Search results

The paper presents a numerical technique for the simulation of the effects of grey‐diffusive surface radiation on fluid flow using a finite volume procedure for two‐dimensional (plane and axi‐symmetric) geometries. The governing equations are solved sequentially, and the non‐linearities and coupling of variables are accounted for through outer iterations (coefficients updates). In order to reduce the number of outer iterations, a multigrid algorithm was implemented. The radiating surface model assumes a non‐participating medium, semi‐transparent walls and constant elementary surface temperature and radiation fluxes. The calculation of view factors is based on the analytical evaluation for the plane geometry and numerical integration for axi‐symmetric geometry. Ashadowing algorithm was implemented for the calculation of view factors in general geometries. The method for the calculation of view factors was first tested by comparison with available analytical solutions for a complex geometric configuration. The flow prediction code combined with radiation heat transfer was verified by comparisons with analytical one‐dimensional solutions. Further test calculations were done for the flow and heat transfer in a cavity with a radiating submerged body. As an example of the capabilities of the method, transport processes in metalorganic chemical vapour deposition (MOCVD) reactors were simulated.

The purpose of this paper is to study the effect of curvature on the magnetic field distribution and no-load rotor eddy current losses in electric machines, particularly in high-speed permanent magnet (PM) machines.

The magnetic field distribution is obtained using conformal mapping, and the eddy current losses are obtained using a cylindrical multilayer model. The analytical results are validated using a two-dimensional finite element analysis. The analytical method is based on a proportional-logarithmic conformal transformation that maps the cylindrical geometry of a rotating electric machine into a rectangular configuration without modifying the length scale. In addition, the appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. Based on this conformal transformation, a coefficient to quantify the effect of curvature is proposed.

Neglecting the effect of curvature can produce significant errors in the calculation of no-load rotor losses when the ratio between the air-gap length and the rotor diameter is large.

The appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. The proportional-logarithmic transformation proposed provides an insight into the effect of curvature on the magnetic field distribution in the air-gap and no-load rotor losses. Furthermore, the proposed curvature coefficient gives a notion of the effect of curvature for any particular geometry without the necessity of any complicated calculation. The case study shows that neglecting the effect of curvature underestimates the rotor eddy-current losses significantly in machines with large gap-to-rotor diameter ratios.

This study aims to describe how creative thinking ability could be improved through correcting the thinking schemata using cool-critical-creative-meaningful (3CM) learning model.

This study implemented mixed methods with explanatory sequential, which means a study that was conducted by collecting quantitative and qualitative data, consecutively. The creative thinking ability was measured through tests and then triangulated with the student teachers answers in the interviews. The qualitative data consisted of creative thinking schemata that were collected with task analysis and think aloud method. The data were analyzed in two stages. Quantitative data analysis was used to identify the effectiveness of 3CM learning. Qualitative data analysis was conducted using Miles and Huberman’s analysis.

The findings presented that 3CM learning model is significantly effective to improve the creative thinking ability of pre-service primary teacher; students with formal, content and linguistic schemata that are good and complete will also have good mathematical creative thinking ability; the mathematical creative thinking ability of student is determined by the completeness of their schemata; and a good and complete schemata (formal, content and linguistic) will help the students to produce several problem-solving alternatives.

Because of the chosen research approach, the research results may lack generalizability. Therefore, researchers are encouraged to test the proposed propositions further.

The results of this study suggest lecturers to give their students a great opportunity to develop their creativity in solving mathematical problems. Lecturers could give the students the opportunity to think systematically by beginning by criticizing the interesting contextual problems and ending with meaningful reflection with adequate learning resources.

3CM learning model is a model that is proven to be effective in helping the students in shaping the thinking schemata well and able to improve the creative thinking ability of the students.

Certain researchers have expressed concerns about inequitable discipline representations in an integrated STEM/STEAM (science, technology, engineering, arts and mathematics) unit that may limit what students gain in terms of depth of knowledge and understanding. To address this concern, the authors investigate the stages of integrated teaching units to explore the ways in which STEAM programs can provide students with a deeper learning experience in mathematics. This paper addresses the following question: what learning stages promote a deeper understanding and more meaningful learning experience of mathematics in the context of STEAM education?

