Dynamic Compression of Rigid and Flexible Risers: Part I — Experimental Results

2003 ◽  
Author(s):  
Andre´ L. C. Fujarra ◽  
Alexandre N. Simos ◽  
Newton Y. Yamamoto
Keyword(s):  
Dynamic Compression ◽  
Critical Issue ◽  
Companion Paper ◽  
Experimental Results ◽  
Small Scale ◽  
Steel Catenary Riser ◽  
Scale Models ◽  
Floating System ◽  
The Subject ◽  
Flexible Risers

Dynamic compression is a critical issue for the viability of submerged lines used in offshore applications, especially for deepwater operations. The subject has been addressed both numerically and analytically. However, few experimental data exist in literature for validation purposes. The aim of this first paper is to present experimental results on the dynamic compression of rigid and flexible risers, obtained in towing-tank tests. Two small-scale models have been built, one emulating the dynamic behavior of a steel catenary riser (SCR) and the other corresponding to a much more flexible case. Uniform circular motion has been applied to the top of the line, representing the floating system oscillation. Four different amplitudes have been considered, each one of them with five different frequencies. The influence of current velocity has also been evaluated. Tension has been measured at the top. In this work the small-scale models and experimental setup are described and some comprehensive results are presented and discussed. In a companion paper, comparisons between theoretical (numerical and analytical) and experimental results are presented.

Dynamic Compression of Rigid and Flexible Risers: Experimental and Numerical Results

2005 ◽  
Vol 128 (3) ◽  
pp. 233-240 ◽  
Author(s):  
Alexandre N. Simos ◽  
André L. C. Fujarra
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Dynamic Compression ◽  
Flexible Structures ◽  
Experimental Results ◽  
Small Scale ◽  
Element Analysis ◽  
Steel Catenary Riser ◽  
Compression Load ◽  
Flexible Risers

Dynamic compression and buckling are critical issues in the viability analysis of rigid and flexible risers developed for offshore applications, especially concerning deep-water operations. Those subjects have been addressed both numerically and analytically. However, few experimental data for validation purposes is found in literature. This paper presents a set of experimental results on the dynamic compression of rigid and flexible risers in catenary configurations, obtained by means of towing-tank tests. Two small-scale models have been built, the first one emulating the dynamic behavior of a steel catenary riser (SCR) and the other representing a much more flexible line. Uniform circular motion has been applied to the top of the models, emulating the floating system first-order oscillations. Different amplitudes of top motion have been considered, each one of them imposed with different frequencies of oscillation. Tension has been measured at the top of the models. The influence of current velocity has also been evaluated. Dynamic tension estimations obtained through finite element analysis are compared to the experimental results. Tension amplitude and critical compression load values are evaluated and compared for both, the steel catenary (SCR) and the flexible models. Comparisons show, in general, a fair agreement between simulations and experiments, reassuring the reliability of numerical models. Results also demonstrate that finite element code provides good predictions of maximum tension loads even when the risers are subjected to high levels of dynamic compression and buckle. Nevertheless, it is clearly noted that difficulties arise in the treatment of flexible structures under severe buckling and torsion. The accuracy of analytical methods proposed for the estimation of critical compression loads is also discussed, based on the experimental results.

Dynamic Compression of Rigid and Flexible Risers: Part II — Comparison of Theoretical and Experimental Results

2003 ◽  
Author(s):  
Alexandre N. Simos ◽  
Andre´ L. C. Fujarra ◽  
Karime H. Alves
Keyword(s):  
Numerical Models ◽  
Dynamic Compression ◽  
Experimental Results ◽  
Dynamic Tension ◽  
Element Analysis ◽  
Analytical Formulation ◽  
Compression Load ◽  
Flexible Risers ◽  
Flexible Models ◽  
Theory And Experiments

In a previous paper, experimental results on the dynamic compression of rigid (steel catenary) and flexible risers were presented. Tests considered different combinations of amplitude and frequencies of top motion and distinct current velocities. In this paper, dynamic tension estimations obtained through finite element analysis and analytical formulation are compared to the experimental results. Tension amplitude and critical compression load values are evaluated and compared both for the steel catenary (SCR) and flexible models. Comparisons have shown, in general, a fair agreement between theory and experiments, reassuring the reliability of numerical models. The results also demonstrate that the analytical formulation applied provides reasonable predictions of maximum tension loads and is able to cope well with the variation of critical load with the frequency of motion.

