Wave Deformation Research Articles

Wavefront Control Strategies for Large Active Thin Shell Primaries with Unimorph Actuators

This paper presents various aspects of the wavefront control strategies for an ultra-lightweight composite reflector made of polymers for the large primary of a space telescope, and the shape control is made by a set of patterned unimorph strain actuators attached to the reflector. It starts with an analytical investigation of the mechanical behaviors of a strain-actuated curved shell, resulting in the accurate prediction of typical features, such as the damped wave deformation at the transition between electrodes and the limited morphing amplitude of a “print-through” actuation, which indicates that the curvature-induced rigidity deteriorates the performances of the forming accuracy of the active reflector and the morphing stroke of the actuators. The morphing capabilities are evaluated with both petal-like segmented and monolithic configured reflectors by numerical tests on forming target shapes of Zernike modes with various patternings of electrodes, and the structural dynamics are examined. Finally, a compound control strategy is proposed, which uses a deformable relay mirror to compensate for the residual surface error corrected partially by the active unimorph primary mirror, showing a great relaxation of the shape error budget of the thin-shell primary, especially for on-axis observation.

Evaluation of CFOSAT Wave Height Data with In Situ Observations in the South China Sea

The wave spectrometer operated by the China–France Oceanography Satellite (CFOSAT) can provide global ocean wave observation data. Although a lot of work on calibration and verification has been carried out in the open oceans dominated by swells, the quality of the data in the relatively enclosed sea area with complex terrain still lacks sufficient examination. The objective of this study is to assess the performance of the significant wave height data of the CFOSAT in the South China Sea (SCS), a unique sea area characterized by semi-enclosed basin and multi-reef terrain, and to recognize the environmental factors affecting the data quality. Compared against the long-term observations from five mooring or buoy sites, we find that the data is well performed in the relatively open and deep areas of the SCS, with an average correlation coefficient as high as 0.87, and a low average root-mean-square error of 0.47 m. However, the combined effects of complex topography, monsoons, and swell proportion variation will affect the performance of data. In the southern deep areas, the waves may be affected by a large number of dotted reefs, leading to wave deformations and energy dissipation in different seasons. In the northern nearshore areas, waves tend to be sheltered by the land or distorted by the shallow topography effects. These processes make it difficult for the swell to fully develop as in the open oceans. The low proportion of swell is a disadvantage for the CFOSAT to correctly observe the wave data and may lead to possible errors. Our results emphasize the importance of more verification when applying the CFOSAT data in certain local seas, and the necessity to adjust the algorithm of inverting wave spectra according to specific environmental factors.

The Large Earthquakes and Deformation Waves as Possible Triggers of Climate Warming in the Arctic and Glacier Destruction in the Antarctic

The Large Earthquakes and Deformation Waves as Possible Triggers of Climate Warming in the Arctic and Glacier Destruction in the Antarctic

Силовой расчет сдвоенного механизма параллельных кривошипов

Design and layout capabilities of gearboxes with flexible and rigid links created on the basis of dual mechanisms of parallel cranks (wave gears with external deformation wave generators of the crank-planetary gearboxes and combined planetary-wave mechanisms) most fully satisfy requirements to the transmission mechanisms of the system automatic control of the antenna drives. Methods for calculating geometric characteristics, power interaction of elements, evaluation of the main quality indicators of the wave gear with external deformation wave generators and recommendations for their use are practically missing in the technical literature (except for works of scientists from the Department of Theory of Mechanisms and Machines, Bauman Moscow State Technical University). Therefore, studies aimed at creating methods of calculating and designing these mechanisms for special drives of the automatic control systems are important. The paper describes technique of power calculation of the double mechanism of the wave gear parallel cranks with the wave external deformation generator making it possible to competently design these drives.

Acoustic Black Holes in a Spinning Beam

Abstract Through creating slow waves in structures, Acoustic Black Hole (ABH) shows promise for potential vibration control applications. However, it remains unclear whether such phenomena can still occur in a structure undergoing high-speed spinning, and if so, what is the interplay among various system parameters and what are the underpinning physical mechanisms. To address this issue, this work establishes a semi-analytical model for a spinning ABH beam based on Euler-Bernoulli beam theory under the energy framework. After its validation, the model is used to reveal a few important vibration features pertinent to the spinning ABH beam through examining its dynamics, modal properties and energy flow. It is shown that the spinning-induced centrifugal effects generate hardening effects inside the structure, thus increasing the overall structural stiffness and stretching the wavelength of the modal deformation of flexural waves as compared with its counterpart at still. Meanwhile, energy flow to the ABH portion of the beam is also adversely affected. As a result, the ABH-induced overall damping enhancement effect of the viscoelastic coating, as observed in conventional ABH beam at still, is impaired. Nevertheless, the study confirms that typical ABH features, in terms of wave compression, energy trapping and dissipation, though affected by the spinning effects, are still persistent in a high-speed spinning structure. This paves the way forward for the embodiment of ABH phenomena in the design of high performance rotating mechanical components such as turbine blades.