The authors carried out a qualitative case study and collected the following data: interviews, lesson observations and analyses of curriculum documents. The authors took a sample of four different STEAM programs in Ontario, Canada: two at nonprofit organizations and two at in-school research sites.

The findings contribute to a curriculum and instructional model which ensures that mathematics curriculum expectations are more explicit and targeted, in both the learning expectations and assessment criteria, and essential to the STEAM learning tasks. The findings have implications for planning and teaching STEAM programs.

The authors derived four stages of the STEAM Maker unit or lesson from the analysis of data collected from the four sites, which the authors present in this paper. These four stages offer a model for a more robust integrated curriculum focusing on a deeper understanding of mathematics curriculum content.

X = multiple interpretations

Stress state has a major influence on different phenomena, namely those involving diffusion and plastic deformation (like crack closure and high‐temperature fatigue crack growth, void formation or ductile fracture). The isolation of plane stress and plane strain states is crucial in fundamental studies of material behavior. The isolation of plane stress state is achieved with thin specimens, whilst the isolation of plane strain state is usually done increasing the thickness or introducing lateral grooves. The purpose of this paper is to propose a specimen geometry able to isolate the plane strain state, based on the standard M(T) geometry.

A numerical study was carried out aiming at obtaining a stress triaxiality parameter, h, as a function of different geometrical features of the specimen, such as the notch radius, notch depth and specimen thickness.

Results show that a pure plane strain state is achievable (i.e. 97 percent of specimen thickness has h>0.97) if a specimen with optimized geometrical features is used, which corresponds to a notch radius of 0.5 mm, a notch depth of 1 mm and a total specimen thickness of 12.56 mm.

This type of specimen geometry is a simple and efficient alternative to other common approaches used to obtain pure plain strain conditions for experimental purposes.

This paper aims to provide a better understanding of the challenges and potential solutions in Visual Simultaneous Localization and Mapping (SLAM), laying the foundation for its applications in autonomous navigation, intelligent driving and other related domains.

In analyzing the latest research, the review presents representative achievements, including methods to enhance efficiency, robustness and accuracy. Additionally, the review provides insights into the future development direction of Visual SLAM, emphasizing the importance of improving system robustness when dealing with dynamic environments. The research methodology of this review involves a literature review and data set analysis, enabling a comprehensive understanding of the current status and prospects in the field of Visual SLAM.

This review aims to comprehensively evaluate the latest advances and challenges in the field of Visual SLAM. By collecting and analyzing relevant research papers and classic data sets, it reveals the current issues faced by Visual SLAM in complex environments and proposes potential solutions. The review begins by introducing the fundamental principles and application areas of Visual SLAM, followed by an in-depth discussion of the challenges encountered when dealing with dynamic objects and complex environments. To enhance the performance of SLAM algorithms, researchers have made progress by integrating different sensor modalities, improving feature extraction and incorporating deep learning techniques, driving advancements in the field.

To the best of the authors’ knowledge, the originality of this review lies in its in-depth analysis of current research hotspots and predictions for future development, providing valuable references for researchers in this field.

Among the different methodologies used for performance control in precision manufacturing, the measurement of metrological test artefacts becomes very important for the characterization, optimization and performance evaluation of additive manufacturing (AM) systems. The purpose of this study is to design and manufacture several benchmark artefacts to evaluate the accuracy of the selective laser melting (SLM) manufacturing process.

Artefacts consist of different primitive features (planes, cylinders and hemispheres) on sloped planes (0°, 15°, 30°, 45°) and stair-shaped and sloped planes (from 0° to 90°, at 5° intervals), manufactured in 17-4PH stainless steel. The artefacts were measured optically by a structured light scanner to verify the geometric dimensioning and tolerancing of SLM manufacturing.

