Full-scale Computational Fluid Dynamics Research Articles

Field test and numerical reconstitution of natural winds at the tunnel entrance section of high-speed railway

PurposeThe purpose of this paper is to understand the natural wind field characteristics of the tunnel entrance section and analyzing the aerodynamic performance of high-speed railway trains (HSRTs) under natural winds.Design/methodology/approachThree typical tunnel entrance section sites, namely, tunnel–bridge in a dry canyon (TBDC), tunnel–bridge in a river canyon (TBRC) and tunnel–flat ground (TF), are selected to conduct a continuous wind field measurement. Based on the measured wind characteristics, the natural winds of the TBDC and TF sites are reconstituted and imported into the two corresponding full-scale computational fluid dynamics models. The aerodynamic loads of the HSRT running on TBDC and TF with reconstituted winds are simply analyzed.FindingsThe von Kármán spectrum can be used to describe the wind field at the tunnel entrance section. In the reconstituted natural wind condition, a time-varying feature of wind speed distribution and leeward side vortex around the HSRT caused by the wind speed fluctuation is found. The fluctuating amplitude of aerodynamic loads at the TBDC infrastructure is up to 97.9% larger than that at the TF infrastructure.Originality/valueThe natural wind characteristics at tunnel entrance sections on the high-speed railway are first measured and analyzed. A numerical reconstitution scheme considering the temporal and spatial variation of natural wind speed is proposed and verified based on field measurement results. The aerodynamic performance of an HSRT under reconstituted natural winds is first investigated.

Numerical investigations on temperature and flow field performance of octagonal culture tank under different physical parameters for fish growth based on computational fluid dynamics

• Both velocity and temperature fields within octagonal rearing tank jointly solved by theory and CFD. • Effects of seven different physical parameters of rearing tank numerically studied. • Average and STD of temperature and velocity for seven horizontal planes used quantitatively to evaluate effects. • Completely mixing flow field & obvious secondary flow existing with increasing inlet velocity by 0.5 m/s. Both velocity and temperature field performance of fish octagonal rearing tank played an important role in the recirculating aquaculture system (RAS). To maintain the water temperature and velocity distributions in the optimal growth conditions for fish, particularly juvenile fish, is a great challenge. To solve this problem, computational fluid dynamics (CFD) was employed to investigate the dynamic temperature and velocity fields in the juvenile fish rearing tank. In this study, a full-scale CFD benchmark model of octagonal rearing tank based on real situation has been firstly validated by comparing on-site measurement data with simulation results. Following that, the effects of several different physical parameters of rearing tank, including inlet flow temperature and velocity, inlet position on the culturing tank wall, water flow inlet diameter and ambient air temperature around RAS on both velocity and temperature field performance were numerically studied, respectively. Meanwhile, average temperature and velocity as well as standard deviation (STD) of temperature and velocity for seven different horizontal plane have been employed to quantitatively evaluate the effects of aforementioned physical parameters on velocity and temperature field performance. Some key findings are found that 1) Benchmark scenario with inlet temperature of 25 °C and inlet velocity of 0.1 m/s could establish dynamic homogeneous temperature and velocity fields, which is suitable for fish growth; 2) Increasing inlet temperature will increase STD of horizontal plane temperature and achieve a maximum approximately 55% at the height of inlet position with inlet temperature of 28 °C; 3) As the inlet diameter increases up to 101.6 mm with inlet velocity 0.1 m/s, which is not only beneficial to clean the solid waste; but also could provide a suitable juvenile fish growth conditions.

