THE TRANSIENT EFFECTS OF FLOOD WATER ON A WARSHIP IN CALM WATER IMMEDIATELY FOLLOWING DAMAGE

2021 ◽  
Vol 152 (A4) ◽  
Author(s):  
G J Macfarlane ◽  
M R Renilson ◽  
T Turner
Keyword(s):  
Equilibrium Position ◽  
Upright Position ◽  
Water Levels ◽  
Transient Effects ◽  
Roll Damping ◽  
Transient Motion ◽  
Flood Water ◽  
Transient Behaviour ◽  
Calm Water ◽  
The Way

The safety of a ship which is damaged below the waterline will depend on the way water floods into the internal compartments. The water will cause the ship to take on an angle of heel and trim which will further affect the flooding into the compartments. The ship’s equilibrium position in calm water can be predicted using hydrostatic theory, however at present it is difficult to predict the transient behaviour between the initial upright position of the ship and its final equilibrium. In some cases, the transient motion may cause a capsize prior to a possible equilibrium position being reached. This paper describes an investigation of this phenomenon using a model of a warship with simplified, typical internal geometry. With the model initially stationary, a rapid damage event was generated, and the global motions measured, along with the water levels in some of the internal compartments, as functions of time. Immediately after the damage occurred the model rolled to starboard (towards the damage). It then rolled to port (away from the damage) before eventually returning to starboard and settling at its equilibrium value. In all the tests conducted the equilibrium heel angle was less than that reached during the initial roll to starboard. This implies that the roll damping, and the way in which the water floods into the model immediately following the damage, could both have a very important influence on the likelihood of survival.

scholarly journals Increase of flood water levels on the middle Danube

2015 ◽  
Vol 366 ◽  
pp. 145-146
Author(s):  
P. Pekarova ◽  
P. Miklanek ◽  
J. Pekar
Keyword(s):  
Water Levels ◽  
Flood Water

Experimental Investigation of Hydrodynamic Coefficients of a Wave-Piercing Tumblehome Hull Form

2007 ◽  
Author(s):  
Christopher C. Bassler ◽  
Jason B. Carneal ◽  
Paisan Atsavapranee
Keyword(s):  
Experimental Investigation ◽  
System Modeling ◽  
Flow Simulation ◽  
Roll Damping ◽  
Hull Form ◽  
Damping Coefficients ◽  
Calm Water ◽  
Forced Roll ◽  
Future Work ◽  
Damping Model

A systematic series of calm-water forced roll model tests were performed over a range of forward speeds using an advanced tumblehome hull form (DTMB model #5613-1) to examine the mechanisms of roll damping. This experimental investigation is part of an ongoing effort to advance the capability to assess seakeeping, maneuvering, and dynamic stability characteristics of an advanced surface combatant. The experiment was performed to provide data for development and validation of a semi-empirical roll damping model for use in validation of ship motion and viscous flow simulation codes, as well as to provide a basis for future work with additional experiments, contributing to the development of an improved analytical roll damping model. Two hull configurations were tested: barehull with skeg, and bare hull with skeg and bilge keels. Measurements of forces and moments were obtained over a range of forward speeds, roll frequencies, and roll amplitudes. Stereo particle-image velocimetry (SPIV) measurments were also taken for both zero and forward speeds. Test data was used to calculate added mass/inertia and damping coefficients. Two different system modeling techniques were used. The first method modeled the system as an equivalent linearly-damped second-order harmonic oscillator with the time-varying total stiffness coefficient considered linear. The second technique used equivalent linear damping, including higher-order Fourier components, and a non-linear stiffness formulation. Results are shown, including plots of added inertia and damping coefficients as functions of roll frequency, roll amplitude, and forward speed and SPIV measurements. Trends from the experimental data are compared to results from traditional component roll damping formulations for conventional hull from geometries and differences are discussed.

Thorough Verification and Validation of CFD Simulation for FPSO Roll Damping

2019 ◽  
Author(s):  
Donghwan Lee ◽  
Zhenjia (Jerry) Huang
Keyword(s):  
Numerical Modeling ◽  
Cfd Simulation ◽  
Development Project ◽  
Model Tests ◽  
Design Tool ◽  
Verification And Validation ◽  
Empirical Formulas ◽  
Roll Damping ◽  
Calm Water ◽  
Offshore Industry

Abstract For floating production platform such as FPSO and FLNG, it is important to use confidently estimated roll damping coefficients in the prediction of its motions in waves since in many cases the roll response is mainly contributed from resonance. Traditionally roll damping prediction was made through model tests or empirical formulas. As computing power and numerical modeling techniques have been improved during last a few decades, offshore industry starts to consider CFD as an alternative engineering and design tool complementary and/or supplementary to physical model tests. This paper presents our verification and validation work of modeling practices with commercially available CFD software for engineering applications for FPSO roll decay damping in calm water. The numerical modeling followed a recommended modeling practice developed by a Joint Development Project – TESK JDP [1].

