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The Nonlinear Instability of a Cylindrical Interface Between Two Hydromagnetic Darcian Flows

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Abstract

This paper investigates the nonlinear instability of an interface between two magnetic fluids separated by a cylindrical interface in porous media. The system is influenced by a uniform axial magnetic field. The magnetic field intensities allow a presence of surface currents at the interface. The transfer of mass and heat across the interface is considered. The solutions of linearized equations of motion, under the appropriate nonlinear boundary conditions, lead to a nonlinear characteristic equation that is governed the behavior of the interface deflection. Drawing on the linear stability theory, Routh–Hurwitz’s criteria are utilized to judge the stability criteria. The coupling of Laplace transforms and Homotopy perturbation techniques are adopted to obtain an approximate analytical solution of the interface profile. The nonlinear stability analysis resulted in two levels of solvability conditions. By means of these conditions, a Ginzburg–Landau equation is conducted. The latter equation represented the nonlinear stability configuration. The magnetic field intensity was plotted versus the wave number of the surface waves. Therefore, the stability picture was divided into stable and as well as unstable regions. Subsequently, the influence of the various physical parameters was addressed.

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Correspondence to Marwa H. Zekry.

Appendices

Appendix A

The coefficients that appearing in Eq. (2.24) may be listed as follows:

$$\begin{aligned}\alpha_{1} &= \frac{G}{RL}\left( {\frac{1}{{\ln \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)}} - \frac{1}{{\ln \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)}}} \right),\,\,\,\,\\ \alpha_{2} &= \frac{G}{{R^{2} L}}\left( {\frac{1}{{\ln \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)}} - \frac{1}{{\ln \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)}}} \right)\\ &\quad\times\left( { - 3 + 2\frac{{\left( {\ln^{2} \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right) - \ln^{2} \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)} \right)}}{{\ln \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)\ln \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)\ln \left( {{a \mathord{\left/ {\vphantom {a b}} \right. \kern-0pt} b}} \right)}}} \right) \end{aligned}$$

and

$$\begin{aligned} \alpha_{3} & = \frac{G}{{R^{3} L}}\left( {\frac{1}{{\ln \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)}} - \frac{1}{{\ln \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)}}} \right)\\ &\quad\times \left( {11 + 12\frac{{\left( {\ln^{2} \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right) - \ln^{2} \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)} \right)}}{{\ln \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)\ln \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)\ln \left( {{a \mathord{\left/ {\vphantom {a b}} \right. \kern-0pt} b}} \right)}}} \right.\\ &\quad\left.{- 6\frac{{\left( {\ln^{3} \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right) - \ln^{3} \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)} \right)}}{{\ln^{3} \left( {{b \mathord{\left/ {\vphantom {b R}} \right. \kern-0pt} R}} \right)\ln^{3} \left( {{a \mathord{\left/ {\vphantom {a R}} \right. \kern-0pt} R}} \right)\ln^{3} \left( {{a \mathord{\left/ {\vphantom {a b}} \right. \kern-0pt} b}} \right)}}} \right). \end{aligned}$$

In formulating Eqs. (2.28)–(2.31) and (2.34), the these coefficients may be listed as:

$$\begin{aligned} L(A_{1} ,A_{2} ) & = I_{1} (kA_{1} )K_{1} (kA_{2} ) - I_{1} (kA_{2} )K_{1} (kA_{1} ),\quad M(A_{1} ,A_{2} ) = I_{1} (kA_{1} )K_{0} (kA_{2} ) - I_{0} (kA_{2} )K_{1} (kA_{1} ), \\ N(A_{1} ,A_{2} ) & = I_{0} (kA_{1} )K_{1} (kA_{2} ) + I_{1} (kA_{2} )K_{0} (kA_{1} ),\quad W(A_{1} ,A_{2} ) = I_{0} (kA_{1} )K_{0} (kA_{2} ) - I_{0} (kA_{2} )K_{0} (kA_{1} ), \\ Q(A_{1} ,A_{2} ) & = I_{0} (kA_{1} )K_{0} (kA_{2} ) + I_{0} (kA_{2} )K_{0} (kA_{1} ),\quad F_{xy}^{cd} = I_{0} (kx)I_{0} (ky)K_{0} (kc)K_{0} (kd), \\ P_{x}^{c} & = I_{0} (kx)K_{0} (kc),\quad X_{xy}^{cd} = I_{0} (kx)I_{0} (ky)K_{0} (kc)K_{1} (kd), \\ Y_{xy}^{cd} & = I_{0} (kx)I_{1} (ky)K_{0} (kc)K_{0} (kd),\quad P_{x}^{c} = I_{0} (kx)K_{0} (kc),\quad V_{x}^{c} = I_{1} (kx)K_{1} (kc), \\ E_{xy}^{cd} & = I_{1} (kx)I_{1} (ky)K_{1} (kc)K_{1} (kd),\quad G_{xy}^{cd} = I_{0} (kx)I_{1} (ky)K_{1} (kc)K_{1} (kd), \\ Z_{xy}^{cd} & = I_{1} (kx)I_{1} (ky)K_{0} (kc)K_{1} (kd),\quad U_{xy}^{cd} = I_{0} (kx)I_{0} (ky)K_{1} (kc)K_{1} (kd), \\ D_{xy}^{cd} & = I_{1} (kx)I_{1} (ky)K_{0} (kc)K_{0} (kd), \\ \end{aligned}$$

