Papers by Keyword: Equation of State

Abstract: This paper presents a two-dimensional numerical model of blast-wave propagation in a gaseous medium based on the compressible Euler equations and an ideal-gas equation of state. The governing conservation laws are discretised with a triangular finite-element formulation and stabilised using a local Lax–Friedrichs (Rusanov) numerical flux; time integration employs an explicit Euler scheme. The implementation generates an n × n mesh over a square domain, assembles the semi-discrete system, and advances the solution to capture the spatio-temporal evolution of pressure, density, and energy. Simulations reproduce the salient physics of explosions in air: rapid energy release at the epicentre, formation and outward propagation of a supersonic shock, a positive overpressure phase followed by rarefaction, and compression/expansion trends consistent with gas dynamics. Quantitatively, the model yields large transient overpressures (up to ~400× atmospheric at early times in the reported case) and density jumps across the shock front. The approach offers a practical tool for analysing sensitivity to initial/boundary conditions and for exploring parameter effects relevant to underground safety and protective-structure design. Limitations and extensions are discussed, including the need to incorporate viscous effects, real-gas thermodynamics, and fluid–structure interaction for confined or complex geometries.

Abstract: Since the emergence of the van der Waals model, a lot of equations of state have been proposed to represent the pressure-volume-temperature (PVT) behavior of pure compounds, as is the case with GEOS3C, which is a form of generalized cubic equation of state that uses a temperature function dependent on three adjustable parameters. As the predictive capacity of an equation of state is directly related to the use of adequate and efficient methods for estimating the model's parameters, it is advised to use the multiobjective optimization in this class of problems, due to the conflicting nature of the objective functions. In this context, a MOPSO algorithm, based on the Pareto dominance principle, is used to estimate the parameters of the GEOS3C, through the minimization of the deviations in the prediction of different thermodynamic properties: saturation pressure, saturated liquid volume, enthalpy of vaporization and isobaric heat capacity, in order to assess whether it is possible to obtain a model parameterization that is adequate to represent the different properties simultaneously. Comparisons with experimental data available in the literature are performed showing that multiobjective optimization offers new perspectives for improvements in the parameters estimation of equations of state compared to traditional methods.

Abstract: Various forms of the equation of state for studying high-pressure behavior of solids have been developed by numerous investigators using phenomenological approaches. A common feature of the phenomenological equation is that they present the relationship between pressure and volume which can be expressed analytically involving two quantities only, viz Bo, B₀’ respectively, the isothermal bulk modulus and its first pressure derivative, both at zero pressure. The present proposal which intend to compare the efficiency of the four equations under close examination reports the V/V_o versus P derived from the new modified forms of Murnaghan equations Birch equation (BE) and Freund-Ingalls (FIE) equation obtained for the best agreement with the available experimental data.

Abstract: An ab-initio investigation on structural, electronic, optical, elastic and thermal properties of CuZr intermetallic compound using full-potential linearized augmented plane wave method in the support of density functional theory at ambient condition have been performed. We have employed the generalized gradient approximation of (PBE) to indulgence the exchange correlation potential by solving Kohn-Sham equations. Total energy of CuZr as a function of the unit cell volume has been calculated using full potential linearized augmented plane wave (FP-LAPW) method in B₁, B₂ and B₃ crystal structure to obtain the ground state properties. The study of different phases regarding their enthalpy vs. pressure variation is also presented. Our calculated structural parameters (a₀ = 3.268 Å, B = 119 GPa and B' = 4.95) of CuZr are consistent with both the available experimental (a₀ = 3.262 Å) and previously presented theoretical data (a₀ = 3.280 Å, B = 121 GPa) for B₂-type (CsCl) crystal structure. The results obtained from density of states (DOS) and optical spectra shows that the present compound is metallic. The value of density of states at the Fermi level N (E_F) is found to 3.89 states/eV which is determined due to the contribution of ‘d’ like states of Cu and Zr and ‘p’ like states of Zr atom. The second order elastic constants are comparatively studied and an excellent agreement is found with other theoretical data. The trend of calculated elastic constants i.e. C₁₁ - C₁₂ > 0, C₁₁ > 0, C₄₄ > 0, C₁₁ + 2C₁₂ > 0 shows the stability criteria for B₂-type (CsCl) crystal structure at ambient pressure. The sound velocities for longitudinal and shear waves, Debye average velocity and Debye temperature have been successfully calculated as a first theoretical prediction.

