Wall Conditions Research Articles

Fully analytical solution framework for general thin-walled composite beams with mixed variational approach

A variationally consistent analytical beam model that describes the theory in a Timoshenko-Vlasov level is developed based on Reissner’s mixed variational theorem. Starting from a shell theory, all the field-governing equations (equilibrium and continuity) and the boundary conditions of the shell wall are derived in closed form, and the mixed method enables finding the explicit forms of the reactive stresses and sectional warpings which are evaluated progressively depending on the level of beam model to be analyzed. The stress recovery part is incorporated in the post-stage of the analysis to compute the layer-wise distribution of stresses over the beam cross-section. The present analysis is validated against numerous benchmark examples available in the literature, including beams with multi-layered strip section, thin-walled anisotropic box sections with elastic couplings, and two-cell airfoil section. The comparison study demonstrates excellent correlations with the results from detailed three-dimensional finite element analysis and other up-to-date beam approaches. Also presented are symbolically expressed stiffness coefficients and the sectional warping modes of coupled composite beams to demonstrate the strength of the proposed beam model.

Vascular Aging and Telomere Biology: The Role of Vitamin D3 Deficiency

Rationale. The impact of vitamin D3 deficiency on the risk and prognosis of numerous chronic diseases has been actively studied for years. Recent research has demonstrated that vitamin D is not merely involved in the control of calcium-phosphorus metabolism, but can also enhance insulin sensitivity, decrease the incidence of type 2 diabetes mellitus (T2DM), obesity and autoimmune destruction of pancreatic β-cells. The influence of vitamin D3 on some cardiometabolic risk factors and cardiovascular disease (CVD) was described. Thus studying the role of vitamin D3 in the development of arteries wall changes in T2DM and IR, and their relationship with biology telomere seems to be quite relevant.Aim. To study the relationship between vitamin D3 deficiency and vascular wall condition, telomere biology in patients with varying insulin sensitivity.Materials and methods. The cross-sectional study involved 305 patients (106 men and 199 women) aged 51.5 ± 13.3 y.o. All patients underwent laboratory and instrumental research methods, study of morphofunctional state vascular wall. Telomere length and telomerase activity were determined using polymerase chain reaction.Results. Totally, 18 patients out of 248 (7.2%) were found to have normal vitamin D3 level (more than 30 ng/ml). In 92.8% of those studied Vitamin D3 insufficiency or deficiency was determined. As increase in vitamin D3 deficiency, an increase in fasting glucose was noted, HbA1c and its elevated concentration, HOMA index, glucose disorders up to T2DM, higher vascular stiffness. Telomerase activity in group with vitamin D3 deficiency was significantly lower than in groups with vitamin D3 insufficiency and normal content. Multiple linear regression analysis revealed that they are independently associated with vitamin D3 in T2DM (B=1.43; st. OR. 0.106; p=0.0001), vascular stiffness (B=0.075; st. OR. 2.11; p=0.017), fasting glucose (B=0.169; st. OR 1.62; p=0.004), HbA1c level (B=0.062; st. OR. 7.4; p=0.001) and the presence of “short” telomeres (B=0.09; st. OR. 1.154; p=0.001). ROC analysis revealed relationships between BMI (0.634, p=0.001), duration of T2DM (0.651, p=0.022), high intima media thickness (0.614, p=0.004), vascular stiffness (0.605, p<0.001), HbA1c (0.588, p=0.022) and presence of vitamin D3 deficiency.Conclusion. In persons with varying insulin sensitivity — from insulin resistance up T2DM is advisable assess vitamin D3 levels for effective prevention of arterial wall changes in addition to traditional CVD risk factors. Availability Vitamin D3 deficiency requires active prevention metabolic disorders and vascular changes.

