Published Test Data Research Articles

Traffic-based quantitative risk analysis of structural fire damage to roadway tunnel linings

This paper demonstrates a quantitative risk analysis (QRA) approach of fire-induced damage to the reinforced concrete linings in roadway tunnels. Large fire events associated with buses and heavy goods vehicles are the focus of this study because their impact on the tunnel linings is structurally significant versus fires from smaller vehicles. The proposed approach accounts for stochastic variations of fire severity and frequency (based on traffic volume and the percentage breakdown by vehicle type) as well as the consequences (structural and economic) of thermal exposure to tunnel linings. The probabilistic distribution of fire size is developed using available weight-in-motion data, and combustible vehicle mass is correlated with the peak heat release rate using published test data and forensic reports. The heat transfer from the vehicle fire to the tunnel linings was modelled by a fast-running computational tool that was previously developed by the authors. Fire-induced damage to the tunnel linings is categorized into three levels of progressive strength reduction and cracking potential. Economic impacts are calculated in terms of estimated repair costs. The proposed approach enables informed decision making for the design or renovation of tunnel fire protection by quantifying the loss potential for severe fire hazards in a given tunnel.

Modeling of Cutting Rock: From PDC Cutter to PDC Bit—Modeling of PDC Bit

Summary In this paper, we integrated our polycrystalline diamond compact (PDC) cutter model (Chen et al. 2021) into a PDC bit model that can predict the weight on bit (WOB), torque on bit (TOB), and imbalanced side force on a bit under given drilling conditions. We first proposed a method to determine the actual cutting plane and depth of cut of each cutter on a PDC bit. Once the two parameters for each cutter are determined, the cutter model can then be applied to calculate the cutting force of each cutter. The final bit force and moment (i.e., WOB, TOB, and imbalanced side force) are calculated as the resultant force and moment of cutting forces of all cutters. The PDC bit model in this paper considers all bit design parameters, including bit matrix geometry, blade profile, cutter layout, and the inclination of each cutter. Furthermore, the bit model also considers some bottomhole assembly (BHA) parameters (e.g., bit tilt angle, location of first fulcrum point, and tool face/steering plane angle), which allows the bit model to simulate a bit under different drilling modes. The bit model is also validated by published test data and field applications. Finally, case studies are conducted, and the influence of bottomhole stresses, BHA parameters, and drilling modes on bit force and moment are discussed. A field application of the bit model is also provided. The bit model can be directly used for PDC bit design and simulation. In fact, this paper presents a general way to integrate a cutter model into a PDC bit model. Readers are also encouraged to apply this method to integrate their own cutter model into a PDC bit model.

Post-fire mechanical properties of carbon steel and safety factors for the reinstatement of steel structures

This paper provides guidance on the post-fire material properties and associated safety factors for structural carbon steel which are required for the assessment and retrofitting of existing steel buildings which have suffered and survived a fire. Nowadays, there is a discrepancy between the methodology which is used in the design stage of a building (mostly based on the partial factor method) and the verification methods used after a fire. In the past decade, a number of researchers have published test data and there is more information available on the mechanical properties of steel following a fire. Nevertheless, a statistical evaluation of these results has yet to be conducted although design codes generally adopt a reliability-based approach for the analysis and assessment of buildings. To fill this gap of knowledge, the current article includes a statistical evaluation of the mechanical data from 718 tests collected from 19 peer-reviewed articles and doctoral theses. The study is done for hot-rolled steel, cold-formed steel as well as wrought or cast iron. By focusing on the effect of a fire on the mechanical properties after cooling, which is mostly related to how the coefficient of variation of their distribution increases, adjusted safety factors are proposed together with a reduced reliability index based on economic and social considerations. It is contended that by following this method, possible misunderstandings can be avoided and decisions on the salvage and rehabilitation of structures can be based on performance data and technical analysis, thus reducing the need for individual judgement.

Prediction of CHF in helical coils

Boiling in helical coils is involved in many applications including nuclear and conventional boilers, air conditioning and refrigeration, and chemical processing. It is therefore important to be able to predict CHF accurately. Many experimental studies have been done and many correlations have been proposed. However, there has been no comprehensive comparison of correlations with data to determine their accuracy. The present study was done to fulfil this need. A database of published test data from 16 sources was prepared and compared to a number of correlations for straight tubes as well as those for coils. The data included six fluids (water, nitrogen, refrigerants), mass flux 89 to 5474 kg m−2 s−1, and critical qualities from −0.5 to 1.16. Tube diameters range from 4.5 to 20 mm and ratio of coil diameter to tube diameter (Dc/Dt) from 6.5 to 108. None of the correlations for coils was found satisfactory. Four of the five straight tube correlations gave fairly good agreement. Ranges of parameters have been identified in which the straight tube correlations can be used for design.

