Scale Physical Model Research Articles

Seasonal and spatial within-marsh differences of biophysical plant properties: implications for wave attenuation capacity of salt marshes

Salt marshes attenuate waves and thus have an important function for coastal protection. Biophysical properties of salt-marsh plants play a key role in the process of wave attenuation and can be differentiated by morphological properties such as stem density, vegetation height and aboveground biomass as well as by biomechanical properties related to stem flexibility. Numerical or physical scale models predicting wave attenuation over vegetated surfaces need to include biophysical properties. However, few studies have quantified morphological and biomechanical properties of salt-marsh plants and fewer have considered seasonal and within-marsh spatial variability of biomechanical properties. The aim of this study was to quantify biophysical properties of the common salt-marsh grasses Spartina anglica and Elymus athericus, including stem flexibility and density as well as aboveground biomass, temporally and spatially. Samples were collected in spring and in summer 2014 at a study site located in the Northern German Wadden Sea. Aboveground biomass was harvested in plots of 50 × 50 cm, stem density was determined by counting and flexibility of plant stems was determined with three-point bending tests. Biophysical properties of both species varied significantly between seasons with plant stem stiffness being 5.0 (S. anglica) and 2.9 times (E. athericus) higher and aboveground biomass being 2.1 (S. anglica) and 1.3 times (E. athericus) higher in summer than in spring. Small-scale spatial differences for those biophysical plant properties were found for S. anglica with plant stem stiffness being 4.0 (spring) and 2.8 times (summer) higher and aboveground biomass being 1.6 (spring) and 1.5 times (summer) higher in a landward than in a seaward-located zone. Small-scale spatial differences of biophysical properties were not found in E. athericus. We conclude that variability in biophysical properties should be considered in models and experiments especially for S. anglica when predicting and quantifying marsh wave attenuation capacity.

Pressures induced by regular waves on a large scale OWC

The traditional function of coastal structures is the protection of the land from the sea. Such a function has been often carried out by breakwaters which dissipate part of the incident wave energy.Recently, the ongoing climate changes and their related issues have moved the attention toward new kinds of coastal structures which can protect the land and human activities and at the same time harvest part of the available wave energy. Such an energy source is alternative to non renewable ones like oil and gas, it is covered by the incentives of the renewable energy sector and it is subjected to an increasing interest of the international community.In such a framework, the present challenge of the coastal engineering is to design hybrid Wave Energy Coverters (WECs) which are: (i) effective in protecting the land, (ii) efficient in extracting wave energy, (iii) economically competitive with the conventional structures, (iv) structurally reliable.In comparison to other WECs, the Oscillating Water Column (OWC) breakwaters are considered among the most promising, therefore it is needed to investigate their design characteristics appropriately. Indeed, the durability of hybrid OWC breakwaters is strongly related to their response to wave action. In particular, the most critical point is the front lip, which is subjected to external wave impact and internal pressures within the chamber, at the same time.The complexity of wave-OWC interactions is studied here by means of a large scale physical model, which has been tested under regular wave conditions. The Power Take Off (PTO) characteristics are replaced here by a circular orifice, whose section has been varied. Such variations of the orifice section cause different types of response of the air inside the pneumatic chamber to external wave forcing.The response of the device under regular waves has been monitored by means of wave gauges and pressure sensors located both at the OWC and along the flume. First, the time evolution of the air pressure signal is analyzed. This is strongly affected by the air compressibility which is the key parameter in this analysis, since it controls the air-water interaction and it influences the whole OWC dynamics.The spectral analyses of the signals of pressure and free surface elevation provide insights on the relationship between water column oscillations and pressures inside and outside the chamber, in terms of both amplitudes and phase lags. It is found that the relation between inner and outer pressures is shown to be related to the resonance coefficient, which is a function of the lag between the flow across the OWC and the forcing outer pressure.

