High Weissenberg number simulations with incompressible Smoothed Particle Hydrodynamics and the log-conformation formulation

Viscoelastic flows occur widely, and numerical simulations of them are important for a range of industrial applications. Simulations of viscoelastic flows are more challenging than their Newtonian counterparts due to the presence of exponential gradients in polymeric stress fields, which can lead to catastrophic instabilities if not carefully handled. A key development to overcome this issue is the log-conformation formulation, which has been applied to a range of numerical methods, but not previously applied to Smoothed Particle Hydrodynamics (SPH). Here we present a 2D incompressible SPH algorithm for viscoelastic flows which, for the first time, incorporates a log-conformation formulation with an elasto-viscous stress splitting (EVSS) technique. The resulting scheme enables simulations of flows at high Weissenberg numbers (accurate up to Wi=85 for Poiseuille flow). The method is robust, and able to handle both internal and free-surface flows, and a range of linear and non-linear constitutive models. Several test cases are considerd included flow past a periodic array of cylinders and jet buckling. This presents a significant step change in capabilties compared to previous SPH algorithms for viscoelastic flows, and has the potential to simulate a wide range of new and challenging applications.Comment: submitted to JNNFM Sept. 2020, revised March 202

A Quantum Computing Algorithm for Smoothed Particle Hydrodynamics

This paper presents a quantum computing algorithm for the determination of function and gradient approximations in the Smoothed Particle Hydrodynamics (SPH) method. The SPH operators and domain discretisation are encoded in a quantum register using a careful normalisation procedure. The SPH summation is then performed via an inner product of quantum registers. This approach is tested in a classical sense for the kernel sum and first and second gradients of a function, using both the Gaussian and Wendland kernel functions, with comparisons for various register sizes made against analytical results. Error convergence is exponential in the number of qubits. It is hoped that this one-dimensional work will provide the foundation for a more general SPH algorithm, eventually leading to the highly efficient simulation of complex engineering problems on emerging quantum computers

Incompressible smoothed particle hydrodynamics (SPH) with reduced temporal noise and generalised Fickian smoothing applied to body–water slam and efficient wave–body interaction

AbstractIncompressible smoothed particle hydrodynamics generally requires particle distribution smoothing to give stable and accurate simulations with noise-free pressures. The diffusion-based smoothing algorithm of Lind et al. (J. Comp. Phys. 231 (2012) 1499–1523) has proved effective for a range of impulsive flows and propagating waves. Here we apply this to body–water slam and wave–body impact problems and discover that temporal pressure noise can occur for these applications (while spatial noise is effectively eliminated). This is due to the free-surface treatment as a discontinuous boundary. Treating this as a continuous very thin boundary within the pressure solver is shown to effectively cure this problem. The particle smoothing algorithm is further generalised so that a non-dimensional diffusion coefficient is applied which suits a given time step and particle spacing.We model the particular problems of cylinder and wedge slam into still water. We also model wave-body impact by setting up undisturbed wave propagation within a periodic domain several wavelengths long and inserting the body. In this case, the loads become cyclic after one wave period and are in good agreement with experiment. This approach is more efficient than the conventional wave flume approach with a wavemaker which requires many wavelengths and a beach absorber.Results are accurate and virtually noise-free, spatially and temporally. Convergence is demonstrated. Although these test cases are two-dimensional with simple geometries, the approach is quite general and may be readily extended to three dimensions

A numerical study of the effect of viscoelasticity on cavitation and bubble dynamics

In the interests of gaining crucial initial insights, a simplified system of governing equations is first considered. The ambient fluid around the bubble is considered incompressible and the flow irrotational.  Viscoelastic effects are included through the normal stress balance at the bubble surface. The governing equations are then solved using a boundary element method. With regard to spherical bubble collapse, the model captures the behaviour seen in other studies, including the damped oscillation of the bubble radius with time and the existence of an elastic-limit solution. The model is extended in order to investigate multi-bubble dynamics near a rigid wall and a free surface. It is found that viscoelastic effects can present jet formation, produce cusped bubble shapes, and generally prevent the catastrophic collapse that is seen in the inviscid cases. The model is then used to investigate the role of viscoelasticity in the dynamics of rising gas bubbles. The dynamics of bubbles rising in a viscoelastic liquid are characterised by three phenomena: the trailing edge cusp, negative wake, and the rise velocity jump discontinuity. The model predicts the cusp at the trailing end of a rising bubble to a high resolution.  However, the irrotational assumption precludes the prediction of the negative wake. The corresponding absence of the jump discontinuity supports the hypothesis that the negative wake is primarily responsible for the jump discontinuity, as mooted in previous studies. A second model confirms that the findings are a faithful account of bubble dynamics in viscoelastic fluids

