Use Of Numerical Models Research Articles

МЕТОД ТА ДОСЛІДЖЕННЯ ТОЧНОСТІ ОБЧИСЛЮВАННЯ МАТЕМАТИЧНОЇ МОДЕЛІ ЕЛЕКТРОГІДРАВЛІЧНОГО ЕФЕКТУ

The mathematical model of the electrohydraulic effect (EHE) is a nonlinear non-stationary system of partial differential equations (PDE), which reflects the motion and contact interaction of two media, gaseous and liquid, under the action of pulsed thermal excitation. Such PDE systems generally do not have analytical solutions and are solved only by numerical methods, which are approximate in nature, i.e. they provide a solution with some error. The peculiarity of the motion of media in the case of EHE is large deformations in the form of flows and vortices. This feature imposes significant restrictions on the choice of the method for solving the PDE model. The widely known Lagrangian finite element method used to solve contact problems, in the case of EHE modeling leads to a pathological change in the shape of the finite elements, and therefore to instability of the calculation process and an unlimited increase in error. In calculation practice, a variant of the finite element method, FEM-ALE, has become widespread. It uses both Lagrangian and Eulerian grids of nodes and a special advection procedure, i.e., transfer by interpolation of the solution from the Lagrangian grid to the Eulerian one, and then vice versa from the Eulerian one to another new Lagrangian grid. Such an additional interpolation procedure, which is used repeatedly in the calculation, leads to additional (in comparison with the Lagrangian FEM) errors. If the causes and kinetics, as well as the methods of error control in the case of the Lagrangian FEM, have been sufficiently studied in the literature, then the kinetics of error development in the simulation of the EGE using the FEM-ALE method has been practically not studied. The article is devoted to the study of the development of errors in the numerical solution in this particular case. An analytical solution of the problem in the asymptotic case for a technological system with a rigid chamber is obtained. This solution is analyzed in comparison with the numerical solution using the FEM-ALE method. Conclusions are made regarding the errors in calculating pressure as the main factor of mechanical impact of EGE on the technological object and technological equipment, as well as errors in calculating deformations of gaseous and liquid media.The scientific novelty consists in the development of a method for determining the accuracy of EHE parameter calculations using the MSE-ALE method. The practical value lies in determining the accuracy of calculating the parameters of the EHE mathematical model, which makes it possible to justify the use of numerical modeling as a method of researching technological processes and systems using EHE

Implementation of PMDL and DRM in OpenSees for Soil-Structure Interaction Analysis

It is widely acknowledged that the effects of soil-structure interaction (SSI) can have substantial implications during periods of intense seismic activity; therefore, accurate quantification of these effects is of paramount importance in the design of earthquake-resistant structures. The analysis of SSI is typically conducted using either direct or substructure methods. Both of these approaches involve the use of numerical models with truncated or reduced-order computational domains. To ensure effective truncation, it is crucial to employ boundary representations that are capable of perfectly absorbing outgoing waves and allowing for the consistent application of input motions. At present, such capabilities are not widely available to researchers and practicing engineers. In order to address this issue, this study implemented the Domain Reduction Method (DRM) and Perfectly Matched Discrete Layers (PMDLs) in OpenSees. The accuracy and stability of these implementations were verified through the use of vertical and inclined incident SV waves in a two-dimensional problem. In terms of computational efficiency, PMDLs require a shorter analysis time (e.g., with PMDLs, the analysis concluded in 35 min as compared to 250 min with extended domain method) and less computational power (one processor for PMDLs against 20 processors for the extended domain method) thus offering a balance between accuracy and efficiency. Furthermore, illustrative examples of the aforementioned implemented features are presented, namely the response analysis of single-cell and double-cell tunnels exposed to plane waves inclined at an angle.

