Misalignment Angle Research Articles

Moving object SINS transfer alignment time synchronization parameters estimation

The main unmanned aerial vehicles launched from a carrier aircraft onboard navigation system, usually, is a strapdown inertial navigation system. The paper considers the influence of the time synchronization error in the strapdown inertial navigation system transfer alignment on a moving base task. The influence of the time synchronization error, as well as the technique of its estimation, is directly the subject of this study. SINS mathematical models are considered on the basis of error equations, the state vector, including errors of coordinates, linear velocities projections, attitude angular errors of the measuring coordinate system relative to the calculated one, accelerometers and gyro systematic errors components are extended by the angles of misalignment of two systems – unmanned aerial vehicle strapdown inertial navigation system and carrier aircraft navigation system and time delay component. The measurement vector includes the difference of the corresponding output parameters of two systems – carrier aircraft strapdown inertial navigation system or its navigation system and unmanned aerial vehicle strapdown inertial navigation system. A simulation was performed, and state vector estimates were obtained.

Trapping effect for QCD axion dark matter

In the early universe, the potential of a scalar field can be significantly modified, and the scalar field may be trapped for a long time in a different location than the current vacuum. The trapping effect can increase or decrease the scalar abundance. For instance, in thermal inflation, a scalar field is trapped at the top of the potential by a thermal effect and dominates the universe to drive inflation for a short period of time. On the other hand, a scalar abundance can be exponentially suppressed in the adiabatic suppression mechanism, where a scalar field moves adiabatically by a time-dependent trapping potential. In this study, we investigate such a trapping effect on the abundance of scalar fields. Specifically, we investigate how the abundance of a scalar field depends on its initial position in the case of a double well potential and identify the physical quantity that controls the abundance. Then, we study the QCD axion abundance for various values of the misalignment angle, where the axon potential receives a large temporal mass due to the Witten effect. We find that the axion abundance is suppressed due to the adiabatic suppression mechanism even when it is trapped near the maximum of the potential, if the trapping effect is sufficiently large.

Influence of Axial Microvibration on the Transient Hydrodynamic Lubrication Performance of Misaligned Journal–Thrust Microgrooved Coupled Bearings under Water Lubrication

The purpose of this study is to explore the transient hydrodynamic coupling mechanism for misaligned journal–thrust microgrooved coupled bearings (referred to as coupled bearings) considering the axial microvibration under water lubrication. In the present model, it is assumed that the misaligned coupled bearing performs a sinusoidal reciprocating micromotion along the axial direction. Based on the developed numerical model, the effects of the working conditions, including the frequency and amplitude of the microvibration, misalignment angle, journal bearing radial clearance, and thrust bearing geometric clearance, on the transient hydrodynamic performance of the coupled bearing are studied. The simulation results indicate that the axial microvibration generates a periodic fluctuation in the load capacity for both the journal and thrust bearings, and the load fluctuation of the journal bearing is generated from the transient hydrodynamics of the thrust bearing. In addition, the negative misalignment mode is beneficial to improve the load capacity of the coupled bearing. Parametric studies demonstrate that although the decreasing microvibration frequency weakens the load capacity of the coupled bearing, it decreases the hydrodynamic load fluctuation. They also reveal that the increasing misalignment angle leads to an increase in the load fluctuation, and it also improves the load capacity.

Effect of dynamic misalignment on the vibration response, trajectory followed and defect-depth achieved by the rolling-elements in a double-row spherical rolling-element bearing

