Update Content - 2023-04-15
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title = "Mass Spring Damper Systems"
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author = ["Dehaeze Thomas"]
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draft = false
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@@ -43,6 +44,14 @@ with:
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- \\(\omega\_0 = \sqrt{k/m}\\) the natural frequency in [rad/s]
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- \\(\xi = \frac{1}{2} \frac{c}{\sqrt{km}}\\) the damping ratio [unit-less]
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A quality factor \\(Q\\) can also be defined:
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\begin{equation}
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Q = \frac{1}{2\xi}
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\end{equation}
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This corresponds to the amplification at the natural frequency \\(\omega\_0\\).
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### Matlab model {#matlab-model}
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@@ -69,7 +78,7 @@ Gw = (c*s + k)/(m*s^2 + c*s + k);
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<a id="figure--fig:mass-spring-damper-1dof-transmissibility"></a>
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{{< figure src="/ox-hugo/mass_spring_damper_1dof_transmissibility.png" caption="<span class=\"figure-number\">Figure 1: </span>1dof Mass spring damper system - Transmissibility" >}}
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{{< figure src="/ox-hugo/mass_spring_damper_1dof_transmissibility.png" caption="<span class=\"figure-number\">Figure 3: </span>1dof Mass spring damper system - Transmissibility" >}}
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## Two Degrees of Freedom {#two-degrees-of-freedom}
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@@ -77,11 +86,11 @@ Gw = (c*s + k)/(m*s^2 + c*s + k);
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### Model and equation of motion {#model-and-equation-of-motion}
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Consider the two degrees of freedom mass spring damper system of Figure [1](#figure--fig:mass-spring-damper-2dof).
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Consider the two degrees of freedom mass spring damper system of Figure [4](#figure--fig:mass-spring-damper-2dof).
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<a id="figure--fig:mass-spring-damper-2dof"></a>
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{{< figure src="/ox-hugo/mass_spring_damper_2dof.png" caption="<span class=\"figure-number\">Figure 1: </span>2 DoF Mass Spring Damper system" >}}
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{{< figure src="/ox-hugo/mass_spring_damper_2dof.png" caption="<span class=\"figure-number\">Figure 4: </span>2 DoF Mass Spring Damper system" >}}
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We can write the Newton's second law of motion to the two masses:
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@@ -145,30 +154,30 @@ G_F1_to_d2 = -m2*s^2/((m1*s^2 + c1*s + k1)*(m2*s^2 + c2*s + k2) + m2*s^2*(c2*s +
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G_F2_to_d2 = (m1*s^2 + c1*s + k1)/((m1*s^2 + c1*s + k1)*(m2*s^2 + c2*s + k2) + m2*s^2*(c2*s + k2));
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```
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From Figure [1](#figure--fig:mass-spring-damper-2dof-x0-bode-plots), we can see that:
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From Figure [5](#figure--fig:mass-spring-damper-2dof-x0-bode-plots), we can see that:
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- the low frequency transmissibility is equal to one
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- the high frequency transmissibility to the second mass is smaller than to the first mass
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<a id="figure--fig:mass-spring-damper-2dof-x0-bode-plots"></a>
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_x0_bode_plots.png" caption="<span class=\"figure-number\">Figure 1: </span>Transfer functions from x0 to x1 and x2 (Transmissibility)" >}}
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_x0_bode_plots.png" caption="<span class=\"figure-number\">Figure 5: </span>Transfer functions from x0 to x1 and x2 (Transmissibility)" >}}
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The transfer function from \\(F\_1\\) to the mass displacements (Figure [1](#figure--fig:mass-spring-damper-2dof-F1-bode-plots)) has the same shape than the transmissibility (Figure [1](#figure--fig:mass-spring-damper-2dof-x0-bode-plots)).
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The transfer function from \\(F\_1\\) to the mass displacements (Figure [6](#figure--fig:mass-spring-damper-2dof-F1-bode-plots)) has the same shape than the transmissibility (Figure [5](#figure--fig:mass-spring-damper-2dof-x0-bode-plots)).
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However, the low frequency gain is now equal to \\(1/k\_1\\).
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<a id="figure--fig:mass-spring-damper-2dof-F1-bode-plots"></a>
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_F1_bode_plots.png" caption="<span class=\"figure-number\">Figure 1: </span>Transfer functions from F1 to x1 and x2" >}}
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_F1_bode_plots.png" caption="<span class=\"figure-number\">Figure 6: </span>Transfer functions from F1 to x1 and x2" >}}
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The transfer functions from \\(F\_2\\) to the mass displacements are shown in Figure [1](#figure--fig:mass-spring-damper-2dof-F2-bode-plots):
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The transfer functions from \\(F\_2\\) to the mass displacements are shown in Figure [7](#figure--fig:mass-spring-damper-2dof-F2-bode-plots):
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- the motion \\(x\_1\\) is smaller than \\(x\_2\\)
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<a id="figure--fig:mass-spring-damper-2dof-F2-bode-plots"></a>
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_F2_bode_plots.png" caption="<span class=\"figure-number\">Figure 1: </span>Transfer functions from F2 to x1 and x2" >}}
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{{< figure src="/ox-hugo/mass_spring_damper_2dof_F2_bode_plots.png" caption="<span class=\"figure-number\">Figure 7: </span>Transfer functions from F2 to x1 and x2" >}}
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## Bibliography {#bibliography}
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