Physical Modeling Approach Research Articles

Laboratory physical modelling of block toppling instability by means of tilt tests

In this paper we present a physical modelling approach where the stability of rock blocks against toppling in the field can be estimated using a tilt table, engineered rock models and 3-D-printed small-scale versions of a natural rock boulder. To achieve this goal, first, simple geometry rock elements are tilted and results interpreted according to analytical formulations. Then, more complex geometry engineered rock blocks, including some whose centers of gravity do not project on the center of the base element, are tested and results properly interpreted. Eventually, the 3-D-printed version of the rock boulder is produced from 3-D point clouds recovered in the field by means of a combination of photogrammetry and laser scanner techniques. Analytical formulations and numerical calculations have been used in order to validate the proposed approach, to explain the physical phenomena involved, and to allow for possible extension of the physical modelling results to different scenarios, such as those considering the influence of water or seismic loading on stability.

A new method in determination of electrical parameters and geometrical structure of a power transformer applicable to failure diagnosis

In transmission and distribution networks throughout the world and in Vietnam nowadays, power transformers that are operating in the networks often are in black-box condition, i.e. there is no internal information available in terms of geometrical structure and material parameters. Geometrical structure of power transformers includes mainly winding structure and additional parts such as a static end ring or a would-in shield coil, if any whereas main materials in power transformers consists of conductive, insulating and magnetic materials… This makes difficulties in faults diagnosis that is based on the approach of physical modeling in general and the so-called electrical equivalentcircuit based modeling in particular since the physical approach requires internal information of power transformers for calculating electrical parameters. In case the electrical equivalent-circuit approach is used, the diagnosis is then conducted based on the change of values of electrical parameters in the circuit before and after an alarm or a suspicious fault that happens when power transformers are in operation. Relevant international investigations conducted recently have mainly focused on test objects as power transformers in grey- or white-box condition, i.e. during manufacturing phase, since they have available geometrical structure and material properties. To show a possibility that blackbox power transformers could be investigated in a physical manner, this article introduces a new method in determining electrical parameters and geometrical structure applied on a black-box power transformer. The research is based on the Frequency Response Analysis technique and has developed recent relevant investigations of the authors. This enables investigations of the value change of electrical equivalent parameters of this transformer on its simulated frequency responses for the purpose of physical fault diagnosis of power transformers later on.

Ship-course modeling and control using the SIMSCAPE physical modeling environment

Simulation is an important tool for evaluating the design of a ship-course control system. The object-oriented modeling supports the physical modeling of a multi-domain dynamical system by using a hierarchical acausal structure, as compared to block diagrams or differential equation-based causal structures. In this paper we describe the use of the SIMSCAPE simulation environment for the physical modeling-based design of the course control system of a ship. The complete model has been implemented by using this physical modeling approach whereby dynamic system equations are transformed into a diagram of interconnected physical blocks so as to represent in this way the true structure of the modeled system. The performance of the course control of the ship model was analyzed by simulation in light of the existing hypothesis and indirect validation tests previously performed with operational data. The results obtained by using sequences of course-changing maneuvers with varying disturbances serve to demonstrate the usefulness of the physical modeling-based approach with high accuracy and small computational cost as compared to the classical differential equation-based or the adimensional block-oriented diagrams. This methodology can be easily extended to other engineering fields provided that a suitable set of SIMSCAPE physical libraries can be used (electrical, mechanical, hydraulics, thermal,…). In fact, the ship-course control system model here developed represents an interesting benchmark in the field of engineering systems to get insight on the physical modeling approach under SIMSCAPE or even under MODELICA, despite its specificity to marine systems.

Physical Modeling of a Sliding Clamp Mechanism for the Spreading of ParB at Short Genomic Distance from Bacterial Centromere Sites.

SummaryBacterial ParB partitioning proteins involved in chromosomes and low-copy-number plasmid segregation are cytosine triphosphate (CTP)-dependent molecular switches. CTP-binding converts ParB dimers to DNA clamps, allowing unidimensional diffusion along the DNA. This sliding property has been proposed to explain the ParB spreading over large distances from parS centromere sites where ParB is specifically loaded. We modeled such a “clamping and sliding” mechanism as a typical reaction-diffusion system, compared it to the F plasmid ParB DNA binding pattern, and found that it can account neither for the long range of ParB binding to DNA nor for the rapid assembly kinetics observed in vivo after parS duplication. Also, it predicts a strong effect on the F plasmid ParB binding pattern from the presence of a roadblock that is not observed in ChIP-sequencing (ChIP-seq). We conclude that although “clamping and sliding” can occur at short distances from parS, another mechanism must apply for ParB recruitment at larger genomic distances.

