Fig. 1

r=1;
l=4;
demiAlpha=(π/3);

lignesHoriz[]:=Module[{a,b,nPas,pas},a=N[-(π/2)+demiAlpha];b=N[((3 π)/2)-demiAlpha];nPas=Round[((40 (π-demiAlpha))/π)];pas=N[((b-a)/nPas)];{Thickness[0.001],Table[Line[{{(l/2),r Cos[a+i pas],r Sin[a+i pas]},{-(l/2),r Cos[a+i pas],r Sin[a+i pas]}}],{i,0,nPas}]}]

arcsSup[]:=Module[{a,b,nPas,pas},a=N[-(l/2)];b=N[(l/2)];nPas=15;pas=N[((b-a)/nPas)];{Thickness[0.001],Table[First[ParametricPlot3D[{-(l/2)+i pas,r Cos[u],r Sin[u]},{u,-(π/2)+demiAlpha,((3 π)/2)-demiAlpha},DisplayFunction->Identity]],{i,0,nPas}]}]

gouttiere[]:=First[ParametricPlot3D[{v,r Cos[u],r Sin[u]},{u,-demiAlpha-(π/2),demiAlpha-(π/2)},{v,-(l/2),(l/2)},DisplayFunction->Identity]]

segmentCirc[x_]:=Module[{a,b,nPas,pas},a=N[-(π/2)-demiAlpha];b=N[-(π/2)+demiAlpha];nPas=Round[((80 demiAlpha)/π)];pas=N[((b-a)/nPas)];Polygon[Table[{x,r Cos[a+i pas],r Sin[a+i pas]},{i,0,nPas}]]]

surface[]:=Polygon[{{(l/2),r Cos[-(π/2)-demiAlpha],r Sin[-(π/2)-demiAlpha]},{(l/2),r Cos[-(π/2)+demiAlpha],r Sin[-(π/2)+demiAlpha]},{-(l/2),r Cos[-(π/2)+demiAlpha],r Sin[-(π/2)+demiAlpha]},{-(l/2),r Cos[-(π/2)-demiAlpha],r Sin[-(π/2)-demiAlpha]}}]

Show[Graphics3D[{lignesHoriz[],arcsSup[],gouttiere[],segmentCirc[-(l/2)],segmentCirc[(l/2)],surface[]},PlotRange->All,ViewPoint->{5,4,1},BoxRatios->{l,2 r,2 r},Boxed->False,Axes->None]]

Fig. 2

<<Graphics`Arrow`

<<TraceGraphiques`

?fenetre

?hachure

r=1;
l=4;
demiAlpha=(π/3);

fenetre[-1,1,-1,1,{300,300}]

fSup[x_]:=Sin[demiAlpha-(π/2)]

fInf[x_]:=-(Sqrt[(r^2)-(x^2)])

cercle[]:=First[ParametricPlot[{r Cos[u],r Sin[u]},{u,-π,π},DisplayFunction->Identity]]

secteur[]:={Line[{{0,0},{r Cos[-(π/2)-demiAlpha],r Sin[-(π/2)-demiAlpha]}}],Line[{{0,0},{r Cos[-(π/2)+demiAlpha],r Sin[-(π/2)+demiAlpha]}}],Text["r",0.7 {r Cos[demiAlpha-(π/2)],r Sin[demiAlpha-(π/2)]+.1 r}]}

angle[]:={Circle[{0,0},0.15 r,{-(π/2)-demiAlpha,-(π/2)+demiAlpha}],Text["α",0.2 r {Cos[-(π/2)],Sin[-(π/2)]}]}

surface[]:={Line[{{r Cos[-(π/2)-demiAlpha],r Sin[-(π/2)-demiAlpha]},{r Cos[-(π/2)+demiAlpha],r Sin[-(π/2)+demiAlpha]}}],{Dashing[{0.01,0.01}],Line[{{r Cos[-(π/2)+demiAlpha],r Sin[-(π/2)+demiAlpha]},{r 1.3,r Sin[-demiAlpha-(π/2)]}}],Line[{{0,-r},{r 1.3,-r}}]}}

hauteur[]:=
	{Arrow[{r 1.2,r Sin[-demiAlpha-(π/2)]},{r 1.2,-r}],
		Arrow[{r 1.2,-r},{r 1.2,r Sin[-demiAlpha-(π/2)]}],
Text["h",{r 1.3,0.5 (-r+r Sin[-demiAlpha-(π/2)])}]}

Show[Graphics[{secteur[],angle[],surface[],hauteur[],cercle[]}],hachure[fInf,fSup,r Cos[-demiAlpha-(π/2)],r Cos[demiAlpha-(π/2)]],AspectRatio->Automatic]