A numerical study of the effect of viscoelasticity on cavitation and bubble dynamics

In this thesis two different models and numerical methods have been developed to investigate the dynamics of bubbles in viscoelastic fluids. In the interests of gaining crucial initial insights, a simplifed system of governing equations is first considered. The ambient fluid around the bubble is considered incompressible and the flow irrotational. Viscoelastic effects are included through the normal stress balance at the bubble surface. The governing equations are then solved using a boundary element method. With regard to spherical bubble collapse, the model captures the behaviour seen in other studies, including the damped oscillation of the bubble radius with time and the existence of an elastic-limit solution. The model is extended in order to investigate multi-bubble dynamics near a rigid wall and a free surface. It is found that viscoelastic effects can prevent jet formation, produce cusped bubble shapes, and generally prevent the catastrophic collapse that is seen in the inviscid cases. The model is then used to investigate the role of viscoelasticity in the dynamics of rising gas bubbles. The dynamics of bubbles rising in a viscoelastic liquid are characterised by three phenomena: the trailing edge cusp, negative wake, and the rise velocity jump discontinuity. The model predicts the cusp at the trailing end of a rising bubble to a high resolution. However, the irrotational assumption precludes the prediction of the negative wake. The corresponding absence of the jump discontinuity supports the hypothesis that the negative wake is primarily responsible for the jump discontinuity, as mooted in previous studies. A second model is developed with the intention of gaining further insight into the role of viscoelasticity and corroborating the finndings of the first model. This second model employs the full compressible governing equations in a two dimensional domain. The equations are solved using the spectral element method, while the two phases are represented by "marker particles". The results are in qualitative agreement with the first model and confirm that the findings presented are a faithful account of bubble dynamics in viscoelastic fluids

System for Removing Pollutants from Incinerator Exhaust

A system for removing pollutants -- primarily sulfur dioxide and mixed oxides of nitrogen (NOx) -- from incinerator exhaust has been demonstrated. The system is also designed secondarily to remove particles, hydrocarbons, and CO. The system is intended for use in an enclosed environment, for which a prior NOx-and-SO2-removal system designed for industrial settings would not be suitable

Is there a bidirectional relationship between sleep and asthma and allergy in a general population?

The presented study aims at examining the relationship between sleep, on the one hand, and allergic asthma, non-allergic asthma, allergic rhinitis, and atopic dermatitis, on the other hand. These afflictions are highly comorbid, and a common denominator is nasal congestion and itching peaking at night, which may disturb sleep. However, previous research has suggested an alternative relationship in which insomnia precedes asthma and allergy. The objective is thus to explore whether there is a bidirectional relationship between sleep and asthma/allergy

Clustering and Alignment of Polymorphic Sequences for HLA-DRB1 Genotyping

Located on Chromosome 6p21, classical human leukocyte antigen genes are highly polymorphic. HLA alleles associate with a variety of phenotypes, such as narcolepsy, autoimmunity, as well as immunologic response to infectious disease. Moreover, high resolution genotyping of these loci is critical to achieving long-term survival of allogeneic transplants. Development of methods to obtain high resolution analysis of HLA genotypes will lead to improved understanding of how select alleles contribute to human health and disease risk. Genomic DNAs were obtained from a cohort of n = 383 subjects recruited as part of an Ulcerative Colitis study and analyzed for HLA-DRB1. HLA genotypes were determined using sequence specific oligonucleotide probes and by next-generation sequencing using the Roche/454 GSFLX instrument. The Clustering and Alignment of Polymorphic Sequences (CAPSeq) software application was developed to analyze next-generation sequencing data. The application generates HLA sequence specific 6-digit genotype information from next-generation sequencing data using MUMmer to align sequences and the R package diffusionMap to classify sequences into their respective allelic groups. The incorporation of Bootstrap Aggregating, Bagging to aid in sorting of sequences into allele classes resulted in improved genotyping accuracy. Using Bagging iterations equal to 60, the genotyping results obtained using CAPSeq when compared with sequence specific oligonucleotide probe characterized 4-digit genotypes exhibited high rates of concordance, matching at 759 out of 766 (99.1%) alleles. © 2013 Ringquist et al