Moment Of Inertia Research Articles

Development of a Virtual Telehandler Model Using a Bond Graph

Recent technological advancements and evolving regulatory frameworks are catalysing the integration of renewable energy sources in construction equipment, with the objective of significantly reducing greenhouse gas emissions. The electrification of non-road mobile machinery (NRMM), particularly self-propelled Rough-Terrain Variable Reach Trucks (RTVRT) equipped with telescopic booms, presents notable stability challenges. The transition from diesel to electric propulsion systems alters, among other factors, the centre of gravity and the inertial matrix, necessitating precise load capacity determinations through detailed load charts to ensure operational safety. This paper introduces a virtual model constructed through multiphysics modelling utilising the bond graph methodology, incorporating both scalar and vector bonds to facilitate detailed interconnections between mechanical and hydraulic domains. The model encompasses critical components, including the chassis, rear axle, telescopic boom, attachment fork, and wheels, each requiring a comprehensive three-dimensional treatment to accurately resolve spatial dynamics. An illustrative case study, supported by empirical data, demonstrates the model’s capabilities, particularly in calculating ground wheel reaction forces and analysing the hydraulic self-levelling behaviour of the attachment fork. Notably, discrepancies within a 10% range are deemed acceptable, reflecting the inherent variability of field operating conditions. Experimental analyses validate the BG-3D simulation model of the telehandler implemented in 20-SIM establishing it as an effective tool for estimating stability limits with satisfactory precision and for predicting dynamic behaviour across diverse operating conditions. Additionally, the paper discusses prospective enhancements to the model, such as the integration of the virtual vehicle model with a variable inclination platform in future research phases, aimed at evaluating both longitudinal and lateral stability in accordance with ISO 22915 standards, promoting operator safety.

Design of Novel Acat Inhibitors as Potent Anti-Hyperlipidemic Agents Using Chemometric Approaches

Aim: A 2D QSAR study of acyl-coenzyme A (CoA): cholesterol acyltransferase (ACAT) inhibitors revealed that electronic, topological, and steric properties are important structural features required for activity against ACAT. Background: In order to interpret the evidence encrypted by the molecular structure of the compounds, a standard physicochemical descriptors-centered, and Quantitative Structure-Activity Relationship (QSAR) approach was implemented on a data set of Indoline derivatives were reported to be acyl-coenzyme A (CoA): cholesterol acyltransferase ACAT inhibitors. Objective: The ACAT enzyme plays an important role in the absorption of dietary cholesterol. Therefore, the inhibition of ACAT is a key strategy or primary objective for the treatment of hypercholesterolemia and atherosclerosis. Method: Chemo metric models were designed by inserting a battery of statistical techniques in the current study that demonstrate the linear approaches of analysis, including multiple linear regression (MLR), partial least square PLS, and non-linear methods such as artificial neural networks (ANN). Result: The activity contributions of these molecules were analyzed through regression equation, and the best QSAR model was created with an excellent correlative and predictive ability. Significant statistical values S = 0.35, F = 60.30, r = 0.92, r² = 0.85, r² (CV) = 0.82 of the designed models were obtained using stepwise MLR and a comparable PLS and FFNN model with r² (CV) = 0.82, 0.88 and 0.86 respectively and the relevant descriptors like inertia moment 1 size, Kier Chiv4 (cluster) index, Kier Chiv6(ring) index offered important information regarding this model. Conclusion: The model reveals that inertia moment 1 size, Kier Chiv4 (cluster) index, and Kier Chiv6 (ring) index are prerequisite descriptors to determine other promising ACAT antagonists with high and liable potency against the target. Therefore, these characteristics may be used efficiently for the design and evaluation of active compounds as new ACAT inhibitors thanks to their utilization.

