Axial Acceleration Research Articles

ESTIMATION OF THE TOLERANCE AREA FOR CORRECTION PARAMETERS IN INDUCTION ACCELERATION SYSTEMS

he issues of formalization and numerical solution of the problems of calculating tolerances for the parameters of corrective elements for a linear induction acceleration system, which are directly related to the performance of a real object, are considered. The key moments of the dynamics of the transverse motion of particles for a specific structure of a linear induction system of acceleration are studied for given values of energy for each of the periods of the resonator. The presence of parasitic electric and magnetic fields, which arise as a result of particle displacement relative to the accelerator axis and change the transverse components of the pulses, is taken into account. The original difference model of the induction system has been transformed into a linear form. To formulate the problem statements for calculating tolerances, the scatter vectors of phase coordinates and tolerances for the correction parameters are introduced. In order to apply the methods of practical stability, the set of tolerances for the parameters of the corrective elements is given in the form of an ellipsoid. Provided that the initial displacements of the transverse coordinates relative to the axis of the accelerator are known constant values, the structured tolerance region was estimated under known linear restrictions on the spread of the phase coordinate vectors. Due to the developed algorithms of practical stability, the original problem of calculating tolerances is reduced to the problem of finding the maximum of a linear form on an ellipsoid. Some important types of restrictions on deviations of phase coordinates concerning the estimation of tolerances on the parameters of the first correction element and the number of particles are investigated. For the case of non-linear dynamic constraints on the spread of the phase coordinate vector, it is proposed to approximate the convex closed set by tangent hyperplanes. From the standpoint of practical stability, the problem of estimating tolerances for the case of given restrictions on the spread of the quality criterion is considered. With the help of practical directional stability algorithms, it is proposed to estimate the maximum tolerance ranges for parameters in terms of volume in the presence of dynamic restrictions on the spread of phase coordinates or a quality criterion.

Real-Time Exercise Mode Identification with an Inertial Measurement Unit for Smart Dumbbells

Exercise is good for health, quality of life, and maintenance of human muscles. Dumbbells are popular indoor exercise equipment with several benefits such as low cost, high flexibility in space and time, easy operation, and suitability for people of all ages. Facilitated by advances in the Internet of Things, smart dumbbells that provide automatic counting and motion monitoring functions have been developed. To perform these tasks, the key process is identification of exercise mode. This study proposes a method to identify essential muscle groups’ (biceps, triceps, and deltoids) exercise modes of a dumbbell using an inertial measurement unit to provide three-axis angular velocities and accelerations. The motion angles were estimated from the axial acceleration and angular velocity. Phase diagrams and time plots of the axial angle, angular velocity, and acceleration were used to extract significant features of each exercise. Machine Learning and weighting functions were developed to combine these features into an identification index value for accurate identification and classification of the exercise modes. An algorithm was developed to verify the exercise mode identification. The results show that the proposed method and weighting function can successfully identify the six exercise modes. The identification algorithm was 99.5% accurate. The exercise mode identification of the dumbbell is confirmed.

FTLE and Surface-Pressure Signature of Dynamic Flow Reattachment During Delta-Wing Axial Acceleration

An experimental investigation was conducted on the aerodynamics of an NACA0012 airfoil wing with triangular planform geometry undergoing steady and axial accelerations at as a model of an unmanned combat air vehicles encountering unsteady environments at pre- and poststall angles of attack (Marzanek, M., and Rival, D., “Separation Mechanics of Non-Slender Delta Wings During Streamwise Gusts,” Journal of Fluids and Structures, Vol. 90, Oct. 2019, pp. 286–296.). Ensemble-averaged flowfields, forces, moments, and surface-pressure distributions were measured in the Optical Towing Tank for Energetics Research facility at Queen’s University. To characterize the evolution of the flowfield coherent structures around a wing under axial gusts or accelerations, a Lagrangian flowfield analysis including the finite-time Lyapunov exponent (FTLE) was conducted. Results indicate that axial acceleration can induce a dynamic flow reattachment at the poststall angle of attack, and clear FTLE ridges extend from the wing surface and travel down the chord as reattachment progresses. A distinct signature in the surface-pressure distribution tracks closely with the location where the FTLE ridges meet the wing. The timing of how this surface-pressure distribution moves aft is shown to correlate with the relatively large-scale fluctuation in the pitching moment. The current work reveals the correlation between FTLE and surface pressure, which further hints at a potential approach of dynamic estimation by using Lagrangian coherent structures.

