Results Of Hydrodynamic Calculations Research Articles

Scattering Study of a Composite Breakwater Placed in Front of an Impermeable Back Wall under the Action of Water Waves

Based on the assumption of linear potential flow theory, the scattering problem of a composite breakwater placed in front of an impermeable back wall is theoretically investigated. The velocity potential in each subregion is found using the eigenfunction expansion method. The boundary conditions of the porous region are treated using Darcy’s law. The semi-analytical solution of a composite breakwater placed in front of an impermeable back wall is then obtained based on the matching conditions of the boundaries of the different regions. The effects of different parameters on the wave loads and wave amplitudes are investigated. In addition, to better understand the performance of the composite breakwater, the scattering problem of the composite breakwater without considering an impermeable back wall is also investigated. The correctness of this theoretical model is verified by comparing the results with previous work. Based on the results of hydrodynamic calculations and analysis of various aspects of a composite breakwater placed in front of an impermeable back wall, the study of the effect of a composite breakwater placed in front of an impermeable back wall allows us to propose a long-term and cost-effective solution for the protection of various marine facilities from wave attacks.

Artificial Neural Network Model for the Evaluation of Added Resistance of Container Ships in Head Waves

The decrease in ship added resistance in waves fits into both the technical and operational measures proposed by the IMO to reduce the emissions of harmful gases from ships. Namely, the added resistance in waves causes an increase in fuel consumption and the emission of harmful gases in order for the ship to maintain the design speed, especially in more severe sea states. For this reason, it is very important to estimate the added resistance in waves with sufficient accuracy in the preliminary design phase. In this paper, the possibility of applying an ANN to evaluate added resistance in waves at the different sea states that the ship will encounter during navigation is investigated. A numerical model, based on the results of hydrodynamic calculations in head waves, and ANN is developed. The model can estimate the added resistance of container ships with sufficient accuracy, based on the ship characteristics, sailing speed, and the sea state using two wave energy spectra.

Third-harmonic generation in an ionized gas and its relation to the residual energy of electrons

The generation of low-order harmonics by a short ionizing laser pulse passing through a gas is investigated in regard to the space-time phase-synchronism conditions. This investigation is based on the results of hydrodynamic calculations for the model of [1] supplemented by taking into account the ionization current [2–5] and on the numerical solution of a one-dimensional time-dependent Schrodinger equation. As applied to the description of the third-harmonic spectrum, the hydrodynamic model with ionization current is shown to be in good agreement with a quantum-mechanical model. In this case, the amplitude of the third harmonic is determined by the intensity of the laser field at the moment of maximal ionization rate; this fact allows one to relate the amplitude of the third harmonic to the residual energy of electrons [5–8] and may provide grounds for the diagnosis of the residual energy by the spectrum of the third harmonic, which is important for the development of X-ray lasers based on ionization nonequilibrium plasma.

Radial pulsations of helium stars and a model for BX CIR

The results of hydrodynamical calculations of radially pulsating helium stars with masses 0.5M ⊙≤M≤0.9M ⊙, bolometric luminosities 600L ⊙≤5×103 L ⊙, and effective temperatures 1.5×104 K≤T eff≤3.5×104 K are presented. The pulsation instability of these stars is due to the effects of ionization of iron-group elements in layers with temperatures T∼2×105 K. The calculations were carried out using opacities for the relative mass abundances of hydrogen and heavy elements X=0 and Z=0.01, 0.015, and 0.02. Approximate formulas for the pulsation constant Q over the entire range of pulsation instability of the hot helium stars in terms of the mass M, radius R, effective temperature T eff, and heavy-element abundance Z are derived. The instability of BX Cir to radial pulsations with the observed period Π=0.1066 d occurs only for a mass M≥0.55M ⊙, effective temperature T eff≥23000 K, and heavy-element abundance Z≥0.015. The allowed mass of BX Cir is in the range 0.55M ⊙≤M≤0.8M ⊙, which corresponds to luminosities 800L ⊙≤M≤1400L ⊙ and mean radii 1.7R ⊙≲R≲2.1R ⊙.

