Rigid Body Motion Model Research Articles

Numerical study on flow characteristics in the primary side of a once-through steam generator under ocean conditions

The flow characteristics of the primary side of the helical coil once-through steam generator (OTSG) have a significant impact on the safe operation of the reactor. Different from the land-based stationary working conditions, the flow of the primary side of the OTSG is influenced by sea waves and winds under ocean conditions. The rigid body motion model is used to calculate the flow of the primary side under different ocean conditions, including heeling, trimming, rolling, pitching, heaving, and combined conditions. The results show that under heeling and trimming conditions, the static pressure of the primary side is different from that under vertical conditions due to the influence of gravity, but its impact on the flow field is relatively small. Under rolling and pitching conditions, the mean flow velocity and pressure drop change periodically with the movement of the OTSG, and the smaller the sway angle, the smaller the variation amplitude of the mean flow velocity and pressure drop. Under the heaving condition, the variation amplitude of the mean flow velocity is greater than that under rolling and pitching conditions, and reverse flow occurs. Under the combined heaving and rolling condition, the mean flow velocity and pressure drop are influenced by the period and amplitude of both the two motions.

Analysis of Convergence Behavior for the Overset Mesh Based Numerical Wave Tank in openfoam

Abstract This paper presents a solution verification and validation study for an overset mesh based numerical wave tank in openfoam, which considers the coupling between a free-surface hydrodynamic flow model, a rigid body motion model, and an overset mesh. The coupling between the rigid body motion solver and the free-surface flow solver was achieved in a segregated manner. Free decay of roll motion of a barge was modeled using the numerical wave tank, and the damping coefficient was selected as the target quantity for solution verification. The least-square based solution verification procedure was adopted, where one of the four types of error estimators was fit to the data in the least-square sense. Both structured and unstructured mesh were tested, and their effects on the convergence order, numerical uncertainty, and error were carefully investigated. From the numerical tests, it is found that the numerical wave tank exhibits a very good convergence property for the floating body problems with structured mesh, i.e., nearly second order in space and first order in time. However, when switching the body-fitted mesh to unstructured mesh, the grid convergence is reduced to first order. Unstructured mesh does not significantly affect the convergence order in time domain, but results in a larger uncertainty due to data scattering.

Effect of rigid body motion in phase-field models of solid-state sintering

In the last two decades, many phase-field models for solid-state sintering have been published. Two groups of models have emerged, with and without the contribution of rigid body motion. This paper first describes the previously published phase-field model with an advection term driven by rigid body motion. The model is then used to investigate the differences between models with and without rigid body motion in new benchmark geometries exhibiting markedly different behavior. Sensitivity studies concerning the parameters of the rigid-body motion model are conducted and their effects on equilibrium and kinetic properties explored. In particular, it is shown by simulations that a shrinkage rate independent of system size requires the inclusion of an advection term. Finally, the reason behind this behavior is explored and implications for diffusion-only models are drawn.

Improved Design and Dynamics Characteristics Research of a Composite Percussion Drilling Tool

Abstract Internal motion and dynamics mechanism studies of a new composite percussion drilling tool aim at reducing stick-slip phenomenon and improving rock breaking efficiency. In this study, experiments are performed using composite percussion drilling tools to investigate its torsional and axial composite impact performance. According to the experimental results, a six degrees-of-freedom (6DOF) rigid body motion model was established to study the passive motion of a torsional hammer. The obtained results, including the tangential acceleration, were verified with experimental data, and the small pressure differences between the high and low pressure areas, which mainly determined by the inlet structure, is the main reason for the poor torsional impact effects. Based on these discoveries, the improved design increases the inlet flow to 17.2% of the total, the pressure differences to 0.05 MPa, and the instantaneous tangential acceleration to 0.198 m/s2, which results in increased tangential acceleration fluctuation amplitude by 1137.5% and greatly improved torsional impact performance. This research can provide a baseline for stick-slip reduction technology optimization.

