scholarly journals Ship Towed by Kite: Investigation of the Dynamic Coupling

2020 ◽  
Vol 8 (7) ◽  
pp. 486 ◽  
Author(s):  
Nedeleg Bigi ◽  
Kostia Roncin ◽  
Jean-Baptiste Leroux ◽  
Yves Parlier
Keyword(s):  
Aerodynamic Characteristics ◽  
Strong Interactions ◽  
Ship Motions ◽  
Dynamic Simulations ◽  
Seakeeping Analysis ◽  
Ship Roll ◽  
The Mean ◽  
The Time Domain ◽  
Monolithic Approach ◽  
Lock In

This paper presents a series of dynamic simulations for a ship towed by kite. To ensure time efficient computations, seakeeping analysis with forward speed correction factors is carried out in the frequency domain and then transformed in the time domain by convolution. The seakeeping modeling is coupled with a zero-mass kite modeling assuming linear dependence of aerodynamic characteristics with respect to turning rate. Decoupled (segregated) and coupled (monolithic) approaches are assessed and compared in different environmental conditions. Results show that in regular beam waves, strong interactions between the kite and the ship motions are captured by the monolithic approach. Around the wave frequency, especially for the lower one tested (0.4 rad/s), a kite lock-in phenomenon is revealed. It is concluded that the mean kite towing force can be increased whereas the ship roll amplitude can even be decreased compared to a non-kite assisted ship propulsion configuration.

A numerical study of the sedimentation of fibre suspensions

1998 ◽  
Vol 376 ◽  
pp. 149-182 ◽  
Author(s):  
MICHAEL B. MACKAPLOW ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Monte Carlo ◽  
Steady State ◽  
Monte Carlo Simulations ◽  
Numerical Study ◽  
Point Particle ◽  
Hydrodynamic Interactions ◽  
Dynamic Simulations ◽  
Slender Body Theory ◽  
Fibre Suspensions ◽  
The Mean

The sedimentation of fibre suspensions at low Reynolds number is studied using two different, but complementary, numerical simulation methods: (1) Monte Carlo simulations, which consider interparticle hydrodynamic interactions at all orders within the slender-body theory approximation (Mackaplow & Shaqfeh 1996), and (ii) dynamic simulations, which consider point–particle interactions and are accurate for suspension concentrations of nl3=1, where n and l are the number density and characteristic half-length of the fibres, respectively. For homogeneous, isotropic suspensions, the Monte Carlo simulations show that the hindrance of the mean sedimentation speed is linear in particle concentration up to at least nl3=7. The speed is well predicted by a new dilute theory that includes the effect of two-body interactions. Our dynamic simulations of dilute suspensions, however, show that interfibre hydrodynamic interactions cause the spatial and orientational distributions to become inhomogeneous and anisotropic. Most of the fibres migrate into narrow streamers aligned in the direction of gravity. This drives a downward convective flow within the streamers which serves to increase the mean fibre sedimentation speed. A steady-state orientation distribution develops which strongly favours fibre alignment with gravity. Although the distribution reaches a steady state, individual fibres continue to rotate in a manner that can be qualitatively described as a flipping between the two orientations aligned with gravity. The simulation results are in good agreement with published experimental data.

Aerodynamic characteristics of delta wing–body combinations at high angles of attack

1994 ◽  
Vol 98 (975) ◽  
pp. 159-170 ◽  
Author(s):  
P. R. Viswanath ◽  
S. R. Patil
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Aerodynamic Characteristics ◽  
Surface Flow ◽  
Flow Visualisation ◽  
Symmetric Flow ◽  
Gradual Process ◽  
Wing Sweep ◽  
The Mean ◽  
High Angles Of Attack

AbstractAn experimental study investigating the aerodynamic characteristics of generic delta wing-body combinations up to high angles of attack was carried out at a subsonic Mach number. Three delta wings having sharp leading edges and sweep angles of 50°, 60° and 70° were tested with two forebody configurations providing a variation of the nose fineness ratio. Measurements made included six-component forces and moments, limited static pressures on the wing lee-side and surface flow visualisation studies. The results showed symmetric flow features up to an incidence of about 25°, beyond which significant asymmetry was evident due to wing vortex breakdown, forebody vortex asymmetry or both. At higher incidence, varying degrees of forebody-wing vortex interaction effects were seen in the mean loads, which depended on the wing sweep and the nose fineness ratio. The vortex breakdown on these wings was found to be a gradual process, as implied by the wing pressures and the mean aerodynamic loads. Effects of forebody vortex asymmetry on the wing-body aerodynamics have also been assessed. Comparison of Datcom estimates with experimental data of longitudinal aerodynamic characteristics on all three wing-body combinations indicated good agreement in the symmetric flow regime.