Abstract: The behavior of concrete under severe loading is of interest, especially for problems like ballistic impact and penetration and near distance explosions, where very high pressures are developed. For these problems the behavior of concrete at very high hydrostatic pressures is of importance. There is very little data available on concrete behavior at that high pressure level. Therefore there is much need for an extensive experimental work in order to provide necessary data and illuminate the rather obscure area of concrete behavior at high pressures. However high pressure controlled testing requires special and expensive equipment, and the testing is associated with a wide variety of technical problems. Recently published experimental data, obtained by utilizing a high-capacity tri-axial press, indicates that concrete that is subjected to high pressures behaves differently than concrete under low uniaxial loading. When uniaxial loading is applied, without any confining pressure, the concrete specimen demonstrates a well-known brittle behavior where failure is caused by a localized damage. Quite to the contrary, at high levels of confining pressures, the concrete behaves like a ductile material, and its failure is associated with diffuse material damage. The experimental data at the very high pressure range is most important to understand the processes of damage evolution that governs the characteristics of the equation of state. This paper presents the development of an experimental setup that is capable of performing confined compression tests of mortar and concrete specimens at high pressures up to 400MPa. The experimental study aims at investigating the effect of water/cement ratio as well as the ratio of fine aggregate on the different branches of the equation of state: active loading and unloading/reloading. The paper presents some of the test results as well as a new equation of state that is based on the multi scale approach. The model is applicable for dry materials; cementitious paste and concrete in which the pores are filled with water should be treated differently to account for the liquid phase.

Abstract: This paper approaches CO2 pipelines operating with high dense compressible flow for Enhanced Oil Recovery (EOR) and/or Carbon Capture & Geological Storage (CCGS). The idiosyncrasies of high pressure CO2 flow are discussed and an appropriate and rigorous steady-state compressible flow pipeline model is disclosed. The model gives three Ordinary Differential Equations (ODE) which result from one-dimensional, one-phase, Mass, Momentum & Energy Balances along the pipeline axial direction. This ODE set is numerically integrated leading to profiles of temperature, pressure and inventory along the pipeline, which are basic for design. An example is explored in the context of a hypothetical EOR CO2 pipeline aligned to the production of CO2 rich natural gas in the Pre-Salt offshore oil and gas fields on the southeast coast of Brazil.

Abstract: The aim of the thesis is to describe of building elements Bond Graph methodology for modeling dynamic systems. Technique of Bond Graph methodology for modeling dynamic systems is demonstrated and its place in the process of modeling of mechanic and electric system and its behavior is discussed. The building elements of bond graphs as source effort and flow, capacitor, resistor, inductor, gyrator and transformer are described.

Abstract: The Joule-Thomson (JT) effect will occur when the gas flows through the components of filters, valves, orifices and end faces in the system of the dry gas seal, which may cause the temperature of the seal gas to decrease, and even the emergence of liquid condensation. Generally, the Joule-Thomson effect is reflected by the Joule-Thomson coefficient. As to the hydrogen, nitrogen, carbon dioxide and air, which are often met in the dry gas seal, the corresponding Joule-Thomson (JT) coefficients were calculated by four classical equations of state (EOS) of VDW, RK, SRK and PR, which are compared with the experimental data in the literature. The results show that the JT coefficients calculated by RK equation are most close to the experimental data in the literature, whose relative error is lowest and less than 4%. When the JT effect of real gas in the dry gas seal is analyzed, the RK equation of state is recommend.

Abstract: There is an important practical value of the state space average method in the modeling of the DC/DC converter. Compared with the state space average method, the equivalent circuit modeling method is more intuitive and the physical meaning is clearer. Under the assumptions of the ideal switch, small signal, small ripple and low frequency, taking Cuk converter as an example, the equation of state and the equation of state of the Ac small signal are deduced. The correctness and rationality of the two methods are proved by using the Matlab / Simulink software, and the stability of the system is improved by designing a PI controller.

Abstract: The structural and elastic properties of some alkaline earth mono-sulphide (AES: AE = Ca, Ba, Sr) under pressure have been investigated using a two body inter ionic potential approach with modified ionic charge (Z_me). The phase transition pressures 39.9 GPa, 17.1 GPa, and 7.2GPa along with volume collapses 6%, 8.5% and 10.8% for CaS, SrS and BaS obtained by this approach, respectively and compared them with experimental measured data reveal good agreement. We have also calculated bulk modulus, pressure derivatives, second order (C₁₁, C₁₂ & C₄₄) and third order elastic constants (C₁₁₁, C₁₁₂, C₁₂₃ etc.) in NaCl (B1) phase which show predominantly ionic nature of these compounds.Keywords: High pressure behavior, equation of state, structural phase transition, second order elastic constants, third order elastic constants.