Centrifuge Tests Research Articles

Formulation Development and Evaluation of Microemulsion Loaded Hydrogel Systems with Plant Bioactives in Combination for Treatment of Psoriasis

Psoriasis is an autoimmune, long-lasting skin disorder affecting about 1 to 3% of the world’s population. Plant bio-actives like flavonoids, alkaloids, glycosides, terpenoids, phenolic acids, peptides, tannins, etc., are considered as the best alternative over synthetic drugs, especially for the topical treatment of such chronic skin ailments to avoid side effects of such synthetic agents. The present study aims at the formulation and characterization of novel topical carrier systems for the incorporation of plant bioactive molecules from the class of alkaloids and flavonoids so as to enhance the therapeutic efficacy, bypass the side effects of synthetic drugs, and improve drug localization in the diseased skin to achieve site-specific action. This work created oil, surfactant, and co-surfactant formulations of plant bio-actives using oleic acid, polysorbate 80, and propylene glycol. Different batches of microemulsions with surfactant: Cosurfactant composition ranging from 25 to 34.8% were prepared and were embedded in a hydrogel system containing gelling agents like sodium alginate and carbapol 940 to get ease of topical application in the treatment of psoriasis. These developed micro-emulates (microemulsion loaded hydrogels) were evaluated for various parameters like viscosity, spreadability, content uniformity, microscopic examination, globule size, zeta potential, polydispersibility index, centrifugation test, dilution test, dye test, percent transmittance, conductivity test, etc. The developed formulations were pharmaceutically stable and efficient.

Analyses of the Suction Anchor–Sandy Soil Interactions under Slidable Pulling Action Using DEM-FEM Coupling Method: The Interface Friction Effect

The microscale mechanisms underlying the suction anchor–sandy soil interaction under slidable pulling actions of mooring lines remain poorly understood. This technical note addresses this knowledge gap by investigating the suction anchor–sandy soil interaction from micro to macro, with a particular emphasis on the effect of interface friction. The discrete element method (DEM) was utilized to simulate the sandy soil, while the finite element method (FEM) was employed to model the suction anchors. The peak pulling forces in numerical simulations were verified by centrifuge test results. The research findings highlight the significant influence of interface friction on the pulling force–displacement curves, as it affects the patterns of suction anchor–sandy soil interactions. Furthermore, clear relationships were established between the magnitude of interface friction, rotation angle, and pullout displacement of suction anchors. By examining the macro-to-micro behaviors of suction anchor–sandy soil interactions, this study concludes with a comprehensive understanding of failure patterns and their key characteristics under different interface friction conditions. The findings proved that the interface friction not only influences the anti-pullout capacity but also changes the failure patterns of suction anchor–soil interactions in marine engineering.

LEAP centrifuge tests on retaining walls at Cambridge University

Retaining walls and other waterfront structures were seen to suffer severe damage due to soil liquefaction in previous earthquakes. As part of the LEAP project, cantilever retaining walls with loose, saturated backfill were tested at various centrifuge centres participating in this endeavour. The toe of the retaining wall penetrated about 0.5 m into the dense sand layer underlying the loose sand layer. Retaining walls with different ratios of the retained height h over the penetration depth d were tested. As part of the LEAP project, additional testing was carried out at Cambridge to consider the effect of the wall size on its deformation following liquefaction. It will be shown that a larger wall will suffer more rotation and wall top displacement than a smaller wall with the same h/d ratio. This can have implications for numerical modelling in terms of how well the constitutive models capture the suppressed soil dilatancy at higher confining pressures.

