Initial Roll Research Articles

Numerical simulation of wedges slamming non-Newtonian fluids based on SPH method

Current research on non-Newtonian fluids using Smoothed Particle Hydrodynamics (SPH) has primarily focused on dynamic behavior, with limited exploration into interactions between rigid bodies and non-Newtonian fluids. Leveraging the SPH method's effectiveness in addressing free surface flow challenges, a two-dimensional numerical model of a rigid body impacting non-Newtonian fluids based on the Herschel-Bulkley-Papanastasiou (HBP) constitutive model is developed within the SPH framework. The study integrates experimental and numerical findings from non-Newtonian dam break scenarios, comparing particle distribution and the evolution of the waterfront over time to ensure accurate representation of non-Newtonian fluid behavior. While ensuring the convergence of SPH results, the research simulates the impact of a wedge on the surface of non-Newtonian fluids. This comparison of the slamming load exerted by non-Newtonian fluids on the wedge serves to validate the accuracy of the numerical method. Furthermore, the study explores the effects of varying initial velocities and roll angles of wedges slamming into specific non-Newtonian fluids. It analyzes fluid jet phenomena and changes in slamming loads.

Bir Konteyner Gemisi İçin Kapsamlı Yalpa Sönümü Değerlendirmesi ve Hareket Analizi

The primary purpose of this study is to investigate the damping characteristics of the ship’s roll motion. The second goal is to explore the damping effects on the solution of roll motion, considering the ship’s forward speed, wave frequency, and initial roll amplitude. Roll motion is a more critical yet less understood response compared to other degrees of freedom due to the complexity arising from viscosity. Roll damping comprises several components, which are divided into five categories with the assistance of empirical formulas created as a result of experiments. Wave damping is calculated by linear diffraction/radiation theory so it is a linear damping. Lift damping is also considered linear. However, eddy making, skin friction, and bilge keel damping are not linear due to dependency on the initial roll amplitude. The effects of roll amplitude, the ship’s forward speed, and wave frequency are investigated in this paper with the empirical formulas developed by Ikeda and Himeno. Frequency domain analyses of the roll motion are also conducted for the selected cases to demonstrate the credibility of the proposed paper. All algorithms have been developed in the MATLAB environment which is embedded with the YTU DEEP Ship Motion Program.

Accumulative roll bonding of aluminum alloy 6082: Microstructural evolution and mechanical properties

AbstractMaterial strengthening is a key objective of researchers and scientists in the present scenario for industrial applications. Although many processes can strengthen and refine grains, severe plastic deformation is the most dominant of all other techniques. Accumulative roll bonding is one of the severe plastic deformation techniques. This study examined how the various accumulative roll bonding cycles at the elevated preheating temperature affected the mechanical characteristics and microstructural evolution of the AA6082 strip. An optical microscope, scanning electron microscope, and electron backscatter diffraction were used to analyze the bonding and microstructural features. To determine mechanical characteristics, tensile and microhardness tests were also performed. The ultrafine grain size was achieved after accumulative roll bonding processing of AA6082. Accumulative roll bonding processing enhances mechanical properties like tensile strength and microhardness during the initial accumulative roll bonding cycle, but these properties grow more slowly at higher accumulative roll bonding cycles. However, the elongation value considerably decreased in the first cycle before stabilizing. The nice bonding between the layers was seen after accumulative roll bonding. Even after accumulative roll bonding, the fracture morphology reveals a ductile mode of fracture.

Analysis of the energy efficiency and control ability under different magnetic flux forms in RPECT