Effects of Notches on Breakdown Pressures and Fracture Evolution in Hydraulic Fracturing

AbstractSustainable ore extraction in cave mining heavily relies on the effective fragmentation or caveability of the orebody. Since cave mining offers substantial benefits, it has gained popularity after preconditioning was introduced to help improve caveability. Therefore, hydraulic fracturing serves as a vital technique for risk management and cave stimulation. The increased rock competency and high stress levels in the rock mass around the orebody significantly influence fracturing and, thus, cavability processes. In order to improve the çefficiency of preconditioning by hydraulic fracturing to specific parts of the non-caving or poorly caving formations, the use of notches as artificial flaws offers an influence on the directionality of fracture propagation; this approach also has the potential to decrease the necessary breakdown pressures, thereby lifting limitations on the design and mechanical capabilities of fracturing campaigns and reducing required breakdown pressures, which could improve hydraulic fracturing capabilities. In this study, we studied the effects of notches on hydraulic fracturing performance under varying stress conditions. A number of hydraulic fracturing experiments were conducted using different notch quantities and spacings. Notches were created parallel to the axis of confining stress, and specimens were then subjected to constant axial loads of 40 MPa under varying confining pressures ranging from 5 to 40 MPa. A supplementary 3-D discrete element method using 3DEC was performed, and the results were compared with the hydraulic fracturing experiment. The 3DEC models incorporated Darcy's Law to describe fluid flow through fractures, and the Mohr–Coulomb softening yield criterion was used to simulate failures on predefined surfaces, providing a thorough hydro-mechanical coupled solution. We found that introducing notches can effectively reduce the pressures needed for fracture initiation and growth. Moreover, with appropriate spacing, fracture direction can be controlled. This knowledge, combined with the use of numerical modelling, has advanced our understanding of fracture behaviour and the influence of notches on propagation paths under different stress regimes. These findings could potentially revolutionise the field of hydraulic fracturing, making it more efficient and sustainable.

Numerical Modeling of Four-Pile Caps Using the Concrete Damaged Plasticity Model

Four-pile caps made from concrete are essential elements for the force transfer from the superstructure to piles or pipes. Due to the difficulties in carrying out full-scale tests and all the instrumentation involved, the use of numerical models as a way to study the mechanical behavior of these elements presents itself as a good alternative. Such numerical studies usually provide useful information for the update and improvement of normative standards and codes. The concrete damaged plasticity (CDP) constitutive model, which combines damage and plasticity with smeared-crack propagation, stands out in the simulation of reinforced concrete. This model is composed of five parameters: dilatation angle (ψ), eccentricity (ϵ), ratio between biaxial and uniaxial compressive strength (σbo/σco), failure surface in the deviator plane normal to the hydrostatic axis (Kc), and viscosity (μ). For unidimensional elements, the values of the CDP parameters are well defined, but for volumetric elements, such as concrete pile caps, there is a gap in the literature regarding the definition of these values. This fact ends up limiting the use of the CDP on these structural elements due to the uncertainties involved. Therefore, the aim of this research was to calibrate two numerical models of concrete four-pile caps with different failure modes for the evaluation of the sensitivity of the CDP parameters, except for ϵ, which remained constant. As a result, the parameters σbo/σco and Kc did not significantly influence the calibration of the force × displacement curves of the simulated structures. Values of ψ and μ equal to 36° and 1 × 10−4, respectively, are recommended for “static” analysis, while for “quasi-static” analysis, ψ values ranging between 45° and 50° are suggested according to the failure mode. The results also showed to be sensitive to the constitutive relation of concrete tensile behavior in both modes of analysis. For geometric parameterization, the “static” analysis is recommended due to the lower coefficient of variation (3.29%) compared to the “quasi-static” analysis (19.18%). This conclusion is supported by the evaluation of the ultimate load of the numerical models from the geometrically parametric study compared to the results estimated by an analytical model.

Development and Implementation of Die Forging Technology Eliminating Flange Welding Operations in Conveyor Driver Forging.