The impact of biofilm on marine current turbine performance

Although several problems related to biofouling of marine current turbines (MCTs) are reported in the literature, the most important one is related to long-term operational performance and maintenance costs. Nevertheless, studies related to the impact of biofouling on MCT performance are rather scarce. In this study, the impact of biofilm on MCT performance is investigated using the Computational Fluid Dynamics (CFD) approach. Biofilm is modelled using previously developed roughness functions implemented in a wall function solver. A verification study is performed to determine sufficient grid spacings and to calculate numerical uncertainty. The validation study is conducted by comparing the obtained results with experimental and numerical ones from the literature. Full-scale CFD simulations are performed for six fouling conditions with varying biofilm height and percentage of surface coverage at eight tip speed ratios (TSRs). The obtained results highlight the significant impact of biofilm on MCT performance reflected in a decrease in the power coefficient, which for the optimal TSR is equal to −10.7% for the R1 fouling condition. Finally, a detailed analysis of the flow around MCTs fouled with biofilm is conducted and the reasons for the detrimental impact of biofilm on MCT performance are discussed.

Prediction of drag and lift forces of a high-speed vessel at full scale by CFD-based GEOSIM method

In this study, it was aimed to obtain an accurate extrapolation method to compute lift and drag forces of high-speed vessels at full-scale by using CFD (Computational Fluid Dynamics) based GEOSIM (GEOmetrically SIMilar) method which is valid for both fully planing and semi-planing regimes. Athena R/V 5365 bare hull form with a skeg which is a semi-displacement type of high-speed vessel was selected with a model family for hydrodynamic analyses under captive and free to sinkage/trim conditions. Total drag and lift forces have been computed for a generated GEOSIM family of this form at three different model scales and full-scale for Fr = 0.8 by an unsteady RANS (Reynolds Averaged Navier–Stokes) solver. k–ε turbulence model was used to simulate the turbulent flow around the hulls, and both DFBI (Dynamic Fluid Body Interaction) and overset mesh technique were carried out to model the heave and pitch motions under free to sinkage/trim condition. The computational results of the model family were used to get “drag-lift ratio curve” for Athena hull at a fixed Fr number and so the corresponding results at full scale were predicted by extrapolating those of model scales in the form of a non-dimensional ratios of drag-lift forces. Then the extrapolated full-scale results calculated by modified GEOSIM method were compared with those of full-scale CFD and obtained by Froude extrapolation technique. The modified GEOSIM method has been found to be successful to compute the main forces (lift and drag) acting on high-speed vessels as a single coefficient at full scale. The method also works accurately both under fully and semi-planing conditions.

Full-scale SPH simulations of ship-wave impact generated sea spray

Sea spray generated by ship-wave impact contributes to marine ice accretion onboard vessels. Limitations in field measurements and model experiments encourage the use of numerical simulation to understand the formation of such spray. In this paper, full-scale computational fluid dynamics (CFD) models of wave-generated sea spray are developed using a smooth particle hydrodynamics (SPH) method. A three-dimensional (3D) numerical wave tank equipped with a flap-type wave maker and a wave absorber is created to produce regular waves of various heights and steepness. A full-scale medium-size fishing vessel (MFV) is modeled to encounter incoming waves at head sea conditions at various forward speeds. Moving ship dynamics with three degree-of-freedom (3-DOF) in waves are resolved instead of mimicking a relative ship speed. The resultant spray water amount is measured using a numerical collection box and compared against field measurements and a theoretical model, where a reasonable agreement is found. The model is able to distinguish between green water and spray water. A multi-phase two-dimensional (2D) simulation is also performed that demonstrates the role of winds in the fragmentation of water sheets into droplets. The simulation results indicate energy released from a surging ship significantly contributes to the generation of spray.

Computational Fluid Dynamics Analysis of Alternative Ventilation Schemes in Cage-Free Poultry Housing.

