In this paper, we introduce a robust method for dynamic characterization of pressure measuring systems used in time-varying pressure applications. The dynamic response of the pressure measuring systems in terms of sensitivity and phase as a function of frequency at various amplitudes of the measurand can be provided. The shock tube which is the candidate primary standard for dynamic pressure calibration at the National Laboratory for pressure, Sweden, was used to realize the dynamic pressure. The shock tube setup used in this study can realize reference pressure with amplitudes up to 1.7 MPa in the frequency range from below a kilohertz up to a megahertz. The amplitude of the realized step pressure was calculated using the Rankine–Hugoniot step relations. In addition, the accurate time of arrival of the generated shock at the device under test (DUT) was measured using an optical probe based on shadowgraphy. The optical detector has a response time in nanosecond time scale which is several orders of magnitude faster than the response time of any pressure measuring system. Hereby, the latency between physical stimuli and response of the DUT can be measured. By the knowledge of the amplitude and the accurate time of arrival of the reference step pressure, the transfer function of the DUT can be calculated and presented in Bode diagrams of sensitivity and phase response versus frequency. The uncertainty in sensitivity and phase measurements was estimated. The information provided by this work is useful for developing reliable models of dynamic pressure measuring system and provide accurate information about their dynamic response. That in turn will contribute to establish a traceability chain for dynamic pressure calibration.

Accurate dynamic pressure measurements are increasingly important. While traceability is lacking, several National Metrology Institutes (NMIs) and calibration laboratories are currently establishing calibration capacities. Shock tubes generating pressure steps with rise times below 1 µs are highly suitable as standards for dynamic pressures in gas. In this work, we present the results from applying a fast-opening valve (FOV) to a shock tube designed for dynamic pressure measurements. We compare the performance of the shock tube when operated with conventional single and double diaphragms and when operated using an FOV. Different aspects are addressed: shock-wave formation, repeatability in amplitude of the realized pressure steps, the assessment of the required driver pressure for realizing nominal pressure steps, and economy. The results show that using the FOV has many advantages compared to the diaphragm: better repeatability, eight times faster to operate, and enables automation of the test sequences.

Experience with wooden multi-storey houses have shown that impact sound insulation is one of most critical issues to ensure a good indoor environment. Even in cases where the impact sound insulation is fulfilled, people perceive the sound from e.g. walking neighbours as very disturbing. To investigate the subjective perception, a test facility is needed which allows for a coherent evaluation of different floor designs by listening test. The facility should ensure, that when comparing different floors, the same excitation by a walker and the same receiving room are involved. Only the floor design should be changed. As a consequence the spread in the data will only be due to the spread in the perception by subjects. In this paper a virtual design tool for low frequency impact sound insulation is presented, which consists of four parts; measured walking forces, floor models, an auralisation system which consists of a grid of loudspeakers simulating the vibration of the floor and a receiving room furnished as a common living room. In a pilot study a listening test is carried out for 13 different floors with different impact sound spectra at frequencies below 100 Hz. The results indicate that the judged annoyance strongly correlates with the judged loudness. However, there is a substantial spread observed in between the subjects participating in the listening tests. To understand this spread, a more extended study is needed with more participants and a classification of the subjects with respect to criteria such as noise sensitivity or age.

Autonomous delivery vehicles – what kind of vehicles are they and does it matter? The project GLAD – Goods deliveries during the last mile of self-driving vehicles explores how tomorrow's small autonomous delivery vehicles (ADV) could operate in the transport system. The goal of the GLAD project is to develop knowledge about the needs and challenges of such vehicles in Sweden before they are in real operation. In the project, there are several work packages that work with different challenges in relation to ADV. To explore these issues, the project has developed a prototype of an ADV, which is based on a vehicle which today is classified as a three-wheeled moped. But designed as an ADV it could be a different kind of vehicle. One result from one of the work packages in the project is that ADVs driving on public roads should maintain the same speed as other traffic to avoid critical traffic situations. This means that ADVs should be able to drive at a maximum speed of 70 km/h. Another requirement is that the ADVs should be able of carrying a load of 500 kg. These requirements are a conclusion from interviews with drivers of small manually driven delivery vehicles about how they experience today's traffic situations, from which type of road they use and how they use their vehicles. The purpose of this report is to identify obstacles and opportunities from a regulatory perspective to implement ADVs in Sweden in a safe way. Rules that may affect the development of ADVs are, for example, whether they are covered by the Machinery Directive or whether they should be type approved. Other rules concern license plates, motor liability insurance, where the vehicles may be driven and driving license requirements. The aim of the legislations is to create a safe vehicle to use. After a review of existing regulations, it is closest at hand that future ADVs, based on the requirements set in the project, are classified as a 4-wheel heavy motorcycle for the transport of goods. The vehicle also needs a type-approval. It can be argued that an ADV with that weight and speed will have a lot to prove from a safety perspective in a type-approval process and that a market introduction is therefore further away in time. If the speed requirements are lowered instead i.e., maximum of 30 km/h, it could be classified as a motor tool. The advantage of motor tools is that these must be CE-marked by the manufacturer, which in turn means that they have a shorter time to market because the process does not involve a type-approval agency.