Aerodynamic Forces on Multiple Unit Trains in Cross Winds

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Christopher J. Baker ◽  
Mark Sterling
Keyword(s):  
Pressure Fluctuations ◽  
Decomposition Analysis ◽  
Aerodynamic Characteristics ◽  
Scale Model ◽  
Fluctuating Pressure ◽  
Time Histories ◽  
Multiple Unit ◽  
The Mean ◽  
Proper Orthogonal ◽  
Natural Wind

This paper describes the results of wind tunnel tests that were carried out to measure the aerodynamic characteristics of an electrical multiple unit (EMU) vehicle in a cross wind. The measurements were made on a 1/30 scale model of the Class 365 EMU in a simulation of the natural wind. The time histories of surface pressures were measured at a large number of points over the vehicle from which the aerodynamic characteristics and force coefficients were determined. This paper describes the complex fluctuating pressure field over the vehicle, through a consideration of the mean and fluctuating pressure coefficients and their spectra, and through a proper orthogonal decomposition analysis, which identifies the major modes of this distribution. The mean, fluctuating, and extreme aerodynamic side and lift forces are also discussed. It is shown that the flow pattern around the vehicle is dominated by large windward roof corner pressure fluctuations.

Assessing the Dynamic Stability of an Offshore Supply Vessel

2011 ◽  
Author(s):  
Vladimir Shigunov ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Jan Kaufmann ◽  
Rasmus Stute
Keyword(s):  
Dynamic Stability ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Ship Motions ◽  
Navier Stokes Equations ◽  
Counter Measures ◽  
Seakeeping Analysis ◽  
Design Speed ◽  
Run Up

The dynamic stability was investigated of a typical offshore service vessel operating under stability critical operating conditions. Excessive roll motions and relative motions at the stern were studied for two loading conditions for ship speeds ranging from zero to the design speed. A linear frequency-domain seakeeping analysis was followed by nonlinear time-domain simulations of ship motions in waves. Based on results from these methods, critical scenarios were selected and simulated using finite-volume solvers of the Reynolds-averaged Navier-Stokes equations to understand the phenomena related to dynamically unstable ship motions as well as to confirm the results of the simpler analysis methods. Results revealed the possibility of excessive roll motions and water run-up on deck; counter measures such as a ship-specific operational guidance are discussed.

scholarly journals THE TIME DOMAIN ANALYSIS ON MOORED SHIP MOTIONS

1988 ◽  
Vol 1 (21) ◽  
pp. 219 ◽  
Author(s):  
Masayoshi Kubo ◽  
Naokatsu Shimoda ◽  
Shunsaku Okamoto
Keyword(s):  
Time Domain ◽  
Integral Method ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Ship Motions ◽  
Convolution Integral ◽  
Quay Wall ◽  
Calculation Results ◽  
The Time Domain

The ship refuge inside a harbor in storm requires the analysis of moored ship motions along a quay wall. In this case the time domain analysis with the convolution integral method becomes effective. But the calculation accuracy is not enough and must be improved to analyze actual moored ship motions. In this paper some methods of the improvement are proposed and their efficiency is verified by comparing the calculation results with the experimental ones.

Control of the Precessing Vortex Core by Open and Closed-Loop Forcing in the Jet Core

2016 ◽  
Author(s):  
Phoebe Kuhn ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Vortex Core ◽  
Oscillation Frequency ◽  
Closed Loop ◽  
Hydrodynamic Instability ◽  
Axial Position ◽  
Hot Wire ◽  
Mean Flow ◽  
Precessing Vortex Core ◽  
The Mean ◽  
Lock In

The precessing vortex core (PVC) is the dominant coherent structure of swirling jets, which are commonly applied in gas turbine combustion. It stems from a global hydrodynamic instability that is caused by internal feedback mechanisms in the jet core. In this work, we apply open and closed-loop forcing in a generic non-reacting jet to control this mechanism and the PVC. Control is exerted by two oppositely facing, counter-phased zero-net mass flux jets, which are introduced radially into the flow through a thin lance positioned on the jet center axis. By using this type of forcing, the instability mode m = 1, corresponding to the PVC, can either be excited or damped. This markedly affects the PVC oscillation frequency and amplitude. The passive influence of the actuation lance on the mean flow field properties and the coherent flow dynamics is studied first without forcing. PIV and hot-wire measurements reveal an effect on the mean flow, but no qualitative changes of the PVC dynamics. Lock-in experiments are conducted, in which the synchronization behavior of the PVC with the forcing is determined. Here, two different cases are considered. First, actuation is applied at different streamwise positions in order to identify the region of highest receptivity towards external forcing. This region of lowest lock-in amplitude is shown to coincide with the location of the wavemaker, shortly upstream of the vortex breakdown bubble. Second, the lock-in behavior at a fixed axial position and various forcing frequencies ff is studied. A linear correlation between the lock-in amplitude and the deviation of the forcing frequency from the natural oscillation frequency |ff – fn| is observed. Closed-loop control is then applied with the aim to suppress the PVC. The actuator lance is positioned in the wavemaker region, where the flow is most receptive. Magnitude and phase of the natural flow oscillation associated with the PVC are estimated from four hot-wire signals using an extended Kalman filter. The estimated PVC signal is phase-shifted and fed back to the actuator. PIV measurements reveal that feedback control achieves a reduction of the PVC oscillation energy of about 40%.

