Control Volume Concept Research Articles

Multiobjective Scheduling of Hybrid Renewable Energy System Using Equilibrium Optimization

Due to increasing concern over global warming, the penetration of renewable energy in power systems is increasing day by day. Gencos that traditionally focused only on maximizing their profit in the competitive market are now also focusing on operation with the minimum pollution level. The paper proposes a multiobjective model capable of finding a set of trade-off solutions for the joint optimization problem, considering the cost of reserve and curtailment of power from renewable sources. Managing a hybrid power system is a challenging task due to its stochastic nature mixed with the objective function and complex practical constraints associated with it. A novel metaheuristic Equilibrium Optimizer (EO) algorithm incepted in the year 2020 utilizes the concept of control volume and mass balance for finding equilibrium state is proposed here for computing the optimal schedule and impact of renewable energy integration on profit and emission for different optimization objectives. In this paper, EO has shown dominant performance over well-established metaheuristic algorithms such as particle swarm optimizer (PSO) and artificial bee colony (ABC). In addition, EO produces well-distributed Pareto-optimal solutions and the fuzzy min-ranking is used as a decision maker to acquire the best compromise solution.

High deposition wire arc additive manufacturing of mild steel: Strategies and heat input effect on microstructure and mechanical properties

Abstract Wire Arc Additive Manufacturing (WAAM) is a layer-by-layer production concept that is proposed as a promising alternative to traditional subtractive techniques due to its potential to manufacture large metallic components of medium geometrical complexity. In recent years, this technology has created interest due to the advantages it proposes, such as a low cost and high deposition rates in comparison with other Additive Manufacturing (AM) techniques. In this study, the Gas Metal Arc Welding (GMAW)-based WAAM system was developed to deposit mild steel material. To that end, a comprehensive methodology to understand the main process variables and their influence in the final component properties is shown. The aim of the present study was to compare the influence of oscillatory and overlapping deposition strategies in terms of productivity, growth per layer, obtained microstructure and mechanical properties using the control volume concept to compare volume-dependent parameters. Although some characteristics of these strategies have been documented in literature, the heat input influence has not yet been comprehensively demonstrated and understood. For example, heat input, analyzed deeply in the present study, is a critical factor for the stability of the WAAM process, influencing the mechanical properties and microstructural evolution of as-fabricated parts. The results indicate that the oscillated strategy increases productivity.

Energy Concepts and Critical Plane for Fatigue Assessment of Ti-6Al-4V Notched Specimens

In the present paper, the fatigue life assessment of notched structural components is performed by applying a critical plane-based multiaxial fatigue criterion. Such a criterion is formulated by using the control volume concept related to the strain energy density criterion. The verification point is assumed to be at a given distance from the notch tip. Such a distance is taken as a function of the control volume radii around the notch tip under both Mode I and Mode III loading. The accuracy of the present criterion is evaluated through experimental data available in the literature, concerning titanium alloy notched specimens under uniaxial and multiaxial fatigue loading.

A method for evaluating the effects of specimen geometry and loading condition on fatigue life of metallic materials

In this paper, the effects of specimen geometry and loading condition on fatigue life are investigated based on statistical analysis and control volume concept. A probabilistic control volume method is developed for correlating the fatigue life of specimens with different control volumes. The predicted P-S-N curves accord with the experimental data for the titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X and the high strength steel JIS SUJ2 in literature. The relative error of the predicted fatigue life at 50% survival probability to that directly analyzed from the conventional testing method is –18.7% for the specimens of titanium alloy. The paper also indicates that the determination of the control volume should be based on the fatigue failure mechanism of specimens, which is appropriate to use the control volume for the interior induced fatigue failure and the control surface with a certain thickness for the surface induced fatigue failure.

