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8/31/2009

Science of Cricket - Contrast Swing

This is the 3rd in a series of posts about swing in cricket. The terminology is introduced gradually, so it is recommneded that you read The Science of Conventional Swing and The Science of Reverse Swing first. This time, we will discuss contrast swing, which is often confused with proper reverse swing. Contrast swing is actually the most simple type of swing conceptually.

We will start with a diagram from Mehta again.
The first major difference you will notice is that the seam is pointed straight. This means that the only difference between the sides of the ball is the roughness. At conventional swing speeds only the boundary layer flow over the rough side will become turbulent, meaning that it will stay attached longer. This means that the pressure exerted on the smooth side will be greater and the ball will move towards the rough side, meaning the ball is moving 'reverse'.

At reverse swing speeds, both sides will transition to turbulence. If the rough side is exceedingly rough, this roughness may have a similar effect as the seam in reverse swing and weaken the boundary layer, causing earlier transition. I think however, that this type of swing would cause minimal ball deflection compared with slower contrast swing or either seamed swing types. Any movement that would occur would be towards the smooth side.

The seam is irrelevent to contrast swing and so this type of swing can be practised with a standard 1/2 taped tennis ball (not 1/2 a ball, 1/2 taped).

A note on speeds: For both slow contrast swing and conventional swing, there is not only an upper limit to the speed the ball is bowled at, but also a lower limit. Below a certain speed, neither side will transition to turbulence. So for you park bowlers out there, you may simply be bowling too slow to swing it. All these speeds mentioned will vary depending on atmospheric conditions, as explained in the post on reverse swing.

Next in the series is spin bowling 'drift'.

8/25/2009

Cricket Dream Team: We Are Winner

Just a little update, in between my science of swing research. With the Ashes over and the Poms somehow winning (despite averaging more than 6 runs per wicket less than the Aussies) you need something to cheer you up. So here are some recent fantasy results:

The Rushed Behind Blog League (as posted previously) came 7th in the overall best leagues competition out of 889. Go team! I reckon we shoulpd be 5th though because two of the leagues above us only did one or two tests. I personally (as the Rushed Behind) came in the top 400 (in 345th for those of you who like exact numbers) out of around 9000 entries after being screwed over by Michael Clarke's duck as captain in the last innings.

In the other Ashes fantasy competition of note, The Rushed Behind finished 9th overall. That's 9th as the 9th best team in total. Unfortunately, I can't tell you how many teams there were in total, because of the poor system used by SBS but I would estimate at least 1000 teams.

I read a great article on DTers the other day on dreamteamtalk.com, so check it out. I'm definately the "Injuries have F*%ked me this year" guy. Who are you?


A rapping cyclist. Now I've seen everything. Its also pretty funny, especially if you are into cycling, or just like seeing someone try to fit words like cardiovascular fitness and cadence into a rap. Disappointed he only has a $5000 bike though, Giant have a $18,499 model. Bonus points for also being Aussie.

8/16/2009

Science of Cricket - Genuine Reverse Swing



The Science of Cricket series continues with the second type of swing bowling, reverse swing. This series will gradually increase in complexity, so you can learn more and understand better by reading them in order. The first in the series is The Science of Cricket - Conventional Swing. Despite common misconceptions, reverse swing is not bowled with a straight seam. That form of swing bowling is contrast swing, to be discussed in the next post. True reverse swing is performed with a similar action to conventional swing but with the rough side at the front of the ball. The seam is still angled, but in this case away from where the bowler wants it to go.

Again, we will start with another diagram from Mehta, who is the media's go-to man when it comes to swing science (and I can't really be bothered drawing my own diagrams, when he has the basic flow ideas right).
So again, we have the ball flowing through a fluid (air). But on this occassion, the ball has the rough side oriented towards the flow. The ball is bowled at a combination of higher speed and/or more roughness at the front of the ball. This causes the boundary layers (layers of fluid near the surface of the ball) at the top and the bottom of the ball to transition to turbulence (irregular, chaotic flow) before the flow hits the seam. In this case, the seam cannot kick the flow into turbulence as it does in conventional swing bowling, as the flow is already turbulent. So the seam strips away the base of the boundary layer (visualise it as a thin stream of fluid flowing over the ball), leaving a thinner boundary layer. Now as discussed in the conventional swing article, any
asymmetry in flow will produce a difference in the separation point of the boundary layer. In this case, as the boundary layer over the top is thinner and has less energy holding it to the ball, it will separate more easily. From this point, the macroscopic consequences of this are a mirror image of conventional swing, with the fluid flowing over the top side of the ball exerting more pressure once the boundary layer has separated. This moves the ball towards the bottom, swinging the ball away from where the seam is directed.