Aspects of rotating anisotropic dark energy stars

By employing modified Chaplygin fluid prescription for the dark energy, we construct slowly rotating isotropic and anisotropic dark energy stars. The slow rotation is incorporated via general relativistic Hartle–Thorne formalism; whereas the anisotropy is introduced through Bowers–Liang prescription. We consider both the monopole and quadrupole deformations and present a complete analysis of rotating dark energy stars. By numerically solving the rotating stellar structure equations in presence of anisotropy, we analyse and quantify various properties of dark energy stars such as mass (M), radius, mass deformation, angular momentum (J), moment of inertia, and quadrupole moment (Q), for three different equation of state parameters. We find that anisotropic slow rotation results in significant deformation of stellar mass and thereby affects other global properties studied. For the values of angular frequencies considered, the effect of anisotropy on the stellar structure is found to be more prominent than that due to rotation. The dimensionless quadrupole moment QM/J2 measuring deviation from a Kerr metric black hole was obtained for anisotropic dark energy stars. We observe that dark energy stars with higher anisotropic strength tend to approach the Kerr solution more closely. We report that our results have considerable agreement with various astrophysical observational measurements. We also find that the dimensionless quadrupole moments of anisotropic dark energy stars corresponding to the canonical mass q¯1.4 have a similar range of values as that of isotropic neutron stars and strange stars.

Stiffness modulation in a 3-DoF pneumatic soft actuator for single-port transvesical prostatectomies

Abstract Soft actuators have demonstrated potential in minimally invasive surgery (MIS), requiring multiple degrees of freedom and stiffness modulation facilitated by pneumatic antagonistic chambers. However, the hollow central passage in these actuators for single-port surgery complicates the internal stress distribution during the inflation of multiple chambers, making stiffness modulation mechanisms difficult to understand. In this study, a finite element analysis model is developed to explore the combined effect of the internal stress distribution and duct structure on the stiffness modulation in soft actuators equipped with multiple pneumatic antagonistic chambers. A prototype is developed to cross-validate the simulation and examine the effects of various antagonistic chambers on the stiffness modulation. The findings confirm that inflating specific chambers alters the internal stress distribution of the actuator by creating bending moments that influence deformation responses to external loads. These moments impact the stiffness and structure of the hollow central duct by modifying its geometrical moment of inertia and affecting the lengths of the tensile and compressive regions during bending, further influencing the stiffness. The effects of bending moments and the geometrical moment of inertia on stiffness modulation vary across different actuator sections owing to the varying lengths of the tensile and compressive regions during bending. These stiffness modulations affect the tip bending, force, and response time. The study findings provide insights into the mechanism of stiffness modulation for the design of soft actuators for complex MIS

Slowly rotating relativistic stars in [formula omitted] theory of gravity

In this paper, we investigate slowly rotating compact stars within the framework of f(R) gravity in a self-consistent way. We derive the equations describing the structure of compact stars in f(R) gravity and solve both the exterior and interior problems simultaneously. The study includes an equation of state. We considerably analyze the moment of inertia and its dependence on the stellar mass and the f(R) gravity. Future studies of the moment of inertia of compact stars may help determine the difference between f(R) gravity and general relativity, providing information on the high field domain of gravity. For our current analysis, we consider five different compact stars, namely, PSR1903+327, PSR1937+21, PSRJ1614−2230, CenX−3, and VelaX−1. To determine the viability of our model, we conduct a number of physical experiments, such as the analysis of energy density and pressure components, equilibrium and energy conditions, stability analysis, and the adiabatic index. The relationship between stellar objects’ mass, energy density, radius, and moment of inertia is observed. Our findings indicate that obtained results are physically adequate and consistent with the model we considered.