A Method for Predicting the Effects of Specimen Geometry and Loading Condition on Fatigue Strength

Specimen geometry and loading condition usually have a great influence on the fatigue strength of metallic materials, which is an important issue in evaluating the reliability of component parts. In this paper, a rotating bending fatigue test is performed at first on an hourglass specimen and a notch specimen of a high strength titanium alloy. Experimental results indicate that, in terms of local stress, the notch specimen endures higher fatigue strength in comparison with the hourglass specimen due to its relatively smaller control volume. Then, a probabilistic control volume method is proposed for correlating the effects of specimen geometry and loading condition on the fatigue strength based on Weibull distribution and the concept of control volume. A simple formula is obtained for the fatigue strength in relation to control volumes, in which the parameter is the shape parameter of Weibull distribution of fatigue strength. The predicted results are in good agreement with the present experimental data for high strength titanium alloy and the data for the high strength steel and the full scale EA4T axle in the literature.

Estimation of Depth of Closure Near Gangneung Port in Korea

Kang, H., Chun, I., and Oh, B., 2018. Estimation of the Depth of Closure Near Gangneung Port in Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1361–1365. Coconut Creek (Florida), ISSN 0749-0208.Various methods to cope with coastal erosion have been tried in the East Coast of Korea, among which the regional sediment management (RSM) is now being perceived as a very efficient way for managing limited sand resources in a macroscopic scale in both time and space. To apply RSM, it is necessary to set up the littoral cell, a control volume concept whose offshore boundary is given by the depth of closure (DOC). In this study, an independent littoral cell near Gangneung Port was set up, and a method to determine its DOC was proposed and applied utilizing the existing data of deep-water wave climate. Within the method, several formulas were tested, and the results showed that that the average DOC of the study area varied from 10 m to 52 m depending on sediment size, wave condition, and the formula used. Finally, the Hallermeier's formula of outer DOC was postulated to give a reasonable DOC of the Gangneung littoral cell.

Surface-atmosphere exchange in a box: Making the control volume a suitable representation for in-situ observations

Using the eddy-covariance (EC) method to determine net surface-atmosphere exchange relies on extensive simplifications of the mass balance concept. Among others, it is assumed that the 3-D flux field within a control volume is divergence-free, which is shown to be violated e.g. from large-eddy simulations. To practically evaluate the severity of these assumptions, case studies have monitored the surrounding of an EC tower, so the control volume can be represented more explicitly. Alternatively, diagnostic tests during data processing can be used to subset the EC data for periods that more likely fulfill the underlying assumptions. However, these existing methods are constrained either by their degree of realism, resource demand, temporal coverage, varying spatial representativeness, or combinations thereof.It is hypothesized that these deficiencies can be overcome by using the environmental response function (ERF) technique: Relating flux observations at very high spatio-temporal resolution to meteorological forcings and surface properties, and utilizing the extracted relationships to map a single, regular and stationary control volume explicitly in 3-D space and time. Here, the novel ERF virtual control volume (VCV) concept and its implications are derived, and Xu et al. (this issue) are presenting its first practical application.Initial results show that even from a single EC tower, ERF-VCV reduces advective errors by at least one order of magnitude, and incorporates net low-frequency flux contributions. In the same process tower location bias is treated through attaining a fixed-frame, thus equitable and time-invariant representation of the net surface-atmosphere exchange across a target domain. With regard to the frequently observed non-closure of the surface energy balance, this offers the potential for reconciling “spatial heterogeneity” and “storage term” theories. In extension, ERF promises a rectifying observational operator for unbiased model-data comparison, assimilation, and process representation at model grid scale.

Fatigue lifetime evaluation of notched components: Implementation of the control volume concept in a strain-based LCF criterion

The goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion, recently proposed by some of the present authors, in estimating the fatigue lifetime of metallic structural components weakened by sharp notches. Such a criterion, based on the critical plane approach, is formulated according to the control volume concept related to the Strain Energy Density (SED) criterion: a material point located at a certain distance from the notch tip is assumed to be the verification point where to perform the fatigue assessment. The above distance is assumed to be a function of both the biaxiality ratio (applied shear stress amplitude over normal stress amplitude) and the control volume radii under pure Mode I and pure Mode III loading conditions. Once the position of the verification point and the orientation of the critical plane are determined, the fatigue lifetime is theoretically evaluated through an equivalent normal strain amplitude acting on the critical plane, together with the tensile Manson-Coffin curve. Some uniaxial and multiaxial LCF data, recently published in the literature for V-notched round bars made of Ti-6Al-4V titanium alloy, are analysed through the present criterion.