Experimental investigation of dynamic behaviour of pile-supported bridges in sandy deposits

This paper presents the results of centrifuge tests performed on reinforced concrete (RC) pile–supported simply supported girder bridge models in non-liquefiable (unsaturated) and liquefiable (saturated) slightly inclined sandy soil sites. The main objectives were to investigate the dynamic response characteristics of RC pile–supported simply supported girder bridges in non-liquefiable and liquefiable soils, examine the mechanisms causing beam collapse and damage to pile–pier yielding, and verify the effectiveness of cable restrainers. The centrifuge tests were conducted in non-liquefiable and liquefiable sites, each consisting of a three-span RC pile–supported simply supported girder bridge model and a control model with a superstructure equipped with a cable restrainer. First, the dynamic characteristic parameters of the soil and structural models in both sites were obtained. Subsequently, the conventional test results were interpreted, including the excess pore pressure ratio, acceleration, and displacement. The analysis included examining the moment demand of the pile–pier structure and seismic damage mechanisms. Finally, a correlation analysis was performed to evaluate the inertial and kinematic effects on the moment demand of the pile–pier structure. The results show that the acceleration response after soil liquefaction at the inclined sites is amplified unilaterally in the downslope direction and spikes appear. The liquefiable foundation is displaced to the downslope. However, major earthquake induces foundation displacement, and liquefaction leads to a longer duration and more significant soil displacement. The installation of cable restraints significantly increased the acceleration response of the superstructure. Still, it effectively reduced the relative displacement of the superstructure and prevented the beam from collapsing. Soil liquefaction decreases the bending moment of the pile–pier structure, and the cable restrainer causes the damage mode of the pile–pier structure to shift from the pile head to the pier bottom. In the non-liquefiable scenario, the bending moment demand at the pile head has a more significant influence on the inertial effect. Additionally, using the cable restrainer system can increase the kinematic effect after liquefaction. The test results can be used to validate numerical models and provide a reference for pile foundation design.

An approach for analysis of a single energy pile subjected to a horizontal load in sand

Many studies on horizontally loaded energy piles have tended to ignore the impact of axial frictional resistance in the analysis processes or lacked experimental validation. The effect of axial frictional resistance may be considered by conveniently calculating the frictional resistance and revealing the mechanism of axial frictional resistance. Our proposed displacement analysis approach takes into account pile-sand axial friction during heating. Validation was carried out through a centrifuge test case. Subsequent parametric analyses explored the influence of pile diameter and Young's modulus on the lateral response of the pile. Comparative results between the centrifuge test and proposed approach underscored its effectiveness in capturing the impact of friction resistance on energy piles during heating. The parametric analyses show that the increase in pile diameter from 0.5 m to 0.7 m and Young's modulus from 10 GPa to 20 GPa led to a decrease in normalized pile top displacement by 50.68% and 28.33%, a decrease in maximum soil pressure in front of the pile by 16.18% and 11.59%, and a decrease in maximum bending stress of the pile by 3.27% and an increase by 14.48%, respectively.

Centrifuge testing on ordinary and hybrid suction caissons subjected to cyclic lateral loading

Hybrid Suction Caissons (HSCs) are innovative structures that amalgamate a shallow foundation (mat or skirted) with an internal caisson. The results of 40g centrifuge tests conducted on the Ordinary Suction Caisson (OSC) and two HSC types installed in medium-dense saturated sand, enduring long-term lateral cyclic loading (600 cycles), are analyzed and discussed in this paper. This research incorporates combined cyclic loading tests, encompassing one-way and two-way cycles in a singular examination to simulate the typhoon and service conditions before and after. The major findings include: (i) HSC, compared to OSC, can effectively harness accumulated rotations of the foundation induced by both one-way and two-way cyclic loading, (ii) adding an outer skirt to HSC, attached to an inner caisson and mat foundation, reduces considerably accumulated rotations induced by one-way cycles, (iii) cyclic loading does not change the unloading stiffness of OSC and HSC without an outer skirt, while increases the unloading stiffness of HSC with an outer skirt, and (iv) analyzing and designing OWT foundations should consider the combined cyclic loading scenario, rather than solely relying on one-way or two-way cyclic loading regimes. Based on the results, a power formula is proposed for estimating caissons' rotations stemming from long-term cyclic loading.