Mechanics of biconcave red blood cells deformed by acoustic tweezers

The deformation of biconcave red blood cells (RBCs) in a fluid environment driven by ultrasonic standing waves is studied theoretically and numerically. The cell contains homogeneous cytosol enclosed by a thin biological membrane. The cell membrane is modeled as a hyperelastic thin shell whose enclosed volume is assumed to be preserved to ensure osmotic equilibrium. Regarding acoustic deformation, the acoustic induced force acting on the cell membrane is calculated based on the acoustic radiation stress theory. The equations governing the interaction of the cell deformation and acoustic wave propagation are then numerically implemented in an axisymmetric finite element framework. The simulation results show that when the biconcave red blood cells are trapped at the pressure node of the acoustic standing wave, they gradually transform into an oblate disc shape with the increase of the acoustic input. Parametric studies are performed to systematically investigate the effects of cell mechanical properties and acoustic wavelength on cell deformation. Given that the mechanical properties of RBCs play an important role in disease development and mechanotransduction, this work is helpful to diagnose RBC-related diseases and study mechanotransduction using acoustic deformation technique.

Application of swarm intelligence for dynamic properties of moored floating structures using two-dimensional fluid dynamic program

This paper presents a numerical investigation into interactions between oscillatory waves and moored floating structures by through applying Swarm Intelligence (SI). The effects of small and large incident waves placing a force on the obstacles were studied using two floating structures composed of a rectangle and a cage kind with taut-moored and slack-moored situations. The aforementioned problem was reduced to solve systems of sparse-nonlinear equations for surge, heave, and pitch responses, as well as mooring forces considering that there is a distorted wave motion due to the presence of the movable obstacle boundary. The particle swarm optimization (PSO) algorithm is proposed here to provide insight into computational intelligence factors affecting calculation results and efficiency. Besides that, a computational fluid dynamic (CFD) program is based on a full Navier-Stokes solver. A series of numerical examinations for selected wave heights and wavelengths including a set of optimization procedures have been taken into account in the evaluation of formulated objective function, F, where the best potential solution is computed at each computational step. Meanwhile, a collection of empirical benchmarks were also developed based on reported measurements in the literature to provide sound empirical support for the theoretical findings. The results show that the optimization method exhibits a favorable convergent behavior (F≈0), where the computed results agree well with the measurements in terms of mean amplitudes of the surge, heave, and pitch responses and peak values of mooring-line tensions. The approach would firmly converge on benchmarks with improved computational steps of 18,321 running for 20.1 wave cycles in the case of the taut-moored rectangular structure. For the slack-moored cage, a satisfactory convergence was achieved using a series of data calibrations into an algorithm that took 27,976 iterations and 24.5 s to complete. Furthermore, CFD captures of wave deformations, dynamic forces, and streamlines were able to qualitatively corroborate the results.

Structural changes in steel during hardening by deformation wave

The article presents results of study possibility of hardening of high-manganese steel X120Mn12 by a deformation wave in the process of wave strain hardening (WSH). Features of the method is possibility of using shock waves for plastic deformation, which significantly expands the technological capabilities for formation of a hardened surface layer. The dominant design and technological parameters of the hardening treatment are established, which have the main influence on the microstructure and hardness of the hardened surface layer. Possibility of a significant increase in hardness and depth of hardened surface layer is established. The depth of hardened layer can reach 6-8 mm, and the hardness can be increased by more than three times. Microstructural analysis showed no cracks. The obtained results of conducted research can be used to develop a technology for strengthening the deformation wave of various heavy-loaded parts made of high-manganese steel.

Investigation of abrasive wear after combined hardening by deformation wave and heat treatment

The article describes a new method of combined hardening, using sequential processing by wave strain hardening (WSH) and heat treatment (HT). The possibility of increasing the hardness of the surface layer by the proposed method while maintaining the impact strength of the material at an acceptable level has been established using the example of steel 65G. The results of studies of operational properties (abrasive wear resistance) of samples after hardening by combined technology are presented. Technological recommendations are given for the choice of hardening modes, which makes it possible to increase the mechanical properties of the material and reduce the abrasive wear of samples made of 65G steel. The proposed technology can be applied to the processing of heavily loaded machine parts operating in aggressive conditions and significant shock loads.