Joined application of a multiaxial critical plane criterion and a strain energy density criterion in low-cycle fatigue

In the present paper, the multiaxial fatigue life assessment of notched structural components is performed by employing a strain-based multiaxial fatigue criterion. Such a criterion, depending on the critical plane concept, is extended by implementing the control volume concept reated to the Strain Energy Density (SED) approach: a material point located at a certain distance from the notch tip is assumed to be the verification point where to perform the above assessment. Such a distance, measured along the notch bisector, is a function of both the biaxiality ratio (defined as the ratio between the applied shear stress amplitude and the normal stress amplitude) and the control volume radii under Mode I and Mode III. Once the position of the verification point is determined, the fatigue lifetime is assessed through an equivalent strain amplitude, acting on the critical plane, together with a unique material reference curve (i.e. the Manson-Coffin curve). Some uniaxial and multiaxial fatigue data related to V-notched round bars made of titanium grade 5 alloy (Ti-6Al-4V) are examined to validate the present criterion.

Lumped Parameter Modelling of Cavitating Orifice Flow in Hydraulic Systems

Gaseous cavitation is an important issue that introduces negative effects on the performance of hydraulic systems. The lumped parameter modelling approach is widely adopted in the research of hydraulic applications due to its quickness and convenience to apply at the system level. For this reason, a novel lumped parameter model of cavitating orifice flow based on a control volume concept is presented in this paper. In particular, a procedure of calibrating the unknown model coefficients is provided by using the computational fluid dynamic (CFD) method as well as test data. A test rig for studying cavitation in an external gear pump is set up with a variable orifice at the inlet port. The four coefficients in the CFD cavitation model is first identified by the measured mass flow rate through the test orifice; then the CFD simulated fluid field offers required information including the average air mass fraction in downstream region to determine the two coefficients of lumped parameter (LP) model. To further verify the calibrated models, another test at a different pump speed is carried out to compare it to the model prediction. Good matching with experiments justifies the proposed approach and the calibration procedure. Suggestions for future work include extending the approach to the study of hydraulic valves and high-speed pumps.

A real-time model of an automotive air propulsion system

This paper develops a real-time automotive air propulsion system for light-duty vehicles. This system consists of a high-pressure air tank, an electric-controlled throttle valve, and a vane-type air motor. The isentropic-nozzle element and control volume concepts were introduced with their governing equations. The tank and throttle valve were modeled as a second-order control volume and nozzle element, respectively. The air motor consisted of four control volumes (12th-order pneumatic dynamics), first-order mechanical dynamics, and a nozzle element as the exhaust port. A 15th-order nonlinear state equation set was derived by integrating these three subsystems. The controlled throttle angle and sequential switch between intake and exhaust processes for the motor chambers allow the whole system to operate properly. A Matlab/Simulink-based simulator was then used for a real-time simulation. Four throttle angles (30°, 50°, 70°, and 90°) were used to show that the derived model is feasible and physically rational. Key variables such as the mass flow rate, temperature, pressure, energy, and mechanical dynamics were investigated in detail for all subsystems. An experimental platform of a 1kW air motor was constructed for model validation. The average experiment/simulation torque error and air flow rate error were 6.15% and 5.34%, respectively. It proves the high accuracy of the model. Future studies with this real-time model should investigate motor specification design, controller design (by hardware-in-the-loop platform), and integration with a light-duty vehicle simulator.