Growth of graphene nanowalls in low-temperature plasma: Experimental insight in initial growth and importance of wall conditioning

Plasma-enabled growth of vertically aligned graphene nanowalls (CNWs) and the influence of plasma parameters are widely investigated to produce high-quality CNWs. The initial growthsteps of CNWs and the impact of the plasma chamber condition still need to be explored. This work investigatesthe initial growth steps of CNWs and the influence of plasma chamber conditions using advanced spectroscopic and microscopic techniques. The changes in substrate surfaces and CNW growth were studied in two steps: pre-treatment and plasma deposition. Angle-resolved NEXAFS observations on the samples produced during both stages suggest that growth starts horizontallyon the substrate and changes to vertical in one critical moment. Also, we observed that CNW growth occurs not only at the deposition stage but also during the pre-treatment stage, indicating the influence of the chamber wall during the growth. Switching from horizontal to vertical orientation could be explained by the surface energy disbalance during the initial growth stages. The pre-treatment and conditioning of the chamber control the oxygen presence and provide a higher amount of carbon precursor for a fast, stable and controllable growth process. These results will direct the future possibilities of upscaling plasma systems for large-scale growth of CNWs for commercial applications by considering the influence of plasma and chamber conditions.

Thermal resistance analysis on conjugate free convective flow in a thick-walled square chamber

A numerical analysis of the conjugate free convective flow of air in a thick-walled square chamber has been conducted in this study. The finite left thick wall is heated with any of the four heating conditions, while the finite right thick surface is kept at a fixed cold temperature, and the remaining walls are assumed to be insulated. The governing equations are simulated via the Galerkin finite element technique with a triangular discretization scheme. Thermal resistance analysis is done for an extensive range of Rayleigh numbers (103 ≤ Ra ≤ 107) under four heating conditions of the left wall: isothermal, linear, sinusoidal, and isoflux. Besides, ten different combinations of wall thickness (0 ≤ t1/L ≤ 0.2 and 0 ≤ t2/L ≤ 0.2, where L is the length of the chamber) and three wall materials, such as glass fiber (ks = 0.035 W/mK), pinewood (ks = 0.15 W/mK), and plexiglass (ks = 0.195 W/mK), are considered in this parametric study. The effects of these parameters are presented in terms of the mean Nusselt number along the left solid-fluid interacting wall and the overall thermal performance index. In addition, qualitative visualization of heatlines, streamlines, and isotherms is illustrated for the optimum condition. Numerical results suggest that wall materials with higher thermal conductivity and lower wall thickness give the highest overall thermal performance for a linear heating condition.

A Case Study on Distresses of Concrete Pavements Supported on a Retaining Wall

Embankments and retaining walls are integral parts of the bridge system and provide a smooth transition from lower elevations (i.e., roadways) to higher elevations (i.e., bridge decks). Performances of pavement structures supported on embankments or retaining walls are directly related to their conditions. This paper presents a comprehensive case study of the evaluation of pavement structures supported on an in-service mechanically stabilized earth (MSE) wall that showed significant distresses, such as lane separation, faulting, lane settlement, and tilting of the MSE wall. The conditions of the pavement structures were evaluated via visual observations, falling weight deflectometer (FWD) tests, and coring through pavement structures. The conditions of the MSE wall were evaluated through dynamic cone penetrometer (DCP) tests, cone penetration tests (CPTs), LiDAR surveys, and soil borings. Detailed analysis of the data obtained in this study provides valuable insights into potential distress mechanisms.