The International Convention for the Safety of Life at Sea (SOLAS) recognises five different fire-extinguishing system solutions for ro-ro spaces on ships; manually activated water spray systems (Resolution A.123(V)), automatic sprinkler or deluge water spray systems and automatic nozzle or deluge water mist systems (MSC.1/Circ.1430), high-expansion foam systems and gas fire-extinguishing systems (FSS Code). A review of potential commercially available alternative systems, their expected performance efficiency and water consumption was made. Based on this review, two alternative fire-extinguishing systems were identified: Compressed Air Foam Systems (CAFS) and foam-water sprinkler/spray systems. Fire suppression performance testing of water spray systems according to the Resolution A.123(V) and MSC.1/Circ.1430, a CAFS and a foam-water spray system were conducted. The water spray system per MSC.1/Circ.1430 had superior performance while the system per Resolution A.123(V) and the foam-water spray system limited the fire size to some degrees. The CAFS provided limited fire suppression performance.

We numerically simulate the hydrodynamic response of a floating offshore wind turbine (FOWT) using computational fluid dynamics. The FOWT under consideration is a slack-moored 1:70 scale model of the UMaine VolturnUS-S semi-submersible platform. The test cases under consideration are (i) static equilibrium load cases, (ii) free decay tests, and (iii) two focused wave cases of different wave steepness. The FOWT is modelled using a two-phase Navier-Stokes solver inside the OpenFOAM-v2006 framework. The catenary mooring is computed by dynamically solving the equations of motion for an elastic cable using the MoodyCore solver. The results are shown to be in good agreement with measurements.

Experimental comparisons between imaging techniques serve to provide confidence in the validity of each technique for the study of multiphase flow systems. Such cross-validation can establish the limitations of each technique quantitatively. In the present paper, the authors report efforts made on the characterization of semi-dilute, mono-dispersed suspensions of rayon fibres in turbulent water flow using Magnetic Resonance Imaging (MRI), Ultrasound Velocity Profiling (UVP) and Electrical Impedance Tomography (EIT). Increasing flow velocities and fibre concentration were studied using these three experimental techniques. For lower fibre concentrations more uniform distributions were observed and as flow velocity increased fibre agglomerations were found in the centre region of the pipe.

Particle motion in fluid is discussed for one-particle systems as well as for dense suspensions, such as cementitious materials. The difference in large particle motion between larger particles and behaviour of fines (<125 μm) is explained, motion of one particle is shown by numerical simulation. It is concluded and highlighted that it is the particular motion of the fines that to a large extent contribute to the rheological properties of a suspension. It is also shown why larger ellipsoidal particles do not necessarily contribute to the increase of viscosity.

Wind-assisted ship propulsion (WASP) has received much attention lately with research focusing on the different sail technologies, ship-hull design optimisation and weather route optimisation. However, the traditional propulsion system is still needed for wind assisted vessels and is associated with several challenges, related to the wide range of operating conditions and propeller loads due to the varying degree of wind-assistance that will occur. In this study we use an interactive design and optimisation methodology applied on propellers of wind-assisted vessels. The methodology involves handling the complete operating profile of the propeller, an optimisation method for interactive cavi-tation evaluation by the blade designer, and the use of a new objective, the total energy consumption (TEC) of the expected operation. We use a case study where the KVLCC2 tanker is retrofitted with six Flettner rotor sails, operating between two fixed destinations at constant speed. The purpose is to investigate to what extent a new propeller design can offer a significantly lower TEC when compared to the existing design. Based on the results of this study, approximately 0.9% further reduction in TEC was achieved with the WASP adapted propeller compared to the existing one.

