Articulated Swimming Creatures

Contribution:
Evaluation:
Reproducibility:
Improvements:

Contribution: The paper presents a simulation environment for articulated virtual creatures swimming in a fluid environment, and an optimization method to find viable swimming "gaits" for any given creature morphology. The simulator uses a voxelization approach along with standard Navier-Stokes equations to simulate the interaction between a creature and its fluid environment. Covariance Matrix Adaptation is then used to optimize control of a given creature as it swims. The results tend to resemble real-world creature movement due to the accurate simulation and effective objective function used in optimization.

Evaluation: The system is evaluated by testing it on models of several different real-world swimming creatures, including a fish, eel, frog and manta ray. Success is measured as how well the resulting motion approximates real motion observed in nature, in addition to how well the creatures can follow a path. Finally the same test is run on a creature morphology that does not exist in nature, with subjective observations on plausibility of the motion made instead of comparison to (non-existent) real-world motion. They also ran the same set of experiments using a much simpler fluid solver and compared the results.

Reproducible: The paper is reproducible due to the high level of detail presented on both how their simulator works and how their optimization routine functions. Almost all of the equations used in simulation are presented. The optimization is not presented in quite as much detail, but the gaps should be fairly easy to fill in by reading about the Covariance Matrix Adaptation method.

Improvement: I have no complaints about this paper. It is very well-organized, well-written and extremely thorough, making it relatively easy to understand the concepts presented within. It is also very thorough in its evaluation and testing of the system.

-- Main.cdoran - 01 Dec 2011

Contribution: The authors attempt to animate swimming creatures while seeking some measure of physical accuracy. To do so, they create a variety of virtual articulated creatures (both based on real animals and purely invented) and optimize control strategies while also simulating fluid dynamics.

Evaluation: Their ambitious goal is hard to evaluate from the onset, and sure enough their results are of "oh, look how pretty it looks" variety. Some of the remarks do make sense, like the fact that the opmitized control strategies ressemble those of real creatures, so in that sense it seems obvious that their approach is reasonable.

Reproducibility: As usual with these papers, the equations seem to be worked out in sufficient details. Not too much detail is given on the experiments, and in particular not too much is mentioned on how the optimization was carried out, which means it could have been either extremely easy or extremely hard.

Improvements: They mention themselves that the voxelization approach is not ideal, and can be improved upon. But all in all, they seem to have succeeded in their goal (which is why their suggested future work doesn't really make sense, swimming at the surface of the water seems like quite a different problem).

-- Main.ginestra - 01 Dec 2011

Contribution:
There are two main contributions of the study. First, they propose an optimization solution for the control of swimming motions of several creatures. Second, their method considers coupling between creature motions and the fluid interactions.

Evaluation:
The study presents results of swimming motions for a variety of animals that have different configurations and constraints. They also successfully tested their method for controlling an artificial creature. They suggest that the resulting motions look natural, and for the short-bodied fish, and the eelm, they are in agreement with the laboratory data in terms of the generated vortex trails. For other creatures, they cannot make a comparison as there is not any data for them.

Reproducibility:
Most of the equations are given and explained throughout the paper. Some of the parameters are also given, e.g. weight values, etc. However there are some parameters that they manually set, e.g. energy bound, which are not stated in the paper. Hence, it's pretty much reproducible but requires some hand tuning of some of the parameters.

Improvements:
The study can be further extended by investigating different functions for the optimization, other than just using a sine function. By that way, they can try to optimize more sophisticated motions, which can then be generalized to generate combinations of those motions. Paper is well-structured, and easy to follow.

-- Main.ooguz - 01 Dec 2011

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Contribution: This paper presents a complete system for controlling a wide variety of aquatic animals in a simulated fluid environment by creature/fluid simulation and optimization of the creature motion parameters. It is able to automatically find the optimal locomotion for an aquatic animal represented by an articulated rigid body system without prior knowledge the animal’s behavior.

Evaluation: The study is evaluated by demonstrating optimized swimming gaits of different aquatic animals and swimming strategies. They also compare the motion in a Navier-Stokes fluid with the motion in a simplified fluid.

Reproducibility: Given the sufficient details presented by the paper, it shouldn’t be hard to reproduce it especially when most of the equations are explained. I found the path following may be a little hard to implement.

Improvement: Overall the paper is very well structured and easy to follow. I can read through without going back and forth. In my opinion the paper does a good job in clearing up confusion. As an example, after watching the video I had questions about why the creatures seem to use so much energy to just make a little move. And I found this is explained well in the ‘limitation’ section.

Baoxuan - 01 Dec 2011

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** Contribution? Provides a tool that can produce physcially realistic aquatic motion for a wide array of creatures. So they don't have to be animated manually.

** How are the results evaluated? They build different creature models and see how they swim with or without defined paths.

** Reproducible? Highly likely. The equations for simulations are given. Controller equations are given, but not the gains and dampling coefficients. Equations to simulate two-way coupling are given. Weights of the objective function terms are given.

** Improvements? The swimming motions don't look very realistic to me. And they probably should compare the motion with real footages in order to make the paper more convincing.

-- Main.shuoshen - 01 Dec 2011

Contibution: The paper presents an approach creating realistic swimming behaviour given the model of a body. The idea of the paper is simple: the liquid is simulated by the Navier-Stokes/Euler equations, and boundary conditions are given by the swimming creature. The gait of the creature is optimized in terms of efficiency (speed) and staying within certain limits of energy consumption.

Evaluation: It's really hard to evaluate appropriately, since it's hard (if possible at all?) to do mocap on real swimming creatures. So the evaluation is confined to "we tried this model and it looks good" - which is acceptable in this case.

Reproducibility: yes, possible to reproduce. It doesn't look like there anything is the paper that won't work, everything is very straightforward.

Improvements: Even though they did state their main limitation in the paper - the parameterization of the joint space, they didn't really elaborate on how important that is. As I understand, if we presume that the gait is parameterized by one sine function, the motion is 'static', i.e. the optimization cannot take into account any obstacles, other streams in the fluid, etc. - basically, everything that may make the motion uneven.

-- MikhailBessmeltsev - 01 Dec 2011

-- MichielVanDePanne - 27 Nov 2011