Tritium removal from JET-ILW after T and D–T experimental campaigns

After the second Deuterium–Tritium Campaign (DTE2) in the JET tokamak with the ITER-Like Wall (ILW) and full tritium campaigns that preceded and followed after the DTE2, a sequence of fuel recovery methods was applied to promote tritium removal from wall components. The sequence started with several days of baking of the main chamber walls at 240 °C and at 320 °C. Subsequently, baking was superimposed with Ion-Cyclotron Wall Conditioning (ICWC) and Glow Discharge Conditioning (GDC) cleaning cycles in deuterium. Diverted plasma operation in deuterium with different strike point configurations, including a Raised Inner Strike Point (RISP) configuration, and with different plasma heating—Ion Cyclotron Resonance Frequency (ICRF) and Neutral Beam Injection (NBI)—concluded the cleaning sequence. Tritium content in plasma and in the pumped gas was monitored throughout the experiment. The applied fuel recovery methods allowed reducing the residual tritium content in deuterium NBI-heated plasmas to about 0.1% as deduced from neutron rate measurements. This value is well below the requirement of 1% set by the maximum 14 MeV fusion neutron budget allocated in the ensuing deuterium plasma campaign. The quantified tritium removal over the course of the experiment was 13.4±0.7×1022 atoms or 0.67±0.03 g with ∼58% attributed to baking, ∼12.5% to ICWC, ∼26% to GDC, and ∼3.5% to first low power RISP plasmas. The experimentally estimated amount of removed tritium is in good agreement with long-term tritium accounting by the JET tritium reprocessing plant, in which the unaccounted amount was reduced by 0.71 g after the cleaning experiment.

SiC as a core-edge integrated wall solution in DIII-D

Silicon carbide (SiC) is a promising material for use in a fusion reactor due to its low hydrogenic diffusivity, high temperature strength and resilience under neutron irradiation [1,2]. To assess SiC as a main wall material in DIII-D, simulations with TRIM.SP and DIVIMP are performed on a well-diagnosed L-mode discharge. The effective charge, Zeff, across the separatrix is used as a figure of merit in comparing SiC to the current graphite walls. It is found that SiC is expected to reduce Zeff, potentially by as much as ∼50 %. It is discussed how SiC may be expected to “self-condition” and create wall conditions similar to siliconization, further lowering Zeff due to efficient oxygen gettering. The potential benefits are reviewed and a path towards SiC walls in DIII-D is presented.

Hubungan Faktor Risiko dengan Kejadian Malaria di Kampung Nolokla Kabupaten Jayapura

Malaria is a dangerous disease and is still a public health problem in Indonesia, caused by parasites of the genus Plasmodium and transmitted by female mosquitoes of the genus Anopheles. The purpose of this study was to analyze the risk factors for the incidence of malaria and measured the magnitude of the various risk factors that influenced the incidence of malaria in Nolokla Village, East Sentani District, Jayapura Regency. This study used a case control study to find out how far the risk factors included the physical environment, the biological environment and the socio-cultural environment on the incidence of malaria. The case group was all people who declared clinical malaria while the control group was those who were declared free of malaria. The number of samples in this study were 60 respondents, the case samples were taken randomly as many as 30 people and the control group was also 30 people were taken by matching method. The results of the bivariate analysis showed that there were four risk factors, namely the breeding site, the condition of the walls of the house, the presence of shrubs and the presence of Anopheles larvae, and there were six risk factors that had no effect on the incidence of malaria so they were not included in the follow-up test. From the multivariate analysis, it was found that the risk factors that influenced the incidence of malaria were breeding site (p=0.035, OR=3.143, 95%CI 1.066-9.267), condition of house walls (p=0.028, OR=4.500, 95%CI=1.094-18,503), presence of shrubs (p=0.006, OR=5,000, 95%CI=1,510–16,560), presence of Anopheles larvae (p 0.028, OR=3,500, 95%CI=1.112-11.017). The most dominant risk factor that may play a role in the incidence of malaria was the presence of shrubs (Exp=3.095). Key words: malaria incidence; API; case control; Nolokla village.