Simple SummaryUncertainty regarding “cage-free” housing guidelines have left egg producers unsure about how to transition to cage-free housing. A primary driving force behind cage-free housing is the perceived animal welfare concerns for caged birds. Therefore, it is of great importance to perform a systematic investigation on specific cage-free facility types with an emphasis on bird comfort assessment. Thus, the goal of this study was to investigate alternative ventilation schemes of a cage-free house to provide practical designs for a comfortable interior environment at the hen level. By modeling four different ventilation schemes in a one-eighth section of a typical floor-raised layer house—indoor temperature, air speed, and static pressure were compared and analyzed quantitatively. Distribution contours and quantitative analysis of airflow, temperature, and pressure suggested that indoor conditions could be maintained at a suitable range uniformly, especially at the hen level. In addition, the ventilation rates of the hen house within four ventilation schemes fell at the higher end of the desired ventilation range, indicating that the barn could be expected to maintain good air quality during cold weather. This study demonstrated that computational fluid dynamics modeling was a powerful tool that facilitated researchers to address animal welfare issues in animal housing designs.This work investigated alternative ventilation schemes to help define a proper ventilation system design in cage-free hen houses with the goal of assuring bird welfare through comfortable conditions. Computational fluid dynamics (CFD) modeling was employed to simulate indoor and outdoor airflows to quantify the effectiveness of ventilation systems in maintaining suitable and uniform living conditions at the hen level. Four three-dimensional CFD models were developed based on a full-scale floor-raised layer house, corresponding to ventilation schemes of the standard top-wall inlet, sidewall exhaust, and three alternatives: mid-wall inlet, ceiling exhaust; mid-wall inlet, ridge exhaust; and mid-wall inlet, attic exhaust with potential for pre-treatment of exhaust air. In a sophisticated and powerful achievement of the analysis, 2365 birds were individually modeled with simplified bird-shapes to represent a realistic number, body heat, and airflow obstruction of hens housed. The simulated ventilation rate for the layer house models was 1.9–2.0 m3/s (4100 ft3/min) in the desired range for cold weather (0 °C). Simulation results and subsequent analyses demonstrated that these alternative models had the capacity to create satisfactory comfortable temperature and air velocity at the hen level. A full-scale CFD model with individual hen models presented robustness in evaluating bird welfare conditions.

Slam load estimation for high-speed catamarans in irregular head seas by full-scale computational fluid dynamics

Global loads acting on high-speed wave-piercing catamarans are investigated using computational fluid dynamics (CFD). Catamaran vessels are subjected to load cases that are not present on mono-hull vessels, such as transverse bending moment, pitch connecting moment and splitting force. As the speed and size of a catamaran increases the severity of loads rises with slam induced effects. Full-scale CFD simulation is undertaken to investigate the pressure distributions and resultant global loads acting on the 98 m INCAT wave-piercer catamaran HSV2 Swift, validated against sea trial tests. Rigid body dynamics are then applied to estimate the internal loads at different sections of the vessel based on the relative hydrodynamic and inertial force distributions. The estimated global loads are then checked according to DNV GL rules by comparing “design load limits”. Global loads are estimated for the 98 m INCAT HSV2 Swift catamaran in headseas at a forward speed of 20 knots. Splitting forces are found to have a longitudinal distribution along the catamaran hull, which causes prying moments. Peak values for LBM are examined relative to corresponding instantaneous wave height prior to the slam event. In addition, it is found that pitch acceleration has a linear correlation with LBM slam loads.

Effective wake estimation of KCS hull at full-scale by GEOSIM method based on CFD

In this study, the effective wake factors of a self-propelled container ship were investigated by Telfer's GEOSIM method based on CFD (Computational Fluid Dynamics). For this purpose, the self-propulsion characteristics of KCS (KRISO Container Ship) at three different model scales and full-scale were determined at Fr = 0.26 by unsteady RANS (Reynolds Averaged Navier-Stokes) solver. All scales corresponded to a wide range of Reynolds numbers. Turbulent flow around the KCS hull has been investigated by the k-ε turbulence model. Heave and pitch motions of KCS hulls have been modeled with the DFBI (Dynamic Fluid Body Interaction) method and overset mesh technique. The rotational motion of KP505 propeller has been simulated using the RBM (Rigid Body Motion) approach. The result obtained by the extrapolation of the effective wake fraction with the GEOSIM method was compared with the full-scale ones of CFD and ITTC methods. The results by the GEOSIM method are more compatible with those of full-scale CFD than the results of 1978 ITTC method. In the wake region, where viscous effects are predominant, the change of effective wake fraction with Reynolds number has been successfully represented by the GEOSIM method, thus more robust and reliable results have been found.