This article presents research results regarding the development of a new manufacturing technology for an element assigned to belt conveyor flights in the extractive industry through hot die forging (of a forging with a double-sided flange) instead of the currently realized process of producing such an element by welding two flanges onto a sleeve or one flange onto a flange forging. The studies were conducted to design an innovative and low-waste technology, mainly with the use of numerical modelling and simulations, partially based on the current technology of producing a flange forging. Additionally, during the development of the forging process, the aspect of robotization was considered, both in respect of the forging tools and the process of transportation and relocation of forging between the impressions and the forging aggregates. A thermo-mechanical model of the process of producing a belt conveyor flight forging with deformable tools was elaborated by means of the Forge 3NxT program. The results of the conducted numerical modelling made it possible, among other things, to develop models of forging tools ensuring the proper manner of material flow and filling of the impressions, as well as temperature and plastic deformation distributions in the forging and also the detection of possible forging defects. For the technology elaborated this way, the tools were built together with a special instrument for flanging in the metal, and technological tests were performed under industrial conditions. The produced forgings were verified through a measurement of the geometry, by way of 3D scanning, as well as the hardness, which definitively confirmed the properness of the developed technology. The obtained technological test results made it possible to confirm that the elaborated construction, as well as the tool impressions, ensure the possibility of implementing the designed technology with the use of robotization and automatization of the forging process.

Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill

Cutting tool coolant channels play a pivotal role in machining processes, facilitating the efficient supply of cooling agents to high-stress areas and effective heat dissipation. Achieving optimal cooling at the tool’s cutting-edge is essential for enhancing production processes. Experimental investigations into tribological stress analysis can be limited in accessing complex tool–workpiece contact zones, prompting the use of numerical modelling to explore fluid dynamics and tribology. In this study, the coolant flow dynamics and heat dissipation in drilling operations were comprehensively investigated through computational fluid dynamics (CFD) modelling. Four twist drill models with varying coolant channel arrangements were studied: standard model drill, standard model drill with notch, profile model drill, and profile model drill with notch. Two distinct approaches are applied to the coolant inlet to assess the impact of operating conditions on fluid flow and heat dissipation at the cutting-edge. The findings emphasize that cutting-edge zones have insufficient coolant supply, particularly in modified drill models such as the standard model drill with notch and profile model drills with and without notch. Moreover, enhanced coolant supply at the cutting-edge is achieved under high-pressure inlet conditions. The standard model drill with a notch exhibited exceptional performance in reducing thermal load, facilitating efficient coolant escape to the flute for improved heat dissipation at the cutting-edge. Despite challenges like dead zones in profile models, the standard-with-notch model yielded the most promising results. Further analyses under constant pressure conditions at 40 and 60 bar exhibited enhanced fluid flow rates, particularly at the cutting-edge, leading to improved heat dissipation. The temperature distribution along the cutting-edge and outer corner demonstrated a decrease as the pressure increased. This study underscores the critical role of both coolant channel design and inlet pressure in optimizing coolant flow dynamics and heat transfer during drilling operations. The findings provide valuable insights for designing and enhancing coolant systems in machining processes, emphasizing the significance of not only coolant channel geometry but also inlet pressure for effective heat dissipation and enhanced tool performance.

Application of Numerical Simulation for Analysis and Optimization of Forging Manufacturing Process

The paper presents the use of numerical modeling results for multivariate simulation of the manufacturing process of a wheel hub forging made of 20 HG alloy. The QForm 3D program was used to analyze the issue, which allowed to analyze the forging process without the need for expensive tools and technological tests. Based on insights from several variants of numerical calculations, new technology solutions were proposed, reducing the number of deficiencies found in industrial practice. In order to obtain full information about the phenomena occurring in the deformation process, numerical calculations were carried out in the areas of material flow, the degree of filling of blanks, the distribution of deformations and stresses in the various stages of the forging process in the die, and the elimination of defects in products. The information obtained formed the basis for proposing the optimal technology for forging wheel hubs.