scholarly journals A Continuous Blood Pressure Estimation Method Using Photoplethysmography by GRNN-Based Model

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7207
Author(s):  
Zheming Li ◽  
Wei He
Keyword(s):  
Blood Pressure ◽  
Estimation Method ◽  
Absolute Error ◽  
Disease Diagnosis ◽  
Generalized Regression Neural Network ◽  
British Hypertension Society ◽  
Proposed Model ◽  
The Mean ◽  
Blood Pressure Estimation ◽  
The Time Domain

Compared with diastolic blood pressure (DBP) and systolic blood pressure (SBP), the blood pressure (BP) waveform contains richer physiological information that can be used for disease diagnosis. However, most models based on photoplethysmogram (PPG) signals can only estimate SBP and DBP and are susceptible to noise signals. We focus on estimating the BP waveform rather than discrete BP values. We propose a model based on a generalized regression neural network to estimate the BP waveform, SBP and DBP. This model takes the raw PPG signal as input and BP waveform as output. The SBP and DBP are extracted from the estimated BP waveform. In addition, the model contains encoders and decoders, and their role is to be responsible for the conversion between the time domain and frequency domain of the waveform. The prediction results of our model show that the mean absolute error is 3.96 ± 5.36 mmHg for SBP and 2.39 ± 3.28 mmHg for DBP, the root mean square error is 5.54 for SBP and 3.45 for DBP. These results fulfill the Association for the Advancement of Medical Instrumentation (AAMI) standard and obtain grade A according to the British Hypertension Society (BHS) standard. The results show that the proposed model can effectively estimate the BP waveform only using the raw PPG signal.

scholarly journals Tuning the Anisotropic Thermal Transport in {110}-Silicon Membranes with Surface Resonances

Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 123
Author(s):  
Keqiang Li ◽  
Yajuan Cheng ◽  
Maofeng Dou ◽  
Wang Zeng ◽  
Sebastian Volz ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Mean Free Path ◽  
Dynamic Simulations ◽  
Resonant Structures ◽  
Thermoelectric Energy ◽  
Thin Membranes ◽  
The Mean ◽  
Equilibrium Molecular Dynamic

Understanding the thermal transport in nanostructures has important applications in fields such as thermoelectric energy conversion, novel computing and heat dissipation. Using non-homogeneous equilibrium molecular dynamic simulations, we studied the thermal transport in pristine and resonant Si membranes bounded with {110} facets. The break of symmetry by surfaces led to the anisotropic thermal transport with the thermal conductivity along the [110]-direction to be 1.78 times larger than that along the [100]-direction in the pristine structure. In the pristine membranes, the mean free path of phonons along both the [100]- and [110]-directions could reach up to ∼100 µm. Such modes with ultra-long MFP could be effectively hindered by surface resonant pillars. As a result, the thermal conductivity was significantly reduced in resonant structures, with 87.0% and 80.8% reductions along the [110]- and [100]-directions, respectively. The thermal transport anisotropy was also reduced, with the ratio κ110/κ100 decreasing to 1.23. For both the pristine and resonant membranes, the thermal transport was mainly conducted by the in-plane modes. The current work could provide further insights in understanding the thermal transport in thin membranes and resonant structures.

scholarly journals Experimental Study on the Spanwise Correlation of Vortex-Induced Force Using Large-Scale Section Model

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Chunguang Li ◽  
Yu Mao ◽  
Yan Han ◽  
Kai Li ◽  
C.S. Cai
Keyword(s):  
Time Domain ◽  
Large Scale ◽  
Correlation Coefficients ◽  
Box Girder ◽  
Pressure Coefficients ◽  
Smooth Flow ◽  
Maximum Value ◽  
Section Model ◽  
The Time Domain ◽  
Lock In

To investigate the spanwise correlation of vortex-induced forces (VIF) of a typical section of a streamlined box girder, wind tunnel tests of simultaneous measurement of force and displacement responses of a sectional model were conducted in a smooth flow. The spanwise correlation of VIF and pressure coefficients on the measurement points of an oscillating main deck were analyzed in both the time domain and frequency domain, respectively. The research results indicated that the spanwise correlation of VIF and pressure coefficients on the measurement points were related to the amplitudes of vortex-induced vibration (VIV), both of them weakened with the increase of spanwise distance; the maximum value of spanwise correlation coefficient is situated at the ascending stage of the lock-in region, rather than at the extreme amplitude point. The amplitudes of VIV showed different impacts on the spanwise correlation of pressure coefficients on the measurement points of the upper and lower surfaces, for which the maximum value of the spanwise correlation coefficients is located at the extreme amplitude point and the ascending stage of the lock-in region, respectively. Furthermore, the spanwise correlation of the pressure coefficients decreases continually from the upstream to downstream of the main deck; large coherence of vortex-induced forces and pressure appears around the frequency of vortex shedding, and the coherence of VIF and pressure becomes smaller with the increase in the spanwise distance.

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