Forced resonance

Forced (resonant) vibration. In forced vibration the usual driving frequency in rotating machinery is the shaft speed or multiples of this speed. 

Damping may be obtained from forced resonance vibration instruments from plots of amplitude of vibration versus frequency through the resonance peak. Figure 6 illustrates such a plot of a resonance peak. Using the notation shown in this figure, the damping may be expressed, as... 

The short-range valence or chemical forces resonance bonding Virtually by definition, the forces between molecules cannot be ascribed to covalent bonds such as those that link atoms within molecules. Hence, such forces may be (and often are) tautologically labeled as noncovalent to distinguish them from the strongest 2c/2e covalent bonds that underlie the formation of molecules. (Nearly as uninformative is the designation weak bonding, which... 

Dynamic mechanical analyzers can further be divided into free resonance analyzers and forced resonance analyzers. In the case of free resonance analyzers, samples are allowed to oscillate freely (e.g., at their natural frequency) until oscillations cease. Forced resonance analyzers are nevertheless more frequently used. They are designed to apply oscillating stress at a fixed frequency and are ideal for scanning material performance over a wide temperature range (Menard, 1999). Sample preparation includes selection of an appropriate clamp system, which is a function of... 

Boccaccini, A.R., Pearce, D.H., Janczak, J., Beier, W., Ponton, C.B. (1997), Investigation of cyclic thermal shock behaviour of fibre reinforced glass matrix composites using non-destructive forced resonance technique , Mater. Sci. Tech., 13, 852-858. 

Bar cross section Shear modulus G (static) G (dynamic) at forced resonance... 

AIMD simulations appear as a promising tool for a first-principles modeling of enzymes. Indeed, they enable in situ simulations of chemical reactions furthermore, they are capable of tEiking crucial thermal effects [53] into account finally, they automatically include many of the physical effects so difficult to model in force-field based simulations, such as polarization effects, many-body forces, resonance stabilization of aromatic rings and hydration phenomena. 

The periods of the first few modes of the seiches are quite close to the characteristic timescales of the wind forcing of the Baltic Sea. The spatial scales of the atmospheric low-pressure systems are comparable with the length scale of the Baltic Sea. Therefore, the first mode will be excited most likely. If strong pressure systems pass the Baltic Sea such that during half of the period of the first mode the wind blows from the southwest to the northeast and during the following half period in the opposite direction then the sea level elevations of the Baltic Sea are forced resonantly and a storm surge may occur. 

Consider a forced resonator obeying the force-balance equation d x t)... 

Analysis of the dynamic mechanical properties of acrylic polymers has been the subject of numerous investigations [169,205 214]. In most of these investigations, the measurements were made using a Rheovibron, which utilizes the forced-resonance principle [203]. 

The thermal properties of polyesters are of the greatest importance for their end applications. The important features of a polymer, such as bond strength, inter-and intra-molecular forces, resonance stability, crystallinity, structural imperfections and molecular weight, are responsible for their thermal behaviour. Long oil polyester resin and styrenated polyester resin are made flame retardant by the incorporation of bis-pyridine, bis-tribromophenoxo copper complex and polydibromophenylene oxide. 

This distribution is also called Lorentz distribution by physicists. It forms the solution to the differential equation that can be used to describe forced resonance. 

In the resonance mode, the 983 operates on the mechanical principle of forced resonant vibratory motion at a fixed amplitude (strain), which is selected by the operator. The arms and sample are displaced by the electromagnetic driver, subjecting the sample to a fixed deformation and setting the system into resonant oscillation. 

The barriers to rotation of biphenyl are 1.8 and 2.5kcal/mol at 90° and 0°, respectively. The planar structure (0°) is clearly resonance stabilized, but when the molecule is planar, the ortho hydrogens on one ring come rather close to the ortho hydrogens on the other ring, and there is a substantial van der Waals repulsion between them. So one set of forces (resonance) is trying to planarize the molecule (torsion angle 0°), while... 

A.R. Boccaccini, D.H. Pearce, J. Janczak, W. Beier, and C.B. Ponton. Investigation of the Cyclic Thermal Shock Behaviour of Fibre Reinforced Glass Matrix Composites Using a Non Destructive Forced Resonance Technique. Mat. Sci. Technol., 13, 852 859 (1997). 

Nanorheology of thin liquid crystal film studied by shear force resonance method... 

Both conventional dielectric measurements and the Kerr effect are experimental techniques which present problems in aqueous systems due to the presence of a large dx. conductance (particularly in the presence of added salts). The recent observation of a forced resonance between shear and electrical fields described in Sect. 2.3 may in future provide another technique suitable for aqueous systems. 

This frequency-type distribution, also called a Lorentz distribution or a Cauchy distribution (named after Hendrick Lorentz and Augustin Cauchy), is applied when describing events that exhibit a truly symmetric array of possible outcomes as in forced resonance, i.e. that due to homogeneous broadening. As a result, these distributions have a narrower FWHM but wider tails than comparative Gaussian distributions and do not have a distinct mean value nor a (the latter is defined from the former). 

Forced resonance devices are better suited for lower elasticity samples like dilute polymer solutions. A mass is oscillated sinusoidally to the resonant frequency of the sample-apparatus combination. The resonant frequency with and without the sample and the energy used to drive at resonance allow calculation of G and G". These devices operate at around 1000Hz. Since both measurements are made on the oscillator, it can be conveniently immersed into a lab beaker or even process equipment as discussed in Section 8.6 (Nametre, 1990). Several different stiffness lumps have been mounted on one shaft to allow G and G" to be determined at several frequencies in one loading (Ferry, 1980 Knudsen et al., 1992). 

The complex dynamic Young s modulus can be determined from the response of a bar-shaped test specimen in a forced-resonance method (186). A shaker drives one end of the specimen (nominally 100 x 6 x 6 mm). Miniature accelerometers are used to measure the driving point acceleration at the shaker and the response of the test specimen as shown in Figure 6. The output signals from the accelerometers are analyzed by a dual-channel fast Fourier transform spectrum analyzer. The analyzer determines the acceleration ratio and phase difference of the two accelerometers, and also provides a random noise source to drive the shaker over... 

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