An experimental study of volcanic tremor driven by magma wagging

SUMMARYProtracted episodes of 0.5–7 Hz pre-eruptive volcanic tremor (PVT) are common at active stratovolcanoes. Reliable links to processes related to magma movement consequently enable a potential to use properties of PVT as diagnostic eruptive precursors. A challenging feature of PVT is that generic spectral and amplitude properties of the signal evolve similarly, independent of widely varying volcano structures and conduit geometries on which most physical models rely. The ‘magma wagging’ model introduced in Jellinek & Bercovici (2011) and extended by Bercovici et al. (2013), Liao et al. and Liao & Bercovici (2018) makes progress because it depends on magma dynamics that are only weakly sensitive to volcano architecture: The flow of gas through a permeable foamy annulus of gas bubbles excites, modulates and maintains a wagging oscillation of a central magma column rising in an erupting conduit. ‘Magma wagging’ and resulting PVT are driven through an energy transfer from a ‘Bernoulli mode’ related to azimuthal variations in annular gas flow speeds. Consistent with observations, spectral and amplitude properties of PVT are predicted to evolve before an eruption as the width of the annulus decreases with increased gas fluxes. To confirm this critical Bernoulli-to-wagging energy transfer we use extensive experiments and restricted numerical simulations on wagging oscillations excited on analogue viscoelastic columns by annular air flows. We also explore sensitivities of the spatial and temporal characters of wagging to asymmetric annular air flows that are intractable in the existing magma wagging model and expected to occur in nature with spatial variations in annulus permeability. From high-resolution time-series of linear and orbital displacements of analogue column tops and time-series of axial deflections and accelerations of the column centre line, we characterize the excitation, evolution, and steady-state oscillations in unprecedented detail over a broad range of conditions. We show that the Bernoulli mode corresponds to the timescale for the buildup of axial elastic bending stresses in response to pressure variations related to air flows over the heights of columns. We identify three distinct wagging modes: (i) rotational (cf. Liao et al. 2018); (ii) mixed-mode and (iii) chaotic. Rotational modes are favoured for symmetric, high intensity forcing and a maximal delivery of mechanical energy to the fundamental magma wagging mode. Mixed-mode oscillations regimes are favoured for a symmetric, intermediate intensity forcing. Chaotic modes, involving the least efficient delivery of energy to the fundamental mode, occur for asymmetric forcing and where the intensity of imposed airflow is low. Numerical simulations also show that where forcing frequencies are comparable to a natural mode of free oscillation, power delivered by peripheral air flows is concentrated at the lowest frequency fundamental mode generally and spread among higher frequency natural modes where air pressure and column elastic forces are comparable. Our combined experimental and numerical results make qualitative predictions for the evolution of the character of volcanic tremor and its expression in seismic or infrasound arrays during natural events that is testable in field-based studies of PVT and syn-eruptive volcanic tremor.

A Machine Learning Classification Model for Monitoring the Daily Physical Behaviour of Lower-Limb Amputees.

There are currently limited data on how prosthetic devices are used to support lower-limb prosthesis users in their free-living environment. Possessing the ability to monitor a patient’s physical behaviour while using these devices would enhance our understanding of the impact of different prosthetic products. The current approaches for monitoring human physical behaviour use a single thigh or wrist-worn accelerometer, but in a lower-limb amputee population, we have the unique opportunity to embed a device within the prosthesis, eliminating compliance issues. This study aimed to develop a model capable of accurately classifying postures (sitting, standing, stepping, and lying) by using data from a single shank-worn accelerometer. Free-living posture data were collected from 14 anatomically intact participants and one amputee over three days. A thigh worn activity monitor collected labelled posture data, while a shank worn accelerometer collected 3-axis acceleration data. Postures and the corresponding shank accelerations were extracted in window lengths of 5–180 s and used to train several machine learning classifiers which were assessed by using stratified cross-validation. A random forest classifier with a 15 s window length provided the highest classification accuracy of 93% weighted average F-score and between 88 and 98% classification accuracy across all four posture classes, which is the best performance achieved to date with a shank-worn device. The results of this study show that data from a single shank-worn accelerometer with a machine learning classification model can be used to accurately identify postures that make up an individual’s daily physical behaviour. This opens up the possibility of embedding an accelerometer-based activity monitor into the shank component of a prosthesis to capture physical behaviour information in both above and below-knee amputees. The models and software used in this study have been made open source in order to overcome the current restrictions of applying activity monitoring methods to lower-limb prosthesis users.

