TRANSVERSE FORCES AND RESULTANT FORCES ON ARRAY OF BI-PILE IN IRREGULAR WAVES

The total transverse forces on each of the two piles in the side-by-side arrangement and tandem arrangement are experimentally investigated in irregular waves and the total in-line wave forces are measured simultaneously. The statistical and spectral characteristics of the transverse forces are analyzed. The ratio of the transverse force on each pile in group to that on a single pile is defined as the transverse groupling-pile factor, KGL. Both the transverse coefficients CLG and KGL for each pile in array are varied with the relative pile distance and KC number and their relationships are presented in this paper. Also the ratio of the resultant wave froce of in-line force and transverse force to the in-line force and the vriation of the resultant coefficient are investigated.

Wave-current forces on bipiles in parallel array

-The inline and lift forces on bipiles in parallel array induced by both irregular waves and currents were investigated experimentally in this paper. The characteristics in both time and frequency domains of inline, lift and resultant forces as well were analyzed. The grouping effect coefficients of inline and resultant forces on two piles related to KC number and relative spacing parameters are given. A comparison of the magnitude and direction of resultant forces on two piles in parallel array with the corresponding values for single cylinder is also made.

Force and impulse multi-sensor based on flexible gate dielectric field effect transistor

Nowadays,force sensors play an important role in industrial production,electronic information,medical health,and many other fields.Two-dimensional material-based filed effect transistor(2D-FET)sensors are competitive with nano-level size,lower power consumption,and accurate response.However,few of them has the capability of impulse detection which is a path function,expressing the cumulative effect of the force on the particle over a period of time.Herein we fabricated the flexible polymethyl methacrylate(PMMA)gate dielectric MoS_(2)-FET for force and impulse sensor application.We systematically investigated the responses of the sensor to constant force and varying forces,and achieved the conversion factors of the drain current signals(I_(ds))to the detected impulse(I).The applied force was detected and recorded by I_(ds)with a low power consumption of~30 nW.The sensitivity of the device can reach~8000%and the 4×1 sensor array is able to detect and locate the normal force applied on it.Moreover,there was almost no performance loss for the device as left in the air for two months.

Pinning Forces in Superconductors from Periodic Ferromagnetic Dot Array

Using the London equation, we derive a formula by which the pinning force from magnetic dots can be cal-culated. We numerically calculate the interaction between ferromagnetic dots and vortices in type II super-conductors under various conditions. It is found that the pinning force of the magnetic dot with 50 nm thick-ness reaches 3.5 × 10-11 N that is one order magnitude stronger than the intrinsic pinning force in cuprate at 77 K. We investigate various parameter dependences of the pinning force. It is found that the most effective way to increase the pinning force is to increase the thickness of the dot. The pinning force is weakly de-pendent on both the size and magnetic permeability of the dots. When temperature increases, the pinning force linearly decreases. And when the magnetic field increases, the attraction force increases linearly in the low field region.

Six-Element Yagi Array Designs Using Central Force Optimization with Pseudo Random Negative Gravity

A six-element Yagi-Uda array is optimally designed using Central Force Optimization (CFO) with a small amount of pseudo randomly injected negative gravity. CFO is a simple, deterministic metaheuristic analogizing gravitational kinematics (motion of masses under the influence of gravity). It has been very effective in addressing a wide range of antenna and other problems and normally employs only positive gravity. With positive gravity the six element CFO-designed Yagi array described here exhibits excellent performance with respect to the objectives of impedance bandwidth and forward gain. This paper addresses the question of what happens when a small amount of negative gravity is injected into the CFO algorithm. Does doing so have any effect, beneficial, negative or neutral? In this particular case negative gravity improves CFO’s exploration and creates a region of optimality containing many designs that perform about as well as or better than the array discovered with only positive gravity. Without some negative gravity these array configurations are overlooked. This Yagi-Uda array design example suggests that antennas optimized or designed using deterministic CFO may well benefit by including a small amount of negative gravity, and that the negative gravity approach merits further study.

