Papers by Keyword: Steady State

Abstract: During high-pressure torsion (HPT), the sample positioned between the plungers of the experimental setup is resistant to fracturing, allowing the HPT process to be sustained almost indefinitely. Despite this, relaxation processes taking place within the sample during HPT lead swiftly to the establishment of a steady state. Factors such as hardness, grain size, the scale of second-phase precipitates, electrical conductivity, lattice spacing, among others, rapidly reach a saturation point, albeit after varying revolutions of the plunger. For instance, in the scenario of HPT involving a binary solid solution accompanied by secondary phase particles that act as sources of dissolved atoms, a dynamic equilibrium and competition emerge between the formation and decomposition of a supersaturated solid solution. Consequently, a specific equilibrium state is achieved with a designated concentration (c_ss) of the second component within the solid solution. This equilibrium state is independent of the initial one (referred to as equifinality). The steady-state concentration c_ss can be identified on the solubility limit line (solvus) of the second component in the phase diagram at an effective temperature T_eff. In copper alloys, the value of T_eff grows as the activation enthalpy for the volume diffusion of the second component increases. This amplification signifies a rise in defect concentration and an activation-driven character of mass transfer during HPT.

Abstract: Recycling of aluminium (Al) from waste aluminium scraps for fabricating aluminium casts is a waste management technique suitable for reducing environmental pollution. The aluminium casts can be further processed into different materials of engineering interests such as heater-cooler (thermal) blocks. In this study, the microstructural characterization of aluminium cast fabricated from recycled aluminium waste and adapted for use via the (steady-state technique) as heater-cooler blocks required in the determination of the thermal conductivity of conducting solid composites was investigated. The characterization was investigated using the Scanning Electron Microscopy (SEM), Energy Displacer Spectroscopy (EDS), X-ray Diffractometer (XRD), and X-ray Fluorescence (XRF). The XRD result confirms the crystalline structure of aluminium on the fabricated aluminium cast. The elemental composition results confirmed that the fabricated cast contains 90% Al, with Silicon (Si) accounting for about 8% of the chemical composition while the remaining 2% was contributed by C, O, Fe, Zn, and Cu. The compositional change observed during characterization was attributed to the recycling process used in fabricating the aluminium cast.

Abstract: Darcy was known as a very generous engineer. He is undoubtedly the father of the science of fluid flow in soils for his experiment on the flow of water through a sand column which was published in his book ‘Les fontaines publiques de la ville de Dijon in 1856, named after him as Darcy’s law. For the practical computation, this equation was developed by Dupuit & Thiem, and then it called Dupuit-Thiem equation. This equation was redeveloped by many researchers in many variations with different parameters especially for radial flow in pumping and recharging systems. Their basic pumping system equations for a confined and unconfined aquifer as well as for full penetration well with a fully perforated casing. In the practical implementation, this condition rarely occurs especially for thick aquifer; therefore many researchers developed a correction for those formulas from full penetration to be partial penetration wells. Partial penetration well is a well which its depth or tip of its casing does not reach an impermeable stratum beneath the aquifer. Despite the correction, those formulas still have difficulty in computing the design of pumping system due to its need for hydraulic gradient data which can only be defined by two real time data of piezometric head before and after pumping related to the horizontal distance of both points. So in this paper will be presented some inventions of computation methods for instance: recharge systems, the drawdown of pumping, pumping on the aquifer, water losses on the lake, permeability test, pumping test analysis and partial penetration well equation.

Abstract: Analytically describing the relationship among steady-state power flow numerical values is a significant proposition. Because the block diagram has the ability to describe the signal transmission analytically, we choose this method to study the steady-state grid’s power transmission rule. Each node or branch is chosen as a basic power transmission unit, and the ratio between the unit’s output power and input power is defined as power transmission gain. The power transmission relationship of each unit can be established according to the circuit analysis, and then the block diagram of each unit can be built on the basis of above relationship. Finally, a block of the whole power grid can be drawn according to the basic units’ connection relationships. The transmission relationship of the whole power grid was analytically expressed by the block diagram simplification method.

Abstract: In this work, a new solution of load control valve based on a hydraulic coupling two-stage principle is proposed. A detailed mathematical model of the valve has been developed. According the model, the steady-state and dynamic characteristics have been studied. The steady state study shows that the valve has an ideal piloted opening function which is not affected by the load pressure or back pressure alteration. Through an insightful analysis based on the linearized model, the dynamic study reveals that the main stage respond as a 1^st order model which is smooth and fast enough compared to the pilot stage, while the pilot stage can be simplified as 2^nd order model which may cause a problem of oscillation or overshot. The transition response of the valve is mainly decided by the pilot stage. Through the study of various parameters, the diameter of the orifice on the pilot piston shows its efficient influence in adjusting the poles in the pilot stage without affecting the steady state operation of the valve. An optimization based on root locus method is implemented and the poles have been deployed to the fastest points without oscillation.

Abstract: The coupled thermo-flowing 3D steady-state model of friction stir welding model is established based on fluid mechanics. With analyzing the impact of pin shoulder and pin on heat producing, the model considers the influence of pin on the heat producing processing. The model applies viscoplastic constitutive equations to describe the material, and turbulence model to simulate the material flowing behavior. With the additional turbulence kinetic energy equations and flow boundary condition equations, the model is established. With Comsol Multiphysics finite analysis software, a process simulation was carried out, and the results reflect that the model can reveal the steady state characteristics of thermo and material flowing behavior of friction stir welding.

Abstract: The creep behaviour of 2% agar gels has been studied under static and dynamic conditions. This biopolymer finds numerous applications depending on their elasticity. In this why, we are interested to determine the viscoelastic behavior of this hydrocolloid in differences phases and we studied the evolution of its strain creep behavior in transient as in steady state. As a result of these actions, the modified Burgers model has been finally developed for the studied agar gels with variables dependent on the shear stress and the parameter values for its creeping part (describing non-linearly viscoelastic properties of this biopolymer). To confirm the mechanical property of the gel, we measured its dynamic modulus. The elastic character is predominant (G' G").

Abstract: Because crosswind affects drivers to control their vehicles safely, the research on flow characteristics in automotive crosswind has a great significance to improve the crosswind stability of the vehicle. By the steady state numerical simulation method, the aerodynamic characteristics of external flow field of Ahmed body in crosswind was investigated. The Ahmed body with 25° slant angle is built in UG NX. The external flow field of the Ahmed body in the wind direction of 0°, 15º, 30° angle is simulated in XFlow software. According to the map of the pressure and velocity distribution, the flow field both before and after, as well as left and right has significant change as the wind direction angle increased, and the trail turbulence intensity also changes. The changes of aerodynamic force and moment affect the driving stability of a motor vehicle.

Abstract: A method for determining whether a multi-input multi-output (MIMO) active noise control (ANC) system can reduce error signals around all sensors to zero at steady state was proposed. The method was converted to determine the solution of linear equations. Three different simulations were conducted to verify the theoretical analysis. Simulation shows that max estimation error of control signals is no greater than 1.87% in amplitude and 2.22 deg. in phase.

Abstract: Artificial ground freezing method is now widely used in many kinds of municipal projects. The existing formulas to calculate the temperature field distribution of single-row piped freezing are all based on the conditions that the temperature of all freezing pipes are equivalent. In this paper, analytical solution to steady-state temperature field of single-row piped freezing with different adjacent pipe surface temperatures was derived based on thermal potential superposition method. And discussions are made to analyze the influence of temperature difference between adjacent pipes and freezing time on temperature distribution of frozen soil.