Effect Of Wave Amplitude Research Articles

On the effect of wave amplitude and corrugation profile of certain types of corrugated channels on thermal performance and entropy generation

This study aims to examine experimentally and numerically the thermal-hydraulic performance and entropy generation of wavy channels: sinusoidal and triangular, and compare them with respect to the straight channel. Various wavy amplitudes and corrugation profiles are considered in a sinusoidal wavy channel and a triangular wavy channel and assessed with the straight channel. Experimental test rig is built and the experiments are carried out on laminar air flow and used to verify the simulation results. The main findings show that the HT rate, fluid flow, and entropy generation are affected by the corrugation profile and wave amplitude of the wavy channel. The maximum Nusselt number of 11.17 occurred in a sinusoidal wavy channel with a wave amplitude equal to 1.75, and high friction factor also happens in this model. It was found that the sinusoidal and triangular wavy channels with A = 0.75 and a flow rate range of 1–1.75 have the highest overall thermal performance factor. Also, the total entropy generation of the straight channel was lower than all corrugated channel models. In conclusion, it has been found that the best compromise between enhanced HT and the accompanying increase in both pressure drop and entropy generation is occurred in case of A = 0.75 at flow rate ranged from 1 to 1.67 LPM.

Improving the performance of mini-channel heat sink by using wavy channel and different types of nanofluids

The combination of nano fluid and changing cross-section mini-channel heat sink effects have become a remarkable choice for the use of thermal devices such as miniature electronic devices to be effectively cooled. In this paper, the comparison of three dimensional straight and wavy channel configuration with using different types nano fluids are numerically investigated. The effects of wave amplitude and A particular type of volume fraction of (Copper Oxide CuO, Dimond Al2O3, Iron Oxide Fe3O4, Titanium Oxide TiO2 and Silver Ag-nano fluids are offered. Three amplitudes of waves (0.15 mm, 0.2 mm and 0.25 mm) and Reynold’s number from 200 to 1000 and concentration volume varieties from 0 to 0.075 are used. The effect on thermal resistance, pressures drop, factor of friction of the mini channel is displayed. It is observed that the mini-channel sink's heat transfer efficiency is greatly enhanced compared to the straight channel in an event of adding distilled water as accoolant. The results indicate that nano fluid and wavy mini-channel can boost the heat sink's hydrothermal efficiency and Ag- water nano fluid in term of heat transfer, it outperforms other nanofluids an enhancement in the Nusselt number reached to 54% at concentration volume 0.075.

Mechanism of Faster CH4 Bubble Growth Under Surface Waves in Muddy Aquatic Sediments: Effects of Wave Amplitude, Period, and Water Depth

Methane (CH4) transport from organic-rich fine-grained (muddy) shallow aquatic sediments to water column is mediated dominantly by discrete bubbles, which is an important natural source of greenhouse CH4. The lifespan of these bubbles within the sediment comprises two successive stages: growth from nucleation up to a mature size and then buoyant ascent toward the sediment–water interface. Bubbles often experience an oscillating overburden load due to the passage of winds and/or storm-induced short period surface waves or long-period tides, which can potentially affect both stages of the bubble’s lifespan. However, little is known about the wave effects over bubble growth phase. In the present work, this subject is investigated using a numerical single-bubble mechanical/solute transport model, which quantifies the effects of different parameters (amplitude and period) of the wave loading and of the water depth, over the bubble growth pattern in sediments and its specific characteristics. It was found that bubbles induce early sediment fracturing in the presence of waves, attributed to the low overburden load appearing at wave troughs. Bubbles at shallow depth rapidly grow at wave troughs by inducing multiple intense fracturing events. However, this ability decreases with an increasing water depth because of a slower solute influx. In the presence of waves, bubbles mature in shorter time, whose contrast to the no wave case is controlled by the ratio of wave amplitude to equilibrium water depth. Due to the higher frequency of occurrence of wave troughs for shorter-period waves, bubble growth is accelerated compared with the case of longer-period waves. Overall, our modeling suggests that the fastest bubble growth can be predicted for higher amplitude, short-period waves traveling in shallow water. We further infer that accelerated bubble growth, along with subsequent wave-induced ascent can sufficiently shorten the bubble’s total lifespan in sediment, which explains the observed episodic in situ ebullitions correlated with wind- or storm-induced waves.

