Experimental Validation of a Quasi-Explicit Hydrodynamic Model: Fishtailing Instability of a Single-Point Moored Tanker in Rigid-Hawser Configuration

2001 ◽  
Vol 45 (04) ◽  
pp. 302-314
Author(s):  
E. A. Tannuri ◽  
A. N. Simos ◽  
A. J. P. Leite ◽  
J. A. P. Aranha
Keyword(s):  
Hydrodynamic Model ◽  
Close Agreement ◽  
Experimental Validation ◽  
Ad Hoc ◽  
Complex Dynamics ◽  
Single Point ◽  
Ocean Current ◽  
High Current ◽  
Dynamic Problems ◽  
High Current Velocity

The extended hydrodynamic model derived in Simos et al (2001), where the yaw velocity terms have been incorporated to the model proposed by Leite et al (1998) while preserving its quasi-explicit feature, is used here to study some typical dynamic problems of moored ships, specifically the fishtailing shtailing instability that may occur in a single-point mooring (SPM) system. Since the intention was to check the hydrodynamic model, the hawser was assumed rigid to avoid the complex dynamics that may occur when the actual hawser slackens and the obtained results were confronted with experimental ones, obtained at the IPT wave tank. The agreement is very good in the sense that not only the limit-cycle amplitudes are compatible but also the time series are very similar. For the VLCC model in ballasted condition (40%) the fishtailing shtailing instability occurs only for a relatively high current velocity and some Froude effect is then detectable. Using results from the static bifurcation experiment an ad hoc correction is proposed for such effect, showing a relatively close agreement between experiments and the theoretical model. This Froude effect correction is, however, not relevant for an actual SPM system subjected to a usual ocean current.

A Quasi-Explicit Hydrodynamic Model for the Dynamic Analysis of a Moored FPSO Under Current Action

2001 ◽  
Vol 45 (04) ◽  
pp. 289-301 ◽  
Author(s):  
A. N. Simos ◽  
E. A. Tannuri ◽  
C. P. Pesce ◽  
J. A. P. Aranha
Keyword(s):  
Hydrodynamic Model ◽  
Experimental Validation ◽  
Single Point ◽  
Cross Flow ◽  
Dynamic Features ◽  
Moment Coefficient ◽  
Current Action ◽  
Proposed Model ◽  
Friction Curve ◽  
Yaw Moment

In an earlier work Leite et al (1998) developed a heuristic hydrodynamic model, based on the shrtwing theory, for the horizontal current forces on an FPSO system. The proposed model was quasi-explicit in the sense that it depends on the ship's main dimensions and on only three hydrodynamic coefficients, namely, the friction coefficient Cf for head on incidence, the drag coefficient CY for a cross-flow, and the related yaw moment coefficient lCY. As discussed in Leite et al (1998), these coefficients could even be estimated from the ITTC friction curve and from Hoerner's sectional results, which would then turn the hydrodynamic model explicit. The model has been tested against experimental results for the horizontal force coefficients, obtained both at IPT and at the Marin wave tank, and it has also been confronted with bifurcation experiments for a turret configuration realized at IPT. The agreement rendered good results in all cases tested. The heuristic approach has now been extended to incorporate the yaw velocity terms while preserving the quasi-explicit feature of the original model. The main purpose of the work herein is to present such a development together with some experimental validation. Using Froude scaling of different ships in distinct ballast conditions, the horizontal forces and moment in the yaw rotating tests were measured at IPT and at Marin and compared with those predicted by the heuristic model, the observed agreement again being fair enough. In an accompanying paper in this issue, the derived mathematical model is tested against experiments that emulate a single-point mooring of a tanker ship in order to disclose the model's ability to cope with the main dynamic features of the fishtailing instability problem.

scholarly journals Modbus Access Control System Based on SSI over Hyperledger Fabric Blockchain

