Kenneth G. McConnell

A model to predict the coupled axial torsion properties of ACSR electrical conductors

The modeling of ACSR (aluminum-conductor steel-reinforced) electrical conductors for dynamic analysis requires some knowledge of the mechanical properties of the conductor. It was found both experimentally and theoretically, using a simple strength of materials approach, that the axial-torsional behavior of ACSR conductors is highly coupled; i.e., axial motion causes torsional motion and vice versa. Although wind-induced oscillation of ACSR power lines has been observed for years, the importance of axial-torsional coupling has not been generally recognized, nor studied. A simplified mathematical model correlated well with experimental measurements for this type of coupled mechanical behavior. It is hoped that being able to control the amount of coupling through cable design may lead to better control of wind-induced oscillations.

A study of the axial-torsional coupling effect on a sagged transmission line

Two mechanisms have been proposed to explain the low-frequency phenomenon of power-transmission-line galloping: the Den Hartog theory and the torsional theory. The current study proposes that the axial-torsional coupling parameter provides one tentative explanation for the torsional theory. Simpsons dynamic model was used as the basic model with modifications made to incorporate the mechanical coupling effects between axial tension and torsion of the conductor. Both the cubic-spline and the Runge-Kutta numerical techniques were used in a computer simulation of conductor dynamics. The validity of the computer-simulation results was checked against the taut string model, Sheas critical-sag criterion, and experiments with a thin-wire catenary. The results from this study show that vertical motion can be mechanically induced by the torsional motion of the cable in the absence of any air flow.

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.

Using strain gages to measure both strain and temperature

A transducer is proposed that measures both temperature and strain by using two different strain gages. The theoretical basis for designing such a transducer is developed. Experimental results indicate that the temperature signal can be measured satisfactorily.

The measurement of flexural stiffness of multistranded electrical conductors while under tension

The ACSR Electrical conductor is a complex structure composed of layers of aluminum wires wrapped around one another over a steel-wire core. Three different test arrangements were considered for testing the static flexural stiffness. The cross-load method was easiest to implement and avoided the problems with load-spacing sensitivity of the couple method which used two forcesQ. However, the maximum usable value of λ for test method one was around 6 or 7. This meant that the test spant had to be changed to satisty this requirement.The experimental results indicate that the static flexural stiffness increased with both axial load and clamping with automotive-type hose clamps. The static values ofEI were closer to the theoretical values predicted by the individual strand assumption than to the solid-body assumption. The dynamic results of Seppa5 and Claren and Diana6 place the flexural stiffness in the range of 74 to 91 percent of the theoretical maximum of the solid body assumption. Thus, it appears that a wide range ofEI values can be obtained under field conditions dependent on both conductor tension and frequency of oscillation.Both testing and calculation showed that cableEI was not a significant factor in modeling the static-equilibrium position of the cable bundles except around the cable supports. The question of dynamic modeling was not addressed as it was the object of the study of obtain what appeared to be the best twisted-bundle configuration by measuring the static-equilibrium positions of the model bundles.

From field vibration data to laboratory simulation

The objective of a test program is to simulate a specified dynamic environment. The question is: How do I go from field-test data to a reasonable laboratory or finite-element simulation? This paper looks at a simple situation of a two degree-of-freedom vehicle that has a broadband excitation source and a two degree-of-freedom test item that can be attached to the vehicle. The paper shows that significantly different field data are obtained depending on field-test conditions, and vastly different simulation results are obtained when using these different field data as laboratory inputs.A relatively simple theoretical model is developed that explains how field data in this case can be modified in the frequency domain to obtain a more realistic laboratory test environment. This presentation shows that a general theory of vibration testing is needed, a theory that provides guidelines for this process of obtaining field data and developing realistic test specifications.

Damping characterization of a filled epoxy used for dynamic structural modeling

This paper presents information on the usefulness of a particular aluminum-particle-filled epoxy for dynamic modeling. Damping characteristics in terms of the loss factor are presented for this epoxy and some structural metals. Though the damping of the epoxy was larger than that of any metal tested, it can still be considered small. Portal frames were modeled using the epoxy. Natural frequencies of vibration for the metal frames and epoxy models were determined. The scaled-epoxy-model frequencies accurately predicted the metal prototype frequencies. A possible area of error is pointed out with respect to the modeling of the shear modulus.

Zero-shift values of automatic and inexpensive strain-gage instrumentation systems

Computer-controlled data-acquisition systems are being used extensively for gathering strain-gage data. This paper explores the relative merits of using modern solidstate digital multi-meters (DDM) to measure the strain-gage resistance directly rather than using a conventional Wheatstone bridge. Both a direct-resistance measurement scheme and a reversed current scheme are compared over long measurements terms of 6 and 12 days using a 6 1/2-digit multimeter. The results show that the reversed current method is superior in maintaining the zero-gage resistance reading at the cost of using several meters. Possibly the direct-resistance method can be improved so that the operation and equipment can be simplified.

Numerically Simulated Results for a Deterministic Excitation with no External Loads

This paper presents a numerical example of the theory presented in Part I [1] where a model is developed to describe the requirements for laboratory simulations of field vibration environments. This example illustrates the application of such a model to simulated data in order to evaluate its accuracy in predicting field interface forces and motions, and in using field data to define appropriate test item inputs in laboratory simulations. It is assumed that no external forces act on the test item in either the field or laboratory environments. All Frequency response functions (FRFs) are calculated for all test structures from a multi degree of freedom (MDOF) discrete linear system. The equations developed in Ref. [1] are employed to estimate field interface forces and test item motions as well as to define test item inputs in the laboratory simulation. The test item motions obtained in all laboratory simulations are compared with the corresponding field motions.

Base strain effects on force measurements

Force transducers directly interact with their environment. In this study, a force transducer is attached to the midpoint of a free-free beam and is used to measure the force on a rigid mass that vibrates with the beam. The ratio of force to mass times acceleration is measured for several different masses over a frequency range that includes the first four odd natural frequencies of the beam. Then the force transducer is mounted so that the beams strain is isolated from the transducer. The tests are repeated. The results dramatically illustrate the effects of base strain on the force measurements. A simple theoretical model is developed that explains the vertical axis shift in the calibration curve.