Ultimate Strength Assessment of Steel-Welded Hemispheres under External Hydrostatic Pressure

This paper focusses on steel-welded hemispherical shells subjected to external hydrostatic pressure. The experimental and numerical investigations were performed to study their failure behaviour. The model was fabricated from mild steel and made through press forming and welding. We therefore considered the effect of initial shape imperfection, variation of thickness and residual stress obtained from the actual structures. Four hemisphere models designed with R/t from 50 to 130 were tested until failure. Prior to the test, the actual geometric imperfection and shell thickness were carefully measured. The comparisons of available design codes (PD 5500, ABS, DNV-GL) in calculating the collapse pressure were also highlighted against the available published test data on steel-welded hemispheres. Furthermore, the nonlinear FE simulations were also conducted to substantiate the ultimate load capacity and plastic deformation of the models that were tested. Parametric dependence of the level of sphericity, varying thickness and residual welding stresses were also numerically considered in the benchmark studies. The structure behaviour from the experiments was used to verify the numerical analysis. In this work, both collapse pressure and failure mode in the numerical model were consistent with the experimental model.

Method to Locate the Toe of a Hydraulic Jump on Sloping Channels

The location of a hydraulic jump is a key parameter for analysing the slab stability of the stilling basin in a sluice. A simple method to locate the toe of a hydraulic jump in sloping channels is presented. The essential idea of this method applies the interacting relationship between the sequent depth and jump length to locate a point, satisfying them both simultaneously. The implementation details and the involved sequent depth and jump length equations of this method are discussed, and verification of the method is also presented. The predicted results match well with the published test data, even for a steep sloping channel up to 45°. The method’s application in the failure analysis of a sluice sloping connecting slab is also presented briefly. It is important for the analysis to account for the static hydraulic jump effect. The proposed method can yield a key parameter for such an analysis.

저널 래버린스 실이 임펠러 추력 및 누설에 미치는 영향

In recent years, turbomachinery pursue high speed operations in compact volume to achieve high specific power. An impeller operating at high rotating speeds increases the compression ratio and results in significant axial thrust forces which must be balanced with balance piston or thrust bearing. A leakage flow flowing through Labyrinth seals located in the gap between the rotor and stator parts also influences the magnitude of the thrust forces. This study develops a predictive model of an impeller coupled with a labyrinth seal to predict the resulted axial thrust force. Firstly, a comparison between the predicted cavity pressure and leakage to the published test data validates the bulk-flow model of the labyrinth seal used in the paper. Then the coupled model of the impeller to the labyrinth seal is verified by comparison of the predicted pressure distributions and leakage flow rates to those from CFD analyses using the k-ε turbulence model. Additionally, the study reports the effects of the labyrinth seal design, operating speed, and lubricant type on the axial thrust force and the leakage flow rate. The results show that the labyrinth seal decreases the leakage flow rate but increases the axial force, implying the need of trade-off between the impeller axial force and leakage flow rate. As the gap between the impeller and casing wall decreases, both the impeller axial force and leakage flow rate decrease. The impeller axial force and the leakage flow rate predicted using refrigerant gas are smaller and less sensitive to the change of the labyrinth seal design when compared to those predicted using air.

Behaviour of grout-filled double-skin tubular steel stub-columns: Numerical modelling and design considerations

The use of grout-filled double-skin tubular (GFDST) sections in civil, bridge and offshore engineering applications is rapidly increasing. The design of such composite members is not directly covered by design codes, despite recent research studies investigating their performance, proposing design equations or modifying existing codified methods. Aiming to extend the available pool of structural performance data, the current study reports the results of an extensive numerical investigation on GFDST stub-columns. Finite element (FE) models, are developed and validated against published test data. A parametric investigation is conducted to evaluate the effect of key parameters, including cross-sectional slenderness, hollow ratio and the effect of concrete infill on the capacity of GFDST members. The numerically obtained load capacities along with collated test data are utilised to assess the applicability of design strength predictions based on European Code (EC4), the American Concrete Institute (ACI) and the analytical models proposed by Han et al. and Yu et al. Overall, the modified Yu et al. provided strength predictions with low scatter, whereas ACI yielded overly conservative predictions particularly for smaller hollow ratios.

