Construction of Explicit and Implicit Symmetric TVD Schemes and Their Applications

A one-parameter family of second-order explicit and implicit total variation diminishing (TVD) schemes is reformulated so that a simplier and wider group of limiters is included. The resulting scheme can be viewed as a symmetrical algorithm with a variety of numerical dissipation terms that are designed for weak solutions of hyperbolic problems. This is a generalization of recent works of Roe and Davis to a wider class of symmetric schemes other than Lax-Wendroff. The main properties of the present class of schemes are that they can be implicit, and, when steady-state calculations are sought, the numerical solution is independent of the time step. Numerical experiments with two-dimensional unsteady and steady-state airfoil calculations show that the proposed symmetric TVD schemes are quite robust and accurate

Construction of Explicit and Implicit Symmetric TVD Schemes and Their Applications

A one-parameter family of second-order explicit and implicit total variation diminishing (TVD) schemes is reformulated so that a simplier and wider group of limiters is included. The resulting scheme can be viewed as a symmetrical algorithm with a variety of numerical dissipation terms that are designed for weak solutions of hyperbolic problems. This is a generalization of recent works of Roe and Davis to a wider class of symmetric schemes other than Lax-Wendroff. The main properties of the present class of schemes are that they can be implicit, and, when steady-state calculations are sought, the numerical solution is independent of the time step. Numerical experiments with two-dimensional unsteady and steady-state airfoil calculations show that the proposed symmetric TVD schemes are quite robust and accurate

An Agent-based approach to modelling integrated product teams undertaking a design activity.

The interactions between individual designers, within integrated product teams, and the nature of design tasks, all have a significant impact upon how well a design task can be performed, and hence the quality of the resultant product and the time in which it can be delivered. In this paper we describe an ongoing research project which aims to model integrated product teams through the use of multi-agent systems. We first describe the background and rationale for our work, and then present our initial computational model and results from the simulation of an integrated product team. The paper concludes with a discussion of how the model will evolve to improve the accuracy of the simulation

Examining the Intersection of Cultural Identities: The Malaysian Chinese Experience

This essay aims to present the intersections that constitute the cultural identity of Malaysian Chinese and suggest how their migration and settlement experiences have shaped their sense of who they are and who they are becoming through personal and family histories. I utilise a methodology analogous to the microhistory framework, where the individual assumes an active role in the process of memory formation and exercises agency in the selection, alteration and transmission of memories. This perspective encourages “understanding people in light of their own experience and their reactions to that experience.”1 Most scholarly publications on Malaysian Chinese identity use a macro-level approach, emphasising the study of social and political institutions while giving less attention to personal introspection and micro-level research. A September 17, 2022, New Straits Times article quoted Danny Wong, a Malaysian historian from Sabah, as saying that family history, tales and memoirs help people comprehend both their past and their future trajectory. Wong believes that scrutinising one’s personal history through the medium of family narratives can lead to a critical evaluation of the interconnectedness of familial, communal and national dynamics. My artworks, reproduced in this article, aim to visually portray these submerged and accumulated layers of intersecting identity through a microhistorical perspective. Through my art, I present the intersecting and multi-layered inner reality that has accumulated traces of lived experiences. This inner reality is distinguished by its multicultural, multi-religious, multi-lingual character and multiracial experiences that combine to influence identity formation, under the impact of constantly changing social environments. The evolution of these inner realities is conveyed using visual assemblages combining printmaking, photography and digital manipulation in order to visually represent the socio-cultural formation of a Malaysian Chinese individual. The artworks reproducedconvey the mutable nature of ethnic identity in conjunction with variables such as geographic location, degree of interaction, era, and age group

Recent developments in accuracy and stability improvement of nonlinear filter methods for DNS and LES of compressible flows