Longitudinal waves in the walls of an annular channel filled with liquid and made of a material with fractional nonlinearity

Purpose of this paper is to study the evolution of longitudinal strain waves in the walls of an annular channel filled with a viscous incompressible fluid. The walls of the channel were represented as coaxial shells with fractional physical nonlinearity. The viscosity of the fluid and its influence on the wave process was taken into account within the study. Metods. The system of two evolutionary equations, which are generalized Schamel equations, was obtained by the two-scale asymptotic expansion method. The fractional nonlinearity of the channel wall material leads to the necessity to use a computational experiment to study the wave dynamics in them. The computational experiment was conducted based on obtaining new difference schemes for the governing equations. These schemes are analogous to the Crank–Nicholson scheme for modeling heat propagation. Results. Numerical simulation showed that over time, the velocity and amplitude of the deformation waves remain unchanged, and the wave propagation direction concurs with the positive direction of the longitudinal axis. The latter specifies that the velocity of the waves is supersonic. For a particular case, the coincidence of the computational experiment with the exact solution is shown. This substantiates the adequacy of the proposed difference scheme for the generalized Schamel equations. In addition, it was shown that solitary deformation waves in the channel walls are solitons.

Nonlinear generation of sound and mean pressure drop in shock–shear interaction

Interactions of shear fluctuations with shock waves are ubiquitous in high-speed flow applications from scramjet propulsion to cosmic events like supernova explosions. They also serve as fundamental building blocks for the study of shock–turbulence interaction. In this work, we study the nonlinear effects in pressure arising due to the interaction of a normal shock with a two-dimensional shear wave. It employs the weakly nonlinear framework (WNLF) developed recently for vorticity amplification by Thakare et al. [“A weakly nonlinear framework to study shock–vorticity interaction,” J. Fluid Mech. 933, A48 (2022)]. The analysis includes the effect of intermodal interactions that is neglected in the widely used linear interaction analysis (LIA) of shock–turbulence interaction. It is found that the deformation of the shock wave and the fluctuation mass flux normal to the shock contribute to the dominant physical mechanisms responsible for the observed nonlinearities. Interestingly, the WNLF predicts a drop in mean pressure behind the shock due to a second-order intermodal interaction, which is consistent with the well-established results by Lele [“Shock-jump relations in a turbulent flow,” Phys. Fluids A 4, 2900–2905 (1992)] at low Mach numbers and brings out additional effects of shock deformation that are important at higher Mach numbers. We extend the WNLF to three-dimensional interaction of homogeneous isotropic turbulence with a normal shock. Comparison with existing direct numerical simulation data shows good agreement for low turbulent Mach numbers, which is a significant improvement over the prediction capability of LIA. We also compute the dilatation fields from WNLF and use them to distinguish between the acoustic and non-acoustic components of the second-order pressure fluctuations generated by the shock wave.

Two Phases of Crustal Shortening in Northeastern Tibet as a Result of a Stronger Qaidam Lithosphere During the Cenozoic India–Asia Collision

AbstractAlthough two phases of Cenozoic crustal deformation in the Qilian Shan thrust belt of northeastern Tibet has been documented, their dynamic causes remain unclear. To address this issue, we investigate whether the mechanical strength of the Qaidam Basin, which is located between the Eastern Kunlun Range and the Qilian Shan, was a controlling factor for the observed deformation history by performing 2‐D thermal–mechanical simulations. Our models consider the division of the Tibetan terranes (i.e., Qilian arc, Kunlun‐Qaidam, Songpan‐Ganzi, Qiangtang, and Lhasa, from north to south) bounded by suture zones. Simulation results show that weak suture zones in central Tibet can lead to peeling off and sinking of the mantle lithosphere beneath the Qiangtang and Songpan–Ganzi terranes. After lithospheric delamination, varying north‐south width, thickness and strength of the Qaidam crust creates three end‐member model results: (a) the mantle lithosphere of the Lhasa terrane delaminates while the mantle lithosphere beneath Eastern Kunlun‐Qaidam terrane and the Qilian Shan thrust belt (KQQ) remains undeformed, (b) the Lhasa mantle lithosphere moves northward while the KQQ mantle lithosphere subducts southward, and (c) the Lhasa mantle lithosphere moves northward while lithospheric thickening occurs north of the Qaidam Basin. Our simulations show that pre‐existing weaknesses in northeastern Tibet can be activated and deformed shortly after the onset of collision, and a second wave of deformation sweeps across northeastern Tibet after lithospheric delamination in northern Tibet.