Reverse swing appears to be later than conventional, but paradoxially, this is because it begins earlier. The only sideways (technically perpendicular to the direction of travel) forces which will act on the ball are those provided by swing, assuming there is no sideways spin on the ball, and any backspin is minimal (we'll get into the effects of that later, in the article on spin "drift" and dip). These forces keep working over time, and so the sideways speed keeps increasing all the way to the keeper. In most (elite level at least) cases of conventional swing bowling the ball is not travelling slow enough to generate any swing before it is close to, or even after bouncing. This means the ball can only generate side force during around the last 8 metres or so of its flight (number will vary rapidly betwen bowlers and conditions, but 8 is good for an example). This is why a conventionally swinging ball will often move rapidly after it has passed the batsman. But a reverse swinging ball can move from the moment it leaves the bowler's hand. This enables it to build up to a high sideways speed by the time it reaches the batsman (where it may sometimes have stopped accelerating sideways). For the same reason, all swinging balls will move faster later in their flight.

If the flow state is between reverse and conventional swing (ie the flow just before the seam (top of the diagrams used) is laminar and the flow over the bottom is turbulent then no swing will result, as both sides will have turbulent boundary layers of similar thickness.

In reverse swing, the smoothness of the "smooth side" is less important than the roughness of the rough side. If this smooth side is too rough, the boundary layer over this section after the seam will increase in thickness, negating the advantage gained by trimming the boundary layer with the seam. This will reduce the amount of movement, and combined with lessening seam protrusion as the ball wears is responsible for the ball stopping genuine reverse swing after a time.

The next post in this series will deal with Contrast Swing, aka "backyard reverse swing".

A "technical" aside, for those who want to know more: The flow will transition from laminar to turbulent at a certain "Reynolds number", smaller for a rougher surface. The Reynolds number is (ball speed*distance travelled along ball/kinematic viscosity) where kinematic viscosity is a property of the atmospheric environment. For example, the kinematic viscosity of the atmosphere is generally 8% higher at 1000m above sea level (lower than the Potchefstroom ground in South Africa) than at sea level, meaning a bowler must bowl 8% faster to get the saame reverse swing. But conventional swing can also be achieved at a speed of 8% faster at this altitude than at sea level. The kinematic viscosity varies all over the Earth too, and varies depending on weather conditions (if anyone reading this has links to measurements of kinematic viscosity, density or dynamic viscosity in sunny compared to overcast conditions, or England compared with Australia (to identify why swing bowling was so prevalent in the Ashes series of 2005 compared with 06/07) then I would appreciate the data) So to allow a ball to reverse swing, you can increase your speed, increase the surface roughness or increase your seam angle (although diverting this from the optimal will reduce the amount of movement, some movement is better than none). If you are trying to swing the ball conventionally then you need to keep the flow below transition over the bottom of the ball until separation (generally somewhere around 90 degrees around the ball). This means you may need to reduce your speed or change the atmospheric conditions, but changing the seam angle will not affect the transition speed. It will still affect the amount the ball swings.

Non-technical aside: Wow, that was a long post.


8/11/2009

Science of Cricket - Conventional Swing

Over the next few posts, The Rushed Behind will enlighten you as to the science of cricket. How do the different types of swing work? What causes "drift" of a spinning ball? Why does the amount of swing differ depending on the atmospheric conditions? These, and possibly more (if I can think of more questions) will be answered over the coming posts. But first, why should you believe my explanations over those of cricketers who claim it is an unexplainable art form? Well, as you will probably be surprised to know, I actually have a degree in Aerospace Engineering. So despite my bowling being more like ex-PM John Howard than Andrew Flintoff I can explain what is going on. And hopefully, in a way that a layman can understand (which is the problem with most other sources of information on these subjects).