Cavitating flows of organic fluid with thermodynamic effect in a diaphragm pump for organic Rankine cycle systems

Diaphragm pumps often experience cavitation and subsequent fluid flow oscillation when delivering an organic fluid in small/micro scale organic Rankine cycle (ORC). The cavitation behaviour of diaphragm pumps has rarely been investigated for organic fluids so far. Three-dimensional, unsteady cavitating flows of organic fluid R245fa in a diaphragm pump were simulated with ANSYS 2019R2 CFX in suction stroke in terms of the k -ω turbulence model, the ZGB cavitation model, rigid body motion model for one-dimensional motion of valve and moving mesh technique for the first time. The thermodynamic effect in cavitation of R245fa was considered. The vapour volume fraction threshold for cavitation inception was determined, and the cavitation inception and cavitation developed states were identified, and vortex production and entropy generation rate during cavitation were clarified. Cavitation inception emerges at the edge of the valve seat, then on the valve surface. With cavitating development, the pressure and force on the valve, valve opening, and velocity oscillate violently due to vapour bubble collapse cycles. Expansion cavitation and flow induced cavitation happen in sequence at different crank rotational angles. The maximum temperature depression is 0.549 K in the cases studied. The volume-integrated entropy generation rate in the valve chamber correlates to cavitation states.

High-Fidelity Computational Fluid Dynamics Modeling and Analysis of a Pressure Vessel-Pipe-Safety Valve System in Gas Service

Abstract A pressurized vessel-pipe-safety valve (PVPSV) system is a common configuration for many energy management systems, and a better understanding of their dynamics is helpful for system design and optimization. In this paper, a method for high-fidelity computational fluid dynamics (CFD) modeling is presented, which can be used to predict dynamic responses of PVPSV systems. For modeling, regions from the vessel outlet to the safety valve exit flange are modeled using a CFD approach; the pressure vessel is set as the boundary and the movement of the valve disk is represented by a one-dimensional (1D) rigid body motion model. Simulations are performed, and both stable and unstable operation are investigated. To establish accuracy, an experimental test rig is designed and constructed to measure the motion of the valve disk and the pressures at different system locations. Comparisons are performed for different dynamic modes and good agreement is obtained, supporting the accuracy of the high-fidelity model in reproducing the dynamic response of PVPSV systems. With the developed model, influences of other variables, such as piping length and safety valve configurations, can also be evaluated. The method presented in this paper can also be used to develop CFD models for other similar systems and should facilitate system design and optimization.

Acceleration Signal Processing Method of Impact Response of Floating Shock Platform Based on Rigid Body Motion Model

Floating shock platform is generally used to test the antishock performance of large shipboard equipment. Shock acceleration signal will produce zero-shift phenomenon in the test measurement process, which will affect the subsequent shock response spectrum analysis. In this paper, a method of shock acceleration signal processing based on rigid body motion revision model is established. The rigid body motion revision model adopts the theory of ship’s seakeeping based on the hypothesis of KrylovFroude, in which the shock wave load of underwater explosion adopts the empirical formula. The bubble pulsation load adopts the GeersHunter spherical bubble model. The empirical mode decomposition method is used to eliminate the trend term of the low-frequency part of the acceleration signal, and the frequency filtering technology is used to eliminate the noise of the high frequency part. The response estimated by the rigid body motion model is used to modify the measured signal. The modified signal is analyzed by shock response spectrum to get the round design spectrum. The validity of the signal is determined by the Pauta criterion. Finally, the shock environment statistics of the whole platform is given. This method can eliminate the low-frequency trend term and high frequency noise and has good robustness. It can be applied to many kinds of signals. This method can provide technical support for antishock performance of shipboard equipment and also applied to other shock signal processing fields.

Comparative Study of the Inline Configuration Wind Farm

Abstract This research provides an in-depth analysis of the flow around the rotor and in the wake of a single horizontal axis wind turbine (HAWT) model at different free stream velocities and tip speed ratios (TSRs). Moreover, it extracts some recommendations that might be beneficial for large-scale projects such as wind farm layout design and power output prediction. For this purpose, modeling and experimental testing of a wind tunnel test section, including a single wind turbine model inside were created and validated against present experimental data of the same model. The large Eddy simulation (LES) was used as a numerical approach to model the Navier–Stokes equations. The computational domain was divided into two areas: rotational and stationary. The unsteady rigid body motion (RBM) model was adopted to represent the rotor rotation accurately.

