Divorce in Japan

[moolooman]

You put my 10 years to shame Paul

[pakalikaPakalika]

Well, the reason I brought up this topic, I met a girl the other day and we came to like each other a lot, and after 2 weeks or so I told her I used to be married and got divorced. She knew I lived with someone for several years, just not that it was official. Well, I was quite shocked to see how much that shocked her. Ok, she's rather young and said she never expected to be with someone who was divorced before, but still, my 2-3 ex-gfs didn't have such a problem with it (sth. she was surprised about). She actually was thinking we shouldn't meet any more, and was a bit relieved that at least I don't have children. There are certainly several reasons for her reaction and way of thinking, one being that she thought it would complicate things a lot (ex-wife disturbing our relationship, money I have to pay, etc. - there's nothing like that though). I told her she can talk with her friends about it too, and see what they think (me actually thinking she was an exception and most young people don't care about such things anymore).
Now the other day she met a (female) friend and they talked about this too, and I asked her what her friend said; apparently she said sth. like "are you sure that's ok? isn't it better to stop seeing him?" ... I couldn't believe it, to say the least. Don't know what I'd have done if I was there that time, but certainly nothing peaceful.. When asking her why her friend would say sth. like that, she said that she probably thought I must have done sth wrong that it came to that.
Sounded to me about the same like the prejudices against blacks or Chinese or so. Someone who has never met me, thinks I'm a bad person because I was unhappy once and wanted to change that (ie. divorce)..
It's impossible for me to see any reason there...

I just asked one of my JTE's the question about this. She is 28 years old. She said she would not mind. So I guess it depends on the person. Each person is different.

[Jeimuzu]

As pakalika wrote, it's all down to the individual.

Horses for courses as some people say.

[moolooman]

But what is the airspeed velocity of a half-laden swallow?

[Paul]

You put my 10 years to shame Paul

Ahhh.....no mooloo I don't, not at all. I'm just older that's all. I am sure you'll get to the same point as me, but by then I'll be at 40 years!

[Paul]

But what is the airspeed velocity of a half-laden swallow?

The airspeed velocity of an unladen swallow depends on many factors and parameters. For example, an African Swallow would tend to travel at a different velocity than an European Swallow. Furthermore, their flight patterns are different, so their instantaneous velocity at a given point will almost always be different. However, technological advances have given way to being able to use swallows to transport husked coconuts across large distances, enabling us to use coconuts on a daily basis, provided we have a large contingent of willing swallows ready to make a nonstop convoy for X amount of time, or however long we wish. Swallows can also be modified, as attaching a 50 newton rocket propulsion system on a 1 kg swallow will result in an acceleration of 50 m/s(2), which is of course negating any air resistance, since swallows have been recorded as outer space fliers. I hope i cleared any doubts about this matter.

What do you mean, an African or European Swallow?
To begin with, I needed basic kinematic data on African and European swallow species.


South African Swallow
(Hirundo spilodera) European Swallow
(Hirundo rustica)
Although 47 of the 74 worldwide swallow species are found in Africa,1 only two species are named after the continent: the West African Swallow (Hirundo domicella) and the South African Swallow (Hirundo spilodera), also known as the South African Cave Swallow.

Since the range of the South African Swallow extends only as far north as Zaire,2 I felt fairly confident that this was the non-migratory African species referred to in previous discussions of the comparative and cooperative weight-bearing capabilities of African and European swallows.3

Kinematic data for both African species was difficult to find, but the Barn or European Swallow (Hirundo rustica) has been studied intensively, and kinematic data for that species was readily available.

It’s a simple question of weight ratios
A 54-year survey of 26,285 European Swallows captured and released by the Avian Demography Unit of the University of Capetown finds that the average adult European swallow has a wing length of 12.2 cm and a body mass of 20.3 grams.4

Because wing beat frequency and wing amplitude both scale with body mass,5 and flight kinematic data is available for at least 22 other bird species,6 it should be possible to estimate the frequency (f ) and amplitude (A) of the European Swallow by a comparison with similar species. With those two numbers, it will be possible to estimate airspeed (U).