О влиянии деформаций астероида при тесном сближении с Землей на его вращательную и орбитальную динамику

During close approach to the Earth, the asteroid’s figure may experience noticeable deformations. Numerical experiments were used to examine the effect of changes in the asteroid’s figure on the magnitudes of disturbances arising in its rotational motion during approach and on the orbital dynamics by changing the magnitude of the Yarkovsky effect. It was found that due to tidal deformation of the asteroid’s figure during approach, accompanied by a change in the moments of inertia, the magnitudes of disturbances in rotation are significantly higher than in the case of an unchanged figure. It was shown that a change of 10–25% in the inertial parameters of the asteroid (99942) Apophis during its approach to the Earth in 2029 leads to a 2–4-fold increase in the sizes of the regions in which the rotational period and the magnitude of the angle characterizing the inclination of the rotation axis to the orbital plane may change. Perturbations in the rotation of the asteroid lead to a change in the parameter A2, which characterizes the Yarkovsky effect, for the size of the region of change of which a similar conclusion is made.

Identification of viscoelastic properties with fluid inertia in a parallel plate with effective mechanical system analyses

Measurement of viscoelastic properties in small amplitude oscillatory shear (SAOS) can be affected by fluid inertia, especially at high frequencies. In this study, we introduce an effective mechanical system approach to address the effects of fluid inertia on the viscoelastic measurement with a SAOS test, employing a parallel plate geometry. In the effective mechanical system approach, viscous, elastic, and inertial properties of a fluid system are modeled systematically by a rotational drag coefficient, a torsional spring constant, and a second moment of inertia, respectively. In this way, we established the analytic solution for the linear viscoelastic behavior of a fluid in the presence of fluid inertia. The shear modulus on the frequency, obtained by the effective mechanical system, reveals that fluid inertia only affects the storage modulus and not the loss modulus. We investigate the behavior of the storage modulus as a function of the gap size, the oscillation frequency, and the disk radius, demonstrating the dependence on the gap size and the frequency. Comparison was made for the shear modulus from the effective mechanical system with viscoelastic flow simulation, employing two viscoelastic (Oldroyd-B and Giesekus) fluid models to validate the accuracy of this approach. The maximum error was found less than 3.3% over the frequency range from 1 to 100 rad/s.

Hamiltonian for complex plasmas

The Hamiltonian for a complex plasma involving dust spinning motion in a magnetic field is proposed. The formulation is in a classical limit of a quantum mechanical approach based on the Dirac equation, a relativistic wave equation in which the spin of particles is considered. The quantum mechanical spin term –γs·B [γ=gq/2m, g=2(Lande´ g−factor),q is a charge, m is a mass of a particle, and s = spin operator] is replaced by –γs·B [γ with g=1, s = I(ω+γB), I is the moment of inertia of a dust particle, and ω is the spinning angular velocity of a dust particle] in a classical limit. The wave–particle interaction involving spin motion is described as an interaction between particles and quasiparticles by the second quantization. The equation of motion with a damping term shows the relaxation of spinning dust particles aligning with the magnetic field.

Mastering seismic time series response predictions using an attention-Mamba transformer model for bridge bearings and piers across varied testing conditions

This research introduces an advanced method for predicting seismic responses and hysteresis curves of instrumented bridge piers and bearings under various loading conditions, leaning solely on a single deep learning architecture and the same hyperparameters tuning. Test specimens are subjected to ground accelerations including vertical seismic loads and axial forces. To accurately capture peak values, particularly on the negative side of the hysteresis loop (unloading region), the model employs a stacked deep architecture. A key component to overcome the challenges is the self-attention-Mamba-driven transformer layer, which enhances the model’s ability to capture long-range dependencies in seismic data. This layer works in conjunction with other deep learning techniques to ensure robust and precise predictions. Implemented with Python’s Keras functional API, the model processes inputs like ground accelerations, actuator loads, effective height, moment of inertia, and superstructure mass. The model is evaluated with a dataset of 95 real-time hybrid simulation (RTHS) tests for lead rubber bearings, 29 RTHS tests for bridge piers, and 17 cyclic tests (10 fast and 7 slow). Extensive hyperparameter tuning demonstrates the model’s proficiency to capture hysteresis and residual deformations accurately. Achieving an impressive correlation with experimentally measured values, ranging from 88.1 to 98.9%, and a reasonable dissipated energy error ratio are notable. The deep learning model reduces the need for additional tests, offering time and cost savings, and provides rapid, and accurate insights into bridge behavior. This supports timely and precise bridge design and aids decision-makers during emergencies.