Dynamic-misalignment beyond a specific limit suggests some abnormal systems’ behaviour and, if not dealt with appropriately may lead to its sudden breakdown. To address this problem spherical rolling-element bearings are used which have the capacity to encounter such misalignment till a certain limit. Investigating this physical mechanism of such bearing's and quantifying the degree as well as nature of dynamic-misalignment can lead to diagnosing the root cause responsible for it. This paper thus aims at understanding the physics governing the vibration response of spherical rolling-element bearing with a localized defect and subjected to dynamic-misalignment at the same time, using numerical simulations and experimental validation. The numerically simulated results firstly show that an increase in radial and axial loads have a contrasting effect on the acceleration response and contact-load shared by the two bearing rows. Secondly, the rolling-elements while following an offset trajectory, significantly affect the bearing's vibration response as compared to an inclined trajectory and the depth achieved by rolling-elements inside defect also varies with varying misalignment angles. Thirdly. with an increase in misalignment, the strange attractors form intermittent behaviour with outer multi-periodic response having hidden chaos. The behaviour observed from the numerically simulated results was also validated from the vibration data obtained experimentally from the test-rig.

Longitudinal compression failure of 3D printed continuous carbon fiber reinforced composites: An experimental and computational study

Fused filament fabrication (FFF) with continuous carbon fiber filaments has proven to be a promising manufacturing technique in engineering applications. To provide guidance in the design of 3D printed carbon fiber reinforced polymer (CFPR) components, the longitudinal compression failure of continuous CFPR composites using the FFF technique is investigated systematically. First, longitudinal compression tests are performed for 3D printed continuous CFRP composites with and without designed waved filaments. The degradation of the failure strength is remarkable when the waved filaments are introduced. Nevertheless, further degradation is limited when more waved filaments are adopted. Next, the fracture morphologies are analyzed, and in-plane and out-of-plane kink-bands are observed in the microscopic images. For the specimens with waved filaments, fracture occurs at the cross-section with the contact region of the waved and regular filaments, as well as the cross-section with the maximum misalignment angle. Correspondingly, a computational framework for 3D printed continuous CFPR composites is established to explore the longitudinal compression failure mechanisms. The meso-scale computational models are reconstructed according to the geometric features of the deposited continuous CFRP filaments and the actual void volume fraction. The elastic properties of the filament are calculated by a micro-scale representative volume element (RVE) model, which is based on the fiber random distribution algorithm. The plastic deformation and failure is described by a filament constitutive model which is established by the Liu-Huang-Stout yield criterion and a simplified Tsai-Wu failure criterion. The experimental validation demonstrates the feasibility of the computational models to predict the stress-strain curves of 3D printed materials, and also capture the realistic longitudinal compression failure behavior.

Analyzing the effect of misalignment on single-filament carbon fiber tensile testing via stereoscopic computer vision imaging

An understanding of the constitutive properties of carbon fibers (CFs) is critical to the accuracy of high-resolution composite simulations and to the development of CF derived from low-cost alternative precursor materials. Single-fiber tensile testing is a capable tool to measure CF properties and is well suited to research efforts where only a small number of fibers may be available. However, single-fiber tensile tests are challenging to conduct due to the difficulty in handling small diameter fibers (5–15 μm), the brittleness of single fibers, and the required nanoscale/microscale resolution of testing equipment. The accuracy of the measured properties depends on several factors, but a critical factor is fiber misalignment, especially at short gauge lengths. Current standards do not address the effect of tensile specimen misalignment on measured properties. This work presents a robust method of fiber alignment using stereoscopic computer vision that enables users to align fibers vertically for tensile testing to improve the accuracy of resulting mechanical properties. Additionally, an analytical relationship between fiber misalignment angle and measured properties is developed and validated against the experimental results. As a result, new best practices for single-fiber tensile testing of CF are recommended.

Sensorless Posture Detection of Reluctance Spherical Motor Based on Mutual Inductance Voltage

In this paper, a sensorless rotor posture detection method based on the mutual inductance voltage of the stator coil is proposed to simplify the position detection element of a reluctance spherical motor. Firstly, the numerical relationship between the stator/rotor pole misalignment angle and the mutual inductance voltage of the stator coil is analyzed, which is used as the basis for judging the spatial position of the rotor. Secondly, an experimental platform is designed to verify the consistency between the calculated value and the experimental value of the mutual inductance voltage and to determine the appropriate excitation signal. Thirdly, based on the real-time voltages generated by the stator coil mutual inductance, an intelligent algorithm is used to invert the 3-DoF (degree-of-freedom) position angle of the spherical rotor combined with the motor structure constraints. The experimental results show that the detection method has a good on-line detection effect, and the population standard deviation is within 1.8° Therefore, the developed technique can be used for replacing the position detection method with sensors.