Wooden floors usually have worse impact sound insulation (ISI) at low frequencies than concrete floors having the same rating level. Rating level is usually expressed by single-number quantities (SNQs), such as weighted normalized impact sound pressure level Ln,w. Psychoacoustic research among wooden floors is very limited although a controlled laboratory experiment is the strongest method to point out the most adequate SNQs to be declared for the floors. The purpose of our study was to determine how four standardized SNQs of ISO 717-2, Ln,w, Ln,w + CI, Ln,w + CI,50, and LiA,Fmax,V,T, and a recently proposed SNQ, Ln,w + CI,25, are associated with the annoyance of natural impact sounds transmitted through wooden floors. Fifteen floors were built in the laboratory based either on cross-laminated timber (heavy) or open box wood (light) slabs. Different coverings and suspended ceilings were applied on these slabs. The ISI was tested within 25–3150 Hz using both tapping machine and rubber ball. Thereafter, five natural impact sounds were recorded for each floor: rubber ball drops, steel ball drops, walking, jumping, and chair pushing. Fifty-two people rated the annoyance of these 75 recorded natural impact sounds in psychophysics laboratory. Annoyance was best associated with Ln,w for all the five impact sound types. That is, measurement of ISI within 100–3150 Hz is sufficient from subjective point of view. All four SNQs based on tapping machine explained annoyance better than the SNQ based on rubber ball. Our results can significantly guide the future research, development, and regulations of wooden floors.

A vented corn starch dust explosion in an 11.5 m3 vessel is studied using both experimental and numerical methods. The reduced explosion overpressure in the vessel is recorded using two pressure sensors mounted on the wall inside of the vessel. Unsteady three-dimensional Reynolds-Averaged Navier-Stokes simulations of the experiment are performed using the Flame Speed Closure (FSC) model of the influence of turbulence on premixed combustion. The model was thoroughly validated in previous studies and was earlier implemented into OpenFOAM CFD software. The self-acceleration of a large-scale flame kernel is associated with the influence of combustion-induced pressure perturbations on the flow of unburned reactants ahead of the kernel. Accordingly, the FSC model is extended by adapting the well-known experimental observations of the self-similarity of the kernel acceleration. Influence of different turbulence models on the simulated results is also explored. Thanks to the extension of the FSC model, the measured time-dependence of the pressure is well predicted when the k-omega-SST turbulence model is used. © 2021 The Authors

Fibre streaks are observed in experiments with fibre suspensions in a turbulent half-channel flow. The preferential concentration methods, most commonly used to quantify preferential particle concentration, are in one dimension found to be concentration dependent. Two different new streak quantification methods are evaluated, one based on Voronoi analysis and the other based on artificial particles with an assigned fixed width. The width of the particle streaks and a measure of the intensity of the streaks, i.e. streakiness, are sought. Both methods are based on the auto-correlation of a signal, generated by summing images in the direction of the streaks. Common for both methods is a severe concentration dependency, verified in experiments keeping the flow conditions constant while the (very dilute) concentration of fibres is altered. The fixed width method is shown to be the most suitable method, being more robust and less computationally expensive. By assuming the concentration dependence to be related to random noise, an expression is derived, which is shown to make the streak width and the streakiness independent of the concentration even at as low concentrations as 0.05 particles per pixel column in an image. The streakiness is obtained by applying an artificial particle width equal to 20 % of the streak width. This artificial particle width is in this study found to be large enough to smoothen the correlation without altering the streakiness nor the streak width. It is concluded that in order to make quantitative comparisons between different experiments or simulations, the evaluation has to be performed with care and be very well documented.

Ship hydrodynamic performance prediction in waves is a common practice in the early stages of the ship design process as the interaction between the ship and waves may adversely affect the hydrodynamic responses of the ship in comparison to calm water. Various well­established numerical and experimental methods are often utilized for prediction of ship performance in waves. Although the model tests are expensive and time­consuming, a high level of accuracy is often achieved in such experiments. On the other hand, with respect to the increased computational power, prediction of ship performance in waves by the numerical methods based on Computational Fluid Dynamics (CFD) techniques are gradually acquiring more popularity. However, the validity of the incorporated discretization schemes and modelling assumptions in these state­of­the­art CFD methods are often overlooked and the method accuracy is mainly assessed through the validation of the results based on the respective model test data. Validation as an engineering exercise aims to show that the right equations are solved, while verification (mathematical exercise) is required to demonstrate that equations are solved right [1]. The eventual objective of this research is to perform verification and validation exercises of a ship performance prediction in regular head waves using CFD, whereas in this paper, the working progress is presented which may be subjected to significant revisions. To this end, extensive attempts have been made to investigate numerical wave propagation without the presence of the hull. Ship responses in waves are significantly influenced by the wave excitation forces. Therefore, not only high level of accuracy is required for the simulation of the numerical waves, but also quantification of the numerical uncertainties are of a great importance. This becomes even more challenging when the ship hydrodynamic responses, such as motions and added resistance in waves, exhibit dependencies on wave steepness. In this paper, the main focus of such uncertainty analyses is on the systematic grid convergence study.