Design and Evaluation of Tea-Plucking Machine for Improving Quality of Tea

Abstract. Tea harvesting has always been tedious work. Tea harvesting mechanization is still incomplete in most tea-planting areas. To improve the mechanization of tea plucking, this article introduces a self-propelled track-type tea-plucking machine which mainly consists of a track chassis, an elevator system, a cutting system, and a transmission system. In this article, the structure and functions of the main parts of the self-propelled tea-plucking machine are introduced in detail. Additionally, the rigid body motion model was established. Next, orthogonal experiments (the factors were travel speed and the speed ratio of cutting to traveling) were conducted with three factor levels, and to choose the optimal factor level combination, fuzzy synthesize evaluation was conducted on the results of the orthogonal experiments. The motion model showing that the cutter moves in a cosine law and that the inertia force of the drive shaft and blades also move in a cosine law while working. The experiment reveals that (1) both travel speed and speed ratio of cutting to traveling have a significant effect on the quality (integrity rate, unpicking rate, stubble unevenness) of plucked tea leaves, and (2) the interaction affects only the integrity rate. The fuzzy synthesize evaluation indicates that the optimal factors are as follows: the cutting speed is 0.3 m/s, and the speed ratio of cutting to traveling is 1.0. With this set of parameters, the plucking integrity increased by 20% compared with Japan’s ride-on-type tea-plucking machine. This research made considerable progress in the mechanization of tea plucking, which reduces the cost for employing pickers, enhances the earnings of farmers by improving the quality and price of tea, and supports the sustainable development of tea industry. Keywords: Agricultural machinery, Experiment, Fuzzy synthesize evaluation, Harvest, Hydraulic, Tea.

Guidance and Attitude Control of Unstable Rigid Bodies With Single-Use Thrusters

In this paper, we introduce a novel computationally efficient and practical algorithm for robust guidance and attitude control of unstable rigid bodies using the discrete fixed-magnitude, fixed-duration actuation representative of single-use thrusters. New guidance and attitude continuous control laws are developed based on the nonlinear rigid-body motion model, where the objective is to intercept a target and maintain the near zero angle of attack. A methodology is then introduced to adapt the continuous control system to discrete impulsive forces with constant magnitude and duration. An actuation management scheme is presented based on the equivalence of the total impulse of the continuous control law and thruster force. Realistic time delays and noise distributions are included in a sensor fusion algorithm based on the extended Kalman filter. Simultaneous control for course corrections to ensure the target interception and stabilization of the vehicle attitude is presented through Monte Carlo simulations with various uniformly distributed direction and velocity errors.

A comparative investigation on motion model of rifle bullet penetration into gelatin

Gelatin is a popular tissue simulant in biomedical applications. The behavior of a bullet and the effects of penetrating a simulant are similar in biological tissue. In order to accurately describe the interaction between a rifle bullet and muscle tissue, this paper discusses the wounding mechanism and the difference between the Bo Janzon (B-J) model, the Karl Sellier (K-S) model, and a three-degree of freedom (DOF) rigid-body motion model previously established by us based on the properties of gelatin. In addition, experiments conducted into rifle bullet penetration into gelatin, with bullet sizes 7.62 × 54mm and 5.8 × 42mm, and acquisition of the corresponding motion law are discussed. Numerical calculations reveal that the motion model has a better fit with experimental values than the B-J and K-S models. Further, it more accurately describes the motion of a rifle bullet penetrating gelatin than the other models and also has good generality. Thus, it can provide a theoretical reference for small arms ammunition design and wound treatment.

Navier–Stokes solver for water entry bodies with moving Chimera grid method in 6DOF motions

A preconditioned Navier–Stokes (NS) method is developed for multiphase flow with application to the water entry problem of moving bodies. The method employs a dual time-preconditioned technique with multiblock and parallel computing to improve the computational productivity. Novel, generalized pseudo-time terms are added into the multiphase NS equations, taking advantage of two previous suggestions reported in the literature. The NS solver is formulated in the moving curvilinear coordinate system for multiphase flow, including water, vapor, and air fluids. In order to handle the motion of an object in three-dimensional (3D) water entry problems, a six degrees-of-freedom (6DOF) rigid body motion model and a moving Chimera grid scheme are dynamically integrated into the NS solver. The Chimera domain decomposition scheme uses an overlapping, embedded, and moving grid approach to facilitate the flow simulation of arbitrary translationally and rotationally complex geometries among various computational blocks. The domain communication module is fully parallel and is ideally suited for handling moving body problems. To demonstrate the capacities of the method, several sets of example computations are performed and presented in this paper.