Analysis of the vibrations due to thermal deflection of the drum in the coiling process

AbstractThe modelling of the coiling process involves a mechanical model of the dynamic system that consists of the rotating coiling drum and the axially and transversally moving strip. Due to the coiling a change of mass in the system takes place. For such a variable mass system a control volume concept has to be introduced in order to get the equations of motion of the dynamic system with variable parameters. A Runge Kutta time integration algorithm is applied to compute the solution. It is assumed that the outer radius of the coiling drum increases linear with the rotation angle. The bending deflection of the shaft results from an inhomogeneous temperature distribution within the coiled material on the coiling drum. Two different boundary conditions of the moving strip have been considered and it is demonstrated that the thermal deflection of the drum has a high influence upon the fluctuation of the strip force. For a given geometry and strip speed we obtain a critical thermal deflection where the minimum strip tension force is zero. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical modelling and analysis of external gear pumps by applying generalized control volumes

Components in gear pumps usually involve complex geometrical arrangements in order to achieve the desired performance. The use of lumped parametric models is considered the most accurate and effective method for investigation of the associated design issues. In this study, the numerical modelling approach based on the lumped parameters and control volume concepts is reviewed, especially for gear teeth within the meshing zone. To apply the approach to the entire gear pump, control volume concepts are generalized to all gear pockets and flow orifices with some reasonable assumptions. The assumptions include instantaneous angular positions, orifice transitions and imagined control volumes with internal flows. The fluid dynamics and pump performance, which even have the measurement difficulties, can be estimated to investigate and optimize the design parameters of gears by the model. A simulation example and its experimental results of a gear machine are presented to validate the proposed approach in this article.

A numerical method of regenerator

A numerical method for regenerators is introduced in this paper. It is not only suitable for the regenerators in cryocoolers and Stirling engines, but also suitable for the stacks in acoustic engines and the pulse tubes in pulse tube refrigerators. The numerical model is one dimensional periodic unsteady flow model. The numerical method is based on the control volume concept with the implicitly solve method. The iteration acceleration method, which considers the one-dimensional periodic unsteady problem as the steady two-dimensional problem, is used for decreasing the calculation time. By this method, the regenerator in an inertance tube pulse tube refrigerator was simulated. The result is useful for understanding how the inefficiency of the regenerator changes with the inertance effect.

Recent developments in the modelling of imperfectly mixed airspaces

This paper discusses the Data-Based Mechanistic (DBM) approach to modelling the micro-climate in agricultural buildings. Here, the imperfect mixing processes that dominate the system behaviour during forced ventilation are first modelled objectively, in purely data-based terms, by continuous-time transfer function relationships. In their equivalent differential equation form, however, these models can be interpreted in terms of the Active Mixing Volume (AMV) concept, developed previously at Lancaster in connection with pollution transport in rivers and soils and, latterly, in modelling the micro-climate of horticultural glasshouses. This can be compared with the incomplete mixing and control volume concepts that have been investigated previously at Leuven. The data used in the initial stages of the research project, as described in the paper, have been obtained from a series of planned ventilation experiments carried out in a large instrumented chamber at Leuven. The overall objectives of this collaborative study are twofold: first, to gain a better understanding of the heat transfer and micro-climate dynamics in the chamber; and second, to develop models that can form the basis for the design of optimal Proportional-Integral-Plus (PIP-LQ) climate control systems for livestock buildings of a kind used previously for controlling the micro-climate in horticultural glasshouses. Although not specifically directed at glasshouse systems, the techniques described in the paper can be applied straightforwardly within a glasshouse context.

Enclosure smoke filling revisited

Building fires go through a series of stages. They start with a fire plume/ceiling jet period during which buoyant fire gases rise to the ceiling and spread radially beneath the ceiling. A second stage, the enclosure smoke-filling period, follows; this second stage is the subject of this paper. It has been more than 20 yr since Zukoski first addressed the smoke filling stage of enclosure fires in terms of thermodynamic control volume concepts and fire plume entrainment, yet his analysis remains pertinent. This paper reviews and extends fire modeling concepts related to enclosure smoke filling developed by Zukoski. The mass-based analysis of Zukoski is recast in terms of the volumetric flow rates typically used for ventilation system design; it is extended to consider global average temperature rise and the effects of oxygen consumption on the maximum global average temperature rise that can be achieved in a closed-room fire. A spreadsheet template is developed to compare hand calculations based on a global analysis with numerical smoke filling calculations. Results of this comparison suggest that there is little difference in conditions predicted with the global hand calculations and the numerical smoke filling calculations; consequently, the hand calculations are suitable for preliminary fire hazard analyses.