A Wireless Inductive-Capacitive Resonant Circuit Sensor Array for Force Monitoring

A wireless passive sensor array based on inductive-capacitive (LC) resonant circuits capable of simultaneously tracking two points of force loading is described. The sensor consisted of a planar spiral inductor connected to two capacitors forming a resonant circuit with two resonant frequencies. When a load was applied to one or both of the parallel plate capacitors, the distance between the plates of the capacitor was altered, thus shifting the observed resonant peaks. Testing illustrated that applied loading to a particular capacitor caused a significant shift in one of the resonant peaks and also a smaller shift in another resonant peak. This interdependence resulted from each capacitive element being connected to the same inductive spiral and was accounted for with a developed analysis algorithm. To validate the experimental observation, a circuit simulation was also generated to model the sensor behavior with changing force/displacement. The novelty of this system lies not only in its wireless passive nature, but also in the fact that a single LC sensor was fashioned to detect more than one point simultaneously.

Central Force Optimization with Gravity <0, Elitism, and Dynamic Threshold Optimization: An Antenna Application, 6-Element Yagi-Uda Arrays

This paper investigates the effect of adding three extensions to Central Force Optimization when it is used as the Global Search and Optimization method for the design and optimization of 6-elementYagi-Uda arrays. Those extensions are Negative Gravity, Elitism, and Dynamic Threshold Optimization. The basic CFO heuristic does not include any of these, but adding them substantially improves the algorithm’s performance. This paper extends the work reported in a previous paper that considered only negative gravity and which showed a significant performance improvement over a range of optimized arrays. Still better results are obtained by adding to the mix Elitism and DTO. An overall improvement in best fitness of 19.16% is achieved by doing so. While the work reported here was limited to the design/optimization of 6- element Yagis, the reasonable inference based on these data is that any antenna design/optimization problem, indeed any Global Search and Optimization problem, antenna or not, utilizing Central Force Optimization as the Global Search and Optimization engine will benefit by including all three extensions, probably substantially.

Theoretical study of the trapping efficiency of an optical tweezers array system

Optical tweezers have been a valuable research tool since their invention in the 1980s. One of the most important developments in optical tweezers in recent years is the creation of two-dimensional arrays of optical traps. In this paper, a method based on interference is discussed to form gradient laser fields, which may cause the spatial modulation of particle concentration. The parameters related to the optical tweezers array are discussed in detail and simulated by the Matlab software to show the influence of important parameters on the distribution of particle concentration. The spatial redistribution of particles in a laser interference field can also be predicted according to the theoretical analysis.

Calculation Method for Forced-Air Convection Cooling Heat Transfer Coefficient of Multiple Rows of Memory Cards

Forced-air convection cooling of high-power electronic devices is widely used, but it has a problem that a rise in temperature of the air used to cool the upstream devices decreases the cooling capa-bility for the downstream devices. In this study we made an experimental apparatus including a memory card array and measured the effect of the rise in temperature of the air on the heat transfer coefficient of the memory cards that were downstream in the air flow. Using these mea-surements, we devised a simple calculation model, called the thermal diffusion layer model, to calculate the heat transfer coefficient of multiple rows of memory cards. The rise in temperature of downstream memory cards due to higher temperature air can be evaluated with a parameter representing the delay of thermal mixing for air. The heat transfer coefficient calculated with the thermal diffusion layer model agreed with our experimental results.

A force feedback master finger in exoskeleton type

In order to eliminate the drawbacks of conventional force feedback gloves, a new type of master fin- ger has been developed. By utilizing three ＂four-bar mechanism joint＂ in series and wire coupling mecha- nism, the master finger transmission ratio is kept exactly 1：1.4：1 in the whole movement range and it can make active motions in both extension and flexion directions. Additionally, to assure faster data transmission and near zero delay in the master-slave operation, a digital signal processing/field programmable gate array （DSP/FPGA-FPGA） structure with 200μs cycle time is designed. The operating modes of the master finger can be contact or non-contact, which depends on the motion states of a slave finger, free motion or constrained motion. The position control employed in non-contact mode ensures unconstrained motion and the force control adopted in contact mode guarantees natural contact sensation. To evaluate the performances of the master finger, an experiment between the master finger and a DLR/HTT dexterous finger is conducted. The results demonstrate that this new type master finger can augment telepresence.