where \((A_{1} ,A_{2} ,x,y,c,d)\,\) are the same as \((\,a,\,b,\,R,\,r).\)

$$\begin{aligned} \varLambda & = 2ik\left( {\mu_{1} W(b,R)N(a,R) + \mu_{2} W(R,a)N(b,R)} \right) \\ & \quad - 2k(\mu_{1} - \mu_{2} )\left( {F_{RR}^{ab} + F_{ab}^{RR} - P_{R}^{R} Q(a,b)} \right.\left. {N(a,R)N(b,R)} \right)\,\eta_{z} \\ & \quad - ik\left( {(\mu_{1} - \mu_{2} )(X_{ab}^{RR} - Y_{RR}^{ab} ) + (\mu_{1} + 2\mu_{2} )(X_{aR}^{bR} - Y_{bR}^{aR} ) + (2\mu_{1} + \mu_{2} )(Y_{ab}^{RR} - X_{bR}^{aR} )} \right)\eta_{z}^{2} . \\ \end{aligned}$$

Appendix B

The coefficients that are appeared in Eq. (2.34) may be listed as follows:

$$\varpi^{2} = \frac{{\alpha_{1} \left( {v_{1} m_{1} \rho_{2} N(R,a)L(R,a) + v_{2} m_{2} \rho_{1} N(R,b)L(a,R)} \right)}}{{\rho_{1} \rho_{2} \left( {\rho_{1} N(R,a)L(R,a) - \rho_{2} N(R,b)L(a,R)} \right)}},$$
$$l_{1} = \frac{{\alpha_{1} L(b,a) - kR\left( {v_{1} m_{1} N(a,R)L(b,R) - v_{2} m_{2} N(b,R)L(a,R)} \right)}}{{ - kR\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$l_{2} = \frac{{V_{1} (\alpha_{1} + v_{1} m_{1} )m_{2} L(R,b)N(R,a) - V_{2} (\alpha_{1} + v_{2} m_{2} )m_{1} L(R,a)N(R,b)}}{{m_{1} m_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$l_{3} = \frac{{2V_{1} \rho_{1} m_{2} L(R,b)N(R,a) - 2V_{2} \rho_{2} m_{1} L(R,a)N(R,b)}}{{m_{1} m_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$l_{4} = T + \frac{{H^{2} }}{k}\left( {\left. {\frac{{h_{1} \mu_{1} (h_{1} \mu_{1} - h_{2} \mu_{2} )^{2} \left( {Q(R,a)W(R,b) - Q(R,b)W(R,a)} \right)}}{{\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)}}} \right) + \frac{{\rho_{1} V_{1}^{2} N(a,R)}}{{km_{1}^{2} L(R,a)}} + \frac{{\rho_{2} V_{2}^{2} N(R,b)}}{{km_{2}^{2} L(b,R)}},} \right.$$
$$s_{1} = \frac{{2m_{1} V_{2} L(R,a)\left( {k\alpha_{1} L(R,b) - \alpha_{2} N(R,b)} \right) - 2m_{2} V_{1} L(R,b)\left( {k\alpha_{1} L(R,a) - \alpha_{2} N(R,a)} \right)}}{{m_{1} m_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\beta_{1} = \frac{{\alpha_{1} \left( {v_{2} m_{2} \rho_{1}^{2} - v_{1} m_{1} \rho_{2}^{2} } \right)N(R,a)N(R,b)N(R,b)N(R,R)L(a,b)}}{{\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$s_{2} = \frac{{k\left( {V_{2} m_{1} \rho_{2} - V_{1} m_{2} \rho_{1} } \right)L(R,a)L(R,b)}}{{m_{1} m_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\beta_{2} = \frac{{\left( {v_{2} m_{2} \rho_{1} + \alpha_{1} (\rho_{1} - \rho_{2} ) - v_{1} m_{1} \rho_{2} } \right)N(R,a)N(R,b)N(R,b)N(R,R)L(a,b)}}{{\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)^{2} }},$$