Experimental and analytical study on uniaxial tensile property of ionomer interlayer at different temperatures and strain rates

The ionomer material is widely used as interlayers in the laminated glass, and its tensile property plays a decisive role in the post-fracture response of the laminated glass. Since the ionomer material is a kind of polymer, its mechanical behaviour is highly affected by strain rate and temperature. In this work, two series of uniaxial tensile tests, low strain rate series (10−3s−1~10−1s−1) and medium to high strain rate series (1 s−1~800 s−1), were conducted over a wide temperature range (−40 °C~80 °C). Details of the test setup and corresponding true stress-true strain curves are presented. Characteristic mechanical parameters are then identified to evaluate the temperature and strain rate effects. It was found that higher strain rate and lower temperature result in higher strength and stiffness but lower ductility. The material shows apparent plasticity as more than 80% deformation is unrecoverable. Based on the observations, G’Sell model is adopted to build the temperature-dependent dynamic constitutive model, which is then validated through comparison between the predicted results and the published test data.

Analyzing filtration flow rate change of woven geotextiles for fine grained slurries

Many studies have been performed in recent years to investigate the dewatering phenomena of slurry using geotextile tubes. The laboratory test methods primarily used the pressure filtration test (PFT) and falling head test (FHT) to evaluate the dewatering nature of geotextiles using slurries with different fines contents. The objective of this paper is to examine and analyze the published test data obtained from various testing conditions, and to develop a general equation that can predict the change of flow rate over time. For the PFT, a power law showed a good fit with test data at different fines content ranges. Furthermore, the change of filtration rate with time decreased with the fines content, indicating that slurry with high fines content resulted in a faster drop in filtration rate than slurry with low fines content. For the FHT, a two-term power law was found to fit all of the test data, indicating a two-stage filtration behavior.

Analytical study on one-way reinforced concrete beam-slab sub-structures under compressive arch action and catenary action

In case of accidental loading, compressive arch action and catenary action in beams and slabs can be mobilised to resist progressive collapse of reinforced concrete structures. Analytical models have been proposed for reinforced concrete beam-column sub-assemblages under compressive arch action and catenary action. Nonetheless, the effects of the slab on load resistance and deformation capacity of one-way beam-slab sub-structures have not been fully investigated. This paper presents a study on the structural behaviour of one-way beam-slab sub-structures subjected to compressive arch action and subsequent catenary action. In the study, an analytical model is developed to predict the load-displacement relationship and the axial force-displacement relationship of sub-structures. The model is developed in accordance with rigid-plastic assumption. Compatibility, equilibrium and constitutive models for steel reinforcement and concrete are taken into account in the model. Hogging and sagging moments are calculated by taking moments about the plastic centres of beam-slab sub-structures. The model is validated against published test data and reasonably good accuracy is obtained in terms of the load resistances under compressive arch action and catenary action. The variation of bending moments, neutral axis depths and steel strains can also be obtained through the analytical model. The model is then used for parametric study of the effects of longitudinal reinforcement, slab width, and thickness on compressive arch action and catenary action. The parametric study shows that the cross-sectional area of longitudinal reinforcement in the slab affects the catenary action capacity and the width and thickness of the slab affects the deformation capacity of one-way beam-slab sub-structures. Finally, conclusions are drawn from the analytical study which can be used in the design of one-way beam-slab sub-structures against progressive collapse.

Generation of mixed mode I/II failure criteria from MMB specimens: an experimental study

Characterization of resistance to delamination is of great importance in selection of composite material. Mixed mode delamination is one of the most serious failure modes in aerospace composites. This article examines the delamination behaviour of mixed mode bending (MMB) test specimens made of glass/epoxy and carbon/epoxy composites. Literature published test data on different composites have been utilzed to identify the best suited failure criterion. Benzeggagh-Kenane (B-K) criterion as well as the polynomial criteria are used to generate failure envelopes from the fracture toughness data of composite specimens. Experiments were conducted on unidirectional fiber reinforced epoxy MMB specimens to analyze the failure trend of laminated composites and to validate the proposed polynomial criteria. Present investigations reveal that both B-K and polynomial criteria fit well for unidirectional specimens and cubic polynomial criterion fits well for angle-ply specimens.

