CFD Analysis of a Captive Bullet Entry in Calm Water With and Without Turbulence

2019 ◽  
Author(s):  
René Bettencourt Rauffus ◽  
António Maximiano ◽  
Luís Eça ◽  
Guilherme Vaz
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Computational Cost ◽  
Longitudinal Force ◽  
The Body ◽  
Test Case ◽  
Vertical Force ◽  
Pitch Moment ◽  
The Difference

Abstract Simulations are carried out for a simplified lifeboat drop test case, which consists of a captive axisymmetric generic lifeboat shape (bullet), that penetrates the water surface at a constant velocity and angle of attack. The quantities of interest are the body fixed longitudinal force FX, vertical force FZ, and pitch moment MYY.This case was previously used in a verification and validation exercise [1]. Here, a step forward in complexity is taken, as the previous numerical model is now supplemented with the eddy-viscosity based turbulence model k–ω SST. Both approaches are then used to simulate two different cases: Case 1 with minimal wake effects; and Case 3 with flow separation and significant wake. The results are compared with the experimental data. The numerical uncertainty is estimated for both models. It is seen that for Case 1 the difference between both models is mostly within the comparison uncertainty, except for the longitudinal force FX, where the turbulent flow predicts a larger force, improving the comparison with the experiments. The loads predicted with turbulent flow stayed mostly within 6 % of the laminar flow. For Case 3 small differences between both models are found during/after the wake collapse stage. However, this difference is often within the comparison uncertainty. A reasonable agreement is found with the experimental data, except for FZ after the bow wake collapse. The turbulent flow improves slightly on the laminar approach regarding the agreement with the experiments, however it can be argued if this difference justifies the increased computational cost of the turbulence model.

scholarly journals Energetically optimal running requires torques about the centre of mass

2012 ◽  
Vol 9 (73) ◽  
pp. 2011-2015 ◽  
Author(s):  
James R. Usherwood ◽  
Tatjana Y. Hubel
Keyword(s):  
Large Body ◽  
The Body ◽  
Moment Of Inertia ◽  
Mechanical Work ◽  
Vertical Force ◽  
Centre Of Mass ◽  
Pitch Moment ◽  
Tail Structure ◽  
Reaction Forces ◽  
Long Head

Bipedal animals experience ground reaction forces (GRFs) that pass close to the centre of mass (CoM) throughout stance, first decelerating the body, then re-accelerating it during the second half of stance. This results in fluctuations in kinetic energy, requiring mechanical work from the muscles. However, here we show analytically that, in extreme cases (with a very large body pitch moment of inertia), continuous alignment of the GRF through the CoM requires greater mechanical work than a maintained vertical force; we show numerically that GRFs passing between CoM and vertical throughout stance are energetically favourable under realistic conditions; and demonstrate that the magnitude, if not the precise form, of actual CoM-torque profiles in running is broadly consistent with simple mechanical work minimization for humans with appropriate pitch moment of inertia. While the potential energetic savings of CoM-torque support strategies are small (a few per cent) over the range of human running, their importance increases dramatically at high speeds and stance angles. Fast, compliant runners or hoppers would benefit considerably from GRFs more vertical than the zero-CoM-torque strategy, especially with bodies of high pitch moment of inertia—suggesting a novel advantage to kangaroos of their peculiar long-head/long-tail structure.

scholarly journals Improving the Stability of the Passenger Vehicle by Using an Active Stabilizer Bar Controlled by the Fuzzy Method

Complexity ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Tuan Anh Nguyen
Keyword(s):  
High Speed ◽  
Control Method ◽  
Spatial Dynamics ◽  
The Body ◽  
Vertical Force ◽  
Dynamics Model ◽  
Track Dynamics ◽  
The Difference ◽  
Lift Off ◽  
The Stability