$$\begin{aligned} s_{3} & = \frac{1}{2}\left( {H^{2} (\mu_{1} h_{1}^{2} - \mu_{2} h_{2}^{2} ) - } \right.\frac{{4\rho_{1} V_{1}^{2} e_{aR}^{aR} }}{{m_{1}^{2} L(a,R)L(R,a)}} + \frac{{4\rho_{2} V_{2}^{2} e_{bR}^{bR} }}{{m_{2}^{2} L(b,R)L(R,b)}} - \frac{{2\rho_{1} V_{1}^{2} \left( {e_{aa}^{RR} + e_{RR}^{aa} } \right)}}{{m_{1}^{2} L(R,a)^{2} }} + \frac{{2\rho_{2} V_{2}^{2} \left( {e_{bb}^{RR} + e_{RR}^{bb} } \right)}}{{m_{2}^{2} L(R,b)^{2} }} \\ & \quad - H^{2} (h_{1} \mu_{1} - h_{2} \mu_{2} )^{2} \left( {\left. {\frac{{\mu_{2} W(R,a)^{2} \left( {D_{RR}^{bb} + U_{bb}^{RR} } \right) + \mu_{2} W(R,a)^{2} V_{R}^{R} \left( {P_{a}^{a} + P_{b}^{b} } \right) - \mu_{1} W(R,b)^{2} \left( {D_{RR}^{aa} + U_{aa}^{RR} } \right)}}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }}} \right)} \right. \\ & \quad + 4H^{2} (h_{1} \mu_{1} - h_{2} \mu_{2} )\left( {\left. {\frac{{h_{1} \mu_{1} W(R,b)N(a,R) + h_{2} \mu_{2} W(R,b)N(a,R)}}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)}}} \right)} \right., \\ \end{aligned}$$
$$\beta_{3} = \frac{{\left( {V_{2} m_{1} \rho_{1} (\alpha_{1} + v_{2} m_{2} ) - V_{1} m_{2} \rho_{2} (\alpha_{1} + v_{1} m_{1} )} \right)N(R,a)N(R,b)N(R,b)N(R,R)L(a,b)}}{{\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)^{2} }},$$
$$s_{4} = \frac{{k\alpha_{1}^{2} (\rho_{1} - \rho_{2} )L(R,a) - \alpha_{2} v_{2} m_{2} \rho_{1} L(R,a)N(R,b) + \alpha_{2} v_{1} m_{1} \rho_{2} L(R,b)N(R,a)}}{{\rho_{1} \rho_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$s_{5} = \frac{{ - 2\alpha_{2} L(a,b)}}{{kR\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$s_{6} = \frac{{H^{2} (\mu_{1} h_{1}^{2} - \mu_{2} h_{2}^{2} )}}{{2k^{2} }}\left( {\frac{{\mu_{2} W(R,a)^{2} W(R,b)^{2} }}{{\left( {\mu_{2} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }} - \left. {\frac{{\mu_{1} W(R,a)^{2} W(R,b)^{2} }}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }}} \right)} \right.,$$
$$\beta_{4} = \frac{{\alpha_{1} \left( {V_{1} m_{2} N(R,a)^{2} L(R,b)^{2} - V_{2} m_{1} N(R,b)^{2} L(R,a)^{2} } \right)}}{{m_{1} m_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\beta_{5} = \frac{{\alpha_{1} L(a,b)\left( {Z_{Rb}^{Ra} + Z_{Rb}^{Rb} + 2G_{RR}^{ab} - G_{Rb}^{aR} + 2Z_{ab}^{RR} + G_{Ra}^{bR} } \right)}}{{kRL(R,a)L(R,b)\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\begin{aligned} \beta_{6} & = \frac{{2\left( {\rho_{1} m_{2}^{2} V_{1}^{2} L(R,b)^{2} N(R,a)^{2} - \rho_{2} m_{1}^{2} V_{2}^{2} N(R,b)^{2} L(R,a)^{2} } \right)}}{{km_{1}^{2} m_{2}^{2} L(R,a)^{2} L(R,b)^{2} }} \\ & \quad + \frac{{h_{2} \mu_{2} H^{2} W(b,R)}}{{k\left( {\mu_{2} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)}} \\ & \quad \left( {(h_{2} (\mu_{1} + 2\mu_{2} ) - 3h_{1} \mu_{1} )N(a,R)} \right. \\ & \quad + \left. {\frac{{2(\mu_{1} - \mu_{2} )(h_{1} \mu_{1} - h_{2} \mu_{2} )W(R,a)\left( { - P_{R}^{R} Q(b,a) + V_{R}^{R} Q(b,a) + D_{RR}^{ab} + F_{ab}^{RR} + U_{ab}^{RR} + X_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right) \\ & \quad - \frac{{h_{1} \mu_{2} H^{2} W(a,R)}}{{k\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)}} \\ & \quad \left( {(h_{1} (2\mu_{1} + \mu_{2} ) - 3h_{2} \mu_{2} )N(b,R)} \right. \\ & \quad - \left. {\frac{{2(\mu_{1} - \mu_{2} )(h_{1} \mu_{1} - h_{2} \mu_{2} )W(R,b)\left( { - P_{R}^{R} Q(a,b) + V_{R}^{R} Q(a,b) + D_{RR}^{ab} + F_{ab}^{RR} + F_{RR}^{ab} + U_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right), \\ \end{aligned}$$
$$\beta_{7} = \frac{{3\left( {V_{1} \rho_{1} m_{2} N(R,a)^{2} L(R,b)^{2} - V_{2} \rho_{2} m_{1} N(R,b)^{2} L(R,a)^{2} } \right)}}{{km_{1} m_{2} L(R,a)^{2} L(R,b)^{2} }},$$
$$\beta_{8} = \frac{{V_{1} \rho_{1} m_{2} N(R,a)^{2} L(R,b)^{2} - V_{2} \rho_{2} m_{1} N(R,b)^{2} L(R,a)^{2} }}{{m_{1} m_{2} L(R,a)L(R,b)\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\beta_{9} = \frac{{\rho_{1} N(R,a)^{2} L(R,b)^{2} - \rho_{2} N(R,b)^{2} L(R,a)^{2} }}{{L(R,a)L(R,b)\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$n_{1} = \frac{{\alpha_{1} }}{k}\left( {\frac{{2\alpha_{1} N(R,a)}}{{\rho_{1} L(R,a)}} - \frac{{2\alpha_{1} N(R,b)}}{{\rho_{2} L(R,b)}}} \right. - \frac{{v_{1} m_{1} N(R,a)\left( {N(R,a)^{2} - L(R,a)^{2} } \right)}}{{\rho_{1} L(R,a)^{3} }} + \left. {\frac{{v_{2} m_{2} N(R,b)\left( {N(R,b)^{2} - L(R,b)^{2} } \right)}}{{\rho_{2} L(R,b)^{3} }}} \right),$$
$$\gamma_{1} = \frac{{2\alpha_{1} }}{k}\left( {\frac{{V_{1} N(R,a)\left( {\alpha_{2} N(R,a) + 2kL(a,R)} \right)}}{{m_{1} L(R,a)^{2} }} + \frac{{V_{2} N(R,b)\left( {\alpha_{2} N(R,b)^{2} + 2kL(b,R)^{2} } \right)}}{{m_{2} L(R,b)^{2} }}} \right),$$
$$\begin{aligned} n_{2} & = L(a,b)\left( {(\rho_{1} - \rho_{2} )(m_{1} v_{1} \rho_{2} - m_{2} v_{2} \rho_{1} )} \right.N(R,a)^{2} N(R,b)^{2} - \alpha_{1} \left( {\rho_{1}^{2} N(R,a)\left( {U_{RR}^{bb} - E_{RR}^{bb} + 2V_{b}^{b} (P_{R}^{R} + V_{R}^{R} )} \right.} \right. \\ & \left. {\quad + D_{bb}^{RR} - E_{bb}^{RR} } \right) - 2\rho_{1} \rho_{2} N(R,a)N(R,b)\left( {V_{b}^{a} P_{R}^{R} + U_{RR}^{ab} - E_{RR}^{ab} + E_{Ra}^{Rb} + V_{a}^{b} P_{R}^{R} + E_{Ra}^{Rb} + D_{ab}^{RR} - E_{ab}^{RR} } \right) + \rho_{2}^{2} N(R,b)^{2} \\ & \quad {{\left. {\left. {\left( {U_{RR}^{aa} - E_{RR}^{aa} + 2V_{a}^{a} P_{R}^{R} + 2E_{Ra}^{Ra} + D_{aa}^{RR} - E_{aa}^{RR} } \right)} \right)} \right)} \mathord{\left/ {\vphantom {{\left. {\left. {\left( {U_{RR}^{aa} - E_{RR}^{aa} + 2V_{a}^{a} P_{R}^{R} + 2E_{Ra}^{Ra} + D_{aa}^{RR} - E_{aa}^{RR} } \right)} \right)} \right)} {\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)^{3} ,}}} \right. \kern-0pt} {\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)^{3} ,}} \\ \end{aligned}$$
