We describe experiments with multi-directional focused waves interacted with a vertical circular cylinder in a 3D wave basin. The focus of this study is on the run-up of multi-directional focused ...waves, wave forces, and wave pressures on the cylinder. Part I, the study on wave run-up, has already been presented by Li et al. (2012). In this paper, the analysis of the wave force on the vertical cylinder is presented.
In this experiment, a cylinder with 0.25m in diameter was adopted and different wave parameters, such as focused wave amplitude, peak frequency, frequency bandwidth and directional spreading index, are considered. The model scale kpa (kp is the wave number corresponding to peak frequency, a is the radium of the cylinder) varies from 0.32 to 0.65. The maximum forces of multi-directional focused wave on cylinder were measured and investigated. The results showed that the wave parameters have a significant influence on the wave force, and that the spatial profile of the surface of multi-directional focused wave can also affect its force on the cylinder, which is different from two-dimensional wave. In addition, the ‘secondary loading cycle’ phenomenon was also observed and discussed. In our experiments, the ‘secondary loading cycles’ occur when kA>0.36 for all cases. While in some referred small scale experiments, the secondary load cycles are observed even for kA=0.2, when the waves are longer enough. To larger model scale, the pronounced secondary load cycle occurs with larger wave steepness waves.
•We measured the multi-directional focused wave impact forces on a vertical cylinder.•We studied the effects of wave parameters on shape of focused wave and wave force.•We observed and investigated the ‘secondary loading cycle’ phenomenon in our experiment.•The ‘secondary loading cycle’ will occur when kA>0.36 for all our large model scale experimental cases.
Background
Previous studies showed that cerebral small vessel disease (cSVD) is a leading cause of cognitive decline in elderly people and the development of Alzheimer’s disease. Although brain ...structural changes of cSVD have been documented well, it remains unclear about the properties of brain intrinsic spontaneous activity in patients with cSVD.
Methods
We collected resting-state fMRI (rs-fMRI) and T1-weighted 3D high-resolution brain structural images from 41 cSVD patients and 32 healthy controls (HC). By estimating the amplitude of low-frequency fluctuation (ALFF) under three different frequency bands (typical band: 0.01–0.1 Hz; slow-4: 0.027–0.073 Hz; and slow-5: 0.01–0.027 Hz) in the whole-brain, we analyzed band-specific ALFF differences between the cSVD patients and controls.
Results
The cSVD patients showed uniformly lower ALFF than the healthy controls in the typical and slow-4 bands (
p
FWE
< 0.05). In the typical band, cSVD patients showed lower ALFF involving voxels of the fusiform, hippocampus, inferior occipital cortex, middle occipital cortex, insula, inferior frontal cortex, rolandic operculum, and cerebellum compared with the controls. In the slow-4 band, cSVD patients showed lower ALFF involving voxels of the cerebellum, hippocampus, occipital, and fusiform compared with the controls. However, there is no significant between-group difference of ALFF in the slow-5 band. Moreover, we found significant “group × frequency” interactions in the left precuneus.
Conclusion
Our results suggested that brain intrinsic spontaneous activity of cSVD patients was abnormal and showed a frequency-specific characteristic. The ALFF in the slow-4 band may be more sensitive to detecting a malfunction in cSVD patients.
The heave plate is the key component of a Spar platform as it can effectively improve the heave response of the platform system by providing additional damping and added mass. This paper investigates ...the hydrodynamic coefficients of heave plates by using forced oscillation model tests. The effects of variables such as the Keulegan–Carpenter (KC) number, frequency of oscillation, plate depth, thickness-to-width ratio, shape of the edge, perforation ratio and hole size on the hydrodynamic coefficients were analyzed. Experiments using a group of three solid or perforated heave plates were also carried out and the experimental results were compared with those for a single plate. The relationship between the spacing of the heave plates and hydrodynamic coefficients was studied.
•The hydrodynamic coefficients of heave plates were investigated using forced oscillation model tests.•The effects of different variables on the hydrodynamic coefficients were analyzed.•Experiments using a group of three solid or perforated heave plates were also carried out.•The relationship between the spacing of the heave plates and hydrodynamic coefficients was studied.