Inward open characterization of EmrD transporter with molecular dynamics simulation

EmrD is a member of the multidrug resistance exporter family. Up to now, little is known about the structural dynamics that underline the function of the EmrD protein in inward-facing open state and how the EmrD transits from an occluded state to an inward open state. For the first time the article applied the AT simulation to investigate the membrane transporter protein EmrD, and described the dynamic features of the whole protein, the domain, the helices, and the amino acid residues during an inward-open process from its occluded state. The gradual inward-open process is different from the current model of rigid-body domain motion in alternating-access mechanism. Simulation results show that the EmrD inward-open conformational fluctuation propagates from a C-terminal domain to an N-terminal domain via the linker region during the transition from its occluded state. The conformational fluctuation of the C-terminal domain is larger than that of the N-terminal domain. In addition, it is observed that the helices exposed to the surrounding membrane show a higher level of flexibility than the other regions, and the protonated E227 plays a key role in the transition from the occluded to the open state.

Solution Conformation of the Unbound HIV-1 Protease Derived from Residual Dipolar Couplings Measured at Ambient and High-Pressure Conditions

The flexibility of the glycine-rich flaps are known to be essential for the catalytic activity of the HIV-1 Protease but their exact conformations at the different stages of the enzymatic pathway remain yet to be determined. While hundreds of crystal structures of protease-inhibitor complexes have been solved, only a dozen of unbound protease structures have been reported to date. These structures reveal a large heterogeneity of flap conformations, ranging from closed, to semi-open and wide-open conformations. We used here NMR spectroscopy to determine the flap orientation of the unbound protease in solution. The conformation of the flaps was determined by comparing the measured residual dipolar couplings to reference crystal structures representing the closed, semi-open and wide-open states. The data clearly indicate that the apo protease adopts a closed conformation in solution, similar to an inhibitor-bound state. We also compared the effect of high-pressure on the flap conformations of an apo and inhibitor-bound protease by measuring backbone residual dipolar couplings up to 1 kbar. A rigid-body motion model was derived to characterize the pressure-induced conformational changes of the flaps. While a minimal rearrangement of the flaps was observed in the case of the inhibitor-protease complex, we observed a significant pressure-induced rotation of the flaps in the case of the apo protease. These results highlight the intrinsic conformational flexibility of the unbound protease and offer a new perspective to understand the mechanism of ligand and inhibitor binding.

Direct Fuel Injector Power Drive System Optimization

Abstract : The objective of this study is to optimize the injector power drive system for improved fuel injection quantity and timing control. The power drive system was optimized for improved injection repeatability under different operating conditions such as fuel supply pressures. A coupled simulation of injector electromagnetic, pintle (needle) rigid body motion and computational fluid dynamics (CFD) model was employed to generate the optimal values of the 1st stage current, the 1st stage on-time and the 2nd stage current. The simulation results were validated against the experimental data measured with a photo detector measurement system.

Tightly-coupled stereo vision-aided inertial navigation using feature-based motion sensors

A tightly-coupled stereo vision-aided inertial navigation system is proposed in this work, as a synergistic incorporation of vision with other sensors. In order to avoid loss of information possibly resulting by visual preprocessing, a set of feature-based motion sensors and an inertial measurement unit are directly fused together to estimate the vehicle state. Two alternative feature-based observation models are considered within the proposed fusion architecture. The first model uses the trifocal tensor to propagate feature points by homography, so as to express geometric constraints among three consecutive scenes. The second one is derived by using a rigid body motion model applied to three-dimensional (3D) reconstructed feature points. A kinematic model accounts for the vehicle motion, and a Sigma-Point Kalman filter is used to achieve a robust state estimation in the presence of non-linearities. The proposed formulation is derived for a general platform-independent 3D problem, and it is tested and demonstrated with a real dynamic indoor data-set alongside of a simulation experiment. Results show improved estimates than in the case of a classical visual odometry approach and of a loosely-coupled stereo vision-aided inertial navigation system, even in GPS (Global Positioning System)-denied conditions and when magnetometer measurements are not reliable.

Use of MRI to assess the prediction of heart motion with gross body motion in myocardial perfusion imaging by stereotracking of markers on the body surface.