Investigation on the motion conditions and dynamic interaction of vehicle and turnout due to differential wheelset misalignment

Assembly deviations of wheelsets cause differential wheelset misalignments and change the wheel-rail contact relationship in railway turnouts. In this paper, the motion conditions of wheelsets under the same bogie are analysed with differential wheelset misalignment based on the mechanical equilibrium condition. A rigid-flexible coupling model of vehicle-turnout dynamic interaction that fully considering different misalignment conditions is established to evaluate the wheel and turnout rails dynamic interaction and vehicle dynamic characteristics. The results show that wheelset misalignment can change wheel load transition position and affect wheel-rail contact conditions, especially when the misalignment direction is toward the switch rail. The larger misalignment angle will increase flange contact range and keep the normal contact stress at a higher level. Both misalignment angle and form determine the wheel-rail vertical force. The lateral force is mainly affected by the superposition effect of the eccentric load and the lateral impact of the wheel load transition.

Misalignment angle measurement and angle measurement deviation compensation of fiber optic gyroscope based on tilt sensor

The misalignment angle of the fiber optic gyroscope (FOG) is a significant factor, which results in the angle measurement deviation in practical engineering applications. On the basis of the deviation compensation model we proposed in the previous research, the misalignment angle of the FOG is taken into consideration to optimize the deviation compensation model and a new method to measure the misalignment angle of the FOG is presented. Finally, the experiments on the misalignment angle measurement and angle measurement deviation compensation are carried out based on the prototype, which consists of the FOG and the tilt sensor. The experimental results show that the angle measurement deviation of the FOG can be further reduced by adopting the new method to measure the misalignment angle and applying it to the optimized model. This research will have important application value in the field of angle measurement based on FOG.

Spin-orbit misalignments in tertiary-induced binary black-hole mergers: Theoretical analysis

Black-hole (BH) binary mergers driven by gravitational perturbations of tertiary companions constitute an important class of dynamical formation channels for compact binaries detected by LIGO/VIRGO. Recent works have examined numerically the combined orbital and spin dynamics of BH binaries that undergo large Lidov-Kozai (LK) eccentricity oscillations induced by a highly inclined companion and merge via gravitational wave radiation. However, the extreme eccentricity variations make such systems difficult to characterize analytically. In this paper, we develop an analytical formalism for understanding the spin dynamics of binary BHs undergoing LK-induced mergers. We show that, under certain conditions, the eccentricity oscillations of the binary can be averaged over to determine the long-term behavior of the BH spin in a smooth way. In particular, we demonstrate that the final spin-orbit misalignment angle $\theta_{\rm sl}$ is often related to the binary's primordial spin orientation through an approximate adiabatic invariant. Our theory explains the "$90^\circ$ attractor" (as found in recent numerical studies) for the evolution of $\theta_{\rm sl}$ when the initial BH spin is aligned with the orbital axis and the octupole LK effects are negligible -- such a "$90^\circ$ attractor" would lead to a small binary effective spin parameter $\chi_{\rm eff}\sim 0$ even for large intrinsic BH spins. We calculate the deviation from adiabaticity in closed form as a function of the initial conditions. We also place accurate constraints on when this adiabatic invariant breaks down due to resonant spin-orbit interactions. We consider both stellar-mass and supermassive BH tertiary companions, and provide simple prescriptions for determining analytically the final spin-orbit misalignment angles of the merging BH binaries.