Driving Behavior Classification and Sharing System Using CNN-LSTM Approaches and V2X Communication

Despite advances in autonomous driving technology, traffic accidents remain a problem to be solved in the transportation system. More than half of traffic accidents are due to unsafe driving. In addition, aggressive driving behavior can lead to traffic jams. To reduce this, we propose a 4-layer CNN-2 stack LSTM-based driving behavior classification and V2X sharing system that uses time-series data as an input to reflect temporal changes. The proposed system classifies driving behavior into defensive, normal, and aggressive driving using only the 3-axis acceleration of the driving vehicle and shares it with the surroundings. We collect a training dataset by composing a road that reflects various environmental factors using a driving simulator that mimics a real vehicle and IPG CarMaker, an autonomous driving simulation. Additionally, driving behavior datasets are collected by driving real-world DGIST campus to augment training data. The proposed network has the best performance compared to the state-of-the-art CNN, LSTM, and CNN-LSTM. Finally, our system shares the driving behavior classified by 4-layer CNN-2 stacked LSTM with surrounding vehicles through V2X communication. The proposed system has been validated in ACC simulations and real environments. For real world testing, we configure NVIDIA Jetson TX2, IMU, GPS, and V2X devices as one module. We performed the experiments of the driving behavior classification and V2X transmission and reception in a real world by using the prototype module. As a result of the experiment, the driving behavior classification performance was confirmed to be ~98% or more in the simulation test and 97% or more in the real-world test. In addition, the V2X communication delay through the prototype was confirmed to be an average of 4.8 ms. The proposed system can contribute to improving the safety of the transportation system by sharing the driving behaviors of each vehicle.

Personal Identification Using Gait Spectrograms and Deep Convolutional Neural Networks.

Human gait can serve as a useful behavioral trait for biometrics. Compared to fingerprint, face, and iris, the most commonly used physiological identifiers, gait can be unobtrusively monitored from a distance without requiring explicit involvement and physical restraint from people. Advances in wearable technology facilitate direct and faithful measurement of gait motions with easy-to-use and low-cost inertial sensors. This study aimed to propose an approach to using kinematic gait data collected with wearable inertial sensors for reliable personal identification. Sixty-nine individuals ranged in age from 24 to 62 years old participated in this study. The 3-axis acceleration and the 3-axis angular velocity signals were measured using the inertial measurement units attached to the feet, shanks, thighs, and posterior pelvis while walking. The gait spectrograms were acquired by applying time-frequency analyses to the lower body movement signals measured in one stride. Among each participant's 15 strides, 12 strides were used in the 4-fold cross validation of the deep convolutional neural network-based classifiers, and the remaining three strides were used to evaluate the classifiers. An accuracy of 99.69% was achieved by using the foot, shank, thigh, and pelvic spectrograms, and the accuracy was 96.89% using only the foot spectrograms. This study has the potential to be applied in behavior-based biometric technologies by confirming the feasibility of the proposed kinematic and spectrographic approaches in identifying personal behavioral characteristics.

Fine scale behaviour and time-budget in the cryptic ectotherm European pond turtle Emys orbicularis.

For ectotherms, behaviour and associated energetic costs are directly related to thermal conditions. In the present context of global change, estimating time-budget for these species is relevant to assess and predict their capacity to adapt to near future. We tested the hypothesis that in ectotherms where reproduction is highly energy consuming, energy expenditure should vary throughout the breeding season with a maximum around nesting events. To test this hypothesis, we assessed the fine-scale behaviour, time-budget and estimated energetic costs in eight adult female European pond turtles Emys orbicularis equipped with data-loggers recording ambient temperature, pressure, light and the animals’ 3-axis acceleration. Deployments occurred over four months throughout the nesting season 2017 in semi-natural captive conditions in Alsace, France. All study turtles showed a clear daily pattern over the 24h cycle, with four distinct phases (referred to as Night, Morning, Midday and Evening), associated with different behaviours and activity levels. Before oviposition, turtles were mostly active during Morning, and activity was positively driven by ambient temperature. Activity levels doubled during the nesting period, mostly due to the increased activity in the Evening, when nesting events occurred. Throughout the active season, basking occurrence at Midday was related to air temperature but cloud coverage was an even more important factor. Our results are a first step in predicting the seasonal time and energy budgets of the European pond turtle, and demonstrate the usefulness of animal-borne accelerometers to study free living freshwater turtles over extended periods of time.

