A numerical investigation into the correction algorithms for SPH method in modeling violent free surface flows

A quantitative comparison of the usual and recent numerical treatments which are applied to the Smoothed Particle Hydrodynamics (SPH) method are presented together with a new free-surface treatment. A series of numerical treatments are studied to refine the numerical procedures of the SPH method particularly for violent flows with a free surface. Two dimensional dam-break and sway-sloshing problems in a tank are modeled by solving Euler's equation of motion utilizing weakly compressible SPH method (WCSPH). Initially, the dam-break benchmark problem is studied by adopting only conventional basic equations of SPH without any numerical remedy and then by considering numerical treatments of interest one after another. In the WCSPH method, the precise calculation of the densities of the particles is vital for the solution, accordingly a density correction algorithm is presented as a basic numerical treatment. Subsequently, Monaghan's (1994) [1] XSPH velocity variant algorithm, artificial particle displacement (APD) algorithm (Shaldoo et al., 2011) [2], and a hybrid combination of velocity updated XSPH (VXSPH) and APD algorithms are implemented separately, but all with the density correction algorithm as a default treatment. The effects of each of these treatments on the pressure and on the free surface profiles are analyzed by comparing our numerical findings with experimental and numerical results in the literature. After the detailed scrutiny on the dam-break problem, sway-sloshing problem is handled with the VXSPH+APD algorithm which has been noted to provide the most reliable and accurate results in the dam-break problem. For the sway-sloshing problem, the time histories of free surface elevations on the left side wall of the rectangular tank are compared with experimental and numerical results available in the literature. It was shown that the VXSPH+APD treatment significantly improves the accuracy of the numerical simulations for violent flows with a free surface and lead to the results which are in very good agreement with experimental and numerical findings of literature in terms of both the kinematic and the dynamic point of view

Sph modelling of long-term sway-sloshing motion in a rectangular tank

This work aims to model long-term simulations of sway-sloshing motion in a partially filled rectangular tank with different water depths and enforced motion frequencies. The lateral motion frequency of the tank is chosen so as to coincide with the lowest theoretical natural frequency for the corresponding beam of the tank and initial depth of water reserve. A truly meshless method, Smoothed Particle Hydrodynamics (SPH) is used to discretize and solve the governing equations. It is shown that numerical results of the proposed SPH scheme are in good agreement with experimental and numerical findings of the literature

Two-year clinical follow-up enhances the diagnosis of early-stage hip osteoarthritis:data from check cohort

OBJECTIVE: To provide a set of diagnostic criteria for early-stage hip osteoarthritis (OA) in primary care, using signs and symptoms monitored over 2 years in individuals with hip pain and/or stiffness. Additionally, the study aimed to see whether these factors were additive to factors based on baseline signs and symptoms only. METHODS: Data of the 543 persons with 735 symptomatic hips were collected from the prospective Cohort Hip and Cohort Knee cohort study. Using data from 5 to 10 years of follow-up, 24 experts (13 general practitioners, 11 secondary care physicians (6 rheumatologists and 5 orthopaedic surgeons)) inspected individuals' medical data on the presence of clinically relevant hip OA. Their diagnoses are used as reference standards. Backward selection method was used to provide models using the factors from baseline to 2 years of follow-up. Additionally, new models were combined with previously published models, using same selection method. Area under the curve (AUC) was calculated after each removal of factors in the final combined models. RESULTS: Radiographic factors and high-sensitive C reactive protein did not end up in any model with change factors only. AUC value (SD) of the final obtained model of change factors was 0.70 (0.01). Adding newly defined factors to previously published models significantly (p&lt;0.0001) increased the AUC value to 0.75 (0.01). CONCLUSION: Final diagnostic criteria, consisting only of the factors obtained through history taking and physical examination, were able to detect early-stage hip OA associated with clinically relevant hip OA 5-10 years later, with 'moderate' precision.</p

A numerical refinement study on the SPH modeling of the violent free surface flows

