Acceleration Force Research Articles

The Design & Implementation of a Self-adaptive Hybrid Electric Skateboard

This paper proposes a novel electric skateboard control architecture to hybridize the skater's manual operation and electric motor drive. The proposed scheme does not need a handheld remote controller for steering; hence provides better man-machine coordination and enhances the safety of new skaters. For this purpose, a torque-speed control algorithm is designed to compensate for the manual acceleration force and rolling resistance by sensing the motor's speed, acceleration, and torque outputs. The compensation level is configurable according to the skater's comfortableness. The proposed electric control solution also enhances the battery mileage per charging and can be applied to various electric skateboards since it does not require a dedicated weight/pressure sensor to detect if the skater is on or off the board. The control scheme is simulated in MATLAB/Simulink and experimentally verified by a controller based on C2000 DSP that supports sensorless brushless DC(BLDC) motor drive.

Revised model of social change and acceleration: the case of Iranian society in the 1960s and 1970s

This article aims to address the processes of social changes in terms of the theory of social acceleration. It begins with an outline of the theory of social acceleration and discusses how an investigation into the driving forces of social acceleration can be used to explain the dynamics of social stability and change. It criticizes the acceleration theory because its focus is merely on high-industrialized western societies as well as the neglect of normative and religious aspects in the processes of social acceleration and change. This article proposes a revised model of social acceleration and applies it to Iranian society. It identifies the main features of acceleration-cycle formed in Iranian society in the 1960s and 1970s to answer the question of why the cycle of acceleration could not establish a self-propelling acceleratory formation as a prime requirement for preserving social stability.

An identification method of floating wind turbine tower responses using deep learning technology in the monitoring system

The acceleration at the tower top and the force on the tower root are the critical indicators for the structural safety of floating wind turbine (FOWT) towers. However, the corresponding monitoring sensors are prone to failure due to the harsh marine environment. Based on the coupling relationship between the tower force and the floating foundation motion responses, a method for identifying the tower top acceleration and the tower root force is proposed based on deep learning technology. Firstly, a 10 MW FOWT model is numerically simulated to obtain the corresponding responses through OpenFAST. Secondly, a multi-layer perception (MLP) model is constructed and trained. The process of determining the optimal sampling frequency is presented. Finally, the single-state and multi-state cases are studied to verify the feasibility of the proposed method. The results show that the proposed method has shown excellent performance in identifying the tower top acceleration and tower root force, which demonstrates its great promise in the field of smart health monitoring technology.

Return to flying duties of German military pilots after recovery from COVID-19

BackgroundPilots are working in a unique and exacting environment with hypobaric hypoxia and acceleration forces. In military flying, missions are often challenging with possible combat scenarios and in remote areas...

Computational investigation on heat transfer of supercritical CO2 in horizontal U-tubes

The convective heat transfer characteristics of sCO2 in a horizontal U-tube are numerically investigated in this work. Considering the special geometry design of U-tube and the great variation of the supercritical fluid (SCF) properties, the reliability of four turbulence models is verified. Effects of operation parameters, buoyancy, flow acceleration and centrifugal force on the heat transfer characteristics are further investigated. Results show that, the position where the Tb is close to the Tpc has an important influence on the heat transfer. Centrifugal force mainly enhances the heat transfer coefficient (HTC) in the U-section and the outlet-section, and restrains the buoyancy and flow acceleration effect. The competition between buoyancy and centrifugal force leads to the enhancement of secondary flow and heat transfer. Finally, new heat transfer correlations which can be used in U-section and outlet-section are proposed in this paper.

Experimental study on the water entry of a 3D bow-flared model with various inclination angles

Oblique water entry of the ship bow has both the complexity of structure shape and the water entry attitude, which involves strong nonlinear free surface effect and thus, complexes the prediction of slamming loads. This paper conducted the drop experimental investigation on the impact hydrodynamics of a 3D bow-flare model with inclination angles to help clarify the impact characteristics. The experimental uncertainty was discussed based on repeatable and oscillation analysis showing good stability. Characteristics of bow-flared model in oblique impact including water entry depth, acceleration, pressure and impact force were analyzed. Differing to simple 3D bodies like cones and cylinders, multiple pressure peaks appear at some positions, which should be paid attention. The influence of inclination angles on pressure was further discussed, showing the pressure at the bottom and leeward side (right side) decreases while it increases on the windward side with inclination angle. These findings offer evidence for a complex interplay between geometric parameters and inclination angles, which could ultimately serve the ship design.

