Estimating gravity component from accelerometers

2019 ◽  
Vol 22 (1) ◽  
pp. 48-53
Author(s):  
Manuel Gil-Martin ◽  
Ruben San-Segundo ◽  
Syaheerah Lebai Lutfi ◽  
Alejandro Coucheiro-Limeres
Keyword(s):  
Gravity Component

scholarly journals Fluctuation analysis in the dynamic characteristics of continental glacier based on Full-Stokes model

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Zhen Wu ◽  
Huiwen Zhang ◽  
Shiyin Liu ◽  
Dong Ren ◽  
Xuejian Bai ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Process ◽  
Great Influence ◽  
Force Balance ◽  
Surface Velocity ◽  
Viscous Force ◽  
Fluctuation Analysis ◽  
Temperature Changes ◽  
Ice Surface ◽  
Gravity Component

AbstractIce thickness has a great influence on glacial movement and ablation. Over the course of the change in thickness, area and external climate, the dynamic process of how glaciers change and whether a glacier’s changes in melting tend to be stable or irregular is a problem that needs to be studied in depth. In our study, the changes in the dynamic process of the No. 8 Glacier in Hei Valley (H8) under the conditions of different thicknesses in 1969 and 2009 were simulated based on the Full-Stokes code Elmer/Ice (http://www.csc.fi/elmer/). The results were as follows: (1) The thickness reduction in glaciers would lead to a decrease in ice surface tension and basal pressure and friction at the bottom, and the resulting extensional and compressional flow played an important role in the variations in glacial velocity. (2) The force at the bottom of the glacier was key to maintaining the overall stress balance, and the glaciers that often melted and collapsed in bedrock were more easily destroyed by the overall force balance and increased change rate of glacial thaw. (3) Temperature changes at different altitudes affected the ice viscous force. The closer the ice surface temperature was to the melting point, the greater the influence of temperature changes on the ice viscous force and ice surface velocity. Finally, we used the RCP 4.8 and 8.5 climate models to simulate the changes in H8 over the next 40 years. The results showed that with some decreases in ice surface compression and tension, the gravity component changes caused by local topography begin to control the ice flow movement on the surface of glacier, and melting of the glacial surface will appear as an irregular change. The simulation results further confirmed that the fluctuation in glacial dynamic characteristics could be attributed to the change in the gravity component caused by ablation.

Carcass Tear Out Load Model for Multi-Layer Pressure Sheath Risers

2014 ◽  
Author(s):  
Claus Egebjerg Kristensen ◽  
Jan Muren ◽  
Geir Skeie ◽  
Håvard Skjerve ◽  
Nils Sødahl
Keyword(s):  
Probability Of Failure ◽  
Simulation Approach ◽  
Axial Loads ◽  
Contributing Factors ◽  
Load Model ◽  
General Terms ◽  
Polymer Properties ◽  
Flexible Risers ◽  
Key Driver ◽  
Gravity Component

Recent failures of multi-layer pressure sheath risers have shown that the carcass may fail in the top termination due to excessive axial loads. This is a new failure mode for flexible risers, recently presented by the authors in more general terms. The present paper explains details of the established load model and the validation against mid-scale tests, risers failed during operation, and operating risers close to failure by this new mode. The key driver in the model is the temperature contraction of pressure sheath layers. Also influenced by changes in polymer properties over the operational history, temperature and time is explained. Other contributing factors in the load model are gravity-component and bore pressure. The prediction model for the carcass loads are developed during Statoils investigation in 2011–12. The model is regarded representative for 20% of the most exposed risers. Several of the input parameters are uncertain and a Monte Carlo simulation approach is selected to study the variability and predict the probability of failure, given that radial contact pressure is sufficiently low. The approach adopted in the model may be applicable to other risers where polymers and steel components act together, and in such circumstances act as a guide for alternative model developments.

scholarly journals A one-dimensional model for wave-induced ice-floe collisions

1991 ◽  
Vol 15 ◽  
pp. 87-95 ◽  
Author(s):  
Hayley H. Shen ◽  
Stephen F. Ackley
Keyword(s):  
Wave Amplitude ◽  
Field Studies ◽  
Added Mass ◽  
Lateral Motion ◽  
Dimensional Model ◽  
One Dimensional ◽  
Ice Floes ◽  
Wave Induced ◽  
Gravity Component ◽  
Dimensional Wave

In this study, the collision of ice floes under the action of a monotonic wave is quantified. The lateral motion of an ice floe caused by the wave is modeled as the sliding of an object under gravity. In this case, the gravity component in the direction of motion varies with time and space as the wave progresses by the floe. Drag and added mass effects are included in the model. Two floes located at different positions are shown to have a net difference in their drift (caused only be repeated wave passages). In most cases, this differential drift eventually causes floe collision. When two floes collide, a spring and dash-pot model is adopted to calculate the contact force. A one-dimensional wave passing through a one-dimensional array of disc-shaped floes is examined. Two phenomena are apparent from the analysis. First, waves have a herding effect that forms bands of floes with the width equal to the wavelength. Secondly, the frequency of collision is sensitive to the elastic properties of the floes and the wave amplitude. With sufficient values of the damping constant, which operates when two floes collide, the floes stay in contact for prolonged periods, indicating the potential to freeze together and form composite floes, as was observed in the field studies.