Physical Table Identification for Nominal Hydraulic Cylinders and its Application to Pressure Estimation

The paper provides the first completed version of our identification approach as an intersection of two existing approaches: the physical model approach and the data table approach, for a set of valve flow blocks in nominal hydraulic cylinder dynamics. As one of the well-known physical models, the standard Bernoulli equation needs more accuracy in some cases owing to the steady flow assumption, whereas many data tables often need an expensive flow measurement. The proposed identification approach gives a new matrix representation that resembles the table representation but does not need any flow measurement as well as the steady flow assumption. In particular, unlike the conventional valve flow blocks, the updated valve flow blocks have no empty components via the projection guaranteeing the optimization. The effectiveness is confirmed experimentally by an application to the pressure estimation. The proposed identification approach will be applicable to other blocks including nonlinear friction blocks.

Characterization of Structural Properties in High Reynolds Hydraulic Jump Based on CFD and Physical Modeling Approaches

AbstractA classical hydraulic jump with Froude number (Fr1=6) and Reynolds number (Re1=210,000) was characterized using the computational fluid dynamics (CFD) codes OpenFOAM and FLOW-3D, whose perf...

Long-Lead-Time Prediction of Storm Surge Using Artificial Neural Networks and Effective Typhoon Parameters: Revisit and Deeper Insight

Storm surge induced by severe typhoons has caused many catastrophic tragedies to coastal communities over past decades. Accurate and efficient prediction/assessment of storm surge is still an important task in order to achieve coastal disaster mitigation especially under the influence of climate change. This study revisits storm surge predictions using artificial neural networks (ANN) and effective typhoon parameters. Recent progress of storm surge modeling and some remaining unresolved issues are reviewed. In this paper, we chose the northeastern region of Taiwan as the study area, where the largest storm surge record (over 1.8 m) has been observed. To develop the ANN-based storm surge model for various lead-times (from 1 to 12 h), typhoon parameters are carefully examined and selected by analogy with the physical modeling approach. A knowledge extraction method (KEM) with backward tracking and forward exploration procedures is also proposed to analyze the roles of hidden neurons and typhoon parameters in storm surge prediction, as well as to reveal the abundant, useful information covered in the fully-trained artificial brain. Finally, the capability of ANN model for long-lead-time predictions and influences in controlling parameters are investigated. Overall, excellent agreement with observations (i.e., the coefficient of efficiency CE > 0.95 for training and CE > 0.90 for validation) is achieved in one-hour-ahead prediction. When the typhoon affects coastal waters, contributions of wind speed, central pressure deficit, and relative angle are clarified via influential hidden neurons. A general pattern of maximum storm surge under various scenarios is also obtained. Moreover, satisfactory accuracy is successfully extended to a much longer lead time (i.e., CE > 0.85 for training and CE > 0.75 for validation in 12-h-ahead prediction). Possible reasons for further accuracy improvement compared to earlier works are addressed.

Solar irradiation on the rear surface of bifacial solar modules: a modeling approach

The transition in the energy sector has started with the growing population leading to the growing energy demands. The use of photovoltaic (PV) technologies has become a crucial way to meet energy demand. There are many ongoing studies for increasing the efficiency of commercial PV modules. One way to increase the energy yield of the PV modules is to use bifacial solar panels by capturing the rear side illumination as well. One of the challenges for estimating the bifacial module performances is to calculate the solar irradiation impinging on the rear side. Many models presented up to now require high computational power, and they are challenging to implement real-life conditions. In this paper, a simple physical modeling approach is presented to calculate the rear side solar irradiation incident on the bifacial modules. For the rear side irradiance estimation, the maximum difference between the measured and calculated rear side irradiance value is approximately 10 W/m2. The model does not require high computational skills since it is neither focused on the view factor nor ray tracing methodologies but instead uses solar geometry. The yield of the module is also modeled, calculated, and compared with the measurements.