POSSIBILITIES OF USING THE ANALYSIS OF OXIDANT-ANTIOXIDANT METABOLIC PROCESSES AND ION EXCHANGE IN PREDICTING THE DEVELOPMENT OF POSTOPERATIVE COMPLICATIONS IN SMALL BOWEL SURGERY

Summary. Introduction. The work is devoted to the study of the possibilities of using the analysis of oxidant-antioxidant metabolic processes and ion exchange in predicting the development of postoperative complications during operations on the small intestine in conditions of a compromised abdominal cavity.
 The aim of the study. To determine the peculiarities of the flow of oxidant-antioxidant metabolic processes and ion exchange during operations on the small intestine in conditions of intra-abdominal infection and to study the clinical effectiveness of their assessment.
 Materials and methods. Research was conducted at the Institute of General and Emergency Surgery of the State University named after V.T. Zaitsev National Academy of Sciences of Ukraine”. The study properly included 88 patients who were divided into three groups: a control group (20 patients), a study group (50 patients).
 Results and discussion. The most common criteria for assessing the viability of an ischemic intestine are subjective assessments of color, motility, and pulsation of mesenteric vessels both during examination and after physical or pharmacological effects. However, such an assessment is subjective, does not always correspond to the actual condition of the intestinal wall, which leads either to an unjustified expansion of the scope of the intervention, or to an erroneous overestimation of the vital function of the damaged intestine.
 As a result of the research, a decrease in the phagocytic activity of neutrophils was found in patients who underwent resection of intestinal segments. In these patients, the development of endogenous intoxication was characterized by a decrease in the level of platelets and indicators of the blood anticoagulation system, leukopenia and methemoglobinemia, which requires antioxidant, antitoxic, as well as anticoagulant and immunological correction.
 The study of the exchange of metal ions in the blood serum of operated patients revealed dynamic changes in their content, iron ions (Fe2+); zinc (Zn2+); copper (Cu2+). The study of ion exchange of metals in the serum of the studied patients revealed significantly (p<0.05) higher levels of iron and copper, which can have an important diagnostic and prognostic value when justifying the scope of surgical intervention.
 The results of studying the state of oxidant-antioxidant processes in the studied patients revealed an increase in the level of lipid peroxidation products: malondialdehyde (secondary products) and diene conjugates (end products); since the LPO system is a primary predictor of future immunodeficiency.
 The correlation analysis revealed a direct correlation between the initial content of cryoglobulins and the presence of postoperative complications (r=0.56, p=0.07 and r=0.53, p=0.052). Detection of high concentrations of cryoglobulins in the blood serum of operated patients already in the first hours allowed us to assume the presence of maximal autoimmune changes in intra-abdominal infection.
 The study of the spectrum of serum protein fractions, lipid peroxidation, the state of antioxidant protection, the activity of liver enzymes, factors of humoral and cellular immunity, revealed pronounced endotoxicosis, functional damage to hepatocytes, a violation of the immune status of the body, which correlated with the severity of pathological changes against the background of intra-abdominal infection.
 Conclusions. Analysis of oxidant-antioxidant metabolic processes, bioenergetic state testified to the stimulation of free radical processes, activation of lipid peroxidation, inhibition of antiradical protection in the studied patients, which in the complex stimulates the development of membrane pathology against the background of endogenous intoxication and inhibition of bioenergetics; there are processes of primary inhibition of non-specific resistance of the organism, in combination with a violation of the regeneration of individual links of the immune system.

A promising protocol for the endothelialization of vascular grafts in an instrumented rotating bioreactor towards clinical application

Pre-endothelialization of a tissue-engineered vascular graft before implantation aims to prevent thrombosis and immunoreactions. This work demonstrates a standardized cultivation process to build a confluent monolayer with human aortal endothelial cells on xenogenous scaffolds. Pre-tested dynamic cultivation conditions in flow slides with pulsatile flow (1 Hz) representing arterial wall conditions were transferred to a newly designed multi-featured rotational bioreactor system. The medium was thickened with 1% methyl cellulose simulating a non-Newtonian fluid comparable to blood. Computational fluid dynamics was used to estimate the optimal volume flow and medium distribution inside the bioreactor chamber for defined wall-near shear stress levels. Flow measurements were performed during cultivation for constant monitoring of the process. Three decellularized porcine arteries were seeded and cultivated in the bioreactor over six days. 1% MC turned out to be the optimal percentage to achieve shear stress values ranging up to 10 dyn/cm2. Vascular endothelial cells formed a continuous monolayer with significant cell alignment in the direction of flow. The presented cultivation protocol in the bioreactor system thus displays a promising template for graft endothelialization and cultivation. Therefore, establishing a key step for future tissue-engineered vascular graft development with a view towards clinical application.