Effect of Pad and Liner Material Properties on the Static Load Performance of a Tilting Pad Thrust Bearing

AbstractTilting pad thrust bearings (TPTBs) control rotor axial placement in rotating machinery, and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a three-dimensional (3D) thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element (FE) structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flowrate, and shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad subsurface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter (OD) operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4 °C and 11 °C (<10%) at laminar and turbulent flow conditions, receptively. Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2-mm-thick babbitt layer (common usage), a steel pad with a 2-mm-thick hard-polymer (polyether ether ketone, e.g., PEEK®) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness; however, its demand for a too large supply flowrate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30 °C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (>3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.

Modular phenomenological model for vented explosions and its validation with experimental and computational results

The present study reports a modular phenomenological model for predicting peak pressure in vented explosions. Modelling assumptions are explained in detail and model components are validated against experimental and computational results. A basic version of this model is reported in our earlier paper (Sinha et al., 2019). Previous experimental and modelling efforts on vented explosion have primarily focussed on idealized condition of empty container with uniformly mixed fuel. However, in real accidents, there are often obstacles in flame path, and a leaked fuel may not get enough time to mix uniformly. These realistic accidental scenarios are accounted for in this extended model. First the model components are assessed using available experimental results. Comparison of flame arrival time and flame propagation inside the enclosure are made, which demonstrate the ability of the model to capture flame propagation accurately. Suggestions are also made for vent panel installation to reduce peak overpressure in accidental explosions.Predictions for external cloud radius and pressure generated by external explosion are found to be in close agreement with the experimentally measured values. The model is further simplified, and a final equation is proposed which depends on two fuel related parameters and two geometric parameters. Fuel dependent parameters are pre-tabulated, and geometric parameters are easy to compute. Procedure to calculate pressure generated by external explosion and internal pressure are outlined in detail. Experimental results available in literature are used to evaluate model predictive capabilities. The model, in principle should be applicable for any gaseous fuel. However, the focus of the present investigation is to assess it for hydrogen explosions. Experimental repeatability is also discussed, and role of wall deflection is highlighted.In parallel to the modelling effort, a dedicated in-house CFD solver HyFOAM is developed utilizing OpenFOAM platform. The HyFOAM predictions are validated against experimental results from the recently published test data involving hydrogen explosion in a 20-foot ISO container (Skjold et al., 2017, 2018, 2019). Moreover, as experimental investigations are expensive and require significant testing and safety infrastructure, a limited number of scenarios can be tested experimentally. In addition to the experimental results, few more cases are simulated using HyFOAM. Phenomenological model results are compared with the CFD results, and a reasonably good match is observed.

Design of quasibrittle materials and structures to optimize strength and scaling at probability tail: an apercu.

The objective in materials or structure design has been to maximize the mean strength. However, as generally agreed, engineering structures, such as bridges, aircraft or microelectromechanical systems must be designed for tail probability of failure less than 10-6 per lifetime. But this objective is not the same. Indeed, a quasibrittle material or structure with a superior mean strength can have, for the same coefficient of variation, an inferior strength at the less than 10-6 tail. This tail is unreachable by histogram testing. So, one needs a rational theory, physically based and experimentally verified indirectly, which is feasible by size effect. Focusing on the results at the writer's home institution, this inaugural article (written three years ex post facto) reviews recent results towards this goal, concerned with quasibrittle materials such as concretes, rocks, tough ceramics, fibre composites, bone and most materials on the micrometer scale. The theory is anchored at the atomic scale because only on that scale the failure probability is known-it is given by the frequency of breakage of bonds, governed by the activation energy barriers in the transition rate theory. An analytical way to scale it up to the macroscale representative volume element (RVE) has been found. Structures obeying the weakest-link model are considered but, for quasibrittle failures, the number of links, each corresponding to one RVE, must be considered as finite. The result is a strength probability distribution transiting from Weibullian to Gaussian, depending on the structure size. The Charles-Evans and Paris laws for subcritical crack growth under static and cyclic fatigue are also derived from the transition-rate theory. This yields a size-dependent Gauss-Weibull distribution of lifetime. Close agreement with numerous published test data is achieved. Discussed next are new results on materials with a well-defined microscale architecture, particularly biomimetic imbricated (or staggered) lamellar materials, exemplified by nacre, a material of astonishing mean strength compared to its constituents. This architecture is idealized as a diagonally pulled fishnet, which is shown to be amenable to an analytical solution of the strength probability distribution. The solution is verified by million Monte Carlo simulations for each of the fishnets of various shapes and sizes. In addition to the classical weakest-link and the fibre-bundle models, the fishnet is found to be the third strength probability model that is amenable to an analytical solution. The nacreous architecture is shown to provide an additional major (greater than 100%) strengthening at the 10-6 failure probability tail. Finally, it is emphasized that the most important consequence of the quasibrittleness, and also the most effective way of calibrating the 10-6 tail, is the size effect on the mean structural strength, which permeates all formulations.

