Relative Motion Research Articles

Compact High-Zoom-Ratio Mid-Wavelength Infrared Zoom Lens Design Based on Particle Swarm Optimization

This paper presents an automated method for solving the initial structure of compact, high-zoom-ratio mid-wave infrared (MWIR) zoom lenses. Using differential analysis, the focal length variation process of zoom lenses under paraxial conditions is investigated, and a model for the focal power distribution and relative motion of three movable lens groups is established. The particle swarm optimization (PSO) algorithm is introduced into the zooming process analysis, and a program is developed in MATLAB to solve for the initial structure. This algorithm integrates physical constraints from lens analysis and evaluates candidate solutions based on key design parameters, such as total lens length, zoom ratio, Petzval field curvature, and focal length at tele end. The results demonstrate that the proposed method can efficiently and accurately determine the initial structure of compact MWIR zoom lenses. Using this method, a mid-wave infrared zoom lens with a zoom ratio of 50×, a total length of less than 530 mm, and the ratio of focal length to total length approximately 2:1 was successfully designed. The design validates the effectiveness and practicality of this method in solving the initial structure of zoom lenses that meet complex design requirements.

Transitory metamaterials based on symmetrical splitting of rotating squares

Abstract Materials exhibiting a negative Poisson's ratio, known as auxetic materials, have garnered significant interest due to their unique mechanical properties and potential applications. This paper introduces a new class of auxetic metamaterials based on modified interconnected rotating rigid squares, where each square can bifurcate into two or quadfurcate into four isosceles right triangles. The study explores three models categorized by their order of bifurcation or quadfurcation, ranging from purely rotating squares (zeroth order) to systems with sub-units exhibiting relative motion (first and second orders). Detailed analyses of the in-plane Poisson's ratio for these models are conducted, focusing on both infinitesimal and finite deformations. The results reveal that the proposed metamaterials demonstrate a transition in Poisson's ratio behavior, characterized either by discontinuity or continuous but non-differentiable Poisson’s ratio at the transitory state between deformation mechanisms. This transition highlights the potential of these metamaterials to exhibit tunable mechanical responses, offering insights into designing materials with customized properties for advanced engineering applications.

An Interpretation Method of Gas–Water Two-Phase Production Profile in High-Temperature and High-Pressure Vertical Wells Based on Drift-Flux Model

With the increasing demand for oil and gas, the depth of some vertical gas wells can reach 6000 m. At this time, the downhole fluid is in a state of high temperature and pressure, and interpretation of the production logging output profile faces the problem of inaccurate production calculations and difficulty judging the water-producing layer. The drift-flux model is usually used to calculate the gas–water two-phase flow. The drift-flux model is widely used to describe the two-phase flow in pipelines and wells because of its accuracy and simplicity. The constitutive correlations used in drift-flux models, which specify the relative motion between phases, have been extensively studied. However, most of the correlations are only extended by laboratory data of small pipe diameters at standard temperature and pressure and do not apply to high-temperature and high-pressure large-diameter gas wells. Therefore, we improved the distribution coefficient and drift velocity of drift-flux correlations in this study for high-temperature and high-pressure gas wells with large pipe diameters. Therefore, this study improved the distribution coefficient and drift velocity of the drift-flux correlations for high-temperature and high-pressure gas wells with large pipe diameters. In practical application, the coincidence rates of gas production and water production calculated by the new drift-flux model were 12.68% and 19.39%, respectively. For high-temperature and high-pressure deep wells, the measurement errors of production logging instruments are significant, and surface laboratory pipelines are challenging to configure and equip with actual high-temperature and high-pressure conditions. Therefore, this study used the method of numerical simulation to study the flow characteristics of the two phases of high-temperature and high-pressure gas and water to provide a basis for identifying the water layer. Combined with the proposed drift-flux correlations and the new method of determining the water-producing layer, a new method of production profile interpretation of high-temperature and high-pressure gas wells is obtained.