In this study, the hydrodynamic performance of a ship in terms of motions and resistance responses in calm water and in regular head waves is investigated for two loading conditions using a Fully Nonlinear Potential Flow (FNPF) panel method. The main focus is understanding the ship responses in a broad range of operational conditions. Comprehensive analyses of the motions and their correlation with the wave making resistance including their harmonics in waves are presented and compared against experimental data. The predicted motions compare well with experimental data but the resistance prediction is not quite as good. The natural frequencies for heave and pitch are estimated from a set of free decay motion simulations in calm water to provide a better insight into the ship behavior near resonance conditions in waves. Interestingly, in addition to the well known peak in the added wave resistance coefficient around wave lengths close to one ship length, a secondary peak is detected in the vicinity of wave lengths with half the ship length. © 2022 The Authors

A new Nordic method to predict rail traffic noise is proposed. It is based on a complete

separation of source emission and sound propagation. Each train is modelled as a number

of point sources each with a certain sound power with or without directivity. The source

model is connected to point source sound propagation theory to yield the sound pressure

level in an arbitrary receiver position. The propagation model is based on accurate

analytical models and it is capable of predicting propagation effects both with and

without the influence of meteorological parameters. In this first version the prediction

method has to rely on old data for the noise emission of trains.

A new Nordic method to predict road traffic noise is proposed. It is based on a complete

separation of source emission and sound propagation. Each vehicle is modelled as a

number of point sources each with a certain sound power with or without directivity. The

source model is connected to point source sound propagation theory to yield the sound

pressure level in an arbitrary receiver position. The propagation model is based on

accurate analytical models and it is capable of predicting propagation effects both with

and without the influence of meteorological parameters.

The present paper describes a method for non-destructive testing of the glass strength. Square 10 × 10 cm2 samples of annealed float glass was inflicted with a controlled defect in the centre of the atmospheric side using Vickers microindentation-induced cracking with a force of 2 N, 5 N and 10 N and compared to an un-indented reference. The samples were non-destructively tested using a nonlinear acoustic wave method resulting in defect values. The average of the defect values was found to linearly correlate to the indentation force in a log–log relationship. The samples were subsequently tested in a ring-on-ring setup that allows for an equibiaxial stress state. The indentation-induced cracking gave practically realistic strength values in the range of 45 to 110 MPa. The individual sample values for failure stress as a function of normalized defect value show linear trends with approximately half of the data within 95% confidence limit. In summary, this study provides an initial proof-of-concept for a non-destructive testing of the strength of glass.

I dagsläget finns endast förstörande metoder för att bestämma hållfastheten för planglas. Det har medfört att på grund av den stora spridningen i hållfasthet av planglas behöver man ta till en stor säkerhetsfaktor. En ”säker” designhållfasthet som med andra ord behöver vara så låg så att risken är minimal att glaset går sönder. Resultatet blir att onödigt mycket glas används eftersom glas i princip alltid är starkare än designhållfastheten. Dessutom finns det idag heller ingen metod som kan mäta att glaset faktiskt upprätthåller designhållfastheten. Det finns med andra många skäl, både miljömässiga och kvalitetsskäl, till att utveckla en icke-förstörande metod till att bestämma hållfastheten av planglas. 

The need to reduce green-house gas emissions from shipping has reborn the interest in wind propulsion for commercial cargo vessels. This places new requirements on the tools used in ship design, as well as the methods usually applied in sailing yacht design. A range of design tools are used by designers at various stages in the design of wind-assisted ships and for different purposes. One important tool is the steady-state velocity prediction program (VPP) which is typically used to predict the speed of the vessel when sailing in a range of wind directions and wind speeds. Steady-state VPPs can be very efficient and fast and may be used to rapidly assess a large number of design alternatives. However, steady-state VPPs are not able to consider dynamic effects such as unsteady wave forces on the hull which may require the rudder to be active to control the heading and course of the vessel. This, in turn, leads to different mean forces than those predicted by a static VPP and therefore the sailing performance may be reduced compared to the predictions of a static VPP. Another effect of the ship’s motions in a seaway is that the angles of attack of the sails fluctuate, which can lead to different optimum sheeting angles and possibly a loss of performance. This study uses an unsteady 3D fully nonlinear potential flow hydrodynamic model coupled with an efficient lifting-line aerodynamic model to investigate the differences in sailing performance of a vessel sailing in steady conditions to the performance when sailing in a seaway and gusty wind based on a spatio-temporal wind model. The analysis shows clearly that the unsteady wind model affects the predicted performance. This is especially the case when sailing close-hauled and on a beam reach, where large changes in the local sail angles of attack can be observed.