Experimental Study of the Coupled Hydrodynamics of a DP Barge Operating Close to a FPSO

2012 ◽  
Author(s):  
Daniel P. Vieira ◽  
Eduardo A. Tannuri ◽  
João Luis B. Silva ◽  
Marcos D. Ferreira
Keyword(s):  
Experimental Study ◽  
Experimental Tests ◽  
Companion Paper ◽  
Small Scale ◽  
Dynamic Positioning ◽  
Mooring System ◽  
Hydrodynamic Coupling ◽  
Wave Basin ◽  
Scale Models ◽  
Industry Experience

The coupled hydrodynamic of a DP Barge operating close to a FPSO is evaluated. Experimental tests in a wave basin were performed to obtain the system dynamic behavior for several relative positions and environmental incidences. Two small scale models with factor 1:48 were tested in three different relative positions, five incidence angles and two irregular seas. The industry experience in operating barges was used to provide the insight to select these configurations. The DP Barge model was equipped with a dynamic positioning (DP) system, in order to keep its position relative to the FPSO. The FPSO model uses a scaled spread mooring system. Motions for DP Barge only were also obtained. Discussions are centered in reduction or amplification of DP Barge motions due the FPSO presence. Results are presented in terms of motions significant amplitude and RAO curves. A numerical model was evaluated and its results compared with the experiments. Some considerations, problems and conclusions about the operation were also obtained. These discussions complement the study presented by Vieira et al. (2011), which explored this operation numerically. A companion paper (Tannuri et al., 2012) will discuss the effects of the hydrodynamic coupling on the DP performance of the barge.

scholarly journals Cognitive map formation through haptic and visual exploration of tactile city-like maps

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Loes Ottink ◽  
Marit Hoogendonk ◽  
Christian F. Doeller ◽  
Thea M. Van der Geest ◽  
Richard J. A. Van Wezel
Keyword(s):  
Visual Information ◽  
Spatial Information ◽  
Cognitive Map ◽  
Visual Exploration ◽  
Distinct Advantage ◽  
Small Scale ◽  
Map Learning ◽  
Scale Models ◽  
Spatial Tasks ◽  
Tactile Maps

AbstractIn this study, we compared cognitive map formation of small-scale models of city-like environments presented in visual or tactile/haptic modalities. Previous research often addresses only a limited amount of cognitive map aspects. We wanted to combine several of these aspects to elucidate a more complete view. Therefore, we assessed different types of spatial information, and consider egocentric as well as allocentric perspectives. Furthermore, we compared haptic map learning with visual map learning. In total 18 sighted participants (9 in a haptic condition, 9 visuo-haptic) learned three tactile maps of city-like environments. The maps differed in complexity, and had five marked locations associated with unique items. Participants estimated distances between item pairs, rebuilt the map, recalled locations, and navigated two routes, after learning each map. All participants overall performed well on the spatial tasks. Interestingly, only on the complex maps, participants performed worse in the haptic condition than the visuo-haptic, suggesting no distinct advantage of vision on the simple map. These results support ideas of modality-independent representations of space. Although it is less clear on the more complex maps, our findings indicate that participants using only haptic or a combination of haptic and visual information both form a quite accurate cognitive map of a simple tactile city-like map.

Wave Energy Hyperbaric Device for Electricity Production

2007 ◽  
Author(s):  
Segen F. Estefen ◽  
Paulo Roberto da Costa ◽  
Eliab Ricarte ◽  
Marcelo M. Pinheiro
Keyword(s):  
Power Generation ◽  
Wave Energy ◽  
Experimental Results ◽  
Electricity Production ◽  
Scale Model ◽  
Small Scale ◽  
Regular Waves ◽  
Hyperbaric Chamber ◽  
Small Scale Model

Wave energy is a renewable and non-polluting source and its use is being studied in different countries. The paper presents an overview on the harnessing of energy from waves and the activities associated with setting up a plant for extracting energy from waves in Port of Pecem, on the coast of Ceara State, Brazil. The technology employed is based on storing water under pressure in a hyperbaric chamber, from which a controlled jet of water drives a standard turbine. The wave resource at the proposed location is presented in terms of statistics data obtained from previous monitoring. The device components are described and small scale model tested under regular waves representatives of the installation region. Based on the experimental results values of prescribed pressures are identified in order to optimize the power generation.

