Maximum Wall Stress Research Articles

Tribological properties of polyaromatic organics as lubricating grease

The tribological properties of polyaromatic organics (xPyE) as lubricating grease additives are studied by simulations and experiments. Molecular Dynamics (MD) simulations are used to simulate the mechanical properties of four kinds of polyaromatic organics (2P1E, 3P2E, 4P3E, and 5P4E) with different aromatic ring numbers and a mass fraction under 300 MPa and 5 m/s relative shear velocity of the two solid walls. The friction force, positive pressure, stress, and adsorption energy are calculated quantitatively. Meantime, the friction coefficient of lubricating grease and the wear morphology of the sample are measured by Multifunctional Friction and Wear Testing Machine. The results show that the organic additives adsorbed on the wall form a protective film during the shearing process, improving the bearing capacity and reducing friction and wear. Among them, the 3P2E organic additive has an appropriate number of aromatic rings. Its single molecular adsorption energy and unit adsorption energy are higher than other organic additives and can uniformly lay on the wall to form a stable, protective film. This demonstrates the best friction performance and improves the load-bearing capacity of the lubricating film, reducing maximum wall stress by 53.4 %.

First assessment of flow phenomena of acute and chronic thrombosis in the jugular veins using new ultrasound vector-flow imaging.

First assessment of flow changes in the jugular veins using high resolution ultrasound vector flow. 15 patients (8 males, 7 females) with an age range of 35 to 82 years (mean age 58.53±12.26 years) were examined by an experienced examiner using high power ultrasound equipment (Resona R9, Mindray) with probe technology (Mindray L9-3U Linear Array transducer, 2.5 to 9.0 MHz). This group was compared with five healthy subjects (mean age 35.4±13.79 years) as a reference. To assess flow changes, the color-coded duplex sonography and the novel vector flow technique were used. The evaluation was performed of vector morphology changes, turbulence, and wall resistance measurements. There were changes after acute and chronic thrombosis in 9 cases, and venous compression in 7 cases. Turbulence was measurable from 0.01 % to 64.44 %, the average turbulence was 19.73±22.06 %. Wall resistance measurement showed values from 0.01 Pa to 3.14 Pa, depending on the age of the thrombosis or compression. The reference veins showed turbulence of 0.94±1.5 % and a mean wall resistance of 0.05±0.05 Pa. There are statistically significant differences between normal and thrombotic or compressed veins in terms of maximum wall stress (p = 0.006) and mean degree of turbulence (p = 0.012), while the difference in mean wall stress is not statistically significant (p = 0.058). Despite still existing technical limitations, the combination of V-flow and wall stress measurements in jugular vein changes suggests a high diagnostic potential.

On the Impact of Residual Strains in the Stress Analysis of Patient-Specific Atherosclerotic Carotid Vessels: Predictions Based on the Homogenous Stress Hypothesis

The identification of carotid atherosclerotic lesion at risk for plaque rupture, eventually resulting in cerebral embolism and stroke, is of paramount clinical importance. High stress in the fibrous plaque cap has been proposed as risk factor. However, among others, residual strains influence said stress predictions, but quantitative and qualitative implications of residual strains in this context are not well explored. We therefore propose a multiplicative kinematics-based Growth and Remodeling (G&R) framework to predict residual strains from homogenizing tissue stress and then investigate its implication on plaque stress. Carotid vessel morphology of four patients was reconstructed from clinical Computed Tomography-Angiography (CT-A) images and equipped with heterogeneous tissue constitutive properties assigned through a histology-based artificial intelligence image segmentation tool. As compared to a purely elastic analysis and depending on patient-specific morphology and tissue distributions, the incorporation of residual strains reduced the maximum wall stress by up to 30%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30\\%$$\\end{document} and resulted in a fundamentally different distribution of stress across the atherosclerotic wall. Regardless residual strains homogenized tissue stresses, the fibrous plaque cap may persistently be exposed to spots of high stress. In conclusion, the incorporation of residual strains in biomechanical studies of atherosclerotic carotids may be important for a reliable assessment of fibrous plaque cap stress.

Acute Mechanical Consequences of Vessel-Specific Coronary Bypass Combinations.