ON HYDRODYNAMIC INTERACTION UPON THE WAVE FORCES ON VERTICAL PILE ARRAY

A systematic study is carried out on the hydrodynamic interaction of single-row vertical pile array with a large number of piles by using the method of wave source distribution. Some new properties for the hydrodynamic interaction among piles are first reported in this paper. The present study shows the importance and necessity of reassessing the hydrodynamic interaction among multiple objects of large number to reach a complete understanding on that subject.

Robust nonlinear control of spacecraft formation flying using constraint forces

A robust nonlinear control method is presented for spacecraft precise formation flying.With the constraint forces and consid-ering nonlinearity and perturbations,the problem of the formation keeping is changed to the Lagrange systems with the holonomic constraints and the differential algebraic equations (DAE).The nonlinear control laws are developed by solving the DAE.Because the traditional numerical solving methods of DAE are very sensitive to the various errors and the resulting con-trol laws are not robust in engineering application,the robust control law designed method is further developed by designing the correct coefficients to correct the errors of the formation array constraints.A numeral study simulated the robustness of this method for the various errors in the formation flying mission,including the initial errors of spacecraft formation,the reference satellite orbit determination errors,the relative perturbation forces model errors,and so on.

Nonlinear control of multiple spacecraft formation flying using the constraint forces in Lagrangian systems

Getting inspiration from the constraint forces in the classical mechanics, we presented the nonlinear control method of multiple spacecraft formation flying to accurately keep the desired formation arrays. Considering nonlinearity and perturbation, we changed the question of the formation array control to the Lagrange equations with the holonomic constraints and the differential algebraic equations (DAE), and developed the nonlinear control for design of the follower spacecraft tracking control laws by solving the DAE. Because of using the idea of the constraint forces, this approach can adequately utilize the characteristic of the dynamic equations, i.e., the space natural forces, and accurately keep the arbitrary formation array. Simulation results of the circular formation keeping with the linear and nonlinear dynamical equations were included to illuminate the control performance.

Hydrodynamic Coefficients for Grouping Piles Under the Action of Irregular Waves

-The hydrodynamic coefficients for each of two piles and three piles in both side-by-side arrangement and tandem arrangement under the action of irregular waves are experimentally investigated. These coefficients vary with the KC number, the relative pile spacing, the number of piles and the pile location, and their relationships are presented in this paper. They can be used in Morison Equation and other equations to calculate directly the in-line wave forces and the transverse forces on each pile in array.

A neural network-based commutation optimization strategy and drive system design for brushless DC motor

An optimized commutation method based on backpropagation(BP)neural network is proposed to resolve the low stability and high-power consumption caused by inaccurate commutation point prediction in conventional commutation strategy during acceleration and deceleration.This article also builds a complete brushless DC motor drive system based on the GD32F103 micro control unit(MCU),with an Artix-7 XC7A35T field programmable gate array(FPGA)to meet the performance requirements of neural network calculation for real-time motor commutation control.Experimental results show that the proposed optimization strategy can effectively improve the system stability during system acceleration and deceleration,and reduce the current spikes generated during speed chan-ges.The system power consumption is reduced by about 11.7%on average.