On the Influence of the Entrance Section on the Rotordynamic Performance of a Pump Seal With Uniform Clearance: A Sharp Edge Versus A Round Inlet

Secondary flows through annular seals in pumps must be minimized to improve their mechanical efficiency. Annular seals, in particular balance piston seals, also produce rotordynamic force coefficients, which easily control the placement of rotor critical speeds and determine system stability. A uniform clearance annular seal produces a direct (centering) static stiffness as a result of the sudden entrance pressure drop at its inlet plane when the fluid flow accelerates from an upstream (stagnant) flow region into a narrow film land. This so-called Lomakin effect equates the entrance pressure drop to the dynamic flow head through an empirical entrance pressure loss coefficient. Most seal designs regard the inlet as a sharp edge or square corner. In actuality, a customary manufacturing process could produce a rounded corner at the seal inlet. Furthermore, after a long period of operation, a sharp corner may wear out into a round section. Notice that to this date, bulk-flow model (BFM) analyses rely on a hitherto unknown entrance pressure coefficient to deliver accurate predictions for seal force coefficients. This paper establishes the ground to quantify the influence of an inlet round corner on the performance of a water lubricated seal reproducing a configuration tested by Marquette et al. (1997). The smooth surface seal has clearance Cr = 0.11 mm, length L = 35 mm, and diameter D = 76 mm (L/D = 0.46). The test case considers design operation at 10.2 krpm and 6.9 MPa pressure drop. Computational fluid dynamics (CFD) simulations apply to a seal with either a sharp edge or an inlet section with curvature rc varying from ¼Cr to 5Cr. Note the largest radius (rc) is just 1.6% of the overall seal length L. Going from a sharp edge inlet plane to one with a small curvature rc = ¼Cr produces a ∼20% decrease on the inlet pressure loss coefficient (ξ). A further reduction occurs with a larger circular corner; ξ drops from 0.43 to 0.17. That is, the entrance pressure loss will be lesser in a seal with a curved inlet. This can occur easily if the inlet edge wears due to solid particles eroding the seal inlet section. Further CFD simulations show that operating conditions in rotor speed and pressure drop do not affect the inlet loss coefficient, while the inlet circumferential swirl velocity does. In addition, further CFD results for a shorter (half) length seal produce a very similar entrance loss coefficient, whereas an enlarged (double) clearance seal leads to an increase in the entrance pressure loss parameter as the inlet section becomes less round. CFD predictions for most rotordynamic coefficients are within 10% relative to published test data, except for the direct damping coefficient C. For the seal with a rounded edge (rc = 5 Cr) at the inlet plane, both the direct stiffness K and direct damping C decrease about 10% compared against the coefficients for the seal with a sharp inlet edge. The other force coefficients, namely cross-coupled stiffness and added mass, are unaffected by the inlet edge geometry. The same result holds for seal leakage, as expected. A BFM incorporates the CFD derived entrance pressure loss coefficients and produces rotordynamic coefficients for the same operating conditions. The CFD and BFM predictions are in good agreement, though there is still ∼10% discrepancy for the direct stiffnesses delivered by the two methods. In the end, the analysis of the CFD results quantifies the pressure loss coefficient as a function of the inlet geometry for ready use in engineering BFM tools.