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5438
Author(s):  
Santiago Figueroa-Lorenzo ◽  
Javier Añorga Benito ◽  
Saioa Arrizabalaga
Keyword(s):  
Control System ◽  
Access Control ◽  
Ad Hoc ◽  
Single Point ◽  
Main Challenge ◽  
Authentication And Authorization ◽  
Access Control System ◽  
Identity Based

Security is the main challenge of the Modbus IIoT protocol. The systems designed to provide security involve solutions that manage identity based on a centralized approach by introducing a single point of failure and with an ad hoc model for an organization, which handicaps the solution scalability. Our manuscript proposes a solution based on self-sovereign identity over hyperledger fabric blockchain, promoting a decentralized identity from which both authentication and authorization are performed on-chain. The implementation of the system promotes not only Modbus security, but also aims to ensure the simplicity, compatibility and interoperability claimed by Modbus.

MACRO-GOM: Long Term Multi-Resolution Ocean Current Reanalysis Dataset for the Gulf of Mexico

2021 ◽  
Author(s):  
Neha Groves ◽  
Ashwanth Srinivasan ◽  
Leonid Ivanov ◽  
Jill Storie ◽  
Drew Gustafson ◽  
...  
Keyword(s):  
High Resolution ◽  
Gulf Of Mexico ◽  
Observational Data ◽  
Hydrodynamic Model ◽  
Life Extension ◽  
Ocean Current ◽  
Reanalysis Dataset ◽  
Time Period ◽  
Offshore Industry

Abstract The Gulf of Mexico's unique circulation characteristics pose a particular threat to marine operations and play a significant role in driving the criteria used for design and life extension analyses of offshore infrastructure. Estimates from existing reanalysis datasets used by operators in GOM show less than ideal correlation with in situ measurements and have a limited resolution that disallows for the capture of ocean features of interest. In this paper, we introduce a new high-resolution long-term reanalysis dataset, Multi-resolution Advanced Current Reanalysis for the Ocean – Gulf of Mexico (MACRO-GOM), based on a state-of the-science hydrodynamic model configured specifically for ocean current forecasting and hindcasting services for the offshore industry that assimilates extensive non-conventional observational data. The underlying hydrodynamic model used is the Woods Hole Group – Tendral Ocean Prediction System (WHG-TOPS). MACRO-GOM is being developed at the native resolution of the TOPS-GOM domain, i.e. 1/32° (~3 km) hourly grid for the 1994-2019 time period (25 years). A 3-level downscaling methodology is used wherein observation based estimates are first dynamically interpolated using a 1/4° model before being downscaled to the 1/16° Inter-American Seas (IAS) domain, which in turn is used to generate time-consistent boundary conditions for the 1/32° reanalysis. A multiscale data assimilation technique is used to constrain the model at synoptic and longer time scales. For this paper, a shorter, 5-year reanalysis run was conducted for the 2015-2019 time period for verification against assimilated and unassimilated observations, WHG's proprietary frontal analyses, and other reanalyses. Both the frontal analyses and Notice to Lesses (NTL) rig mounted ADCP data was withheld from assimilation for comparison. Offshore operations in the GOM can benefit from an improved reanalysis dataset capable of assimilating existing non-conventional observational datasets. Existing hindcast and reanalysis model datasets are limited in their ability to comprehensively and reliably quantify the 3D circulation and kinematic properties of the main features partly because of limited assimilation of observational data. MACRO-GOM incorporates all the advantages of available HYCOM-based reanalyses and further enhances the resolution, accuracy, and reliability by the assimilation of over three decades of WHG's proprietary datasets and frontal analyses for continuous model correction and ground-truthing. The final 25-year high resolution dataset will provide highly reliable design and operational criteria for new and existing infrastructure in GOM.

