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visits member for 4 years, 8 months
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Started programming on a ZX spectrum in the 80's and have moved through Assembly, Turbo Pascal, C++, C#, Fortran. My main area of focus is engineering and scientific computing like numerical methods and 3D graphics.


1h
comment Creating a structural dynamic model using only modal test data
Isn't $\phi^\intercal K \phi$ a matrix with the natural frequencies in the diagonals. So you can construct this experimentally by finding said natural frequencies.
2d
revised Is torque still a vector in 2 Dimensions?
edited body
2d
answered Is torque still a vector in 2 Dimensions?
2d
answered A metal block in a tub of frictionless ball bearings
Jul
30
comment Why spinning a pen makes it easier to remove it from the stand?
Is there suction created when not spun?
Jul
30
comment What happens to the kinetic energy of a dropped ball when it comes to rest on the ground?
Did you hear that BAM? Is the sand hot afterwards? Did you have to wear goggles to prevent sand grains getting into your eyes?
Jul
30
comment Ball flying towards me or me flying towards ball
Maybe an equation that shows that force/impulse is a result of "relative momentum" (however you define that) would improve the answer.
Jul
30
comment How can we account for a friction force changing sign in a conservation of energy equation?
If there is friction, how is there conservation of energy?
Jul
30
comment Rotation matrix of Euler's equations of rotation relative to inertial reference frame
I thought you don't integrate $\dot{R}$ directly, but integrate the euler angles (and their derivatives).
Jul
30
comment Rotation matrix of Euler's equations of rotation relative to inertial reference frame
It is all explained here: cs.cmu.edu/~baraff/sigcourse/notesd1.pdf
Jul
30
answered Conical train wheels
Jul
29
revised Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?
deleted 19 characters in body
Jul
29
comment Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?
Point taken. I will correct.
Jul
29
answered Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?
Jul
29
comment Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?
${\rm d} | \vec{v} | $ is confusing notation. Did you mean ${\rm d} \sqrt{ \vec{v}\cdot \vec{v}}$? Because I took it as $\sqrt{ {\rm d}\vec{v} \cdot {\rm d}\vec{v} }$.
Jul
29
comment Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?
Since $t$ is a scalar, $$\| \frac{{\rm d}\vec{v}}{{\rm d}t} \| = \frac{\| {\rm d}\vec{v}\|}{{\rm d}t} = \frac{{\rm d}\| \vec{v}\|}{{\rm d}t} $$
Jul
29
comment Virtual work (generalized forces) for rotation with Euler angles
Equation 7.2.31 in ocw.mit.edu/courses/mechanical-engineering/…
Jul
29
comment Virtual work (generalized forces) for rotation with Euler angles
Actually it comes from the power calculation. It is the unique value that maintains the powerflow through a joint. I also found it in slide 21 of diku.dk/OLD/undervisning/2005f/101/lecture11.pdf and slide 32 of homes.cs.washington.edu/~todorov/courses/amath533/…
Jul
29
answered Virtual work (generalized forces) for rotation with Euler angles
Jul
29
comment Virtual work (generalized forces) for rotation with Euler angles
Did you mean $\dot{\omega}=$ or ${\omega}=$ ? Angular velocity is $\omega=f(\dot{\phi},\ldots)$ and angular acceleration is $\dot{\omega}=f(\dot{\phi},\ddot{\phi},\ldots)$