Premature coronary artery bypass graft (CABG) failure has been linked to geometric, mechanical, and compositional discrepancies between host and graft tissues. Acute hemodynamic disturbances and the introduction of wall stress gradients trigger a myriad of mechanobiological processes at the anastomosis that can be associated with restenosis and graft failure. Although the origins of coronary artery disease dictate the anastomotic target, an opportunity exists for graft-vessel optimization through rationale graft selection. Here we explored the four distinct regions of the left (L) and right (R) ITA (1 = proximal, 2 = submuscular, 3 = middle, 4 = distal), and four common target vessels in the coronary circulation including the proximal and distal left anterior descending (PLAD & DLAD), right coronary (RCA), and left circumflex (LCX) arteries. Benchtop biaxial mechanical data was used to acquire constitutive model parameters of these tissues and enable vessel-specific computational models to elucidate the mechanical consequences of 32 unique graft-target combinations. Simulations revealed the maximum principal wall stresses for the PLAD, RCA, and LCX occurred when anastomosed with LITA1, and the maximum flow-induced shear stress occurred with LITA4. The DLAD, on the other hand, reached stress maximums when anastomosed to LITA4. Using a normalized objective function of simulation output variables, we found LITA2 to be the best graft choice for both LADs, RITA3 for the RCA, and LITA3 for the LCX. Although mechanical compatibility is just one of many factors determining bypass graft outcomes, our data suggests improvements can be made to the grafting process through vessel-specific regional optimization.

A comparative study on computational fluid dynamic, fluid-structure interaction and static structural analyses of cerebral aneurysm

ABSTRACT Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) are increasingly used to predict the hemodynamic and structural behaviors of cerebral aneurysms (CAs) whilst a less-pursued method is the static structural analysis (SSA) using the finite element method. In this paper, hemodynamic parameters including the flow velocity and wall shear stress predicted by CFD and FSI are compared whilst structural parameters including the wall displacement and wall stress predicted by SSA and FSI are compared for four patient-specific CA models under different systolic/diastolic pressures. The predicted distribution patterns of the same parameters for the same CA model under different pressures are similar. However, the percentage differences of the maximum hemodynamic parameters increase with increasing pressure. Conversely, the percentage differences of the maximum structural parameters decrease from a few to less than 1.5% when the systolic/diastolic pressure changes from 120/80 to 180/110 mmHg. The ratio of the computation times for CFD, SSA and FSI is typically 75:1:165. If the maximum wall stress under either ongoing or temporary hypertension is the most critical factor for immediate rupture and, thus, clinical treatment of CAs, SSA can provide a low cost and efficient predictions close to those of FSI for assessing the rupture risk.

Hemodynamic simulation of abdominal aortic aneurysm on idealised models: Investigation of stress parameters during disease progression

Background and ObjectiveAnalysis and prediction of rupture risk of abdominal aortic aneurysms (AAA) facilitates planning for surgical interventions and assessment of plausible treatment modalities. Present approach of using maximum diameter criterion, is giving way to hemodynamic and bio-mechanical based predictors in conjunction with Computational fluid dynamic (CFD) simulations. Detailed studies on hemodynamic and bio-mechanical parameters at the stage of maximum growth/rupture is of practical importance to the clinical community. However, understanding the changes in these parameters at different stages of growth, will be useful for clinicians, in planning routine monitoring to reduce the risk of sudden rupture. This is particularly useful in medical resource starved nations. Present study investigates the hemodynamic and bio-mechanical changes occurring during the growth stages of aortic aneurysms using fluid structure interaction (FSI) studies. MethodSix idealized fusiform aneurysm models spanning high (shorter) and low (longer) values of the shape index (DHr), have been analysed at three different stages of growth viz, a Dmax of 3.5cm, 4.25cm, 5cm. Pulsatile Newtonian blood flow, passing through an elastic arterial vessel wall with uniform thickness is assumed. Two-way coupled fluid structure interaction have been employed for the numerical simulation of blood flow dynamics and arterial wall mechanics. ResultsWall shear stress (WSS) parameters and vonmises stress indicators, co-relating rupture and thrombus formation, have been extracted and reported, at each growth stage. When the aneurysm progresses in diameter, the areas recording abnormally low TAWSS, as well as areas of high/low OSI were found to increase at different rates for shorter and longer aneurysms. Moreover, drastic increase in the maximum wall stresses (MWS) and wall displacement were observed as the aneurysm approached the critical diameter. ConclusionHemodynamic predictors were found to be highly dependent on the shape index (DHr), when the aneurysm was small, whereas significant influence of DHr on the wall stresses happens, as the aneurysm approaches the critical diameter. Inconsistent variation of these indicators exhibited by shorter aneurysms (high DHr) at different growth stages, demands routine monitoring (using scans), of such aneurysms, to prevent unexpected rupture.