The multifunctional use of an aqueous battery for a high capacity jellyfish robot.

The batteries that power untethered underwater vehicles (UUVs) serve a single purpose: to provide energy to electronics and motors; the more energy required, the bigger the robot must be to accommodate space for more energy storage. By choosing batteries composed primarily of liquid media [e.g., redox flow batteries (RFBs)], the increased weight can be better distributed for improved capacity with reduced inertial moment. Here, we formed an RFB into the shape of a jellyfish, using two redox chemistries and architectures: (i) a secondary ZnBr2 battery and (ii) a hybrid primary/secondary ZnI2 battery. A UUV was able to be powered solely by RFBs with increased volumetric (Q ~ 11 ampere-hours per liter) and areal (108 milliampere-hours per square centimeter) energy density, resulting in a long operational lifetime (T ~ 1.5 hours) for UUVs composed of primarily electrochemically energy-dense liquid (~90% of the robot's weight).

Optimizing hardware configuration for solar powered energy management in battery ultracapacitor hybrid electric vehicles

The design and construction of an adaptive energy management system incorporating a 12 V–2 Ah battery and a 1F ultracapacitor for solar powered hybrid electric vehicles are presented in this paper. The primary storage battery’s longevity and overall system efficiency are intended to be increased by the EMS’s ability to forecast driving circumstances and lessen the load on it. The method optimizes power distribution among numerous energy storage sources by using sophisticated hardware configurations. Using Arduino Uno software, the EMS continuously modifies power distribution in response to driving circumstances and vehicle energy needs. To conduct a thorough assessment of the system, a mechanical configuration was created to replicate the vehicle’s dynamics. This included situations in which the vehicle moved only by using its moment of inertia and not the accelerator. Testing under diverse operating conditions, such as braking, acceleration, and varying slopes is made possible by this configuration. According to experimental data, peak battery stress is significantly reduced by about 33.33%, resulting in longer battery life. With minimal energy losses of 4.3–4.9%, the system regularly achieves power efficiency ranging from 95.1 to 95.7%. Furthermore, the suggested hardware-based EMS lowers overall energy loss by roughly 10.36%, highlighting its dependability and effectiveness in contrast to traditional techniques. The longevity and efficiency of the system are enhanced by the balanced power distribution between the battery, ultracapacitor, and solar sources, which prevents any one source from being overloaded. Overall, the suggested energy management system is successful in improving energy distribution and extending the lifespan and performance of HEV components.

Low intensity, high frequency vibration training to improve musculoskeletal function in a mouse model of volumetric muscle loss.

This study's objective was to investigate the extent to which two different levels of low-intensity vibration training (0.6 g or 1.0 g) affected musculoskeletal structure and function after a volumetric muscle loss (VML) injury in male C57BL/6J mice. All mice received a unilateral VML injury to the posterior plantar flexors. Mice were randomized into a control group (no vibration; VML-noTX), or one of two experimental groups. The two experimental groups received vibration training for 15-min/day, 5-days/week for 8 weeks at either 0.6 g (VML-0.6 g) or 1.0 g (VML-1.0 g) beginning 3-days after induction of VML. Muscles were analyzed for contractile and metabolic adaptations. Tibial bone mechanical properties and geometric structure were assessed by a three-point bending test and microcomputed tomography (µCT). Body mass-normalized peak isometric-torque was 18% less in VML-0.6 g mice compared with VML-noTx mice (p = 0.030). There were no statistically significant differences of vibration intervention on contractile power or muscle oxygen consumption (p ≥ 0.191). Bone ultimate load, but not stiffness, was ~16% greater in tibias of VML-1.0 g mice compared with those from VML-noTx mice (p = 0.048). Cortical bone volume was ~12% greater in tibias of both vibration groups compared with VML-noTx mice (p = 0.003). Importantly, cross-section moment of inertia, the primary determinant of bone ultimate load, was 44% larger in tibias of VML-0.6 g mice compared with VML-noTx mice (p = 0.006). These changes indicate that following VML, bones are more responsive to the selected vibration training parameters than muscle. Vibration training represents a possible adjuvant intervention to address bone deficits following VML.