Freeform surface topography model for ultraprecision turning under the influence of various errors

This work establishes an accurate freeform surface topography model considering geometric errors, tracking errors, and cutting forces. Regarding geometric errors, based on the theory of multibody systems and homogeneous coordinate transformation, the transfer relationship between various geometric errors and the tool error in the workpiece coordinate system is described. Using the continuous acceleration Position-Velocity-Time (PVT) interpolation method, the offset discrete points caused by geometric errors are interpolated and rediscretized, and the accurate mathematical model between the tool errors (position and posture) in the workpiece coordinate system and the topography of the freeform surface is established. Based on the model, the influence of geometric errors on the contour errors of freeform surfaces is accurately calculated, and the contribution and similarity of the effects of various geometric errors on the contour errors of freeform surfaces are analyzed. For dynamic-dependent factors, a second-order system with two degrees of freedom on the X or Z axis is established. According to the simplified result of the equivalent system, the contour error of the freeform surface caused by the tracking error and cutting force is analyzed. For the tracking error, under the condition of constant rotation velocity of the spindle, the change of the slope of the freeform surface along the circumferential direction causes the change in the velocity and acceleration of the motion axis; thus, the corresponding area of the surface has a larger contour error. For cutting force, the change of the slope of the freeform surface along the circumferential direction changes the tool working rake angle, the tool working clearance angle, and the shearing angle, resulting in a change in the cutting force. Moreover, the change of cutting speed is accompanied by the change of cutting force. An experiment verifies the effectiveness of the proposed modeling method. In addition, the modeling method provides an effective solution for the calculation of the contribution rate of different error sources to the contour error of the freeform surface.

Dynamic analysis and vibration reduction of mechanical-hydraulic coupled tunnel boring machine (TBM) main drive system

Tunnel Boring Machine always works in the changeable geologies with multiple drivers, which leads to severe vibration of the TBM main drive system and key component failures. The vibration characteristics of TBM under different working conditions and the vibration reduction analysis have important meanings. First of all, by considering the time-varying random loads of the cutters, the contact force of the gears, the stiffness of the main bearing, and the stiffness of the cylinders, a mechanical-hydraulic coupling nonlinear dynamic model of the TBM main drive system was built according to the assembly relationship and load transmission path of the main drive system. Secondly, the dynamic model of the TBM main drive system is verified by comparing the theoretical vibration with the real vibration of the TBM main drive system. The error of the vibration acceleration is 10% to 30%. Three typical loads are defined under typical working conditions, and the vibrations of the TBM main drive system under three typical loads were analyzed. Finally, the sensitivity analysis of the cylinder damping shows that the damping at the position of the propulsion cylinder has a great influence on the vibration of the TBM main drive system. The results show that when the damping coefficient is 2.5 × 106 N·s/m, the maximum reduction of axial acceleration of cutterhead is 0.64 g, and that of the main beam front section is 0.55 g. The variable damping coefficient vibration reduction strategies under three typical loads are verified.

Feasibility of Bilinear Mechanical Characterization of the Abdominal Aorta in a Hypertensive Mouse Model

A change in elastin and collagen content is indicative of damage caused by hypertension, which changes the non-linear behavior of the vessel wall. This study was aimed at investigating the feasibility of monitoring the non-linear material behavior in an angiotensin II hypertensive mice model. Aortas from 13 hypertensive mice were imaged with pulse wave imaging (PWI) over 4 wk using a 40-MHz linear array. The pulse wave velocity was estimated using two wave features: (i) the maximum axial acceleration of the foot (PWVdia) and (ii) the maximum axial acceleration of the dicrotic notch (PWVend−sys). The Bramwell–Hill equation was used to derive the compliance at diastolic and end-systolic pressure. This study determined the potential of PWI in a hypertensive mouse model to image and quantify the non-linear material behavior in vivo. End-systolic compliance could differentiate between the sham and angiotensin II groups, whereas diastolic compliance could not, indicating that PWI can detect early collagen-dominated remodeling.