Large deformation analysis of spudcan settlement during operation

Jack-up rigs have been utilized to support booster stations in wind farms or to provide accommodation in oil and gas developments. In these scenarios, the dissipation of excess pore pressures and subsequent spudcan settlement during operation phase are of concern. However, predicting the spudcan settlement in naturally structured soil remains challenging. A large deformation finite element method, within the framework of effective stress analysis, has been developed to investigate the penetration and subsequent settlement of the spudcan footing. The inherent structure of cohesive soil and its degradation caused by spudcan penetration are described using the Structured Cam-Clay model. The large deformation approach is validated by comparisons with existing centrifuge tests. Parametric studies are then conducted with various operational loads and installation depths of spudcans. A backbone curve is provided, to estimate the history of spudcan settlement in kaolin with inherent structure. The distribution of excess pore pressures around the spudcan under different operation period is explored as well. A normalised dissipation curve at the largest cross-section of the spudcan during the operation phase is presented.

Comparative analysis of two intergranular strain-based hypoplastic models through elemental and centrifuge testing

While hypoplastic models have demonstrated accurate predictions of sand behavior under monotonic loading, their accuracy diminishes when applied to cyclic loading conditions. To address this limitation, the intergranular strain approach is used as an extension to the model. The current investigation focuses on the analysis of two variants: the original Intergranular Strain (IS) approach proposed by Niemunis and Herle (1997) and the Intergranular Strain Anisotropy (ISA) by Fuentes et al. (2019). Although both models have the same objective, they present distinct mathematical structures and therefore different repercussions on the simulations. In this study, sand Hypoplasticity is enhanced with IS and ISA, and employed to simulate a series of experimental tests conducted on Fontainebleau sand. These tests encompass isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests, while considering different initial densities and test characteristics. Furthermore, the calibrated models were applied to simulate a series of centrifuge tests, involving a pile embedded in the same sand, which is subjected to various episodes of monotonic and cyclic lateral loading. A comparison and discussion of the similarities and differences in elemental and finite element predictions, arising from the two intergranular strain formulations is presented.

Evaluation of deformation for two-dimensional (2D) and three-dimensional (3D) braced excavation in clays with centrifuge modelling and numerical analysis

This study presents an improved in-flight strutting system for centrifuge modelling. Based on the centrifuge model test data, the mobilizable strength design (MSD) method was revised. The modified MSD method extends to the prediction of three-dimensional (3D) deformations in retaining walls due to excavation activities. Initially, an improved in-flight excavation tool used in centrifuge tests was employed to investigate the impacts of staged excavation on the characteristics of wall displacement and ground settlement in two-dimensional (2D) braced excavation. Subsequently, 2D and 3D finite element analyses, calibrated against the centrifuge test data and considering the small strain effect, were conducted to assess the performance of wall displacement, ground settlement, and movement of the underground soil induced by the braced excavation. Moreover, this research proposes a straightforward predictive model based on the modified MSD, specifically for calculating the deformation along the length of retaining walls in 3D braced excavations. The insights and the modified MSD method given in this study may facilitate the design of foundation pit projects, especially when the 3D effects are an essential detail to be considered in these projects.

Centrifuge Modelling of Composite Bucket Foundation Breakwater in Clay under Monotonic and Cyclic Loads

This study investigates the monotonic and cyclic performance of composite bucket foundation breakwater in clay through centrifuge modeling. The application of monotonic loads simulates extreme wave conditions, and cyclic load corresponds to long-term serviceability conditions. In centrifuge tests, three typical soil strengths were tested, and two load eccentricities were simulated to check the influence of wave force height. Multiple measurements were conducted, including rotation angle, horizontal displacement, vertical settlement, and pore pressure variation. When soil strength increases in monotonic centrifuge tests, the ultimate bearing capacity of the bucket foundation experiences significant growth, and the foundation failure pattern varies. In responding to the monotonic test, the foundation’s rotation center constantly moved downward during the loading process, indicating that the deeper soil would be activated to resist the horizontal loading. In contrast, the rotation center movement in the symmetric centrifuge test was opposed to the non-symmetric test because the deeper soil was required to provide resistance to balance the more severe load under the non-symmetric loading condition. It should be noted that non-symmetric loading does not impact the bucket foundation as seriously as symmetric loading. The utilization of deep-soil resistance in non-symmetric tests is beneficial in controlling deformation.