2D FLOOD INUNDATION SIMULATION BASED ON A LARGE SCALE PHYSICAL MODEL USING COURSE NUMERICAL GRID METHOD

The implementation of various 2D numerical modeling techniques in the flood inundation analysis is vastly explored. However, understanding of the flood inundation uncertainty of this technique still limited. This paper evaluates 2D hydraulic models (HEC-RAS) in term of ability to simulate the surface flow of the large scale physical model. A physical model was developed based on high-resolution DEM (0.5m resolution) data of Sungai Bertam with scale 1/25. A total area of 23 m x 7 m and 20.8 m channel length was constructed. The experimental physical model was run with various inflow value and used to calibrate and analyze the numerical simulation. Although the simulated result showed a good agreement with the physical model experiment, some uncertainty still needs to consider. This uncertainty happens due to the change in channel geometry which leads to the turbulence phenomenon.

Procedure for predicting part load resonance in Francis turbine hydropower units based on swirl number and local cavitation coefficient similitude

• Part load resonance conditions in a Francis turbines prototype are predicted. • Reduced scale model measurements and eigenvalue calculations are required. • High accuracy is achieved using a local cavitation coefficient. • Two methods to transpose pressure wave speed values are evaluated. • Signal processing is used to detect the generating unit eigenfrequencies. Francis turbines operating at part load conditions develop a cavitation precessing vortex known as a vortex rope in the draft tube cone below the runner outlet. At part load conditions, this vortex precession acts as an excitation source inducing pressure pulsations in the whole hydraulic system at the vortex precession frequency. Simultaneously, the lower pressure levels in the vortex core can lead to cavitation development, increasing the local flow compliance and reducing drastically the pressure wave speed. As a result, the eigenfrequencies of the hydraulic circuit are lowered and may match the vortex rope excitation frequency, leading to undesired resonance conditions. This paper presents a procedure to predict this type of resonance phenomenon in turbine prototypes by performing reduced scale physical turbine model measurements and eigenvalue calculations with linearized system matrices. This new procedure requires the transposition of hydroacoustic parameters from the reduced scale physical model to the prototype scale based on the swirl number and the local cavitation coefficient similarity. The procedure is validated by measurements performed on a turbine prototype featuring a peak of power swings and pressure pulsations in the predicted operating conditions.

Computer Aided Design to Produce High-Detail Models through Low Cost Digital Fabrication for the Conservation of Aerospace Heritage

Aerospace heritage requires tools that allow its transfer and conservation beyond photographs and texts. The complexity of these engineering projects can be collected through digital graphic representation. Nevertheless, physical scale models provide additional information of high value when they involve full detailed information, for which the model in engineering was normally one more product of the manufacturing process, which entails a high cost. However, the standardization of digital fabrication allows the manufacture of high-detail models at low cost. For this reason, in this paper a case study of the graphic reengineering and planning stages for digital fabrication of a full-scale high-detail model (HDM) of the spatial instrument of the European Space Agency, named the Solar Orbiter mission Polarimetric and Helioseismic Imager (SO/PHI), is presented. After the analysis of this experience, seven stages of planning and graphic reengineering are proposed through collaborative work for the low cost digital manufacture of HDMs.

CFD modelling of a small–scale fixed multi–chamber OWC device

Wave Energy Converters (WECs) have excellent potential as a source of renewable energy that is yet to be commercially realised. Recent attention has focused on the installation of Oscillating Water Column (OWC) devices as a part of harbor walls to provide advantages of cost–sharing structures and proximity of power generation facilities to existing infrastructure. In this paper, an incompressible three–dimensional CFD model is constructed to simulate a fixed Multi–Chamber OWC (MC–OWC) device. The CFD model is validated; the simulation results are found to be in good agreement with experimental results obtained from a scale physical model tested in a wave tank. The validated CFD model is then used for a benchmark study of 96 numerical tests. These investigate the effects of the PTO damping caused by the power take–off (PTO) system on device performance. The performance is assessed for a range of regular wave heights and periods. The results demonstrate that a PTO system with an intermediate damping can be used for all chambers in the MC–OWC device for most wave period ranges, except for the long wave periods. These require a higher PTO damping. An increased incident wave height reduces the device capture width ratio, but there is a noticeable improvement for long wave periods.

Investigating the Impact of Caving on Longwall Mine Ventilation Using Scaled Physical Modeling.

In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a two-part heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation.