Unmanned aerial vehicle transport of frozen blood samples using phase change materials

Appropriate cryopreservation of blood samples during transit from the point of collection to testing sites is an important element of quality sample management in clinical and veterinary diagnostics and research. Here, a heat-insulated design that employs 23.3% w/w salt water as the phase change material (PCM) for encapsulating a 1.5-mL vial of frozen blood sample was studied to assess its efficacy in maintaining sub-zero temperatures during transport. A two-dimensional finite element numerical simulation model with 5457 elements was found to exhibit mesh independence with 10% convergence error. For the PCM pre-cooled in dry ice and vial sample kept initially at 20 °C before flight, this model is predicted to maintain a stable transport temperature of −20 °C for at least 70 min. It also predicted to have uniform temperature distribution across the PCM holder, PCM, sample vial and sample. Experimental data obtained using a thermocouple confirmed the accuracy of the simulation model. Sensor data collected from a bespoke unmanned aerial vehicle (UAV) allowed mapping of the acceleration forces during flight and facilitated the development of a mechanical setup to experimentally show that frozen samples are protected from shear forces generated under mimicked transport conditions. The capability of real-time sample temperature monitoring with feedback control on UAV flight path demonstrates the viability of the drone delivery system for quality transport of thermal-sensitive samples. • UAV transport of frozen blood samples done here with salt water phase change material. • 2D finite element model achieved mesh independence with 10% convergence error. • 70 min stable transfer at −20 °C attained after 30 min of dry ice pre-cooling. • Sensor data from UAV mimicked the flight conditions in a sloshing test setup. • Preliminary tests with frozen sheep's blood show lower coagulation from sloshing.

Controlling isolation system of initial combustion engines

To evaluate the effect of the engine vibration on the vehicle's ride comfort and improve the vehicle's ride comfort, three types of engine’s isolation systems including the traditional rubber mount (TRM), hydraulic mount (HM), and semi-active HM controlled by the PID control (SHM) are proposed. A dynamic model of the inline 4-cylinder engine is established to determine the excitation force of the engine. By the combination of the random excitation of the vehicle floor affecting the engine isolation system, the isolating performance of the TRM, HM, and HM is then simulated and evaluated on isolating the engine vibration and improving the vehicle’s ride comfort. Both the root mean square (RMS) values of the engine acceleration response (aRMSe) and isolation force (FRMS) of engine isolation systems are given as the objective functions. The research results show that the engine vibration combined with the excitation of the road surface roughness significantly affects the vehicle’s ride comfort. By using the SHM, both the engine acceleration and isolation force are significantly reduced in comparison with the TRM. Especially, the values of the aRMSe and FRMS are remarkably decreased by 9.32 % and 9.69 % in comparison with the TRM. Thus, to improve the vehicle's ride comfort and reduce the effect of the engine's vibration on the ride comfort, the engine isolation system used by the TRM needs to be replaced by using the SHM.

The influence of snow deposits on thermal efficiency of vacuum tube collectors

Global warming promotes the acceleration forces all countries to reduce fossil energy sources and increase renewable energy sources with the development of environmentally friendly resource-saving technologies. The vast territory of Russia is permafrost or has seasonally frozen soils. The use of renewable energy sources, especially solar energy sources, is especially important for such territories.The article presents the experimental results of the operating modes of a pilot industrial solar hot water supply system with two vacuum tube collectors after snow pollution or icing of pipe surfaces. This technique is used to measure the hourly values of thermal energy from the conversion of solar radiation by collectors with polluted and cleaned collector surfaces on a sunny day after snowfall or icing. The average hourly value of solar insolation (with contaminated surfaces and after their cleaning) is obtained by integrating the meter recordings on the incident heat flux from the sun (by 600 values each) at an interval of 6 seconds. It is found that when the collector pipe surface is iced, the decrease in the thermal energy supply is maximum and amounts to 36.96 %. In other cases it varies from 8.51 to 13.47 %.