Optimization of geopolymer pervious concrete design using multi-phase discrete element modeling

This study aims to optimize mix designs of geopolymer pervious concrete using multi-phase discrete element modeling. Metakaolin based geopolymer concrete was prepared with different mix designs for laboratory testing. A multi-phase discrete element model (DEM) for pervious concrete was developed with randomly generated porous structure and realistic contact models between each component. Contact model parameters were calibrated using orthogonal analysis based on measurements of mechanical strengths and elastic modulus. Results of model validation indicate that the developed numerical model has good reliability to predict mechanical properties of pervious concrete with the influence of porosity. Both actual and simulated pervious concrete specimens present consistent crack propagation patterns and failure behavior. The optimization of mixture design is conducted by considering aggregate gradation and aggregate to paste ratio of geopolymer pervious concrete, which are based on experimental results and post-calibration simulations. The gradation with larger size aggregate is suitable for preparing geopolymer pervious concrete with higher permeability and tensile strength. More importantly, it is feasible to reduce paste content in geopolymer pervious concrete while maintaining similar or even higher mechanical strengths, which reduces the embedded carbon footprint. The study findings demonstrate the beneficial use of numerical modeling to determine the optimized mix design of composite material such as geopolymer pervious concrete.

Imperfections for the calculation of steel structures by the finite element method. Part 1

It is well known that imperfections are always present in structural elements. Imperfections can significantly affect the behavior and bearing capacity of steel structures, especially in the case of stability-related tasks. Therefore, inconsistencies must be taken into account in the loadbearing capacity model and their correct application (setting the shape and value) is a key point in the numerical analysis process. In recent decades, much attention has been paid in the domestic scientific space to updating imperfection models for use in numerical models, including taking into account modern more accurate manufacturing and installation technologies for steel structures. The purpose of this study is an analytical review and analysis of scientific research and technical literature, followed by synthesis and elaboration of recommendations on imperfections in relation to the calculation of steel structures using computer modeling technology, including the finite element method. The results of the study contain instructions on how to set the shapes and values of imperfections for different groups of imperfections. The article consists of two parts. The first part is devoted to the study of geometric imperfections, residual stresses and rules for the combination of imperfections, the second part of the article is devoted to equivalent imperfections.

Determination of emission factors from a landfill through an inverse methodology: Experimental determination of ambient air concentrations and use of numerical modelling

The application of numeric modelling for determining the impact of landfills needs for reliable emission source data. In this study, a methodology for the characterization of the emission profiles of the different sources present in landfills for emission factors determination, applying an indirect methodology, is presented. Ambient air concentrations of volatile organic compounds (VOCs), hydrogen sulphide (H2S) and ammonia (NH3) were determined in three potentially emission sources in Can Mata landfill (Hostalets de Pierola, Catalonia, Spain): dumping areas, pre-closed zone and leachate reservoir as well as in biogas, for the determination of emission factors. Multi-sorbent bed and Tenax TA tubes were used for a wide range of VOCs sampling, and analysis was conducted through TD-GC/MS. H2S and NH3 were sampled and analysed using Radiello passive samplers. The highest total VOC (TVOC) concentrations were found in dumping areas (0.7–3.5 mg m−3), followed by leachate reservoir (0.3–0.6 mg m−3) and pre-closed area (77–165 μg m−3). On the other hand, the highest H2S and NH3 concentrations were found in leachate reservoir, presenting values of 0.8–1.1 mg m−3 and 1.7–1.8 mg m−3, respectively. With the application of odour thresholds to the concentrations obtained, the most critical compounds regarding odour annoyances were determined. The highest odour units (O.U.) were found in leachate reservoir due to H2S concentrations, whereas VOCs contributed mainly to O.U. in the dumping areas. The obtained ambient air concentrations were used for the indirect determination of the emission factors through numerical modelling using a Eulerian dispersion model. The emission factors obtained for the landfill for TVOC, H2S and NH3 were in the range of 0.44–10.9 g s-1, 0.16–1.02 g s−1 and 0.23–1.82 g s−1, respectively, depending on the emission source. Reliable emission factors are crucial to obtain landfill impact maps, which are essential for the correct management of these facilities.