Piloted Flight Simulation of Helicopter Recovery to the Queen Elizabeth Class Aircraft Carrier

This Paper describes how flight simulation has been used to investigate helicopter recovery operations to the deck of HMS Queen Elizabeth, the United Kingdom’s new aircraft carrier. A helicopter flight simulation environment has been developed in which the unsteady airflow over the ship has been created using full-scale computational fluid dynamics. A six-degree-of-freedom motion flight simulator has been used to conduct real-time piloted deck landings where a helicopter flight dynamics model representative of a Sikorsky SH-60B Seahawk helicopter was recovered to the designated rotorcraft landing spots toward the stern of the ship. A test pilot was instructed to land the helicopter and to give workload ratings for the difficulty of the task when flying in relative winds from Ahead, and 45 deg and 90 deg from starboard. The workload ratings, along with the corresponding pilot control activity and helicopter positional accuracy, are discussed in relation to the airflow to which the helicopter was subjected. The Paper demonstrates how flight simulation could be used to support flight trials and helicopter clearance activities but also notes that real-world trials data are needed to compare with the simulations before the techniques can be beneficially deployed.

Ship Airwakes in Waves and Motions and Effects on Helicopter Operation

Insight into the effects of motions and waves on a ship airwake can be used to provide information regarding safe conditions for at sea flight operations and pilot training. We present a study on the effects of waves and motions on a ship's airwake and a helicopter operating above the flight deck using full scale computational fluid dynamics simulations. The ONR Tumblehome Ship (ONRT) geometry is analyzed in wind and regular head waves corresponding to nominal sea states 3 and 6. In order to separate the effects of waves and motions, simulations are conducted for both sea states with combinations of: waves and motions, waves and no motions, no waves with motions, and no motions or waves. A triple velocity decomposition is conducted in order to quantify changes in the airwake due to motions and waves. The aerodynamic loads on a helicopter hovering in the airwake are studied with one-way and two-way coupling approaches. The one-way coupled analysis uses the velocity field data from the full scale airwake simulations along with disk actuator theory to calculate thrust fluctuations for three different rotor sizes operating above the flight deck. In the two-way coupled study a helicopter loosely based on the Sikorsky SH-60 Seahawk hovering above the flight deck of the ONRT is simulated, including dynamic overset grids of the main rotor, tail rotor and fuselage. This approach captures the interaction between the rotor downwash and the ONRT airwake. The study shows that for the lower sea state 3 the motions and waves have little effect on the airwake behavior, exhibiting little change with respect to the baseline case without motions and waves. At sea state 6 the flow field is modified significantly, which also affects the forces on the helicopter. Force fluctuations show main peaks at the wave encounter frequency and the blade passage frequency, as well as higher harmonics. The one-way coupling approach shows that larger rotors effectively filter out small scale fluctuations while smaller diameter rotors are affected by smaller flow structures.

Effect of roughness in full-scale validation of a CFD model of self-propelled ships

This paper presents a comparison of full-scale computational fluid dynamics (CFD) simulations with speed trial measurements for a ro-ro vessel and a general cargo vessel. Significant work has been done on validating CFD simulation in model scale. However, in full-scale very few publicly available studies have been conducted due to limited access of validation data. The present study includes extensive validation and verification of both resistance, propeller open-water and self-propulsion simulations in both model and full-scale. The self-propulsion simulations include modelling of the free surface and rotation of the 3D propeller. Full-scale resistance and propeller open-water as well as model scale self-propulsion simulations show good agreement with towing tank measurements and predictions. However, the full-scale self-propulsion simulations using the traditional approach of including the roughness as a point force estimated by an empirical formula significantly underestimate the power from the speed trial measurements. By including the effect of hull and propeller roughness directly into the CFD model, by modifying the wall functions, the discrepancy between CFD and speed trial measurements decreases significantly. This indicates that inclusion of a roughness model directly into the CFD simulation could be a more accurate method than the traditional approach of using empirical formulas originally designed for towing tank extrapolation.