Numerical study on the attenuation of high-amplitude stress wave in rock bar along with rock damage evolution

The attenuation of high-amplitude stress waves in the rock and the rock failure caused by the stress waves have significance for vibration source analysis and rock engineering support design, where the interactions between the two deserve further study. In this paper, a FEM based numerical investigation on high-amplitude stress wave attenuation and rock damage evolution in one-dimensional rock bar is performed, aiming to understand the interaction between the variation of rock damage and wave attenuation. The numerical model is calibrated by experimental results. The spatial distribution of damage in rock bar is quantified by statistical windows. The effects of wave amplitude and heterogeneity index of rock on wave attenuation as well as the distribution of damage are analysed in details. The results indicate that the high-amplitude stress wave decays exponentially in the rock bar, and the attenuation of wave becomes significant as the incident wave amplitude increases. The incident wave amplitude corresponding to the lower limit of the amplitude effect is approximately 30% of the static compressive strength of rock, while that corresponding to the upper limit is the dynamic compressive strength of rock. Under the same incident wave amplitude, the attenuation of stress wave is more obvious in the rock with higher heterogeneity. The rock damage is quantified in a specific window, and its spatial distribution is described along with the movement of the window. The rock damage is concentrated in a region near the incident end. The damage development in space is consistent with that of high-amplitude stress waves and is more obvious in the models with higher heterogeneity. Findings in this work is helpful for the understanding of interaction between high-amplitude stress wave attenuation and rock damage and facilitate design and protection of rock engineering.

Comparison of Co- and counter-current modes of operation for wavy minichannel heat sinks (WMHSs)

This study aims to make a comprehensive comparison between the applications of co- and counter-current modes in the wavy minichannel heat sinks (WMHSs). In this regard, the effects of wave-amplitude (wa) and wave-length (wl) are studied at different levels. Water is used as coolant over the Reynolds number (Re) range of 100–900. Nusselt number ratio, friction factor ratio, performance index, max. base temperature difference, and pumping power are reported as quantitative results. An experimental study is also carried out to establish required data for the validation. The outputs illustrate that for both the current modes, the dependence of thermal and hydraulic characteristics on Re increases with increasing wa and decreasing wl, while the counter-current mode is more impressed by the increase of Re compared to the co-current mode. In summary, the Nusselt number ratio ranges from 1.22 to 2.96 for the co-current mode and from 1.23 to 3.17 for the counter-current mode, and the friction factor ratio ranges from 1.09 to 2.73 for the co-current mode and from 1.10 to 2.92 for the counter-current mode, and the range of performance index is from 1.18 to 2.12 for the co-current mode and from 1.19 to 2.22 for the counter-current mode. Eventually, it is found that at the same pumping powers, replacing the co-current mode with the counter-current mode can significantly boost the temperature uniformity in WMHS. The max. base temperature of about 0.84 K is recorded for WMHS with wl = 5 mm at Re = 900. It is worthy to note that the superiority of the counter-current mode increases with increasing wa and decreasing wl.

Time-domain numerical research of the hydrodynamic characteristics of a trimaran in calm water and regular waves

As a special type of high-speed vessel, the hydrodynamic performance of trimanran is not yet fully understood and is still under investigation. In this paper, a viscous method is established based on RANS to study the resistance in calm water, added resistance and motion response in head waves of various wave amplitudes. Results from numerical simulation show satisfactory agreement with the experimental data. In addition, the effect of hull attitude on resistance in calm water and the effect of wave amplitude on added resistance, as well as motion response are analysed. The results show that the resistance of the trimaran in calm water is significantly influenced by the hull attitude at high speed, however, this resistance could be underestimated if the ship attitude is ignored because of the miscalculation of the free surface and the resistance of outriggers. It is found that the added resistance induced by the center hull composes the dominant part of the total added resistance and the non-dimensional value of added resistance is decreased with wave amplitude, while the influence of wave amplitude on the non-dimensional results of heave and pitch motion is not significant.