The rollover phenomenon is a particularly dangerous problem. This phenomenon occurs when the driver travels at high speed and suddenly steers. Under the influence of centrifugal force, the body vehicle will be tilted and cause the wheels to lift off the road. To solve this problem, the method of using an active stabilizer bar has been proposed. The active stabilizer bar is controlled automatically by a previously designed controller. The performance of the active stabilizer bar depends on the selected control method. Previous research often only used a half-car dynamics model combined with a linear single-track dynamics model to simulate the vehicle’s oscillation. In addition, most of the research focuses only on the use of linear control methods for the active stabilizer bar. Therefore, the performance of the stabilizer bar is not guaranteed. This paper focuses on establishing the model of spatial dynamics combined with the nonlinear double-track dynamics model that fully describes the vehicle’s oscillation most accurately. Besides, the fuzzy control method is proposed to control the operation of the hydraulic stabilizer bar. This is a completely novel model, and it is suitable for the actual traveling conditions of the vehicle. Also, simulations are done based on different scenarios. The results of the paper showed that the values of the roll angle, the difference in the vertical force at the wheels, and the displacement of the unsprung mass were significantly reduced when the vehicle used the active stabilizer bar, which is controlled by an intelligent control method. Therefore, the stability and safety of the vehicle have been guaranteed. This result will be the basis for performing other more complex research in the future.

scholarly journals Direct Numerical Simulation of separated turbulent flow in axisymmetric diffuser

2021 ◽  
Vol 2103 (1) ◽  
pp. 012214
Author(s):  
A S Stabnikov ◽  
D K Kolmogorov ◽  
A V Garbaruk ◽  
F R Menter
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Model Improvement ◽  
Good Agreement

Abstract Direct numerical simulation (DNS) of the separated flow in axisymmetric CS0 diffuser is conducted. The obtained results are in a good agreement with experimental data of Driver and substantially supplement them. Along with other data, eddy viscosity extracted from performed DNS could be used for RANS turbulence model improvement.

CFD Verification and Validation Study for a Captive Bullet Entry in Calm Water

2017 ◽  
Author(s):  
António Maximiano ◽  
Guilherme Vaz ◽  
Jule Scharnke
Keyword(s):  
Free Surface ◽  
The Body ◽  
Load Test ◽  
Verification And Validation ◽  
Vertical Force ◽  
Time Step ◽  
Pitch Moment ◽  
The Impact ◽  
Modelling Error ◽  
Quantities Of Interest

As a step towards complex impact loads cases, e.g. lifeboat drop tests or ship/platform slamming in waves, a verification and validation (V&V) study is carried out with an open-usage community based CFD code ReFRESCO for a simple impact load test case: a captive axisymmetric generic lifeboat shape (bullet) that penetrates the water surface at a constant velocity and angle of attack. The quantities of interest are the body fixed longitudinal force FX, vertical force FZ, and pitch moment MYY. The influence of the iterative convergence level, domain size and free surface modelling are investigated. Seven different grids and four time steps were used to assess the grid and time step sensitivity, in a total of 28 calculations. For the tested grids and time steps it was found that the results are more sensitive to the grid resolution than to the time step. The pressure distribution on the hull is correlated with the trends observed in the loads, and the relation between between relative and static pressure is found to be important for the calculated loads. An experimental test campaign was previously carried out by MARIN, and its results are used to validate the simulations performed. A very good match between experiments and simulations is found. A V&V study is performed for the quantities of interest at nine different time instants covering the impact phase. The numerical uncertainties are obtained from a solution verification procedure [1]. The experimental uncertainties are estimated, and a validation exercise carried out according to the ASME standards [2]. The outcome of the validation exercise is an estimated 95 % confidence interval for the modelling error, δM. For FX the modelling error is below 15 N, for 8 out of 9 time instants. For FZ the modelling error is below 14 N, except at the time instants where, due to vibrations in the experimental setup, a larger value (up to 23 N) is found. For MYY the modelling error is under 5N m. These results provide confidence in ReFRESCO for the simulation of free surface impact flows.

