Impact of the equivalent center of mass separating from the sliding surface on the isolation performance of friction pendulum bearings

A new equivalent center of mass model of FPBs (friction pendulum bearings) is introduced, and based on this model, coefficient j of the equivalent center of mass separating from the sliding surface is defined. It is thought in theory that j has a significant impact on the isolation parameter of FPBs, since the equivalent post-yielding stiffness and friction coefficients are not simply determined by sliding radius and sliding friction pairs. The results of numerical simulation analysis using ABAQUS conducted on two groups of FPBs support this viewpoint. For FPBs with the same sliding radius and sliding friction pairs, the FPB modules of structural analysis software such as ETABS could only distinguish the equivalent transformation using j one by one. The seismic response data obtained in a base isolation calculation example of FPBs are very different, which reveals that j’s impact on the isolation effectiveness of FPBs cannot be ignored. The introduction of j will help improve the classical structural theory of FPBs and the weak points of structural analysis software based on this theory, which is important in achieving more accurate analyses in structural design.

The Contribution of the Gravitational Propagation Delay to Orbital and Center of Mass Motions

Recent measurements have shown that gravitational waves and thus the gravitational interaction propagate with the speed of light. The propagation delay of the gravitational interaction in orbiting systems couples the orbital and center of mass motions. This causes the orbits to spiral out and the center of mass to accelerate. It is one of a number of small effects modifying the Kepler orbits. The calculations show that the analytical describable expansion of the semimajor axis started at a time that is less than the age of the systems. This could be caused by a collision of a system component in the past. The effect of this propagation delay on the motion of the Earth Moon and the Brown Dwarf 569Bab binary star system is analyzed. These systems were chosen because a considerable amount of measured astronomical data is available. The calculated results are in excellent agreement with the measured data. In galaxies, too, the energy transfer from the orbit of the star cloud to the center of mass motion causes the galaxies to ac-celerate. If galaxies are considered to be molecules of the universe, then the acceleration of the galaxies will cause the molecular gas to heat and expand. Alternatively, the loss in orbital internal energy of the galaxies should be included in the mass and energy in the calculation of the expanding Universe.

Interaction between an Accelerated Mass in Straight Motion and a Hidden Energy Reservoir as a Strict Mathematical Consequence of Special Relativity

A. Einstein and H.A. Lorentz had found that the mass of an accelerated body traveling at relativistic velocity appears to depend on whether the acceleration is performed in the direction of motion or in a transverse direction. E.P. Epstein rejected this result in the “Annalen der Physik”;he rather postulated an additional force that turns up when the body is accelerated in the longitudinal direction. It can be shown that the concept of an increased longitudinal mass is based on a simple mathematical error. When correcting this error, it turns out that Epstein’s additional, hidden force is indispensable in order to avoid an inner inconsistency of Special Relativity. It does most of the total work absorbed by the moving object, and is thus responsible for most of the increase in its energy (=mass), given the speed attained is relativistic. In other words: While the total force on the body needed to maintain a constant acceleration a0 is “(1-v2/c2)-1ma0=m0(1-v2/c2)-3/2a0”, the technical force needed to maintain that acceleration amounts only to “ma0=m0(1 - v2/c2)-1/2a0”. The total energy of two objects that undergo a symmetrical, elastic head-on collision is therefore not conserved during the collision, thus requiring the involvement of a hidden reservoir of energy. This result is confirmed by calculations that use the concept of momenergy. The phenomenon of an apparent disappearance of energy has been noticed in particle physics already (target-experiment), but its consequences have been ignored. Instead, an explanation has been given (reduced “energy of the center of mass”) which is inconsistent and violates the relativity principle.

Hydrodynamic Analysis of C-start in Crucian Carp

The kinematics of turning maneuvers of startled Crucian Carp (Carassius auratus) are presented. All escape responses observed are C-type fast-starts. The position of the center of mass and the moment of inertia of the fish are calculated. The results show that the position of the center of mass is always at 35% of the length of the fish from the head and the position of the center of mass and moment of inertia can be considered unchanged during C-start of Crucian Carp. Hydrodynamic analysis of the C-start is given based on the kinematics data from our experiments. The C-start consists of three stages. In stage 1, the tail fin of fish rapidly flaps in one direction, and a large moment acts on the fish′s body, which rotates around the center of mass with an angular acceleration. In stage 2, the tail fin flaps more slowly in the opposite direction at slower speed, the fish′s body rotates around the center of mass with angular deceleration and the center of mass of the fish moves along an arc. In stage 3, the moment approximately equals zero, the fish′s body stops rotating and the center of mass the moves along a straight line.