The need to reduce green-house gas emissions has renewed the interest in wind propulsion for commercial cargo vessels. When designing such modern “sailing” ships, naval architects often lean on methods and tools originally developed for the design of sailing yachts. The most common tool today is the steady-state Performance Prediction Program (PPP), typically used to predict quantities like speed, leeway, heel of the vessel when sailing in a range of wind directions and wind speeds. Steady state PPPs are very efficient and can be used to rapidly assess a large number of design alternatives. PPPs are, however, not able to consider dynamic effects such as unsteady sail forces due to ship motions in waves or the turbulent structure of the natural wind. In this paper we present time-domain simulations with a Dynamic Performance Prediction Program (DPPP) that can take the “unsteadiness” of the natural environment into account. The program is based on coupling an unsteady 3D fully nonlinear potential flow hydrodynamic solver to an efficient lifting-line aerodynamic model. Particular attention is paid to a recently implemented unsteady aerodynamic model that employs an indicial response method based on Wagner’s function. The usefulness of such advanced simulations for performance prediction in moderate environmental conditions is investigated for a wind-powered cargo vessel with wing sails. Control system strategies such as sheeting of the wing sails close to stall are studied.

Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was ballasted to half submergence, thereby floating with the waterline at the equator when at rest in calm water. Heave decay tests were conducted, wherein the sphere was held stationary and dropped from three drop heights: a small drop height, which can be considered a linear case, a moderately nonlinear case, and a highly nonlinear case with a drop height from a position where the whole sphere was initially above the water. The precision of the heave decay time series was calculated from random and systematic standard uncertainties. At a 95% confidence level, uncertainties were found to be very low—on average only about 0.3% of the respective drop heights. Physical parameters of the test setup and associated uncertainties were quantified. A test case was formulated that closely represents the physical tests, enabling the reader to do his/her own numerical tests. The paper includes a comparison of the physical test results to the results from several independent numerical models based on linear potential flow, fully nonlinear potential flow, and the Reynolds-averaged Navier–Stokes (RANS) equations. A high correlation between physical and numerical test results is shown. The physical test results are very suitable for numerical model validation and are public as a benchmark dataset. © 2021 by the authors.

Densification around railway stations and near infrastructure can lead to benefits from the climate and resource efficiency point of view. Living near infrastructure nodes can reduce car dependency and enable more sustainable travel. At the same time, noise from rail traffic causes annoyance and negative health effects for residents, and densification can therefore lead to an increase in the number of people exposed to noise, with increased social costs as a result.

The purpose of the project is to facilitate the implementation of noise measures in the infrastructure at railway stations, thereby enabling climate smart and sustainable densification in public transport-related locations, as well as efficient use of resources at the source. The goal is to compile a digital toolbox with methodology and sample collection for demonstration of technical noise-reducing measures in railway infrastructure.

The digital toolbox contains auralization of different track-close noise measures for different train types, which can be used as a complement to traditional noise predictions to create a more realistic experience of the sound environment. The auralizations are based on recordings of train passages in station-close locations, which have been corrected with calculated insertion losses for the various measures.

In addition, the socio-economic costs of noise and the corresponding benefits for a noise measure are calculated using updated valuation models based on WHO's latest recommendations. The results are compared with the current official Swedish valuation model ASEK.

The project uses co-creation to develop the tool where design and content are prioritized at a workshop together with the intended target group. The tool is openly available and an executable version for PC can be downloaded via https://sourceforge.net/projects/ljudmiljo-i-stationssamhallen/. The source code is openly accessible via https://github.com/larssonkrister/Stationsnara/.

Fluid instabilities limit the ability of features to hold their shape in many types of 3D printing as liquid inks solidify into written structures. By 3D printing directly into a continuum of jammed granular microgels, these instabilities are circumvented by eliminating surface tension and body forces. However, this type of 3D printing process is potentially limited by inertial instabilities if performed at high speeds where turbulence may destroy features as they are written. Here, we design and test a high-speed 3D printing experimental system to identify the instabilities that arise when an injection nozzle translates at 1 m/s. We find that the viscosity of the injected material can control the Reynold's instability, and we discover an additional, unanticipated instability near the top surface of the granular microgel medium.

An investigation of fire and explosion hazards of different types of alternativefuel vehicles in tunnels is presented. The different fuels are divided into four types:liquid fuels, liquefied fuels, compressed gases, and electricity, and detailed parameters are obtained. Three types offire hazards for the alternativefuel vehicles: pool fires, jet fires and fireballs are identified andinvestigated in detail. Fromthe perspective of pool fire size, the liquid fuels pose equivalent or evenmuch lower fire hazards compared to the traditionally used fuels, but theliquefied fuels may pose higher hazards. For pressurized tanks, the fires are generally much larger in size butshorter in duration. The gas releases from pressure relief devices and the resulting jet firesare highly transient. Forhydrogen vehicles, the fire sizes are significantly higher compared to CNGtanks, while flame lengths only slighter longer. Investigation of the peakoverpressure in case of an explosion in a tunnel was also carried out. Theresults showed that, for the vehicles investigated, the peak overpressure of tankrupture and BLEVE are mostly in a range of 0.1 to 0.36 bar at 50 m away. Thesituations in case of cloud explosion are mostly much more severe andintolerable. These hazards need to be carefully considered in both vehiclesafety design and tunnel fire safety design. Further researches on thesehazards are in urgent need.