A wave basin experiment has been performed to investigate the interactions between multi-directional focused wave and vertical bottom-mounted cylinder. In this paper, a study on wave run-up on a ...vertical bottom-mounted cylinder is presented. For all experimental cases, the ratio of the water depth and cylinder diameter ratio (d/D) is equal to 2.0 and the ratio of the wave height and water depth (2A/d) is varied in the range of (0.12, 0.60), where A is the focused amplitude. The experimental results showed that the focused wave parameters, including wave steepness, frequency bandwidth, and directional spreading index, had significant impacts on the wave run-up on a cylinder. More specifically, the focused wave run-up increased as these parameters increased, and the maximum value of the measured wave run-up ratio could be as high as 1.68. The variations of the multi-directional focused wave run-up around the cylinder were also analyzed. The wave run-up at the front of the cylinder was greater than that at the other positions around the cylinder. The wave run-up reached the lowest values at 135°. The associated focused wave parameters also impacted the wave run-up distribution around the cylinder.
► We studied the multi-directional focused wave run-up on a vertical cylinder. ► We investigated the impacts of wave parameters on the wave run-up. ► The focused wave run-up increased as wave steepness, frequency bandwidth increased. ► A unidirectional wave can generate larger wave run-up than a multidirectional wave. ► The wave parameters also impacted the wave run-up distribution around the cylinder.
A three-dimensional numerical wave tank was developed based on Reynolds averaged Navier–Stokes equations and the volume of fluid method. The moving boundary method is adopted in this model to ...generate water waves. Piston-type wave-makers are mimicked for the total replication of the physical wave tank conditions. Two-dimensional regular and irregular waves are simulated, with the capability to trigger the active wave absorption algorithm. The two-sided wave-maker system with L-type arrangement is adopted in this model to expand the effective wave areas for three-dimensional waves. Oblique regular waves and multidirectional random waves are simulated, yielding a good agreement with theoretical solutions. The results indicate that this numerical model is an effective tool to provide finer details or complement data unavailable due to the physical setting of a tank experiment.
In this series of two papers, we report on the irregular wave extension of the second-order coupling theory of numerical and physical wave model described in Z. Yang, S. Liu, H.B. Bingham and J. Li. ...Second-order theory for coupling numerical and physical wave tanks: Derivation, evaluation and experimental validation. Coast. Eng. 71, 37–51. We also correct several errors which unfortunately appeared in that manuscript. In the present part I, the full second-order coupling theory for irregular wave is described in detail. The new second-order coupling signal is presented including both superharmonics and subharmonics and covering wavemaker configurations of the piston- and flap-types. The second-order dispersive correction allows for an improved nonlinear transfer of wave information between the two models. For practical implementation, the coupling equations are solved by a combined five-point Lagrange interpolation and the fourth-order Runge–Kutta scheme, with a numerical velocity time series which is decomposed by the Newton–Raphson iterative method. Analytical evaluations on the suppression of spurious free waves and the relative errors of the resultant bound waves have been conducted by considering a 2nd-order, bi-chromatic wave over a range of dimensionless water depth and oscillation frequency combinations, indicating that the resultant wave quality is significantly improved using the second-order coupling theory. A separate verification combining numerical and experimental model of the theory will be presented in Part II by the same authors.
•A second-order coupling of numerical and physical models for irregular waves is proposed.•A series of practical implementation problems are solved.•Model's performance has been analytically estimated by nonlinear bichromatic waves.•Analytical results support the present method.
A full second-order theory for coupling numerical and physical wave tanks is presented. The ad hoc unified wave generation approach developed by Zhang et al. Zhang, H., Schäffer, H.A., Jakobsen, ...K.P., 2007. Deterministic combination of numerical and physical coastal wave models. Coast. Eng. 54, 171–186 is extended to include the second-order dispersive correction. The new formulation is presented in a unified form that includes both progressive and evanescent modes and covers wavemaker configurations of the piston- and flap-type. The second order paddle stroke correction allows for improved nonlinear wave generation in the physical wave tank based on target numerical solutions. The performance and efficiency of the new model is first evaluated theoretically based on second order Stokes waves. Due to the complexity of the problem, the proposed method has been truncated at 2D and the treatment of regular waves, and the re-reflection control on the wave paddle is also not included. In order to validate the solution methodology further, a series of nonlinear, periodic waves based on stream function theory are generated in a physical wave tank using a piston-type wavemaker. These experiments show that the new second-order coupling theory provides an improvement in the quality of nonlinear wave generation when compared to existing techniques.