Roll profile electromagnetic control technology (RPECT), which has the flexible control ability of the roll profile, is a new roll gap control technology that can be applied in the cold rolling process. The electromagnetic stick (ES) is generally used as the main bulging driving to adjust the roll profile. However, the ES structure can be changed with the variation of the electromagnetic flux forms, which further results in the difference of the energy efficiency and control ability. In this paper, the transverse magnetic flux form (TMF) and longitudinal magnetic flux form (LMF) of RPECT are proposed, and the principles of TMF and LMF are analyzed, and their advantages in the heat transfer paths are discussed. To conduct the parameterized impact analysis, the electromagnetic-thermal-structural coupled model matching the two electromagnetic flux forms are established and verified. Through the analysis of the current density, the current frequency, the external cooling and the initial roll temperature, the results show that the variation of the current densities, the current frequencies or the initial roll temperatures can change the control ability of RPECT, while changing the external cooling can not affect that of RPECT. The energy efficiency intersection of TMF and LMF can be achieved by changing the current density or current frequency separately. However, compared with changing the current frequency, increasing the current density of TMF to two times of LMF at different initial roll temperatures can realize the energy efficiency intersection of TMF and LMF, which is the best way to achieve this goal.

Analysis of Roll Decay for Surface-Ship Model Experiments With Uncertainty Estimates

Abstract Roll decay of David Taylor model basin (DTMB) Model 5720, a 23rd-scale free-running model of the research vessel (R/V) Melville, is evaluated with uncertainty estimates. Experimental roll-decay time series was accurately modeled as an exponentially decaying cosine function, which is the solution of a second-order ordinary differential equation for damping coefficient of less than one (N < 1). The curve-fit provides damping coefficient (N), period (T), and offset. Roll period in calm water was dependent on Froude number (Fr) and initial roll angle (a). Roll decay data are from 76 runs for three nominal Froude numbers, Fr = 0, 0.15, and 0.22. The initial roll angle variation was 3 deg–25 deg. The natural roll period was 2.139 ± 0.041 s (±1.9%). The decay coefficient data were approximated by a plane in three dimensions with Fr and initial roll amplitudes (a) as the independent variables. Curve-fit results are compared to decay coefficient by log decrement and period from time between zero crossings. Examples demonstrate average values for a single roll decay event from log decrement are the same as values by the curve-fitting method within uncertainty estimates. The uncertainty estimate for the decay coefficient is significantly less by curve-fit method in comparison to log-decrement method. By log decrement, the relative uncertainty increases with decreasing roll amplitude peak; consequently, focus should be on the damping coefficient at the largest peaks, where the uncertainty is the smallest.

Note on Coarse Alignment of Gyro-Free Inertial Navigation System

In this note, the feasibility of initial alignment of a gyro-free inertial navigation system (GF-INS) is investigated. Initial roll and initial pitch are obtained using leveling of conventional INS since centripetal acceleration is very small. The equation for the initial heading cannot be used since the GF inertial measurement unit (IMU) cannot directly measure the Earth rate. A new equation is derived to obtain the initial heading from GF-IMU accelerometer outputs. Initial heading is expressed in the accelerometer outputs of two configurations, which satisfies a specific condition among 15 GF-IMU configurations presented in the literature. The initial heading error to arrangement and accelerometer error is quantitatively analyzed from the initial heading calculation equation of GF-INS and the initial heading error analysis of the general INS. The initial heading error is investigated when gyroscopes are used with GF-IMU. The results show that the initial heading error depends more on the performance of the gyroscope than that of the accelerometer, and the initial heading cannot be obtained within a practical error level by using only GF-IMU, even when an extremely accurate accelerometer is used. Therefore, aiding sensors have to be used in order to have a practical initial heading.

Dynamic modeling and vibration characteristics analysis of parallel antenna

Abstract. Research on the vibration characteristics of the mechanical systems is a necessary step for the stable and reliable operation of high-end equipment. The 6 degrees of freedom parallel mechanism is proposed for the supporting mechanism of the antenna. First, the dynamic equations of the moving platform and branch of the mechanism are established. The closed-form dynamics of the mechanism are derived based on the Newton–Euler method. In addition, the vibration equation of the parallel antenna is established based on the vibration theory, and the relationship between the natural frequency, displacement response, and vibration frequency is obtained. Afterward, the pitch and roll poses of a 1.8 m aperture antenna are developed based on a MATLAB software simulation. The actuation forces of parallel antenna under no-load and load conditions are simulated. Finally, the natural frequencies and vibration modes of the initial position and roll (20∘) are simulated based on the Adams software vibration analysis module. Furthermore, the relationship between the displacement response of the moving platform and the resonant frequency is studied based on the harmonic response analysis. The control strategy based on the dynamic model improves the control accuracy of parallel antenna. This research work provides a guarantee for the dynamic characteristics analysis and engineering application of parallel antenna.