$$\begin{aligned} \gamma_{2} & = - km_{1} V_{2} \rho_{2} (\rho_{1} N(R,a)L(R,b)\left. {\left( {3G_{Ra}^{Rb} + 2Z_{ab}^{RR} + Z_{Ra}^{Rb} - 3Z_{Ra}^{Rb} - 2G_{RR}^{ab} - G_{Rb}^{Ra} } \right) + 2\rho_{2} N(R,b)^{2} L(R,a)^{2} } \right) \\ & \quad - {{km_{2} V_{1} \rho_{1} (\rho_{2} N(R,b)L(R,a)\left. {\left( {3G_{Rb}^{Ra} + 2Z_{ab}^{RR} + Z_{Rb}^{Ra} - 3Z_{Ra}^{Rb} - 2G_{RR}^{ab} - G_{Ra}^{Rb} } \right) + 2\rho_{1} N(R,a)^{2} L(R,b)^{2} } \right)} \mathord{\left/ {\vphantom {{km_{2} V_{1} \rho_{1} (\rho_{2} N(R,b)L(R,a)\left. {\left( {3G_{Rb}^{Ra} + 2Z_{ab}^{RR} + Z_{Rb}^{Ra} - 3Z_{Ra}^{Rb} - 2G_{RR}^{ab} - G_{Ra}^{Rb} } \right) + 2\rho_{1} N(R,a)^{2} L(R,b)^{2} } \right)} {m_{1} m_{2} }}} \right. \kern-0pt} {m_{1} m_{2} }} \\ & \quad \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)^{2} , \\ \end{aligned}$$
$$\begin{aligned} n_{3} & = \frac{{V_{2} N(R,b)}}{{km_{2} L(R,b)^{3} }}\left( {m_{2} v_{2} \left( {2V_{b}^{b} \left( {P_{R}^{R} + V_{R}^{R} } \right) + D_{bb}^{RR} + U_{RR}^{bb} - E_{RR}^{bb} - E_{bb}^{RR} } \right)} \right. \\ & \quad + \left. {\alpha_{1} \left( {2V_{b}^{b} \left( {P_{R}^{R} + 3V_{R}^{R} } \right) + D_{RR}^{bb} + U_{RR}^{bb} - 3E_{RR}^{bb} - 3E_{bb}^{RR} } \right)} \right) \\ & \quad - \frac{{V_{1} N(R,a)}}{{km_{1} L(R,a)^{3} }}\left( {m_{1} v_{1} \left( {2V_{a}^{a} \left( {P_{R}^{R} + V_{R}^{R} } \right) + D_{aa}^{RR} + U_{RR}^{aa} - E_{RR}^{aa} - E_{aa}^{RR} } \right)} \right. \\ & \quad + \left. {\alpha_{1} \left( {2V_{a}^{a} \left( {P_{R}^{R} + 3V_{R}^{R} } \right) + D_{aa}^{RR} + U_{RR}^{aa} - 3E_{RR}^{aa} - 3E_{aa}^{RR} } \right)} \right), \\ \end{aligned}$$
$$\begin{aligned} \gamma_{3} & = \frac{1}{2}\left( {\frac{{4\rho_{1} V_{1}^{2} N(R,a)\left( {2E_{aR}^{aR} - E_{RR}^{aa} - E_{aa}^{RR} } \right)}}{{m_{1}^{2} L(R,a)^{3} }}} \right. - \frac{{4\rho_{2} V_{2}^{2} N(R,b)\left( {2E_{bR}^{bR} - E_{RR}^{bb} - E_{bb}^{RR} } \right)}}{{m_{2}^{2} L(R,b)^{3} }} \\ & \quad - \frac{{(h_{1} \mu_{1} - h_{2} \mu_{2} )\mu_{2} H^{2} \left( {D_{RR}^{bb} + U_{bb}^{RR} + V_{R}^{R} P_{b}^{b} } \right)W(a,R)}}{{\left( {\mu_{2} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }} \\ & \quad \left( {\frac{{2(h_{1} \mu_{1} - h_{2} \mu_{2} )(\mu_{1} - \mu_{2} )W(R,a)\left( { - P_{R}^{R} Q(b,a) + V_{R}^{R} Q(b,a) + D_{RR}^{ab} + F_{RR}^{ab} + F_{ab}^{RR} + U_{ab}^{RR} + X_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right. \\ & \quad + \left. {(h_{2} (\mu_{1} + 2\mu_{2} ) - 3h_{1} \mu_{1} )N(a,R)} \right) - \frac{{(h_{1} \mu_{1} - h_{2} \mu_{2} )\mu_{1} H^{2} \left( {D_{RR}^{aa} + U_{aa}^{RR} + V_{R}^{R} P_{a}^{a} } \right)W(R,b)}}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }}\left( {(h_{1} (2\mu_{1} + \mu_{2} ) - 3h_{2} \mu_{2} )N(b,R)} \right. \\ & \quad - \left. {\frac{{2(h_{1} \mu_{1} - h_{2} \mu_{2} )(\mu_{1} - \mu_{2} )W(R,b)\left( { - P_{R}^{R} Q(a,b) + V_{R}^{R} Q(a,b) + D_{RR}^{ab} + F_{RR}^{ab} + F_{ab}^{RR} + U_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right), \\ \end{aligned}$$
$$n_{4} = \frac{{V_{2} m_{1} L(R,a)\left( {2k\alpha_{2} L(R,b) - 3\alpha_{3} N(R,b)} \right) - V_{1} m_{2} L(R,b)\left( {2k\alpha_{2} L(R,a) - 3\alpha_{3} N(R,a)} \right)}}{{m_{1} m_{2} L(R,a)L(R,b)\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\gamma_{4} = \frac{{\alpha_{1} }}{k}\left( {\frac{{N(R,a)\left( {\alpha_{2} m_{1} v_{1} N(R,a) + 2k\alpha_{1} L(a,R)} \right)}}{{\rho_{1} L(R,a)^{2} }} - \frac{{N(R,b)\left( {\alpha_{2} m_{2} v_{2} N(R,b) - 2k\alpha_{1} L(R,b)} \right)}}{{\rho_{2} L(R,b)^{2} }}} \right),$$
$$n_{5} = \frac{4}{k}\left( {\frac{{V_{2} \rho_{2} N(R,b)\left( {N(R,b) + L(R,b)} \right)\left( {N(R,b) + L(b,R)} \right)}}{{m_{2} L(R,b)^{3} }} - \frac{{V_{1} \rho_{1} N(R,a)\left( {N(R,a) + L(R,a)} \right)\left( {N(R,a) + L(a,R)} \right)}}{{m_{1} L(R,a)^{3} }}} \right),$$
$$\begin{aligned} n_{6} & = \frac{{(h_{1} \mu_{1} - h_{2} \mu_{2} )H^{2} W(R,b)}}{k}\left( { - \frac{{\mu_{2} W(R,a)\left( {(h_{2} \mu_{2} - 2h_{1} \mu_{1} )W(R,a)N(b,R) - 2h_{2} \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)}}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }}} \right. \\ & \quad + \left. {\frac{{\mu_{1} W(a,R)\left( {h_{1} \mu_{2} P_{R}^{a} W(R,a)N(b,R) + N(a,R)\left( {h_{1} \mu_{1} \left( {P_{a}^{R} W(b,R) + 2W((R,b))} \right) - 2h_{2} \mu_{2} W(R,b)} \right)} \right)}}{{\left( {\mu_{2} P_{R}^{a} W(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)} \right)^{2} }}} \right) \\ & \quad - \frac{T}{2} - \frac{{3\rho_{1} V_{1}^{2} N(R,a)\left( {N(R,a) + L(R,a)} \right)\left( {N(R,a) + L(a,R)} \right)}}{{km_{1}^{2} L(R,a)^{3} }} \\ & \quad + \frac{{3\rho_{2} V_{2}^{2} N(R,b)\left( {N(R,b) + L(R,b)} \right)\left( {N(R,b) + L(b,R)} \right)}}{{km_{2}^{2} L(R,b)^{3} }}, \\ \end{aligned}$$
$$n_{7} = \frac{{2\alpha_{1} L(a,b)}}{{k^{2} RL(R,a)L(R,b)}} + \frac{{2\alpha_{1} N(R,a)^{3} }}{{kL(a,R)^{3} }} + \frac{{2\alpha_{1} N(R,b)^{3} }}{{kL(R,b)^{3} }},$$