Techniques and Applications in Water Science and Engineering

This Special Issue of Water on “Techniques and Applications in Water Science and Engineering” publishes selected high-quality research papers presented at the Inaugural International Symposium on Water Modelling (iSymWater2019). The symposium was hosted by Beijing Normal University and Manchester Metropolitan University, and took place during 8–10 July 2019 in Beijing, China. A wide range of research topics were considered, including hydraulic modelling, hydro-environment modelling, hydro-ecology modelling, water management simulation, physical experiments, and software. The Issue reports eight papers by researchers from many institutions around the world, and focuses on solving sustainable water challenges through theoretical and physical modelling approaches.

Large-scale testing of a hydraulic non-linear mooring system for floating offshore wind turbines

The mooring system has been recognised as a key area of expense that needs to be addressed to improve the cost competitiveness of floating offshore wind turbines. The devices installed to date have generally adopted designs from the oil and gas industry using heavy mooring materials, providing the required safety margins but with a significant degree of conservatism. Recent interest in the usage of lighter and more compliant mooring materials has shown that they have the potential to reduce peak line loads, which would in-turn reduce costs. However, the lack of operational experience with such materials has limited their adoption in a risk averse industry. This paper reports on the large-scale physical testing of a hydraulic-based mooring component with non-linear stiffness characteristics. The performance of the device is characterised in a laboratory both statically and dynamically, as well as in conditions representative of operating in a sea state using a combined physical and numerical modelling approach. The results show that the dynamic stiffness of the component is a function of load history and hydraulic pre-charge pressure, while the inclusion of the device as part of the OC4 semi-submersible floating wind platform can reduce the peak mooring line loads by up to 9%. Beyond the physical test results, the calculations suggest that the peak load reduction in the modelled scenarios could be as much as 40% if the device can be scaled further. The paper supports the adoption of innovative mooring systems through dedicated component and performance testing.

Surface anthropogenic heat islands in six megacities: An assessment based on a triple-source surface energy balance model

Anthropogenic heat flux (AHF) is a main contributor to the formation of surface urban heat islands (SUHI). Megacities in particular are facing severe problems due to excessive population growth, urban area expansion, human activity, increased energy consumption, and increased anthropogenic heat. In this study, a physical modeling approach based on a triple-source surface energy balance (triple-SEB) model was developed to uncover the effect of AHF on land surface temperature (LST) and surface anthropogenic heat island (SAHI) intensity. For this purpose, satellite imagery along with climatic and meteorological data from 1985 to 2019 were studied for six selected megacities: Los Angeles, Atlanta, Athens, Istanbul, Tehran, and Beijing. First, LST and the fraction of different surface covers were calculated by using a single-channel algorithm and a normalized spectral mixture analysis model, respectively. In the second step, impervious surface cover (ISC) and the urban main boundary area (UMBA) of each city were extracted based on the biophysical composite index and city clustering algorithm, respectively. In the third step, anthropogenic LST (ALST) was modeled using a triple-SEB model. In the fourth step, the ALST and UMBA were used together to model SAHI intensity at different dates. Finally, the relationship between the estimated ALST and ISC, as well as between SAHI and ISC, was examined. Results show that the average value of estimated ALST for the megacities increased from 2.02, 0.55, 0.61, 0.64, 0.58, and 0.72 to 2.99, 1.73, 1.66, 1.19, 2.32, and 2.76 °C, respectively. The coefficient of determination between the mean value of ISC and the estimated ALST for all megacities yielded 0.8, which was higher than that between ISC and satellite-derived LST. Moreover, the SAHI intensity for these megacities was found to have increased to 0.73, 0.92, 0.95, 0.98, 0.95 and 1.32 °C, respectively, which can be predicted by ISC with a coefficient of determination of 0.78, 0.79, 0.79, 0.73, 0.71 and 0.52, respectively. This suggests that the triple-SEB model proposed by this study allowed for independent modeling of AHF's influence on SUHI and a better determination of the effect of ISC on LST and SUHI intensity. This approach facilitated comparative analysis of LST and SAHI for a city at different times as well as SAHIs in different cities with different geographic and climate settings.

Assessment of disturbance impact of hydraulic jacked-in pile penetration in artificial clayey soil

The jacked-in pile method provides a substitute procedure that permits the installation of pre-formed piles with negligible vibration in a noiseless manner, thereby reducing noise impacts in marine and urban environments. This research was carried out by using a small-scale physical modelling approach to examine the movement of soil during pile installation. The model soil was formulated from a mix of amorphous silica and mineral oils; the resulting mixture was subjected to consolidation in a transparent chamber. The model pile was driven vertically down the mid-point of the soil model at different vertical speeds using a strain control device. The array of soil displacement dispersal was obtained by utilising the close-range photogrammetry and particle image velocimetry techniques. The deformation of soil during pile installation was found to decrease with progressive increase of the penetration rate. This result can be employed in the assessment of the disturbance effects of pile installation on underground services and archaeological relics beneath the ground in both urban and marine environments.