Study on dynamic responses of particle in aggregate mixture during the laboratory compaction utilizing Smart Aggregate

Knowing compaction process of pavement at meso-scale is of great significance for improving the material design and construction quality. This study aims to investigate dynamic responses of particle in aggregate mixture during compaction by using a Smart Aggregate. As the compaction method and material composition have significant influence on dynamic responses of the particle in compaction process, various compaction methods, including impact, vibration, static and gyratory compaction, were first conducted on lubricated mixtures in the laboratory. Then, number of contact points and movements of the Smart Aggregate in mixture were analyzed in different stages of gyratory compaction process. Additionally, effects of critical influencing material factors, including lubrication effect, particle size, aggregates packing and gradation on the particle movement in mixture were discussed. Results indicate that the dynamic responses (i.e. acceleration, rotation and contact force) of the Smart Aggregate exhibited significant relation to the loading mode of compaction efforts. Regarding to gyratory compaction, drastic particle movement and sharp increase in number of contact points mainly occurred in the first stage in which the reduced height of specimen was more than 1 mm. Although lubrication had a marked impact on compaction of aggregates system, its influence on movement could be negligible for the Smart Aggregate. Those adjacent aggregates with particle size less than 4.75 mm performed well in terms of restricting the movement of the Smart Aggregate. After filling fine aggregates with particle size less than 2.36 mm into packed aggregates, the deviation of change in acceleration amplitude and relative rotation was reduced to a low level. Compaction methods, adjacent particles’ size and aggregates packing had significant influences on the dynamic responses of the Smart Aggregate.

Vibration control of an articulated tower with a tuned mass damper subjected to the inertial force of ground acceleration

ABSTRACT This research proposes a new approach, in which a tuned mass damper (TMD) is installed in an articulated tower subjected to moving loads caused by ground. Then, the vibration equations of the system are formulated for analyzing and selecting the optimal parameters of the tuned mass damper to reduce the harmful vibrations. The maximization of equivalent viscous resistance method is applied to determine the optimum parameters of the tuned mass damper. The purpose of designing the tuned mass damper is to suppress the vibrations of the articulated tower. The results show that the vibration of the articulated tower is effectively eliminated by using the optimum parameters of the tuned mass damper in this paper. In particular, the optimum expressions are given in analytical solutions, which involve the parameters in well-understood forms to derive the exact solution of the optimum parameter. These optimum expressions, helping the researchers easily design the tuned mass damper on controlling vibrations of the articulated tower.

Pulse chirp enhances the laser acceleration of neutral particles.

Accelerating neutral atoms is challenging because such particles are not directly manipulated by electric and magnetic fields as charged particles. In our acceleration scheme, the excited atom requires a sufficiently high gradient acceleration force. The key challenge in laser acceleration experiments is that not only must the photon energy excite atoms to the Rydberg state, but also atoms must not be ionized in an intense laser field. In this Letter, we propose using a chirped laser pulse to achieve the objectives above. The enhancement effect of the pulse chirp on the laser acceleration of neutral particles is investigated via numerical simulation and analytical analysis.

Generalized Rayleigh‐Taylor Instability: Ion Inertia, Acceleration Forces, and E Region Drivers

AbstractA linear theory of the generalized Rayleigh‐Taylor instability (GRTI) is derived which includes ion inertia and acceleration forces, as well as E region drivers: the zonal neutral wind and plasma drift. This is in contrast to the F region drivers (aside from gravity): the meridional neutral wind and the meridional/vertical plasma drifts. Both a local theory and a flux‐tube integrated theory are presented with application to the onset of ionosphere irregularities associated with equatorial spread F. Inertia and acceleration forces do not affect the growth rate of the GRTI for nominal ionospheric conditions, but the E region zonal drifts can significantly increase or decrease the growth rate of the GRTI in the equatorial and mid‐latitude ionosphere depending on their direction.

Magnetic Force Calculation in Reluctance Force Launcher

To study the clamping device in reluctance force launcher, the Maxwell stress tensor method is extended to contact force calculations. It is generally believed that the Maxwell stress tensor method is only suitable for objects surrounded by air or vacuum. However, in this article, the Maxwell stress tensor applicable to ferromagnetic materials is re-derived, and the classical Maxwell stress tensor is successfully reproduced. Its integral region is determined as the outer surface of the interface between the object and the outside world, which means that the Maxwell stress tensor method can be used for contact force calculations. Subsequently, the Maxwell stress tensor method was used for force studies in the clamping device. The needed clamping force of the clamping device is calculated. The reducing effect of ferromagnetic materials on the clamping force and the effect on the acceleration force of the projectile are analyzed. Finally, based on the determined integral region, the reason why the integral result of Maxwell stress tensor method is related to the integral path is successfully explained, which provides another theoretical basis for the contact force calculation method in this article.