$$n_{8} = \frac{{\rho_{2} N(R,b)\left( {L(R,b)^{2} - 2N(R,b)^{2} } \right)}}{{kL(R,b)^{3} }} - \frac{{\rho_{1} N(R,a)\left( {L(R,a)^{2} - 2N(R,a)^{2} } \right)}}{{kL(R,a)^{3} }},$$
$$n_{9} = \frac{{\rho_{2} V_{2} N(R,b)\left( {2N(R,b)^{2} - L(R,b)^{2} } \right)}}{{km_{2} L(R,b)^{3} }} - \frac{{\rho_{1} V_{1} N(R,a)\left( {2N(R,a)^{2} - L(R,a)^{2} } \right)}}{{km_{1} L(R,a)^{3} }},$$
$$n_{10} = \frac{{2\alpha_{1} }}{k}\left( {\frac{{V_{2} N(R,b)\left( {N(R,b)^{2} - L(R,b)^{2} } \right)}}{{m_{2} L(R,b)^{3} }} - \frac{{V_{1} N(R,a)\left( {N(R,b)^{2} - L(R,b)^{2} } \right)}}{{m_{1} L(R,a)^{3} }}} \right),$$
$$n_{11} = \frac{{3\alpha_{3} L(a,b)N(R,R)}}{{\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)}},$$
$$n_{12} = \frac{{2k\alpha_{1} \alpha_{2} (\rho_{1} - \rho_{2} )L(R,a)L(R,b) + m_{1} v_{1} \rho_{2} \alpha_{3} N(R,a)L(R,b) - m_{2} v_{2} \rho_{1} \alpha_{3} N(R,b)L(R,a)}}{{\rho_{1} \rho_{2} \left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\gamma_{5} = \alpha_{1} L(a,b)N(R,R)(\rho_{1} N(R,a)(3L(b,R) + 2\alpha_{2} N(R,b)) - \rho_{2} N(R,b)(3L(a,R) + 2\alpha_{2} N(R,a))),$$
$$\gamma_{6} = \frac{{\rho_{1} N(R,a)}}{L(a,R)} + \frac{{\rho_{2} N(R,b)}}{L(R,b)},$$
$$\begin{aligned} \gamma_{7} & = \frac{{(h_{1} \mu_{1} - h_{2} \mu_{2} )\mu_{2} H^{2} W(R,a)W(R,b)^{2} }}{{\left( {\mu_{1} P_{b}^{R} W(b,R)N(a,R) + \mu_{2} P_{R}^{a} W(R,a)N(b,R)} \right)^{2} }}\left( {(h_{2} (\mu_{1} + 2\mu_{2} ) - 3h_{1} \mu_{1} )N(a,R)} \right. \\ & \quad + \left. {\frac{{2(h_{1} \mu_{1} - h_{2} \mu_{2} )(\mu_{1} - \mu_{2} )W(R,a)\left( {\left( {V_{R}^{R} - P_{R}^{R} } \right)Q(b,a) + D_{RR}^{ab} + F_{ab}^{RR} + F_{RR}^{ab} + U_{ab}^{RR} + X_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right) \\ & \quad + \frac{{(h_{1} \mu_{1} - h_{2} \mu_{2} )\mu_{1} H^{2} W(R,b)W(R,a)^{2} }}{{\left( {\mu_{1} P_{b}^{R} W(b,R)N(a,R) + \mu_{2} P_{R}^{a} W(R,a)N(b,R)} \right)^{2} }}\left( {(h_{1} (2\mu_{1} + \mu_{2} ) - 3h_{2} \mu_{2} )N(b,R)} \right. \\ & \quad - \left. {\frac{{2(h_{1} \mu_{1} - h_{2} \mu_{2} )(\mu_{1} - \mu_{2} )W(R,\gamma )\left( {\left( {V_{R}^{R} - P_{R}^{R} } \right)Q(a,b) + D_{RR}^{ab} + F_{ab}^{RR} + F_{RR}^{ab} + U_{ab}^{RR} + X_{ab}^{RR} } \right)}}{{\mu_{1} W(R,b)N(a,R) - \mu_{2} W(R,a)N(b,R)}}} \right), \\ \end{aligned}$$
$$\gamma_{8} = \frac{{\alpha_{1} \alpha_{2} L(a,b)\left( {Z_{Rb}^{Ra} + Z_{Ra}^{Rb} + 2G_{RR}^{ab} - G_{Rb}^{Ra} + 2Z_{ab}^{RR} + 2G_{Ra}^{Rb} } \right)}}{{kRL(R,a)L(R,b)\left( {\rho_{1} N(R,a)L(R,b) - \rho_{2} N(R,b)L(R,a)} \right)}},$$
$$\gamma_{9} = \frac{{\alpha_{1} \alpha_{2} }}{k}\left( {\frac{{V_{1} N(R,a)^{2} }}{{m_{1} L(R,a)^{2} }} - \frac{{V_{2} N(R,b)^{2} }}{{m_{2} L(R,b)^{2} }}} \right),$$