Validating Numerical CFD Simulations With Experimental Data for Turbulence Phenomena in Axial Flow Gas Turbine Diffusers

2009 ◽  
Author(s):  
Farrokh Zarifi-Rad ◽  
Hamid Vajihollahi ◽  
James O’Brien
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Axial Flow ◽  
Experimental Results ◽  
Scale Model ◽  
Data Set ◽  
Pressure Profiles ◽  
Scale Models ◽  
Inlet Conditions

Scale models give engineers an excellent understanding of the aerodynamic behavior behind their design; nevertheless, scale models are time consuming and expensive. Therefore computer simulations such as Computational Fluid Dynamics (CFD) are an excellent alternative to scale models. One must ask the question, how close are the CFD results to the actual fluid behavior of the scale model? In order to answer this question the engineering team investigated the performance of a large industrial Gas Turbine (GT) exhaust diffuser scale model with performance predicted by commercially available CFD software. The experimental results were obtained from a 1:12 scale model of a GT exhaust diffuser with a fixed row of blades to simulate the swirl generated by the last row of turbine blades five blade configurations. This work is to validate the effect of the turbulent inlet conditions on an axial diffuser, both on the experimental front and on the numerical analysis approach. The object of this work is to bring forward a better understanding of velocity and static pressure profiles along the gas turbine diffusers and to provide an accurate experimental data set to validate the CFD prediction. For the CFD aspect, ANSYS CFX software was chosen as the solver. Two different types of mesh (hexagonal and tetrahedral) will be compared to the experimental results. It is understood that hexagonal (HEX) meshes are more time consuming and more computationally demanding, they are less prone to mesh sensitivity and have the tendancy to converge at a faster rate than the tetrahedral (TET) mesh. It was found that the HEX mesh was able to generate more consistent results and had less error than TET mesh.

scholarly journals Roughness Lengths for Momentum and Heat Derived from Outdoor Urban Scale Models

2007 ◽  
Vol 46 (7) ◽  
pp. 1067-1079 ◽  
Author(s):  
M. Kanda ◽  
M. Kanega ◽  
T. Kawai ◽  
R. Moriwaki ◽  
H. Sugawara
Keyword(s):  
Wind Direction ◽  
Roughness Length ◽  
Scale Dependence ◽  
Scale Model ◽  
Small Scale ◽  
Physical Scale ◽  
Scale Models ◽  
Roughness Lengths ◽  
Urban Sites ◽  
Obstacle Height

Abstract Urban climate experimental results from the Comprehensive Outdoor Scale Model (COSMO) were used to estimate roughness lengths for momentum and heat. Two different physical scale models were used to investigate the scale dependence of the roughness lengths; the large scale model included an aligned array of 1.5-m concrete cubes, and the small scale model had a geometrically similar array of 0.15-m concrete cubes. Only turbulent data from the unstable boundary layers were considered. The roughness length for momentum relative to the obstacle height was dependent on wind direction, but the scale dependence was not evident. Estimated values agreed well with a conventional morphometric relationship. The logarithm of the roughness length for heat relative to the obstacle height depended on the scale but was insensitive to wind direction. COSMO data were used successfully to regress a theoretical relationship between κB−1, the logarithmic ratio of roughness length for momentum to heat, and Re*, the roughness Reynolds number. Values of κB−1 associated with Re* for three different urban sites from previous field experiments were intercompared. A surprising finding was that, even though surface geometry differed from site to site, the regressed function agreed with data from the three urban sites as well as with the COSMO data. Field data showed that κB−1 values decreased as the areal fraction of vegetation increased. The observed dependency of the bulk transfer coefficient on atmospheric stability in the COSMO data could be reproduced using the regressed function of Re* and κB−1, together with a Monin–Obukhov similarity framework.