Performance Analysis of Acceleration and Inertial Force of Electromagnetic Suspension Inertial Stabilizer

In this paper, the structural characteristics of electromagnetic suspension (EMS) inertial stabilizers are analyzed firstly, and then a mechanical analysis of a single mass block and double mass block is carried out. The relationship model between the inertial anti-rolling mass block and inertial force transmitted to the ship is established. The inertial force is determined by the number of coil turns, coil current, mass block, mass of the ship, electromagnet current, rate of change of the electromagnet current, air gap between the electromagnet and inertial mass block, and rotational angular speed. Through theoretical analysis, it is found that the response speed of inertia force is directly related to the electromagnetic coil current, the voltage at both ends of the electromagnetic coil, the coil resistance and the air gap. It is concluded that the response speed of the inertia force can be controlled by controlling the coil current, adjusting the voltage at both ends of the coil and adjusting the air gap. The inductance of the electromagnetic coil will also increase the nonlinearity of the inertial anti-roll system. On the basis of theoretical analysis, a digital simulation of EMS inertial stabilizer is carried out by MATLAB and ANSYS MAXWELL2D. Finally, a single mass block system of EMS inertial stabilizer is designed and tested. During the test, a 1.5 V sinusoidal excitation voltage is added to the electromagnetic coil after the mass block is suspended stably, and the maximum acceleration values of the inertial anti-rolling mass block and hull are 10.29 m/s2 and 1.27 m/s2. Finally, the theoretical analysis results, digital simulation results and experimental results are analyzed, which verifies the correctness of the acceleration and inertia force performance analysis of the EMS inertial stabilizer.

Формирование коаксиальных полей остаточных напряжений в полотне круглой пилы

The working tool of machines with circular cutting units is a circular saw, the condition of which largely determines the quality of material processing. Circular saw blades in the process of operation are subjected to a complex effect of force and temperature factors that cause elongation and deformation of the saw blade, and the occurrence of internal stresses that take it out of the flat form of elastic balance and reduce the tool’s performance. The ability of saws to resist these factors is determined by the rigidity and stability of the saw blade. It is customary to consider a circular saw blade consisting of three zones: peripheral, middle and central. The middle part has the greatest influence on the stability of the saw blade. Initially, after manufacturing, the saw blade has a flat shape of balance, which can be disturbed by any external impact on the saw during the cutting process. The balance disturbance causes the blade and the cutting edge of the saw to deviate from the initial operating condition and reduce the accuracy and quality of wood processing. In order to prevent the influence of external forces, coaxial zones of plastic deformation of a certain width are formed in the middle part of the blade. In this case, under the influence of the created stresses, the effect of web tension appears. In world practice, two methods of forming such zones are used: forging and rolling. The creation of normalized stresses in the circular saw blade is carried out by local mechanical contact action of the working body of the saw tool on the steel saw blade in certain places of the middle zone. Compressive stresses compensating the forces of centrifugal acceleration, the thermal heating of individual zones of the saw blade, the external longitudinal and transverse bending forces that occur in the blade during wood processing are formed in the treated annular zones. The considered methods for creating annular zones of plastic deformation fields involving mechanical action on the saw blade have significant drawbacks, the elimination of which requires fundamentally new technical solutions. It is proposed to form coaxial fields of residual stresses of the saw blade by thermoplastic action consisting in creation of normalized residual stresses in the saw blade by concentrated thermal action on local annular zones coaxially located along the saw blade for the entire thickness of the saw. The formation of coaxial circular fields of residual stresses in the circular saw blade is simulated. The considered method of saw preparation will increase its stability in the process of operation.

Design of a Semiactive TMD for Lightweight Pedestrian Structures Considering Human–Structure–Actuator Interaction

Lightweight pedestrian structures constructed with high strength-to-weight ratio materials, such as fiber-reinforced polymers (FRP), may experience large accelerations due to their lightness, thus overcoming the serviceability limit state. Additionally, uncertainties associated with human–structure interaction phenomena become relevant. Under these circumstances, variations in pedestrian actions could modify the modal properties of the coupled human–structure system and classical approaches based on passive Tuned Mass Dampers (TMD) do not offer an effective solution. An alternative solution is to use a Semiactive TMD (STMD), which includes a semiactive damper that, when properly designed, may be effective for a relatively broad frequency band, offering a robust solution when significant uncertainties are present. Thus, this paper presents a design methodology for the design of STMDs applied to lightweight pedestrian structures including human–structure and actuator–structure interaction. A multiobjective optimization procedure has been proposed to simultaneously minimize structure acceleration, inertial mass, and maximum damper force. The methodology has been applied to a lightweight FRP footbridge. Realistic simulations, including system uncertainties, interaction phenomena, nonlinear damper model, noise-contaminated signals, and the practical elements (in-line digital filters) needed for the successful implementation of the control law, validate the methodology. As a conclusion, the STMD is more effective than its passive counterpart in both, canceling the response or achieving similar performance with significant lower inertial mass.