The results provide design recommendations for precision SLM manufacturing of 17-4PH parts. Regarding geometrical accuracy, it is recommended to avoid surfaces with 45° negative slopes or higher. On the other hand, the material shrinkage effect can be compensated by resizing features according to X and Y direction.

No previous work has been found that evaluates accuracy when printing inwards (pockets) and outwards (pads) geometries at different manufacturing angles using SLM. The proposed artefacts can be used to determine the manufacturing accuracy of different AM systems by resizing to fit the build envelope of the system to evaluate. Analysis of manufactured benchmark artefacts allows to determine rules for the most suitable design of the desired parts.

The aim of the research is to conduct a study into a configuration of an aircraft system with a focus on aerodynamics. In addition, trim condition and static stability constraints were included. The main application of this system is suborbital space flights. The presented concept of a modular airplane system (MAS) consists of two vehicles: a Rocket Plane and a Carrier. Both are designed in tailless configurations but coupled formed a classic tail aircraft configuration, where the Rocket Plane works as the empennage. The most important challenge is to define the mutual position of those two tailless vehicles under the assumption that each vehicle will be operating alone in different flight conditions while joined in one object create a conventional aircraft. Each vehicle configuration (separated and coupled) must fulfil static stability and trim requirements.

Aircrafts’ aerodynamic characteristics were obtained using the MGAERO software which is a commercial computing fluid dynamics tool created by AMI Aero. This software uses the Euler flow model. Results from this software were used in the static stability and trim condition analysis.

The main outcome of this investigation is a mutual position of the Rocket Plane and the Carrier that fulfils project requirements. Also, the final configuration of both separated vehicles (Rocket Plane and Carrier) and the complete MAS were defined. In addition, it was observed that in the case of classic aircraft configuration which is created by connecting two tailless vehicles increasing horizontal tail arm reduces static stability. This is related to a significantly higher mass ratio of the horizontal tail (the Rocket Plane) with respect to the whole system. Moving backward, the Rocket Plane has a notable effect on a position of a centre of gravity of the whole system static stability. Moreover, the impact of the mutual vehicles’ position (horizontal tail arm) and inclination angle on the coupled vehicle lift to drag ratio was analysed.

In terms of aerodynamic computation, MGAERO software using an inviscid flow model, therefore, both a friction drag and breakdown of vortex are not considered. But the presented research is for the computation stage of the design, and the MGAERO software guarantees satisfactory accuracy with respect to the relatively low time of computations. The second limitation is that the presented results are for the conceptual stage of the design and dynamic stability constraints were not taken into account.

The ultimate goal of the coupled aircraft project is to conduct flying tests and the presented result is one of the milestones to achieve this goal.

A design process for a conventional aircraft configuration is well known however, there are not many examples of vehicles that consist of two coupled aircrafts where both vehicles have similar mass. The unique part of this paper includes results of the investigation of the mutual position of the vehicles that can fly alone, as well as in coupled form. The impact of the position of the centre of gravity on trim conditions and static stability of the coupled configuration was investigated.

The development of micro‐electro‐mechanical systems (MEMS) for use in military and consumer electronics necessitates an analysis of MEMS component reliability. The understanding of the reliability characteristics of SCSi within MEMS structures should be improved to advance MEMS applications. Reliability assessments of MEMS technology may be used to conduct virtual qualification of these devices more efficiently. The purpose of this paper is to create a simple, inexpensive test methodology to use the dynamic fracture strength of a MEMS device to predict its reliability, and to verify this method through experimentation.

The dynamic fracture strength of single crystal silicon (SCSi) was used to model MEMS devices subjected to high shock loading. Experimentation with SCSi MEMS structures was performed following the proposed test methodology. A probabilistic distribution for bending of Deep Reactive Ion Etching (DRIE) processed SCSi around the <110> directions was generated as a tool for assessing product reliability.

Post shock test inspections revealed that failures occurred along {111} planes. Additional experiments provided preliminary estimates of the fracture strength for bending of DRIE processed SCSi around the <100> directions in excess of 1.1 GPa.

This paper proposes a test methodology for an efficient method to assess the reliability of processed SCSi based on dynamic fracture strength.