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- Type:
- Image
- 摘抄:
- Oxycomanthus bennetti, current from right
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/13/2017
- 更改日期:
- 02/13/2017
- 创建:
- 2017-02-13
- 证书:
- Attribution-NonCommercial 4.0 International
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- Type:
- Image
- 摘抄:
- Oxycomathus bennetti
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/13/2017
- 更改日期:
- 02/13/2017
- 创建:
- 2017-02-13
- 证书:
- Attribution-NonCommercial 4.0 International
-
- Type:
- Image
- 摘抄:
- Oxycomanthus bennetti
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/13/2017
- 更改日期:
- 02/13/2017
- 创建:
- 2017-02-13
- 证书:
- Attribution-NonCommercial 4.0 International
-
- Type:
- Image
- 摘抄:
- Oxycomathus bennetti with Pontiometra andersoni above; current from left
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/13/2017
- 更改日期:
- 02/13/2017
- 创建:
- 2017-02-13
- 证书:
- Attribution-NonCommercial 4.0 International
-
- Type:
- Article
- 摘抄:
- Not available.
- 作者:
- Gregory, Irene; Figueroa, Fernando; Cohen, Kelly; Ingham, Michel; Atkins, Ella; Obayashi, Shigeru; Truszkowski, Walt; Garg, Sanjay; Blackmore, Lars; Doyle, Richard, and Nguyen, Nhan
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2009-03
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- For the systematic development of feedback flow controllers, a numerical model that captures the dynamic behaviour of the flow field to be controlled is required. This poses a particular challenge for flow fields where the dynamic behaviour is nonlinear, and the governing equations cannot easily be solved in closed form. This has led to many versions of low-dimensional modelling techniques, which we extend in this work to represent better the impact of actuation on the flow. For the benchmark problem of a circular cylinder wake in the laminar regime, we introduce a novel extension to the proper orthogonal decomposition (POD) procedure that facilitates mode construction from transient data sets. We demonstrate the performance of this new decomposition by applying it to a data set from the development of the limit cycle oscillation of a circular cylinder wake simulation as well as an ensemble of transient forced simulation results. The modes obtained from this decomposition, which we refer to as the double POD (DPOD) method, correctly track the changes of the spatial modes both during the evolution of the limit cycle and when forcing is applied by transverse translation of the cylinder. The mode amplitudes, which are obtained by projecting the original data sets onto the truncated DPOD modes, can be used to construct a dynamic mathematical model of the wake that accurately predicts the wake flow dynamics within the lock-in region at low forcing amplitudes. This low dimensional model, derived using nonlinear artificial neural network based system identification methods, is robust and accurate and can be used to simulate the dynamic behaviour of the wake flow. We demonstrate this ability not just for unforced and open-loop forced data, but also for a feedback-controlled simulation that leads to a 90% reduction in lift fluctuations. This indicates the possibility of constructing accurate dynamic low-dimensional models for feedback control by using unforced and transient forced data only.
- 作者:
- Luchtenburg, D. M.; Cohen, Kelly; Seidel, Jurgen; Fagley, Casey, and Siegel, Stefan G.
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2008-09
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- The effectiveness of a small array of body-mounted sensors, for estimation and eventually feedback flow control of a D-shaped cylinder wake is investigated experimentally. The research is aimed at suppressing unsteady loads resulting from the von-Kármán vortex shedding in the wake of bluff-bodies at a Reynolds number range of 100–1,000. A low-dimensional proper orthogonal decomposition (POD) procedure was applied to the stream-wise and cross-stream velocities in the near wake flow field, with steady-state vortex shedding, obtained using particle image velocimetry (PIV). Data were collected in the unforced condition, which served as a baseline, as well as during influence of forcing within the “lock-in” region. The design of sensor number and placement was based on data from a laminar direct numerical simulation of the Navier-Stokes equations. A linear stochastic estimator (LSE) was employed to map the surface-mounted hot-film sensor signals to the temporal coefficients of the reduced order model of the wake flow field in order to provide accurate yet compact estimates of the low-dimensional states. For a three-sensor configuration, results show that the estimation error of the first two cross-stream modes is within 20–40% of the PIV-generated POD time coefficients. Based on previous investigations, this level of error is acceptable for a moderately robust controller required for feedback flow control.