scholarly journals GEOTROPIC CREEPING OF YOUNG RATS

1927 ◽  
Vol 10 (4) ◽  
pp. 525-532 ◽  
Author(s):  
G. Pincus
Keyword(s):  
Gravitational Effect ◽  
Upward Movement ◽  
Young Rats ◽  
Gravity Component

The rate of upward creeping in negatively geotropic rats aged 13 to 14 days is a function of the gravitational stimulus. The rate of upward movement on the creeping plane, like the angle of orientation, is directly proportional to the logarithm of the gravity component. The variability in the speed of creeping decreases in proportion to the logarithm of the gravitational effect. When weights are attached to the animals' tails the rate of upward creeping varies almost directly as the logarithm of the attached weight, and the speed of creeping is still proportional to the angle of upward orientation.

scholarly journals Numerical investigation on the effect of the vessel rolling angle and period on the energy harvest

2021 ◽  
pp. 147509022110024
Author(s):  
Boyang Li ◽  
Rui Zhang ◽  
Qingyong Yang ◽  
Baoshou Zhang ◽  
Longjin Wang
Keyword(s):  
Mathematical Model ◽  
Angular Displacement ◽  
Mechanical Energy ◽  
Average Power ◽  
Energy Harvest ◽  
Matlab Simulation ◽  
Rolling Angle ◽  
Instantaneous Power ◽  
The Mathematical Model ◽  
Gravity Component

In order to harvest effectively the mechanical energy produced in the process of vessel rolling, an energy harvest unit installed on the vessel is designed to utilize the mechanical energy. Firstly, the structure of the unit is proposed, and the relevant mathematical model is established. The solution of the mathematical model is given by Newmark- β method. Then, the influence of vessel rolling period and angle on the unit’s power and related parameters of the block is studied by MATLAB simulation. The results show that when the vessel is rolling, the energy harvest unit has a considerable power generation effect, the rolling period and angle of the vessel have a great impact on the power of the unit. Under the condition of the same period, the vessel with a larger rolling angle corresponds to larger peak gravity component, peak angular displacement, peak linear velocity of block and average power of the unit. In addition, under the same sea conditions, numerical simulations carried out on the rolling motion of 70,000, 100,000, and 150,000-ton bulk vessels and related parameters of the unit, indicating that the instantaneous power of the unit is not uniform in actual sea conditions, but it can output power continuously.

Speed Estimation using Smartphone Accelerometer Data

2019 ◽  
Vol 2673 (3) ◽  
pp. 65-73
Author(s):  
Ilyas Ustun ◽  
Mecit Cetin
Keyword(s):  
Kinetic Theory ◽  
White Noise ◽  
Calibration Method ◽  
Speed Estimation ◽  
Vehicle Speed ◽  
Accelerometer Data ◽  
Model Accuracy ◽  
Lower Margin ◽  
Sample Data ◽  
Gravity Component

This paper is focused on developing an algorithm to estimate vehicle speed from accelerometer data generated by an onboard smartphone. The kinetic theory tells that the integration of acceleration gives the speed of a vehicle. Thus, the integration of the acceleration values collected with the smartphone in the direction of motion would theoretically yield the speed. However, speed estimation by the integration of accelerometer data will not yield accurate results, as the accelerometer data in the direction of motion is not pure acceleration, but involves white noise, phone sensor bias, vibration, gravity component, and other effects. To account for these sources of noise and error, a calibration method that can adjust the speed at certain times or points is needed. The exact times when the vehicle stops and starts are identified and used to calibrate the estimated speed. Based on the collected sample data, the proposed method yields that the estimated speed is on average within 10 mph of the actual speed, with a lower margin at the street-level driving. This suggests that with more information to calibrate the speed, the model accuracy can be improved further.

scholarly journals A one-dimensional model for wave-induced ice-floe collisions

1991 ◽  
Vol 15 ◽  
pp. 87-95 ◽  
Author(s):  
Hayley H. Shen ◽  
Stephen F. Ackley
Keyword(s):  
Wave Amplitude ◽  
Field Studies ◽  
Added Mass ◽  
Lateral Motion ◽  
Dimensional Model ◽  
One Dimensional ◽  
Ice Floes ◽  
Wave Induced ◽  
Gravity Component ◽  
Dimensional Wave

In this study, the collision of ice floes under the action of a monotonic wave is quantified. The lateral motion of an ice floe caused by the wave is modeled as the sliding of an object under gravity. In this case, the gravity component in the direction of motion varies with time and space as the wave progresses by the floe. Drag and added mass effects are included in the model. Two floes located at different positions are shown to have a net difference in their drift (caused only be repeated wave passages). In most cases, this differential drift eventually causes floe collision. When two floes collide, a spring and dash-pot model is adopted to calculate the contact force. A one-dimensional wave passing through a one-dimensional array of disc-shaped floes is examined. Two phenomena are apparent from the analysis. First, waves have a herding effect that forms bands of floes with the width equal to the wavelength. Secondly, the frequency of collision is sensitive to the elastic properties of the floes and the wave amplitude. With sufficient values of the damping constant, which operates when two floes collide, the floes stay in contact for prolonged periods, indicating the potential to freeze together and form composite floes, as was observed in the field studies.