Analysis on damage characteristics and detonation performance of solid rocket engine charge subjected to jet

To further explore the damage characteristics and impact response of the shaped charge to the solid rocket engine (SRE) in storage or transportation, protective armor was designed and the shelled charges model (SCM)/SRE with protective armor impacting by shaped charge tests were conducted. Air overpressures at 5 locations and axial acceleration caused by the explosion were measured, and the experimental results were compared with two air overpressure curves of propellant detonation obtained by related scholars. Afterwards, the finite element software AUTODYN was used to simulate the SCM impacted process and SRE detonation results. The penetration process and the formation cause of damage were analyzed. The detonation performance of TNT, reference propellant, and the propellant used in this experiment was compared. The axial acceleration caused by the explosion was also analyzed. By comprehensive comparison, the energy released by the detonation of this propellant is larger, and the HMX or Al particles contained in this propellant are more than the reference propellant, with a TNT equivalent of 1.168–1.196. Finally, advanced protection armor suggestions were proposed based on the theory of woven fabric rubber composite armor (WFRCA).

Development of a new method for assessing otolith function in mice using three-dimensional binocular analysis of the otolith-ocular reflex

In the interaural direction, translational linear acceleration is loaded during lateral translational movement and gravitational acceleration is loaded during lateral tilting movement. These two types of acceleration induce eye movements via two kinds of otolith-ocular reflexes to compensate for movement and maintain clear vision: horizontal eye movement during translational movement, and torsional eye movement (torsion) during tilting movement. Although the two types of acceleration cannot be discriminated, the two otolith-ocular reflexes can distinguish them effectively. In the current study, we tested whether lateral-eyed mice exhibit both of these otolith-ocular reflexes. In addition, we propose a new index for assessing the otolith-ocular reflex in mice. During lateral translational movement, mice did not show appropriate horizontal eye movement, but exhibited unnecessary vertical torsion-like eye movement that compensated for the angle between the body axis and gravito-inertial acceleration (GIA; i.e., the sum of gravity and inertial force due to movement) by interpreting GIA as gravity. Using the new index (amplitude of vertical component of eye movement)/(angle between body axis and GIA), the mouse otolith-ocular reflex can be assessed without determining whether the otolith-ocular reflex is induced during translational movement or during tilting movement.

Unsteady shock wave dynamics in accelerating and decelerating flight

AbstractIncreasingly agile manoeuvre is an advantage in the flight of aircraft, missiles and aerial vehicles, but the principles of accelerating aerodynamics in the transonic regime are only now being fully investigated. This study contributes to the understanding of shock and separation effects on drag during axial acceleration, using a simple geometric configuration. Unsteady shock wave behavior was numerically investigated for an axisymmetric cone-cylinder using a commercial solver and the Moving Reference Frame acceleration technique. This acceleration technique was validated using unsteady numerical and experimental methods. The cone-cylinder was accelerated from Mach number 0.6 to Mach number 1.2 at 100g constant and deceleration was from Mach number 1.2 until Mach number 0.6 at –100g constant. Three cone angles were tested for the cone-cylinder with uniform cylinder diameter. Acceleration through the transonic Mach regime was characterised by a delayed and gradual shock wave development when compared to steady state, demonstrating a clear flow history effect. Deceleration through the transonic Mach regime was characterised by shock wave propagation from the base to the nose. New flow structures appeared during deceleration that do not have counterparts in the steady state, including shock interactions and propagating expansion-compression features. Gross changes in the unsteady drag coefficient curves for each cone-angle are explained with reference to unsteady shock wave behaviour for accelerating and decelerating motion.