Enhancement of Soft Soil Behaviour by using Floating Bottom Ash Columns

The current disposition worldwide is for sustainable construction, and the application of by-products is one of the ways to achieve it. In this research, bottom ash was used as a substitute material in a granular column to decrease settlement and enhance the bearing capacity of soft soil. Bottom ash is a derivate of the coal burning process, it has similar engineering properties to sand and fine gravel. A set of reduced scale physical modelling tests were performed on floating bottom ash columns to assess the improvement in the bearing capacity of the composite ground. The results clearly showed that the bearing capacity of the model soil was greatly improved with the installation of bottom ash column sand. There was an obvious enhancement of the load capacity of the granular columns when they were encased. The usage of bottom ash instead of aggregate or sand for granular columns will reduce the project cost and it aligns with the goal of sustainable construction development.

Analysis of Temperature Losses of the Liquid Steel in a Ladle Furnace During Desulfurization Stage

In this research, a multiphase numerical simulation (steel–slag–argon) was carried out by coupling the VOF model with the transitory heat losses of the liquid steel during the injection of argon in the secondary refining process. To model the radiation in the free surface of the ladle, three models, P-1, discrete ordinates, and Rosseland, were considered. The thermal behavior of magnesia-carbon (MgO-C) and high alumina (Al2O3), which are commonly used in the industry, as a work wall was compared. Likewise, the behavior of two slag of different chemical composition was analyzed with two layer thicknesses. The results of the fluid dynamics agreed with those obtained in a physical scale model with the PIV technique. In addition, it was found that the Rosseland model allowed to quantify the radiative heat losses with a good approximation according to the results obtained in the industry. It was observed that the more viscous slag with greater thickness reduced the opening of the slag layer. Finally, the heat losses in the liquid steel could be controlled by manipulating the variables of thickness and viscosity of the slag and also the type of refractory of the ladle.

Prediction of hydro-acoustic resonances in hydropower plants by a new approach based on the concept of swirl number

ABSTRACTHydropower plant units operating in off-design conditions are subject to cavitation flow instabilities, potentially inducing hydro-acoustic resonances under certain conditions. They can be predicted by using one-dimensional numerical models of hydropower plants that rely on a proper modelling of the draft tube cavitation flow in off-design conditions. The latter is based on hydro-acoustic parameters that can be identified experimentally on the reduced scale physical model of the prototype on its complete operating range, which however requires an important number of measurements during model testing to consider the influence of both the head and the discharge. This article proposes a new methodology enabling the prediction of resonance conditions excited by a draft tube cavitation vortex on the complete head range of a hydropower plant unit. The methodology relies on the experimental identification at the model scale of the hydro-acoustic parameters and their transposition from the model to the prototype scale. By expressing the precession frequency of the vortex and the hydro-acoustic parameters of the draft tube cavitation flow as a function of the runner outlet flow swirl number, their value can be predicted on the complete part load operating range of the prototype whatever the value of both the head and discharge. The computation of the first natural frequency with a 1D numerical modelling of the hydropower plant enables finally the prediction of resonance conditions, which are compared with those identified by measurements on the full-scale machine.

JETTY DESIGN USING DUAL LIFE-CYCLE AND PHYSICAL MODELING APPROACH – COOS BAY, OR

The advantages of risk-based methodologies over traditional deterministic analyses have been well documented for the design of coastal projects. The consideration of probabilistic forcing allows for the application of a life-cycle approach that can be used to optimize structure design, including the quantification of uncertainty. Damage progression and functional performance can be assessed over the project’s design life and can be considered in the design process. A lifecycle modeling approach was developed and applied, in conjunction with a 1:55 scale physical model, to the design of the North jetty major maintenance repair in Coos Bay, Oregon.

A VORTEX DROP STRUCTURE AS DEAERATION SYSTEM FOR A SUBMARINE OUTFALL PIPELINE

Use of submarine outfall pipelines became more common since World Bank Group issued a new guideline for maximum emissions levels for thermal power plants in 1998 (van Dijk, 2005). The more restrictive levels for temperature increase at the receiving water, requires outfall systems to conduct the water down to greater depths to achieve the required dilution standard. However, air entrainment control into outfall pipes could be challenging, especially for discharges with high flowrates for which conventional deaeration chambers become too large. The problem could turn more difficult in coastal shelf areas at seismic zones, where the hydraulic height of the incoming flow must be effectively controlled and the design not only has to pursue hydraulic objectives but also stability requirements for these massive structures subjected to relevant seismic thrusts. A vortex drop structure was designed for the cooling water discharge system of a thermal power plant in Mejillones Bay, Chile. The structure addresses the elevation difference between the return flow pipe and the ocean outfall pipelines while adhering to the spatial restrictions at the project site. Energy dissipation as well as limitation of air entrainment into the outfall pipelines were critical design considerations. Tests where done on a 1:12.5 scale (Froude) physical model. Prototype structure is under construction. Operation is planned to start on mid-2018.