Spectral Theory of Turbulent Heat Transfer in the Presence of a Rough Wall.

Using the phenomenological theory of turbulence, a direct link between the Stanton number-a dimensionless number that represents the ratio of transferred heat to the thermal capacity of the fluid-and the scalar spectrum is established for both smooth wall and rough wall conditions. The effect of different scales of motion on heat transfer is demonstrated by investigating relevant limits of the scalar spectrum. It is shown that two important observations in literature-the lack of increase in heat transfer beyond a certain roughness size and the nonclassical Prandtl number scaling-are reproduced if only the viscous inertial and diffusive range of the scalar spectrum is accounted for.

Analysis of periodic pulsating blood flow of fractional Maxwell power-law fluid in carotid artery with elastic vessel wall

Hemodynamic analysis reveals a highly significant effect on the prevention, diagnosis, and treatment of human vascular diseases. This article goes deeply into the periodic pulsatile blood flow in the carotid artery with an elastic vessel wall. In view of blood rheological experimental data, the constitutive equation of fractional Maxwell power-law fluid with yield stress, which can describe the four characteristics of yield stress, viscoelasticity, shear thinning, and thixotropy is established. Meanwhile, drawing support from the data of pulsatile flow, the finite Fourier series of pressure gradient with a period of 1 s has been proposed. Leading into Hooke’s law can build the fluid-structure coupling boundary condition of blood flow and elastic vessel wall. The numerical solutions are got hold of finite difference method integrated with the newly developed L1-algorithm, and their convergence and stability of which are verified. The axial velocities of blood under different constitutive relationships are compared. The results throw light that other constitutive relationships underestimate the velocity of blood. Furthermore, the flow rate and wall shear stress on different fluid are calculated. It can be concluded that compared with Bingham fluid, the maximum and minimum flow rate/wall shear stress of fractional Maxwell power-law fluid with yield stress increases by 19% and 32%, respectively. The flow rate lags behind the pressure gradient and has time delay effect, on the contrary, the velocity of blood vessel wall is keeping pace with the pressure gradient. The effects of relevant physical parameters on velocity are discussed. In addition, the spatiotemporal distribution of blood flow in cerebral artery and femoral artery are analyzed.

Comparison of ion cyclotron wall conditioning discharges in hydrogen and helium in JET

This paper explores the plasma parameters of helium and hydrogen Ion Cyclotron Wall Conditioning (ICWC) discharges performed in JET as part of a He/H fuelling changeover experiment. The conducted study shows that plasma with a higher density is formed in helium than in hydrogen. A distinct glow in the ion cyclotron resonance zone is observed throughout the discharge in He. In H-ICWC discharges, a lower radio-frequency coupling efficiency and coupled power was observed than in He-ICWC discharges. While the helium concentration decreased with the number of H-ICWC pulses and the same for hydrogen in He-ICWC, which is the intended result of the plasma wall interaction in the ICWC changeover procedure, the main features of hydrogen as well as the helium IC discharge do not change dramatically.

Time fractional analysis of generalized Casson fluid flow by YAC operator with the effects of slip wall, and chemical reaction in a porous medium

The key aim of the present work is to apply the Yang-Abdel-Cattani operator of fractional order derivative with Rabotnov exponential kernel to the mass-heat transfer of the generalized Casson fluid with generalized Fick's and Fourier's laws. The flow is analyzed in a porous medium under the effects of chemical molecular diffusivity, heat generation and slip wall condition on the fluid velocity. The medium through which the fluid is flowing is subjected to the effects of Newtonian heating. The YAC operator of fractional order can describe the generalized memory effects more suitably than the other fractional operators. So for the sake of a better interpretation of the rheological behavior of the Casson fluid we have used the fractional operator of YAC with Rabotnov exponential kernel. The technique of the Laplace transform is used to acquire the exact analytical solution of the problem in the Mittag-Leffler form. Through MathCAD software physical behaviors of various parameters are investigated on the heat, mass and velocity of the fluid during the flow in a porous medium.

