Laboratory-scale investigation of a periodically forced stratified basin with inclined endwalls

We present results of numerical simulations of a stratified reservoir with a three-layer stratification, subject to an oscillating surface shear stress. We investigate the effect of sloped endwalls on mixing and internal wave adjustment to forcing within the basin, for three different periods of forcing. The simulations are carried out at a laboratory scale, using large-eddy simulation. We solve the three-dimensional Navier–Stokes equations under the Boussinesq approximation using a second-order-accurate finite-volume solver. The model was validated by reproducing experimental results for the response of a reservoir to surface shear stress and resonant frequencies of internal waves. We find interesting combinations of wave modes and mixing under variation of the forcing frequencies and of the inclination of the endwalls. When the frequency of the forcing is close to the fundamental mode-one wave frequency, a resonant internal seiche occurs and the response is characterized by the first vertical mode. For forcing periods twice and three times the fundamental period, the dominant response is in terms of the second vertical mode. Adjustment to forcing via the second vertical mode is accompanied by the cancellation of the fundamental wave and energy transfer to higher-frequency waves. The study shows that the slope of the endwalls dramatically affects the location of mixing, which has a feedback on the wave field by promoting the generation of higher vertical modes.

Fans arrangement analysis in oil forced air natural cooling method of power transformer radiator

The cooling of radiators in power transformers employing natural oil-air forced method is the purpose of this study. Two modes used for cooling fans, namely vertical and horizontal placement, will be compared as well. Four sets of radiators have been studied in this research, and in each set, 14 fins and three fans with a diameter of half a meter have been used. The fans will be arranged such that three of them will be placed under the radiator (in vertical position) in the first case, while in the second case, they will be located in one side of the radiator (in horizontal position). The results derived from the comparisons indicate the superiority of the horizontal mode in heat transfer against the vertical mode. Furthermore, it is notable that if the internal fan is disconnected, the cooling can be enhanced with the help of some existing points in the vertical mode. The improvement in heat transfer rate can be observed through locating the vertical fans optimally, once compared to the horizontal placement. The lower reliability of the vertical mode can be detected once the side fans are disconnected, while in any cases, the heat transfer superiority is achievable for horizontal mode. That is because, the disconnection of one of the fans, leads to the negligence of the radiators major parts in the vertical mode.

Numerical and Observational Analysis of the Hydro-Dynamical Variability in a Small Lake: The Case of Lake Zirahuén, México

Lake Zirahuén is one of the ecologically better preserved and small-sized lakes in Mexico. Observations revealed that Lake Zirahuén is subjected to a consistent diurnal wind because of the presence of a valley–mountain breeze that triggers semidiurnal and 3–8 h variability oscillations, with the latter among the natural frequencies of the lake, whereas the former and the principal forcing are in near resonance with the second vertical mode. The thermodynamic variability was greater in the metalimnion where the analysis of eigenfunctions shows that higher modes (>2) are important at depths below the thermocline. The numerical modeling adequately described the water temperature evolution and surface layer currents in an averaged manner. The daily observations showed drifts in surface currents, acquiring velocities of up to 0.1 m/s, owing to wind stress, which caused an increase in temperature at the northern section of the lake. Data averaged over three months revealed that the surface currents flow northward with an anticyclonic return to the east part and a pair of cyclonic returns to the northwestern and southwestern parts of the lake; whereas at the vertical, the structure showed two circular regions divided by the thermocline located at a depth of 15–20 m.