The myosin activator omecamtiv mecarbil improves wall stress in a rat model of chronic aortic regurgitation.

In patients with chronic aortic regurgitation (AR), excessive preload and afterload increase left ventricle wall stress, leading to left ventricular systolic dysfunction. Thus, the objective of the present study was to evaluate the effects of the myosin activator omecamtiv mecarbil (OM) on left ventricle wall stress in an experimental rat model of severe chronic AR. Forty adult male Wistar rats were randomized into two experimental groups: induction of AR (acute phase) by retrograde puncture (n = 34) or a sham intervention (n = 6). Rats that survived the acute phase (n = 18) were randomized into an OM group (n = 8) or a placebo group (n = 10). Equal volumes of OM (1.2 mg/kg/h) or placebo (0.9% NaCl) were continuously infused into the femoral vein over 30 min. OM significantly decreased end‐systolic and end‐diastolic and maximum wall stress in this experimental rat model of chronic severe AR (p < 0.001) and increased systolic performance assessed by fractional shortening and left ventricle end‐systolic diameter; both p < 0.05). These effects were correlated with decreased indices of global cardiac function (cardiac output and stroke volume; p < 0.05) but were not inferior to baseline pump indices. Infusion with placebo did not affect global cardiac function but decreased end‐systolic wall stress (p < 0.05) and increased systolic performance (all p < 0.001). In the sham‐operated (control) group, OM decreased diastolic wall stress (p < 0.05). Based on these results, OM had a favorable effect on left ventricle wall stress in an experimental rat model of severe chronic AR.

Impact of the excitation frequencies on wall stresses in a storage tank

This research addresses the experimentally determined relationship between the excitation frequency and both hoop and axial wall stresses in an upright water storage tank. A low-density polyethylene tank, utilising six water height to tank radius ratios (aspect ratios), was tested using a shake table. The tank is unrestrained at the base, i.e., uplift can occur. Harmonic excitations with eight frequencies that cover the dominant frequencies of recorded strong earthquakes were applied. Additionally, Ricker wavelet excitations of two different dominant frequencies, within the earthquake range, were considered. The maximum wall stresses calculated from experimental data and those from a nonlinear elastic spring-mass model were compared. The results reveal that, under low dominant-frequency excitations, the sloshing behaviour governs the development of wall stresses. In contrast, under high-frequency excitations, uplift determines the wall stresses. Uplift and sloshing occur simultaneously, and the contribution of each of these factors to wall stresses depends upon the aspect ratio and both the frequency and acceleration of the excitation. The spring-mass model tends to overestimate both hoop and axial stresses when the aspect ratio is higher than two, regardless of the excitation frequency.

Angiography-Based 4-Dimensional Superficial Wall Strain and Stress: A New Diagnostic Tool in the Catheterization Laboratory.

A novel method for four-dimensional superficial wall strain and stress (4D-SWS) is derived from the arterial motion as pictured by invasive coronary angiography. Compared with the conventional finite element analysis of cardiovascular biomechanics using the estimated pulsatile pressure, the 4D-SWS approach can calculate the dynamic mechanical state of the superficial wall in vivo, which could be directly linked with plaque rupture or stent fracture. The validation of this approach using in silico models showed that the distribution and maximum values of superficial wall stress were similar to those calculated by conventional finite element analysis. The in vivo deformation was validated on 16 coronary arteries, from the comparison of centerlines predicted by the 4D-SWS approach against the actual centerlines reconstructed from angiograms at a randomly selected time-point, which demonstrated a good agreement of the centerline morphology between both approaches (scaling: 0.995 ± 0.018 and dissimilarity: 0.007 ± 0.014). The in silico vessel models with softer plaque and larger plaque burden presented more variation in mean lumen diameter and resulted in higher superficial wall stress. In more than half of the patients (n = 16), the maximum superficial wall stress was found at the proximal lesion shoulder. Additionally, in three patients who later suffered from acute coronary syndrome, the culprit plaque rupture sites co-localized with the site of highest superficial wall stress on their baseline angiography. These representative cases suggest that angiography-based superficial wall dynamics have the potential to identify coronary segments at high-risk of plaque rupture and fracture sites of implanted stents. Ongoing studies are focusing on identifying weak spots in coronary bypass grafts, and on exploring the biomechanical mechanisms of coronary arterial remodeling and aneurysm formation. Future developments involve integration of fast computational techniques to allow online availability of superficial wall strain and stress in the catheterization laboratory.