Dynamic similarity criteria for simple cases of buildings and structures aerodynamics

The work concerns dynamic similarity criteria of various phenomena occurring in hydraulics and fluid dynamics originally derived from ratios of forces and forces moments affecting these phenomena. The base of dynamic similarity criteria formulations and considerations is A.Flaga’s method and procedure for determining dynamic similarity criteria in different issues of fluid-solid interactions i.e. at different fluid-solid relative motions. The paper concerns the determination and analysis of dynamic similarity criteria for various practical problems encountered mainly in hydraulics and fluid dynamics at steady, smooth fluid onflow in front of a solid. Moreover, the cases of mechanically induced vibrations of a body in a stationary fluid moving with constant velocity in front of the body have been presented.

The Use of Air Pressure Measurements Within a Sealed Moonpool for Sea-State Estimation

To assess the viability of locations for wave energy farms and design effective coastal protection measures, knowledge of local wave regimes is required. The work described herein aims to develop a low-cost, self-powering wave-measuring device that comprises a floating buoy with a central moonpool. The relative motion of the water level in the moonpool to the buoy will pressurise and depressurise the air above the water column. The variation in air pressure may then be used to estimate the sea-state incident upon the buoy. Small-scale proof of concept tank testing was conducted at a 1:20 scale and at a larger 1:2.4 scale before a full-scale prototype was deployed at the Smartbay test site facility in Galway Bay, Ireland. A number of techniques by which full-scale sea states may be estimated from the pressure spectrum are explored. A successful technique, based on the average of multiple linear squared magnitude of the transfer functions obtained under different wave regimes is developed. The applicability of this technique is then confirmed using validation data obtained during the full-scale sea trials. While the technique has proven useful, investigation into potential seasonal bias has been conducted, and suggestions for further improvements to the technique, based on further calibration testing in real sea states, are proposed.

Perturbation Methods in Solving the Problem of Two Bodies of Variable Masses with Application of Computer Algebra

The classical many-body problem is not integrable, so perturbation theory based on an exact solution to the two-body problem is usually applied to investigate the dynamics of planetary systems. However, in the case of variable masses, the two-body problem is not integrable, in general, and application of perturbation theory is required to investigate it, as well. In the present paper, we use the perturbation theory to derive the differential equations determining the orbital elements of the relative motion of one body around the other. Two models of the perturbed aperiodic motion on conic and quasi-conic sections are considered and compared. Special attention is paid to the practically important case of small eccentricities, when the perturbing forces may be replaced by the corresponding power series expansions. The differential equations of the perturbed motion are averaged over the mean anomaly, and the evolutionary equations describing the behavior of the orbital elements over long periods of time are obtained for two models. Comparing the corresponding solutions to the evolutionary equations, we have shown that both models demonstrate similar behavior with regard to the secular perturbations of the orbital elements. However, the second model, based on the aperiodic motion on a quasi-conic section, is more appropriate for generalization to the many-body problem with variable masses. All the relevant symbolic and numerical calculations are performed with the computer algebra system Wolfram Mathematica.

Cosmological recession of the Galilean moons from Jupiter

It is suggested that local cosmological expansion occurs in the Jupiter satellite system. First, the relative mean motion accelerations of Io, Europa, and Ganymede are close to the current value of the Hubble‐Lemaître parameter. Second, the rate of orbital expansion of these moons, as determined by tidal resonance theory, is similar to the expansion rate of the Universe. These findings are in conflict with the widely held view that cosmological expansion does not operate at the local level.

Bound state of asymmetric pure-quartic solitons in motion.

In this Letter, we investigate the binding mechanism and motion dynamics of the bound state consisting of two pure-quartic solitons (PQSs) with unequal intensities and find that their movement occurs as an entity under the Raman self-frequency shift. By calculating the forces that induce the relative motion between the unequal PQSs, we derive the balanced conditions for maintaining a near-constant separation and the constant phase profile between them. The predictions are validated by the numerical simulations. Our work provides insights into the intrinsic features of symmetry-broken localized structures in nonlinear-dispersive systems, stimulating interest in asymmetric multi-soliton states with intriguing dynamics.