Possible Seismogenic-Trigger Mechanism of Activation of Glacier Destruction, Methane Emission and Climate Warming in Antarctica

A seismogenic-trigger mechanism is proposed for the rapid activation of the destruction of cover and shelf glaciers in West Antarctica at the end of the 20th and the beginning of the 21st centuries, accompanied by the release of methane from the underlying hydrate-bearing sedimentary rocks and consequent rapid climate warming. This mechanism is associated with the action of deformation waves in the lithosphere-asthenosphere system, resulting from the strongest earthquakes occurring in the subduction zones surrounding Antarctica – Chile and Kermadec-Macquarie. Disturbances in the lithosphere are transmitted over long distances of the order of 3000 km, and the additional stresses associated with them, which come to Antarctica several decades after earthquakes, lead to a decrease in the adhesion of glaciers to underlying rocks, accelerated sliding of glaciers and the development of faults in them. This process, in turn, results in a reduction of pressure on the underlying sedimentary layers containing gas hydrates, which lead to methane emission and climate warming. The considered hypothesis leads to the conclusion that in the coming decades the processes of destruction of glaciers and climate warming in Antarctica will speed-up due to an unprecedented increase in the number of strongest earthquakes in the subduction zones of the South Pacific Ocean in the late 20th and early 21st centuries.

Creation of heterogeneously modified structure by wave deformation hardening methods

The article describes the possibilities of formation of a heterogeneously modified structure by wave deformation hardening. The results of studies of wave deformation hardening both separately and as part of a combined treatment before chemical-thermal treatment and strengthening heat treatment are presented. Recommendations on hardening modes that allow to form a heterogeneously modified structure with both high hardness and plasticity are given.

Numerical Simulation on Reduced Runup Height of Solitary Wave by Fixed Submerged and Floating Rectangular Obstacles

The wave runup height is one of the most important parameters for affecting the design of coastal structures such as dikes, revetments, and breakwaters. In this study, SWASH (Zijlema et al., 2011), a non-hydrostatic pressure numerical model, was used to analyze the effect of reducing The wave runup height of solitary waves by submerged and floating rectangular obstacles. It was confirmed that the SWASH model reproduces the propagation, breaking, and runup of solitary waves quite well. In addition, it was confirmed that the wave deformation of the solitary wave by submerged and floating rectangular obstacles was well reproduced. Finally, we conducted an examination of the effect of reducing the runup height of submerged and floating rectangular obstacles. Reduced runup heights are calculated and the characteristics of runup height reduction according to the dimensions of the obstacle were analyzed. The energy attenuation effect of the floating obstacle is greater than the submerged obstacle, and it is shown to be more effective in reducing the runup height.

Research on the Dynamic Behaviors in the Sliding Friction of Silicone

With the promotion of soft viscoelastic materials in the field of flexible bionic robots, the behavior of sliding friction between soft viscoelastic materials and rigid materials such as metals has attracted great attention. In this study, the research object was silicone, and a research method combining a dynamic force testing technique and a non-contact optical testing technique for deformation and strain was proposed to study the frictional behavior of silicone and the effect of the tooth structure surface on the sliding friction. We analyzed the temporal changes in the friction force for different loads, the dynamic characteristics of large deformation and micro-strain on the front side (define the contact surface as the bottom surface) of the silicone. The results showed that within a certain range, the sliding friction coefficient of the silicone increased monotonically with increasing load, and there were stick-slip and deformation waves during the relative motion. The larger the load was, the faster the deformation wave propagated, and the tooth structure surface had sliding friction anisotropy.