The focus of the present study is analyzing the best position of a sprinkler nozzle in a tunnel cross-section in the Muskö tunnel, south of Stockholm, Sweden. Activation of the sprinklers installed along the centerline and along the sidewall is investigated through analysis of full scale experiments and by three dimensional numerical modelling. Then the tunnel velocity is analyzed by one dimensional numerical modelling for various fire locations in the Muskö tunnel. For both activating the automatic sprinklers nearby the fire and avoiding activation of the sprinklers further downstream, the automatic sprinklers are recommended to be installed along the centerline of the tunnel. It has also been found that the tunnel velocity varies significantly with the fire location. When the fire is on the left side of the tunnel, the flow velocity mostly remains in a range of 1 m/s (positive or negative) within the first 10 minutes, which helps early activation of the automatic sprinklers. When the fire is on the right side of the tunnel, the flow velocity mostly remains within a range of -1 m/s and 1 m/s within the first 5 minutes, and the velocity mostly increases to 2 m/s at around 10 min. Therefore, the scenario for fire located on the left side is better than that for fire on the right side, especially when it is located between the middle of the right section and the right portal. As one typical case with fire on the right side, the tunnel velocity maintains at 1 m/s for the first 5 min and gradually increases to 2 m/s at 10 min. Under such conditions, the automatic sprinkler system is expected to perform well. 

The critical velocity and backlayering length in sloped tunnels are investigated by numerical simulations using FDS. Simulation in two full-scale tunnels, with negative slopes ranging up to -18 % and heat release rates from 5 to 100 MW were carried out.

The results show that NFPA 502 equation significantly overestimates the effect of negative slopes.

The equation proposed by Atkinson and Wu is found to be in closer agreement with the results. A simplified correlation, i.e. Eq. (12), is proposed and recommended for practical use.

The previous correlation for dimensionless backlayering length, Eq. (3), is valid for tunnels of various slopes and aspect ratios, and can be used for prediction of backlayering length.

Over the decades, computational methods have been used to model and describe the flow and ionization dynamics in plasma torches. However, the impact of the operational parameters such as gas flow rate, swirl number and input current density on flow is still inexplicit. In this study, the flow in a non-transferred plasma torch is modelled using COMSOL Multiphysics, and the influence of these parameters is studied. The analysis is carried out on an axisymmetric geometry with the conical-shaped cathode, nozzle-shaped anode, and Argon is used as the plasma gas. A thermal plasma (equilibrium discharges) is considered, i.e., the plasma is under partial to complete local thermodynamic equilibrium in which the magnetohydrodynamic (MHD) equations are solved. This is treated in the Equilibrium Discharge Interface in COMSOL’s plasma module that has been used in the present study. The laminar flow analysis is performed for low-velocity cases and turbulent flow analysis for higher velocities. It was found that the velocity increase across the plasma arc due to ionization and gas expansion, could be observed only for sufficiently high plasma inflow velocities. The position of the plasma arc is determined for different operating conditions. It was further found that the velocity has a negligible effect on the length of the plasma arc, whereas the dependency of the arc length and attachment point on the anode wall, to the input current density and cathode tip temperature is well explained. The paper concludes by presenting the variations in temperature and velocity of plasma arc due to swirling inflow

Motion sickness may be a factor detrimental to the experience of self-driving cars. This study investigates whether auditory displays can support in lowering passengers' feeling of motion sickness by allowing them to anticipate upcoming manoeuvres. Twenty participants took part in the study and rode on a specially designed test track with and without auditory display while performing a reading task. The display provided information about upcoming car manoeuvres, which were identified as being motion sickness inducing and the sounds were designed to resemble the actual sound of the manoeuvres taking place. Sounds representing acceleration, deceleration and left and right turns were played slightly in advance of the upcoming manoeuvre. Participants rated their motion sickness at regular intervals during the ride as well as before and after the ride. The results showed that illness ratings in the auditory display condition were statistically lower significantly compared to the condition without sound. The sounds were also judged as intuitive and helpful by the users who reported willingness to use them when riding autonomous cars in the future, especially while reading or working. These results have implications for the interaction design of self-driving cars and can guide future auditory display research. 

Hydrofoils are a current hot topic in the marine industry both in high performance sailing and in new passenger transport systems in conjunction with electric propulsion. In the sailing community, the largest impact is seen from the America’s cup, where boats are sailed at more than 50 knots (over 100 km/h) with 100% “flying” time. Hydrofoils are also becoming popular in the Olympics, as in the 2024 Olympic games 5 gold medals will be decided on foiling boats/boards. The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be. The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake set-up might be preferred in search for minimum drag. © 2022 by the authors. 