Improved Estimation of Bearing Pads' Inlet Temperature: A Model for Lubricant Mixing at Oil Feed Ports and Validation against Test Data

Energy efficient operation of fluid film bearings demands savings in delivery flow while also managing to reduce the temperature in the fluid film and bearing pads. To achieve this goal, tilting pad journal bearings (TPJBs) implement a variety of oil feed arrangements, use pads with highly conductive material and engineered back surface, and also end seals to keep (churning) lubricant within the bearing housing. This paper introduces a novel model for the mixing of flow and thermal energy transport at a lubricant feed port and which sets the temperature of the lubricant entering a pad leading edge. Precise estimation of this temperature (and inlet oil viscosity) largely determine the temperature, and the current model aids to deliver improved temperature predictions in conditions that limit a conventional model, including the ability to impose an actual lubricant supplied flow, specifically when the bearing is operating in either an over-flooded or a reduced flow conditions. An empirical groove efficiency parameter regulates the temperature of the above-mentioned flows to represent conventional and direct lubricant feeding arrangements as well as end-sealed (flooded) or evacuated bearing configurations. Predicted temperatures are compared against published test data for two bearings while revealing the advantages of the novel model, in particular for operation under lubricant starvation. This paper delivers recommendations for the feed port efficiency parameter for various types of oil supply configurations. This parameter, not being a function of bearing operating conditions, allows for proper sizing of pumps, oil reservoirs, and heat exchangers in lube oil delivery systems for a packaged-unit machine.

Numerical modeling of concentration polarization and inorganic fouling growth in the pressure-driven membrane filtration process

Concentration polarization and surface fouling may be two of the most remarkable features in the pressure-driven membrane filtration process. A new numerical simulation model is proposed in this paper to study the concentration polarization (CP) and the inorganic fouling growth. The numerical study is based on the lattice Boltzmann method (LBM), which allows a simultaneous solution of the Navier–Stokes equations and the convection-diffusion equation. Simulation results are verified by comparisons with published CP and permeate flux data under the same operating conditions. Then the model is extended to predict CP in a spacer filled desalination channel. The prediction result indicates that there is a higher fouling potential near the spacer filaments due to higher CP values in that area. Coupling of the CP prediction model with gypsum growth kinetics provides an approach to study the inorganic fouling growth on the membrane surface at a single crystal level, with respect to a given solution supersaturation near the membrane surface. Predicted equivalent radius and accumulated mass of the growing gypsum crystal, under the effects of growth retardation by bicarbonate, agree with published test data and analytical results. The presented numerical model enables a direct evaluation of the impacts on the surface crystal development in the presence of antiscalants. This numerical model can be applied to identify suitable operating conditions, assist in dose selection of antiscalants when required properties are available, and predict the fouling mitigation effects in the pressure-driven membrane filtration process.

A review of split-cycle engines

This article reviews split-cycle internal combustion engine designs. The review includes historical work, assessment of prototypes and discussion of the most recent designs. There has been an abundance of split-cycle engine designs proposed since the first in 1872. Despite this, very few prototypes exist, and no split-cycle engines are reported to be in series production. The few split-cycle prototypes that have been developed have faced practical challenges contributing to limited performance. These challenges include air flow restrictions into the expansion cylinder, late combustion, thermal management issues, and mechanical challenges with the crossover valve actuation mechanism. The main promoted advantage of split-cycle engines is the increased thermal efficiency compared to conventional internal combustion engines. However, an efficiency improvement has not thus far been demonstrated in published test data. The thermodynamic studies reviewed suggest that split-cycle engines should be more efficient than conventional four-stroke engines. Reasons why increased thermal efficiency is not realised in practice could be due to practical compromises, or due to inherent architectural split-cycle engine design limitations. It was found that the number of split-cycle engine patents has increased significantly over recent years, suggesting an increased commercial interest in the concept since the possibility of increased efficiency becomes more desirable and might outweigh the drawbacks of practical challenges.

Ultimate strength formulation considering failure mode interactions of ring-stiffened cylinders subjected to hydrostatic pressure

This paper outlines empirical formulas to provide adequate predictions of the ultimate strength of ring-stiffened cylinders under hydrostatic pressure. The ultimate strength formulation was derived from published test data found in the open literature. The formulas consider the failure mode interactions, which include the parameter of shell yielding, inter-frame buckling, overall buckling, and stiffener tripping. The failure modes were inserted in the quadratic Merchant-Rankine formula. Afterward, the knockdown factors were empirically derived to best fit the actual collapse pressure. It is found that the proposed formulation can predict the ultimate strengths of ring-stiffened cylinders more accurately and consistently than other codified rules (PD5500, GL, ABS, API). The simple criterion for the assessment of failure modes was also provided. Furthermore, parametric studies were conducted to observe the effect of the design parameter on sizing the ring-stiffened cylinder when the failure modes can be predicted.