Identification of Bearing Clearance in Sugar Centrifuge Using Dimension Theory and Support Vector Machine on Vibration Measurement

Abstract Bearing fatigue life is significantly influenced by bearing clearance. Vibration monitoring of bearing clearance deviations can efficiently reveal bearing wear and give sufficient lead time for maintenance. This study investigates the dynamics of roller bearings utilizing the dimension theory with the support vector machine (SVM) technique for diagnosing the bearing clearance faults of revolving machines. The generation of local defects in rotating machines is closely related to the clearance behavior of the rotor-bearing system. A dynamic model of bearing with dimension theory by matrix method with SVM is developed for characteristics of bearing clearance considering the influence of local defects on the inner and outer bearings races. The characteristics of bearing internal radial clearance considering the impact of the defect on the bearing are analyzed. An experimental study has been performed to capture the vibration signature of radial clearance for different speeds and radial loads of the rotor. The rotor-bearing system equations are numerically integrated, and the results are validated with experimental findings. The collective effects among the four parameters (radial load, speed, defect size, radial clearance) are investigated in detail for the rotor-bearing system. The noisy signal is subsequently eliminated using the modulation signal bispectrum (MSB), and the peaks of the MSB results are represented by the bearing clearance indicator. The efficiency and reliability of the stated approach are evaluated using a specialized bearing test and a run-to-failure sugar centrifuge test. The results suggest that the proposed approach can detect a change in bearing clearance up to 40 µm.

Measuring water holding capacity in poultry meat

In the current scientific literature, one can find >100 different methods to evaluate water-holding capacity in fresh and cooked meat. The main concepts are based on removing some of the water by either gravity, application of pressure (e.g., centrifugal force), and heating while measuring water exudate to predict the water holding capacity (WHC) during storage, processing, cooking, and/or distribution. More sophisticated methods include nuclear magnetic resonance (NMR) in which the relaxation of water molecules within a meat protein/gel system is measured to predict how the water (75% in lean meat) will behave during processing. Overall, the number of tests reported is also so high because there are quite big variations in test conditions (e.g., 750-30,000 g for centrifugal testing). The aim of this article (outcome of a symposium on methods for poultry meat characterization) is to help the reader navigate through the different setups and suggest standardized testing based on scientific principles. The recommended WHC test is the application of low centrifugal force (750 g so sample is not permanently deformed) to a protein gel, while the sample is placed on a screen platform to avoid reabsorbing the liquid separating during the slowing down of the centrifuge. It is also recognized that some meat samples (e.g., high in fat) might require a different g-force, so it is recommended to employ both the conditions mentioned above and the lab-specific conditions. Our overall goal should always be to increase uniformity in test procedures, which will enhance our capabilities to compare results among research groups.

Icephobic Coating Based on Novel SLIPS Made of Infused PTFE Fibers for Aerospace Application.