► This study presents a full second-order theory for coupling numerical and physical wave tanks. ► Both progressive and evanescent modes are included. ► The accuracy and efficiency have been evaluated through a series of nonlinear wave generations. ► The new method offers good performance when compared to existing techniques.
This paper provides an experimental validation of the second-order coupling theory outlined by Yang et al. (Z. Yang, S. Liu, H.B. Bingham and J. Li., 2013. Second-order coupling of numerical and ...physical wave tanks for 2D irregular waves. Part I: Formulation, implementation and numerical properties, submitted for publication) using 2D irregular waves. This work provides a second-order dispersive correction for the physical wavemaker signal which improves the nonlinear transfer of information between the numerical and physical models compared to the first-order method of Zhang et al. (2007). The important nonlinear parameters and numerical performance were theoretically investigated in Part I. In the present Part II, careful experimental validation is carried out using a sequence of progressively more complex analytical and numerical target waves. The results demonstrate clearly that improved performance is achieved by using the second-order correction. When controlling with a second-order coupling signal, two key points are notable: (i) The higher harmonics underlying the numerical waves are accurately captured and transferred into the physical model. (ii) The second-order behavior leads to an unwanted spurious freely propagating second harmonic that is substantially reduced when compared to an identical wave paddle operating with a first-order coupling signal. Using nonlinear regular (monochromatic), bi-chromatic and irregular wave cases as well as varying coupled wave tank bathymetries, both these aspects are verified over a broad range of wave frequencies and shown to be extensively applicable to physical wave tanks.
•Completion of the second-order coupling model becomes available for experiments.•Monochromatic, bi-chromatic, irregular wave cases and varying bathymetries are validated.•Good qualitative and quantitative evidence are demonstrated for the present method.•The model has utility to couple the numerical and physical models up to second order.
The results of laboratory measurements of large focusing wave groups, which were generated using the New Wave theory, are presented. The influences of both the steepness and frequency bandwidth on ...focused wave characteristics were examined. The influence of frequency bandwidth on focused wave groups with small and moderate steepness was very small. However, for cases with the large steepness, the nonlinearity increased with increasing bandwidth frequency and widened free-wave regimes are identified for those cases with large steepness at the focal location. The underlying nonlinear phase coupling of focused waves was examined using wavelet-based bicoherence and biphase, which can detect nonlinear phase coupling in a short time series. For wave groups with large initial steepness, as wave groups approached the focal location, the values of bicoherence between primary waves and its higher harmonics progressively increased to 1 and the corresponding biphase was gradually close to zero, suggesting that an extreme wave event can be produced by considering Stokes-like nonlinearity to very high-order. Furthermore, the fast change of bicoherence of focused wave groups indicates that the nonlinear energy transfer within focusing waves is faster than that of nonfocusing wave trains.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Two series of 5-iodo-1,2,3-triazole derivatives containing azobenzene group(s) were synthesized and their gelling properties were tested. Those containing two azobenzene groups (
B
series) have ...better gelation performance than those containing one azobenzene group (
A
series). The microstructure of organogels and the driving force of gelation were investigated by scanning electron microscopy and
1
H NMR, respectively. It was found that π-π stacking, van der Waals interaction, and dipole-dipole interaction were the main forces of gelation. All the tested organogels are photoresponsive and those from
B
series are smarter than that from
A
series. Henry
δ
p
-
δ
h
diagrams of compounds
A1
,
A2
, and
B2
were constructed on the basis of their gelation performance and the Hansen solubility parameters of related solvents. The constructed Henry
δ
p
-
δ
h
diagrams can be used to estimate the behavior of three compounds in any untested solvent.
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