Recent Developments in the Modelling and Control of Climate and Ventilation in Agricultural Buildings

This paper discusses the Data-Based Mechanistic (DBM) approach to modelling the micro-climate in agricultural buildings. Here, the imperfect mixing processes that dominate the system behaviour during forced ventilation are first modelled objectively, in purely data-based terms, by continuous-time transfer function relationships. In their equivalent differential equation fonn, however, these models can be interpreted in terms of the Active Mixing Volume (AMV) concept, developed previously at Lancaster in connection with pollution transport in rivers and soils and, latterly, in modelling the microclimate of horticultural glasshouses. This can be compared with the incomplete mixing and control volume concepts that have been investigated previously at Leuven. The data used in the initial stages of the research project, as described in the paper, have been obtained from a series of planned ventilation experiments carried out in a large instrumented chamber at Leuven. The overall objectives of this collaborative study are two-fold: first, to gain a better understanding of the heat transfer and micro-climate dynamics in the chamber; and second, to develop models that can form the basis for the design of optimal ProportionalIntegral- Plus (PIP-LQ) climate control systems for livestock buildings of a kind used previously for controlling the micro-climate in horticultural glasshouses.

OPTIMAL DESIGN OF NONLINEAR STRUCTURES AND MECHANICAL SYSTEMS

This paper presents an optimal structural design system based on a variational theory of design sensitivity analysis for linear and nonlinear structures and mechanical systems. So called flexible systems and structures, as well as design and control variables, are treated within a unified frame. The concept of an auxiliary system, the principle of virtual work, and a Lagrangean-Eulerian description of the deformations and design variations, are used to develop the unified viewpoint. Finite element and finite difference methods are used for spatial and time discretization of the sensitivity equations. The isoparametric concept of the finite element formulation is related to the concept of control volume. The concept of a design element is used for the design modeling of the structure and to generate the analysis model from the design model. Structural analysis and optimization codes are combined to create an optimal design capability. Optimalily criteria methods and nonlinear programming are applied as optimizers. Numerical applications are performed.

Mathematical and Numerical Properties of Control-Volume, Finite-Element Scheme for Reservoir Simulation

Summary This paper presents the mathematical properties of a control-volume, finite-element (CVFE) scheme. We show that appropriate constraints on finite-element grids and convenient definitions for volumes and transmissibilities lead to a convergence property for the CVFE scheme. This convergence property proves that use of the CVFE scheme is mathematically correct for reservoir simulation. With the control-volume concept, the local balances of each component are fully satisfied. Because the discretized equations resulting from the scheme can be solved by classic methods, the CVFE scheme can be implemented easily in a general-purpose simulator. In the implementations in this paper, we use prismatic finite elements for 3D full-field simulations and triangles for 2D simulations. The grid is generated with automatic techniques, popular in structural engineering, resulting in numerical diffusion that is as isotropic as possible; therefore, grid-orientation effects are controlled and accuracy is easily improved through natural grid refinement. Examples show that, for the same accuracy, computational costs are lower for results obtained with the CVFE scheme than for those obtained with finite-difference grids. The CVFE scheme is an excellent alternative to flexible gridding techniques used in finite-difference simulators because the entire reservoir can be gridded as required, without use of special techniques for local grid modifications.

Design optimization of non‐linear structures with rate‐dependent and rate‐independent constitutive models

AbstractA design optimization process for non‐linear structures with history‐dependent materials modelled using the endochronic constitutive theory is described. This constitutive model does not use the concept of a yield surface and describes plastic, viscoplastic and viscoelastic behaviour with one set of equations. Therefore, development of the yield surface is not traced in numerical calculations, simplifying the implementation of response and sensitivity analyses. The total Lagrangian formulation incorporating both geometric and material non‐linear effects is used. Shape, non‐shape and material design parameters are treated simultaneously using the control volume concept, and static and dynamic problems are treated. A simple structure is optimized for several cases of static and impact loading conditions to demonstrate the procedure. Plastic and viscoplastic material behaviour as well as shape and non‐shape design parameters are treated in the example problems.