scholarly journals GEOTROPISM OF AGRIOLIMAX

1927 ◽  
Vol 10 (5) ◽  
pp. 757-765 ◽  
Author(s):  
Ernst Wolf
Keyword(s):  
Body Mass ◽  
Glass Plate ◽  
The Body ◽  
Direct Proportion ◽  
Threshold Difference ◽  
Young Rats ◽  
Coefficient Of Variability ◽  
Longitudinal Muscles ◽  
Gravity Component

On an inclined glass plate the slug Agriolimax orients and creeps upward or downward. The angle of orientation on the plane (θ) is proportional to the logarithm of the component of gravity in the creeping plane. The coefficient of variability of the measured values of (θ) decreases linearly as the logarithm at the gravity component in the creeping plane increases. The cosine of the angle of orientation decreases almost directly in proportion to the sine of the angle of inclination of the creeping plane to the horizontal, as previously found for young rats (Crozier and Pincus). But a more satisfactory formulation for the present case shows that the sine of the angle of orientation (θ) decreases in direct proportion to the increase of the reciprocal of the sine of the angle of inclination of the creeping plane. This formulation is derived from the theory that the geotropic orientation is limited by the threshold difference between the pull of the body mass on the mutually inclined longitudinal muscles at the anterior end of the slug.

Simple shear is not so simple! Kinematics and shear senses in Newtonian viscous simple shear zones

2012 ◽  
Vol 149 (5) ◽  
pp. 819-826 ◽  
Author(s):  
SOUMYAJIT MUKHERJEE
Keyword(s):  
Pressure Gradient ◽  
Shear Zone ◽  
Simple Shear ◽  
Shear Zones ◽  
Horizontal Shear ◽  
Flow Parameters ◽  
Uniform Shear ◽  
Shear Sense ◽  
Simple Shear Deformation ◽  
Gravity Component

AbstractThis work develops an analytical model of shear senses within an inclined ductile simple shear zone with parallel rigid boundaries and incompressible Newtonian viscous rheology. Taking account of gravity that tends to drive the material downdip and a possible pressure gradient that drives it upward along the shear zone, it is shown that (i) contradictory shear senses develop within two sub-zones even as a result of a single simple shear deformation; (ii) the highest velocity and least shear strain develop along the contact between the two sub-zones of reverse shear; (iii) for a uniform shear sense of the boundaries, a zone of reverse shear may develop within the top of the shear zone if the pressure gradient dominates the gravity component; otherwise it forms near the bottom boundary; (iv-a) a ‘pivot’ defined by the intersection between the velocity profile and the initial marker position distinguishes two sub-zones of opposite movement directions (not shear sense); (iv-b) a pivot inside any non-horizontal shear zone indicates a part of the zone that extrudes while the other subducts simultaneously; (v) the same shear sense develops: (v-a) when under a uniform shear of the boundaries, the shear zone remains horizontal and the pressure gradient vanishes; or alternatively (v-b) if the shear zone is inclined but the gravity component counterbalances the pressure gradient. Zones with shear sense reversal need to be reinterpreted since a pro-sheared sub-zone can retro-shear if the flow parameters change their magnitudes even though the same shear sense along the boundaries is maintained.

scholarly journals Dynamic feedforward control in decoupling space for a four-degree-of-freedom parallel robot

2019 ◽  
Vol 16 (1) ◽  
pp. 172988141882045 ◽  
Author(s):  
Xiaogang Song ◽  
Yongjie Zhao ◽  
Lei Jin ◽  
Peng Zhang ◽  
Chengwei Chen
Keyword(s):  
Dynamic Model ◽  
Robust Stability ◽  
Control Method ◽  
Feedforward Control ◽  
Mass Matrix ◽  
Parallel Robot ◽  
Degree Of Freedom ◽  
Gravity Component ◽  
Modal Space ◽  
Control Accuracy

This article proposes a dynamic feedforward control method for a four-degree-of-freedom parallel robot in decoupling space to improve the control accuracy and robust stability. The mass matrix and the gravity component are obtained from the rigid-body dynamic model that is formulated by means of the link Jacobian matrices and the principle of virtual work. Then using the positive definiteness of the mass matrix and singular value decomposition algorithms, a decoupling transformation matrix is obtained to convert the physical joint space to the decoupling modal space. In the modal space, a decoupling closed-loop controller design has been implemented for each driven leg. Afterward, by applying the gravity component of the dynamic model, a feedforward control subsystem has been designed to compensate the influence of gravity load on the parallel robot, which can further reduce the negative impacts caused by modeling inaccuracies. This numerical simulation analysis shows that the ideal control accuracy and robust stability have been achieved using the dynamic feedforward decoupling control method for the nonlinear and strongly coupled systems of the parallel robot. The described controller has a simple structure and can be easily realized in practice.

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