In order to maintain airspeed velocity, a swallow needs to beat its wings forty-three times every second, right?
Actually, wrong. By comparing the European Swallow with bird species of similar body mass, we can estimate that the swallow beats its wings 18 times a second with an amplitude of 18 cm:

Species Body mass Frequency Amplitude
Zebra Finch 13 g 27 Hz 11 cm
European Swallow 20 g ≈ 18 Hz? ≈ 18 cm?
Downy Woodpecker 27 g 14 Hz 29 cm
Budgerigar 34 g 14 Hz 15 cm
Note that even the tiny Zebra Finch flaps its wings no more than 27 times a second while cruising.

If we ignore body mass and look only at bird species with a similar wingspan, we can estimate an average frequency of 14 beats per second and an amplitude of 23 cm:

Species Wingspan Frequency Amplitude
Budgerigar 27 cm 14 Hz 15 cm
European Swallow ≈ 28–30 cm ≈ 14 Hz? ≈ 23 cm?
Downy Woodpecker 31 cm 14 Hz 29 cm
European Starling 35 cm 14 Hz 26 cm
By averaging all 6 values, we can estimate that an average European Swallow flies at cruising speed with a frequency of roughly 15 beats per second, and an amplitude of roughly 22 cm.

Skip a bit, Brother
Last month’s article on The Strouhal Number in Cruising Flight showed how simplified flight waveforms that graph amplitude versus wavelength can be useful for visualizing the Strouhal ratio (fA/U), a dimensionless parameter that tends to fall in the range of 0.2–0.4 during efficient cruising flight.

For a European Swallow flying with our estimated wingbeat amplitude of 24 cm, the predicted pattern of cruising flight ranges from a Strouhal number (St) of 0.2:


... to a less efficient 0.4:


If the first diagram (St = 0.2) is accurate, then the cruising speed of the European Swallow would be roughly 16 meters per second (15 beats per second * 1.1 meters per beat). If the second diagram (St = 0.4) is accurate, then the cruising speed of the European Swallow would be closer to 8 meters per second (15 beats per second * 0.55 meters per beat).

If we settle on an intermediate Strouhal value of 0.3:


We can estimate the airspeed of the European Swallow to be roughly 11 meters per second (15 beats per second * 0.73 meters per beat).

Three shall be the number thou shalt count
Airspeed can also be predicted using a published formula. By inverting this midpoint Strouhal ratio of 0.3 (fA/U ≈ 0.3), Graham K. Taylor et al. show that as a rule of thumb, the speed of a flying animal is roughly 3 times frequency times amplitude (U ≈ 3fA).5

We now need only plug in the numbers:

U ≈ 3fA
f ≈ 15 (beats per second)
A ≈ 0.22 (meters per beat)
U ≈ 3*15*0.22 ≈ 9.9
... to estimate that the airspeed velocity of an unladen European Swallow is 10 meters per second.

Oh, yeah, I agree with that
With some further study, it became clear that these estimates are accurate, though perhaps coincidental.

An actual study of two European Swallows flying in a low-turbulence wind tunnel in Lund, Sweden, shows that swallows flap their wings much slower than my estimate, at only 7–9 beats per second:

“Compared with other species of similar size, the swallow has quite low wingbeat frequency and relatively long wings.” 7
The maximum speed the birds could maintain was 13–14 meters per second, and although the Lund study does not discuss cruising flight in particular, the most efficient flapping (7 beats per second) occurred at an airspeed in the range of 8–11 meters per second, with an amplitude of 90–100° (17–19 cm).

And there was much rejoicing
Averaging the above numbers and plugging them in to the Strouhal equation for cruising flight (fA/U = 7 beats per second * 0.18 meters per beat / 9.5 meters per second) yields a Strouhal number of roughly 0.13:


... indicating a surprisingly efficient flight pattern falling well below the expected range of 0.2–0.4.

Although a definitive answer would of course require further measurements, published species-wide averages of wing length and body mass, initial Strouhal estimates based on those averages and cross-species comparisons, the Lund wind tunnel study of birds flying at a range of speeds, and revised Strouhal numbers based on that study all lead me to estimate that the average cruising airspeed velocity of an unladen European Swallow is roughly 11 meters per second, or 24 miles an hour.

[Paul]

But what is the airspeed velocity of a half-laden swallow?

Oh the answer is;

11 meters per second, or 24 miles an hour.

[himitsu]

thx pakalika