Sneakier Submarines with Actuators

Submarines are already pretty silent and deadly. Most are either nuclear powered or have one or more diesel engines. Some use fuel cell technology to reduce the number of moving parts. Once the engines power the onboard batteries, that power spins the propeller allowing the craft to go under water for long periods at a time. German U-Boats may no longer be the enemy under water but it's still crucial that submarines are able to go silent at depth and be capable of quick and quiet escapes whenever possible. Everything that goes into the shape and power of the submarine is meant to reduce its noise.

Researchers modelled a submarine hull as a cylindrical shell with two cone shells on either end. They converted the displacement components of the cylinder to wave propagation equations and used a point force representation for the propeller as a Fourier series. The goal was to reduce the sound generated in the radial direction from propeller movement both from the propeller itself and vibration and displacement of the hull as a result of the propeller movement.

The researchers proposed an array of 60 commercial off the shelf linear actuators in a ring around the aft cone forward of the propeller.

The actuators act as a mass-spring dampening system. Their effectiveness would depend on what kind of controls were used in the feedback system to power the actuators. They examined both Active Vibration Control (AVC) and Active Structural Acoustic Control (ASAC).

The researchers found actuators could be effective at reducing radial sound generated from hull vibration. Both systems of controls they used can be seen in the above figures from their study. The actuators were especially effective at lower frequencies. That's probably a good thing as propellers typically have lower RPMs than the engines that power them. Though it's hard to see the Navy attaching a ring of off the shelf actuators to the hull of a submarine it is interesting to think what the implications might be or how actuators might reduce noise in similar applications. Or if actuators can be proven to reduce the noise what more practical mechanisms might mimic actuators successfully enough to reduce the sound profile of a submarine even further.


Caresta, M. (2011) Active control of sound radiated by a submarine in bending vibration. Journal of Sound and Vibration 330 (2011) 615–624.

Ways to f@# a conference call

What is life but periods of restlessness and waiting in between thrilling conference calls? If you'd like to frost my cookies with your incompetence, here are some great methods:

• Call in with your crappiest, off-brand cell phone, preferably with poor reception wherever you are
• Call while driving so you are distracted
• Bonus points for revving your engine, leaving the windows down, listening to the radio, and yelling at other drivers
• Don't bother to use the mute button, we know it's difficult, and we all love to hear your background noise
• Call in from home where we can hear your kids and dogs in the background
• Bonus points for any reference to a comfy chair and good dinner being made that rubs it in for the rest of us still in the office
• If you're going to call in from a conference room, sit as far away from the phone as possible
• Talk quietly if the phone is far away from you
• Scream into the phone if you're holding it to your ear
• Get distracted doodling and make everyone repeat the issue for you when your status comes up
• Eat while on the call
• Preferably something loud and crunchy or at least loud packaging
• Talk to passersby without muting your phone, hey Joe! Have a nice weekend?
• Let us all know what important meeting you really need to get to, we certainly have nothing better to do
• If sick sniffle constantly and sneeze loudly into the receiver
• Assign work to people who couldn't make it to the meeting and forget to tell them

That's all for now. I expect to see a comprehensive powerpoint on this on my desk in the morning. I don't care if you have to work all night, but I can't pay you overtime.

Now they get their own button?

Anyone stopped by Technorati lately?

What's this all about? A whole button for women bloggers and women's issues? A whole month is just never enough for these people is it.

Actually, I can't decide whether this is a cool thing, or gimicky, or patronizing...I mean it's better than Science Cheerleaders, but where is it in the spectrum? All good? Do I like them featuring women bloggers in the same way I expect to see women speakers at tech conferences? Or does it seem like an effort to save face without actually changing the way women are treated, like a corporate diversity program. If you have an opinion, tell me.