Cardiorespiratory Responses to Flywheel-Based Inertial Training Squats With Varying Moments of Inertia.

Mitchinson, CJ, Best, S, Caruso, J, and Bollinger, LM. Cardiorespiratory responses to flywheel-based inertial training squats with varying moments of inertia. J Strength Cond Res XX(X): 000-000, 2024-Flywheel-based inertial training (FIT) has gained popularity as a means to enhance muscle hypertrophy. Other applications, such as aerobic exercise training, remain unexplored. The aim of this study was to determine the cardiorespiratory responses to acute FIT with varying moments of inertia (MOIs). Methods: Overall, 20 (10 M, 10 F) healthy, physically active subjects underwent maximal graded exercise testing and completed 3 bouts of FIT exercise (1 familiarization session and 2 identical data collection sessions). Subjects completed quarter squats (60° peak knee flexion) at a pace of 50 squats·minute-1 until volitional fatigue. Flywheel-based inertial training MOI was increased by 0.005 kg·m2 every 3 minutes until a final workload of 0.020 kg·m2. Heart rate and gas exchange data were collected continuously and averaged over the final 60 s of each stage. Data were analyzed by a linear mixed model. Results: During the final testing session, there was a main effect of MOI to increase heart rate (HR), V̇o2, and RER. Men displayed greater oxygen consumption, but asimilar %V̇o2peak compared with women. We noted a significant inertia × sex interaction where RER tended to be lesser in women at higher MOI. In the final stage of exercise (MOI: 0.020 kg·m2), HR and V̇o2 were approximately 75-80 and 55% of peak, respectively, and RER was approximately 0.95-1.00. Conclusions: FIT quarter squats elicit moderate HR and V̇o2 responses, but near-maximal RER suggests a novel metabolic training stimulus. This exercise may supersede thelactate threshold and may not be sustainable for prolonged times. The physiological and performance effects of training in this manner are unclear.

Efficiency and explainability of design‐oriented machine learning models to estimate seismic response, fragility, and loss of a steel building inventory

AbstractMachine learning (ML) has recently been used as an efficient surrogate to estimate different steps of performance‐based earthquake engineering (PBEE), from dynamic structural analysis to fragility and loss assessments. However, due to the varied data, models, and features in existing literature, the relative efficiency of ML models across different PBEE steps remains unclear. Additionally, the black‐box nature of advanced ML algorithms limits their ability to provide design‐oriented insights, hindering the broader application of ML in PBEE‐based design. This study provides a comprehensive comparison of the accuracy and explainability of design‐oriented ML models across different steps of PBEE using a consistent database of 621 steel moment frames with varying designs and geometry. Eight ML algorithms were used in a careful training workflow comprising feature selection, hyperparameter tuning, cross‐validation, and model inference. The sensitivity of model accuracy to representative PBEE outputs—maximum responses, median fragility, and expected annual loss—was assessed using statistical measures. In addition, the explainability of the best models for each step was examined to explore the relationship between design parameters and the corresponding PBEE output. The results show that while ML models can reasonably map design parameters to all different PBEE outputs, models accuracy was higher for drift responses, median fragilities, and component‐based loss metrics. In addition, the optimal algorithm remained the same across different PBEE steps, where support vector machines and random forests provided the highest accuracy with an average R2 of 0.93 and 0.91 over different outputs on the test set. Although the selected feature sets varied across outputs and algorithms, height, number of stories, fundamental period, and the minimum of the beams’ moment of inertia were influential for both models and notably affected different PBEE outputs.