Free Surface Motion of a Liquid Pool with Isothermal Sidewalls as a Benchmark for Marangoni Convection Problems

In single phase flows, benchmarks like the lid driven cavity have become recognized as fundamental tests for newly developed computational fluid dynamics, CFD, codes. For multiphase free surface flows with variable surface tension, the presently studied pool with isothermal sidewalls is suggested as it is the simplest domain where Marangoni effects can dominate. It was also chosen due to its strange sensitivity to the initial setup which is discussed at length from a chosen number of ‘scenarios’. It was found that the fluid interface can reverse deformation by a change in the top boundary condition, the liquid equation of state, and the gravity level. For the top boundary condition, this reversal is due to vapor expansion within the closed volume, creating an additional convection mechanism. Not only does the interface reverse, but the peak height changes by more than an order of magnitude at the same Marangoni number. When including gravity, the peak velocity can increase significantly, but it can also cause a decrease when done in combination with a change in the top wall boundary condition. Finally, thermal expansion of the liquid phase causes the peak velocity to be reduced, with additional reductions from the gravity and top wall condition. The differences in each scenario could lead to significant errors in analyzing a practical application of Marangoni flows. Therefore, it is important to demonstrate that a new CFD code can not only resolve Marangoni convection, but also has the capability to resolve the scenario most relevant to the application at hand.

Optimization of Wall-Conditioning Techniques on the MT-II Tokamak

The MT-II is a small spherical tokamak that is currently under construction at the Pakistan Tokamak Plasma Research Institute. Wall conditioning of the MT-II vacuum vessel (VV) is an essential step to achieve a good quality vacuum for plasma experiments. This study presents an overview of the wall-conditioning techniques implemented on the MT-II VV, including baking and glow discharge cleaning (GDC). Prior to wall conditioning, the system is checked via a helium leak test machine and residual gas analyzer (RGA) to identify and remove leaks. The VV walls are baked at ~180 °C to get rapid desorption of water vapors and other impurities. After the baking process, the partial pressure of most of the carbon- and oxygen-containing impurities is reduced. In particular, the partial pressure of water vapors is reduced by 93%. Consequently, the total leak and outgassing rate is significantly reduced. To further improve the vacuum condition in the vessel, hydrogen GDC is carried out. The fill hydrogen pressure and anode voltage are optimized to get a stable glow discharge. The RGA scan shows that GDC reduces the partial pressure of H2O, O2, and CO2 by 57%, 63%, and 51%, respectively. The results signify that baking and GDC are effective techniques for wall conditioning of the MT-II VV.

Risk factors of malaria transmission in mining workers in Muara Enim, South Sumatra, Indonesia

Eliminating malaria by 2030 is stated as goal three in the UN’s Sustainable Development Goals (SDGs). However, malaria still remains a significant public health problem. This study aims to identify the factors determining malaria transmission in artisanal or small-scale miner (ASM) communities in three villages: Tanjung Agung, Tanjung Lalang, and Penyandingan, located in the Tanjung Enim District, Muara Enim, South Sumatra, Indonesia. Researchers conducted a cross-sectional study involving 92 participants from the study area. They used a logistic regression model to investigate the risk factors related to malaria occurrence. The multivariable analysis revealed that age (Adjusted Prevalence Ratio (APR) = 7.989 with 95% CI 1.724–37.002) and mosquito breeding (APR = 7.685 with 95% CI 1.502–39.309) were risk factors for malaria. On the other hand, higher education (APR = 0.104 with 95% CI 0.027–0.403), the use of mosquito repellent (APR = 0.138 with 95% CI 0.035–0.549), and the condition of house walls (APR = 0.145 with 95% CI 0.0414–0.511) were identified as protective factors. The current study highlights age and mosquito breeding sites as risk factors for malaria. Additionally, higher education, insect repellent use, and the condition of house walls are protective factors against malaria. Therefore, reducing risk factors and increasing protective measures through effective communication, information, and education are highly recommended to eliminate malaria in mining areas.