Nova nucleosynthesis

We report on the results of hydrodynamic calculations, with updated nuclear reaction rates and opacities, which examine the consequences of the accretion process on 1.25M ⊗ white dwarfs since that is the most probable mass for the white dwarf in V1974 Cyg 1992.

Simulation of electrostatic and hydrodynamic properties of Serratia endonuclease.

We analyze the electrostatic and hydrodynamic properties of a nuclease from the pathogenic gram-negative bacterium Serratia marcescens using finite-difference Poisson-Boltzmann methods for electrostatic calculations and a bead-model approach for diffusion coefficient calculations. Electrostatic properties are analyzed for the enzyme in monomeric and dimeric forms and also in the context of DNA binding by the nuclease. Our preliminary results show that binding of a double-stranded DNA dodecamer by nuclease causes an overall shift in the charge of the protein by approximately three units of elementary charge per monomer, resulting in a positively charged protein at physiologic pH. In these calculations, the free enzyme was found to have a negative (-1 e) charge per monomer at pH 7. The most dramatic shift in pKa involves His 89 whose pKa increases by three pH units upon DNA binding. This shift leads to a protonated residue at pH 7, in contrast to the unprotonated form in the free enzyme. DNA binding also leads to a decrease in the energetic distances between the most stable protonation states of the enzyme. Dimerization has no significant effect on the electrostatic properties of each of the monomers for both free enzyme and that bound to DNA. Results of hydrodynamic calculations are consistent with the dimeric form of the enzyme in solution. The computed translational diffusion coefficient for the dimer model of the enzyme is in very good agreement with measurements from light scattering experiments. Preliminary electrooptical calculations indicate that the dimer should possess a large dipole moment (approximately 600 Debye units) as well as substantial optical anisotropy (limiting reduced linear electric dichroism of about 0.3). Therefore, this system may serve as a good model for investigation of electric and hydrodynamic properties by relaxation electrooptical experiments.

The evolution of radiation-dominated stars. I - Nonrotating supermassive stars

view Abstract Citations (125) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Evolution of Radiation-dominated Stars. I. Nonrotating Supermassive Stars Fuller, G. M. ; Woosley, S. E. ; Weaver, T. A. Abstract The evolution of nonrotating supermassive stars (M approximately equal to or greater than 5 x 10 to the 4th solar masses) is examined in detail using the results of hydrodynamic calculations which include post-Newtonian approximations to general relativistic gravity, an equation of state which includes electron-positron pairs, and all relevant nuclear reactions. These calculations are followed through the period of quasi-static contraction, the general relativistic instability, and the eventual collapse to a black hole or disruption via a thermonuclear explosion. It is found that stars with mass M equal to or greater than 10 to the 5th solar masses and initial metallicities Z equal to or less than 0.005 do not explode. The objects with Z equal to or greater than 0.005 do explode because of the burning hydrogen by the beta-limited CNO cycle. Explosion energies range from 2.0 x 10 to the 56th ergs for stars of mass M about 10 to the 5th solar masses to 2.5 x 10 to the 57th ergs for M about 10 to the 6th solar masses. For those stars that do not explode the collapse to a black hole is found to be nonhomologous. Publication: The Astrophysical Journal Pub Date: August 1986 DOI: 10.1086/164452 Bibcode: 1986ApJ...307..675F Keywords: Stellar Evolution; Stellar Structure; Supermassive Stars; Black Holes (Astronomy); Electron-Positron Pairs; Equations Of State; Hydrogen; Light Curve; Stellar Radiation; Astrophysics; STARS: EVOLUTION; STARS: INTERIORS; STARS: MASSIVE full text sources ADS | data products SIMBAD (1) NED (1)