Shaking Table Test on the Seismic Response of Buried Oil and Gas Pipelines under the Bidirectional Nonuniform Seismic Excitation

This paper studies the seismic response of buried oil and gas pipelines under the bidirectional nonuniform excitation. Based on the bidirectional shaking table array test, the loading and testing scheme is designed and developed, analyzing the strain response of the buried oil and gas pipeline under the bidirectional uniform and nonuniform seismic excitation, as well as the acceleration response and displacement response characteristics of the pipeline and the surrounding soil body and their change rule by the test. The test proves to show that the developed bidirectional laminar shear continuum model soil box can meet the requirements of the bidirectional nonuniform seismic excitation and continuous laminar shear deformation of the soil. The peak strains of the pipeline in axial and bending caused by nonuniform excitation are larger than those of the pipeline under uniform excitation, the degree of unevenness in the distribution along the axial direction is greater, and the strain curves are large in the middle and small at both ends along the axial direction of the pipe. The acceleration responses of the pipeline and the soil body under the bidirectional nonuniform excitation are larger than those under the uniform excitation. The acceleration response of both the pipe and the soil under the nonuniform excitation is larger than that under the uniform excitation, and the differences are shown in the transverse and axial directions, the peak acceleration response of the soil body under the nonuniform excitation is about three times that of the transverse direction, and more peak points appear in the axial and transverse acceleration responses of the pipe under the nonuniform excitation as the loading level increases, the peak displacement response of the soil body increases gradually with the height, but the fluctuation range of the peak displacement of the soil body nearby the pipe is larger. The soil displacement curve starts to smooth out when the loading level reaches 1.0 g, and the axial displacement decreases, which indicates that the interaction between the pipe and soil is more intense and the relative motion between the pipe and soil is more obvious under the nonuniform excitation, and the soil is more likely to be damaged and enter the nonlinear stage. Therefore, it is necessary to analyze and design the seismic performance of buried pipes considering the nonuniform seismic excitation.

Розрахунок оптимальних параметрів коректувальних елементів в індукційних системах прискорення

The formulations of a number of optimization problems for a linear induction acceleration system with respect to the adjustment parameters are considered. The dynamics of the transverse motion of electrons in the horizontal plane is investigated in the presence of given energy values for each resonator period: the particles at the initial moment of time are somewhat displaced relative to the accelerator axis (we neglect the displacements of the ends of the solenoids and the centers of the accelerating gaps relative to the accelerator axis). A connection is established between the initial and final coordinates and the components of the momentum. The presence of parasitic electric and magnetic fields arising as a result of the displacement of particles relative to the axis of the accelerator, which change the transverse components of the pulses, is taken into account. For the mathematical formulation of problems, in order to apply algorithms of practical stability, the original difference model of the induction system was converted to a linear form. By introducing into consideration the vector of parameters, the scatter of phase coordinates, and tolerances on the parameters, the problem of calculating the tolerances for given linear constraints on the scatter of phase coordinates for the corresponding inhomogeneous system is formulated. For the case of nonlinear dynamic constraints on the spread of the vector of phase coordinates, it is proposed to approximate a convex closed set by tangent hyperplanes. Numerical estimation of the range of tolerances for the parameters of correcting elements is reduced to the problems of practical stability of discrete parametric systems. In this case, the region of the initial conditions on the state vector, the tolerances on the parameters, are given structurally in the form of an ellipsoid, which makes it possible to numerically solve the original problem as an extremal one. From the standpoint of practical stability in the corresponding space of functions, the problem of assessing the range of tolerances for the parameters of correcting elements in the presence of specified restrictions on the spread of the quality criterion is considered. Attention is focused on an important class of problems of numerical modelling of a linear induction acceleration system − problems of practical stability. Numerical estimation of the region of initial displacements of the transverse coordinates of the linear induction acceleration system in the given structures in the presence of linear constraints on the vector of phase coordinates in dynamics is carried out. Key words: modeling, induction system of acceleration, solenoid, parameters, elements of correction, optimization, stability

Intelligent Tire Sensor-Based Real-Time Road Surface Classification Using an Artificial Neural Network.