Self-mode transition, oscillation and inverse hysteresis in ECR discharges

Positive and negative feedback of microwave (MW) ECR (electron cyclotron resonance) discharges in cross magnetic field were manipulated by a three-stub coaxial tuner. Unstable ECR discharges in the positive feedback region, such as the self-mode transition between the ordinary (O)-wave mode and extraordinary (X) one, inverse hysteresis, and oscillation, were investigated using a time-resolved MW power meter, high speed camera, and thermocouple. In the positive feedback region, the self-O → X wave mode discharge transition can be driven under the “hot” wall condition, while the counterpart, namely the self-X → O wave mode transition, is observable for the “cold” wall; the inverse hysteresis and oscillation take place at low and moderate gas flow rates, respectively. The mechanism underlying the self-mode transitions and instabilities is the discharge shift due to the gas heating effect. For MW ECR discharges to become stable, as indicated in previous experiments, they should be mismatched in the negative feedback region.

Evaluation of flushing parameters for clear view vascular endoscopy

Abstract Vascular diseases like aneurysms or atherosclerosis belong to the leading causes of death. For diagnosis and treatment, medical imaging is essential. Standard imaging methods are Ultrasound, X-ray-based Angiography, Computed tomography or Magnet Resonant Imaging. Additionally, Intravascular Ultrasound or Optical Coherence Tomography are available for intravascular imaging. One imaging technique for direct investigation of the inner vessel is vascular endoscopy, also called angioscopy. It is based on the insertion of an optical endoscope into the blood vessel for direct imaging. Dependent on the vessel diameter, these endoscopes have to be very small. Angioscopy can provide valuable information about the condition of the vessel wall and serve for procedure observation or implant assessment. But angioscopy requires the absence of blood for a clear field of view. In prior research, we have already developed methods for the placement of a tiny optical fiber inside a catheter combination. As an essential step toward a clinical study, we now want to evaluate the flushing parameters needed to achieve a clear field of view for the endoscope. The parameters are affected by the blood flow and vessel diameter. We designed a test setup that allows angioscopic examination and the simulation of realistic conditions, such as blood flow and different vessel diameters and that includes a test pattern for image quality assessment.

Turbulent boundary layer over porous media with wall-normal permeability

Porous walls are a widely used passive flow control technique, which shows potential in reducing skin friction and mitigating flow-introduced noise. In the present study, porous media with wall-normal permeability is applied to a flat plate to investigate its interaction with the turbulent boundary layer at the Reynolds number based on friction velocity of Reτ=225. Time-resolved planar and tomographic particle image velocimetry were employed to identify the impact on mean statistics and coherent structures. An overall skin friction reduction of 22% is achieved. The porous wall induces counter-rotating streamwise vortex pairs at the spanwise sides of each pore, leading to momentum transport and the generation of alternative low- and high-speed regions close to the wall. Slip velocity is obtained, associated with the reduction in turbulent fluctuations and Reynolds shear stress. The streamwise velocity streaks and the hairpin vortices are significantly distorted compared with the smooth wall condition due to the downwash and upwash motion, featuring a notable reduction in the number and scale of the coherent structures, in which the skin friction reduction mechanism is related to. The proper orthogonal decomposition analysis returns the most energetic unsteady modes. Although the wall-coherent mode type remains to dominate the production of turbulent fluctuations, the scale and energy content of wall-incoherent modes increase, confirming the modification of the distribution and scale of near-wall turbulent structures.