A physical model approach to nonlinear vertical accelerations and mooring loads of an offshore aquaculture cage induced by wave-structure interactions

A grand aim of aquaculturists is to investigate the interactions between the oceanic environment and aquaculture structures, in order to make the structures more durable to loads caused by waves and current. To that end, we investigate the effects of extreme wave conditions by leveraging a physical model approach. We assume that the floating collar of the cage moves with the wave in heave, leading to extreme conditions. Thus, the wavelength is much larger than the size of the floating collar model and the wave frequency is much lower than the natural period of heave. For the floating collar model without netting, under wave-only conditions, the first- and second-harmonic components of the vertical acceleration are proportional to the wave amplitude ζa, and square of the wave amplitude ζa2, respectively. The third- and fourth-harmonic components exhibit oscillations at non-dimensional wave number νa≈0.055 due to the change of free surface. For the floating cage model under combined waves and current conditions, the first-harmonic component is more likely proportional to ζa, while the second-harmonic component shows erratic behavior. The effects of mooring loads in front and aft mooring lines are also assessed.

Analysis of the Flow in a Typified USBR II Stilling Basin through a Numerical and Physical Modeling Approach

Adaptation of stilling basins to higher discharges than those considered for their design implies deep knowledge of the flow developed in these structures. To this end, the hydraulic jump occurring in a typified United States Bureau of Reclamation Type II (USBR II) stilling basin was analyzed using a numerical and experimental modeling approach. A reduced-scale physical model to conduct an experimental campaign was built and a numerical computational fluid dynamics (CFD) model was prepared to carry out the corresponding simulations. Both models were able to successfully reproduce the case study in terms of hydraulic jump shape, velocity profiles, and pressure distributions. The analysis revealed not only similarities to the flow in classical hydraulic jumps but also the influence of the energy dissipation devices existing in the stilling basin, all in good agreement with bibliographical information, despite some slight differences. Furthermore, the void fraction distribution was analyzed, showing satisfactory performance of the physical model, although the numerical approach presented some limitations to adequately represent the flow aeration mechanisms, which are discussed herein. Overall, the presented modeling approach can be considered as a useful tool to address the analysis of free surface flows occurring in stilling basins.

Development and validation of an energy simulation for a desktop additive manufacturing system

The assessment and minimization of energy consumptions of additive manufacturing (AM) processes are currently emerging research tasks. It is evident that the energy consumption of an AM process can be one or two orders of magnitude higher than conventional manufacturing processes. For improving the sustainability performance of AM, the energy use of AM should be evaluated and optimized in the design phase for planning products and AM processes. In order to support the quantification and evaluation of the energy consumption of AM, we have developed an energy simulation of a desktop AM system by using a physical modeling approach. Moreover, experiments have been carried out to validate and confirm the simulation accuracy and reliability. The result of the experimental validation has shown that the accuracy of the developed simulation approach can be up to approximately 98 %.

A combined physical and DEM modelling approach to improve performance of rotary dryers by modifying flights design

To characterize the drying process in the Gol-E-Gohar pelletizing plant ball mill the material veiling profile (material showering) was studied by physical modeling and DEM. To simulate the trajectory of particles in the dryer in a reasonable period of time the GPU parallel processing was implemented in the DEM codes. After calibration of DEM parameters by using the model dryer, various flight designs were then employed in the simulation to find an appropriate veiling profile. It was found that by decreasing the release angle of flights from 70° to less than 40° the coverage of hot gas tunnel cross section by particles increases from 41.6% to 89.6%. The simulations also indicated that by changing the flight edge from the raised edge to the rectangular tooth-like type, the coverage of hot gas tunnel cross section could reach 97.1% and more uniform veiling profile could be obtained. Evaluation of the grinding performance over a period of 15 months showed an increase of 17 t/h in the throughput in the case of the new flights in mill No. 1 while for the same period, mill No.2 experienced a decrease of 7 t/h in the throughput with the original flights for the same feed.