Numerical Simulation of Compensation Injection Problems Near Deep Excavations

The stress-strain state (SSS) of the “ground foundation – foundation pit under the protection of a fence – compensation injection zone” system is complex, multifactorial and transforming in space. Taking into account a wide range of phenomena when changing the SSS of the soil base is associated with significant difficulties, especially without the use of numerical modeling using software and computer systems. Numerical modeling in the implementation of the finite element method (FEM) for the problems of complex interaction of a soil basis with underground structures during compensatory grouting makes it possible to assign injection zones in any position in space (horizontally, vertically, at an angle), determine the necessary injection parameters to achieve the building lifting of the soil basis when solving the inverse problem. In this study, using examples of numerical modeling of compensation grouting problems near the pit fence with different locations of existing buildings, the authors identified the determining factors affecting the distribution of internal forces in the enclosing structures of the excavation, as well as on the existing structures of the underground structure. The results of comparison of calculations in two-dimensional and three-dimensional formulations are presented, an increase in the bending moment of the retaining wall when carrying out work on compensatory injection by 187-279% is shown for different parameters of the distance to the grouting horizon. The results of the conducted studies confirm the need to take into account the increase in internal efforts during the work on compensatory injection in the structures of the pit fences when assigning reinforcement. In addition, in some cases it is necessary to provide additional protective measures to prevent a negative impact on the constructed underground structures to reduce emergency situations.

Energy distribution of fragments from H2 and H2 + dissociation by electron impact for the use in numerical models applied to negative ion sources

In negative hydrogen ion sources, the kinetic energy of the atoms is directly related to the negative ion yield at the caesiated converter, with a larger contribution from hot atoms. The energy distribution of hydrogen atoms is related to the formation process: either the kinetic energy release, resulting from dissociation of the hydrogen molecules or molecular ions, or the proton neutralization either in the volume or during reflection at walls. The interpretation of recent experimental measurements related to the translational energy distribution of atoms or positive ions could profit from accurate inclusion of the initial energy distribution in numerical models. In this work, we focus on the calculation of the kinetic energy release for the various dissociation channels due to electron impact on H2 and H2 +, in the Franck-Condon and delta approximation. Since in negative ion sources non-equilibrium vibrational distributions of H2 are found, the energy distribution of fragments is calculated for all vibrational levels. The inverse cumulative distribution functions related to the main dissociation processes are given, as well as the cumulative distributions for all dissociation channels by electron impact, for simple implementation in Monte Carlo numerical simulations. Finally, the application of the method to few cases of interest for negative ion sources is discussed.

Fast segregation of thermal response functions in short-term for vertical ground heat exchangers

A detailed understanding of the short-term performance of the ground heat exchanger (GHE) is a major concern in the design of ground-source heat pumps (GSHP), as it has a significant impact in the efficiency and costs of the facility. The use of numerical models or artificial intelligence techniques may help in the short-term, although they are generally very time-consuming, becoming unpractical in numerous cases. The aim of this work is to obtain the thermal response factors according to the GHE, segregating the transient borehole behavior from the soil effect, based on a previous study which applies experimental data from thermal response tests (TRT) to the finite line source (FLS) model. The proposed method implies an extensive study of the fluid temperature as well as the development of new auxiliary thermal resistances related to the borehole and fluid, avoiding the implementation of numerical models. This procedure has been validated with the temperature outcomes of a 3D numerical model, obtaining low deviations, into a range of ±0.1 K, and mean absolute deviations below 0.01 K.