A comparative study of the numerical treatmentsthat are commonly used in Smoothed Particle Hydrodynamics(SPH) together with relatively a new one, namely ArtificialParticle Displacement algorithm is presented. As a benchmark study, two-dimensional dam-break problem is investigated bymeans of weakly compressible SPH approximation using Eu-ler’s equation of motion with artificial viscosity. After adoptingstandard SPH discretization schemes and equations without anynumerical remedies, three different treatments are sequentiallytested on the dam-break problem. In weakly compressible SPHapproximation, the precise calculation of the densities of theparticles is vital for the overall accuracy of the solution. Inorder to have an improved density field, a density correctionalgorithm is incorporated into the numerical algorithm as abasic numerical treatment. Subsequently, XSPH velocity variantalgorithm [1] and artificial particle displacement (APD) algo-rithm [2] are implemented concurrently in conjunction with thedensity correction algorithm. The effects of each treatment onthe calculated free surface profiles, pressure values and the totalmechanical energy of the system are compared methodically. Theeffects of the numerical treatments particularly on the dynamiccharacteristics of the free surface flow in the dam-break testcase are shown. The outcomes of the simulations show thatdensity correction algorithm to large extent circumvents densityfluctuation induced numerical issues in dam-breaking problem.It is further noted that the combined usage of the APD treatmentand the density correction algorithm gives the most compatibleresults with those of the experimental studies

Modelling of wave generation in a numerical tank by SPH method

There have been many mathematical and physical modelling strategies to represent a numerical wave tank that can generate the desired wave spectrums. Presently, one of the recent methodologies that have certain intrinsic capabilities for the investigation of free-surface hydrodynamic problems, namely, Smoothed-Particle-Hydrodynamics (SPH) technique, has been utilized for the modelling of a numerical wave tank. The Navier–Stokes and continuity equations are utilized for governing the fluid motion through Weakly Compressible SPH (WCSPH) approach which couples pressure and density by an equation of state. As one of the major numerical treatments, kernel gradient normalization is included into the present SPH method together with the numerical treatments, namely, well-known density smoothing algorithm, hybrid velocity variance-based free surface (VFS), and artificial particle displacement (APD) algorithms. The generation of regular and irregular waves is performed by a moving boundary at the inlet where natural damping is targeted by utilizing a dissipative beach at the end of numerical wave tank. A wide range of test cases in terms of wave-lengths and steepness ratios have been investigated for the regular wave simulations. Although the wave-maker is forced linearly to oscillate sinusoidally at the inlet of the tank, due to the relatively high wave steepness ratios applied, the non-linear character of the free-surface has been clearly observed with the performed Fast Fourier Transform analyses. Wave energy densities of the SPH results have also been compared with the linear theory expectations per unit wave-length. To scrutinize the conditions for the wave-breaking inception, three additional wave steepness values have been simulated at a single wave-length value. As a further examination of the proposed SPH scheme, JONSWAP irregular wave spectrum has been utilized with both flap and piston type moving boundaries. In the light of performed simulations, the proposed SPH numerical scheme can provide robust and consistent results while generating regular and irregular wave systems in deep water conditions. Furthermore, it is observed that it has the capability of capturing the non-linear characteristics of generated waves with high sensitivity, including the wave-breaking phenomenon

On the SPH modelling of flow over cylinder beneath to a free-surface

This work aims to model flow around rigid cylinder beneath to a free surface by using a particle based Lagrangian method, namely, Smoothed Particle Hydrodynamics (SPH) which has clear advantages on modeling nonlinear violent free surface problems. This problem which is also regarded as 2-d wave making problem in marine hydrodynamics literature is carried out for three different positions of cylinder centre with two different Froude numbers. The fluid motion is governed by continuity and Eulers equations while Weakly Compressible SPH (WCSPH) approximation together with artificial viscosity term is employed for the numerical discretization of the problem domain. Hybrid Velocity-updated XSPH and Articial Particle Displacement (VXSPH+APD) correction algorithm [1] and standard density correction treatment is also added into the numerical scheme. The Reynolds number is chosen as close to 200 for all cases where three dimensionality first starts to be effective in the flow domain [2]. As the flow characteristics are metastable [12], the free-surface deformations, drag and the lift force on the body shows periodic variation during the evolution of the flow. Free-surface deformations at the maximum and minimum lift instants are compared with the results of Reichl et.al. [12] for the first two cases. The last case considers a higher Froude number and deeper cylinder position where lift and drag forces are compared with the findings of [22]. It is observed that the obtained free-surface profiles, mean values of drag and lift forces give consistent results in a good with the referred literature data

Diagnostic criteria for early hip osteoarthritis: First steps, based on the CHECK study