An increased share of construction with timber is one possible way of achieving more sustainable and energy-efficient life cycles of buildings. The main reason is that wood is a renewable material and buildings require a large amount of resources. Timber buildings taller than two storeys were prohibited in Europe until the 1990s due to fire regulations. In 1994, this prohibition was removed in Sweden.

    Some of the early multi-storey timber buildings were associated with more complaints due to impact sound than concrete buildings with the same measured impact sound class rating. Research in later years has shown that the frequency range used for rating has not been sufficiently low in order to include all the sound characteristics that are important for subjective perception of impact sound in light weight timber buildings. The AkuLite project showed that the frequency range has to be extended down to 20 Hz in order to give a good quality of the rating. This low frequency range of interest requires a need for knowledge of the sound field distribution, how to best measure the sound, how to predict the sound transmission levels and how to correlate numerical predictions with measurements.

    Here, the goal is to improve the knowledge and methodology concerning measurements and predictions of low frequency impact sound in light weight timber buildings. Impact sound fields are determined by grid measurements in rooms within timber buildings with different designs of their joist floors. The measurements are used to increase the understanding of impact sound and to benchmark different field measurement methods. By estimating transfer functions, from impact forces to vibrations and then sound pressures in receiving rooms, from vibrational test data, improved possibilities to correlate the experimental results to numerical simulations are achieved. A number of excitation devices are compared experimentally to evaluate different characteristics of the test data achieved. Further, comparisons between a timber based hybrid joist floor and a modern concrete floor are made using FE-models to evaluate how stiffness and surface mass parameters affect the impact sound transfer and the radiation.

    The measurements of sound fields show that light weight timber floors in small rooms tend to have their highest sound levels in the low frequency region, where the modes are well separated, and that the highest levels even can occur below the frequency of the first room mode of the air. In rooms with excitation from the floor above, the highest levels tend to occur at the floor levels and in the floor corners, if the excitation is made in the middle of the room above. Due to nonlinearities, the excitation levels may affect the transfer function in low frequencies which was shown in an experimental study. Surface mass and bending stiffness of floor systems are shown, by simulations, to be important for the amount of sound radiated.

    By applying a transfer function methodology, measuring the excitation forces as well as the responses, improvements of correlation analyses between measurements and simulations can be achieved.

The flow pattern in the grooves plays a major role for the homogeneity of refining as well as for the transfer and loading of fiber flocs in refining position on the bar edges. However, it is an area where very little information is available. In the present study, flow conditions in the grooves in a Low-Consistency (LC) - disc refiner were studied both experimentally and numerically. The experimental study involved high-speed imaging through a 3 cm peephole into a commercial refiner. The Computational Fluid Dynamics (CFD) simulation focused on the flow condition in a radial groove, considering both Newtonian and non-Newtonian flows. Flow conditions for stator and rotor grooves were modeled along the groove at different angular speeds and pressure differences over the refiner. Both the experimental and the modeling results show a dual flow pattern in the grooves; a rotational/spiral movement at the top of the groove and a flow in the direction of the groove at the bottom, which to the authors knowledge has not been reported in literature. The strong vortical motion at the top of the grooves observed both for the rotor and the stator are believed to be important for placing the fibers onto the bar edges and to induce shear forces in such a way that the fibers get treated. Moreover, a large sensitivity to suspension properties in terms of the development of flow pattern was detected.

First, we define in this paper two benchmark flows readily usable by anyone calibrating a numerical tool for concrete flow prediction. Such benchmark flows shall allow anyone to check the validity of their computational tools no matter the numerical methods and parameters they choose. Second, we compare numerical predictions of the concrete sample final shape for these two benchmark flows obtained by various research teams around the world using various numerical techniques. Our results show that all numerical techniques compared here give very similar results suggesting that numerical simulations of concrete filling ability when neglecting any potential components segregation have reached a technology readiness level bringing them closer to industrial practice.

The measurement of fluid dynamic quantities are of great interest both for extending the range of validity of current correlations to be used in equipment design and for verification of fundamental hydrodynamic models. Studies where comparisons are made between imaging techniques serve to provide confidence on the validity of each technique for the study of multiphase flow systems. The advantage of cross-validation is that it can help establish the limitations of each technique and the necessary steps towards improvement. A small amount of comparative studies are found in the literature and none of them reports the study of settling particles suspension flow using simultaneously Ultrasonic Velocity Profiling (UVP), Magnetic Resonance Imaging (MRI) and Electrical Impedance Tomography (EIT), at least not to the best of the authors knowledge. In the present paper the authors report efforts made on the characterization of dilute suspensions of glass particles in turbulent flow, with increasing flow velocities and particles concentrations, in a pilot rig at a laboratorial scale, using both MRI, EIT and UVP: direct comparisons of EIT, MRI and UVP measurements acquired and mixture model numerical simulations are presented and the level of agreement explored.