Generalized Generosity: How the Norm of Generalized Reciprocity Bridges Collective Forms of Social Exchange

2021 ◽  
pp. 000312242110074
Author(s):  
Monica M. Whitham
Keyword(s):  
Social Exchange ◽  
Causal Model ◽  
Social Bonds ◽  
Strong Support ◽  
Affect Theory ◽  
Small Scale ◽  
Group I ◽  
The Subject ◽  
Generalized Exchange ◽  
Strong Norm

This study examines the potential for small-scale acts of giving that are not directly reciprocated, or generalized generosities, to build social bonds and promote contributions to the group. Social exchange theorists define such acts as generalized exchange. The potential for generalized exchange to build strong social bonds relative to other forms of exchange is the subject of theoretical debate. In this article, I build on two prominent theories of social exchange—affect theory and the theory of reciprocity—to propose that a strong norm of generalized reciprocity may bridge the connective benefits of generalized exchange with the connective benefits of productive exchange, which is a collaborative form of social exchange that involves sharing pooled resources. I argue that a strong norm of generalized reciprocity will activate mechanisms theorized to build strong social bonds in generalized and productive exchange systems, and will promote additional behavioral investments into the group. I test my argument with a controlled laboratory experiment, finding strong support for the proposed causal model. The results of this study have implications for research on generosity, collective action, collaboration, sense of community, and social capital.

Structures and phase transitions in barium sodium niobate tungsten bronze (BNN)

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Thomas A. Whittle ◽  
Christopher J. Howard ◽  
Siegbert Schmid
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Tungsten Bronze ◽  
Standard Setting ◽  
Experimental Results ◽  
Temperature Structure ◽  
Sodium Niobate ◽  
Tetragonal Tungsten Bronze ◽  
Space Group ◽  
The Subject

The room-temperature structure of the filled tetragonal tungsten bronze, Ba2NaNb5O15 (BNN), has been the subject of a number of studies, and these studies have given an almost corresponding number of different results. From a group theoretical examination of the different possibilities and a review of the published experimental results we conclude that the room-temperature structure is that proposed by Labbé et al. [J. Phys. Condens. Matter (1989), 2, 25–43] in the space group Bbm2 (Ama2 in standard setting) on a 2\sqrt{2}a × \sqrt{2}a × 2c cell. Upon heating, the structure remains ferroelectric but becomes tetragonal (space group P4bm) at 550 K, then paraelectric (space group P4/mbm) at and above 860 K.

Fine-Scale Fire Spread in Pine Straw

Fire ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 69
Author(s):  
Daryn Sagel ◽  
Kevin Speer ◽  
Scott Pokswinski ◽  
Bryan Quaife
Keyword(s):  
Fire Spread ◽  
Small Scale ◽  
Natural Setting ◽  
Fine Scale ◽  
Prescribed Burn ◽  
Fire Dynamics ◽  
Rate Of Spread ◽  
Scale Models ◽  
Fire Front ◽  
Visible Images

Most wildland and prescribed fire spread occurs through ground fuels, and the rate of spread (RoS) in such environments is often summarized with empirical models that assume uniform environmental conditions and produce a unique RoS. On the other hand, representing the effects of local, small-scale variations of fuel and wind experienced in the field is challenging and, for landscape-scale models, impractical. Moreover, the level of uncertainty associated with characterizing RoS and flame dynamics in the presence of turbulent flow demonstrates the need for further understanding of fire dynamics at small scales in realistic settings. This work describes adapted computer vision techniques used to form fine-scale measurements of the spatially and temporally varying RoS in a natural setting. These algorithms are applied to infrared and visible images of a small-scale prescribed burn of a quasi-homogeneous pine needle bed under stationary wind conditions. A large number of distinct fire front displacements are then used statistically to analyze the fire spread. We find that the fine-scale forward RoS is characterized by an exponential distribution, suggesting a model for fire spread as a random process at this scale.

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