- 作者:
- Cohen, Kelly; Stalnov, Oksana; Fono, Ilan; Seifert, Avi, and Palei, Vitali
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2007-02
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- The effect of feedback flow control on the wake of a circular cylinder at a Reynolds number of 100 is investigated in direct numerical simulation. The control approach uses a low-dimensional model based on proper orthogonal decomposition (POD). The controller applies linear proportional and differential feedback to the estimate of the first POD mode. The range of validity of the POD model is explored in detail. Actuation is implemented as displacement of the cylinder normal to the flow. It is demonstrated that the threshold peak amplitude below which the control actuation ceases to be effective is in the order of 5% of the cylinder diameter. The closed-loop feedback simulations explore the effect of both fixed-phase and variable-phase feedback on the wake. Whereas fixed-phase feedback is effective in reducing drag and unsteady lift, it fails to stabilize this state once the low drag state has been reached. Variable-phase feedback, however, achieves the same drag and unsteady lift reductions while being able to stabilize the flow in the low drag state. In the low drag state, the near wake is entirely steady, whereas the far wake exhibits vortex shedding at a reduced intensity. A drag reduction of 15% of the drag was achieved, and the unsteady lift force was lowered by 90%.
- 作者:
- Cohen, Kelly; Siegel, Stefan, and McLaughlin, Thomas
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2006-06
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- The effectiveness of a sensor configuration for feedback flow control on the wake of a circular cylinder is investigated in both direct numerical simulation as well as in a water tunnel experiment. The research program is aimed at suppressing the von Kármán vortex street in the wake of a cylinder at a Reynolds number of 100. The design of sensor number and placement was based on data from a laminar two-dimensional simulation of the Navier–Stokes equations for the unforced condition. A low-dimensional proper orthogonal decomposition (POD) was applied to the vorticity calculated from the flow field and sensor placement was based on the intensity of the resulting spatial eigenfunctions. The numerically generated data was comprised of 70 snapshots taken over three cycles from the steady state regime. A linear stochastic estimator (LSE) was employed to map the velocity data to the temporal coefficients of the reduced order model. The capability of the sensor configuration to provide accurate estimates of the four low-dimensional states was validated experimentally in a water tunnel at a Reynolds number of 108. For the experimental wake, a sample of 200 particle image velocimetry (PIV) measurements was used. Results show that for experimental data, the root mean square estimation error of the estimates of the first two modes was within 6% of the desired values and for the next two modes was within 20% of the desired values. This level of error is acceptable for a moderately robust controller.
- 作者:
- Cohen, Kelly; Siegel, Stefan, and McLaughlin, Thomas
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2006-01
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- A short computational program was undertaken to evaluate the effectiveness of a closed-loop control strategy for the stabilization of an unstable bluff-body flow. In this effort, the non-linear one-dimensional Ginzburg–Landau wake model at 20% above the critical Reynolds number was studied. The numerical model, which is a non-linear partial differential equation with complex coefficients, was solved using the FEMLAB®/MATLAB® software packages and validated by comparison with published literature. At first, a model independent approach was attempted for wake suppression using feedback control. The closed-loop system was controlled using a conventional proportional-integral-derivative (PID) controller as well as a non-linear fuzzy controller. A single sensor is used for feedback, and the actuator is represented by altering the boundary conditions of the cylinder. Simulation results indicate that for a single sensor scheme, the increase in the sophistication of the control results in significantly shorter settling times. However, there is only a marginal improvement concerning the suppression of the wake at higher Reynolds numbers. The feedback control design was then augmented by switching over to a model-dependent controller. Based on computationally generated data obtained from solving the unforced wake, a low-dimensional model of the wake was developed and evaluated. The low-dimensional model of the unforced Ginzburg–Landau equation captures more than 99.8% of the kinetic energy using just two modes. Two sensors, placed in the absolutely unstable region of the wake, are used for real-time estimation of the first two modes. The estimator was developed using the linear stochastic estimation scheme. Finally, the loop is closed using a PID controller that provides the command input to the variable boundary conditions of the model. This method is relatively simple and easy to implement in a real-time scenario. The control approach, applied to the 300 node FEMLAB® model at 20% above the unforced critical Reynolds number stabilizes the entire wake. Compared to the model-independent controllers, the controller based on the low-dimensional model is far more effective in the suppression of the wake at higher Reynolds numbers. Furthermore, while the latter approach employs only the estimated temporal amplitude of the first mode of the imaginary part of the amplitude, all higher modes are stabilized. This suggests that the higher order modes are caused by a secondary instability that is suppressed once the primary instability is controlled.
- 作者:
- Myatt, James; Cohen, Kelly; Siegel, Stefan; McLaughlin, Thomas, and Gillies, Eric
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2005-09
- 证书:
- All rights reserved