Comparative Study of Aortic Wall Stress According to Geometric Parameters in Abdominal Aortic Aneurysms

In abdominal aortic aneurysm (AAA), the rupture of the aortic tissue is directly related to wall stress. Thus, the investigation of maximum wall stress is a necessary procedure to predict the aortic rupture in AAA. In this study, computational simulations were performed to investigate the correlation between peak wall stress (PWS) and AAA geometry. The Holzapfel model and various orientations of the collagen fibers and thicknesses of the layers of the aorta were employed in the simulation. The material constants used in the Holzapfel model were estimated from the examination and analysis of the biaxial tensile test results of the normal abdominal aorta and AAA. The aneurysm diameter, height, neck angle, and iliac angle were selected as geometric factors affecting the AAA rupture. In addition, a simulation scenario was conceived and created based on the measurement results using the computed tomography data of patients with AAA. Accordingly, the correlation between the PWS and AAA geometry was estimated.

Rupture Risk Assessment of Cervical Spinal Manipulations on Carotid Atherosclerotic Plaque by a 3D Fluid-Structure Interaction Model.

Method The FSI model, based on MRI data of an atherosclerosis patient, was used to simulate the deformations of the plaque and lumen during the process of two kinds of typical cSMT (the high-speed, low-amplitude spinal manipulation and the cervical rotatory manipulation). The biomechanical parameters were recorded, such as the highest wall shear stress (WSS), the maximum plaque wall stress (PWS), the wall tensile stress (Von mises stress, VWTS), and the strain. Result The max_WSS was 33.77 kPa in the most extensive deformation. The highest WSS region on the plaque surface was also the highest PWS region. The max_PWS in a 12% stretch was 55.11 kPa, which was lower than the rupture threshold. The max_VWTS of the cap in 12% stretch which approached the fracture stress level was 116.75 kPa. Moreover, the vessel's max_VWTS values in 10% and 12% stretch were 554.21 and 855.19 kPa. They were higher than the fracture threshold, which might cause media fracture. Meanwhile, the 7% stretched strain was 0.29, closed to the smallest experimental green strains at rupture. Conclusion The carotid arteries' higher stretch generated the higher stress level of the plaque. Cervical rotatory manipulation might cause plaque at a high risk of rupture in deformation after 12% stretch and more. Lower deformation of the plaque and artery caused by the high-speed, low-amplitude spinal manipulation might be safer.

Predictors of Abdominal Aortic Aneurysm Risks.

Computational biomechanics via finite element analysis (FEA) has long promised a means of assessing patient-specific abdominal aortic aneurysm (AAA) rupture risk with greater efficacy than current clinically used size-based criteria. The pursuit stems from the notion that AAA rupture occurs when wall stress exceeds wall strength. Quantification of peak (maximum) wall stress (PWS) has been at the cornerstone of this research, with numerous studies having demonstrated that PWS better differentiates ruptured AAAs from non-ruptured AAAs. In contrast to wall stress models, which have become progressively more sophisticated, there has been relatively little progress in estimating patient-specific wall strength. This is because wall strength cannot be inferred non-invasively, and measurements from excised patient tissues show a large spectrum of wall strength values. In this review, we highlight studies that investigated the relationship between biomechanics and AAA rupture risk. We conclude that combining wall stress and wall strength approximations should provide better estimations of AAA rupture risk. However, before personalized biomechanical AAA risk assessment can become a reality, better methods for estimating patient-specific wall properties or surrogate markers of aortic wall degradation are needed. Artificial intelligence methods can be key in stratifying patients, leading to personalized AAA risk assessment.

