The frequency components of fluid-lift forces acting on a cylinder oscillating in still water

A circular cylinder oscillating with sinusoidal motion in still water is a simple experimental model of circular structural members exposed to continuous wave motion. The measured fluid forces are analyzed using a unique Fourier technique from which fluid-force components can be understood and predicted for structural analysis.     

Active notch filters for extending frequency response of accelerometers

The useable frequency range of lightly damped accelerometers is limited to 0.2 of their mounted natural frequency for amplitude distortions of less than 5 percent, while phase distortion is not a major problem until near resonance. There have been situations where the measured motion contains unforeseen high-frequency components which are distorted due to the accelerometer transfer function. There are several ways to overcome amplitude distortion of the higher-than-anticipated frequency components: (1) change instrumentation to an accelerometer which has a higher natural frequency, (2) establish data-analysis techniques which will account for the amplitude distortion, or (3) set up a notch filter circuit which has a transfer function that is the reciprocal of the accelerometer transfer function. The objective of this paper is to present several such circuits and to discuss what happens when the transfer functions are mismatched as to natural frequency of the accelerometer vs. the center frequency of the filter and accelerometer damping vs. filter damping. The results show that the useful frequency range of the accelerometer can be extended to near resonance if (a) the accelerometer-mounted natural frequency and the filter center frequency are matched within ±2 percent and (b) the damping ratios are matched within a factor of two.     

Nuclear magnetic spin-rotational relaxation times for linear molecules

The stochastic differential equation study of nuclear magnetic relaxation by spin-rotational interactions is applied to the linear rotator model of the molecule. Inertial effects are included in the calculations, which are performed analytically. Expressions are derived for the spin-rotational contributions to the longitudinal and transverse relaxation times, and for the spin-rotational correlation time.     

Experimental cross verification of damping in three metals

In order to ensure a valid damping measurement based on a proposed mathematical model, various laboratory techniques may be employed which require relatively simple instrumentation from which cross correlation of the data may be obtained. Measurements were made (utilizing an accelerometer, strain gages, and a sound-level meter) under forced (3-dB frequency band or amplification factor Q) and free-vibration conditions at the fundamental and higher axial modes. Analysis (based on the viscous and complex-moduli theories) of the material damping of an aluminum alloy 2024-T4 in longitudinal vibrations shows good cross correlation between theories and experimental methods. These methods were extended to damping measurements of yellow brass and commercial steel. A multiple regression analysis was employed in the damping data reduction and was found to be useful in eliminating the data scatter. A sound-level meter was used as a noncontacting test method which proved useful even though its use does have drawbacks.     

Unleashing a Microcomputer in the Laboratory,Part III

Experimental Techniques -     

A mathematical model of hysol 8705 under impact loading

The mechanical properties of Hysol 8705,a low-modulus viscoelastic material, were investigated experimentally under impact loading. The experimental results reveal that the material behavior under investigation is nonlinear. Empirical relationships between various important parameters, which characterize the mechanical properties of the material, were established. A three-parameter solid type of mathematical model consisting of a spring and Kelvin element in series was found to satisfactorily reproduce the experimental impact-property data of this material. The spring and dashpot elements were found to be nonlinear and strain-rate dependent.     

The Controlled Release of Bioactive Compounds from Polymeric Systems

The ability to effect profound changes in the growth and behavior of living systems through the application of minute quantities of biologically active compounds has lead to development of the multibillion dollar pest control industry. Indeed, the introduction of modern chemical pesticides was originally thought to represent the “ultimate weapon” in man's age-old battle with pests [1]. Not until the late fifties and early sixties was it recognized that the continued use of this weapon, in its present form, might well result in a Pyrrhic victory for man. As a consequence of this realization, the concept of efficient pest control has undergone considerable modification in recent years. The undesirable secondary and tertiary effects of the highly successful long-lived pesticides has caused their use to be severely restricted [2]. An additional general concern is the often gross excess of applied pesticide in relation to that necessary to achieve control of the pest in the target area. For example, depending on the method of application and the climatic conditions, as much as 60 to 90% of the applied pesticide never reaches its objective [3]. In addition, the effective concentration of the pesticide is further reduced by leaching and soil erosion after application [4, 5].