Study of dynamic coefficients of water film in marine stern tube bearing considering roughness and deformation

Dynamic analysis of water-lubricated marine stern tube bearing is incompatible with that of ordinary oil-lubricated bearing due to the deformation of compliant bushes and non-negligible roughness effects. A modified bearing dynamic analysis model embracing roughness and dynamic characteristics of a non-metal bush is proposed. Based on the model, Reynolds equations of perturbed pressures of water film considering roughness, deformation, and misalignment simultaneously are derived for the first time and solved by coupling the finite difference method and the finite-element method. The results show that dynamic coefficients are enhanced due to roughness when the minimum film thickness ratio exceeds a threshold around 2. The roughness effect is debilitated but the valid range of roughness is extended when bush deformation is considered. Additionally, dynamic coefficients of rougher bearing become obviously smaller than those of smoother bearing as the misalignment angle grows.

Analysis of misaligned journal bearing lubrication performance considering the effect of lubricant couple stress and shear thinning

ABSTRACT This paper investigates journal bearings, and builds a lubrication model taking into account misalignment, the lubricant couple stress effect and shear thinning. In order to explore the sensitivity of couple stress fluid lubrication performance to oil film thickness, we introduce the critical oil film thickness coefficient. The results show that the sensitivity increases with the increase of the couple stress coefficient, and it is highest in the area of minimum oil film thickness. Compared with a parallel journal, increases in the misalignment angle strengthen the effect of couple stress. Shear thinning also plays an important role in bearing lubrication performance. For a low oil inlet temperature, the effect of shear thinning increases with the increase of the couple stress parameter. For a high oil inlet temperature, the influence is negligible. An increase in the misalignment angle will not further enhance the effect of shear thinning.

Design and Analysis of LoS-MIMO Systems With Uniform Circular Arrays

We consider the design of a uniform circular array (UCA) system under array misalignment over line-of-sight (LoS) channels. UCAs have been considered as useful array structures since their LoS channels can be diagonalized without the channel state information at the transmitter (Tx). However, such a characteristic holds only when transceiver arrays are perfectly aligned. To overcome this difficulty, we propose an optimal design method and transceiver architectures for UCA systems under array misalignment that achieve channel capacity without knowledge of misalignment angles. To this end, we first verify that the singular values of the misaligned UCA system are independent of tilting and center-shift and small relative array rotation, but fluctuate with the Radii Product to Distance Ratio (RPDR). Using the result, we present an optimal design method for UCA systems that performs an one-dimensional search for the RPDR to maximize channel capacity, and we show that a simple zero-forcing (ZF) receiver can achieve the maximum channel capacity because of the channel characteristic at the optimal design criteria. Additionally, we propose a low-complexity precoding scheme for UCA systems in which the optimal design criteria cannot be fulfilled. The simulation results demonstrate the validity of the proposed design method and transceiver architectures.

Calculation model of the slightly misaligned optical multi-pass cell based on the augmented 4*4 matrix

A novel augmented 4*4 matrix model for the slightly misaligned optical multi-pass cell whose spherical mirrors are not coaxial due to the presence of small misaligned angle and linear displacement of the spherical mirrors is reported. The augmented 4*4 matrix model is proposed to describe the behavior of light rays in the misaligned optical multi-pass cell. By augmented 4*4 matrix model, a series of numerical calculation are performed to validate that the incident light ray remains unchanged, and then retrace the same spot pattern. It is found that the set of spot patterns from numerical analysis displays a displacement on the surface of the mirror and the misaligned optical elements increase the loss and reduce pass counts. More importantly, the augmented 4*4 matrix model can be used to analyze the misalignment sensitivity of the optical multi-pass cells.