Weekend Confessions: Envy

I am a bad person because I often feel superior from other people's failures. When I think I have taken a better path there is a spark of glee from me when others stumble and fall on their own paths. I think it is because I am envious. I don't want to feel like someone made a better choice than me, so I look for ways to justify what I've done and am secretly ecstatic when things don't work out for them. There is a part of me that justifies this by running through all the things they might have the better hand than me on, looks, money, better car, better job. And when they screw up, and I am happy about it, I tell myself that it's okay to feel smug because afterall they already have numerous advantages over me. I feel remorse and guilt over plenty of things in my life, but this attitude is not one of them. I know somewhere it is wrong to feel this way, that even if I am not acting that the attitude is getting through and could be hurting people or alienating colleagues. But despite all that, I continue to revel in other seeemingly successful people's shortcomings.

Design Fridays: Mimicking Nature

Two researchers, from South Africa and California, have designed what they think will be a more aerodynamically efficient plane. Saving fuel might not be on the priority list for the military's fastest fighter jets, but it is important to long range, endurance vehicles and especially to commercial aviation. The designers, Huyssen and Spedding, believe the crooked wings and shortened tail will decrease the amount of drag the aircraft experiences thereby reducing its fuel consumption.

 

 These design changes make it look more like a bird than your typical fixed-wing aircraft. Just in time for a non-flying bird-centric holiday. Even the designers don't know yet how much of an effect this will have or how practical it will be. But we might see some elements incorporated into other designs rolling out in the next decade or so. I can't wait for the Turkey plane in a year from now. Gobble gobble.

DARPA Thursdays: Phantom ship chases subs

There seems to be a trend in autonomous, constantly patrolling vehicles lately what with Solar Impulse's 24 hour flight and Boeing's plan for a five year flight. So it should come as no surprise the DARPA is trying to develop a pilotless robot ship that could automatically chase enemy subs around without needing control or direction. It would need to be light and carry a lot of fuel for this kind of stamina which it does and will be made from aluminum. But at 62 ft long with a high point of 45 ft it doesn't sound like it will be too sneaky. It'll use an obstacle avoidance system which is pretty common for autonomous vehicles in other mediums. I suspect in a few years we'll see requests for proposal of versions of this craft that are mostly imperceptible to sonar or otherwise difficult to track by the subs they are chasing. The general idea is shooting it down will only create a red flag for someone to chase down thereby giving away the location of the escaping sub. But from what I know of the military they don't like their expensive unmanned crafts to suffer enemy fire if they can help it.

December 1st: World AIDs Day

For personal reasons the plight of AIDs victims, both locally and worldwide, means a lot to me. It's not as easy to discuss at the office as is many other good causes or at least not at my current office. But in the past I worked alongside HIV positive survivors. And they were as normal as you and me. Outwardly they were healthy but I know many struggled with health problems. I attended the 50th birthday of somebody who had been diagnosed 10 years before and thought it was a death sentence. I held back tears when he quietly said he was happy to reach age 50 because when he was diagnosed he didn't think he would live that long.

 

Antiretrovirals in treating AIDs have come a long way. Early drugs had horrible side effects so those with the disease suffered both from immune deficiency related problems as well as terrible side effects just to keep themselves alive. The drugs have improved a lot since then. And maybe that's why people start to forget. It's no longer an immediate death sentence. But neither is it something that doesn't cut back the invaluable lifespans of people just like you and me. So we can not forget. We have to hope for a cure. And more importantly, a wider availability of treatment for the people who need it. The drugs are very expensive and as we all know there is a healthcare crisis in this country. Many people do not have health insurance to afford the drugs and neither can they afford the regular care and treatment they need to keep living with the disease. We need to keep pressing so that we don't leave behind the people in this country who could be so easily treated. And of course it is imperative that becomes a worldwide mandate where lifesaving drugs and medical care continue to be made available to the people who need it everywhere.

 

I don't ask you to donate to an AIDs charity today, but if you can I hope you do. You can stop by AIDS.gov to read more about efforts and events going on today (and year round). Read the statement from the Whitehouse and from our secretary of state as well as many of the international sites promoting this event. You can stop by GiveWell.org and Keep a Child Alive. I hope you will at least take today to become aware of the events in your community and be not afraid to discuss this with your friends and colleagues.