The development of slippery surfaces has been widely investigated due to their excellent icephobic properties. A distinct kind of an ice-repellent structure known as a slippery liquid-infused porous surface (SLIPS) has recently drawn attention due to its simplicity and efficacy as a passive ice-protection method. These surfaces are well known for exhibiting very low ice adhesion values (τice < 20 kPa). In this study, pure Polytetrafluoroethylene (PTFE) fibers were fabricated using the electrospinning process to produce superhydrophobic (SHS) porous coatings on samples of the aeronautical alloy AA6061-T6. Due to the high fluorine-carbon bond strength, PTFE shows high resistance and chemical inertness to almost all corrosive reagents as well as extreme hydrophobicity and high thermal stability. However, these unique properties make PTFE difficult to process. For this reason, to develop PTFE fibers, the electrospinning technique has been used by an PTFE nanoparticles (nP PTFE) dispersion with addition of a very small amount of polyethylene oxide (PEO) followed with a sintering process (380 °C for 10 min) to melt the nP PTFE together and form uniform fibers. Once the porous matrix of PTFE fibers is attached, lubricating oil is added into the micro/nanoscale structure in the SHS in place of air to create a SLIPS. The experimental results show a high-water contact angle (WCA) ≈ 150° and low roll-off angle (αroll-off) ≈ 22° for SHS porous coating and a decrease in the WCA ≈ 100° and a very low αroll-off ≈ 15° for SLIPS coating. On one hand, ice adhesion centrifuge tests were conducted for two types of icing conditions (glaze and rime) accreted in an ice wind tunnel (IWT), as well as static ice at different ice adhesion centrifuge test facilities in order to compare the results for SHS, SLIPs and reference materials. This is considered a preliminary step in standardization efforts where similar performance are obtained. On the other hand, the ice adhesion results show 65 kPa in the case of SHS and 4.2 kPa of SLIPS for static ice and <10 kPa for rime and glace ice. These results imply a significant improvement in this type of coatings due to the combined effect of fibers PTFE and silicon oil lubricant.

A strain-hardening macro-element model for pile groups under vertical–horizontal-moment loading

Pile foundations supporting wind turbines, silos, elevated water tanks or bridge piers are frequently subjected to multi-component loads, which may lead to significant rotations and settlements compromising the safe operation of the structure. The prediction of these displacements is of major concern and can be easily carried out using force-resultants plasticity models, also referred to as ‘macro-elements’, stemming from the idea of describing the foundation behaviour by a single upscaled constitutive relationship between generalized forces and displacements. When properly formulated, they can reproduce key aspects of the mechanical response of the foundation at low computational cost as compared to numerical analysis. To this end, a new macro-element for pile groups formulated in the classical framework of strain-hardening elasto-plasticity is presented and discussed. The required model parameters can be calibrated by closed-form equations and additional few data of numerical and/or experimental nature. The proposed mathematical framework is finally validated against the results of centrifuge tests and 3D finite element analyses.

Dynamic Earthquake Response of 3-DOF Structure with Substructures by Centrifuge Test

Dynamic Earthquake Response of 3-DOF Structure with Substructures by Centrifuge Test

Simplified method for evaluating tunnel response induced by a new tunnel excavation underneath

AbstractTo estimate the tunnel response induced by a new tunnel excavation underneath, theoretical solutions are proposed in this study. The overlying tunnel is idealized as an infinite Timoshenko beam resting on the Kerr foundation model, then the vertical force balance equation is established. The unloading stress can be expressed as Fourier cosine series and a theoretical solution can be derived. The effectiveness of the proposed method is verified by a centrifuge test and an actual field measurement, which are extracted from previous investigations. Calculation results from the proposed method show good accord to centrifuge test results and field‐measured data. Meantime the predictions given by the proposed method are more accurate to estimate tunnel response compared with the previous method. Parametric analysis indicates that the volume loss ratio and the vertical clearance between two tunnels, are both significantly alleviate the tunnel response, but the effect of tunnel shear stiffness is slight. The theoretical solutions can be adopted to predict the overlying tunnel response induced by tunneling underneath in real projects.