Multi-scale modeling of gas-phase reactions in metal-organic chemical vapor deposition growth of WSe2

We present a multi-scale computational approach to model the gas-phase chemical kinetics for Metal-Organic Chemical Vapor Deposition (MOCVD) of WSe2 using W(CO)6 and H2Se as gas-phase precursors. This framework combines Quantum Mechanical (QM) methods based on Density Functional Theory (DFT), ReaxFF-based reactive molecular dynamics, and Computational Fluid Dynamics (CFD) to efficiently model the gas-phase physiochemical processes leading to WSe2 growth in a cold-wall horizontal MOCVD chamber. A detailed gas-phase chemical kinetic reaction model is developed to describe all major chemical reaction pathways from the precursors W(CO)6 and H2Se to the most thermodynamically stable molecules, with quantified kinetic rate constants. First QM calculations are performed to suggest key reaction types and to provide the necessary training set to determine ReaxFF reactive force-field parameters for the W/H/C/O/Se system. Using the developed force field, ReaxFF simulations are performed to identify all major chemical reaction pathways and determine their associated activation energies. Other kinetic parameters, together with the thermal and transport properties of all species involved, are estimated using well-established theories or correlations. This chemical kinetic model with thermal and transport parameters is then integrated into a reacting flow solver for full-scale CFD simulations of the MOCVD chamber under realistic operating conditions, to demonstrate its capabilities in predicting the major processes in the gas phase and qualitatively estimating thin film growth behavior. The predicted gas-phase concentrations of tungsten chalcogenides at the growth substrate correlate well with experimental measurements of average film thickness across the substrate, which suggests that crystal growth may result from surface deposition reactions of these species. This computational framework for the gas-phase chemical kinetics in MOCVD (prior to surface deposition and subsequent crystal growth) can thus test experimental MOCVD conditions, generate insights into more effective growth protocols, shed light on the significance of reactor geometry, and improve the reproducibility of MOCVD results across different experimental growth chambers. The computational framework is also transferable to other CVD chemistries.

A comprehensive hydrodynamic analysis of a full-scale oxidation ditch using Population Balance Modelling in CFD simulation

This work exhibits the importance of the experimental validation when full-scale computational fluid dynamics (CFD) models are developed to provide a detailed analysis of the spatial variations in 3D of the fluid flow inside aerated tanks. Single-phase and two-phase CFD models were performed to study the fluid behaviour carefully by means of the velocity profiles and the aeration pattern in a full-scale oxidation ditch. Air hold-up, bubble size distribution and interfacial area density were calculated by polydisperse models where Population Balance Model (PBM) was governed by break-up and coalescence; the free-surface approach allowed the CFD model to describe the three-dimensional effect of bubbly plumes in large scales in detail. Tracer tests were carried out to obtain the flow pattern and the hydraulic distribution of the flow into two wastewater treatment lanes in order to define the boundary conditions for the model correctly. Despite the difficulty of performing velocity measurements of the fluid in 3D, with and without air bubbles, these provided essential information to validate the CFD model. From this analysis, several simulations were performed to improve the hydrodynamics and the operation of the process by relocating the propellers.

A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part I Experiment

A ducted photovoltaic façade (DPV) unit was studied using experimental prototype and simulated in a full scale computational fluid dynamics (CFD) model. The study comes in two parts; this is Part I, as detailed in the title above, and Part II is titled “A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part II CFD Simulation”. The process adopted in the experimental study is replicated in the simulation part. The aim was to optimize the duct width behind the solar cells to allow for a maximum buoyancy-driven cooling for the cells during operation. Duct widths from 5 to 50 cm were tested in a prototype. A duct width of 45 cm had the maximum calculated heat removed from the duct; however, the lowest cell-operating temperature was reported for duct width of 50 cm. It was found that ΔT between ducts’ inlets and outlets range from 5.47 °C to 12.32 °C for duct widths of 5–50 cm, respectively. The ducted system enhanced module efficiency by 12.69% by reducing photovoltaic (PV) temperature by 27 °C from 100 °C to 73 °C. The maximum measured heat recovered from the ducted PV system was 422 W. This is 48.98% from the incident radiation in the test. The total sum of heat recovered and power enhanced by the ducted system was 61.67%.