Objectives. Although there is a general focus on early diagnosis and treatment of hip OA, there are no validated diagnostic criteria for early-stage hip OA. The current study aimed to take the first steps in developing diagnostic criteria for early-stage hip OA, using factors obtained through history taking, physical examination, radiography and blood testing at the first consultation in individuals presenting with hip pain, suspicious for hip OA, in primary care. Methods. Data of the 543 individuals with 735 symptomatic hips at baseline who had any follow-up data available from the prospective CHECK cohort study were used. A group of 26 clinical experts [general practitioners (GPs), rheumatologists and orthopaedic surgeons] evaluated standardized clinical assessment forms of all subjects on the presence of clinically relevant hip OA 5-10 years after baseline. Using the expert-based diagnoses as reference standard, a backward selection method was used to create predictive models based on pre-defined baseline factors from history taking, physical examination, radiography and blood testing. Results. Prevalence of clinically relevant hip OA during follow-up was 22%. Created models contained four to eight baseline factors (mainly WOMAC pain items, painful/restricted movements and radiographic features) and obtained area under the curve between 0.62 (0.002) and 0.71 (0.002). Conclusion. Based on clinical and radiographic features of hip OA obtained at first consultation at a GP for pain/stiffness of the hip, the prediction of clinically relevant hip OA within 5-10 years was 'poor' to 'fair'

Purification and sorting of halloysite nanotubes into homogeneous, agglomeration-free fractions by polydopamine functionalization

Halloysite nanotubes (HNTs) have attracted great attention in the field of nanotechnology as natural, high value-added nanomaterials. Despite their significant potential as carriers of active agents and fillers in nanocomposite structures, inhomogeneity of HNTs in terms of length and diameter along with their a lomeration tendency poses important obstacles for the utilization of them in a wider range of applications. Here, a facile, three-step separation protocol that allows the sorting of HNTs into agglomeration-free, uniform size fractions is reported. The protocol consists of coating of HNTs with polydopamine to impart hydrophilicity and aqueous dispersibility, followed by their ultrasonication and centrifugation at varying velocities for size-based separation. Particle size distribution analysis by scanning electron microscopy and dynamic light scattering has demonstrated that the separation protocol resulted in uniform HNT fractions of varying agglomeration states and particle sizes. The highest quality fraction obtained with 18% yield was free of agglomerations and consisted of HNTs of uniform lengths and diameters. The polydopamine coating on HNTs which facilitated the separation was demonstrated to be removed by a simple heat treatment that preserved the crystal structure of HNTs. The impact of the separation protocol on the loading and functionalization capacity of halloysites was investigated. Highest quality HNTs presented 4.1-fold increase in lumen loading and 1.9-fold increase in covalent surface coupling ratios compared to the loading and functionalization ratios obtained with raw HNTs. Similarly, sorted, high-quality HNTs were demonstrated to be better dispersed in a polymeric matrix, resulting in polymeric nanocomposites with significantly enhanced mechanical properties compared to nanocomposites prepared with raw HNTs. The three-step separation protocol presented here provides a toolbox that allows sorting of raw HNTs into uniform fractions of different size ranges, from which HNTs of desired qualities required by different applications can be selected

Association analyses of depression, anxiety, and physical fitness parameters in Turkish obese adults

Objective: This study aims to investigate the associations among depression, anxiety, aerobic exercise capacity, body fat percentage, sum of skinfolds, abdomen circumference, and waist to hip ratio on the basis of body mass index (BMI) in adults. Methods: The subjects of the study were 60 obese participants (30 women, 30 men) with BMIs over 30 kg/m(2) and 60 healthy controls (30 women, 30 men) with BMIs of 18-25 kg/m(2). Body fat percentage was calculated from the skinfold thicknesses using the formula. Body circumference measurements were performed using a tape measure. Maximal aerobic capacity (VO(2)max) was determined by Astrand submaximal exercise protocol. Two self-reported questionnaires, Beck Depression Inventory (BDI) and Beck Anxiety Inventory (BAI), were administered to all participants. Results: BMI, body fat percentage, sum of skinfolds, abdomen circumference, and waist to hip ratio were found to be higher in obese groups as compared to the controls, while VO(2)max (ml/kg/min) values were lower in both genders. In males, BAI scores and mild-level anxiety percentage values were higher in the obese group than in the control group. There was no significant difference for BDI scores and levels between the obese and control groups in both genders. There was also no significant difference in BAI scores and levels between the obese and control groups in women. Conclusion: The fact that physical fitness being found poor in obese shows the existence of a condition that might constitute an increased tendency for obesity-related disorders. In addition, it was suggested that, in Turkey, attitudes toward obesity change depending on gender