The Effect of Roll Rate on Simulated Entry Vehicle Ballistic Range Tests

Free-flight computational fluid/rigid-body dynamics simulations are now being explored as a way to augment physical experiments for characterizing the dynamic behavior of blunt-body atmospheric entry vehicles. Initializing these simulations with accurate initial conditions is critical to achieving validation against experimental results and characterizing vehicle behavior. This paper explores the impact of a nonnegligible initial roll rate on numerical free-flight simulations of ballistic range tests using the FUN3D Navier–Stokes flow solver and POST2 trajectory propagator. These ballistic range shots were performed on a model of the Supersonic Inflatable Aerodynamic Decelerator at the NASA Ames Hypervelocity Free-Flight Aerodynamics Facility. In the absence of measured roll data, a method for reconstructing the initial roll rate is developed assuming that a nonnegligible roll rate accounts for the exchange in amplitude between the experimental pitch and yaw data. Simulations of three shots spanning a range of initial roll rates are executed to evaluate the new method. Results are validated against the physical ballistic range tests. Simulations with the reconstructed roll rate are more accurate to the experimental data than those assuming a negligible initial roll rate. Direct calculation of the pitch damping coefficient also captures the effect of roll rate on pitching moment.

Analyzing the accumulative roll bonding deformation zone behavior by FEM, upper bound, and experimental methods

Kinematically admissible velocity field assumption is a significant step in analyzing metal forming processes by the upper bound method (UBM). While the rotational triangular velocity field is the most compatible one in simple rolling, there is no evidence for prevailing of this velocity field in accumulative roll bonding (ARB). Accordingly, in this article, the geometry of the prevailing velocity field at the deformation zone of simple rolling (SR), and twice-rolled ARB samples were investigated through two distinct methods including experimental tests, and finite element simulation (FEM). It was proved that: 1) rotational triangle velocity field is quietly detectable in SR and ARB samples, 2) at the strip contact surfaces of ARB samples, the surface discontinuities affect the geometry of velocity field, and 3) the number of appeared rotational triangles at the deformation zone can be related to the initial roll diameter/initial sheet thickness ratio (D0/H0 while ignoring roller flattening). These results were used to propose an angular velocity field containing a discontinuity at the ARB strip interfaces. In the next step, the effects of three independent parameters including strip/rollers friction, the angular velocity of rollers, and strip's yield strength on the geometry of the prevailing velocity field were evaluated for both SR and ARB at two different D0/H0 and thickness reductions.

Effect of initial roll or pitch angles on the vortex-induced motions (VIM) of floating circular cylinders with a low aspect ratio

The vortex-induced motions (VIM) is a phenomenon that can promote large oscillatory amplitudes on circular platforms in the horizontal plane, such as spar or monocolumn production, storage, and offloading system (MPSO). Floating offshore wind turbines (FOWT) can use a spar-type platform to support the turbine, and due to the wind incidence, roll or pitch angles can occur. The main goal of this work was to experimentally investigate the effect of the initial roll or pitch angles on the VIM amplitudes of a floating circular cylinder with a low aspect ratio. Four different initial angle conditions were carried out, namely vertical, roll angle, positive pitch angle, and negative pitch angle. The Reynolds number range performed was 12,000<R<100,000. The results of VIM amplitudes showed that the yaw motion was affected by the initial pitch angle. The initial pitch angles proved to be responsible for creating a geometric asymmetry of the body and promoted more significant yaw motions than the case without initial angle conditions. The yaw motions started to be substantial after the mean pitch angle of the cylinder reached 3°. The yaw motion increased as the reduced velocity was increased and showed to be essential to be correctly modeled and analyzed in the case of VIM on FOWT.