Simulation tools for thermal management of datacenters help to improve layout of new builds or analyse thermalproblems in existing data centers. The development of LBMon remote GPUs as an approach for such simulations is discussedmaking use of VirtualGL and prioritised multi-threadedimplementations of an existing LBM code. The simulation isconfigured to model an existing and highly monitored test datacenter. Steady-state root mean square averages of measured andsimulated temperatures are compared showing good agreement.The full capability of this simulation approach is demonstratedwhen comparing rack temperatures against a time varyingworkload, which employs time-dependent boundary conditions.

The extremely rapid reflection of a shock wave from the end wall generated in the shock tube, in addition to the high-frequency content of pressure, inevitably also excites mechanical vibrations. These can potentially produce acceleration-induced spurious signals as part of the dynamic output of the pressure measurement system being calibrated. This paper proposes and evaluates a method for correcting the frequency response of a pressure measurement system obtained with a calibration using a shock tube for the acceleration-induced errors due to vibrations. The proposed method is based on the predetermined frequency response of the pressure measurement system to the accelerations and simultaneous measurements of the vibration accelerations of the pressure sensor during its calibration in the shock tube. The acceleration-induced errors were corrected for a piezoelectric pressure measurement system calibrated in a diaphragmless shock tube developed at the National laboratory for pressure and vacuum at RISE Research Institutes of Sweden, where different vibrational conditions were induced by changing the initial driver pressure, while keeping the initial driven pressure constant. The uncertainty of the correction of the frequency response of the piezoelectric pressure measurement system being calibrated was determined by considering the uncertainty contributions of the measured acceleration frequency response of the pressure measurement system, the measured acceleration of the pressure sensor during its calibration in the shock tube, the generated reference end-wall step pressure and the repeatability of the correction. The results show that the proposed method effectively eliminates acceleration-induced errors in the sensitivity and phase frequency responses of an acceleration-sensitive piezoelectric pressure measurement system being calibrated with a shock tube.

The effect of surface tension on global stability of co-flow jets and wakes at a moderate Reynolds number is studied. The linear temporal two-dimensional global modes are computed without approximations. All but one of the flow cases under study are globally stable without surface tension. It is found that surface tension can cause the flow to be globally unstable if the inlet shear (or, equivalently, the inlet velocity ratio) is strong enough. For even stronger surface tension, the flow is restabilized. As long as there is no change of the most unstable mode, increasing surface tension decreases the oscillation frequency. Short waves appear in the high-shear region close to the nozzle, and their wavelength increases with increasing surface tension. The critical shear (the weakest inlet shear at which a global instability is found) gives rise to antisymmetric disturbances for the wakes and symmetric disturbances for the jets. However, at stronger shear, the opposite symmetry can be the most unstable one, in particular for wakes at high surface tension. The results show strong effects of surface tension that should be possible to reproduce experimentally as well as numerically.

The spectral/hp element method combines the geometric flexibility of the classical h-type finite element technique with the desirable numerical properties of spectral methods, employing high-degree piecewise polynomial basis functions on coarse finite element-type meshes. The spatial approximation is based upon orthogonal polynomials, such as Legendre or Chebychev polynomials, modified to accommodate a C0 - continuous expansion. Computationally and theoretically, by increasing the polynomial order p , high-precision solutions and fast convergence can be obtained and, in particular, under certain regularity assumptions an exponential reduction in approximation error between numerical and exact solutions can be achieved. This method has now been applied in many simulation studies of both fundamental and practical engineering flows. This paper briefly describes the formulation of the spectral/hp element method and provides an overview of its application to computational fluid dynamics. In particular, it focuses on the use of the spectral/hp element method in transitional flows and ocean engineering. Finally, some of the major challenges to be overcome in order´to use the spectral/hp element method in more complex science and engineering applications are discussed

The dynamic behavior of ink movement under nip-pressure of a printing press has been studied. The theoretical model employed originates from the Bosanquet model that was previously applied to situations of constant or zero external pressures. In the present work, we extend the model to a printing situation where a time-dependent nip pressure presents. The general solution of the model for a simple liquid has been worked out, as in most situations the ink's continuous phase can be approached as a Newtonian fluid, e.g. mineral oil in offset and water in flexo etc. The general solution is of analytical form thanks to the possibility to expand the nip-pressure profile into a Fourier series. For illustrative purposes, simulations with three model profiles, one rectangular, one sinusoidal, and one joint sinusoidal, have been performed. It is found that the profile of the nip-pressure plays a dominant role in liquid transfer and setting.