So, first off is conventional swing. The key to conventional swing (from here on, just swing) is the seam. Lets consider a cricket ball with an angled seam, like the one drawn by Mehta below.
The fluid (air) flow over the top of the ball (as seen in the picture above) is disturbed by the seam, causing the boundary layer (fluid near the surface of the ball) to become turbulent. At this point, you are probably wondering what turbulent means. Any flow can be either laminar, turbulent or in transition between the two states. Laminar flow is nice and steady while turbulent flow has vortices and rotation of fluid. However, turbulent flow can stay attached for longer (because of the irregularities in the flow, but you don't need to know that) so the flow over the top remains attached for longer. This means that there is separation of the boundary layer earlier on the bottom of the ball and so the fluid exerts more pressure on the ball here, without the effect of the boundary layer. So there is more pressure on the bottom than the top, and the ball is moved by this pressure, towards the top.

However, the point of separation will also depend on the speed the ball is travelling at, and the smoothness of the front side. If the speed is too high or the ball is too rough then the boundary layer on the smooth side will transition towards turbulence, negating the advantage of the seam kicking the top flow into turbulence. This will negate the conventional swing, causing a straight ball and the bowler to look silly if he planned on swinging it. This is what happens when the ball stops swinging after a while as it gets roughed up. The ball may not swing from the start, as the lacquer is often less smooth than the leather of the ball itself. This will decrease the transition speed of the bottom side and so the ball will not swing. This is what is happening with the Duke balls used in England in the Ashes at the moment, with the ball starting to swing once the lacquer comes off. The wear on the ball will also lessen the effect of the seam, reducing the protuberance and potentially keeping the flow laminar for longer, reducing swing.

There are situations where conventional swing may only happen after the ball has bounced, if the seam is still in a good position and the bounce of the ball has reduced the speed below the threshold speed, but the seam position is so critical that this is rare.

Next Post - Reverse Swing

8/09/2009

Cricket: Australia Smash the Broad Poms

It was a return to the tradition of Ashes cricket for the 4th test, with Australia smashing the Poms by an innings and 80 runs. The English were bowled out for a paltry 102 in the first dig, with only Cook(30), Prior(37) and Extras(17) getting into double figures. Collingwood got the dreaded -20 points for a duck. Top marks if you picked Extras in your Dream Team. Siddle(5/21) and Clark(3/18) showed that good line and length and decent pace are all you need to bowl if the pitch is doing a bit.

Australia then piled on 445 in reply, thanks to North(110), Clarke(93), Ponting(78) and Watson(51). There were also decent bowler-batting scores for Johnson(27) and Clark(32). Australia scored at 4.27 runs per over, ensuring no economy rate bonuses for the English bowlers. The game was probably over as a contest once the Aussies past 300, but for DTers, the game isn't over until the last ball. Stewie Broad picked up 6/91 to be the pick of the bowlers while Anderson and Swann went wicketless (leaving Swann with 0 points up to this point). Katich got the -20, but 2 catches in Englands 1st innings meant that he wasn't looking at a negative score.

England tried a bit in their 2nd dig, but never had a chance to make a game of it. Their horrid batting lineup failed again, with Bopara getting a 1st baller and Bell and Collingwood getting 7 between them. Strauss(32) and Cook(30) got starts as did Prior(22), but it was the bowlers who shone for astute coaches. Stuart Broad got a swashbuckling 61, and Swann moved off the donut with 62 while Harmison got 19 not to ease the pain of those coaches who traded Broad for him, thinking Stewie would be dropped.

What happened in AFL Dream Team? Don't Go There!

8/07/2009

Soccer: Leeds United - Most Loathed Club In England

A survey has revelaed that Leeds United, currently stuck in the League 1 (3rd tier) are the most loathed club in England. As a Leeds United fan, its great that fans of other clubs still remember who we are. In fact, pretty much the only blogs you'll get from me regarding English soccer will be about Leeds (probably a bit about Adelaide United (Aus) too). I notice we've signed Patrick Kisnorbo, sometimes Australian international over the off-season who should strengthen the backline and add to the Aussie toughness with Neil Kilkenny. Leeds have had a good pre-season, including draws against Premier division Blackburn and Newcastle. Leeds first game of the season is tomorrow against Exeter, with the club looking to get an automatic promotion spot after missing out in the playoffs for the past two years.