Implementing and sustaining Point of Care ROTEM® into a trauma activation protocol for the management of patients with traumatic injury: A mixed-methods study

BackgroundUp to 40% of patients with traumatic injury experience critical bleeding, many requiring transfusion of blood products. International transfusion guidelines recommend the use of viscoelastic testing to guide blood product replacement. We implemented a Point of Care ROTEM® blood test for trauma patients who present and initiate a trauma activation. ObjectivesThe aim of this study was to undertake an evaluation of the implementation data to identify factors which helped and hindered this new practice. MethodsA sequential mixed-methods design was conducted to evaluate intervention implementation. The intervention was designed with interprofessional collaboration and incorporated education and skills training supplemented with a decision aide. Patients aged ≥ 18 years who met the trauma activation criteria were included. Data collection occurred throughout the 21-month implementation period inclusive of initial roll out, maintenance and sustainability and include the number of ROTEM® blood tests taken and clinical characteristics of patients. Individual interviews were conducted with health professionals with experience of the intervention after the implementation period was complete. ResultsA total of 1570 eligible patients were included. The number of patients who had a ROTEM® blood test taken increased over time to 63%. The proportion of patients having a ROTEM® blood test obtained was higher for major trauma patients (n=162, 66.9%) who were admitted to the Intensive Care Unit. Regression analysis found trauma service presence on arrival and the sustainability phase of implementation increased the likelihood of having a ROTEM® taken. Qualitative data suggest that a more tailored approach to intervention implementation would assist with adoption. ConclusionImplementation of new practice requires careful planning and should be undertaken with input from end-users. Continuous evaluation is necessary to support ongoing implementation and sustainability. To ensure effective implementation occurs, complex interventions need to be made workable and integrated in everyday health care practice.

A new analytical model to predict the profile and stress distribution of tube in three-roll continuous retained mandrel rolling

To minimize the adjustments to the initial roll speed setting in tube manufacturing, both the tube profile and the tube stress distribution during the rolling are needed to be predicted before the actual rolling. While predicting the tube profile is to make the rolling reach to the metal flow balance state efficiently, predicting the tube stress distribution is to decrease the potential formation of the rolled defects caused by the non-ideal stress distribution in tube at each pass. This requires the rolling model to combine the prediction of tube profile with the prediction of stress distribution of tube in its formulation. A new analytical model which can meet the above requirements is presented in this paper. The mechanics of rolling tube in three-roll continuous retained mandrel rolling has been analyzed in the model. Validity of the model has been examined by hot rolling experiments at the plant. According to the experimental results, the predicted tube profiles are in good agreement with the measured, with the prediction errors of cross-sectional areas being in the range of 0.8∼2.5 %. The theoretical initial roll speed setting calculated based on the proposed model can be applied directly to tube manufacturing, with further adjustments at the mill being less than 4 %. The predicted roll forces calculated based on the proposed model have a maximum deviation from the measured less than 15 %. In general, the hot rolling experimental results at the plant have proved the validity of the proposed model.

Balancing Community and Local Needs

This paper examines the decision points over the course of ten years for developing an Institutional Repository. Specifically, the focus is on the impact and influence from the open-source community, the needs of the local institution, the role that team dynamics plays, and the chosen platform. Frequently, the discussion revolves around the technology stack and its limitations and capabilities. Inherently, any technology will have several features and limitations, and these are important in determining a solution that will work for your institution. However, the people running the system and developing the software, and their enthusiasm to continue work within the existing software environment in order to provide features for your campus and the larger open-source community will play a bigger role than the technical platform. These lenses are analyzed through three points in time: the initial roll out of our Institutional Repository, our long-term running and maintenance, and eventual new development and why we made the decisions we made at each of those points in time.

THE TRANSIENT EFFECTS OF FLOOD WATER ON A WARSHIP IN CALM WATER IMMEDIATELY FOLLOWING DAMAGE

The safety of a ship which is damaged below the waterline will depend on the way water floods into the internal compartments. The water will cause the ship to take on an angle of heel and trim which will further affect the flooding into the compartments. The ship’s equilibrium position in calm water can be predicted using hydrostatic theory, however at present it is difficult to predict the transient behaviour between the initial upright position of the ship and its final equilibrium. In some cases, the transient motion may cause a capsize prior to a possible equilibrium position being reached.&#x0D; This paper describes an investigation of this phenomenon using a model of a warship with simplified, typical internal geometry. With the model initially stationary, a rapid damage event was generated, and the global motions measured, along with the water levels in some of the internal compartments, as functions of time. Immediately after the damage occurred the model rolled to starboard (towards the damage). It then rolled to port (away from the damage) before eventually returning to starboard and settling at its equilibrium value. In all the tests conducted the equilibrium heel angle was less than that reached during the initial roll to starboard. This implies that the roll damping, and the way in which the water floods into the model immediately following the damage, could both have a very important influence on the likelihood of survival.