Microhabitat characteristics and reproductive status of male Euchordodes nigromaculatus (Nematomorpha)

1999 ◽  
Vol 73 (1) ◽  
pp. 91-93 ◽  
Author(s):  
F. Thomas ◽  
A. Schmidt-Rhaesa ◽  
R. Poulin
Keyword(s):  
New Zealand ◽  
Current Velocity ◽  
Physical Characteristics ◽  
Reproductive Status ◽  
Mountain Stream ◽  
High Current ◽  
Free Living ◽  
High Current Velocity

In a sample of 61 free-living, postparasitic male Euchordodes nigromaculatus collected from a mountain stream in New Zealand, we found that only large males are found in areas of high current velocity. Thirty-five of the 61 males still contained gametes; these worms were found in wider, deeper, and slower-flowing parts of the stream relative to worms that had released their gametes. These results suggest that the physical characteristics of the immediate microhabitat of male worms can determine their probability of mating.

Lab-Scale, Closed-Loop Experimental Characterization, Model Refinement, and Validation of a Hydrokinetic Energy-Harvesting Ocean Kite

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Ayaz Siddiqui ◽  
Kartik Naik ◽  
Mitchell Cobb ◽  
Kenneth Granlund ◽  
Chris Vermillion
Keyword(s):  
Closed Loop ◽  
High Efficiency ◽  
Complex Dynamics ◽  
Water Channel ◽  
Full Scale ◽  
Ocean Current ◽  
Model Refinement ◽  
Dynamics And Control ◽  
And Control ◽  
Channel Environment

Abstract This paper presents a study wherein we experimentally characterize the dynamics and control system of a lab-scale ocean kite, and then refine, validate, and extrapolate this model for use in a full-scale system. Ocean kite systems, which harvest tidal and ocean current resources through high-efficiency cross-current motion, enable energy extraction with an order of magnitude less material (and cost) than stationary systems with the same rated power output. However, an ocean kite represents a nascent technology that is characterized by relatively complex dynamics and requires sophisticated control algorithms. In order to characterize the dynamics and control of ocean kite systems rapidly, at a relatively low cost, the authors have developed a lab-scale, closed-loop prototyping environment for characterizing tethered systems, whereby 3D printed systems are tethered and flown in a water channel environment. While this system has been shown to be capable of yielding similar dynamic characteristics to some full-scale systems, there are also fundamental limitations to the geometric scales and flow speeds within the water channel environment, making many other real-world scenarios impossible to replicate from the standpoint of dynamic similarity. To address these scenarios, we show how the lab-scale framework is used to refine and validate a scalable dynamic model of a tethered system, which can then be extrapolated to full-scale operation. In this work, we present an extensive case study of this model refinement, validation, and extrapolation on an ocean kite system intended for operation in the Gulf Stream or similar current environments.

scholarly journals Determining the optimum orientation of a greenhouse on the basis of the total solar radiation availability

2011 ◽  
Vol 15 (1) ◽  
pp. 215-221 ◽  
Author(s):  
Snezana Dragicevic
Keyword(s):  
Solar Radiation ◽  
Close Agreement ◽  
Experimental Validation ◽  
Global Solar Radiation ◽  
Climatic Conditions ◽  
Total Solar Radiation ◽  
Radiation Data ◽  
Solar Greenhouse ◽  
South Wall ◽  
East West

This paper presents an approach to determining the optimum orientation of a greenhouse for year round applications for different climatic conditions. The most commonly used uneven-span single shape of greenhouse in east-west and north-south orientation have been selected for comparison. Total solar radiation input to each wall, included surfaces and roofs, is computed for both solar greenhouse orientation and compared for each month of the year at different latitudes at the northern hemisphere. Experimental validation is carried out for the measured global solar radiation data for horizontal surface and south wall at (44?N and 20?E), Belgrade, Serbia. The predicted and measured values are in close agreement. Results shows that east-west orientation of uneven-span solar greenhouse is the best suited during each months for all analyzed latitudes.