Hydrological projections based on the coupled hydrological–hydraulic modeling in the complex river network region: a case study in the Taihu basin, China

2014 ◽  
Vol 6 (2) ◽  
pp. 386-399 ◽  
Author(s):  
Liu Liu ◽  
Zongxue Xu
Keyword(s):  
Land Cover ◽  
Regional Climate ◽  
Hydraulic Modeling ◽  
Water Levels ◽  
Future Climate ◽  
Baseline Scenario ◽  
Climate Scenarios ◽  
Flood Water ◽  
Taihu Basin ◽  
The Impact

Water resources in the Taihu basin, China, are not only facing the effects of a changing climate but also consequences of an intensive urbanization process with the abandonment of rural activities and the resulting changes in land use/land-cover. In the present work, the impact of climate change and urbanization on hydrological processes was assessed using an integrated modeling system, coupling the distributed hydrological model variable infiltration capacity and the hydraulic model ISIS, while future climate scenarios were projected using the regional climate model providing regional climate for impact studies. Results show a significant increasing trend of impervious surface area, while other types of land cover exhibit decreasing trends in 2021–2050. Furthermore, mean annual runoff under different future climate scenarios will increase, especially during flood seasons, consistent with the changes in precipitation and evapotranspiration for both spatial and temporal distribution. Maximum and mean flood water levels under two future scenarios will be higher than levels under the baseline scenario (1961–1990), and the return periods of storms resulting in the same flood water level will decrease significantly in comparison to the baseline scenario, implying more frequent occurrence of extreme floods in future. These results are significant to future flood control efforts and waterlog drainage planning in the Taihu basin.

scholarly journals Long-term dynamics of maximum flood water levels in the middle course of the Ob River

2019 ◽  
Vol 400 ◽  
pp. 012004
Author(s):  
V A Zemtsov ◽  
D A Vershinin ◽  
V V Khromykh ◽  
O V Khromykh
Keyword(s):  
Water Levels ◽  
Flood Water ◽  
Ob River

Achieving Flood Reduction with Natural Water Retention Measures in Agricultural Catchments in Ireland 

2021 ◽  
Author(s):  
Pia Laue ◽  
Paul Quinn ◽  
Mary Bourke ◽  
Darragh Murphy ◽  
Mark Wilkinson ◽  
...  
Keyword(s):  
Land Use ◽  
Natural Water ◽  
Water Retention ◽  
Water Storage ◽  
Sediment Traps ◽  
Water Levels ◽  
Storm Events ◽  
Peak Reduction ◽  
Flood Water ◽  
The Impact

<p>In recent decades, land-use and climate change have dramatically altered catchment runoff rates. For example, agriculture intensification has led to increased flood risks by decreasing  soil permeability and reducing channel-floodplain connectivity. Natural Water Retention Measures (NWRM) is an approach that has been adopted European-wide for the attenuation of peak floods and the provision of wider ecosystem services. A reduction in peak flow is achieved by increasing water storage potential in the landscape and by modifying natural flow pathways. In agricultural areas (~70% of Irish land use),  runoff attenuation features such as offline ponds, earthen bunds, sediment traps and leaky dams are frequently deployed natural retention measures.</p><p>Despite the growing evidence across Europe of their efficacy for flood peak reduction, water quality enhancement and biodiversity on the local scale, NWRM features have not been adopted in Ireland as a flood mitigation approach. In order to build a case that will help address this, this presentation will detail a NWRM demonstrate site in Ballygow, Co. Wexford.  The construction and instrumentation of a network of features developed at the field-scale (~1km<sup>2</sup>) is shown. This site is an intensive pasture, small-hold farm. We aim to quantify the effectiveness of these NWRM features to demonstrate their potential to attenuate flood peaks on agricultural areas using temporary storage, whilst minimising the impact on farming.</p><p>The constructed measures consist of a flood swale that connects the channel to the floodplain during high flows, an earthen bund, an offline pond with a sediment trap, that can retain the water from the channel and contributing field slopes, for <12 hours. On-site video footage and eyewitnesses confirm that the flood water flows along the field without draining back into the stream. At approximately 800m across the field, the water is retained temporarily, permitting water storage and the opportunity for suspended sediment to settle out of the water column. Flood water is returned to the channel via a perched 20 cm diameter pipe in the bund. Four automated water level recorders (In-Situ Rugged Troll 100) continuously monitor water levels in the stream and the offline pond at 5 min intervals. In addition, local rainfall (EML Event Logger) is monitored. These data are used to identify the hydrograph characteristics of several storm events and are used to determine the effectiveness of the NWRM structures for flood attenuation. The quantification of the effectiveness of NWRM features will use the observed time series combined with hydraulic and hydrological modelling. </p><p>The quantitative evidence provided by our findings will contribute to establishing vital evidence for the implementation of local and national NWRM schemes in Ireland.</p>