Hydrodynamics of Atlantic salmon culture tank: Effect of inlet nozzle angle on the velocity field

The aquaculture industry is increasingly interested in using larger rearing tanks of near 1000 m3 to achieve production and economic benefits. Higher Reynolds number due to that order of tank size makes the flow fully turbulent. This paper presents a full-scale computational fluid dynamics (CFD) model of an existing culture tank of 788 m3 size was developed, based on time-dependent incompressible unsteady Reynolds averaged Navier-Stokes (URANS) formulation with the realizable k-ε viscous model. The tank has two inlet pipes, placed closed to side walls of the tank. Each pipe has 11 inlet nozzles, which introduce the flow into the tank parallel to the walls. This base case was validated against the experimental velocity measurements using Acoustic Doppler Velocimetry (ADV) at predefined locations across the central vertical plane of the tank.Turbulence characteristics and hence the hydrodynamic performance of the tank are influenced by inflow characteristics. To conclude this, two redesigns were developed and contrasted with the base design for various flow parameters from the viewpoint of the tank's performance. Redesign 1 has the nozzles turned towards the centre by 42°, while Redesign 2 has bottom 5 nozzles directing the flow towards the centre with the rest injecting the flow parallel to the wall. Distribution of turbulence parameters and vortices reveal that the inflow with a radial component improves the mixing and flow uniformity characteristics of the tank. The present study has shown that relatively minor construction changes aided by CFD can result in major changes in the hydrodynamic properties of large culture tanks for Atlantic salmon.

Computational and experimental modelling study of the unsteady airflow over the aircraft carrier HMS Queen Elizabeth

This paper describes a comprehensive experimental and computational modelling study of the aerodynamic environment around the UK's new Queen Elizabeth Class (QEC) aircraft carriers. The study has been performed to support the integration of the F-35B Lightning II multi-role fighter with the UK Royal Navy's flagship, HMS Queen Elizabeth. Unsteady airwakes have been generated using Computational Fluid Dynamics (CFD) and have been incorporated into the F-35/QEC Integration Flight Simulator at BAE Systems Warton and into the HELIFLIGHT-R research simulator at the University of Liverpool.A small-scale experiment has also been conducted in which a 1.4 m long (1:200) scale model of the QEC was submerged in a water channel and Acoustic Doppler Velocimetry was used to measure the unsteady flow around the ship. Delayed Detached Eddy Simulation CFD was used to model the flow in the water channel and the computed unsteady flow field has been compared with the experimental measurements. The results show generally excellent agreement between the model-scale experiment and CFD. Building on this, full-scale 30-s CFD airwakes have been generated for the nearfield area surrounding the QEC, and for about 400 m astern of the ship to capture the disturbed air flow along the fixed-wing approach glideslope.

Aerodynamic drag in competitive tandem para-cycling: Road race versus time-trial positions

An athlete's riding posture is a key element for aerodynamic drag in cycling. Tandem cycling has the complication of having two athletes in close proximity to each other on a single tandem bicycle. The complex flow-field between the pilot and stoker in tandem cycling presents new challenges for aerodynamic optimisation. Aerodynamic drag acting on two tandem road race setups and two track time-trial setups were analysed with computational fluid dynamics (CFD) simulations. For validation purposes, wind tunnel measurements were designed providing drag measurements from both tandem athletes simultaneously using a quarter-scale model. A max drag force deviation of 4.9% was found between the wind tunnel experiments and CFD simulations of the quarter-scale geometry. Full-scale CFD simulations of upright, crouched, time-trial and frame-clench tandem setups were performed. The drag force experienced by individual athletes in all investigated tandem setups was compared to that of solo riders to enhance understanding of the aerodynamic interaction between both tandem athletes. The most aerodynamic tandem setup was found to be the frame-clench setup which is unique to tandem cycling and had a CDA of 0.286 m2, and could provide an advantage of 8.1 s over a standard time-trial setup for a 10 km time-trial event.