Interference effects in differential cross sections for two-electron transfer

AbstractDifferential cross sections for simultaneous capture of both electrons by alpha particles from helium targets are computed. Employed are several quantum-mechanical distorted wave four-body methods of first- and second-orders. The main focus is on the cross section sensitivity as a function of different perturbation interactions and scattering states. Two aspects are considered. One is for theories with the same perturbation interactions and different scattering states. The other is for theories with the same scattering states and different perturbation interactions. In this context, the interference effect on two levels is examined. One compares the yields from the internuclear potential and the interactions between nuclei and two electrons. The other contrasts the contributions from the channel states with and without the distorted waves generated by the relative motions of nuclei. Depending on the employed theory, differential cross sections can be strongly or mildly influenced by the variability in all the mentioned frameworks. The salient illustrations are reported at intermediate energies 180-900 keV for which the experimental data are available. It is found that the second-order theories are in much better agreement with the measured cross sections than the first-order theories.

Motion-deblurring ghost imaging for an axially moving target.

For lensless ghost imaging (GI) with thermal light, the axially relative motion constrained in the range of the system's depth of focus (DOF) can still cause image blurring because of a variable magnification. We propose a motion-deblurring GI system with pseudo-thermal light, which can overcome the resolution degradation caused by the axial motion. Both the analytical and experimental results demonstrate that high-resolution GI can be always obtained as long as the target's random motion range is smaller than the system's DOF, without using the prior information of motion estimation. We also show that the system's DOF can be extended by optimizing the geometrical shape of the laser spot on the rotating ground glass disk (RGGD). The imaging performance comparison between the proposed GI system and the corresponding lensless GI system is also discussed. This technique can promote the practical application of GI in the field of moving-target detection and recognition.

Measuring Relative Motion to Develop an Interface that Off-loads the Lower Limb

Abstract This investigation seeks to understand how the interfaces between fracture orthoses and the body affect the relative motion between the user and device. Excessive relative motion can inadvertantly load the fracture and prevent healing. Identifying interfaces that minimize relative motion will inform the designs of future fracture orthoses. Three types of interfaces were tested: a thigh corset, a sling that loaded the ischium, and a sling that loaded the patellar tendon. Eighteen able-bodied participants were fitted with an adjustable Interface Testing System (ITS) that redirected loads away from the foot and lower leg to more proximal parts of the body using different combinations of the three interfaces. A video motion capture system measured the relative motion between the ITS and the participants while varying the type of interface, load through the ITS, and tightness of the thigh corset. Average relative motion varied from 1.6-6.5 cm across all conditions. The thigh corset combined with either the ischial sling or patellar tendon-bearing sling allowed the least relative motion of the interface conditions tested. However, the combinations differ in the sagittal profile they create for the user as well as the breadth of injuries they can treat. All of these factors need to be considered in the design of future fracture orthoses.

Seismic Analysis of Irregular Building Subjected to Pounding

Earthquakes have always been a source of great devastation for humanity. With the fast growth of metropolitan cities, land limitation has become a critical issue, resulting in the construction of high-rise buildings very close to each other. Such buildings are prone to seismic pounding. During earthquake, the buildings vibrate out of phase and at rest separation is deficient to accommodate their relative motions. It can be prevented by ensuring safe separation distances between buildings. However, achieving the necessary separations is often not feasible in metropolitan areas due to high land values and limited land availability. Different combinations of 12-storey and 8-storey buildings with varying plan irregularities were considered for the analytical study using ETABS software. The pounding effect depends on building characteristics, ground motion characteristics and soil structure interaction. The parameters like displacement, impact force, and storey shear were determined.

Generalization Process of the Integrated Mathematical Model Created for the Development of the Production Geometry of Complicated Surfaces

Computer modelling of technical constructions is increasingly carried out using software that includes more detailed knowledge, which requires an increase in the level as well as an expansion of the scope of the geometric knowledge. A significant part of motion transmission mechanisms are worm drive pairs, for which the separation of the parts dealing with the theoretical and practical problems found in the literature can be experienced in numerous instances. Due to the different technical features, in many cases the helical surfaces are not designed and manufactured in a geometrically correct way, or the best solution is not the compulsory chosen. The geometric model describing the production process of the worm surfaces provides the basis for examining the deviation between the surface mathematically determined by the designer and the surface produced. An integrated mathematical kinematic model was developed for the production geometrical analysis of the elements of cylindrical and conical worm gear drive pairs for machining with a traditional thread grinding machine, which causes a serious pitch fluctuating error among several other problems in the case of machining the conical worm. Modelling of the production process of surfaces and the simultaneous study of the manufacturing errors is basically performed with the toolbox of descriptive geometry, including the use of the projective invariants. Knowing the inheritance of the invariants of projective geometry, the aim was the mathematical generalization of the integrated model and the creation of a projective relationship between the reference surfaces of conical and cylindrical spiral surfaces. As a result, the improved constructive geometric model was created, in which the method of analytically creating the projective geometric relationship between the reference surfaces of conical and cylindrical helicoid surfaces has been described for the first time in this article. This procedure is considered the most important result of the present article. Another significance of the further development presented is that during production of the conical helicoid surface, the thread pitch fluctuation has been eliminated. The results obtained, consisting of an improved geometric model, lead to a new geometry of the technological environment regarding the relative position of the cutting tool and the workpiece as well as the relative motion between them.