Lava Falls: The Blood of Oasis Civilization

2011 ◽  
Author(s):  
William deBuys
Keyword(s):  
North America ◽  
Colorado River ◽  
Grand Canyon ◽  
Space Time ◽  
Water Levels ◽  
Outdoor Adventure ◽  
Roller Coaster ◽  
Defining Moment ◽  
The Way

Rightly or wrongly, everything challenging on a whitewater river in North America gets compared to the booming rapid that culminates, in space, time, and difficulty, a river trip through the Grand Canyon. Say “Lava” to anyone who has tasted whitewater, and the association to Lava Falls Rapid is automatic. A friend who guides trips on some of Alaska’s wildest rivers bristles when she hears the name Lava North applied to the most sphincter-tightening, life-or-death rapid on the mighty Alsek River. “It shows how Grand Canyon–centric the rafting world is,” she says. Advocates for other rivers say much the same. Still, Lava is king, and the Colorado River, for which Lava is a mere riffle in its eons of canyon carving, is the most mythic of river kingdoms. If you have a weakness for wild rivers, eventually you float the Colorado, and eventually you make your way to the Grand Canyon and to Lava. The drop at Lava Falls is thirteen feet almost immediately, followed by fourteen more in a few hundred yards. At most water levels, Lava earns a difficulty rating of ten, on a scale of ten. It confronts you at mile 179 on the 226-mile voyage from Lees Ferry to Diamond Creek, an incomparable outdoor adventure. The trip has the shape of a well-crafted novel. It establishes its themes in the red-rock stillness of Marble Canyon. It tests its characters in the churning whitewater of the Inner Gorge. Then Lava comes exactly where a novelist would place the climax, about four-fifths of the way through the saga. All the way down the river, you have had Lava in the back of your mind. Everything that precedes it feels like lead-up. Everything that follows is coda, resolution, release, perhaps recovery. The crux of the tale, the defining moment, resides in the hurricane waters of Lava Falls. By the time our small flotilla got there, we’d courted disaster at Crystal, dodged the rock horns of Horn Creek Rapid, ridden the roller coaster of Granite, and thrashed and crashed our way through scores of other rapids.

scholarly journals Time-Dependent Performance of a Multi-Hop Software Defined Network

2021 ◽  
Vol 11 (6) ◽  
pp. 2469
Author(s):  
Tadeusz Czachórski ◽  
Erol Gelenbe ◽  
Godlove Suila Kuaban ◽  
Dariusz Marek
Keyword(s):  
Packet Loss ◽  
Network Optimization ◽  
Transient Analysis ◽  
Network Performance ◽  
Computation Time ◽  
Software Defined Network ◽  
Transient Effects ◽  
Statistical Accuracy ◽  
Design Of Algorithms ◽  
Transient Behaviour

It has been recently observed that Software Defined Networks (SDN) can change the paths of different connections in the network at a relatively frequent pace to improve the overall network performance, including delay and packet loss, or to respond to other needs such as security. These changes mean that a network that SDN controls will seldom operate in steady state; rather, the network may often be in transient mode, especially when the network is heavily loaded and path changes are critically important. Hence, we propose a transient analysis of such networks to better understand how frequent changes in paths and the switches’ workloads may affect multi-hop networks’ performance. Since conventional queueing models are difficult to solve for transient behaviour and simulations take excessive computation time due to the need for statistical accuracy, we use a diffusion approximation to study a multi-hop network controlled by SDN. The results show that network optimization should consider the transient effects of SDN and that transients need to be included in the design of algorithms for SDN controllers that optimize network performance.

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