Ross Lyon - Saint or AFL Dream Team Devil?

Dream Team (DT) gets serious this week, with the first week of finals kicking off. So Ross Lyon decides to "withdraw with injury" 5 of his players, 4 of which are critcial DT players for many coaches. Riewoldt, Goddard, Montagna and Hayes (as well as Baker, who is of no interest to DTers) have been left out of the side to face Hawthorn. They are all listed as "unsure of exact diagnosis or prognosis" on the prime DT injury source. The only silver lining is that my man Geary and 'possible cover if you had him at the start of the year and got too many injuries to cash cow him' Dawson come back. On the downside, Gilbert has been kept back becuase of this resting policy too. I'm betting the Ross Lyon is playing someone who has a ton of St Kilda players in his DT finals series. For disgraceful coaching like this, Ross Lyon goes onto the RB Shit List.

Then chuck in Chappy's hamstring, Ellis, Grimes left out so Melbourne don't win too many games with a "hip", Skipworth omitted, Dazzle, Sidebottom, Barham, Harding, Ballantyne suspended and doubts on Stevie J and Jolly and you've got the DT week from hell. I'm carrying 2 donuts, but I know of people who have 6 or 7.

Nathan Lovett-Murray (of little DT importance) is still playing, despite being charged by police for possessing ecstasy. Looks like the AFL have taken the Tom Boonen route on this one. But then its no surprise, with the soft drugs policy they have. The AFL are content to go Dodo, sticking their head in the sand about anything they don't want to know about. Like tanking. Several clubs are obviously tanking this year, with coaches selecting vastly weakened sides (and constantly leaving out Jack Grimes). The players would never play at less than 100%, but the coaches certainly would.

Australia held out for a draw in the 3rd Ashes test, with Brett Lee and Brad Haddin possible inclusions for the 4th game, starting tonight. Flitoff has fitness concerns, but he has before every game this series. He'll play. Haddin should be fit enough to takes the gloves from Manou (who just shaded Hilfenhaus with the bat in the last test, scoring 21 runs in 2 innings (1 not out) to Hilfy's 20. The Haus did only get one inning though) but Lee will probably be left out. Australia's bowling attack in general seems uncertain still, so your only cricket DT certainties for Aus are Hilfo and Johnno (Hilfenhaus and Johnson to any Poms reading). Stuart Broad's spot in the Pommy side is uncertain too, with Sidebottom brought into the squad. But really, cricket DT is simple compared to trying to dodge tanks in AFL DT.

Edit: Add Bock and Fisher to the list of outs and 2 more donuts makes 4 for the Rushed Behind.

8/02/2009

Cycling: Astarloza - A Star Loser !

Mikel Astarloza, the Spanish cyclist who won stage 16 of this year's Tour De France and finished 11th overall has tested positive for EPO. It is not yet known what type of EPO (presumably CERA) but SBS has reported that it was during an out of competition test. A disciplinary hearing will be held next month by the UCI to determine his punishment (probably a 2 year suspension) after he tested positive on the 26th of June. The UCI needs to act faster on these cases, the sample was taken before the TDF and yet Astarloza was still able to compete. But at least thats another cheat forcibly removed from the peloton. Astarloza's stage win in the TDF this year was his first professional stage win (he won the 2003 Tour Down Under around South Australia) but he had consistantly finished highly overall in major stage races such as the Dauphine Libre and Le Tour. There was no obvious upspike in his form this year, indicating that he had been doping for several years before this. I have added him and Danilo Di Luca to the shit list for being cheating gits.


In other news, after the flurry of recent postings, I've decided to finally get a related address. So this blog is now at rushedbehind.blogspot.com. Neat hey. If you are reading this, you are on the new site. The whole blog has been moved, so all the archives are still here. Call me a traditionalist, but I reckon a blog should have an address related to its name. So if you still have the old site bookmarked, change it now. And if you don't have this site bookmarked, what a great opportunity to do so. I don't know if the rss feeds were affected, so if you use these, you might want to check it out. But if you are getting this, then you will get all future posts. I do seem to have somehow lost my blogroll, so this will be refilled gradually, as I remember which blogs were worth reading.

Go rain, go! You are Australia's only hope at staving off defeat (and poor fantasy cricket scores from Brad Haddin given his late withdrawal after my kiss of death)!


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