The effect of wave amplitude on S-wave velocity in porous media: an experimental study by Laser Doppler Interferometry

Rock physics models are widely used for reservoir characterisation in seismic studies. By improving the models, especially for reservoir rocks, more realistic characterisations can be achieved. To calibrate such models the elastic properties of reservoir porous rocks have been measured by ultrasonic techniques for many years. In conventional ultrasonic methods the local strain inside the wave is much higher than that in field experiments. Up until now, it has not been clear how the velocity of the ultrasonic wave depends on the strain, however this knowledge is important for interpretation of the results of the experiments. This work is an extension of our previous study on the effect of the strain amplitude on wave velocity. This paper focuses on S-wave velocity and its dependency on strain-amplitude effect for porous media (Bentheimer sandstone) and reference media (aluminium). In this study we: (1) directly measured the particle displacement in the ultrasonic wave using a Laser Doppler Interferometry (LDI) and (2) measured the changes in P and S-waves velocities by variations of increasing amplitudes applied to a source transducer from 43 to 400 volts. We measured the velocity using a conventional ultrasonic method and linked the changes of velocity to the measured local strain in the wave which we measured by LDI. The study indicated that for the unconfined Bentheimer sandstone, increasing the local strain produced by an ultrasonic wave from (3.6) 10−7 to (5.7) 10−6 resulted in the S-wave velocity decreasing by 4.75%. Using the LDI technique we also investigated the strains at different points on the surface produced by an S-wave transducer.

Mechanism and sensitivity for broadband energy harvesting of an adaptive bistable point absorber wave energy converter

The adaptive bistable point absorber wave energy converter (WEC) concept proposed by Zhang et al. (Applied Energy 2018(228), pp. 450–467) is further investigated by exploring the underlying mechanism and sensitivity related to the broadband energy harvesting of this device. The mechanism can be explained in two different ways: (i) the broadband power capture is due to the fact that the adaptive bistable mechanism introduces both negative (at low wave frequencies) and positive (at high wave frequencies) stiffness to the device; and (ii) an inherent ‘phase control’ feature is observed especially at low wave frequency region. The variation of initial conditions of floater motion only has an observable influence at intermediate wave frequencies corresponding to chaotic response of the floater. The broad frequency bandwidth can be realized through different combinations of main and auxiliary springs' stiffness. The effects of wave amplitude on broadband energy harvesting can be categorized according to an optimum amplitude (if existing) into a gradual reduction for a larger wave amplitude and a quick drop for a smaller amplitude.

Bulk moduli and seismic attenuation in partially saturated rocks: hysteresis of liquid bridges effect

ABSTRACTA key task of exploration geophysics is to find relationships between seismic attributes (velocities and attenuation) and fluid properties (saturation and pore pressure). Experimental data suggest that at least three different factors affect these relationships, which are not well explained by classical Gassmann, Biot, squirt‐flow, mesoscopic‐flow and gas dissolution/exsolution models. Some of these additional factors include (i) effect of wettability and surface tension between immiscible fluids, (ii) saturation history effects (drainage versus imbibition) and (iii) effects of wave amplitude and effective stress. We apply a new rock physics model to explain the role of all these additional factors on seismic properties of a partially saturated rock. The model is based on a well‐known effect in surface chemistry: hysteresis of liquid bridges. This effect is taking place in cracks, which are partially saturated with two immiscible fluids. Using our model, we investigated (i) physical factors affecting empirical Brie correlation for effective bulk modulus of fluid, (ii) the role of liquids on seismic attenuation in the low frequency (static) limit, (iii) water‐weakening effects and (iv) saturation history effects. Our model is applicable in the low frequency limit (seismic frequencies) when capillary forces dominate over viscous forces during wave‐induced two‐phase fluid flow. The model is relevant for the seismic characterization of immiscible fluids with high contrast in compressibilities, that is, for shallow gas exploration and CO2 monitoring.

