Optical interferometry and Gaia parallaxes for a robust calibration of the Cepheid distance scale

We present the modeling tool we developed to incorporate multi-technique observations of Cepheids in a single pulsation model: the Spectro-Photo-Interferometry of Pulsating Stars (SPIPS). The combination of angular diameters from optical interferometry, radial velocities and photometry with the coming Gaia DR2 parallaxes of nearby Galactic Cepheids will soon enable us to calibrate the projection factor of the classical Parallax-of-Pulsation method. This will extend its applicability to Cepheids too distant for accurate Gaia parallax measurements, and allow us to precisely calibrate the Leavitt law's zero point. As an example application, we present the SPIPS model of the long-period Cepheid RS Pup that provides a measurement of its projection factor, using the independent distance estimated from its light echoes.

Pulsation Energy in the Suction Manifold of a Reciprocating Compressor as a Measure for Parameter Sensitivity

Gas pulsations in a compressor suction manifold radiate noise and reduce the efficiency of the compressor. The objective of this paper is to identify and quantify the effects of modeling assumptions and uncertainties in input parameters on the pulsation model output predictions and to estimate the sensitivity of the model to changes in the input design parameters. A unique method of sensitivity analysis is presented that uses the total pulsation energy in the suction manifold of a compressor as a measure of gas pulsations. This method is used to determine the sensitivity of the gas pulsations in the suction manifold to input design parameters. First, the gas pulsations in the suction manifold are calculated using linear acoustic theory. Second, the effects of varying several different design parameters of the suction manifold on gas pulsations are analyzed, and the three most important parameters are selected. Next, energy due to gas pulsations in the suction manifold due to these design parameter variations is calculated. Suction manifold radius was identified as the most critical parameter, followed by width and depth. The optimized values of manifold radius resulted in an overall reduction of up to 24% in the gas pulsation energy compared to the pulsation energy at the nominal design parameter values in the suction manifold.

Pressure Pulsation Analysis of Aircraft Hydraulic Power Pipelines System

The output pressure pulsation model for the aircraft hydraulic power pipelines was established by the methods of transfer function and fluid network chain-rules; the dissipation caused by frequency-dependent friction was taken into account. Dynamic characteristics of hydraulic system were discussed in frequency-domain and time-domain respectively, the pumping excitation frequency influenced the frequency-response of hydraulic pipeline system, and several resonance frequency bands were obtained. The inverse fast Fourier transform was applied to simulate the transient pressure pulsation waves under pump starting and steady-running state.

Active Air Control System Development Using Charge Air Integrated Manifold Engine Numerical Simulation (CAIMENS)

This paper reports on an investigation into the transient, compressible flow physics that impact the trapped equivalence ratio. A comprehensive, variable geometry, multicylinder turbocharger-reciprocating engine computer simulation (T-RECS) has been developed to illustrate the effect of airflow imbalance on an engine. A new model, the charge air integrated manifold engine numerical simulation (CAIMENS), is a manifold flow model coupled with the T-RECS engine processor that uses an integrated set of fundamental principles to determine the crank angle-resolved pressure, temperature, burned and unburned mass fractions, and gas exchange rates for the cylinder. CAIMENS has the ability to show the transient impact of one cylinder firing on each successive cylinder. The pulsation model also describes the impact of manifold pressure drop on in-cylinder peak pressure and the pressure wave introduced to the intake manifold by uncovering the intake ports. CAIMENS provides the information necessary to quantify the impact of airflow imbalance, and allows for the visualization of the engine system before and after airflow correction. The model shows that not only does the manifold pressure drop have a significant impact on the in-cylinder peak pressure but it also has an impact on the pressure wave introduced to the intake manifold as the ports are opened. Also, each cylinder has a considerable impact on the airflow into each successive cylinder.

The Variability Of RSG : HV2576

The Harvard Variable HV2576, as a red supergiant in the Large Magallanic Cloud, has a complex light variation, which is not explained well. The existing one-period non-linear pulsation model deviated clearly from its light curve. We tried to fit the light curve by a superposition of several harmonic pulsations. By using the PDM, PERIOD04 and SparSpec codes to analyze the light variation, two periods with 525 and 261 days are well established. Furthermore, the 261-day period is found to change according to the wavelet analysis. In addition, the noise obeying the 1/f law. Based on all these facts, we suggest that the light variation of HV2576 may be due to huge convection cells that interplay with oscillation or the third very long period.