Performance characterization and modeling of an oscillating surge wave energy converter

Testing wave energy converters in the ocean could be expensive and complex, which necessitates the use of numerical modeling. However, accurately modeling the response of wave energy converters with high-fidelity simulations can be computationally intensive in the design stage where different configurations must be considered. Reduced-order models based on simplified equations of motion can be very useful in the design, optimization, or control of wave energy converters. Given the complex dynamics of wave energy converters, accurate representation, and evaluation of relative contributions by different forces are required. This effort is concerned with a performance characterization of the hydrodynamic response of an oscillating surge wave energy converter that is based on a reduced-order model. A state-space model is used to represent the radiation damping term. Morison’s representation of unsteady forces is used to account for the nonlinear damping. Wave tank tests are performed to validate simulations. A free response simulation is used to determine the coefficients of the state-space model. Torque-forced simulations are used to identify the coefficients of the nonlinear damping term for different amplitudes and wave frequencies. The impact of varying these coefficients on the response is investigated. An assessment of the capability of the model in predicting the hydrodynamic response under irregular forcing is performed. The results show that the maximum error is 3% when compared with high-fidelity simulations. It is determined that the nonlinear damping is proportional to the torque amplitude and its effects are more pronounced as the amplitude of the flap oscillations increases.

Eco-Resilient (ECORE) Concrete Constructions: A New Challenge and A New Concept

This paper presents a new concept concerning the development of eco-resilient concrete constructions, that is to say constructions with a reduced carbon footprint and which can withstand mechanical stress and physico-chemical attacks worsened by climate change. After a critical analysis of current research and development policies in the field of concrete construction, a new global approach is proposed which should allow this concrete construction profession to better respond to the challenges caused by global warming. This approach is based on two strong ideas a) The use of fiber concretes in combination with passive or active reinforcements in all constructions susceptible to crack b) The use of numerical models based on non-linear finite element calculations in order to optimize the design of eco-resilient concrete constructions.

ФОРМИРОВАНИЕ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ МАССИВА ШТАБЕЛЯ КУЧНОГО ВЫЩЕЛАЧИВАНИЯ ЗОЛОТА

Engineering and geological conditions of formation and operation of the technogenic massif of sandy-clay clay pelletised ores of gold heap leaching stack were investigated. Key factors determining the formation of stress-strain state of heap leaching stack were identified. The formation of the stress-strain state of the stack massif was evaluated. The main research methods included the use of numerical modelling of the stress-strain state of the stack massif with the application of continuum mechanics methods. It was established that the optimal approach to the assessment of the stress-strain state is a complex analysis based on an algorithm approximated to the conditions of formation and operation of the heap leach stack array. The modelling takes into account the stages of stack construction, compaction from the impact of mining transport equipment, as well as the weight of overlying rocks, taking into account different degrees of water saturation during operation. Filtration modelling made it possible to determine the zone of full saturation at given irrigation parameters. The formation of the stress-strain state of the heap leaching gold stack massif and its stability were analysed by longitudinal and cross-sectional modelling.

Machine Learning Model for Primary Solar Resource Assessment in Colombia

This work introduces a Machine Learning (ML) model designed to predict solar radiation in diverse cities representing Colombia's climatic variability. It is crucial to assert that the amount of solar energy received in a specific region is directly related to solar radiation and its availability, which is influenced by each area's particular climatic and geographic conditions. Due to the high variability and resulting uncertainty, various approaches have been explored, including the use of numerical models to estimate solar radiation. The primary objective of this study was to develop and validate an ML model that accurately predicts solar radiation in cities. The methodology employed was specific to data treatment and ML model development. It was structured into three fundamental stages: clustering, estimation, and response, considering that the model is based on historical data. The obtained results were assessed using appropriate statistical definitions, not only determining the model's efficiency in terms of prediction but also considering interactions between data for the approximation and prediction of solar radiation. In this context, it is crucial to emphasize that the research contributes to understanding solar radiation in Colombia. This study underscores the importance of developing ML models to predict solar radiation, emphasizing the need to consider the country's climatic diversity. The results obtained, following the model's application, provide valuable information for comprehending and anticipating the availability of this primary resource.