Numerical study of the wave-induced slamming force on the elastic plate based on MPS-FEM coupled method

Slamming is the phenomenon of structure impacting the water surface. It always results in the extremely high load on the structure. This paper is mainly concerned with the slamming force caused by the wave-plate interaction. In this paper, the process of solitary wave impacting onto the horizontal plate is simulated with the help of the moving particle semi-implicit and finite element coupled method (MPS-FEM). The MPS method is adopted to calculate the fluid domain while the structural domain is solved by FEM method. In the first series of simulations, the profiles of the solitary waves with various amplitudes, which are generated in the numerical wave tank, are compared with the theoretical results. Thereafter the interaction between the solitary waves and a rigid plate is simulated. The effects of wave amplitude, as well as the elevation of the plate above the initial water level, on the slamming force are numerically investigated. The calculated results are compared with the available experimental data. Finally, the interactions between the solitary waves and the elastic plate are also simulated. The effects of the structural flexibility on the wave-induced force are analyzed by the comparison between the cases with elastic and the rigid plate.

Effects of geometrical parameters on thermal-hydraulic performance of wavy microtube

Laminar flow and heat transfer characteristics of water flow through wavy microtubes (WMTs) with different values of wave length (l) and wave amplitude (a) are investigated experimentally. The tested WMTs are fabricated from copper microtube with the internal diameter of 914 μm. Experiments encompass the Reynolds numbers from 640 to 1950. In order to validate the experimental setup and create a base line for comparison, initial tests are also carried out for a straight microtube. The results show that both the heat transfer coefficient and the pressure drop are strongly affected by the studied geometrical factors. For a given Reynolds number, these parameters increase as the wave length decreases and the wave amplitude increases. However, in the studied ranges, the effect of wave amplitude is more than that of wave length. A considerable thermal-hydraulic factor of 1.78 is obtained for a WMT with l = 14.3 mm and a = 6 mm. Finally, correlations are developed to predict the Colburn factor and friction factor of water flow in the WMTs.

Flow characteristics and heat transfer performance of half-corrugated microchannels

The single-phase pressure drop and heat transfer performance of half-corrugated microchannels under a low Reynolds number (<900) are studied via three-dimensional numerical simulation and experiment. Comparative studies between half-corrugated and flat-bottom copper microchannels are analyzed to access the pressure drop and thermal performance enhancement. Compared with flat bottom microchannels, the half-corrugated mirochannels have a significant pressure drop diminution at a given Reynolds number. The wave length of the half-corrugated microchannels has a strong impact on the pressure drop, and the effect of wave amplitude can be neglected at a Reynolds number of 153–814 (flow speed of 0.2–1.2m/s). In addition, the heat transfer performance for half-corrugated microchannels is enhanced when the effective heat flux is beyond 150kWm−2. The flow behaviors of the microchannels with different half-corrugated structures are obtained from three-dimensional numerical simulations and are applied to explain the enhanced heat transfer and lower pressure drop. Moreover, a new parameter, the relative thermal-hydraulic performance index G, is defined to evaluate the overall performance of the half-corrugated microchannels. Compared with double sinusoidal corrugated microchannels, the half-corrugated microchannels possess excellent overall performance.