PROPELLER SHAFTING DYNAMICS UNDER IMPULSE ACTION

Propeller shafts and countershafts are bent quite often on sea and river vessels. The cause of the curvature is a strong load on this node of the ship’s power plant. In addition to bending, the shafting experiences longitudinal and transverse loads with a dynamic and static component. A large number of scientific papers have been devoted to the study of the dynamics of the propeller and shafting. However, the problem has not been completely solved, and the increase in damages during the shafting operation and its intensive wear only confirm the relevance of further research in this direction. The aim of the work is to determine the dynamic forces in the shafting, which occur during impulse action due to the propeller impact on the ice. A model of a two-stage elastic rod with inert disks at the ends is presented in the paper. It allows considering different situations of dynamic impact on the shafting and propeller. The following design features such as different stiffness of the shaft sections, different speed of elastic waves of deformation (different densities and modules of elasticity on the shaft sections), reduced inertial load from the moving parts of the drive, can be taken into account in the model. It is concluded that the frequency of the main form of oscillations mainly depends on the inertial loads concentrated at the ends and the shaft rigidity. The proposed simplified model of the inertialess shaft makes it possible to determine the angles of rotation of the shaft sections with sufficient accuracy. For different sections of the stepped shaft, the dynamic torque coefficient can differ significantly.

Spatiotemporal characterization of wave-augmented varicose explosions

The onset of three-dimensional instabilities during “Wave-Augmented Varicose Explosions” (WAVE) liquid disintegration is characterized for an annular flow of a shear-thinning slurry that is fed into a central transonic steam flow. Droplet production inside the nozzle is enhanced by ligaments radially flicking up from the slurry wave into the steam flow with radial:axial velocity ratios exceeding 0.5. The wave also leaves residual ligaments in its wake, which facilitate further disintegration. After birth, a wave spends 80% of the wave cycle period building up to peak height at the nozzle exit. Two effervescent mechanisms are provided as 1) steam penetrates the rising wave and surface deformation allows steam fingers to force through, and 2) the wave collapses on itself, trapping steam. Baroclinic torque drives the development of Rayleigh-Taylor (RT) instabilities and reaches values on the order of 1×1013 1/s2. Both RT and Kelvin-Helmholtz instabilities are self-amplified in a viscosity-shear-temperature instability cycle because the slurry is non-Newtonian. Velocities inside the nozzle (wave formation region) are generally azimuthally similar (two-dimensional), but those outside the nozzle (radial bursting region) are azimuthally uncorrelated (three-dimensional). Inter-variable correlations show significant decoupling of quantities beyond the nozzle exit, and local strain rate fluctuations were found to correlate particularly well with bulk system pulsation. Although adaptive mesh refinement (AMR) can provide computationally efficient resolution of gas–liquid interfaces, this technique produced different results than an equivalent non-dynamic mesh when modeling WAVE. Gradients were particularly affected by AMR, and turbulent kinetic energy showed differences greater than 150% outside the nozzle.

Numerical Investigation of Ship Waves and Associated Hydrodynamics Over a Sloping Bed With a Non-Hydrostatic Model

Abstract The ship waves and related hydrodynamics over a sloping bed are investigated numerically in this paper, and we aim to clarify the characteristics of ship wave deformation and its hydrodynamic effects. Laboratory experiments are performed with a self-propelled ship model to produce various wave conditions over a sloping bed in the water flume, providing the datasets for validation works of numerical simulations. With the implementation of model sensitivity analysis, numerical calculations of ship-induced waves and flow velocities are completed using the non-hydrostatic model in XBeach and compared against experimental measurements. The results show that the model is not only able to calculate primary and secondary waves well, but also the ship-induced near-bed velocity when ship waves are prominent in the water flume. Further numerical investigations of ship wave transformation and associated hydrodynamic effects are conducted over a sloping bed under different ship speed conditions. The ship wave height and run-up variations along the cross-shore transect clearly indicate the wave energy dissipation due to breaking and bottom friction. The ship-induced flow velocities are found to be mainly contributed by the low-frequency primary waves in our numerical experiments.

Кинематика волновых зубчатых передач с генератором волн внешнего деформирования

The development of automatic control systems, tracking systems and industrial robotics requires the creation of new generation drive systems with high efficiency, kinematic accuracy, reliability, durability with small axial and radial dimensions and weight. To implement tracking systems with power differentials, transmission mechanisms with two degrees of freedom are required to provide the transformation and summation of two movements of drive motors into the required movement of the drive output shaft. These requirements in single-channel tracking systems are well met by strain wave gears (SWG) with low-inertia disk and ring wave generators. They allow for wide layout possibilities, the ability to route cables through the hollow central shaft of the drive, high torsional rigidity and low moments of inertia, which are in the range of 250 to 400 times less than those of cam wave generators, thus ensuring high drive speed. There are practically no publications, except domestic ones, devoted to the study of SWG with ring wave generators. This scientific direction of research is carried out at the Bauman Moscow State Technical University. Structural schemes of SWG with ring generators of external deformation waves are considered, the features of the kinematics of these gears are studied, and recommendations for improving their quality indicatorsare proposed