Consider a homogeneous and constant cross-section SWCNT with external exciting pressure as illustrated in Figure 1.
Figure 1 Schematic of the pressurized CNT.
By employing the classic Euler-Bernoulli beam model, the nonlinear vibration of figure 1 can be modelled as;
(1)
Substituting for the pressure term,
.(2)
Method of solution via TDTM
Since the resulting model in equation (4) contains a nonlinear foundation term, the model generally becomes nonlinear and difficult to solve using Laplace and Fourier methods. As a result, TDTM is employed. This method predicts excellently when engaged to handle nonlinear models. In this present study, the nonlinear transient model in Eq. (2) will be solved analytically using the TDTM and verify after removing the nonlinear term with Integral transform method.
Basic principle of the TDTM
TDMT is an extension of the Classical DTM but the former differs from the later due to the inclusion of transient term transformation together with the spatial term. Some basic TDTM recursive relations are shown below Table 1:
1.
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2.
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3.
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4.
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5.
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6.
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7.
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8.
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9.
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10.
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11.
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Table 1 TDTM recursive relations
Method of solution: Transient differential transform method (TDTM)
Recall that the nonlinear transient governing equation as shown in Eq. (2) may be expressed as,
(3)
Subject to the pinned-pinned conditions:
Applying the TDTM illustrated in table 1, the recursive relation of Eq. (3) becomes;
(4)
Where the recursive term
(5)
On re-arranging Eq. (4), we have the finalized TDTM recursive equation as
(6)
Subject to the TDTM transformed conditions:
(7)
Where the constants will be determined by the remaining two boundary conditions. Solving Eq. (6) with Eq. (7), the term by term TDTM solutions are obtained as shown below:
TDTM series solution is generally represented as;
(8)
The TDTM series solution then becomes;
Equation (9) is the desired TDTM solution that represents deflection of the SWCNT.
Determination of the SWCNT Bending moment and Shear force from TDTM
The Bending moment is related to the SWCNT deflection by
(10)
Similarly, the Shear force is related to the SWCNT deflection by
(11)
Substituting Eq. (9) into Eqs. (10-11), we have for the nonlinear bending moment,
(12)
With a shear force expressed as,
(13)
Verification
The present study is verified with numerical method and a good agreement is reached as shown (Table 2):
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Mode Shap
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Mode
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Numerical method
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Present study(TDTM)
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1
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3.141593
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3.141593
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2
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6.283185
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6.283185
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3
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9.424778
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9.424778
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4
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12.56637
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12.56637
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5
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15.70796
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15.70796
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Table 2 Verification of present study with numerical method
Influence of Pressure, temperature and foundation parameters on CNT deflection
Figures 4–7 depict the influence of external pressure, temperature and foundation parameter on the steady state response of the CNT. Increasing external pressure results in a corresponding increase in the deflection of the CNT. When the pressure distributed at the CNT surface is converted into a resultant force, it acts at the mid-point of the nanotube span. At that point, the shearing force will be zero while bending moment will be maximum. This results in an increase in CNT deflection. Furthermore, an increase in foundation parameter and temperature have an attenuating attribute on CNT response (Figures 2–4).
Figure 2 Influence of uniformly distributed pressure on deflection.
Figure 3 Influence of temperature on CNT deflection.
Figure 4 Influence of foundation on CNT deflection.
Figure 5 First mode dynamic response of CNT.
Figure 6 Second mode dynamic response of CNT.
Figure 7 Third mode dynamic response of CNT.
Figure 8 Forth mode dynamic response of CNT.
Dynamic response of the SWCNT
Figures 5–8 illustrate the multi-dimensional dynamic response of the CNT for different modes. The transient responses depict the possibility of tracking the behaviour of the CNT at any instance. This analysis is vital as it helps in the monitoring and adjustment of the CNT during use.
The Shear force and bending moment of the SWCNT
Figures 8–12 depict the multi-dimensional Shearing force and bending moment diagram of the CNT for bi-modal cases. Locations with maximum bending moments are observed to possess minimum shear force. The combination of these responses and the mode shape of the structure may be used to track location of anti-nodes for resonance prevention.
Figure 9 First mode shear force of CNT.
Figure 10 Second mode shear force of CNT.
Figure 11 First mode Bending moment of CNT.
Figure 12 Second mode Bending moment of CNT.
Validation
The present study is also reduced and compared with those of previous studies with good agreements established as demonstrated below (Table 3):
Mode
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Reference 40
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Mode shape reference 37
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Present study linearized
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1
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3.141593
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3.14159
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3.14159
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2
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6.283185
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6.28319
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6.28319
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3
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9.424778
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9.42478
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9.42478
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4
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-
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12.5664
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12.5664
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5
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-
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15.70796
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15.70796
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