Added mass and wave radiation damping for flow-induced rotational vibrations of skinplates of hydraulic gates

One observed vibration mode for Tainter gate skinplates involves the bending of the skinplate about a horizontal nodal line. This vibration mode can be approximated as a streamwise rotational vibration about the horizontal nodal line. Such a streamwise rotational vibration of a Tainter gate skinplate must push away water from the portion of the skinplate rotating into the reservoir and draw water toward the gate over that portion of the skinplate receding from the reservoir. The induced pressure is termed the push-and-draw pressure. In the present paper, this push-and-draw pressure is analyzed using the potential theory developed for dissipative wave radiation problems. In the initial analysis, the usual circular-arc skinplate is replaced by a vertical, flat, rigid weir plate so that theoretical calculations can be undertaken. The theoretical push-and-draw pressure is used in the derivation of the non-dimensional equation of motion of the flow-induced rotational vibrations. Non-dimensionalization of the equation of motion permits the identification of the dimensionless equivalent added mass and the wave radiation damping coefficients. Free vibration tests of a vertical, flat, rigid weir plate model, both in air and in water, were performed to measure the equivalent added mass and the wave radiation damping coefficients. Experimental results compared favorably with the theoretical predictions, thus validating the theoretical analysis of the equivalent added mass and wave radiation damping coefficients as a prediction tool for flow-induced vibrations. Subsequently, the equation of motion of an inclined circular-arc skinplate was developed by incorporating a pressure correction coefficient, which permits empirical adaptation of the results from the hydrodynamic pressure analysis of the vertical, flat, rigid weir plate. Results from in-water free vibration tests on a 1/31-scale skinplate model of the Folsom Dam Tainter gate are used to demonstrate the utility of the equivalent added mass coefficient.

Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer

Over the recent years chirped-pulse, Fourier-transform microwave (CP-FTMW) spectrometers have chan- ged the scope of rotational spectroscopy. The broad frequency and large dynamic range make possible structural determinations in molecular systems of increasingly larger size from measurements of heavy atom (13C, 15N, 18O) isotopes recorded in natural abundance in the same spectrum as that of the parent isotopic species. The design of a broadband spectrometer operating in the 2–8 GHz frequency range with further improvements in sensitivity is presented. The current CP-FTMW spectrometer performance is benchmarked in the analyses of the rotational spectrum of the water heptamer, (H2O)7, in both 2– 8 GHz and 6–18 GHz frequency ranges. Two isomers of the water heptamer have been observed in a pulsed supersonic molecular expansion. High level ab initio structural searches were performed to pro- vide plausible low-energy candidates which were directly compared with accurate structures provided from broadband rotational spectra. The full substitution structure of the most stable species has been obtained through the analysis of all possible singly-substituted isotopologues (H218O and HDO), and a least-squares rm(1) geometry of the oxygen framework determined from 16 different isotopic species compares with the calculated O–O equilibrium distances at the 0.01 Å level.

Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer

Over the recent years chirped-pulse, Fourier-transform microwave (CP-FTMW) spectrometers have changed the scope of rotational spectroscopy. The broad frequency and large dynamic range make possible structural determinations in molecular systems of increasingly larger size from measurements of heavy atom (C-13, N-15, O-18) isotopes recorded in natural abundance in the same spectrum as that of the parent isotopic species. The design of a broadband spectrometer operating in the 2-8 GHz frequency range with further improvements in sensitivity is presented. The current CP-FTMW spectrometer performance is benchmarked in the analyses of the rotational spectrum of the water heptamer, (H2O)(7), in both 2-8 GHz and 6-18 GHz frequency ranges. Two isomers of the water heptamer have been observed in a pulsed supersonic molecular expansion. High level ab initio structural searches were performed to provide plausible low-energy candidates which were directly compared with accurate structures provided from broadband rotational spectra. The full substitution structure of the most stable species has been obtained through the analysis of all possible singly-substituted isotopologues ((H2O)-O-18 and HDO), and a least-squares r(m)((1)) geometry of the oxygen framework determined from 16 different isotopic species compares with the calculated O-O equilibrium distances at the 0.01 angstrom level. (C) 2013 Elsevier B.V. All rights reserved.