Estimating Building Envelope Thermal Characteristics From Single-Point-in-Time Thermal Images

2016 ◽  
Author(s):  
Salahaldin Alshatshati ◽  
Kevin P. Hallinan ◽  
Robert J. Brecha
Keyword(s):  
Surface Temperature ◽  
Thermal Imaging ◽  
Experimental Validation ◽  
Single Point ◽  
Thermal Characteristics ◽  
Weather Conditions ◽  
Building Envelope ◽  
Thermal Images ◽  
Thermal Capacitance ◽  
R Value

Energy efficiency programs implemented by utilities in the U.S. have rendered savings costing on average $0.03/kWh [1]. This cost is still well below energy generation costs. However, as the lowest cost energy efficiency measures are adopted, the cost effectiveness of further investment declines. Thus, there is a need to develop large-scale and relatively inexpensive energy auditing techniques to more efficiently find opportunities for savings. Currently, on-site building energy audits process are expensive, in the range of US$0.12/sf – $0.53/sf, and there is an insufficient number of professionals to perform the audits. Here we present research that addresses at community-wide scales the characterization of building envelope thermal characteristics via drive-by and fly-over GPS linked thermal imaging. A central question drives this research: Can single point-in-time thermal images be used to infer R-values and thermal capacitances of walls and roofs? Previous efforts to use thermal images to estimate R-values have been limited to stable exterior weather conditions. The approach posed here is based upon the development of a dynamic model of a building envelope component with unknown R-value and thermal capacitance. The weather conditions prior to the thermal image are used as inputs to the model. The model is solved to determine the exterior surface temperature, ultimately predicted the temperature at the thermal measurement time. The model R-value and thermal capacitance are tuned to force the error between the predicted surface temperature and the measured surface temperature from thermal imaging to be near zero. The results show that this methodology is capable of accurately estimating envelope thermal characteristics over a realistic spectrum of envelope R-values and thermal capacitance present in buildings nationally. With an assumed thermal image accuracy, thermal characteristics are predicted with a maximum error of respectively 20% and 14% for high and low R-values when the standard deviation of outside temperature over the previous 48 hours is as much as 5°C. Experimental validation on a test facility with variable surface materials was attempted under variable weather conditions, e.g., where the outdoor air temperature experiences varying fluctuations prior to imaging. The experimental validation realized errors less than 20% in predicting the R-value even when the standard deviation of outdoor temperature over the 48 hours prior to a measurement was approximately 5°C.

scholarly journals Decentralizing Private Blockchain-IoT Network with OLSR

2021 ◽  
Vol 13 (7) ◽  
pp. 168
Author(s):  
Xuan Chen ◽  
Shujuan Tian ◽  
Kien Nguyen ◽  
Hiroo Sekiya
Keyword(s):  
Ad Hoc ◽  
Single Point ◽  
Environmental Data ◽  
Base Stations ◽  
Raspberry Pi ◽  
Access Points ◽  
Link State ◽  
Underlying Network ◽  
Transmission Quality ◽  
Iot Devices

With data transparency and immutability, the blockchain can provide trustless and decentralized services for Internet of Things (IoT) applications. However, most blockchain-IoT networks, especially those with a private blockchain, are built on top of an infrastructure-based wireless network (i.e., using Wi-Fi access points or cellular base stations). Hence, they are still under the risk of Single-Point-of-Failure (SPoF) on the network layer, hindering the decentralization merit, for example, when the access points or base stations get failures. This paper presents an Optimized Link State Routing (OLSR) protocol-based solution for that issue in a private blockchain-IoT application. By decentralizing the underlying network with OLSR, the private blockchain network can avoid SPoF and automatically recover after a failure. Single blockchain connections can be extended to multiple ad hoc hops. Services over blockchain become flexible to fit various IoT scenarios. We show the effectiveness of our solution by constructing a private Ethereum blockchain network running on IoT devices (i.e., Raspberry Pi model 4) with environmental data sensing (i.e., Particular Matter (PM)). The IoT devices use OLSR to form an ad hoc network. The environment data are collected and propagated in transactions to a pre-loaded smart contract periodically. We then evaluate the IoT blockchain network’s recovery time when facing a link error. The evaluation results show that OLSR can automatically recover after the failure. We also evaluate the transaction-oriented latency and block-oriented latency, which indicates the blocks have a high transmission quality, while transactions are transferred individually.

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