Disquisitions Relating to Principles of Thermodynamic Equilibrium in Climate Modelling.

We revisit the fundamental principles of thermodynamic equilibrium in relation to heat transfer processes within the Earth’s atmosphere. A knowledge of equilibrium states at ambient temperatures (T) and pressures (p) and deviations for these p-T states due to various transport ‘forces’ and flux events give rise to gradients (dT/dz) and (dp/dz) of height z throughout the atmosphere. Fluctuations about these troposphere averages determine weather and climates. Concentric and time-span average values <T> (z, Δt)) and its gradients known as the lapse rate = d < T(z) >/dz have hitherto been assumed in climate models to be determined by a closed, reversible, and adiabatic expansion process against the constant gravitational force of acceleration (g). Thermodynamics tells us nothing about the process mechanisms, but adiabatic-expansion hypothesis is deemed in climate computer models to be convection rather than conduction or radiation. This prevailing climate modelling hypothesis violates the 2nd law of thermodynamics. This idealized hypothetical process cannot be the causal explanation of the experimentally observed mean lapse rate (approx.−6.5 K/km) in the troposphere. Rather, the troposphere lapse rate is primarily determined by the radiation heat-transfer processes between black-body or IR emissivity and IR and sunlight absorption. When the effect of transducer gases (H2O and CO2) is added to the Earth’s emission radiation balance in a 1D-2level primitive model, a linear lapse rate is obtained. This rigorous result for a perturbing cooling effect of transducer (‘greenhouse’) gases on an otherwise sunlight-transducer gas-free troposphere has profound implications. One corollary is the conclusion that increasing the concentration of an existing weak transducer, i.e., CO2, could only have a net cooling effect, if any, on the concentric average <T> (z = 0) at sea level and lower troposphere (z < 1 km). A more plausible explanation of global warming is the enthalpy emission ’footprint’ of all fuels, including nuclear.

Numerical Simulation of Micro-Bubbles Dispersion by Surface Waves

This paper presents an algorithm for numerical modeling of bubble dispersion occurring in the near-surface layer of the upper ocean under the action of non-breaking two-dimensional (2D) surface waves. The algorithm is based on a Eulerian-Lagrangian approach where full, 3D Navier-Stokes equations for the carrier flow induced by a waved water surface are solved in a Eulerian frame, and the trajectories of individual bubbles are simultaneously tracked in a Lagrangian frame, taking into account the impact of the bubbles on the carrier flow. The bubbles diameters are considered in the range from 200 to 400 microns (thus, micro-bubbles), and the effects related to the bubbles deformation and dissolution in water are neglected. The algorithm allows evaluation of the instantaneous as well as statistically stationary, phase-averaged profiles of the carrier-flow turbulence, bubble concentration (void fraction) and void-fraction fluxes for different flow regimes, both with and without wind-induced surface drift. The simulations results show that bubbles are capable of enhancing the carrier-flow turbulence, as compared to the bubble-free flow, and that the vertical water velocity fluctuations are mostly augmented, and increasingly so by larger bubbles. The results also show that the bubbles dynamics are governed by buoyancy, the surrounding fluid acceleration force and the drag force whereas the impact of the lift force remains negligible.

Experimental investigation of water entry of dimpled spheres

This study presents the experimental results of the vertical water entry of dimpled spheres. The role of the number and arrangement of the surface dimples under different impact velocities in the air cavity formation/evolution/collapse is mainly considered. The diameter of all the spheres is fixed, and they all enter into a tank filled with tap water. Hence, in all experiments, the Bond number and Capillary length are the same, but the Reynolds, Weber, Capillary, and Froude numbers will vary concerning the difference in impact velocities. A PcoDimax-S high-speed camera visualizes dimpled spheres' trajectory at a frame rate of 1 to 2kfps. In addition to the cavity dynamics, the motion kinetics of the spheres (comprising trajectory, velocity, acceleration, and hydrodynamic force coefficient) is also studied. One important outcome is that dimples are crucial in air entrainment cavity formation, even if the spheres impact the water at low velocities. Also, the results show that at a given impact velocity, increasing the number of dimples can change the pinch-off regime from shallow-seal to deep-seal. In addition, surface dimples improve the descent velocity and acceleration and reduce the hydrodynamic force coefficient.