scholarly journals Motion Analysis of Butterfly-Style Flapping Robot Using CFD Based on 3D-CAD Model and Experimental Flight Data

2021 ◽  
Vol 33 (2) ◽  
pp. 216-222
Author(s):  
Keisuke Sanuki ◽  
◽  
Taro Fujikawa
Keyword(s):  
Flow Field ◽  
Motion Analysis ◽  
The Body ◽  
Cad Model ◽  
Cfd Analysis ◽  
Flight Data ◽  
3D Cad ◽  
Pitch Moment ◽  
The Difference ◽  
Analysis System

In this paper, a computational fluid dynamics (CFD) analysis system based on a 3D-CAD model of a butterfly-style flapping robot using its experimental flight data is proposed. The butterfly-style flapping robot can control its attitude by changing its flapping and lead-lag angles; however, measuring the lift, thrust, and body pitch moment directly during flight is difficult. In the case of the flight motion analysis of insects, the state of flight has been photographed, and numerical analysis has been performed to obtain the flow field around the wings. However, when performing the motion analysis of hardware, it is difficult to reflect the shape of the body accurately using this method. In this study, a CFD analysis system considered the shape of the developed butterfly-style flapping robot as 3D-CAD data and analyzed the flow field around the wings using the experimental flight data of the hardware. The results of motion analysis showed that the attitude during flight differs due to the difference in lifts and body pitch moments in the flight experiment data of the hardware with different neutral angles of the flapping wings.

Evaluation of Parametric Models Dedicated to a Magnetorheological Actuator Including Uncertainty and Sensitivity Analyses

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
Philippe C. Fernandes Teixeira ◽  
Núbia dos Santos Saad ◽  
Fabian Andres Lara-Molina ◽  
Aldemir Ap Cavalini ◽  
Valder Steffen
Keyword(s):  
Experimental Data ◽  
Computational Cost ◽  
Parametric Models ◽  
Sensitivity Analyses ◽  
Engineering Systems ◽  
Hysteretic Model ◽  
Mr Dampers ◽  
Interval Approach ◽  
The Difference ◽  
Parametric And Nonparametric Approaches

Abstract Semi-active actuators have been used in engineering systems for vibration control purposes. For instance, magnetorheological (MR) dampers are applied in support of vehicle seats and smart suspensions of bridges and buildings. Parametric and nonparametric approaches were developed to model MR actuators, in which the former presents well-established and representative models. In this context, this work aims at comparing the so-called Bingham, modified Bouc-Wen (BW), and hysteretic models dedicated to MR actuators. Typical inverse problems were solved to minimize the difference between the forces determined by using these models and experimental data. The obtained results demonstrated that the hysteretic model is better adapted to represent the considered MR actuator, presenting lower computational cost and easy implementation. Additionally, uncertainty and sensitivity analyses based on the interval approach were applied on the updated MR models aiming to determine the working envelopes associated with the most important parameters of the models.

Determination of Cavity Detachment for Sheet Cavitation

2007 ◽  
Vol 129 (9) ◽  
pp. 1105-1111 ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Experimental Data ◽  
Special Kind ◽  
Flow Speed ◽  
The Body ◽  
Bodies Of Revolution ◽  
Suggested Approach ◽  
Sheet Cavitation ◽  
Fluid Theory ◽  
Entire Flow ◽  
The Difference

Sheet cavitation has been traditionally analyzed with ideal fluid theory that employs the cavitation number as the single parameter. However, characteristics of cavitation can significantly depend on location of cavity detachment. According to known experimental data, this location is influenced by the freestream speed and the body/hydrofoil size. As shown in this paper, it takes place because of the combined effect of the Reynolds number and Weber number. Here, sheet cavitation is considered as a special kind of viscous separation caused by the cavity itself. The viscous-inviscid interaction concept is employed to analyze the entire flow. Validation of the suggested approach is provided for hydrofoils and bodies of revolution. The effects of flow speed, the body size, and its surface wettability are illustrated by comparison of computed cavity length/shape to the known experimental data. The difference between cavity detachment in laminar and turbulent boundary layers is discussed.

