Practical considerations in aeroelastic design

The structural design process for large transport aircraft is described. Critical loads must be determined from a large number of load cases within the flight maneuver envelope. The structural design is also constrained by considerations of producibility, reliability, maintainability, durability, and damage tolerance, as well as impact dynamics and multiple constraints due to flutter and aeroelasticity. Aircraft aeroelastic design considerations in three distinct areas of product development (preliminary design, advanced design, and detailed design) are presented and contrasted. The present state of the art is challenged to solve the practical difficulties associated with design, analysis, and redesign within cost and schedule constraints. The current practice consists of largely independent engineering disciplines operating with unorganized data interfaces. The need is then demonstrated for a well-planned computerized aeroelastic structural design optimization system operating with a common interdisciplinary data base. This system must incorporate automated interfaces between modular programs. In each phase of the design process, a common finite-element model for static and dynamic optimization is required to reduce errors due to modeling discrepancies. As the design proceeds from the simple models in preliminary design to the more complex models in advanced and detailed design, a means of retrieving design data from the previous models must be established

Effect of side chains on the dielectric properties of alkyl esters derived from palm kernel oil

Alkyl ester derivatives were synthesized from laboratory purified palm kernel oil. The steps in the synthesis involved transesterification of palm kernel oil to produce a methyl ester, followed by epoxidation and then the grafting of side chains by esterification with propionic and butyric anhydride. The dielectric and thermal properties of the ester derivatives were analyzed and compared with the methyl ester. The melting point of the ester derivatives were found to reduce with side chain attachment and antioxidant improved its thermal stability. The dielectric loss was dominated by mobile charged particles and the chemical modification appeared to increase the rate at which electric double layer was formed at the electrode-liquid interface. The esters possessed excellent breakdown strengths suggesting that the processing to optimize their physical properties did not have a negative influence on their electrical breakdown strength. This product may prove useful as an insulation fluid in Electrical Power Transformers

Influence of the temperature on the dielectric properties of epoxy resins

Electrical degradation processes in epoxy resins, such as electrical treeing, were found to be dependent on the temperature at which the experiments were carried out. Therefore, it is of considerable research interest to study the influence of temperature on the dielectric properties of the polymers and to relate the effect of temperature on these properties to the possible electrical degradation mechanisms. In this work, the dielectric properties of two different epoxy resin systems have been characterized via dielectric spectroscopy. The epoxy resins used were bisphenol-A epoxy resins Araldite CY1301 and Araldite CY1311, the later being a modified version of the former with added plasticizer. The CY1301 samples were tested below and above their glass transition temperature, while the CY1311 were tested well above it. Both epoxy systems possess similar behaviour above the glass transition temperature, e.g. in a flexible state, which can be characterized as a low frequency dispersion (LFD). On the other hand, it was found that below the glass transition temperature CY1301 samples have almost “flat” dielectric response in the frequency range considered. The influence of possible interfacial features on the measured results is discussed

Influence of absorbed moisture on the dielectric properties of epoxy resins

The dielectric response of two bisphenol-A epoxy resin systems Araldite CY1301 (Tg ~ 50°C) and Araldite CY1311 (Tg ~0°C) was studied at different levels of absorbed moisture. The dielectric measurements were carried out over the frequency range 1 mHz to 100 kHz and the results were characterised in terms of dc bulk electrical conduction and dielectric processes. The characteristic parameters (frequency and magnitude) of all processes have been found to be moisture dependent. In both resins above the glass transition temperature, absorbed moisture was found to be implicated in the formation of a bulk quasi-dc dielectric response consistent with cluster formation of the absorbed water molecules

The measurement of very low conductivity and dielectric loss in XLPE cables: A possible method to detect degradation due to thermal aging

The dielectric response of crosslinked polyethylene (XLPE) insulated, miniature power cables, extruded with inner and outer semicons, was measured over the frequency range 10-4 to 104 Hz at temperatures from 20 to 100 °C. A dielectric spectrometer was used for the frequency range 10-4 to 10-2 Hz. A bespoke noise-free power supply was constructed and used to measure the dc conductivity and, using a Fourier transform technique, it was also used to measure the very low dielectric tanδ losses encountered at frequencies of 1 to 100 Hz. Tanδ measurements of <;10-5 were found in this frequency range and attributed to a β-mode dielectric relaxation lying above 100 Hz due to motion of chain segments in the amorphous region and an β-mode relaxation lying below 1 Hz window due to twists of chains in the crystal lamellae. The dc conductivity measurements were consistent with those of the dielectric spectrometer and indicate lower dc conductivities in vacuum degassed cables than have been previously reported for XLPE (less than 10-17 S.m-1). The conduction process is thermally activated with an activation energy of approximately 1.1 eV. Higher conductivities were found for non-degassed cables. A transformer ratio bridge was used for measurements in the range 1 to 10 kHz; loss in this region was shown to be due to the series resistance of the semicon layers. Thermal ageing of the cables at 135 °C for 60 days caused significant increases in the conductivity and tanδ and it is considered that such measurements may be a sensitive way of measuring electrical degradation due to thermal aging