Nonlinear vibration analysis of the large-amplitude asymmetric response of ship roll motion

Ship roll motion is the single most important factor responsible for ship capsizes. Yet, there is still much to be understood about this subject; especially, how critical parameters influence the asymmetric response during large initial roll amplitudes. Consequently, this paper presents an investigation of the nonlinear vibration of the large-amplitude asymmetric response during ship roll motion. The dynamic model governing the roll motion accounted for quadratic damping and cubic nonlinear restoring moment with softening behaviour. The continuous piecewise linearization method was adopted to solve the governing model. Hence, the effect of four critical parameters (i.e. initial roll amplitude, added mass, quadratic damping and nonlinear restoring moment) on the asymmetric roll response and capsize tendency was investigated. It was observed that capsize tendency was strongly linked to the offset of the equilibrium point and the asymmetric response, which amplified the initial roll amplitude. An increase in the initial roll amplitude or quadratic damping produced a stronger asymmetric response and an increased capsize tendency, while an increase in the added mass or nonlinear restoring moment weakened the asymmetric response and decreased the capsize tendency. Also, an increase in any of the four critical parameters produced a decrease in the frequency of vibration.

Aerodynamic Performance of the InSight Mars Lander

The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission touched down in Elysium Planitia on 26 November 2018, becoming NASA’s eighth successful entry, descent, and landing (EDL) at Mars. InSight inherited the successful 2008 Phoenix (PHX) EDL system, flying a nonspinning, ballistic trajectory with a 70 deg sphere–cone aeroshell (2.65 m diameter), a disk–gap–band parachute, and pulsed terminal descent and landing engines. InSight and Phoenix exhibited similar behavior, primarily in terms of trim attitude and an uninitiated roll reversal correlated with dynamic pressure, although the behaviors observed for InSight were more severe. For InSight, the initial clockwise roll and nonzero trim angle of attack were significant contributors to a short timeline, larger-than-predicted deceleration loads, and cross-track and up-track errors in landing location. The InSight and Phoenix reconstructions together indicate behavior more characteristic of a single, continuous instability region, suggesting that errors in the trim behavior from hypersonic nonequilibrium aerodynamics predictions along the dynamic pressure pulse may have a more substantial impact on nonspinning, ballistic entry vehicle performance.

URANSE-Based Numerical Prediction for the Free Roll Decay of the DTMB Ship Model

In the present study, Computational Fluid Dynamics (CFD) is used to investigate the roll decay of the benchmark surface combatant DTMB-5512 ship model appended with bilge keels, sailing in calm water at different speeds (Fr = 0.0, 0.138, 0.2, 0.28 and 0.41) and with different initial roll angles. The numerical simulations are carried out using the viscous flow solver ISIS-CFD of the FINETM/Marine software provided by NUMECA. The solver uses the finite volume method to build the spatial discretization of the transport equation to solve the unsteady Reynolds-Averaged Navier–Stokes equations. Two-phase flow approach is applied to model the air–water interface, where the free surface is captured using the volume of fluid method. The closure to turbulence is achieved by making use of the blended Menter shear stress transport and the explicit algebraic Reynolds stress models. First, a systematic validation against the experimental data at medium speed and initial roll angle of 10° are performed; then, the effect of the initial roll angle and ship speed is later studied. Numerical errors and uncertainties are assessed using grid and time step convergence study based on Richardson Extrapolation method. A special focus on the flow in the vicinity of the bilge keels during the simulation is also investigated and presented in the form of velocity contours and vortical structure formations. The resemblance between the CFD results and experimental data for roll motion and flow characteristics are within a satisfactory congruence; however, some discrepancies are recorded for the over predicted roll amplitudes in the second and, sometimes, the third roll cycle, which appeared mostly in the cases with high initial roll angles.