Qualitative Study of the Transport of Microplastics in the Río de la Plata Estuary, Argentina, through Numerical Simulation

Information about the sources, sinks, dynamics, and how environmental variables affect the transport of microplastics (MPs) from continental deposits to marine systems is still limited. Most of the knowledge about the distribution of plastic in the oceans comes from the use of numerical models to understand the routes of MPs moving in aquatic systems. The Río de la Plata (RdP) is an estuary located on the eastern coast of South America and is one of the most anthropized watercourses in the region. In this study, the trajectory of MPs in the RdP was examined through the implementation, for the first time for the region, of numerical simulation models. The impact of the estuary’s hydrodynamic characteristics, winds, and MP morphological properties on their trajectory was investigated. The simulations produced demonstrated a high correlation between the hydrodynamics of the Río de la Plata and the trajectory of positively buoyant MPs. The wind was identified as a significant driving force in the simulation of MP motion dynamics. Modifications in the size of the MPs have more influence on the trajectory than their morphology. The results constitute an initial step toward understanding the dynamics of these emerging pollutants in one of South America’s most important basins.

The use of numerical models within the BIM environment, for the issue of Cultural heritage restoration. Buildings designed until 1940 in Albania

The study is related to the historical and architectural heritage of the city of Tirana, based on the period of Italian influence until 1940. The stock of these buildings represents an interesting case, in terms of research, since they are close to the 100th anniversary after the construction and have great values for the city, as well as architectural heritage. The lifespan of these objects depends on interventions over the years, conservation, updating with digital monitoring technology and the inclusion of BIM and h-BIM tools in the treatment process. It is important to mention that the building does not only need facade maintenance and refinishing, but by getting to know its fragile parts we can have a seismic retrofit strategy ready. Specifically, this research focuses on several digitization processes, 3D models, simulation and intervention proposals. One of the main aspects is the communication between computer models, dealing with the FEM numerical model and the architectural model inside and outside the BIM environment, reducing the gap between them and without major data loss. After analyzing the collapse scenarios, it is intended to increase the accuracy of seismic retrofit interventions, with the sensitivity that belongs to a cultural heritage object. The application of numerical models for legacy objects presents a challenge since the complexity of handling an old building, the parameters of materials, calibrations and approaching the real response of the building in a seismic situation is known. Applications through BIM tools and files with numerous numerical data tend to make a contribution to the field of seismic engineering and heritage restoration in Albania. Variants with proposals on seismic retrofit strategies for protected buildings will be given at the end of this study.

Numerical Modelling of Thermoacoustic Stirling Engines & Refrigerators

Thermoacoustic machines depend on the complex relationship between thermodynamics and acoustics, and thus understanding it is vital in order to analyse the working principles and optimise parameters (i.e. geometrical or operational) to improve their performance. This paper investigates how numerical modelling can be used to explore this relationship and compares the accuracy of the performance predictions for different numerical simulation software. The software used included one designed for modelling Stirling machines called ‘Sage’ and one designed for modelling thermoacoustic machines called ‘DeltaEC’. To compare their results a model of both a thermoacoustic Stirling engine and refrigerator were developed from existing models in published papers, which contained experimental data to validate the numerical models. The results from the thermoacoustic Stirling engine model show that there is good agreement between the predictions from DeltaEC and the experimental data, as well as relatively good agreement between the Sage and DeltaEC predictions. However, due to Sage requiring a different approach to model the boundary conditions for the standing wave type machine (i.e. one end closed) the predictions varied slightly from those by DeltaEC. The results from the thermoacoustic Stirling refrigerator model, however, show improved agreement between the predictions from Sage and DeltaEC – potentially due to Sage and DeltaEC using a similar approach to model the boundary conditions for the travelling wave type (i.e. two open ends). Overall, it was found that although both can accurately model travelling wave thermoacoustic machines, the nature of Sage’s solving method makes it more complex to model the standing wave type compared to DeltaEC. A discussion on the use of numerical models as a tool for better understanding thermoacoustic machines, and the importance of the accuracy of the results to allow for optimisation and improvement in their design is presented.