Effects of surface roughness on scratch resistance and stress-strain fields during scratch tests

A three-dimensional scratch model is proposed to numerically investigate the effects of surface roughness on the scratch resistance, stress concentration, residual stress and plastic deformation during scratch tests, with the help of the finite element method. Without loss of generality, the surface roughness of a coating is modelled by a sinusoidal function. The stress and plastic strain fields with various geometry parameters of roughness are obtained and discussed. In comparison with a smooth coating, the stress concentration, the residual stress, and the scratch resistance are significantly intensified and the plastic strain is increased by a factor of five in a corrugated coating, which may tremendously reduce the material performance. Consequently, the effects of surface roughness should not be ignored in both experiments and simulations. The geometry of roughness is determined by both the wave amplitude and wavelength, and their influences on the tribological behaviors can be significant. While existing experiments are only focused on the roughness in vertical direction (corresponding to the wave amplitude), the effects of wave amplitude and wavelength can be qualitatively different in many aspects and should be considered separately. The scratch depth and the area of contact region between the indenter and coating are not very sensitive to a moderate change in the wave amplitude, while they are reduced obviously with a rising wavelength. While the stress concentration increases monotonously with a rising amplitude, it becomes more complex and the decrease of wavelength can reduce the stress concentration in some cases. A growth in roughness by a large wave amplitude or a small wavelength leads to an enhancement on scratch friction coefficient and friction resistance, which is qualitatively consistent with experiments. The findings here contribute to a new way for quantitative evaluations of the effect of surface roughness and should be beneficial to modelling and simulation in scratch tests and also to the optimum designs on the surface coating for experiments.

Active Control of a Very Large Floating Beam Structure

In this paper, a novel boundary control method is investigated to suppress the vertical vibration of a very large floating structure (VLFS) with regular waves. The VLFS can be described as a distributed parameter system with partial differential equation (PDE). The proposed boundary controllers are developed based on Lyapunov's direct method to act on the upstream and downstream ends of the VLFS, respectively. Along with the suitable choice of control parameters, the proposed controllers could stabilize the vertical vibration of the VLFS subjected to regular waves. This study verifies the effectiveness of the proposed control methods to the VLFS. Then, the effects of wave amplitude and bending rigidity on the hydroelastic response of the VLFS are investigated.

Performance of nanofluid flow in corrugated minichannels heat sink (CMCHS)

Firstly, a brief review of previous works on the nanofluid flow in the minichannels heat sink (MCHS) is carried out. Then, the corrugated minichannels heat sink (CMCHS) and Al2O3/water nanofluid are proposed aiming more compact equipment and efficient cooling. The effects of geometrical parameters, nanoparticles weight fraction, and flow rate are investigated. Experimental tests are performed in a precise close loop setup with the ability to produce a constant heat flux. The results show that the CMCHSs can improve the heat transfer performance, albeit with a penalty in the pressure drop compared with the straight MCHS. It is also found that both the heat transfer enhancement and the pressure drop penalty augment, as the wave-length decreases and wave-amplitude increases. However, in the studied ranges, the effect of wave-amplitude is more than that of wave-length. The base temperature and convective thermal resistance are found to drop by decreasing the wave-length and by increasing the wave-amplitude. At a heater power of 50W, the lowest base temperature of 30.5°C is achieved by using a CMCHS of 20mm wave-length and 2mm wave-amplitude. It is detected that the thermal–hydraulic performance of CMCHSs improves, as the weight fraction of nanoparticles increases. Noticeable average performance factor of 2.68 is obtained for the simultaneous utilization of corrugated minichannels and Al2O3/water nanofluid inside the MCHS.

Natural convection flow of viscous fluid over triangular wavy horizontal surface

The purpose of this paper is to conduct a numerical study of natural convection flow along an irregular semi-infinite triangular wavy horizontal surface. Coordinate transformation is introduced to transform the boundary layer equations into a form which is more suitable for numerical integration. Implicit finite difference iterative numerical scheme is employed to produce solutions of the problem. Effect of wave amplitude is studied in detail. Important features of the flow field are discussed graphically in terms of skin friction, heat transfer rate, streamlines and isotherms. Although amplitude of the wavy surface play its role in enhancement in the heat transfer rate but it is found difficult to accomplish numerical computations for a>1.5. Thus, it is concluded that heat liberation is more effective in sinusoidal wavy surface than in triangular surface.