Penetration Behavior of Jack-up Leg with Spudcan for Offshore Wind Turbine to Multi-layered Soils Using Centrifuge Tests

This study examined the jack-up spudcan penetration for a new type of offshore wind substructure newly proposed using the jack-up concept to reduce construction costs. The jack-up spudcan for offshore wind turbines should be designed to penetrate a stable soil layer capable of supporting operational loads. This study evaluated multi-layered soil conditions using centrifuge tests: loose sand over clay and loose sand–clay–dense sand. The penetration resistance profiles of spudcan recorded at the centrifuge tests were compared with the ISO and InSafeJIP methods. In the tests, a spudcan punch-through effect slightly emerged under the sand-over-clay condition, and a spudcan squeezing effect occurred in the clay-over-sand layer. On the other hand, these two effects were not critically predicted using the ISO method, and the InSafeJIP result predicted only punch-through failure. Nevertheless, ISO and InSafeJIP methods were well-matched under the conditions of the clay layer beneath the sand and the penetration resistance profiles at the clay layer of centrifuge tests. Therefore, the ISO and InSafeJIP methods well predict the punch-through effect at the clay layer but have limitations for penetration resistance predictions at shallow depths and strong stratum soil below a weak layer.

Emulsions containing allantoin and D-panthenol as attractive moisturizing agents

Dry skin is the common problem affecting people which triggers many unpleasant symptoms such as roughness, peeling, burning, itching and greater sensitivity to injury and external conditions. One method to assess the water loss of skin is transepidermal water loss (TEWL) measurement. Various active substances, for instance allantoin and D-panthenol, can be used to overcome the symptoms of the dry skin. In this study, emulsions containing allantoin and D-panthenol as moisturizing agents and various oils (liquid paraffin, Cannabis sativa, Baobab and Coconut oil) were developed. The prepared emulsions were characterized by: visual and microscopic appearance and pH values. Stability analysis was conducted by centrifuge test and sensory test using sensory sensation was evaluated. Rheological experiments were performed using a rheometer, while mechanical and adhesion tests by texture analyzer. TEWL values were measured using a tewameter, after application of the emulsions to the responders skin. TEWL study noticed that regular permanent use of moisturizing emulsions with allantoin and D-panthenol limited the water loss. In conclusion, it can be stated that emulsions containing allantoin and D-panthenol as active agents and Coconut oil as oily ingredient are attractive formulations with moisturizing effect and good application features.

STUDI STABILITAS FORMULASI SELF NANO EMULSIFYING DRUG DELIVERY SYSTEM (SNEDDS) EKSTRAK DAUN SERUNAI SEBAGAI ANTI DIABETES DENGAN VARIASI KONSENTRASI ASAM OLEAT

Management of diabetes mellitus can use chemical drugs and traditional medicine. One of the medicinal plants used by the community is chrysanthemum leaves (C.Odorata). The use of traditional medicine still has drawbacks, one of which is that its pharmacological effects are relatively weak and slow, affecting bioavailability and the therapeutic effect is not optimal. The aim of the study was to determine the stability of the formulation of the SNEDDS of chrysanthemum leaf extract as an anti-diabetic agent and to determine the effect of variations in the concentration of oleic acid in the formulation of the SNEDDS on evaluation and stability testing. This research method uses the Quasy Experimental Design method. The simplicia was made into an extract and then made into a nanoemulsion preparation with varying concentrations of oleic acid. The results of this study in the centrifugation test were stable at F3. Unstable hot-cold and freeze-thaw cycle tests. Stable resistance to dilution test at F2 250 ml. Week 0 and 4 accelerated storage tests were stable on F3 and F1. The evaluation results showed that variations in the concentration of oleic acid had no effect on particle size and PDI values ​​but had an effect on the transmittance value (%) as shown in the One Way Anova statistical analysis (p&lt;0.05). The evaluation results showed that F2 with 10% oleic acid concentration was a stable formula because it had the smallest particle size and PDI (Polydispers Index) value.

Seismic performance of a nonhomogeneous slope reinforced by anchored piles using centrifuge tests

Seismic performance of a nonhomogeneous slope reinforced by anchored piles using centrifuge tests