Recent progress in the improvement of numerical stability and accuracy of the Yee and Sjögreen [49] high order nonlinear filter schemes is described. The Yee & Sjögreen adaptive nonlinear filter method consists of a high order non-dissipative spatial base scheme and a nonlinear filter step. The nonlinear filter step consists of a flow sensor and the dissipative portion of a high resolution nonlinear high order shock-capturing method to guide the application of the shock-capturing dissipation where needed. The nonlinear filter idea was first initiated by Yee et al. [54] using an artificial compression method (ACM) of Harten [12] as the flow sensor. The nonlinear filter step was developed to replace high order linear filters so that the same scheme can be used for long time integration of direct numerical simulations (DNS) and large eddy simulations (LES) for both shock-free turbulence and turbulence-shock waves inter- actions. The improvement includes four major new developments: (a) Smart flow sensors were developed to replace the global ACM flow sensor [21,22,50]. The smart flow sensor provides the locations and the estimated strength of the necessary numerical dissipation needed at these locations and leaves the rest of the flow field free of shock-capturing dissipation. (b) Skew-symmetric splittings were developed for compressible gas dynamics and magnetohydrodynamics (MHD) equations [35,36] to improve numerical stability for long time integration. (c) High order entropy stable numerical fluxes were developed as the spatial base schemes for both the compressible gas dynamics and MHD [37,38]. (d) Several dispersion relation-preserving (DRP) central spatial schemes were included as spatial base schemes in the frame- work of our nonlinear filter method approach [40]. With these new scheme constructions the nonlinear filter schemes are applicable to a wider class of accurate and stable DNS and LES applications, including forced turbulence simulations where the time evolution of flows might start with low speed shock-free turbulence and develop into supersonic speeds with shocks. Representative test cases for both smooth flows and problems containing discontinuities for compressible flows are included

TTA school-based research consortium initiative, the evaluation, final report

This is the final report of the evaluation of th School-Based Research Consortium Initiative which ran in England from 1998 to 2001. The initiative was sponsored via a public/private partnership between the Teacher Training Agency (TTA), a UK Government agency, and the Centre for British Teachers (CfBT), a private not-for-profit company. The aim of the initiative was to create local infrastructures of support and action for teachers to engage ‘in and with’ research. Those infrastructures were made up of consortia, consisting in each case of a small number of schools together with a university department of education and at least one local education authority (LEA). Over the three years that it ran, the initiative spawned a considerable range and volume of research activities, including peer observation of teaching, peer review of videos of teaching, interview-based study, surveys measuring such things as rewards and sanctions in the classroom. In addition to well-developed teacher-university collaborations and some joint work with local education authorities, there were many examples of teacher-teacher collaboration (some of it between different schools), and also times when teachers and pupils worked together to devise, carry out or interpret research activity. In practice, the initiative created an environment in which it was possible to develop new research relationships across a range of partners, rather than merely transfer the locus of research to schools. Three aspects of teacher experience of the initiative are important to highlight. The first was the overwhelming testimony of teachers that the value of the initiative for them was the rediscovery of their professional confidence in a climate of low trust accountability, characterised by constant monitoring, target setting and bureaucratic demands. The second was the growth of familiarity with research practices that teachers gained through working collaboratively with their peers, with pupils, and with colleagues from the university. The third was how the process of research itself was necessarily situated in teachers’ own practices

Non-Linear Filtering and Limiting in High Order Methods for Ideal and Non-Ideal MHD

The adaptive nonlinear filtering and limiting in spatially high order schemes (Yee et al. J. Comput. Phys. 150, 199–238, (1999), Sjogreen and Yee, J. Scient. Comput. 20, 211–255, (2004)) for the compressible Euler and Navier–Stokes equations have been recently extended to the ideal and non-ideal magnetohydrodynamics (MHD) equations, (Sjogreen and Yee, (2003), Proceedings of the 16th AIAA/CFD conference, June 23–26, Orlando F1; Yee and Sjogreen (2003), Proceedings of the International Conference on High Performance Scientific Computing, March, 10–14, Honai, Vietnam; Yee and Sjogreen (2003), RIACS Technical Report TR03. 10, July, NASA Ames Research Center; Yee and Sjogreen (2004), Proceedings of the ICCF03, July 12–16, Toronto, Canada). The numerical dissipation control in these adaptive filter schemes consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free from numerical dissipation contamination. The numerical dissipation considered consists of high order linear dissipation for the suppression of high frequency oscillation and the nonlinear dissipative portion of high-resolution shock-capturing methods for discontinuity capturing. The applicable nonlinear dissipative portion of high-resolution shock-capturing methods is very general. The objective of this paper is to investigate the performance of three commonly used types of discontinuity capturing nonlinear numerical dissipation for both the ideal and non-ideal MHD