Wall stresses in dual bottom purged steel making ladles

Dual gas purging is often done in a ladle to accelerate the refining operations in steel industries. The purged gas, mainly argon imparts momentum to the molten metal and establishes a turbulent recirculating flow in the melt, which generates shear stresses on the ladle walls. These stresses in-turn leads to the erosion of the refractory lining, which is undesirable. A three dimensional, transient, multi-phase turbulent model has been developed to predict the shear stress distribution along the wall in dual plug, bottom purged ladles. A parametric study has been performed to understand the dependence of wall stresses on various operating parameters like argon flow rate, metal bath depth, slag thickness as well as on the configuration of the gas injectors. A dimensionless correlation is proposed using regression analysis that predicts the maximum wall stress in the form of skin friction coefficient in terms of the above parameters.

Fluid-structure interaction modeling of aneurysmal arteries under steady-state and pulsatile blood flow: a stability analysis

Tortuous aneurysmal arteries are often associated with a higher risk of rupture but the mechanism remains unclear. The goal of this study was to analyze the buckling and post-buckling behaviors of aneurysmal arteries under pulsatile flow. To accomplish this goal, we analyzed the buckling behavior of model carotid and abdominal aorta with aneurysms by utilizing fluid-structure interaction (FSI) method with realistic waveforms boundary conditions. FSI simulations were done under steady-state and pulsatile flow for normal (1.5) and reduced (1.3) axial stretch ratios to investigate the influence of aneurysm, pulsatile lumen pressure and axial tension on stability. Our results indicated that aneurysmal artery buckled at the critical buckling pressure and its deflection nonlinearly increased with increasing lumen pressure. Buckling elevates the peak stress (up to 118%). The maximum aneurysm wall stress at pulsatile FSI flow was (29%) higher than under static pressure at the peak lumen pressure of 130 mmHg. Buckling results show an increase in lumen shear stress at the inner side of the maximum deflection. Vortex flow was dramatically enlarged with increasing lumen pressure and artery diameter. Aneurysmal arteries are more susceptible than normal arteries to mechanical instability which causes high stresses in the aneurysm wall that could lead to aneurysm rupture.

Innovative approach to determine the minimum wall thickness of flexible buried pipes

This paper uses a finite element based approach to provide a comprehensive understanding to the behaviour and the design performance of buried uPVC pipes with different diameters. It also investigates pipes with good and poor haunch support and proposes minimum safe wall thicknesses for these pipes. The results for pipes with good haunch support showed that the maximum pipe wall stress and deformation increase as the diameter increased. The results for pipes with poor haunch support showed an increase in the dependency of the developed vertical displacement on the haunch support as the diameter or the backfill height increased. Additionally, poor haunch support was found to increase the soil pressure, with the effect increasing as the diameter increased. The design of uPVC pipes for both poor and good haunch support was found to be governed by critical buckling. A key outcome is a new design chart for the minimum wall thickness, which enables the robust and economic design of buried uPVC pipes. Importantly, the methodology adopted in this study can also be applied to the design of flexible pipes manufactured from other materials, buried under different conditions and subjected to different loading arrangements.

Hydriding-Induced Wall Stress Evaluation of a Prototype Four-Inch Short (FISH) Tritium Hydride Bed

The hydriding-induced wall stress evaluation of a prototype Four-Inch SHort (FISH) tritium hydride bed revealed that the advanced design features do not result in additional strain on the process vessel walls during simulated operation. The maximum tensile wall stress measured at high hydrogen loadings (H/M > 0.7) was determined to be <40% of the ASME allowable limit for 316L stainless steel. Variation in wall stress with hydride loading was also examined via stepwise protium absorption and desorption. Minimal hydriding-induced wall stress was observed in the optimal operating range of the hydride material. The results described herein are in good agreement with previous studies on similar hydride storage beds without the advanced design features. Completed verification of ASME compliance for the FISH bed is a major milestone in its qualification for tritium service.

EFFECTS OF HYPERTENSION AND PRESSURE GRADIENT IN A HUMAN CEREBRAL ANEURYSM USING FLUID STRUCTURE INTERACTION SIMULATIONS

Fluid–structure interaction (FSI) simulations were carried out in a human cerebral aneurysm model with the objective of quantifying the effects of hypertension and pressure gradient on the behavior of fluid and solid mechanics. Six FSI simulations were conducted using a hyperelastic Mooney–Rivlin model. Important differences in wall shear stress (WSS), wall displacements, and effective von Mises stress are reported. The hypertension increases wall stress and displacements in the aneurysm region; however, the effects of hypertension on the hemodynamics in the aneurysm region were small. The pressure gradient affects the WSS in the aneurysm and also the displacement and wall stress on the aneurysm. Maximum wall stress with hypertension in the range of rupture strength was found.