Rotordynamic Performance of the Interlocking Labyrinth Seal With a Tilting Rotor

Abstract Numerical analysis model of an interlocking labyrinth seal (ILS) is established for studying the effect of tilting rotor on its rotordynamic characteristics. The dynamic characteristic identification method based on infinitesimal theory is applied to solve the dynamic force coefficient of the seal with arbitrary elliptical orbits and eccentric positions under field conditions. The paper investigated the dynamic characteristics of the interlocking labyrinth seal with various misalignment angles (θ = 0, 0.1 deg, 0.2 deg, 0.3 deg, 0.4 deg, 0.5 deg, 0.6 deg), different pressure ratios (Pin = 6.9 bar, PR = 0.5, 0.8), locations of misalignment center (Loc = 0, L/2, L). Results show that the tilting rotor could minimize the leakage flow rate of the ILS. When the misalignment angle θ = 0.6 deg, the mass flow rate can be reduced about 2.5%. The effect of each cavity in the ILS on the stability of the system is different. The cavity with the inlet close to the rotor and the outlet away from the rotor helps to improve the system stability due to its locally antirotational flow. The effective damping of the entire ILS increases as the misalignment angle increases. The system shows the best stability when the misalignment center is close to the seal inlet. The tilting rotor has a positive effect on the stability of the ILS only except for high whirling frequency (>100 Hz) under Loc = L.

Determination of angular stiffness coefficient of the annular seal by experiment-calculation

Hydrodynamic forces in annular seals of centrifugal pumps create a significant effect on the vibrational activity of the rotor as a whole. Theoretical and experimental studies of various authors made it possible to establish the structure of hydrodynamic forces and determine the magnitude of the coefficients of radial forces. The authors of this work obtained quantitative load characteristics of the rotor in an annular seal at specially created laboratory experimental stands at various pressure drops and significant angles of misalignment of the rotor axis relative to the seal axis. Static experiments were also conducted with annular seals of various lengths with a constant differential pressure of the liquid and a fixed angle of misalignment of the rotor axis relative to the axis of the annular seal. The given misalignment angle was obtained as a result of the action of various external forces on the rotor. In addition to static experiments, dynamic rotor tests were carried out. Experimentally obtained amplitude - frequency characteristics of the forced radial - angular oscillations of the rotor, which is dynamically mounted in two symmetrical annular seals. From the experimental characteristics, the critical frequency of the rotor angular oscillations in the seals was determined. According to theoretical formulas, taking into account the value of the coefficient of angular stiffness of the annular seal, the frequency of the natural angular oscillations of the rotor in the annular seals was calculated. A comparison of theoretical and experimental values indicates their good quantitative agreement.

Analysis of Wind-wave Effect on Short-term FOWT Power Loss

The paper analyses the effects of wind misalignment, wave oscillatory movement and wind-wave misalignment onto the performance of floating offshore wind turbines (FOWT) and how they affect the power generation. The study focuses on short term prediction to match network requirements for electric energy management avoiding overloads or consumers demand mismatching. The research studies individual as well as combined effects to determine the reduction in power generation due to these effects. The predictive model is based on meteorological data for different marine stations where wind farms are either located or considered for feasible installations. The results of the modelling predict the wind misalignment is more important than wave motion effects. Power loss due to wind-wave misalignment increases with wave height and with misalignment angle. The effects are negligible for wave heights of 0.4 and 1.25 m, with almost null effects for wave height of 2.5 m., with a power reduction less than 4%. The effects, however, are significant for wave heights of 4 and 6 m, especially in this latter case, where power loss varies from 11% for wind-wave misalignment angle of 15° to more than 96% for an angle of 45°. Experimental results match theoretical predictions within 96% accuracy.