Optimization of Heat Exchange in Manifold-Microchannel Grooves

Manifold-microchannel (MM) combinations used on heat transfer surfaces have shown the potential for superior heat transfer performance to pressure drop ratio when compared with chevron-type corrugations for plate (frame) heat exchangers (PHEs). This paper presents an advanced genetic algorithm (GA)-based procedure for analyzing and optimizing the MM-based PHE. One distinctive feature of the implementation is the blended variable formulation for the chromosomes to allow the use of continuous variables rather than the bitwise variables in standard GA methods. The resulting GA procedure is particularly well suited for PHEs for several reasons, including the fact that it does not require continuous variables or functional dependence on the design variables. In addition, the computational effort required for the GA technique in the current implementation scales linearly with the number of design variables, making it appropriate for MM-based PHEs, which have several variables. The computed results compare well with experimental data and show better performance compared to conventional PHEs of the same volume utilizing chevron corrugations. Although a full-scale computational fluid dynamics (CFD) analysis may give more accurate results than the semi-empirical approach used in this paper, the former cannot efficiently support rapid concept de-selection during the preliminary stage of design. Optimization based on CFD also can usually not support discontinuous functions. To improve the fidelity of the current analysis, a discrete, finite-volume-type, one-dimensional (1D) reduced-order modeling is carried out, in addition to a purely bulk approach. Our discrete approach obviates the need for the є-NTU-type models.

Predicting scour beneath subsea pipelines from existing small free span depths under steady currents

An equation was developed to predict current-induced scour beneath subsea pipelines in areas with small span depths, S. Current equations for scour prediction are only applicable to partially buried pipelines. The existence of small span depths (i.e. S/D < 0.3) are of concern because the capacity for scour is higher at smaller span depths. Furthermore, it is impractical to perform rectification works, such as installing grout bags, under a pipeline with a small S/D. Full-scale two-dimensional computational fluid dynamics (CFD) simulations were performed using the Reynolds-averaged Navier–Stokes approach and the Shear stress transport k–ω turbulence model. To predict the occurrence of scour, the computed maximum bed shear stress beneath the pipe was converted to the dimensionless Shields parameter, and compared with the critical Shields parameter based on the mean sediment grain size. The numerical setup was verified, and a good agreement was found between model-scale CFD data and experimental data. Field data were obtained to determine the mean grain size, far field current velocity and to measure the span depths along the surveyed pipe length. A trend line equation was fitted to the full-scale CFD data, whereby the maximum Shields parameter beneath the pipe can be calculated based on the undisturbed Shields parameter and S/D.

Fire behaviour of gypsum plasterboard wall assemblies: CFD simulation of a full-scale residential building

Gypsum “dehydration” phenomena, occurring when gypsum plasterboard wall assemblies are exposed to a high temperature environment, result in water vapour production and subsequent dispersion in the fire compartment; these phenomena are often neglected in relevant Computational Fluid Dynamics (CFD) simulations. Aiming to investigate the impact of gypsum dehydration in full-scale CFD simulations of lightweight drywall buildings, the FDS code is used to simulate a two-storey residential building, exposed to a typical domestic fire scenario. The building employs a structural steel frame combined with gypsum plasterboard wall assemblies. Temperature-dependent thermo-physical properties are used for all construction materials. The effects of gypsum dehydration are assessed by using two alternative modelling approaches, an effective specific heat model and a solid reaction kinetics model; the obtained predictions are compared to a benchmark test case, where no such phenomena are modelled. The obtained results demonstrate that when the highly endothermic gypsum dehydration phenomena are simulated, lower overall heat release rates, gas and wall surface temperatures are predicted. In addition, the developed solid reaction kinetics model allows, for the first time, quantitative predictions of gypsum dehydration induced water vapour production and dispersion phenomena.