Vehicles today have many advanced driver assistance control systems that improve vehicle safety and comfort. With the development of more sophisticated vehicle electronic control and autonomous driving technology, the need and effort to estimate road surface conditions is increasing. In this paper, a real-time road surface classification algorithm, based on a deep neural network, is developed using a database collected through an intelligent tire sensor system with a three-axis accelerometer installed inside the tire. Two representative types of network, fully connected neural network (FCNN) and convolutional neural network (CNN), are learned with each of the three-axis acceleration sensor signals, and their performances were compared to obtain an optimal learning network result. The learning results show that the road surface type can be classified in real-time with sufficient accuracy when the longitudinal and vertical axis acceleration signals are trained with the CNN. In order to improve classification accuracy, a CNN with multiple input that can simultaneously learn 2-axis or 3-axis acceleration signals is suggested. In addition, by analyzing how the accuracy of the network is affected by number of classes and length of input data, which is related to delay of classification, the appropriate network can be selected according to the application. The proposed real-time road surface classification algorithm is expected to be utilized with various vehicle electronic control systems and makes a contribution to improving vehicle performance.

Analytical Investigation of Propellant Slosh Stability Boundary on a Space Vehicle

The effect of propellant sloshing upon the stability of a liquid-propelled space vehicle in a high-g environment has been studied extensively. For a typical space vehicle with thrust vector control and a single slosh tank, the Bauer slosh danger zone is located between the vehicle center of mass and the center of percussion while ignoring effects, like aerodynamics and axial acceleration. If the slosh mass is located between these two locations, baffles may be required to provide additional damping for stability. Although this criterion is widely used in the launch-vehicle flight control community, its application is limited to the aforementioned configuration and assumptions. In this work, the methodology behind the classic single-tank criteria is extended to other tank configurations and includes previously ignored effects. First, a vehicle with a single centerline tank and a pair of outboard reaction jets, rather than thrust vectoring, for attitude control is studied. Second, the impacts of aerodynamics and vehicle axial acceleration on the classic single-tank criteria are analyzed. Finally, the variation of the classic danger zone for a tandem tank configuration, where the tanks are located along the vehicle centerline or symmetrically offset from the centerline, is investigated.

A system to monitor one’s nearsightedness implicitly

The number of nearsighted young people grows rapidly because of over-use of eyes, and it becomes a wide health problem in the world. Efficient vision monitoring methods are required to determine whether people are getting nearsightedness problem in the early stages so as to take further treatment. Current technologies for vision examination are usually either expensive or time costly. This paper proposes a nearsightedness monitoring system, which exploits the widely used smartphones to detect the deterioration of nearsightedness by monitoring and analyzing the the distance between the eyes and the smartphone screen. The detection process is implicit since the system is implemented on the daily used phones and people do not have to be interrupted frequently. The proposed system consists of two key components: activity recognition component and the eye detecting component. The activity recognition component is used to determine whether a person is watching the phone. Once a person is watching the phone, the eye detecting component can be triggered to take a picture using the front camera and localize the two eyes. The distance between eyes and the screen is estimated by the ratio of the two-eye distance in the picture and the width of the picture. This paper uses the 3-axis acceleration sensor and the front camera which are equipped on most of the smartphones for activity recognition and eye detection respectively. A prototype has been developed in order to evaluate the effectiveness of the system under various environmental conditions. From more than half year monitoring period which consisted of about 20 volunteers, we were able to accurately detect the degradation of nearsightedness in two volunteers.

Broadband Vibration Sensor Using Reflected Excessively Tilted Fiber Grating With Clamped Beam

A broadband vibration sensor using reflected excessively tilted fiber grating (ExTFG) with clamped beam was proposed. The two ends of reflected ExTFG were fixed, and the fiber grating part was suspended, thus forming a clamped beam structure. The resonance frequency and vibration mode of the proposed sensor were calculated and analyzed by numerical calculation and software simulation. Axial strain, acceleration response and vibration frequency detection experiments were designed and conducted. Experimental results showed that the axial strain sensitivity of TE/TM mode was −2.57 pm/ $\mu \varepsilon $ and −1.6 pm/ $\mu \varepsilon $ , respectively. The first-order resonant frequency of the sensor was 1900Hz with a flat region ranging from 100 Hz to 800 Hz, and the maximum acceleration sensitivity of TE/TM mode in the flat region was 38.79 mV/g and 31.43 mV/g at 800Hz, respectively. In addition, it could detect the vibration frequency range of 100–10000 Hz, and provide a highest signal-to-noise ratios (SNR) of 55.1 dB at 1900 Hz. The proposed sensor possessed a wide response frequency range, and was able to realize dual-parameter detection for acceleration and vibration frequency, which would make its good application prospects in the mechanical vibration detection for large-scale projects.