A new reciprocating straight propulsion for high propulsive hydrodynamic efficiency

The majority of underwater vehicles currently use screw propellers as propulsion method. Despite screw propellers are being promoted to increase the efficiency through better designs and technologies, the circumferential flow caused by the rotation of screw propeller results in wasted energy. This paper proposes an ideal reciprocating straight propulsion paradigm that eliminates this waste by implementing straight backward thrust based on a foldable mechanism. This mechanism can implement a maximized propulsion during the propelling stroke and a minimized resistance during recovery by folding and unfolding the mechanism, which can be adjusted passively via the relative motion between the thruster mechanism and water avoiding using sensors and actuations. This principle makes the reciprocating straight propulsion simple and reliable to be achieved in practice. Besides, a modularized propulsion system with four identical independently thrusters based on the proposed mechanism was proposed, achieving various motion modes in underwater vehicles. The proposed propulsion mechanism was theoretically analyzed and verified through simulations and prototype tests. In mooring tests, the thrust provided by the proposed mechanism is similar to the simulation results. The propulsion performance indicator of an underwater vehicle with the proposed propulsor reached 66 %. The mechanism could turn even with one-sided propulsion.

Single-pixel imaging of a moving target using only Hadamard patterns for simultaneous localization and reconstruction

Relative motion degrades the image quality of single-pixel imaging (SPI) while imaging the moving targets. Motion compensation strategies are effective in improving the imaging quality. However, the existing methods often require the use of additional patterns for target localization, which increases the sampling time. What we believe is a novel motion compensation method for SPI with Hadamard geometric moments is proposed based on the sparsity of geometric moment patterns in the Hadamard domain. Parts of Hadamard patterns are used for localization and reconstruction, simultaneously, thus target localization does not require additional patterns. In addition, our method effectively improves the localization accuracy in large-scale scenes due to the absence of binarization error while enhancing the quality of the reconstructed images. Many simulations and experiments are performed to verify the accuracy and effectiveness of the proposed method and the results show that the proposed SPI system improves the imaging quality (with lower MSE and higher PSNR) while imaging moving targets in 512 × 512-sized scenes.

Hydrodynamic analysis of floating photovoltaic system constrained with rigid connectors

With the expansion of floating photovoltaics, rigid connectors offer advantages over polyester ropes by reducing the relative motion of floats and simplifying the layout of the connection system. However, the overall stability and safety of the floating photovoltaic system may be compromised if a wave crest occurs at the connection point of the rigid connector during motion. Furthermore, the rigid connectors with different degrees of freedom significantly impact the motion of the floats and their connection loads. In this study, three types of single-rod rigid connector models with varying constraints are established through numerical simulation to explore the feasibility of applying single-rod rigid connectors with different degrees of freedom in photovoltaic systems. Based on their degrees of freedom, these connectors are classified as cardan, purely rigid, and hinged. An analysis of float motion and connector loads in two-floating, four-floating, and eight-floating systems shows that as the number of floats increases, the axial distance between them decreases, resulting in more intense motion. Despite this, the eight-floating system maintains a certain safety distance. The maximum load on the connectors occurs in the middle of the multi-floating system, and releasing degrees of freedom can help mitigate some of the load effects.

