Software development, particularly of complex scientific applications, requires a detailed understanding of the problem(s) to be solved and an ability to translate this understanding into the generic constructs of a programming language. We believe that such knowledge – information about a code’s “building blocks”, especially the low-level functions and procedures in which domain-specific tasks are […]
A spectral/hp element discretisation permits both geometric flexibility and beneficial convergence properties to be attained simultaneously. The choice of elemental polynomial order has a profound effect on the efficiency of different implementation strategies with their performance varying substantially for low and high order spectral/hp discretisations. We examine how careful selection of the strategy minimises computational […]
There is a growing interest in high-order finite and spectral/hp element methods using continuous and discontinuous Galerkin formulations. In this paper we investigate the effect of h– and p-type refinement on the relationship between runtime performance and solution accuracy. The broad spectrum of possible domain discretisations makes establishing a performance-optimal selection non-trivial. Through comparing the […]
Flow past a circular cylinder is investigated in the subcritical regime, below the onset of Bénard-von Kármán vortex shedding at Reynolds number Rec≃47. The transient response of infinitesimal perturbations is computed. The domain requirements for obtaining converged results is discussed at length. It is shown that energy amplification occurs as low as Re=2.2. Throughout much […]
Exim is the standard mail-server of the majority of Linux distributions. Typically, it requires minimal maintenance, but when configuring it, or occasionally when something goes wrong, you have to intervene. Here are a few useful Exim commands: Get the version of Exim: Testing Check the routing of an email address: Note: To ignore a scanner […]
SSH is a highly versatile and secure protocol, allowing remote shell access (through the ssh command) and secure file transfer (through the scp command). SSHFS extends the file transfer concept to provide a filesystem client via FUSE (Filesystem in USErspace). Assuming you already have shell access to a remote machine, it is trivial to mount […]
These are instructions for allowing SSH access to hosts on an internal network via a public-facing HTTP proxy. Configure Apache2 proxy Here is the fundamental configuration components needed to establish a proxy. This assumes the apache2 proxy modules are already enabled. Additional to this, you should have a normal site definition (for snooping visitors), and […]
Here are useful tips I found when dealing with MySQL servers. Repairing crashed tables Sometimes a MySQL utility will report an error such as: You can check the index files using the myisamchk utility, which should show an output similar to: No errors reported In this case, the table is fine, but just marked as […]
Results are presented from a numerical study of transient growth experienced by infinitesimal perturbations to flow in an axisymmetric pipe with a sudden 1–2 diametral expansion. First, the downstream reattachment point of the steady laminar flow is accurately determined as a function of Reynolds number and it is established that the flow is linearly stable […]
Transient growth is quantitatively examined in two prototype separated flows using Direct Numerical Simulation (DNS). Separated flows typically exhibit regions of convective instability due to the inflectional velocity profiles inherent in the shear flow. This can lead to the transient growth of small disturbances by many orders of magnitude. After reviewing the mathematical tools and […]