Grid convergence of high order methods for multiscale complex unsteady viscous compressible flows

Grid convergence of several high order methods for the computation of rapidly developing complex unsteady viscous compressible flows with a wide range of physical scales is studied. The recently developed adaptive numerical dissipation control high order methods referred to as the ACM and wavelet filter schemes are compared with a fifth-order weighted ENO (WENO) scheme. The two 2-D compressible full Navier–Stokes models considered do not possess known analytical and experimental data. Fine grid solutions from a standard second-order TVD scheme and a MUSCL scheme with limiters are used as reference solutions. The first model is a 2-D viscous analog of a shock tube problem which involves complex shock/shear/boundary-layer interactions. The second model is a supersonic reactive flow concerning fuel breakup. The fuel mixing involves circular hydrogen bubbles in air interacting with a planar moving shock wave. Both models contain fine scale structures and are stiff in the sense that even though the unsteadiness of the flows are rapidly developing, extreme grid refinement and time step restrictions are needed to resolve all the flow scales as well as the chemical reaction scales. Our computations were all made on uniform grids, and our conclusions cannot be directly carried over to, for example, curvilinear grids

Accuracy consideration by DRP schemes for DNS and LES of compressible flow computations

Several dispersion relation-preserving (DRP) spatially central discretizations are considered as the base scheme in the framework of the Yee & Sjögreen low dissipative nonlinear filter approach. In addition, the nonlinear filter of Yee & Sjögreen with shock-capturing and long time integration capabilities is used to replace the standard DRP linear filter for both smooth flows and flows containing discontinuities. DRP schemes for computational aeroacoustics (CAA) focus on dispersion error consideration for long time lin- ear wave propagation rather than the formal order of accuracy of the scheme. The resulting DRP schemes usually have wider grid stencils and increased CPU operations count compared with standard central schemes of the same formal order of accuracy. For discontinuous initial data and long time wave propa- gation of smooth acoustic waves, various space and time DRP linear filter are needed. For acoustic waves interacting with shocks and turbulence induced noise, DRP schemes with linear filters alone usually are not capable of simulating such flows. The investigation presented in this paper is focused on the pos- sible gain in efficiency and accuracy by spatial DRP schemes over standard central schemes having the same grid stencil width for general direct numerical simulations (DNS) and large eddy simulations (LES) of compressible flows. Representative test cases for both smooth flows and problems containing discontinuities for 3D DNS of compressible gas dynamics are included

Simulation of Richtmyer–Meshkov instability by sixth-order filter methods

Simulation of a 2-D Richtmyer–Meshkov instability (RMI), including inviscid, viscous and magnetic field effects was conducted comparing recently developed sixthorder filter schemes with various standard shock-capturing methods. The suppression of the inviscid gas dynamics RMI in the presence of a magnetic field was investigated by Samtaney and Wheatley et al. Numerical results illustrated here exhibit behavior similar to the work of Samtaney. Due to the different amounts and different types of numerical dissipation contained in each scheme, the structures and the growth of eddies for the chaotic-like inviscid gas dynamics RMI case are highly grid size and scheme dependent, even with many levels of refinement. The failure of grid refinement for all studied numerical methods extends to the viscous gas dynamics case for high Reynolds number. For lower Reynolds number, grid convergence has been achieved by all studied methods. To achieve similar resolution, standard shock-capturing methods require more grid points than filter schemes and yet the CPU times using the same grid for all studied methods are comparable