Study of Helicity in Typhoon Rainfall Regions——A Case Study of Typhoon "Muifa"

Using the center of figure method and center of mass method, precipitation and heavy precipitation processes caused by No. 9 typhoon ＂ Muifa＂ in 2011 were analyzed based on helicity, and the mechanism of typhoon rainfall was interpreted from the relation between helicity and ener- gy. The results showed that horizontal helicity checked the diffusion of nonlinear energy and maintained the development of the system. Precipitati- on mainly appeared on the southeast of vertical helicity, while heavy precipitation mainly occurred on its southwest. Compared with the center of fig- ure method, the center of mass method had good results, especially for heavy precipitation. Vertical helicity at 700 hPa reflected system deviation in rainfall regions well and had the best correction effect on rainfall intensity and regions

Thruster direction controlling of assembled spacecraft based on gimbal suspension

The attitude control system design and its control effect are affected considerably by the mass-property parameters of the spacecraft. In the mission of on-orbit servicing, as fuel is expended, or the payloads are added or removed, the center of mass will be changed in certain axe; consequently, some thrusters＇ directions are deviated from the center of mass（CM） in certain plane. The CM of assembled spacecraft estimation and thruster direction control are studied. Firstly, the attitude dynamics of the assembled spacecraft is established based on the Newton-Euler method. Secondly, the estimation can be identified by the least recursive squares algorithm. Then, a scheme to control the thrusters＇ directions is proposed. By using the gimbal installed at the end of the boom, the angle of the thruster is controlled by driving the gimbal; therefore, thrusters can be directed to the CM again. Finally, numerical simulations are used to verify this scheme. Results of the numerical simulations clearly show that this control scheme is rational and feasible.

Effects of a 12-week online Tai Chi intervention on gait and postural stability in individuals with Parkinson’s disease

Parkinson's disease(PD)affects gait and postural stability.Tai Chi(TC)is recommended for PD for management of the condition,however biomechanical understanding to its effects on gait and postural stability is limited.This study aimed to examine the effects of an online 12-week biomechanical-based TC intervention on gait and posture in people with PD.Fifteen individuals in early-stage PD were recruited(Hoehn&Yahr stages 1-2).The TC intervention program was 60min session,three times weekly for 12 weeks.The pre-and post-intervention test in obstacle crossing,timed-up-and-go(TUG)test,and single leg standing(SLS)with eyes open(EO)and closed(EC)were conducted.Gait speed,crossing stride length,clearance height of the heel and toe,anterior-posterior(AP)and medial-lateral(ML)displacement and velocity of the center of mass(COM)and separation of the COM-center of pressure(COP)were analyzed.The participants significantly improved their pre-vs.post-TC intervention performance on TUG test(p=0.002).During obstacle crossing,the participants significantly increased crossing stride length of the trailing foot,increased AP COM displacement and decreased ML COM-COP separation(p<0.05);the maximal dorsiflexion angle of the leading limb significantly increased and maximal plantarflexion angle of the trailing limb significantly decreased(p<0.05).A 12-week biomechanical-based online TC training was effective towards improvement of gait and postural stability among people in the early-stage of PD.The TC program and online training could be applied for management of PD.

Development of agricultural bionic four-legged robot:Effect of head movement adjustment on the stability of goats

The four-legged bionic robot for agriculture has been one of the hotspots in the field of robotics.The farmland environment is complex,and the balance requirement of quadruped bionic robot is higher.However,head adjustment is a key factor affecting the balance of quadruped animals.Based on this,this study takes the four-legged animal goat as an example to investigate the effect of goat head movement adjustment on the balance of goat.In this study,the head and neck of goats were simplified to a two-link model.The kinematics model was established by D-H method.MATLAB software was used to solve it.Origin software was used to draw the movement track of the center of mass of the head.The center of mass movement of the head is a quarter ellipse.Then,the goat walking experiments were carried out on the different slopes(0°,5°,10°,15°,20°,25°,30°,35°and 40°).MATLAB software was used to fit the movement data of goat head.The movement of the center of mass of the goat's head corresponds to Fourier 6.The result is:the determination coefficient is 0.8629,and the mean variance is 0.019.When the slope gradient gradually increases,the volatility gradually increases and is cyclical.The results of this study verify the rationality of the four-legged bionic mechanism under various parameters and reveal the mechanism of goat walking with an appendage at the head.

Dynamics of Particles Around a Regular Black Hole with Nonlinear Electrodynamics

We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential are analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.

Effect of slope inclination on step friction coefficient of human being

Effect of slope inclination on step friction coefficient of human being was studied by gait friction tester developed by Henan University of Science and Technology.It is beneficial to improving the safety of human beings while walking on a ramp.Based on the trajectory of mass center of body(MCOB)and the mechanical analysis of human body while walking,conclusion could be drawn that the required step frictional coefficient(RSFC)exhibited an"M"shaped curve during the foot contacting with the ground and got its maximum and minimum values when MCOB of the subject was at the highest and lowest position respectively.Moreover,the first peak of RSFC decreases firstly and then increases,while the second peak of RSFC increases with the increase of slope inclination at the experimental condition.The position of pivotal point is decided by the relative size of slope inclination and the angle between the plumb line through MCOB and the line from foot to MCOB.