SINS/DVL Integrated System With Current and Misalignment Estimation for Midwater Navigation

Motivated by the problem that water-track Doppler Velocity Log (DVL) cannot effectively suppress the error accumulation of strap-down inertial navigation system (SINS), this paper proposes a novel SINS/DVL integrated navigation algorithm for deep and long cruising range Human Occupied Vehicle (HOV). Such algorithm decomposes the navigation process into two tightly coupled working modes: alignment mode and navigation mode. In the alignment mode, HOV is controlled to perform horizontal circular motion for several minutes to realize Self-Aided SINS. Combining the precise navigation solutions provided by Self-Aided SINS and measurements from DVL with water track, recursive least square (RLS) algorithm is adopted to estimate heading misalignment angle between SINS and DVL and horizontal ocean current velocity. In the navigation mode, both horizontal ocean current velocity obtained in the alignment mode and DVL measurements are utilized to assist SINS, thus enabling SINS/DVL/Current integrated navigation. A square trajectory with a navigation-grade inertial measurement unit (IMU) is simulated to evaluate the proposed SINS/DVL integrated navigation algorithm. Simulation results show that the proposed SINS/DVL integrated navigation is capable of suppressing SINS error divergence effectively and efficiently. In addition, the feasibility and effectiveness of Self-Aided SINS based on horizontal circular motion is also verified by field test with real IMU data.

A New Kalman Filter-Based In-Motion Initial Alignment Method for DVL-Aided Low-Cost SINS

The inertial measurement unit (IMU) biases, DVL lever arm and installation misalignment angles between IMU and doppler velocity log (DVL) have a great influence on in-motion initial alignment for DVL-aided low-cost strap-down inertial navigation system (SINS). A new Kalman filter-based initial alignment method is proposed in this paper. To weaken the effects of IMU biases, DVL lever arm and installation misalignment angles between IMU and DVL, a closed-loop scheme is presented to simultaneous estimate and compensate these parameter errors and the body attitude matrix based on a linear state-space model, which improves the accuracy of vector observations. The constant matrix from initial body frame to initial navigation frame can be determined based on the vector observations by Davenport's q-method. Simulation results illustrate that, for the DVL-aided low-cost SINS, the alignment performance of the proposed initial alignment method is better than that of the compared initial alignment methods.

Dynamic loads in self-aligning gear transmissions of heavy loaded machines

Purpose. Development of a mathematical model of a heavy loaded gear transmission with a self-aligning drive gear; evaluation of the dynamic load on the gear transmission in the gear alignment process. Methodology. The calculation schematic and equations of the relative motion of the self-aligning drive gear are formed using the methods of rigid body dynamics. Analytical expressions for the gear self-alignment time, collision velocity during the alignment and dynamic load factor are obtained by integrating an ordinary differential equation. Methods of the linear theory for oscillations are used to determine the dynamic factor. Findings. The article investigates the state-of-art design and mathematical models of the self-aligning gear. An equation for the relative motion of the moving part of the gear has been formed using the methods of rigid body dynamics. It is shown that by using the proposed hypotheses, the movement of the gear can be reduced to rotation about the instantaneous axis. The influence of geometric and dynamic parameters of the ball mill drive on dynamic loads in the open gear transmission is investigated. The gear alignment speed dependences on the tooth mesh misalignment angle in the gear transmission and the inertial parameters of the gear have been obtained. The obtained dependencies were used to calculate the time and speed of the gear alignment in the open gear transmission of the ball mill 5.5 6.5 (central discharge ball mill). It is shown that in the real range of mesh misalignment angles and gear parameters, the time of the gear alignment is several orders of magnitude less than the time of teeth re-engagement. In the presence of the variable component of the mesh misalignment angle, the gear will constantly make a relative motion with strikes; depending on the current value of the mesh misalignment angle, the dynamic load on the gear transmission can be significant. It is shown that when assessing the efficacy of self-aligning gears, it is necessary to take into account a possible increase in dynamic loads. The dynamic factor and the load factor are calculated for the nominal value of the mesh misalignment angle in the open gear transmission of 5.5 6.5 ball mills. Originality. A mathematical model of the dynamics of a self-aligning gear transmission in heavy duty machine drives has been developed. A quantitative assessment of internal dynamic load factor in an open gear transmission of 5.5 6.5 ball mills has been carried out. Practical value. A method for determining the dynamic component of the load on a gear transmission containing a self-aligning drive gear has been developed.