Assessment of Hoisting Conveyance Guiding Forces Based on Field Acceleration Measurements and Numerical Simulation

Shafts play a key role in the operation of mining plants. They connect underground excavations with the surface and provide the ability to transport people, equipment, and raw materials. The nature of the dynamic interaction of a conveyance moving at a significant speed along deformed guide rails is complex, and the method of assessing the interaction of hoisting conveyances with shaft steelwork, despite ongoing research, still requires further understanding and improvement. Misalignments of the guide rails and conveyance movements transverse to the shaft axis induce impact (guiding) forces, which are the key design parameters of shaft steelwork. The reliable assessment of guiding forces allows the design of safe and economical steelworks and the assessment of their structural safety during operation under deformations and corrosive deterioration. Determining the value of guiding forces requires their field measurements or the use of approximate empirical formulas. Both methods have their limitations—measurement is expensive and interferes with normal shaft operation, while empirical formulas are subject to high error due to the lack of consideration of many structural details specific to each shaft that significantly affect the behavior of the system. This study presents a new method for using a relatively simple-to-implement measurement of hoisting conveyance acceleration to assess guiding forces. A finite element model of the skip and steelwork was built, and simulations of the conveyance interaction with the structure were carried out. A strong relationship between the sliding plate’s impact point location and the guiding force was found. Extreme values of the guiding force were observed in the vicinity of the bunton connection. The study showed that reducing the skip load mass does not affect the force value. Simplified methods of calculating the moments of inertia of the hoisting conveyance significantly overestimate the code-based values of the guiding forces. The presented method considers the actual stiffness and mass distribution of hoisting conveyance and, therefore, allows for a more accurate estimation of the guiding forces and the transport of larger loads. This data-driven approach allows for the continuous monitoring of the guiding forces, the adjustments of the hoisting parameters, the rational planning of repairs, and a reduction in the replacement of corroded shaft steelwork.

The development of compensatory ability for a sexually-selected ornament in stalk-eyed flies

Female preference for longer eyespan has driven exaggerated sexual dimorphism in several species of stalk-eyed flies. Longer eyespan increases a fly’s moment of inertia, and flies experience significant increase in body mass across age as they mature sexually. These costs may impact flight behavior and fitness through maneuverability and predator evasion, and appear ameliorated by co-selection for compensatory traits, as flies with longer eyespans tend to have larger thoraces and wings, allowing them to perform turns similar to flies with shorter eyespans. However, the capacity to compensate for a potentially costly ornament may not be limited to morphological traits which are fixed at the time of eclosion: as flies age, they also accumulate thorax mass and improve their flight performance. The purpose of this study was to investigate the compensatory ability of two populations of stalk-eyed flies (Teleopsis dalmanni and Diasemopsis meigenii) through comparing morphology and flight performance relative to eyespan. ‘Over-compensators’ should exhibit greater morphological and/or performance traits relative to eyespan, whereas ‘under-compensators’ should exhibit relatively less across these metrics. Flight performance was assessed using high-speed videography and variable-density gas-mixtures to determine maximal flight capacity. Young adult flies eclosed as ‘under-compensators’, with less thorax mass, wing velocity and flight capacity relative to their eyespan as compared to older flies. As flies aged and accumulated thorax mass, they became ‘over-compensators’. Thus, compensation for long eye-stalks is not a fixed trait; instead, variation in compensatory ability appears to be associated with the development of thorax muscle and flight performance across age.

Inertial and elastic properties of general composite beams

Slender composite structures can be modeled using engineering beam models with properties computed using a cross-sectional analysis program, such as VABS. These properties are given in terms of the mass matrix, stiffness matrix, and compliance matrix in a general coordinate system. The invariance of strain energy and kinetic energy is employed to rigorously transform sectional properties into different coordinate systems with parallel shifts and rotations. Additionally, the computation of commonly used inertial properties (mass center, principal inertial axes, and mass moments of inertia) from the mass matrix, and commonly used elastic properties (extension stiffness, bending stiffness, torsion stiffness, tension center, shear center, principal bending axes, principal shear axes, etc.) from the compliance matrix, is elucidated. The elastic properties are given for both the Timoshenko model and the Euler–Bernoulli model. The definitions for shear center and twist center are clarified and consistently generalized for composite beams. Isotropic homogeneous beams are used to illustrate how to relate commonly used engineering beam properties with the compliance matrix and the stiffness matrix for composite beams. Finally, engineering beam properties necessary for general-purpose aeromechanical analysis programs such as CAMRAD II are derived from the properties computed by VABS.

