies is carried out. As an example, the design of a midplane symmetric aluminum beam of constant depth supporting three nonstructural masses is considered. Web thickness and chord member areas were determined so as to achieve minimum structural mass while maintaining the fundamental frequency at or above 30 Hz.

Ultrasound imaging method and apparatus for generating pulse width modulated waveforms with reduced harmonic response

Abstract: An improvement to the method for harmonic imaging including the steps of transmitting ultrasonic energy at a fundamental frequency, and receiving reflected ultrasonic energy at a harmonic of the fundamental frequency is provided. The transmitting step includes the step of transmitting a waveform comprising at least a sequence of at least a first and second pulse characterized by first and second pulse durations, respectively, where the second pulse duration is different than the first duration. This arrangement can reduce harmonic energy in the waveform. The system (10) includes a transmit beam former (12) that supplies high voltage transmit waveform in a plurality of channels via a TX/RX switch (14) to a transducer array (16).

Fourier Transform Rheology of Branched Polyethylene: Experiments and Models for Assessing the Macromolecular Architecture

Abstract: Fourier transform rheology (FTR) consists of analyzing the frequency spectrum of the nonlinear torque response obtained during large-amplitude oscillatory shear. In the present work, the analysis has been carried out in the whole complex space and was especially focused on the study of the third complex harmonic I*3/I1 (= I*(3ω1)/I1, where I1 is the spectrum intensity at the fundamental frequency ω1), the intensity I3/I1 (= |I*3/I1|), and the phase shift Φ3 of I*3/I1. The accuracy of FTR to characterize the architecture of linear, sparsely, and densely branched polyethylene regarding the number of branches and their length has been shown. A modified Wagner integral model and a differential multimode pompom model were used to simulate FTR experiments. Nonlinear parameters of each model were determined by fitting the curve of the third complex harmonic I*3/I1 versus the strain amplitude γ0 with the experimental data. Good results have been obtained with the modified Wagner model. Whereas, the pompom model a...

High impedance fault analyzer in electric power distribution

Abstract: A system (Fig. 3) and method for detecting an abnormality in a network (10) for distributing or transmitting electric power at a predetermined fundamental frequency. The system produces a signal (40) representing the fundamental frequency and another signal (42) representing a harmonic current occuring in the network. The phasor relation between the fundamental voltage and harmonic current representing signal are compared (44). The system produces a signal (82) indicating the occurence of a high impedance fault in response to a predetermined change in the compared phasor relationship. Embodiments (Figs. 5 and 6) are disclosed utilizing expression of signals within the network in polar coordinates, as well as embodiments (Fig. 11) utilizing signals expressed in rectangular coordinates. Such embodiments include both circuitry for detecting zero crossing phenomena, as well as circuitry for producing representation of signal phasor products.