Normal Mode Spectra of Idealized Baroclinic Waves

Normal modes are used to investigate the contributions of geostrophic vortices and inertia–gravity waves to the energy spectrum of an idealized baroclinic wave simulation. The geostrophic and ageostrophic modal spectra (GE and AE, respectively) are compared to the rotational and divergent kinetic energy (RKE and DKE, respectively), which are often employed as proxies for vortex and wave energy. In our idealized f-plane framework, the horizontal modes are Fourier, and the vertical modes are found by solving an appropriate eigenvalue problem. For low vertical mode number n, both the GE and AE spectra are steep; however, for higher n, while both spectra are shallow, the AE is shallower than the GE and the spectra cross. The AE spectra are peaked at the Rossby deformation wavenumber knR, which increases with n. Analysis of the horizontal mode equations suggests that, for large wavenumbers k≫knR, the GE is approximated by the RKE, while the AE is approximated by the sum of the DKE and potential energy. These approximations are supported by the simulations. The vertically averaged RKE and DKE spectra are compared to the sum of the GE and AE spectra over all vertical modes; the spectral slopes of the GE and AE are close to those of the RKE and DKE, supporting the use of the Helmholtz decomposition to estimate vortices and waves in the midlatitudes. However, the AE is consistently larger than the DKE because of the contribution from the potential energy. Care must be taken when diagnosing the mesoscale transition from the intersection of the vortex and wave spectra; GE and AE will intersect at a different scale than RKE and DKE, despite their similar slopes.

Coupled and Multimode Tailboom Vibration Control Using Fluidic Flexible Matrix Composite Tubes

This paper covers the modeling and testing of a helicopter tailboom integrated with a fluidic flexible matrix composite (F2MC) damped vibration absorber. In an advance over previous work, the F2MC absorber presented in this paper treats a combination of tailboom lateral, torsional, and vertical vibrations. A finite element structural model of a laboratory-scale tailboom is combined with a model of attached F2MC tubes and a tuned fluidic circuit. Vibration reductions of over 75% in a coupled 26.8-Hz lateral bending/torsion tailboom mode are predicted by the model and measured experimentally. These results demonstrate that F2MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A new absorber with a fluidic circuit that targets two tailboom vibration modes is designed and experimentally tested. On the lab-scale tailboom testbed, the absorber with this circuit is shown to provide vibration reductions of over 60% in both a 12.2-Hz vertical mode and a 26.8-Hz lateral bending/torsion mode. Using this new absorber, vertical and lateral/torsion mode damping are achieved with almost no added weight relative to a purely vertical absorber.

Vertical Modes and Effective Stability of Quasi-2-Day Waves

A quasi-2-day wave is known as a convectively coupled westward inertia–gravity (WIG) wave with a shallower equivalent depth (or slower phase speed) than the dry counterpart. This study investigates the relationship between the phase speed of quasi-2-day waves and effective static stability in terms of a vertical mode perspective. By using WIG filters with different equivalent depths, different phases of the 2-day wave are identified by filtering brightness temperature data obtained from geostationary satellites. The composite time series and the vertical modes in the tropical atmosphere are calculated from reanalysis data. The large-scale dynamical fields of the composite WIG waves are explained by the superposition of the first four baroclinic modes. Phase speed of the moist vertical mode is computed by applying the Radon transform to the mode transform coefficient. Different vertical modes share a common phase speed, which is slower than its dry counterpart, implying that the wave is not dispersive. To address the question of what slows the vertical modes, the effective static stability is evaluated by defining the degree of cancellation between diabatic heating and adiabatic cooling due to the ascent. This cancellation is confirmed to be almost complete for the first baroclinic mode as expected theoretically. The effective static stability is found to be higher for a higher vertical mode, but this change over different vertical modes is not as rapid as predicted from nondispersiveness. Possible reasons for this disagreement are discussed herein.

Early steps in the evolution of vertical transmission revealed by a plant-bacterium symbiosis

ABSTRACTVarious plant species establish intimate symbioses with bacteria within their aerial organs. The bacteria are contained within nodules or glands often present in distinctive patterns on the leaves in what is commonly referred to as leaf nodule symbiosis. We describe here a highly specific symbiosis between a wild yam species from Madagascar, Dioscorea sansibarensis and bacteria of the species Orrella dioscoreae. Using whole genome sequencing of plastid and bacteria from wild-collected samples, we show phylogenetic patterns consistent with a vertical transmission of the symbionts. Unique among leaf nodule symbioses, the bacteria can be cultured and are amenable to comparative transcriptomics and phenotypic characterization, revealing a potential role in complementing the host’s arsenal of secondary metabolites. We propose a very recent acquisition of the vertical mode of transmission in this symbiosis which, together with a large effective populations size explain the cultivability and remarkable lack of genome reductive evolution in O. dioscoreae. We leverage these unique features to reveal pathways and functions under positive selection in these specialized endophytes, highlighting the mechanisms enabling a permanent association in the phyllosphere.