Data-driven modeling for river flood forecasting based on a piecewise linear ARX system identification

Most of the studies related to the rainfall-runoff modeling of rivers consist of data-driven models, given that the corresponding physical modeling approaches are based on a thorough geological knowledge of the river in addition to a time consuming simulation. Indeed, flood forecasting services have the difficult task of avoiding natural and human disasters and choose for that to use input-output or grey box models for their simplicity and easy calibration updates. However, these models are not evolving according to the variations of environmental conditions or need at least the evapotranspiration and the soil humidity measurements in addition to the rainfall quantity. This paper gives an alternative approach to the existing rainfall/runoff linear and nonlinear models by the utilization of a hybrid system consisting in a Piecewise Auto-Regressive eXogeneous (PWARX) structure identified using an approach that alternates between data assignment and parameter estimation. The usage of this special kind of nonlinear systems bears a potential to handle the nonlinearities and varying-time delays mainly induced by the soil water storage and evapotranspiration.

Spatial connectivity pattern of expanding gilthead seabream populations and its interactions with aquaculture sites: a combined population genetic and physical modelling approach

In gilthead seabream the number of domesticated individuals increased annually, and escape events occur regularly in the Adriatic Sea. Still there is a lack of population genetic characteristics and evidence of the extent and geographic scale of interbreeding resulting from fish-farm escapees. We screened 1586 individuals using a panel of 21 neutral microsatellite loci in several consecutive years and here report on the medium-scale detection of hybrid and farmed seabream in the natural environment. Wild adults showed a lack of genetic structure within basin and sampling years and reduced connectivity with wild offspring collection, suggesting their temporal residency within the Adriatic. On the contrary, by linking the results of multiannual genetic analyses with the results of coupled hydrodynamic and individual based models (IBM-Ichthyop), we observed a strong connection of wild seabream associated with tuna-aquaculture sites and offspring from the nursery grounds, indicating that the surroundings of tuna sea-cage farms can function as a spawning grounds. The study results present the genetic baseline of wild and farmed strains from the eastern Adriatic Sea, as a first step toward development of a mitigation strategy for fish escapees aimed at controlling further erosion of genetic integrity.

From Microstructure to Performance: A Detailed Multi-Level Study of SOFC Anodes

In anode-supported Solid Oxide Fuel Cells the fuel electrode is usually realized by a supporting substrate and an anode functional layer, both based on nickel/zirconia-cermets with different specific microstructural properties. These two layers have to be designed to fulfill the requirements with respect to electronic and ionic conductivity, diffusive gas transport and hydrogen electrooxidation. In this study a physical meaningful modelling approach describing the coupling of the abovementioned processes in a transmission line model is applied to investigate the impact of material and microstructural properties. Selected material and microstructural parameters were varied to elucidate their impact on the area specific resistance of the anode. Performance simulations were carried out over wide temperature and gas composition ranges. The investigations revealed that an increased ionic conductivity of the zirconia matrix enhances penetration depth and performance. The decrease in particle and pore sizes results in a decreased charge transfer resistance but an increased Knudsen diffusion.

A consistent approach for fluid‐structure‐contact interaction based on a porous flow model for rough surface contact

SummarySimulation approaches for fluid‐structure‐contact interaction, especially if requested to be consistent even down to the real contact scenarios, belong to the most challenging and still unsolved problems in computational mechanics. The main challenges are 2‐fold—one is to have a correct physical model for this scenario, and the other is to have a numerical method that is capable of working and being consistent down to a zero gap. Moreover, when analyzing such challenging setups of fluid‐structure interaction, which include contact of submersed solid components, it gets obvious that the influence of surface roughness effects is essential for a physical consistent modeling of such configurations. To capture this system behavior, we present a continuum mechanical model that is able to include the effects of the surface microstructure in a fluid‐structure‐contact interaction framework. An averaged representation for the mixture of fluid and solid on the rough surfaces, which is of major interest for the macroscopic response of such a system, is introduced therein. The inherent coupling of the macroscopic fluid flow and the flow inside the rough surfaces, the stress exchange of all contacting solid bodies involved, and the interaction between fluid and solid are included in the construction of the model. Although the physical model is not restricted to finite element–based methods, a numerical approach with its core based on the cut finite element method, enabling topological changes of the fluid domain to solve the presented model numerically, is introduced. Such a cut finite element method–based approach is able to deal with the numerical challenges mentioned above. Different test cases give a perspective toward the potential capabilities of the presented physical model and numerical approach.