Pr-Ge-Ne : Efficient Encoding of Pervasive Video Sensing Streams by Pruned Generative Networks

While video sensing, performed by resource-constrained pervasive devices, is a key enabler of many machine intelligence applications, the high energy and bandwidth overheads of streaming video transmission continue to present formidable deployment challenges. Motivated by the recent advancements in deep learning models, this paper proposes the usage of a Generative Network-based technique for resource-efficient streaming video compression and transmission. However, we empirically show that while such generative network based models offer superior compression gains compared to H.265, additional DNN optimization mechanisms are needed to substantially reduce their encoder complexity. Our proposed optimized system, dubbed Pr-Ge-Ne , adopts a carefully pruned encoder-decoder DNN, on the pervasive device, to efficiently encode a latent vector representation of intra-frame relative motion, and then uses a generator network at the decoder to reconstruct the frames by overlaying such motion information to ‘animate’ an initial reference frame. By evaluating three representative streaming video datasets, we show that Pr-Ge-Ne achieves around \(6\) - \(10\) fold reduction in video transmission rates (with negligible impact on the accuracy of machine perception tasks) compared to H.265, while simultaneously reducing latency and energy overheads on a pervasive device by \(\sim\) 90% and 15-50%, respectively.

Studies of stationary features in jets: BL Lacertae

Context. High-resolution very long baseline interferometry observations have revealed a quasi-stationary component (QSC) in the relativistic jets of many blazars, which represents a standing recollimation shock. VLBA monitoring of the BL Lacertae jet at 15 GHz shows the QSC at a projected distance of about 0.26 mas from the radio core. Aims. We study the trajectory and kinematics of the QSC in BL Lacertae on sub-parsec scales using 15 GHz VLBA data of 164 observations over 20 years from the MOJAVE program and 2 cm VLBA Survey. Methods. To reconstruct the QSC’s intrinsic trajectory, we used moving average and trajectory refinement procedures to smooth out the effects of core displacement and account for QSC positioning errors. Results. We identified 22 QSC reversal patterns with a frequency of ∼1.5 per year. Most reversals have an acute angle < 90° and a few have a loop-shaped or arc-shaped trajectory. Where observed, combinations of reversals show reversible and quasi-oscillatory motion. We propose a model in which a relativistic transverse wave passes through the QSC, generating a short-lived reverse motion, similar to the transverse motion of a seagull on a wave. According to the model, relativistic waves are generated upstream and the reverse motion of the QSC is governed by the amplitude, velocity, and tilt of the wave as it passes through. The apparent superluminal speeds of the QSC (∼2 c) are then due to the relativistic speed of the jet’s transverse wave (< 0.3 c in the host galaxy rest frame) combined with the relativistic motion towards the observer. The measured superluminal speeds of the QSC indirectly indicate the presence of relativistic transverse waves, and the size of the QSC scattering on the sky is proportional to the maximum amplitude of the wave. We find that most of the transverse waves are twisted in space. In the active state of the jet, the directions of the twisting waves are random, similar to the behaviour of the wave in a high-pressure hose, while in the jet stable state, the wave makes quasi-oscillations with regular twisting. Conclusions. The study of QSC dynamics in BL Lac-type blazars is important for evaluating the physical characteristics of relativistic transverse jet waves. The latter have important implications for jet physics and open up possibilities for modelling the physical conditions and location in the jet necessary for the excitation of relativistic transverse waves.

Investigation of excellence in Nd-YAG laser cutting of Al6061-T6 thin sheet using GRA coupled with PCA

Abstract Cutting flying materials with minimum deviations and metallurgical damages is always preferred for airframe work in aircraft industries. In the present scenario, the laser cutting process has become the preferred choice for fine cutting of sheet materials with close tolerances. This paper reports the investigation of excellence in pulsed laser cutting of Al-alloy (Al6061-T6) sheet. Five quality characteristics for quantifying the dimensional accuracy (i.e., kerf width and deviation at the top and bottom side) and metallurgical damage (i.e., heat-affected zone) have been considered for the proposed work. These characteristics depend on the lamp current, laser parameters (pulse width and frequency), and relative motion between the sheetmetal and laser source. The experiments were performed using the design of the experiments technique. Further, the results of laser cutting have been optimized by using grey relational analysis (GRA) coupled with principal component analysis (PCA). The application of GRA-PCA is found capable of optimizing all five process responses at a time. The unevenness within the kerf is reduced by 22% and 32% at the top and bottom sides, respectively.

Counterintuitive properties of relativistic relative motion for accelerated observers

Counterintuitive properties of relativistic relative motion for accelerated observers