PHYSICAL MODELLING OF PROPELLER SCOUR ON AN ARMOURED SLOPE

CITIC Pacific Mining (CPM) is proposing to increase throughput at their existing Sino Iron Terminal in Cape Preston, Western Australia, using self-propelled Handysize transshipment shuttle vessels (TSV) instead of dumb barges. Initial assessment using various desktop methods (PIANC, 2015) indicated that the armoured rock slope adjacent to the berth face would incur damage due to wash from the vessel side thrusters and the main propeller. Large scale (13.5:1) physical model tests were undertaken in a 6 m x 15 m x 1.4 m deep basin at UNSW to measure wash velocity and armour stability. The physical modelling demonstrated that the rock slope was more stable than expected, but that some armour was mobilized. Additional tests were also completed to investigate the efficacy of Articulated Concrete Block Mattresses (ACMs) to protect the rock slope from propeller wash.

OBSERVATIONS OF BEACH-DUNE MORPHOGOLICAL RESPONSE TO STORM WAVES USING LIDAR BATHYMETRIC MAPPING IN A WAVE BASIN

Waves during major storms can cause significant changes to coastal morphology (Lee et al., 1998). The beach-dune system is known to be highly vulnerable to erosion when the wave run-up exceeds the threshold of the base of the dune in the collision regime, according to the Storm Impact scale defined by Sallenger (2000). Detailed bathymetric measurements are very difficult to obtain during storms due to the hazardous wave conditions. However, bathymetric surveys can be easily and intermittently performed during smaller scale physical model experiments (e.g., Hamilton et al., 2001) and high resolution can be achieved using laser scanning with Light Detection and Ranging (LIDAR) sensors (Smith et al., 2017). In the present study, a laboratory experiment of beach-dune morphology change is conducted in a rectangular wave basin that has recently been used to simulate erosion of a 2-dimensional sand dune (Berard et al., 2017). The objective of the present study is to investigate the 3-dimensional morphologic response of a sand beach-dune system to storm waves approaching at an oblique angle.

VIOLENT IN-CHAMBER LOADS IN AN OSCILLATING WATER COLUMN CAISSON

In 2009, four of 16 chambers in the Mutriku breakwater-integrated Oscillating Water Column (OWC) were badly damaged by storms, probably due to breaking wave loads, and slam within the chamber. To minimize exposure of future plant to such risks, it is necessary to characterise wave conditions under which such an installation could experience impact loads. This characterisation can be crucial to controling the power-take off resistance to increase the survability of the device during extreme weather. Large scale physical model tests in the Grosse Wellenkanal (GWK) included a video camera installed inside the chamber facing the rear chamber wall. Pressure sensors in the ceiling of the chamber were utilised to quantify the water loads. In-chamber impact pressures of up to 8 ρgH were recorded on the chamber ceiling, associated with the ‘sloshing’ observed. The “sloshing” phenomenon is not uncommon and should be considered in design processes.

The Performance of a Sand Reinforced with Coconut Fibers Through Plate Load Tests on a True Scale Physical Model

The Performance of a Sand Reinforced with Coconut Fibers Through Plate Load Tests on a True Scale Physical Model