Intermolecular Clamping by Hydrogen Bonds: 2-Pyridone center dot NH3

A combined spectroscopic and ab initio theoretical study of the doubly hydrogen-bonded complex of 2-pyridone (2PY) with NH3 has been performed. The S-1 <- S-0 spectrum extends up to approximate to 1200 cm(-1) above the 0(0)(0) band, close to twice the range observed for 2PY. The S-1 state nonradiative decay for vibrations above approximate to 300 cm(-1) in the NH3 complex is dramatically slowed down relative to bare 2PY. Also, the Delta v=2,4,... overtone bands of the v(1)' and v(2)' out-of-plane vibrations that dominate the low-energy spectral region of 2PY are much weaker or missing for 2PY center dot NH3, which implies that the bridging (2PY)NH center dot center dot center dot NH3 and H2NH center dot center dot center dot O=C H-bonds clamp the 2PY at a planar geometry in the S-1 state. The mass-resolved UV vibronic spectra of jet-cooled 2PY center dot NH3 and its H/D mixed isotopomers are measured using two-color resonant two-photon ionization spectroscopy. The S-0 and S-1 equilibrium structures and normal-mode frequencies are calculated by density functional (B3LYP) and correlated ab initio methods (MP2 and approximate second-order coupled-cluster, CC2). The S-1 <- S-0 vibronic assignments are based on configuration interaction singles (CIS) and CC2 calculations. A doubly H-bonded bridged structure of C-S symmetry is predicted, in agreement with that of Held and Pratt [J. Am. Chem. Soc. 1993, 115, 9718]. While the B3LYP and MP2 calculated rotational constants are in very good agreement with experiment, the calculated H2NH center dot center dot center dot O=C H-bond distance is approximate to 0.7 angstrom shorter than that derived by Held and Pratt. On the other hand, this underlines their observation that ammonia can act as a strong H-bond donor when built into an H-bonded bridge. The CC2 calculations predict the H2NH center dot center dot center dot O distance to increase by 0.2 angstrom upon S-1 <- S-0 electronic excitation, while the (2PY)NH center dot center dot center dot NH3 H-bond remains nearly unchanged. Thus, the expansion of the doubly H-bonded bridge in the excited state is asymmetric and almost wholly due to the weakening of the interaction of ammonia with the keto acceptor group.

Femtosecond Rotational Raman Coherence Spectroscopy of Cyclohexane in a Pulsed Supersonic Jet

We combine the technique of femtosecond degenerate four-wave mixing (fs-DFWM) with a high repetition-rate pulsed supersonic jet source to obtain the rotational coherence spectrum (RCS) of cold cyclohexane (C(6)H(12)) with high signal/noise ratio. In the jet expansion, the near-parallel flow pattern combined with rapid translational cooling effectively eliminate dephasing collisions, giving near-constant RCS signal intensities over time delays up to 5 ns. The vibrational cooling in the jet eliminates the thermally populated vibrations that complicate the RCS coherences of cyclohexane at room temperature [Bragger, G.; et al. J. Phys. Chem. A 2011, 115, 9567]. The rotational cooling reduces the high-J rotational-state population, yielding the most accurate ground-state rotational constant to date, B(0) = 4305.859(9) MHz. Based on this B(0), a reanalysis of previous room-temperature gas-cell RCS measurements of cydohexane gives improved vibration rotation interaction constants for the v(32), v(6), v(16), and v(24) vibrational states. Combining the experimental B(0)(C(6)H(12)) with CCSD(T) calculations yields a very accurate semiexperimental equilibrium structure of the chair isomer of cyclohexane