Our Bodies, Whose Property?

2013 ◽  
Author(s):  
Anne Phillips
Keyword(s):  
Labor Markets ◽  
Personal Autonomy ◽  
The Body ◽  
Body Parts ◽  
Complex Issue ◽  
Human Organs ◽  
Property Owners ◽  
The Common ◽  
The Difference ◽  
The Right

No one wants to be treated like an object, regarded as an item of property, or put up for sale. Yet many people frame personal autonomy in terms of self-ownership, representing themselves as property owners with the right to do as they wish with their bodies. Others do not use the language of property, but are similarly insistent on the rights of free individuals to decide for themselves whether to engage in commercial transactions for sex, reproduction, or organ sales. Drawing on analyses of rape, surrogacy, and markets in human organs, this book challenges notions of freedom based on ownership of our bodies and argues against the normalization of markets in bodily services and parts. The book explores the risks associated with metaphors of property and the reasons why the commodification of the body remains problematic. The book asks what is wrong with thinking of oneself as the owner of one's body? What is wrong with making our bodies available for rent or sale? What, if anything, is the difference between markets in sex, reproduction, or human body parts, and the other markets we commonly applaud? The book contends that body markets occupy the outer edges of a continuum that is, in some way, a feature of all labor markets. But it also emphasizes that we all have bodies, and considers the implications of this otherwise banal fact for equality. Bodies remind us of shared vulnerability, alerting us to the common experience of living as embodied beings in the same world. Examining the complex issue of body exceptionalism, the book demonstrates that treating the body as property makes human equality harder to comprehend.

Theory-Practice Gap: The Experiences of Nigerian Nursing Students

2018 ◽  
Vol 20 (1) ◽  
Author(s):  
Titilayo Dorothy Odetola ◽  
Olusola Oluwasola ◽  
Christoph Pimmer ◽  
Oluwafemi Dipeolu ◽  
Samson Oluwayemi Akande ◽  
...  
Keyword(s):  
Clinical Practice ◽  
Nursing Students ◽  
Developing Country ◽  
The Body ◽  
Clinical Staff ◽  
Clinical Settings ◽  
Practice Gap ◽  
The Difference ◽  
Analyse Data ◽  
Theory Practice Gap

The “disconnect” between the body of knowledge acquired in classroom settings and the application of this knowledge in clinical practice is one of the main reasons for professional fear, anxiety and feelings of incompetence among freshly graduated nurses. While the phenomenon of the theory-to-practice gap has been researched quite extensively in high-income country settings much less is known about nursing students’ experiences in a developing country context. To rectify this shortcoming, the qualitative study investigated the experiences of nursing students in their attempt to apply what they learn in classrooms in clinical learning contexts in seven sites in Nigeria. Thematic content analysis was used to analyse data gained from eight focus group discussions (n = 80) with the students. The findings reveal a multifaceted theory-practice gap which plays out along four tensions: (1) procedural, i.e. the difference between practices from education institutions and the ones enacted in clinical wards – and contradictions that emerge even within one clinical setting; (2) political, i.e. conflicts that arise between students and clinical staff, especially personnel with a lower qualification profile than the degree that students pursue; (3) material, i.e. the disconnect between contemporary instruments and equipment available in schools and the lack thereof in clinical settings; and (4) temporal, i.e. restricted opportunities for supervised practice owing to time constraints in clinical settings in which education tends to be undervalued. Many of these aspects are linked to and aggravated by infrastructural limitations, which are typical for the setting of a developing country. Nursing students need to be prepared regarding how to deal with the identified procedural, political, material and temporal tensions before and while being immersed in clinical practice, and, in so doing, they need to be supported by educationally better qualified clinical staff.

Sign in / Sign up

Export Citation Format

Share Document