A loading model for an OWC caisson based upon large-scale measurements

Wave energy is one of the most promising marine energy resources in terms of the scale of the resource, but there remains little technology convergence and costs remain at near-prohibitive levels. Of many wave energy converter (WEC) concepts that have been developed over the years, the oscillating water column (OWC) stands out for its simplicity and low maintenance cost. Quite some experience of actual OWC operation has been gained to date from small, stand-alone pilot schemes. One way to reduce costs is the integration of an OWC-WEC into a breakwater, enabling some degree of cost-sharing between energy and harbour or coastal defence functions. A major problem encountered during the design of an OWC-WEC scheme remains the uncertainty in the wave loads, with their critical influence upon capital cost. A model to estimate forces acting on an OWC chamber in a caisson breakwater is proposed in this paper. Horizontal forces on the front (curtain) wall and the rear (in-chamber) wall are predicted. In addition, and unlike a conventional caisson breakwater, vertical forces acting on the caisson chamber ceiling will have considerable effect on sliding and overturning characteristics of the breakwater structure. The proposed model enables the prediction of chamber pressures which in turn influence the chamber vertical force. The new model has been compared with results from large scale physical model measurements from tests carried out in the very large wave channel, GWK, in Hannover (Germany). Forces under both regular and irregular wave conditions were measured. The comparisons show that the model fits well with the test results to the factor of 1 ± 0.2 for the regular wave cases and to the factor of 0.8 ± 0.2 for irregular wave cases. This model will enable the structural design of caisson breakwater-integrated OWCs to be approached with uncertainties reduced to those comparable with conventional caisson design.

Simulations and Measurements of Eddy Current Magnetic Signatures

Abstract Eddy current magnetic signature is, together with magnetization of ferromagnetic hull, mechanisms and devices on board, corrosion related and stray field sources one of the main sources of ship’s magnetic signature. Due to roll, pitch and yaw of the ship in external magnetic field, eddy currents are induced in conducting materials on board ship, mainly in conducting hull. Flow of those currents is a source of magnetic field around a ship. Principal eddy current component is related to roll movement as it depends on rate of change of external field which is the highest for roll. Induced currents have both in-phase and quadrature components. Magnitude of the eddy current magnetic field can have significant effect on total magnetic field signature after degaussing for ships such as mine sweepers and mine hunters. Paper presents calculations and simulations as well as measurements of model and physical scale model made of low magnetic steel performed in Maritime Technology Center. Contribution of eddy current magnetic field in total field in low roll frequencies has been estimated.

A Model Free Control Based on Machine Learning for Energy Converters in an Array

This paper introduces a machine learning based control strategy for energy converter arrays designed to work under realistic conditions where the optimal control parameter can not be obtained analytically. The control strategy neither relies on a mathematical model, nor does it need a priori information about the energy medium. Therefore several identical energy converters are arranged so that they are affected simultaneously by the energy medium. Each device uses a different control strategy, of which at least one has to be the machine learning approach presented in this paper. During operation all energy converters record the absorbed power and control output; the machine learning device gets the data from the converter with the highest power absorption and so learns the best performing control strategy for each situation. Consequently, the overall network has a better overall performance than each individual strategy. This concept is evaluated for wave energy converters (WECs) with numerical simulations and experiments with physical scale models in a wave tank. In the first of two numerical simulations, the learnable WEC works in an array with four WECs applying a constant damping factor. In the second simulation, two learnable WECs were learning with each other. It showed that in the first test the WEC was able to absorb as much as the best constant damping WEC, while in the second run it could absorb even slightly more. During the physical model test, the ANN showed its ability to select the better of two possible damping coefficients based on real world input data.

Experimental and Numerical Collaborative Latching Control of Wave Energy Converter Arrays

A challenge while applying latching control on a wave energy converter (WEC) is to find a reliable and robust control strategy working in irregular waves and handling the non-ideal behavior of real WECs. In this paper, a robust and model-free collaborative learning approach for latchable WECs in an array is presented. A machine learning algorithm with a shallow artificial neural network (ANN) is used to find optimal latching times. The applied strategy is compared to a latching time that is linearly correlated with the mean wave period: It is remarkable that the ANN-based WEC achieved a similar power absorption as the WEC applying a linear latching time, by applying only two different latching times. The strategy was tested in a numerical simulation, where for some sea states it absorbed more than twice the power compared to the uncontrolled WEC and over 30% more power than a WEC with constant latching. In wave tank tests with a 1:10 physical scale model the advantage decreased to +3% compared to the best tested constant latching WEC, which is explained by the lower advantage of the latching strategy caused by the non-ideal latching of the physical power take-off model.