Localized matter-waves patterns with attractive interaction in rotating potentials

We consider a two-dimensional (2D) model of a rotating attractive Bose-Einstein condensate (BEC), trapped in an external potential. First, an harmonic potential with the critical strength is considered, which generates quasi-solitons at the lowest Landau level (LLL). We describe a family of the LLL quasi-solitons using both numerical method and a variational approximation (VA), which are in good agreement with each other. We demonstrate that kicking the LLL mode or applying a ramp potential sets it in the Larmor (cyclotron) motion, that can also be accurately modeled by the VA.Comment: 13 pages, 11 figure

Effects of temperature upon the collapse of a Bose-Einstein condensate in a gas with attractive interactions

We present a study of the effects of temperature upon the excitation frequencies of a Bose-Einstein condensate formed within a dilute gas with a weak attractive effective interaction between the atoms. We use the self-consistent Hartree-Fock Bogoliubov treatment within the Popov approximation and compare our results to previous zero temperature and Hartree-Fock calculations The metastability of the condensate is monitored by means of the $l=0$ excitation frequency. As the number of atoms in the condensate is increased, with $T$ held constant, this frequency goes to zero, signalling a phase transition to a dense collapsed state. The critical number for collapse is found to decrease as a function of temperature, the rate of decrease being greater than that obtained in previous Hartree-Fock calculations.Comment: 4 pages LaTeX, 3 eps figures. To appear as a letter in J. Phys.

Aging of Kraft paper insulation in natural ester dielectric fluid

The aging behavior of transformer insulation Kraft paper aged in a natural ester oil, recently developed from palm kernel oil, is compared to the behavior of paper samples aged in mineral insulating oil. This study aimed to investigate the effect of the natural ester oil on the aging of cellulose insulation paper if used as an alternative insulating fluid in transformers. Thermally upgraded insulation paper was aged in both insulating fluids together with strips of galvanized steel, copper and aluminium to represent the transformer, under nitrogen pressure in a sealed mild steel pressure vessel for 150 degC for 28, 56, and 84 days. The degradation after aging was assessed using tensile strength and breakdown strength measurements of the paper. The paper samples impregnated with natural ester fluid exhibited similar behavior before and after aging, with an approximately 5% reduction in tensile strength after 28 days of ageing. Two sets of response were obtained for paper samples aged in mineral insulating oil under the same ageing conditions; the paper closer to the copper strips had a faster degradation rate (~35% reduction). The natural ester fluid retarded the aging of the Kraft paper. The characteristic breakdown strength of natural ester impregnated paper was found to be, on the average, 42% better than that of mineral oil impregnated paper

Electrical Conduction and Dielectric Breakdown Characteristics of Alkyl Ester Dielectric Fluids obtained from Palm Kernel Oil

Naturally occurring palm kernel oil (PKO) and its ester derivatives are being considered as sustainable alternatives to synthetic oils for use as dielectric fluids. This paper reports on their dielectric properties, which have been studied and compared to BS148 mineral oil. The low frequency complex dielectric response of the PKO and its derivatives are related to ionic conduction and electrode polarization phenomena. The purified PKO has an electrical conductivity of 3.04 ?? 10-12 Sm-1 at 30°C; this is 10 times lower than crude PKO but about 10 times greater than the BS148 oil. The bulk conductivity is thermally activated, activation energy = 0.47 eV, and influenced by viscosity. The ester derivatives have a higher conductivity than the PKO, which is related to ionic impurities introduced during processing. The breakdown field was measured in a bespoke cell enabling smaller volumes of oil (15 ml) than that used in ASTM D1816. The characteristic ac breakdown strength of purified PKO and is alkyl esters were found to be in the range, 41 to 43 kV/mm, which is significantly higher than the mineral oil (27 kV/mm). The results support the proposition that a dielectric fluid derived from palm kernel oil, once re-purified, may be a suitable replacement for mineral oil based fluids in HV electrical equipment

Collective excitations of atomic Bose-Einstein condensates

We apply linear-response analysis of the Gross-Pitaevskii equation to obtain the excitation frequencies of a Bose-Einstein condensate confined in a time-averaged orbiting potential trap. Our calculated values are in excellent agreement with those observed in a recent experiment.Comment: 11 pages, 2 Postscript figures, uses psbox.tex for automatic figure inclusion. More info at http://amo.phy.gasou.edu/bec.htm