Semi-Active Control for a Helicopter with Multiple Landing Gears Equipped with Magnetorheological Dampers

Due to their extensive use in various applications, helicopters need to be able to land in a variety of conditions. Typically, a helicopter landing gear system with skids or passive wheel-dampers is designed based on only one critical touchdown condition. Thus, this helicopter landing gear system may not perform well in different landing conditions. A landing gear system with magnetorheological (MR) dampers would be a promising candidate to solve this problem. However, a semi-active controller must be designed to determine the electrical current applied to the MR damper to directly manage the damping force. This paper presents a new skyhook controller, called the skyhook extended controller, for a helicopter with multiple landing gears equipped with MR dampers to reduce the helicopter’s acceleration at the center of gravity in off-normal landing attitude conditions. A 9-DOF simulation model of a helicopter with multiple MR landing gears was built using RECURDYN. To verify the effectiveness of the proposed controller, co-simulations were executed with RECURDYN and MATLAB in different initial pitch and roll angles at touchdown. The main simulation results show that the proposed controller can greatly decrease the peak and rms acceleration of the helicopter’s center of gravity compared to a traditional skyhook controller and passive damper.

A mobile stereo vision system with variable baseline distance for three-dimensional coordinate measurement in large FOV

A novel mobile stereo vision system (MSVS) with variable baseline distance for three-dimensional (3D) coordinate measurement in large field of view (FOV) is established herein. Each independent mobile camera can rotate in the horizontal and vertical directions, and the position of the cameras are obtained by differential GPS in real time. In order to achieve rapid camera calibration in large FOV, a simplified model of MSVS based on differential GPS is constructed in this paper. A six-point method is proposed to quickly estimate the camera’s initial parameters (i.e. focal length, initial roll, pitch, and yaw angles) in the situation that the approximate value of the initial yaw angle is unknown. Moreover, the camera’s roll angle is equivalent to its approximate value measured by a high-precision inclinometer during the movement, and the unknown extrinsic parameters of each camera are reduced to the pitch and yaw angles after the camera moves. The refined pitch and yaw angles are eventually estimated by only using a single control point, which makes it possible that the 3D coordinate can be measured online after the camera moves. The computer simulation verifies the effectiveness of the extrinsic parameters calibration method using a single control point. The quantitative results demonstrate that the standard deviation of the focal length of the camera does not exceed 0.028 mm, and the mobile camera’s pitch angle and yaw angle estimated by a single control point is extremely close to the reference values. In addition, the average error of the 3D coordinate on each axis after the camera moves is smaller than 0.08 m in the measuring distance of 100 m, and that on X-axis and Z-axis is comparable and does not exceed 0.35 m. The proposed methods are suitable for the occasions that high accuracy is not required in the field of 3D coordinate measurement in large FOV.

String (In)Stability Issues with Broken Supersymmetry

We review the main results of our investigations motivated by the tadpole potentials of ten--dimensional strings with broken supersymmetry. While these are at best partial indications, it is hard to resist the feeling that they do capture some lessons of String Theory. For example, these very tadpole potentials lead to weak-string-coupling cosmologies that appear to provide clues on the onset of the inflation from an initial fast roll. The transition, if accessible to us, would offer a natural explanation for the lack of power manifested by the CMB at large angular scales. In addition, the same tadpole potentials can drive spontaneous compactifications to lower--dimensional Minkowski spaces at corresponding length scales. Furthermore, the cosmological solutions exhibit an intriguing ``instability of isotropy that, if taken at face value, would point to an accidental origin of compactification. Finally, symmetric static \(AdS \times S\) solutions driven by the tadpole potentials also exist, but they are unstable due to mixings induced by their internal fluxes. On the other hand, the original Dudas--Mourad solution is perturbatively stable, and we have gathered some detailed evidence that instabilities induced by internal fluxes can be held under control in a similar class of weak--coupling type-IIB compactifications to Minkowski space.