Appendix C

The coefficients that are appeared in Eqs. (3.8), (4.3) and (4.16) may be listed as follows:

$$\varGamma = - \frac{{k^{3} l_{3}^{2} }}{k}\left( {\frac{{h_{1} \mu_{1} (h_{1} \mu_{1} - h_{2} \mu_{2} )Q(R,a)W(R,b)}}{{\mu_{2} P_{{_{R} }}^{a} Q(R,a)N(b,R) + \mu_{1} P_{b}^{R} W(b,R)N(a,R)}} + \left. {\frac{{h_{2} \mu_{2} (h_{2} \mu_{2} - h_{1} \mu_{1} )W(R,a)Q(R,b)}}{{\mu_{1} P_{b}^{R} W(b,R)N(a,R) + \mu_{2} P_{a}^{R} W(R,a)N(b,R)}}} \right)} \right.,$$
$${\rm K} = kl_{3}^{2} \varpi^{2} - kl_{2}^{2} - k^{3} l_{3}^{2} \left( {T + \frac{{\rho_{1} V_{1}^{2} N(a,R)}}{{km_{1}^{2} L(R,a)}} + \frac{{\rho_{2} V_{2}^{2} N(R,b)}}{{km_{2}^{2} L(b,R)}}} \right),$$
$$\begin{aligned} a_{1} & = s_{1} - \frac{{\beta_{1} n_{3} }}{{\gamma_{3} }},\,\;\;a_{2} = s_{2} - \frac{{\beta_{2} n_{3} }}{{\gamma_{3} }},\,\;\;a_{3} = - \frac{{\beta_{4} n_{3} }}{{\gamma_{3} }},\;\;\,a_{4} = s_{1} - \frac{{\beta_{5} n_{3} }}{{\gamma_{3} }}, \\ a_{5} & = - \frac{{\beta_{6} n_{3} }}{{\gamma_{3} }},\;\;\,a_{6} = - \frac{{\beta_{7} n_{3} }}{{\gamma_{3} }},\;\;\,a_{7} = - \frac{{\beta_{8} n_{3} }}{{\gamma_{3} }},\, \\ \end{aligned}$$
$$\begin{aligned} a_{8} & = s_{1} - \frac{{\beta_{9} n_{3} }}{{\gamma_{3} }},\;\;\,a_{9} = s_{3} - \frac{{\beta_{3} n_{3} }}{{\gamma_{3} }},\;\;\,a_{10} = n_{4} - \frac{{n_{3} \gamma_{4} }}{{\gamma_{3} }},\;\;\,a_{11} = - \frac{{n_{3} \gamma_{5} }}{{\gamma_{3} }}, \\ a_{12} & = - \frac{{n_{3} \gamma_{6} }}{{\gamma_{3} }},\;\;\,a_{13} = - \frac{{n_{3} \gamma_{8} }}{{\gamma_{3} }},\;\;\,a_{14} = - \frac{{n_{3} \gamma_{9} }}{{\gamma_{3} }}, \\ \end{aligned}$$
$$a_{15} = - \frac{{n_{3} \gamma_{7} }}{{\gamma_{3} }},\quad a_{16} = n_{1} - \frac{{n_{3} \gamma_{1} }}{{\gamma_{3} }},\quad a_{17} = n_{2} - \frac{{n_{3} \gamma_{2} }}{{\gamma_{3} }},\quad \sigma^{2} = - \frac{{3l_{1} n_{12} }}{{l_{4} n_{11} }},\quad b_{1} = \frac{{l_{2} n_{11} - 3l_{3} n_{12} }}{{l_{4} n_{11} }},$$
$$\begin{aligned} b_{2} & = \frac{{\varpi^{2} n_{11} a_{12} + 3n_{11} a_{10} - 3n_{12} a_{11} - 3n_{12} a_{13} }}{{4l_{4} n_{11} }},\,\;\;b_{3} = \frac{{\varpi^{2} n_{8} n_{11} - 3n_{7} n_{11} + 3n_{11} a_{16} - 3n_{12} a_{17} }}{{4l_{4} n_{11} }},\,\;\;b_{4} = \frac{{3n_{5} n_{12} }}{{4l_{4} n_{11} }}, \\ b_{5} & = \frac{{3a_{14} }}{{4l_{4} }},\;\;\,b_{6} = \frac{{3n_{10} n_{11} - 3n_{9} n_{12} }}{{4l_{4} n_{11} }},\,\;\;b_{7} = \frac{{3n_{10} n_{11} - 3n_{9} n_{12} }}{{4l_{4} n_{11} }}\;\;{\text{and}}\;\;b_{8} = \frac{{3a_{15} }}{{4l_{4} }}. \\ \end{aligned}$$

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Moatimid, G.M., El-Dib, Y.O. & Zekry, M.H. The Nonlinear Instability of a Cylindrical Interface Between Two Hydromagnetic Darcian Flows. Arab J Sci Eng 45, 391–409 (2020). https://doi.org/10.1007/s13369-019-04192-z

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