User experience of lower extremity exoskeletons and its improvement methodologies: A narrative review.

In this review, user experience (UX) of recent lower limb exoskeletons (LLEs) and its improvement methodologies are investigated. First, statistics based on standardised and custom UX evaluations are presented. It is indicated that, LLE users have positive UX, especially in the aspects of safety, dimension and effectiveness. Further, overall, UX levels of ankle and hip-knee exoskeletons are higher than those of other exoskeleton types; unilateral LLEs have higher mean UX levels than that of the bilateral ones. Then, design practices for improving UX are studied; the focused points are burden reduction and improvement of device fit. The former is achieved through lightweight design and approaches that reduce device's moment of inertia (MOI) at mechanical joints. Works on the latter refer to the endeavours to enhance static and dynamic fit; they mainly rely on the optimisations of human-robot interface (HRS) and endeavours to rectify misalignment of axes of mechanical and anatomic joints, respectively. The following section is control approaches to enhance wearing comfort level; it is mainly focused on adaptive, interaction and compensation-based controls. Finally, existing problems and future directions are stated and prospected respectively.

Librations and obliquity of the largest moons of Uranus

Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity. We find that if the Uranian satellites were two-layer solid bodies, libration measurement accuracies from around 0.25 m for Oberon to around 6 m for Miranda would rule out the possibility of homogeneous interiors. In combination with independent estimates of the mean moment of inertia (MOI), libration measurements could also be used to detect the presence of an ocean, the measurement precision required for this depending on the actual value of the libration amplitude. To compute the obliquity, we first build series for the orbital precession of all five satellites with a secular perturbations model. With the exception of Miranda, we show that due to the mutual gravitational interactions between the satellites, the obliquity of the large Uranian moons exhibits relatively large periodic variations around the mean value. We find that an obliquity measurement accuracy from around 1 m for Ariel to around 400 m for Oberon can rule out the homogeneous case. The presence of an internal global ocean could allow a resonant amplification of the obliquity, facilitating its detection. If no such resonance occurs, the obliquity would be almost indistinguishable from that expected for a solid body. The effect of tidal deformations on the rotation of the small to medium-sized Uranian moons is showed to be limited. Librations would be reduced by up to 10% and obliquity increased by up to 15% for Titania and Oberon, the effects being negligible for Miranda.

In-orbit system identification of a flexible satellite with variable mass using dual Unscented Kalman filters

Modern space mission concepts are increasingly dependent on the robust and reliable deployment of spacecraft with large appendages, such as antennas, booms or solar panels. Such deployment requires the ability to properly capture and control the coupled system dynamics, which requires accurate in-orbit system identification of the mass and structural properties. This paper utilises dual Unscented Kalman filters (DUKF) to develop an online system identification strategy that captures both the structural and mass properties, and the attitude and orbit dynamics. The dynamics of the flexible multibody problem are derived from the Lagrangian equations, with the flexible body characteristics modelled with finite element software. A genetic algorithm is used to optimise the accelerometer placement, and hence improve the DUKF performance. We demonstrate that this approach can accurately capture the coupled attitude, orbit, and structural dynamics, as well as being able to provide in-orbit updates for mass properties such as the moment of inertia. The methodology is explored for two illustrative cases: one in which the initial moment of inertia is incorrectly characterised, one in which the moment of inertia changes with time. In both cases, the DUKF approach captures both the system dynamics and the mass properties, which are captured with an error of less than 1%.