Current-Bounded Commutation of a Long-Stroke Magnetically Levitated Stage with Moving Coils

Magnetically levitated stages（MLS） have potentials to obtain good motion performances in high vacuum environment. Yet the electromagnetic forces/torques corresponding to six degrees of freedom（DOF） motions have coupling relationship with each current of coil array, and this coupling is still associated with the relative positions between the mover and the stator of the stage. So it is quite difficult to control the 6-DOF motions of the stage. By reasonable commutation of coil array, this complicated coupling relationship can be decoupled. The analytical force/torque-decomposing model of the stage is established first. Then the initial currents of coil array are commutated based on the pseudo inverse of the analytical force/torque-decomposing model matrix. And then the coil array currents are commutated again with different current bounds given to the initial currents as well as in the sense of minimum 2-norm of currents vector. Using the long stroke magnetically levitated stage with moving coils under investigation as examples, the currents of coil array are commutated with different current bounds adopting the proposed commutation method, the determination of current bound and the current bounds＇ influences on the heat-losses in coil array are analyzed, and the effectiveness of implementation algorithm of proposed commutation method is discussed. Simulation, analysis and discussion results indicate that the currents of coil array within the given current bound can be solved analytically by proposed commutation method, and the implementation algorithm does not need any searching or iteration. By the current-bounded commutation method proposed, the amplitude of coil array currents can be limited within an appropriate current bound（This is very beneficial to the improvement of the reliability and motion performance of the stage）, as well as these currents can also generate the desired forces and torques.

Oscillations of elastically mounted cylinders in regular waves

Under the assumption of potential flow and linear wave theory, a semi-analytic method based on eigenfunciton expansion is proposed to predict the hydrody-namic forces on an array of three bottom-mounted, surface-piercing circular cylinders. The responses of the cylinders induced by wave excitation are determined by the equa-tions of motion coupled with the solutions of the wave radiation and diffraction problems. Experiments for three-cylinder cases are then designed and performed in a wave flume to determine the accuracy of this method for regular waves.

Adhesion hysteresis of a film-terminated fibrillar array

Motivated by the recent biomimic design of microstructured adhesive surfaces,we study adhesion between a film-terminated fibrillar array and a rigid substrate.Using a two-dimensional model and ignoring the deformation of the fibers and the backing layer,we show that the adhesion behavior is dominated by a dimensionless parameter reflecting the global flexibility of the terminal film.In particular,if the parameter is larger than 0.4,the adhesion is reversible;otherwise one or more hysteresis loops will appear after an approach-retraction cycle,leading to significant increase in the specific separation work.The result is expected to help not only optimal design of the structure,but also other applications such as micro-manipulation in micromechanical systems.

Multi-Objective Optimization of Torsion Springs for Solar Array Deployment

For solar array deployment,most existing studies mainly focus on modeling method of deployment dynamics,characteristics of hinges,and synchronization mechanisms.However,torsion springs,which work as the drive mechanisms,have hardly attracted people's attention.In this study,the influence of the parameters of torsion springs on the deployment behavior of a solar array system with clearance joint is investigated by simulation experiments.The experimental results indicate that the deployment performances are very sensitive to the parameter values of the torsion spring.Suitable torsion springs are highly needed to improve the deployment dynamics of solar array system.Therefore,a multi-objective optimization method for the design of torsion springs is proposed.The objective of the optimization is to make the contact-impact force in revolute joint and the mass of the torsion spring minimum under the constraints of deployment time and structure strength.Finally,the effectiveness of the multi-objective optimization method is verified by an optimization example of solar array system.

Assembling and Test of a Halbach Array Magnet System for Lorentz Forece Velocimetry in Electrolytes

The paper presents a Halbach array magnet system(HAMS)for the application within a very first Lorentz force velocimetry(LFV)experiment for electrolytic flows.Here the design,assembling procedure and characterization method are presented under consideration of the strict limited weight of the system.HAMS increase the Lorentz force outcome by a factor of three compared to the currently used simple magnet systems.Furthermore the fluid profile influence on a LFV measurement on electrolytes is investigated numerically-directly on the planned test setup-and presented for the first time.Here the Lorentz forces,generated by the HAMS,decreases by 8%comparing an ideal plug-like profile at the inlet with a semi-parabolic profile arising near the outlet of the experiment.