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Resolving the Role of Surface Pressure Gradients on the Positional State of Short Cylinders in Nearshore Environments.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Resolving the Role of Surface Pressure Gradients on the Positional State of Short Cylinders in Nearshore Environments./
作者:	Marquardt, Spencer.
面頁冊數:	1 online resource (224 pages)
附註:	Source: Masters Abstracts International, Volume: 84-05.
Contained By:	Masters Abstracts International84-05.
標題:	Ocean engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29392263click for full text (PQDT)
ISBN:	9798352953549

Resolving the Role of Surface Pressure Gradients on the Positional State of Short Cylinders in Nearshore Environments.
Marquardt, Spencer.

Resolving the Role of Surface Pressure Gradients on the Positional State of Short Cylinders in Nearshore Environments. - 1 online resource (224 pages)

Source: Masters Abstracts International, Volume: 84-05.

Thesis (M.S.)--University of New Hampshire, 2022.

Includes bibliographical references

The causes of munition mobility in nearshore regions are not well understood phenomena; and in situ measurements of positional state, orientation, and the local flow field are complicated by the high energy nature of the surf and swash zones. A pressure mapped munition (PMM) has been developed to autonomously measure the surface pressure and attitude to overcome some of these challenges.The PMM is a self-contained, Lagrangian instrument representative of 105-155~mm shells, that is capable of autonomously recording surface pressure and attitude for up to 100~h.The PMM utilizes 16 high resolution pressure sensors distributed around its surface to measure deviations in the local pressure field caused, in part, by the formation of and eventual shedding of vorticies. An internal inertial measurement unit (IMU) is used to make synchronous measurements of the PMM's attitude.Nearby vertical pressure variability is measured using a second instrument, the pressure stick (PS), to characterize the presence of momentary liquefaction events that can also factor into positional state changes of unexploded ordinance (UXO).This thesis summarizes three deployments of the PMM at Wallis Sands Beach, a medium sloping beach in New Hampshire, with a relatively uniform alongshore profile, then data collected in October 26-27, 2021 during a large nor'easter, is examined in detail. Pressure time series collected with the PMM and PS are used to characterize the nearshore wave climate, and offshore conditions are measured at the Jeffreys Ledge waverider buoy. The pressure and attitude records from the PMM are used along with shallow water approximations for linear wave theory to calculate the average depth of the PMM, peak wave period, and significant wave height to broadly determine under which conditions the PMM is mobile.Time series of the surface pressure gradients are approximated by taking the difference between sensor values on opposing sides of the PMM, while the location of sensors is determined by the attitude time series.Non-dimensional characterizations of the horizontal mobilizing forces acting on the PMM are given in a form similar to the Sleath parameter with a wave component, Swave, and residual component, Sresidual.The resolution of the pressure sensors is 0.06~cm, and the resulting surface pressure gradient estimates are measured with a total error of ±ε = 1.4 cm.Positional state of the PMM is inferred based on changes in attitude and on characterizations of the surface pressure variability, where transport occurs when the PMM is rolling multiple times about its long axis at more than 360°s.Smaller wobbling motions are defined between 0.5-360°s. The PMM is assumed proud when the standard deviation of the vertical and/or horizontal pressure gradients exceed a critical threshold of 0.15.Similarly, if the standard deviation of the pressure gradients are below 0.07, the PMM is assumed to be buried.Offshore motion of the PMM is highly correlated to the presence of vertical and horizontal surface pressure gradients indicative of vortex development around the PMM, corresponding with upward and offshore forcing.The effects of vortex shedding are seen in both the vertical and horizontal pressure gradients, evidenced by deviations from the expected hydrostatic pressure field around the surface of the PMM that reach 2-3 times. These occurrences are commensurate with long period (15-40 s) wave draw-down and swash oscillations, attributable to infragravity motions while momentary bed liquefaction is indicated. Onshore motion is seen during times when the PMM is partially or fully exposed to free stream flows and Swave exceeds a critical threshold as oncoming waves and wave bores pass over the PMM.At these times the vertical pressure gradients are elevated and there is a horizontal pressure gradient acting in the onshore direction.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798352953549Subjects--Topical Terms:

660731
Ocean engineering.
Subjects--Index Terms:

Coastal researchIndex Terms--Genre/Form:

542853
Electronic books.

Resolving the Role of Surface Pressure Gradients on the Positional State of Short Cylinders in Nearshore Environments.
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520 $a The causes of munition mobility in nearshore regions are not well understood phenomena; and in situ measurements of positional state, orientation, and the local flow field are complicated by the high energy nature of the surf and swash zones. A pressure mapped munition (PMM) has been developed to autonomously measure the surface pressure and attitude to overcome some of these challenges.The PMM is a self-contained, Lagrangian instrument representative of 105-155~mm shells, that is capable of autonomously recording surface pressure and attitude for up to 100~h.The PMM utilizes 16 high resolution pressure sensors distributed around its surface to measure deviations in the local pressure field caused, in part, by the formation of and eventual shedding of vorticies. An internal inertial measurement unit (IMU) is used to make synchronous measurements of the PMM's attitude.Nearby vertical pressure variability is measured using a second instrument, the pressure stick (PS), to characterize the presence of momentary liquefaction events that can also factor into positional state changes of unexploded ordinance (UXO).This thesis summarizes three deployments of the PMM at Wallis Sands Beach, a medium sloping beach in New Hampshire, with a relatively uniform alongshore profile, then data collected in October 26-27, 2021 during a large nor'easter, is examined in detail. Pressure time series collected with the PMM and PS are used to characterize the nearshore wave climate, and offshore conditions are measured at the Jeffreys Ledge waverider buoy. The pressure and attitude records from the PMM are used along with shallow water approximations for linear wave theory to calculate the average depth of the PMM, peak wave period, and significant wave height to broadly determine under which conditions the PMM is mobile.Time series of the surface pressure gradients are approximated by taking the difference between sensor values on opposing sides of the PMM, while the location of sensors is determined by the attitude time series.Non-dimensional characterizations of the horizontal mobilizing forces acting on the PMM are given in a form similar to the Sleath parameter with a wave component, Swave, and residual component, Sresidual.The resolution of the pressure sensors is 0.06~cm, and the resulting surface pressure gradient estimates are measured with a total error of ±ε = 1.4 cm.Positional state of the PMM is inferred based on changes in attitude and on characterizations of the surface pressure variability, where transport occurs when the PMM is rolling multiple times about its long axis at more than 360°s.Smaller wobbling motions are defined between 0.5-360°s. The PMM is assumed proud when the standard deviation of the vertical and/or horizontal pressure gradients exceed a critical threshold of 0.15.Similarly, if the standard deviation of the pressure gradients are below 0.07, the PMM is assumed to be buried.Offshore motion of the PMM is highly correlated to the presence of vertical and horizontal surface pressure gradients indicative of vortex development around the PMM, corresponding with upward and offshore forcing.The effects of vortex shedding are seen in both the vertical and horizontal pressure gradients, evidenced by deviations from the expected hydrostatic pressure field around the surface of the PMM that reach 2-3 times. These occurrences are commensurate with long period (15-40 s) wave draw-down and swash oscillations, attributable to infragravity motions while momentary bed liquefaction is indicated. Onshore motion is seen during times when the PMM is partially or fully exposed to free stream flows and Swave exceeds a critical threshold as oncoming waves and wave bores pass over the PMM.At these times the vertical pressure gradients are elevated and there is a horizontal pressure gradient acting in the onshore direction.
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538 $a Mode of access: World Wide Web
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653 $a Liquefaction
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710 2 $a University of New Hampshire. $b Ocean Engineering. $3 3346665
773 0 $t Masters Abstracts International $g 84-05.
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