Preoperative Image-Based Simulation of Carotid Artery Stenting Considering Agatston Score of Calcified Plaques

The role of calcification inside fibroatheroma during carotid artery stenting operation is controversial. Cardiologists face a major problem in placing stents: “plaque protrusion” i.e. elastic fibrous caps containing early calcifications that penetrate inside the stent. The aim of this work is to assess the contribution of calcification to plaque vulnerability by using image-based models of carotid artery stenting. Technically, Finite Element Analysis was used to simulate the balloon and stent expansion as a preoperative virtual framework. A nonlinear static structural analysis was performed on 20 image-based models of patients reconstructed from Multidetector Computer Tomography (CT) angiography acquisitions. Subject-specific local Elastic Modulus (EM) of calcified plaques was estimated using the Agatston Calcium (Ca) score, as obtained from CT images. The main findings from the personalized simulations are that maximum values of von Mises stress of 102kPa and 329kPa are obtained on calcified plaques when patient-specific balloon pressure expansion and stent self-expansion, respectively, are modeled. In modeling stent expansion procedure, it is observed a statistically significant positive correlation for EM of calcification with maximum stress (R=0.55; p=0.013) and Plaque Wall Stress (PWS) (R=0.47; p=0.038), while no significant correlation is observed for Ca score with maximum stress (R=0.28; p=0.23) and PWS (R=0.27; p=0.26), this last result suggesting a moderate impact of Ca score in plaque rupture. The approach proposed here could enrich the arsenal of tools available for pre-operative prediction of carotid artery stenting procedure in the presence of calcified plaques. Keywords: Atherosclerotic calcification, calcified plaques, carotid artery stenting, finite element analysis, plaque mechanics, subject-specific model.

Carotid wall stress calculated with continuous intima-media thickness assessment using B-mode ultrasound

Cardiovascular risk is normally assessed using clinical risk factors but it can be refined using non-invasive infra-clinical markers. Intima-Media Thickness (IMT) is recognized as an early indicator of cardiovascular disease. Carotid Wall Stress (CWS) can be calculated using arterial pressure and carotid size (diameter and IMT). Generally, IMT is measured during diastole when it reaches its maximum value. However, it changes during the cardiac cycle and a time-dependant waveform can be obtained using B-mode ultrasound images. In this work we calculated CWS considering three different approaches for IMT assessment: (i) constant IMT (standard diastolic value), (ii) estimated IMT from diameter waveform (assuming a constant cross-sectional wall area) and (iii) continuously measured IMT. Our results showed that maximum wall stress depends on the IMT estimation method. Systolic CWS progressively increased using the three approaches (p<0.024). We conclude that maximum CWS is highly dependent on wall thickness and accurate IMT measures during systole should be encouraged.

CFD modelling of unsteady electro-osmotic permeate flux enhancement in membrane systems

Electro-osmotic flow (EOF) perturbations induced near the membrane surface are a promising approach to increase wall shear, which in turn has the potential to slow the onset of fouling for nanofiltration and reverse osmosis processes. As such, it is important to understand the mechanisms that increase wall shear and mass transfer resulting from time-varying EOF perturbations. In this paper, a Computational Fluid Dynamics (CFD) model is used to simulate spatially-uniform unsteady EOF with permeation inside a 2D unobstructed empty membrane channel. Time-averaged permeate flux is used to measure productivity and maximum shear rate is used as a proxy measure for fouling reduction/prevention. The dependencies of solute concentration amplitude and maximum wall stress on slip velocity amplitude are shown to be linear, both in terms of homogeneity and additivity. This implies that time-averaged hydrodynamics and mass transfer do not vary significantly regardless of changes in the frequency and amplitude of the slip velocity, because the effect is cancelled within the time oscillation period. Nevertheless, there are still advantages for this type of perturbation, as larger slip velocity frequency and amplitude increase the maximum wall stress with a negligible change in time-averaged pressure drop, which may have advantages for limiting concentration polarisation and fouling.