Heat transfer and flow characteristics in a channel with one corrugated wall

The present study numerically investigates the characteristics of three-dimensional turbulent flow and heat transfer in the channel with one corrugated wall heated with constant temperature by means of large eddy simulation. The corrugated wall is sinusoidal in the streamwise and spanwise directions. The Reynolds number in terms of bulk velocity and channel half-height is fixed at 2800 and the wave amplitude to wavelength ratio is varied in the range α/λ =0.01, 0.02, 0.04 in the streamwise direction and β/λ =0.01, 0.02, 0.04 in the spanwise direction. The results show that flow separation bubbles appear and near-wall streamwise vortices are generated with larger population in the upslope region of the bottom wall as wave amplitude increases. Compared with flat wall, the corrugated geometry increases the pressure coefficient and decreases the friction coefficient on the corrugated wall, and consequently increases the total drag coefficient owing to the increase of pressure coefficient, as expected, the heat transfer is higher. The waves in the spanwise direction converge the vortices into the trough along the streamwise direction and push them away from the bottom wall. Finally, thermal performance factor is defined and the effects of wave amplitude on the thermal performance are scrutinized.

Drag force control of flow over wavy cylinders at low reynolds number

Three-dimensional numerical simulations on the laminar flow around a circular cylinder with different diameter along the spanwise leading to a type of sinusoidal waviness, named wavy cylinder are performed at low Reynolds number. A series of wavy cylinders with different combinations of spanwise wavelength and wave amplitude are conducted at a Reynolds number of 100. The optimal range of wavelength and the effect of wave amplitude are obtained. The results show that the 3-D free shear layers from the cylinder are more difficult to roll up to vortex and hence the wake formation lengths of some typical wavy cylinders are larger than that of the circular cylinder and in some cases the free shear layers even do not roll up into vortex behind the cylinder. The mean drag coefficients of the typical wavy cylinders are less than that of a corresponding circular cylinder with the same mean diameter; also the fluctuating lift coefficients are reduced. The reduction of mean drag coefficient and fluctuating lift coefficient of wavy cylinder increases with the value of wavy amplitude. Furthermore, a typical wavy cylinder model at Re=150 is also simulated and found that the control of flow induced vibration by modifing the spanwise wavelength of cylinder has a relationship with the variation of Reynolds number.

Finit-element analysis of two-dimensional peristaltic flows. 2nd Report, Pressure-flow characteristics.

A numerical method employing a finite-element method is adopted for an investigation of peristaltic pumping in which both the wall-wave slope and the wave amplitude are large. Various peristaltic flows are calculated at moderate Reynolds number, and the effect of wave amplitude, wall slope, and the Reynolds number on the pumping performance is considered. It is shown that the effect of large wall slope makes the pressure rise at zero time-mean flow increase remarkably. The effect of fluid inertia makes the pressure rise decrease in case of small amplitude, while it makes the pressure rise increase for large amplitude.

Frequency Response in Regular Waves

The first report of the present investigation treats several methods of predicting the dynamic behaviour of an articulated column in regular waves. A straightforward solution is to integrate the equations of motion describing the behaviour of a column in waves to obtain timehistories of the motion. However, about thirty to forty periods of oscillations are required for the pitching motion of a column in regular waves to fall into a steady oscillatory state, in other words, for the transient oscillatory motion of a column to disappear. Besides, the phase lag of a column predicted by the direct integration of the equations of motion definitely differs from the experimental results. To the contrary, analytical methods proposed by the authors enables us to calculate the characteristics of frequency response of an articulated column directly and in a short time. Predicted frequency response determined by the analytical method excellently agrees with the experimental results. In addition, it is found that the effect of wave amplitude on the frequency response of an articulated column is negligibly small, as far as the results of present investigation are concerned.