The aim of this study is to determine using MRI in volunteers whether the rigid-body-motion (RBM) model can be approximately used to estimate the gross body-motion of the heart from that of external markers on patient's chest. Our target clinical application is to use a visual-tracking-system (VTS) which employs stereoimaging to estimate heart motion during SPECT/CT and PET∕CT myocardial perfusion imaging. To investigate body-motion separate from the respiration the authors had the volunteers hold their breath during the acquisition of a sequence of two sets of EKG-triggered MRI sagittal slices. The first set was acquired pre-motion, and the second postmotion. The motion of the heart within each breath-hold set of slices was estimated by registration to the semiautomatic 3D segmentation of the heart region in a baseline set acquired using the Navigator technique. The motion of the heart between the pre- and postmotion sets was then determined as the difference in the individual motions in comparison to the Navigator sets. An analysis of the combined motion of the individual markers on the chest was used to obtain an estimate of the six-degree-of-freedom RBM from the VTS system. The metric for judging agreement between the motion estimated by MRI and the VTS was the average error. This was defined as the average of the magnitudes of the differences in the vector displacements of all voxels in the heart region. Studies with the Data Spectrum Anthropomorphic Phantom and "No-Motion" studies in which the volunteer did not intentionally move were used to establish a baseline for agreement. With volunteer studies a t-test was employed to determine when statistically significant differences in Average Errors occurred compared to the No-motion studies. For phantom acquisitions, the Average Error when the motion was just translation was 0.1 mm. With complex motions, which included a combination of rotations and translations, the Average Error increased to 3.6 mm. In the volunteers the Average Error averaged over all No-Motion acquisitions was 1.0 mm. For the case of translational motion, which might be expected to be RBM, the Average Error averaged over all volunteer studies increased to 2.6 mm, which was statistically different from the No-Motion studies. For the case of bends and twists of the torso, which would be expected to challenge the RBM model, the Average Error averaged over all such volunteer studies was 4.9 mm and was again statistically different. Investigations of motion of the arm including just bending at the elbow and leg motion resulted in Average Errors which were not statistically different from the No-Motion studies. However, when shoulder movement was included with arm motion the Average Error was near that of torso bends and twists, and statistically different. Use of the RBM model with VTS predictions of heart motion during reconstruction should decrease the extent of artifacts for the types of patient motion studied. The impact of correction would be less for torso bends and twists, and arm motion which includes the shoulders.

Experimental and numerical investigation of an unsteady supercavitating moving body

In the last decade much research works has been carried out in order to improve the operation and speed of the underwater vehicles. In this study important supercavitation features including formation, evolution and loss of supercavitation and partial cavitation for an underwater moving body are both experimentally and numerically investigated. To achieve this goal the natural supercavitation experiment was conducted through a moving body and the trajectory of the body and the shape of supercavity profile were recorded by a high speed camera. For the numerical simulation of the underwater moving body the unsteady Reynolds averaged Navier–Stokes equations are coupled to a six-degree-of-freedom (6DOF) rigid body motion model. The numerical results are validated by comparing the predicted trajectory and velocity of the body with presented experimental data. A good agreement between the predicted and experimental values ensures the accuracy of the prepared numerical algorithm that used in the present study. The results reported in this paper illustrate that the above experimental method and numerical algorithm can be one of the most powerful and beneficial tools for the supercavitating underwater vehicles optimization and performance analysis.

Calculation of Rigid-Body Motion of Integrated Raft Isolation System

Integrated raft isolation system (IRIS) has some advantages over raft system of much smaller scale, such as higher isolation efficiency, less use of elastic couplings, etc. But the calculation of IRIS’s dynamic characteristics is complex. Finite element method usually adopted by raft designers is inefficient due to the iterative nature of design process. In this paper a six-degree-of-freedom rigid-body motion model is presented to calculate the static，quasi-static and rigid-body mode behavior of IRIS. The model is especially suitable to compare different design schemes and select out feasible ones efficiently at the initial design stage of IRIS.

Distortional buckling of thin-walled inclined lipped channel beams bending about the minor axis

Based on the Generalised Beam Theory (GBT), two computing models are presented to analyse the distortional critical stress of cold-formed thin-walled inclined lipped channel beams bending about the minor axis. The computing model of rigid-body motion ignores the transverse bending deformation of the flange. However, the bending deformation of the flange is accounted for in the transverse bending computing model. Based on the transverse bending computing model, this paper puts up a simple method to take into account the in-plane bending of the flange. The results given by the rigid-body motion computing model does not correlate as well as those given by the transverse bending computing model with the results available in the literature. The accuracy of the transverse bending computing model is verified through comparison of its results with the known results. The comparisons demonstrate the importance of the bending deformation of the flange on the distortional buckling of cold-formed thin-walled channel beams bending about the minor axis.